1
Q
What is the peripheral nervous system (PNS)?
A
The PNS connects the body’s periphery to the central nervous system (CNS). It carries messages back and forth between the body and the brain.
2
Q
What is the afferent division of the PNS responsible for?
A
It brings information from internal and external environments to the CNS.
3
Q
What is the efferent division of the PNS responsible for?
A
It sends out responses from CNS that control effectors such as skeletal muscles, tissues, and organs.
4
Q
What are the two types of control in the efferent division?
A
Conscious control through the somatic system and subconscious control through the autonomic system.
5
Q
What does the Peripheral Nervous System (PNS) consist of?
A
Nerve fibres that carry information between the CNS and other parts of the body.
6
Q
What does the afferent division of the PNS do?
A
It sends information from the internal and external environment to the CNS.
7
Q
What is the visceral afferent pathway?
A
It carries incoming information from internal organs (viscera) in body cavities.
8
Q
What kind of information does the afferent division send?
A
Sensory information from both internal and external environments to the CNS.
9
Q
What do visceral afferents help with?
A
They bring signals from organs like the heart or stomach to help maintain balance and homeostasis
10
Q
What does the sensory afferent division do?
A
It carries information from the body to the central nervous system (CNS).
11
Q
What does somatic (body sense) sensation include?
A
Sensations from the body surface such as touch, pressure, pain, and proprioception (position sense)
12
Q
What are special senses?
A
Vision, hearing, taste, smell, and equilibrium (balance).
13
Q
What helps us interpret and respond to our surroundings?
A
The special senses (vision, hearing, taste, smell, and balance).
14
Q
What happens to the body during the fight-or-flight response?
A
The body readies itself to either fight or flee a situation.
15
Q
What role does the afferent division of the PNS play in the fight-or-flight response?
A
It enhances systems and provides more information to the CNS about the external environment that influences decision-making.
16
Q
What kind of information does the afferent division gather during fight-or-flight?
A
It gathers sensory information such as sights and sounds and sends it to the brain.
17
Q
What responses are activated by the CNS during fight-or-flight?
A
Faster heart rate, sharper vision, and increased alertness for decision-making.
18
Q
What is somatosensation?
A
- your body’s sense of touch and physical feeling
- receptors in your body send signals to your brain so you can feel touch, temperature, and pain
19
Q
Where is the primary somatosensory area located?
A
In the parietal lobes of the cerebral cortex
20
Q
What do receptors in somatosensation do?
A
They integrate and create the sensory modalities that allow us to feel different sensations
21
Q
What types of receptors are involved in somatosensation?
A
- thermoreceptors
- mechanoreceptors
- photoreceptors
- chemoreceptors
22
Q
What do thermoreceptors detect?
A
changes in temperature (heat and cold)
23
Q
What do mechanoreceptors detect?
A
pressure and touch (stretch)
24
Q
What do photoreceptors detect?
A
light
25
What do chemoreceptors & osmoreceptors detect?
chemical changes in body fluids such as those involved in taste and smell
26
What does the body constantly gather information from to create sensations?
The body constantly gathers information from both internal and external environments.
27
What is the function of visceral (internal) afferents?
Visceral afferents send signals front your internal organs (heart and stomach) to your brain, without you noticing, to keep your body balanced and working normally
28
What is the function of sensory (external) afferents?
Sensory afferents bring information from the body surface and special senses, such as touch, vision, hearing, taste, and smell.
29
What is the purpose of sensory afferents from the external environment?
They allow us to interact with and respond to our surroundings.
30
What are the four main types of sensations?
- visceral afferent: feels things inside the body
- sensory afferent: all incoming sensory signals to the brain
- somatic sensation: feels things outside the body
- special senses: special senses from specific organs (vision, hearing, taste, smell, balance)
31
Why can humans only detect a limited range of energy forms?
- humans have receptors that can only detect certain things, like light, sound and temperature
- cannot pick up things like magnetic or radio waves
32
Why is sensory information not recorded perfectly in the brain?
Because our brain’s information channels are not high-fidelity recorders — the brain filters, fills in, and interprets data.
33
What part of the brain manipulates sensory data to shape perception?
The cerebral cortex further processes and interprets sensory data using past experiences.
34
What are receptors in the nervous system?
Receptors are specialized structures located at the peripheral endings of afferent neurons.
35
What is the main job of receptors?
Their main job is to detect stimuli (any detectable change in the internal or external environment) and convert them into electrical signals (transduction)
36
What types of stimuli can receptors detect?
Receptors can detect heat, light, sound, pressure, or chemical changes.
37
What happens when a receptor detects a stimulus?
It converts that form of energy into an electrical signal that the nervous system can understand.
38
What is the process of converting a stimulus into an electrical signal called?
This process is called transduction
39
How do receptors act like translators in the nervous system?
They turn mechanical, chemical, or other types of energy into action potentials that travel to the CNS for interpretation.
40
What is an adequate stimulus?
An adequate stimulus is the specific type of energy that a receptor is specialized to respond to best.
41
What does each receptor in the body respond best to?
Each receptor is specialized to respond best to one kind of energy, such as light, sound, or pressure.
42
What is an example of an adequate stimulus for the eyes, ears, and skin?
Eyes respond best to light, ears to sound waves, and skin to heat or touch.
43
What does the sensation we feel depend on — the stimulus type or the receptor?
It depends on the receptor, not the stimulus type
44
What is an example of receptors responding weakly to a different stimulus?
When you bump your head and “see stars,” mechanical pressure stimulates the eye’s light receptors.
45
What is the threshold in receptor?
The threshold is the minimum amount of stimulation needed to activate a receptor and produce a sensation.
46
What are photoreceptors and what do they respond to?
Photoreceptors respond to visible wavelengths of light and allow us to see.
47
What are mechanoreceptors and what do they respond to?
Mechanoreceptors respond to mechanical energy such as stretch, pressure, or vibration.
48
What are examples of mechanoreceptors?
Mechanoreceptors detect movement or pressure (stretch)
- stretch receptors in muscles
- hair cells in ear for hearing
- baroreceptors that detect blood pressure
49
What are thermoreceptors and what do they respond to?
Thermoreceptors respond to heat and cold.
50
What do osmoreceptors detect?
Osmoreceptors detect how concentrated our body fluids are
51
Why are osmoreceptors important?
They help maintain water balance and osmotic pressure, especially in areas like the hypothalamus.
52
What do chemoreceptors respond to?
Chemoreceptors respond to specific chemicals.
53
What are examples of chemoreceptors?
Chemoreceptors sense chemicals - like smell, taste, oxygen, or carbon dioxide levels in your blood
54
What is the overall function of receptor types in the body?
Each receptor type is specialized to sense and respond to different internal and external changes.
55
Why is afferent input essential?
Afferent input is essential for controlling efferent output, which allows the body to respond, move, and maintain homeostasis.
56
What happens without sensory (afferent) input?
Without sensory input, we couldn’t interact with or even be aware of our environment.
57
What is the role of the reticular activating system (RAS) in the brainstem?
It keeps you awake, alert and aware by processing sensory signals
58
What does central processing of sensory information allow us to do?
It allows us to perceive and interpret the world around us—how we experience sight, sound, and touch depends on how the brain processes incoming signals.
59
What can happen to selected sensory information delivered to the CNS?
It may be stored for future reference, helping us remember past experiences like familiar smells or sounds.
60
How can sensory stimuli affect our emotions?
Sensory input can trigger emotional responses—such as comfort, joy, fear, or sadness—based on past experiences.
61
What role does sensory information play beyond survival?
It shapes our memories and emotions, not just our awareness and actions.
62
What can receptors be classified as?
Receptors may be part of a sensory neuron itself or a separate cell that connects to one
- some receptors are neurons (like touch receptors)
- others are cells that talk to neurons (like taste or hearing receptors)
63
What happens when a stimulus is detected by a receptor?
The stimulus changes the receptor’s membrane permeability, allowing ions to move differently across the membrane.
64
What does the change in receptor permeability lead to?
It leads to a graded receptor potential.
65
What is a graded receptor potential?
It’s the first step in converting a physical stimulus into an electrical signal that the nervous system can understand.
66
What does a change in membrane permeability usually cause?
It causes the nonselective opening of small ion channels, allowing sodium ions to enter the cell.
67
What happens when sodium ions enter the receptor cell?
It produces a receptor (generator) potential.
68
What does the magnitude of the receptor potential represent?
The intensity of the stimulus.
69
What happens if the receptor potential reaches a sufficient magnitude?
It produces an action potential.
70
How is the action potential carried to the CNS?
It is propagated along an afferent fibre to the central nervous system.
71
What is a receptor potential (or generator potential)?
It’s a small electrical change produced when a receptor detects a stimulus.
72
What happens if a receptor potential is large enough to reach threshold?
It triggers the opening of sodium (Na⁺) channels in the nearby region of the afferent neuron’s membrane.
73
What does the opening of Na⁺ channels cause in the afferent neuron?
It initiates an action potential that carries the sensory signal toward the CNS.
74
What does a receptor potential represent in the process of sensation?
It’s the step that converts a detected stimulus into an electrical signal that can travel to the brain.
75
How is a receptor potential converted into an action potential?
It depends on the type of receptor — either a specialized afferent ending or a separate receptor cell.
76
What happens in a specialized afferent ending when a stimulus occurs?
The stimulus opens sodium (Na⁺) channels directly, creating a receptor potential.
77
After sodium enters in a specialized afferent ending, what happens next?
The signal spreads, more sodium channels open, an action potential starts, sending the message to the brain or spinal cord
78
What extra step occurs in a separate receptor cell?
The receptor lets calcium (Ca+) in, which makes it release neurotransmitters to send the signal to the sensory neuron
79
What happens after neurotransmitters bind to the afferent neuron?
They open chemically gated sodium channels, triggering an action potential in the neuron.
80
In both receptor types, how does the signal progress?
The signal begins as a graded potential and becomes an all-or-none action potential that the nervous system can process.
81
Where does the action potential start in afferent neurons?
It starts near the receptor, at the end of the neuron where the stimulus is detected
82
Where does the action potential begin in interneurons and efferent neurons?
It begins at the axon hillock, located next to the cell body.
83
Why do afferent neurons have a different initiation site for action potentials compared to interneurons and efferent neurons?
Because sensory neurons receive signals from outside the body, while interneurons and motor neurons process and send signals within the nervous system.
84
How do tonic receptors respond to sustained stimulation?
- tonic receptors adapt slowly or not at all
- they keep sending signals the whole time a stimulus is present - they don’t stop quickly
* Tonic = Time (tonic receptors keep firing over time as long as the stimulus is there)
85
What is an example of tonic receptors?
Muscle stretch receptors and joint proprioceptors
- because your brain needs constant information about your body’s position and muscle length - not just when it changes
86
How do phasic receptors respond to stimulation?
They adapt quickly and stop firing if the stimulus continues (watch or T-shirt example)
87
What is an example of phasic receptors?
Tactile receptors in the skin (touch)
- respond quickly at first, then stop firing
- when you put on a watch, you feel it right away, you don’t feel it again until you take it off (even though the stimulus has been the same all day)
Phasic = Phast (react fast to change, then stop when its constant)
88
What is the main function of phasic receptors?
To detect changes in touch or pressure rather than constant sensations.
89
How does a tonic receptor respond to a sustained stimulus?
It adapts slowly or not at all and continues to send signals during the entire stimulus.
90
What kind of information do tonic receptors provide?
Continuous information about a constant stimulus.
91
How does a phasic receptor respond to stimulation?
It adapts rapidly, firing mainly at the beginning and end of a stimulus.
92
What is the “off response” in a phasic receptor?
The second spike that occurs when the stimulus is removed (taking off your watch)
93
What do phasic receptors detect?
Changes in stimulus intensity rather than ongoing conditions.
94
What is an example of phasic receptor activity in everyday life?
Feeling your watch when you first put it on or take it off.
95
What does the first-order sensory neuron do?
It is the afferent neuron with its peripheral receptor that first detects the stimulus.
96
Where is the second-order sensory neuron located?
Either in the spinal cord or medulla.
97
What does the second-order sensory neuron do?
It synapses with the third-order neuron.
98
Where is the third-order sensory neuron located?
In the thalamus.
99
What is phantom pain?
Pain that occurs when a person feels pain in a limb that has been amputated.
100
Why does phantom pain occur?
Because the brain still gets signals from the nerve pathway that used to go to the missing limb, so it feels like the limb is still there
101
What can cause the brain to interpret pain in a missing foot?
Irritation of the nerve endings in the stump can send signals that the brain interprets as pain in the missing foot.
102
What does new research suggest causes phantom pain?
Brain remapping when the cortical area that processed the missing limb’s signals is taken over by nearby regions.
103
What does brain remapping in phantom pain lead to?
Misinterpretation of sensory input as pain from the absent body part.
104
What does “coding of sensory information” refer to?
How different properties of a stimulus are distinguished by the nervous system.
105
How is the type of stimulus distinguished?
The type of stimulus is identified by which receptor is activated and where the signal goes in the brain
106
How is the location of a stimulus distinguished?
The brain knows where a stimulus is by which sensory area is activated and where that signal goes in the brains map
107
How is the intensity of a stimulus distinguished?
The brain knows how strong a stimulus is by how often neurons fire and how many are activated
108
What is a receptive field?
The area of skin that one somatosensory neuron responds to
109
How does receptive field size affect tactile acuity?
The smaller the receptive field, the greater the tactile acuity
- you can tell exactly where you’re being touched
- example: fingertips and lips sense tiny differences
110
Which body areas have small receptive fields and greater sensitivity?
Fingertips
111
Which body areas have large receptive fields and less sensitivity?
Areas like the elbow, back, or thighs, its harder to pinpoint touch here
112
What is lateral inhibition?
A process that sharpens contrast and improves localization.
113
How does lateral inhibition affect acuity?
It sharpens contrast and helps pinpoint the exact location of a touch stimulus.
114
What happens when several receptors are activated by a stimulus?
The neuron receiving the strongest input inhibits the weaker neighbouring neurons.
115
What does lateral inhibition do?
It sharpens contrast by inhibiting neighbor neurons, reduces background signals and makes the central point of stimulation stand out more clearly.
116
What happens when you press the tip of a pencil on your skin?
The receptor directly under the point is most strongly stimulated, while surrounding receptors are only slightly activated.
117
What prevents a blurred sensation when receptors are stimulated?
The central pathway inhibits the weaker neighbouring pathways through lateral inhibition.
118
What does lateral inhibition do?
It enhances contrast and allows the brain to pinpoint the exact location of the stimulus.
119
Which sensory systems have the strongest lateral inhibition?
Touch and vision
120
What does strong lateral inhibition provide?
The most precise localization of the stimulus.
121
What are mechanoreceptors sensitive to?
Pressure, stretch, vibration, acceleration, and sound.
122
What are the five types of mechanoreceptors?
(Please Make My Feelings Real)
1. Pacinian Corpuscles: deep pressure & vibration
2. Meissner’s corpuscles: light touch
3. Merkel’s discs: steady pressure & texture
4. Ruffini corpuscles: stretch of skin
5. Free nerve endings: pain & temperature
123
What do mechanoreceptors detect?
Different types of mechanical forces like pressure, vibration, and stretch.
124
What do mechanoreceptors allow us to feel?
Touch and body position.
125
What type of receptors are Pacinian and Meissner’s corpuscles?
Rapidly adapting (phasic) receptors.
126
What does it mean that Pacinian and Meissner’s corpuscles are rapidly adapting?
They respond quickly at the start and end of a stimulus
127
What is the function of Pacinian corpuscles?
- detect deep pressure and vibration (around 250 Hz)
- think pacinian = pressure + pulses
- located deep in the skin
- fast adaption (phasic)
128
Where are Pacinian corpuscles located?
Deep skin layers, joints, and tendons
129
What is the function of Meissner’s corpuscles?
Detect light touch, texture changes, and low vibration
Meissners = Mild touch
130
Where are Meissner’s corpuscles located?
Fingertips, lips, and nipples
131
What is an example of a stimulus detected by Pacinian corpuscles?
deep pressure and vibration like when your phone vibrates
132
What is an example of a stimulus detected by Meissner’s corpuscles?
light touch like a gentle brush on your fingertips
133
What type of adaptation do Merkel’s discs and Ruffini corpuscles have?
Slow (tonic) adaptation
134
What is the function of Merkel’s discs?
Slowly sense steady pressure, shape, and texture
Merkel = material texture
135
Where are Merkel’s discs located?
Fingertips and touch domes
136
What is the function of Ruffini corpuscles?
adapt slowly (tonic) and respond to skin stretch and joint movement
Ruffini = rub/stretch
137
Where are Ruffini corpuscles located?
Deep dermis, ligaments, and joints.
138
What do Merkel’s discs help you feel?
The edges of an object through steady pressure and texture.
139
What do Ruffini corpuscles help the brain detect?
Finger position and movement.
140
What are free nerve endings known as?
The simplest and most abundant receptors.
141
What do free nerve endings detect?
Touch, pressure, temperature, and pain.
142
Where are free nerve endings found?
In the skin, cornea, and other tissues.
143
Are free nerve endings myelinated?
Some are myelinated; others are not.
144
What sensations do free nerve endings respond to?
Touch, temperature, and pain.
145
What is an example of free nerve endings in action?
When you rub your eye or touch a hot surface, they send protective signals.
146
What other sensations are free nerve endings responsible for?
Itching and tickling.
147
What is pain primarily considered?
A protective mechanism meant to alert that tissue damage is occurring or is about to occur.
148
What causes the sensation of pain?
Activation of nociceptors, the body’s warning system for tissue damage
149
What is the purpose of pain?
It alerts us to potential harm and helps trigger protective actions, such as pulling away from danger.
150
How does the storage of painful experiences in memory help us?
It helps us avoid potentially harmful events in the future.
151
What is the overall function of pain in the body?
To serve as a warning system that helps prevent or minimize tissue damage.
152
What is the sensation of pain accompanied by?
Motivated behavioural responses and emotional reactions.
153
What can influence the subjective perception of pain?
Past or present experiences.
154
What do prostaglandins do in relation to pain?
They lower the threshold for nociceptor activation, making receptors more sensitive and enhancing the pain response.
155
How do pain relievers reduce pain?
By blocking prostaglandins.
156
Why is pain considered unique?
Because it includes emotional and behavioural responses, such as crying or withdrawal.
157
How can fear or emotions affect pain?
Fear and past experiences can heighten the perception of pain.
158
What are nociceptors?
Pain receptors that do not adapt to sustained or repetitive stimulation, keeping us aware of danger.
159
What are the three categories of nociceptors?
- mechanical
- thermal
- chemical nociceptors
160
What do mechanical nociceptors respond to?
Mechanical damage (cutting, crushing, pinching)
161
What do thermal nociceptors detect?
Extreme heat or cold.
162
What do chemical nociceptors respond to?
Irritating chemicals, such as those released from injured tissue
163
What is the function of nociceptors as a group?
They protect the body by detecting different kinds of harmful stimuli.
164
How do prostaglandins affect nociceptors during tissue injury?
They make nociceptors more sensitive, which increases pain perception.
165
What are nociceptors?
Specialized sensory receptors that detect actual or potential tissue damage from things like pressure, heat, or irritating chemicals.
166
What are the two types of pain fibres?
A-delta fibres
C-fibres
167
What are the characteristics of A-delta fibres?
- large, myelinated, transmit signals quickly
- carry sharp, immediate pain from cold, warmth or mechanical stimuli
- fast, sharp pain
168
What are the characteristics of C-fibres?
- small, unmyelinated, transmit signals slowly
- producing dull, aching pain that lingers
- slow dull pain
169
What kind of pain do A-delta fibres produce?
Sharp, immediate pain such as from a cut or burn
170
What kind of pain do C-fibres produce?
Slow, dull, aching pain
171
What chemicals are linked to slow pain, and what do they activate?
- chemicals like bradykinin trigger polymodal nociceptors (pain receptors that respond to heat, mechanical pressure, or chemical irritation)
172
What are the general characteristics of A-delta fibres?
Small and myelinated.
173
What stimuli do A-delta fibres respond to?
Fast pain, cold, warmth, and mechanical stimuli
174
How is pain from A-delta fibres described?
Sharp, stabbing, or acute.
175
What is the receptor classification of A-delta fibres?
Free nerve ending.
176
What are the general characteristics of C fibres?
Small and unmyelinated.
177
What stimuli do C fibres respond to?
Slow pain, heat, cold, and mechanical stimuli.
178
How is pain from C fibres described?
Burning, aching, or throbbing
179
What is the receptor classification of C fibres?
Free nerve ending.
180
What happens when pain signals reach the spinal cord?
When pain signals reach the spinal cord, they connect with new neurons in the dorsal horn and release chemicals that pass the message on
181
What are the two best-known pain neurotransmitters?
Substance P
Glutamate
182
What is the function of Substance P?
Substance P helps send pain signals up the spinal cord to the brain so you can feel and recognize pain
183
What is the role of Glutamate in pain processing?
It is a major excitatory neurotransmitter that strengthens pain transmission and makes neurons more sensitive
184
Why might an injured area, like sunburned skin, feel extra tender?
Because glutamate increases neuron sensitivity, enhancing pain transmission.
185
What is neuropathic pain?
Pain that occurs without tissue damage due to abnormal signaling within nerves or spinal pathways
186
What can cause neuropathic pain?
Damaged fibres sending false pain messages to the brain, as seen in conditions like diabetic neuropathy.
187
What does the brain’s built-in analgesic system do?
It suppresses pain transmission as impulses enter the spinal cord.
188
What does the brain’s analgesic system depend on?
The presence of opiate receptors.
189
What are the body’s natural pain relievers?
Endorphins, Enkephalins, Dynorphin
190
What are endogenous opiates?
Naturally occurring chemicals in the body that reduce pain, including endorphins, enkephalins, and dynorphin
191
How do endogenous opiates reduce pain perception?
- they act like morphine
- blocking the release of Substance P and reducing pain signals
192
What happens when a noxious stimulus (painful stimulus) activates a nociceptor?
Substance P is released in the dorsal horn of the spinal cord
193
What does Substance P do after being released?
It stimulates ascending pathways to the thalamus, somatosensory cortex, and limbic system.
194
What is the role of the thalamus, somatosensory cortex, and limbic system in the pain pathway?
They localize, perceive, and give emotional meaning to pain.
195
What part of the brain increases alertness in response to pain?
The reticular formation
196
What structures form the descending analgesic pathway?
The periaqueductal gray matter, medulla, and reticular formation.
197
What do the periaqueductal gray matter, medulla, and reticular formation release?
They release natural painkillers (endogenous opiates) like endorphins, that bind to opiate receptors
198
What do endogenous opiates do in the analgesic pathway?
They block Substance P, preventing pain impulses from reaching the brain
199
What does the blocking of Substance P result in?
Transmission of pain impulses to the brain is blocked, reducing pain perception.
200
When can the body’s natural analgesic system cause pain relief?
During exercise, stress, or when using drugs like morphine that mimic endogenous opiates
201
What is the main purpose of the eye’s protective mechanisms?
To help protect the eyes from injury.
202
How is the eyeball protected structurally?
It is sheltered by a bony socket in which it is positioned.
203
What role do the eyelids play in eye protection?
They act like shutters, protecting the eye from environmental hazards such as dust and light.
204
What do the eyelids protect the eye from?
Dust, bright light, and other environmental hazards.
205
What is the function of eyelashes in eye protection?
Eyelashes trap fine, airborne debris such as dust before it can fall into the eye.
206
What do tears do for the eyes?
Tears lubricate, cleanse, and have bactericidal properties to kill bacteria.
207
Where are tears continuously produced?
By the lacrimal glands.
208
How do tears help protect the eyes during blinking?
Tears spread across the eye’s surface to keep it moist and protected.
209
How many tissue layers enclose the eye?
The eye is enclosed by three tissue layers.
210
What does the outer layer of the eye include?
The sclera and cornea (shapes and protects)
211
What is the sclera?
- tough outer layer of connective tissue
- visible white part of the eye
- protects it
212
What is the cornea and what is its function?
The cornea is the transparent outer layer of the eye that lets light rays pass into the interior of the eye
213
What does the middle layer of the eye contain and what is its function?
The middle layer is the choroid, which contains blood vessels that nourish the retina
214
What structures does the choroid form at the front of the eye?
The ciliary body and iris.
215
What is the innermost layer of the eye?
The retina.
216
What does the retina contain and what is its function?
It contains rods and cones, the photoreceptors that convert light into nerve impulses.
217
How many fluid-filled cavities are inside the eye and what separates them?
Two fluid-filled cavities separated by the lens.
218
What does the posterior (back) cavity contain and what is its function?
- contains vitreous humour, a gel-like fluid that helps maintain the sphere shape of the eyeball
219
What does the anterior (front) cavity contain and what does it do?
- contains aqueous humour, a watery fluid that nourishes the cornea and lens
220
Where is aqueous humour produced?
By the capillary network within the ciliary body.
221
What condition can occur if aqueous humour doesn’t drain properly?
Pressure builds up and can cause glaucoma, which may damage the retina and optic nerve.
222
Where is aqueous humour formed?
It is formed by a capillary network in the ciliary body.
223
Through which structure does aqueous humour drain?
It drains into the canal of Schlemm.
224
Where does aqueous humour eventually go after draining?
It eventually enters the blood.
225
What is the iris? STUDY
The coloured, ring-shaped part of the eye made of smooth muscle.
226
What does the iris control? STUDY
It controls how much light enters the eye by adjusting the pupil’s size
Bright light = pupils constrict (get small)
Dim light = pupils dilate (get big)
227
What two smooth muscle networks are found in the iris? stzudyz
The circular (constrictor) muscle
The radial (dilator) muscle
228
What determines eye colour? STUDY
Pigment in the iris.
229
Why is iris recognition used for identification? STUDY
Each person’s iris pattern is unique, making it a reliable form of identification.
230
What is the pupil? STUDY
The pupil is the round opening in the centre of the iris through which light enters the eye.
231
What happens when the circular (constrictor) muscle contracts, and which system controls it? STUDY
The pupil becomes smaller (constricts), controlled by the parasympathetic system, which protects the eye in bright light.
232
What happens when the radial (dilator) muscle contracts, and which system controls it? STUDY
The pupil dilates, controlled by the sympathetic system, allowing more light in during dim conditions.
233
What is the function of the balance between constriction and dilation? STUDY
It automatically regulates how much light reaches the retina.
234
What is light? STUDY
Light is a form of electromagnetic radiation - variable wavelength and amplitude
235
What determines the brightness of light? STUDY
The amplitude of the light wave determines brightness.
236
How do light rays travel? STUDY
Light rays radiate outward in all directions.
237
What happens to light rays when they pass through a dense medium? STUDY
They slow down and change course (bend).
238
What are the two main refractive structures of the eye? STUDY
The cornea and the lens.
239
Which structure contributes most extensively to the eye’s total refractive ability? STUDY
The cornea.
240
Why does the cornea’s refractive ability remain constant? STUDY
Because its curvature never changes.
241
How does the lens adjust its refractive ability? STUDY
By changing its curvature as needed for near or far vision.
242
What is the main function of the cornea and lens together?
To focus light from objects that are near or far onto the retina.
243
What happens to light when it passes through a curved surface?
Light bends, or refracts, when passing through a curved surface.
244
What does a convex lens do to light rays?
bends light rays inward, bringing them together
245
What does a concave lens do to light rays?
bends light rays outward, spreading them apart
246
What happens to light rays from distant objects as they enter the eye?
The light rays are parallel and need less bending to focus on the retina.
247
What happens to light rays from near objects as they enter the eye?
The light rays are diverging (spreading apart) and need more bending (refraction) by the lens to focus clearly on the retina
Near objects more work for your eyes, lens must get rounder (more curved) to bend rays enough
“Near means bend more”
248
What does the eye do to focus on near objects?
The lens becomes stronger and more curved to bend light rays enough to focus clearly on the retina
249
What is accommodation? STUDY
The change of strength/shape of the lens to focus on near or far objects
250
What controls the process of accommodation? STUDY
ciliary muscle and suspensory ligaments
251
What happens to accommodation ability with age? STUDY
It decreases because the lens becomes less elastic and loses its ability to change shape.
252
What is the condition called when the lens loses its ability to accommodate with age? STUDY
Presbyopia
253
Around what age does presbyopia typically begin to appear?
Around age 45 to 50.
254
What structure forms a circular ring around the lens?
The ciliary muscle.
255
What happens when the ciliary muscle relaxes?
The suspensory ligaments pull the lens flat for distant vision
256
What happens when the ciliary muscle contracts?
The suspensory ligaments loosen, and the lens becomes more rounded for near vision.
257
What does the change in lens curvature accomplish?
It increases the lens’s refractive power so light focuses properly on the retina.
258
What is emmetropia? STUDY
Emmetropia is normal vision, where light from a distant object focuses exactly on the retina without the lens needing to adjust (no accommodation)
- Emme = perfect vision
- light focuses on (not in front or behind) the retina
- Emmetropia = easy focus distant
259
What happens in emmetropia when looking at a far object? STUDY
The light is focused on the retina without accommodation.
260
What happens when the eye shifts focus from a far object to a near one?
The ciliary muscle contracts, the lens becomes more rounded, and light rays stay focused on the retina.
261
How does the lens change to focus on near objects?
The strength of the lens increases by becoming more curved.
262
Where is the image focused in emmetropia?
Directly on the retina, producing a sharp, clear picture.
263
What is myopia? STUDY
Myopia, or nearsightedness, occurs when the eyeball is too long or the lens is too strong.
264
Where does light from distant objects focus in myopia? STUDY
In front of the retina, making distant vision blurry.
265
Why can people with myopia see near objects clearly? STUDY
Because light from near objects focuses correctly on the retina without the need for accommodation.
266
How can myopia be corrected? STUDY
With a concave lens, which diverges light rays slightly before they enter the eye so the image focuses on the retina.
267
In myopia, which type of vision is better — near or far? STUDY
Near vision is better than far vision.
268
What is hyperopia?STUDY
Hyperopia, or farsightedness, occurs when the eyeball is too short or the lens is too weak.
269
Where are far objects focused in hyperopia? STUDY
On the retina only with accommodation.
270
Where are near objects focused in hyperopia? STUDY
Behind the retina, even with accommodation, making near vision blurry.
271
Which type of vision is better in hyperopia — near or far? STUDY
Far vision is better than near vision.
272
How can hyperopia be corrected? STUDY
With a convex lens, which converges light rays before they enter the eye so the image focuses directly on the retina.
273
Is the retina a separate organ or part of another system? STUDY
The retina is an extension of the central nervous system (CNS), not a separate organ.
274
What are the three layers of excitable cells in the retina? STUDY
Rods and cones – outermost layer, detect light (photoreceptors)
Bipolar cells – middle layer, relay signals
Ganglion cells – innermost layer, form the optic nerve
275
What is the function of the optic disc (blind spot)? STUDY
The optic disc has no rods or cones, so no image can be detected there.
276
How does light reach the photoreceptors in the retina? STUDY
Light passes through the front layers of the retina before reaching the rods and cones at the back.
277
What forms the optic nerve? STUDY
Axons of the ganglion cells come together to form the optic nerve.
278
What is the fovea?
The fovea is a pinpoint depression at the retina’s center that contains only cones, responsible for the most distinct and sharpest vision.
279
What is the macula lutea?
The macula lutea surrounds the fovea and has a high cone density and high visual acuity, making it crucial for detailed vision.
280
What is macular degeneration?
Macular degeneration is the loss of central photoreceptors in the macula, leading to loss of central vision but preserved peripheral vision — often described as “doughnut-shaped” vision.
281
Why does the fovea provide the clearest vision?
Because light strikes the photoreceptors directly, with no other retinal layers blocking it.
282
What are the two types of photoreceptors, and what do they detect?
Rods: Active in dim light - detect shapes and movement
Cones: Active in bright light - detect color
283
What are the three main parts of a photoreceptor?
Outer segment – detects light and contains photopigments
Inner segment – contains metabolic machinery
Synaptic terminal – sends signals to bipolar cells
284
What are the two components of photopigments and their roles?
Opsin: Protein in the disc membrane
Retinene (retinal): Vitamin A derivative that absorbs light
285
What happens when light hits a photopigment?
Light causes a chemical change in the photopigment, which starts the visual signal.
286
What are photoreceptors?
Specialized cells in the retina (rods and cones) that detect light and convert it into electrical signals for the brain.
287
What is found in the outer part of rods and cones?
The outer segment is packed with discs containing light-sensitive photopigments.
288
What do photopigments do?
They absorb light and trigger a chemical reaction that starts the process of turning light into electrical nerve signals.
289
What happens to photopigments when exposed to light?
The structure of the photopigment changes, initiating the visual signal to the brain.
290
What pigment is found in rods, and what is its function?
Rhodopsin is the pigment in rods
It absorbs all visible wavelengths and provides vision in shades of grey (black & white vision)
291
What pigments are found in cones, and what do they do?
Cones contain three pigments—red, green, and blue—each responding selectively to different wavelengths of light to make color vision possible.
292
How many photopigments are there in total?
There are four photopigments—one in rods (rhodopsin) and three in cones (red, green, and blue).
293
Where are rods and cones concentrated in the retina?
Rods: Found mainly in the outer retina, active in low light
Cones: Concentrated in the macula and fovea, active in bright light and responsible for sharp color vision
294
What is dark adaptation?
The process that allows you to gradually distinguish objects as you enter a dark area.
295
What causes dark adaptation?
It occurs due to the regeneration of rod photopigments that were broken down by previous light exposure.
296
What chemical messenger keeps photoreceptors active in the dark?
cGMP (cyclic guanosine monophosphate) keeps sodium channels open, allowing sodium to enter the cell
297
What happens to photoreceptors in the dark?
They stay depolarized and continue releasing neurotransmitters until light exposure changes their state
298
How do our eyes adjust to the dark over time?
As we stay in darkness, rod pigments regenerate, improving our ability to see in low light.
299
What is light adaptation?
The process that allows you to gradually distinguish objects as you move into an area with more light.
300
What causes light adaptation?
It occurs due to the rapid breakdown of cone photopigments in bright light.
301
What happens to cGMP levels in light?
cGMP decreases, which causes Na+ channels to close = hyperpolarized
302
What happens to photoreceptor activity in bright light?
The cell becomes less active and stops sending signals, helping the eyes adjust to the brightness.
303
Which photoreceptors are mainly active during light adaptation?
Cones, since they function best in bright light and are responsible for color and sharp vision.
304
What is phototransduction?
The process by which light energy is converted into electrical signals in the photoreceptors.
305
What happens in the dark during phototransduction?
cGMP levels are high Na⁺ channels remain open The cell is depolarized Neurotransmitters are released Bipolar cells are inhibited, so no signal is sent to the brain
306
What happens in the light during phototransduction?
- light activates rhodopsin
- cGMP levels decrease
-Na⁺ channels close
- cell becomes hyperpolarized
- Less neurotransmitter (glutamate) is released
- Bipolar and ganglion cells are activated
- Signal sent to brain
307
Which cells form the optic nerve and carry the visual signal to the brain?
The ganglion cells.
308
How do bipolar cells contribute to the visual pathway?
They relay signals between photoreceptors and ganglion cells, allowing visual information to pass to the brain.
309
What type of vision do cones provide?
Colour vision (red, green, and blue pigments).
310
How do rods and cones differ in sensitivity?
Rods: High sensitivity (function well in dim light)
Cones: Low sensitivity (function only in bright light)
311
How do rods and cones differ in visual acuity?
Rods: Low acuity (less sharp)
Cones: High acuity (sharp, detailed vision)
312
What type of vision are rods responsible for?
Night vision (scotopic vision).
313
What type of vision are cones responsible for?
Day vision (photopic vision).
314
How do rods and cones differ in retinal convergence?
Rods: Much convergence in retinal pathways (many rods share one ganglion cell)
Cones: Little convergence (one cone connects to one bipolar/ganglion cell)
315
Where are rods and cones most concentrated?
Rods: More numerous in the periphery of the retina. Cones: Concentrated in the fovea and macula lutea.
316
What does colour vision depend on?
Colour vision depends on how cone photoreceptors respond to different wavelengths of light.
317
What are the three types of cones, and what wavelengths are they most sensitive to?
Blue cones – short wavelengths Green cones – medium wavelengths Red cones – long wavelengths
318
Do cones respond only to one wavelength?
No, each cone responds most effectively to one wavelength but can also respond to varying degrees to others.
319
How does the brain interpret colour?
The brain interprets colour based on the ratio of stimulation among the three types of cones.
320
What do DNA studies show about cone pigments?
DNA studies show there is a variable number of genes coding for cone pigments.
321
What does having multiple genes for red cone pigments allow?
It allows some people to detect finer shades in the red range.
322
What causes colour blindness?
Colour blindness occurs when one or more cones photoreceptor is missing or not functioning properly.
323
What is the most common type of colour blindness?
Red-green colour blindness, where individuals have difficulty distinguishing between red and green hues.
324
How do individuals with colour blindness perceive colours?
They rely more on light intensity and position rather than true colour.
325
Is colour blindness genetic or acquired?
It is usually genetic, but can also result from damage to the eye or visual pathways.
326
Where does the visual pathway begin?
It begins at the retina.
327
What happens at the optic chiasm?
Fibres cross over to the opposite side — fibres from the inner (medial) halves of each retina cross over, while fibres from the outer (lateral) halves remain on the same side.
328
What do the optic tracts carry?
They carry information from the lateral half of one retina and the medial half of the other retina to the thalamus and visual cortex.
329
Why is crossing at the optic chiasm important?
It allows each half of the brain to process the opposite visual field.
330
What happens if there’s damage along the visual pathway?
Damage at different points causes distinct visual deficits, such as: Loss of vision in one eye (optic nerve damage) Loss of peripheral vision (optic chiasm damage) Loss of one visual field in both eyes (optic tract or occipital lobe damage)
331
What is the overlapping area seen by both eyes at the same time called?
The binocular field of vision.
332
What is binocular vision important for?
Depth perception — it allows the brain to judge distance and create a 3D image.
333
How does the brain create depth perception?
The brain combines input from both eyes, comparing the slightly different angles of each image to judge distance and depth.
334
Can depth be estimated with one eye?
Yes — the brain can still estimate depth using size and distance cues, though less accurately.
335
What is the function of the aqueous humour?
It’s a clear watery fluid that is continually formed and carries nutrients to the cornea and lens.
336
What is the function of bipolar cells?
They are important in retinal processing of light stimulus.
337
What is the blind spot?
The point on the retina where the optic nerve exits, lacking photoreceptors — also called the optic disc.
338
What is the function of the choroid?
It’s pigmented to prevent light scattering and contains blood vessels that nourish the retina.
339
What does the ciliary body do?
It produces aqueous humour and contains ciliary muscle.
340
What is the function of the ciliary muscle?
It’s important in accommodation — adjusting the lens shape for near or far vision.
341
What do cones do?
They’re responsible for high acuity, colour, and day vision.
342
What is the function of the cornea?
It contributes most extensively to the eye’s refractive ability.
343
What is the fovea and its function?
It’s the exact centre of the retina, providing the region of highest acuity.
344
What is the function of ganglion cells?
They’re important in retinal processing of light stimulus and their axons form the optic nerve.
345
What is the function of the iris?
It varies the size of the pupil through muscle contraction and is responsible for eye colour.
346
What is the function of the lens?
It provides variable refractive ability during accommodation (changing shape to focus on near or far objects).
347
What is the macula lutea responsible for?
It has high visual acuity due to its abundance of cones.
348
What is the function of the optic disc?
It marks the first part of the visual pathway to the brain (the blind spot, where no photoreceptors are present).
349
What does the optic nerve do?
It carries visual information from the retina to the brain.
350
What is the pupil and what does it do?
It’s the round opening in the middle of the iris that permits variable amounts of light to enter the eye.
351
What is the retina responsible for?
It contains photoreceptors (rods and cones) and is responsible for black-and-white, high-sensitivity, and night vision.
352
What is the function of rods?
They’re responsible for high sensitivity and night vision (detecting light and dark).
353
What does the sclera do?
It’s a protective connective tissue coat that forms the visible white part of the eye.
354
What is the function of suspensory ligaments?
They’re important in accommodation and connect the ciliary muscle to the lens.
355
What is the vitreous humour and its function?
It’s a semi-fluid, jelly-like substance between the lens and retina that helps maintain the eye’s spherical shape.
356
What are cranial nerves?
Twelve pairs of nerves that emerge directly from the brain (not the spinal cord) and primarily serve the head and neck region.
357
What is the function of the olfactory nerve (CN I)?
Sense of smell — transmits information from the nasal mucosa to the olfactory bulb.
358
Is the olfactory nerve sensory, motor, or both?
Sensory only.
359
What is the function of the optic nerve (CN II)?
Vision — carries visual information from the retina to the brain.
360
Is the optic nerve sensory, motor, or both?
Sensory only.
361
What is the function of the oculomotor nerve (CN III)?
Motor control of most eye movements, including the ciliary muscle, pupil constriction (iris), and eyelid elevation.
362
Is the oculomotor nerve sensory, motor, or both?
Motor.
363
What is the reticular formation?
A network of neurons in the brain stem that integrates sensory input such as visual, auditory, and sensory signals from the spinal cord.
364
Where is the reticular formation located?
In the brain stem.
365
What does the reticular formation do?
It integrates sensory input from various sources (visual, auditory, sensory) and helps regulate brain activity.
366
What is the Reticular Activating System (RAS)?
A system of ascending fibres from the reticular formation that activate the cerebral cortex.
367
What is the main function of the RAS?
To maintain wakefulness, alertness, and attention.
368
How does the RAS help process sensory information?
It filters important sensory information, allowing the brain to focus on significant stimuli.
369
What type of impulses does the reticular formation receive?
Visual, auditory, and sensory impulses from the spinal cord.
370
What part of the brain does the RAS activate?
The cerebral cortex.
371
Why is the RAS important for consciousness?
Because it keeps the cerebral cortex active, maintaining wakefulness and awareness of surroundings.
372
How many cranial nerves are there?
Twelve (12) pairs — numbered I to XII.
373
What is Cranial Nerve I and what does it do?
Olfactory nerve (I) – Sensory → carries smell information from the nasal mucosa to the olfactory bulb.
374
What is Cranial Nerve II and what is its function?
Optic nerve (II) – Sensory → transmits visual information from the retina to the brain.
375
What is Cranial Nerve III and what muscles does it control?
Oculomotor nerve (III) – Motor → moves most extra-ocular muscles, constricts pupil (iris muscles), and controls lens shape (ciliary muscle).
376
What is Cranial Nerve IV and its main action?
Trochlear nerve (IV) – Motor → controls the superior oblique muscle, which moves the eye down and inward.
377
What is Cranial Nerve V and its two key functions?
Trigeminal nerve (V) – Both sensory and motor → provides sensation to the face and head and controls chewing (mastication).
378
What is Cranial Nerve VI and its role in eye movement?
Abducens nerve (VI) – Motor → moves the lateral rectus muscle, which abducts the eye (lateral movement).
379
What is Cranial Nerve VII and what are its functions?
Facial nerve (VII) – Both sensory and motor → controls facial expression muscles, secretes saliva and tears, and carries taste from anterior 2/3 of the tongue.
380
What is Cranial Nerve VIII and what are its branches?
Vestibulocochlear nerve (VIII) – Sensory → Cochlear branch: hearing; Vestibular branch: balance and equilibrium.
381
What is Cranial Nerve IX and what does it control?
Glossopharyngeal nerve (IX) – Both sensory and motor → Sensory: taste from posterior 1/3 of tongue, sensation in pharynx; Motor: swallowing and salivation.
382
What is Cranial Nerve X and why is it unique?
Vagus nerve (X) – Both sensory and motor → Motor: muscles of larynx, pharynx, and viscera (thoracic & abdominal organs); Sensory: from thoracic and abdominal organs; helps regulate heart rate and digestion.
383
What is Cranial Nerve XI and its function?
Accessory nerve (XI) – Motor → controls neck and shoulder muscles (trapezius and sternocleidomastoid).
384
What is Cranial Nerve XII and what does it do?
Hypoglossal nerve (XII) – Motor → controls tongue movements for speech and swallowing.
385
Which cranial nerves are purely sensory?
CN I (Olfactory), CN II (Optic), CN VIII (Vestibulocochlear).
386
Which cranial nerves are purely motor?
CN III (Oculomotor), CN IV (Trochlear), CN VI (Abducens), CN XI (Accessory), CN XII (Hypoglossal).
387
Which cranial nerves are mixed (both sensory and motor)?
CN V (Trigeminal), CN VII (Facial), CN IX (Glossopharyngeal), CN X (Vagus).
388
What is a good mnemonic for remembering cranial nerve types (Sensory, Motor, or Both)?
“Some Say Marry Money But My Brother Says Big Brains Matter More.”
389
When pressure on the eye activates photoreceptors, the brain interprets it as light. What principle does this illustrate?
A. Sensation depends on which receptor is stimulated, not the type of stimulus
B. The brain interprets all stimuli as pressure
C. Thresholds for all receptors are the same
D. Photoreceptors can only respond to light stimuli
E. Strong stimuli activate all receptor types equally
A. Sensation depends on which receptor is stimulated, not the type of stimulus.
(This describes the “law of specific nerve energies” — the type of receptor determines the perceived sensation.)
390
Which type of pain fibre is responsible for carrying dull, aching pain that lasts longer?
A. A-delta fibres
B. C fibres
C. Motor fibres
D. Myelinated sensory fibres
B. C fibres.
(C fibres are unmyelinated, slow-conducting fibres that transmit long-lasting, dull, aching pain.)
391
Which of the following correctly describes the macula lutea?
A. It is the pinpoint depression at the retina’s center responsible for the sharpest vision.
B. It is the area surrounding the fovea, rich in cones and important for detailed vision.
C. It is the point where the optic nerve leaves the eye, creating a blind spot.
D. It contains only rod cells and is responsible for night vision.
B. It is the area surrounding the fovea, rich in cones and important for detailed vision.
(The macula lutea surrounds the fovea and contributes to high-acuity vision under bright light.)
392
What is the main difference between rods and cones in terms of the type of vision they provide and the lighting conditions in which they function best?
Rods function in dim light (night vision) and provide black-and-white vision with high sensitivity but low acuity.
Cones function in bright light (day vision) and provide colour vision with high acuity but low sensitivity.
393
The diagrams show two types of vision problems caused by differences in lens strength or eyeball length. What do labels (a) and (b) represent?
(a) Lens too strong / eye too long
(b) Lens too weak / eye too short
A. (a) Myopia – nearsightedness; (b) Hyperopia – farsightedness
B. (a) Hyperopia – farsightedness; (b) Myopia – nearsightedness
C. (a) Myopia – nearsightedness; (b) Normal vision
D. (a) Hyperopia – farsightedness; (b) Normal vision
A. (a) Myopia – nearsightedness; (b) Hyperopia – farsightedness.
(In myopia, the focal point is in front of the retina; in hyperopia, the focal point is behind it.)
