1
Q
What is Afferent division
A
- Afferent neurons carry nerve impulses from pheripehral receptors to the CNS
- Have a long cell body with a single long dendrite and a short axon
- Once appropraite stimulus is reached
- conducts actions potentials twoards the cell bodys in the horn
- Found in clisters called ganglia immediately external to the spine
- Axons extend into the dorsal horn the spinal cord
2
Q
What is receptor threshold
A
- Receptors are located at peripheral endings of afferent neurons responding to stims
- Both internal and external stimulu required threshold before they are activated
- to inform the CNS that the threshold stim has been reached
- Afferent neyrons use action potentials to propagate this signal
- Conversion of an environmental signal to an eelctrical signal is called transduction
3
Q
What are the properteis of receptors
A
use 4 properties to allow the CNS to diffentiate them
MODALITY
* Each receptor is specialized to respond to a different type of energy or stimulus
* Photreceptors - respond to light
* Mechanoreceptors - Respond to mechanical energy. Skeletal muscles are sensitive to stretches and receptors in the ear contain fine heair cells that bend in response to sound waves
* Thermoreceptors - sensitive to heat
* Chemoreceptors - Sensitive to specific chemicals such as taste, smell, contents of the digestive tract
* Some sense the presence of oxygen in blood
LOCATION
* brain can sue identifiable sites to know activated afferent fibers
* Receptive field - each neuron has a region of the environment it is sensitive. This is called the receptive field, if a stim appears in the neurons field, the neuron will fire and the location is communicated
- Multiple sensors - Brain compares inputs from more than 1 sensor, eyes, ears
- Gradients - With smell we can determine location based on gradients
- if something smells we can move to its itensity. The more intense, that measn we are at the source
INTENSITY
* Action potentials are all ore nothing. Intensity is described are more frequent firings of the neurons
DURATION
* afferent neurons encode for different tupes of duration and communicate to the CNS
* Some cells fire only if the stim is present
* SOme cells fire as the stim goes on then stop and fire when the stim goes of
4
Q
what is receptor transduction
A
- Receptors can be specialized endings of an afferent neurons or a seperate receptor cell closely associatd with the pheripher ending in the neuron
- Activation works the same
- Stim causes Ca2+ channels to open and allow it to enter
- They will depolarize the membrane
- This forces the exocytosis of neurotransmitters
5
Q
What are receptors create graded potentials
A
- Receptor and generator potentials are graded potentials in that their aimplitide and duration can vary depending on the strength and duration of the stimulus
- If graded potentials are of sufficent magnitude theu will initaite an action potentail in the afferent neuron
- Specialized afferent endings - The receptor potential itself causes the afferent nerve fiber to reach threshold an trigger action potential
- Seperate receptor cell - When receptor potential is strong, it released a chemical messenger that diffuses to the afferent neuron and opens chemically gated sodium channels. If threshold is achieved, then the afferent nerve fiber will initiate and propagate an action potential
6
Q
What is receptor adaptation
A
- Receptors themself also have the ability to regulate their responses and this is called adaptation
- Stim of same intensity does not always bring about the same magnitude of receptor potential
- In some stims, receptors adapt to the signal by enhancing or lessning their response
- There are two different types of receptors that vary in their speed of adaptation
7
Q
What are tonic receptors
A
- Slow adapting or do not adapt at all
- Important where near constant signal from the stim is neccessary
- msucle stretch receptpr - as CNS constantly requires knowledge of the state of contraction of all skeletal muscles
- Pain receptors are also tonic, as CNS requires knowlege of pain and potentially dangerous stims
8
Q
what are phasic receptors
A
- Rapidly adapting
- They work like a light switch. SIgnal when on, signal when off
- They stop generating action potentials even when the stim is still there
- When the stim is gone, They will signal once more
- Mechanoreceptors are an example of this
- Like wearing a watch or ring - initial wear will annoy u then u get used to it
- This happens from Rapidly adapting pacinian corpuscle
- Deformations in the corpuscle causes the potenials to be generated
- Because these receptors are constantly changing, oertime they will not be afected by the stimulus
9
Q
What is a brief overview of pain
A
- Called nociceptors, and give an unpleasent sensation
- Defence to alert the CNS
- include external and internal events and can include percieved evemts that are observed
10
Q
What are the types of nociceptors
A
- Mechanical nociceptors - Respond to physical damage such as cutting or crushing
- Thermal nociceptors - Respond to temperature, especially heat
- Chemical noiceptors - Respond to noxious chemicals which can be internal or external
- Nociceptors are specialized nerve endings on afferent fibers
- They are called pain fibers
- Two categories, sharp and dull, fast and slow
11
Q
What are fast and dull Pain receptors
A
FAST pain fibers
* A-delta fibers are responsible for
* temperature
* chemical
* mechanical stims
* associated with sharp,stabbing intense pain from stimulation
SLOW pain fibers
* C-fibers
* Unmyelinated so they are slow
* SImilar to fast pain receptors
* Respond to chemical
* temperature
* mechanical
* Unlike A-delta fibers, they are polymordial receptors
* The sensation is burning, aching or throbbing
* associated with slow pain pathways is the bradykinin
* once activated, can directly stimulate noiceptors
* There is no adaptation to the stim, nociceptors are stimulated until the bradykinin is removed which explains the long lasting persistnt pain
12
Q
How does the brain process pain
A
- When action potential reaches the end of afferent pain fiber axon
- Triggers the release of a neurotransmitter
- Substance P coexists with glutamate to activate ascending pathway
- Transmit the pain signals to higher levels for further processing
CORTEX
* Cortical somatosensory processing localized the painto a discrete body regions
* Locates the pain
THALAMUS
* Processing allows for the perception of pain
RETICULAR FORMATION
* Increases the level of alertness and awareness of painful stimuli
HYPOTHALAMUS/LIMBIC SYSTM
* Recieves input from the thalamus and reticular formation and allows for behaviour and emotional responses to the stimuli
13
Q
What is Gluatamate
A
- Amino acids that also function as neurotransmitters
- released by nociceptor nerve endings
- activate post synpatic glutamate receptor on neurons
- Has two actions depending on which type of receptor on the dorsal horn neurons are activated.
- eitehr
- AMPA
- NMDA
14
Q
what is AMPA
A
- Activation causes permeability that generates action potentials
- Dorsal horn neuron and send signal to higher brain centers
- the AMPA channel depolarization occurs only whe na certain level of depolarization is reached will the mG ion in the NMDA channel be dislodged and the NMDA channel will be activated
15
Q
what is an NMDA receptor
A
- Once activated allows calcium to enter the neuron
- Mg2+ will block the receptor on default. It can be removed and it allows Ca to flow in
- Leads to the activation of a second messenger pathway that results in the neuron being more excitable than normal
- Explains why injured areas are more sensitive to a stim
- that would not normally cause pain
- Example is the pain felt when clothing rubs against a sunburn
16
Q
What is the endogenous analgesic system
A
- After intial pain, there is a decrease in the receptor.
- Activation of a descing pathway that in turn activates inhibitory neurons in the dorsal horn
- The axons of these interneurons terminate on the afferent fibers of the nerve terminals
- They release endogenous opiates - pain killers produced by the body
- They supress neurotransmitters released from afferent pain fibers
- Exogenous opiates are not produces by the body like morphine, they activate the opioid receptor and decrease pain
17
Q
What happens when light enters the eye
A
- Eye will regulate how much light can enter by expanding and contracting the iris
- Size can be adjusted by 2 contractions
- Controlled by the autonomic system
PUPILARY CONSTRICTION
* Causes by parasympthatic activity
* One set of muscles organized in circular fashion
* These muscles constrict to make the pullp smaller
PUPILLARY DILLATION
* Caused by sympathetic stimulation
* One set of muscles is organized in radial fashion
* These muscles contract to dillate and allow more light to go in
18
Q
Why does light have to be focused
A
- Light waves radiate outwards from their source
- all incoming rays must be focused onto a single point to allow the eye to process them
- This processes of the light bending is called refraction
19
Q
What does the cornea do
A
- Contributes to most of the reflective ability
- Large density difference at the air-cornea boundary
- The refractory ability of the cornea remains constant as the curve of the cornea cannot be altered
- In some persons, the cornea is uneven this is called astigmatism
20
Q
What does the lens do
A
- Convex structire behind the pupil
- Allows light to focus futher on the retina
- Unlike the cornea it is adjustable
21
Q
A
22
Q
Lens accommodation
A
- The eye can adjust to maintain focus
- controlled bu the cilliary muscle
- When this muscle relaxes, the ligaments pull the lense int oa flatter, less convex shape
- When the muscles contract, it reduces the tension of the ligaments and the lens becomes more convex
- cilliary muscle contraction is also controlled by the ANS
DISTANT LIGHT SOURCES - When the light source is more than 6m away from the lens, the light rays enter parallel when they enter the eye
NEAR LIGHT SOURCES
* When the light is closer than 6m to the lens the light rays are diverging when they enter the eye
* The eye accommoodates by changing shape of the lens so it has a greater ability to bend light, allowung the eye to focus the image
* It will become wider and fatter
23
Q
What is the retina
A
- an extension of the CNS
- Direct connection to the optical nerve
- each retina has 1mil nerve fibers into the brain
- The lens wants to focus light on the retina to convert light energy into electrical signals, sent to the CNS
- The structure of the retina is complex and has many layers. Can be divided into 3 layers of excitable cells
24
Q
What are the rods and cones of the retina
A
- Contained on the outermost layer
- Cones see colours
- rods are for vision in low lighting
25
What are bipolar cells of the retina
* Middle layer cells
* involved in transmission of signals from the rods and cones to the ganglion cells
26
What are ganglion cells
* Neurons located at the inner surface of the retina
* Axons of the ganglion cell make up the optical nerve
27
What is the optical blindspit
Retina is continous throughout the entire surface of the eye. The exception is on the optical disc where ganglion cell axons bundle together to form optic nerves and leave behind the eye
This region has no rods or cones and cannot see
High visual input usually fills this in so it isnt notices
28
Briefly describe the central processing of vision
* Transmitted to the thalamus
* thalamus does initial processing, seperayes visual stims, colours, forms, depth, and movement
* relay to the zones in the cortex
* Thalamus is the integrating center for all sensory input
* Organized into functional cortex with alternating collumns, devoted to left and right
29
How does visual processing work
* Not simple
* 2 eyes
* they are also offset
* 2 eyes improves depth perceptio
* Perseon with 1 eye has poor depth perception
30
Describe the visual pathway
Visual fields are divided into 2 fields
Red and green
Neurons from left topic nerve cross to the right brain
Happens with some neurons from the right optic nerve
**Overall, viusion to the right visual field is procesed in the left side of the brain and vision in the left field ir processed by the right side of the brain **
31
What are the different types of sound waves
PITCH
* Determined by frequency of vibrations. The greater the frequency, the greater the pitch
INTENSITY
* Intensity or loudness dependso n the amplitude of the sound waves
* greater the amplitude, the louder the sound
TIMBER
* Quality of sound
* Overtones that superimpose on pitch
* Timber allows us to distinguish notes between voices and intruments even with same tone and loudness
32
What is the anatomy and function of the external ear
PINNA
* External skin covered cartillage that collects sound waves
* pinnae are essential for the location of sound
* Two ears allows for better precise pinpointing
EAR CANAL
* conducts soundwaves towars the tympanic membrane
* entrance to the ear is guared by fine heair and special cells that secrete ear wax
* The hair prevents airborne particles from entering the canal
* Aids against bacteria by making the environment more toxic
33
Whats is the anatomy and function of the middle ear
* Made up of 3 bones
* Malleus - attached to tympanic membrane like a drum
* Incus - attaches to the stapes
* Stapes - conencts to the oval window of the Ampulla
* Transfers the sound waves into fluid ripples in the inner ear
* as the tympanic membrane vibrates it acts as drum and transfers vibrations to the incus which transfers to the stapes then the oval window
* **Amplifies sound by 22x**
34
What is the anatomy of the inner ear
* Oval window waves are converted to mechanical energy in the form of fluid movement
COCHLEA
* responsible for the perception of hearing
* spiral shape used for pitch discrimination
ORGAN CORTI AND BASILAR MEMBRANE
* transform cochlear fluid vibrations into action potentials propagating auditory messages to the cortex
* changes of membrane potential in these cells match the frequency of the original sound stimulus
OUTER HAIR CELLS
* Transform cochlear fluid vibrations into action potentials, propagating auditory messages to the cortex
* Changes of membrane potential in these cells match the frequency of the orignal sound stimulus
INNER HAIR CELLS
* do not transmit signals to the brain
* modify electrical signalling of the inner hair cells
* Enhance the response of inner hari cells making them more sensitive sound intensity and pitch
35
What is pitch discriminationa and how does it work
* Depends on the shape of basilar membrane
* goes from being narrow at the oval window to narrow at the far end
* Higher pitches are detected at the narrow end of the cochlea at the beggining and lower pitches are detected more into the spiral
* The spiral is made of basilar membrane
* Hair cells in the region become deformed when the discrminant pitch reaches their sectiona nd they transmit to afferent neurons
* **These signals pass through the brainstem**
* For alertness, and arousal, and the thalamus. The thalamus sorts out these signalsand sends them to higher processing centers
36
What is the vestibular apparatus
* Fluid filled sac that contains sensory hairs
* Triggered by the movemnt of fluid
* neuronal signals initiated in the vestibular appratus do not reach conscious awareness
* Some people have very sentive apparatus that casue them to feel dizziness and nausea - This is called motion sickness
* Integrated with the rest of afferent signals from the skin, eyes, muscles and joints
* Maintains balance and posture
* allows the eyes to remain fixed when turning the head
* percieve motion and orientation
37
What are chemo receptors
* Taste and smell rely on these
* Trigger release of appetite and igestive juices
* Used to detect if something is pleasureable or undesireable
* Stimulated by chemicals
38
What are the bodily factors of taste
* Known as gustation - ssenation when tongue receptors react with taste receptors in the oral cavity
* TONGUE
* Most taste receptors are here and organized into buds
TASTE BUDS
* Small bumps that cover the tongie called papillae
* within each tehre is 100 buds
* Each taste bud has 40 taste receptors
* Buds have a limited lifespan of 10 days and are receplaced often
* The have little holes that allow fluids to interact with the receptors
TASTE RECEPTOR CELLS
* When a tastant binds to its receptor, creates a depolarizing potential, can initiate an action potenial in the nerve endings of afferent neurons
AFFERENT NEURONS
* Send signals to the brain stem
* before going to the cortical gustatory area
* This is a region of the parietal lobe in the somatosensory cortex
* from brainstem, they go to hypothalamus and limbic system to distinguish between unpleaseant and unpleasant
* May trigger any ssociated behavioural responses
39
What are the different taste discriminations
SALTY
* Stimmed by salts
* Receptors allow Na In to depolarize the cell
SOUR
* stimulated by acids
* Free H+ acid increase ECF + concentration and reduce the flow of K+
SWEET
* stimed by glucose
* glucose activates G protein and generates cAMP that inhibits K channel
* Artifical sweeteners are designed to interat with sweet taste cells but contain no calories and cannot produce ATP
BITTER
* most diverse
* from vaffiene, nicotine, morphine
* Most poisons are bitter
* protective mechanism
UNAMI
* triggered by amino acids like glutamate
* involve G proteins
* senses protein rich foods and gives meaty flavour
40
How does smell work
* Olfaction is the chemoreceptor that forms smell
* on top of the nasal cavioty
* olfactory mucus located at the ceiling of the nasal cavity, contains the olfaction receptor
* Supporting cells secrete mucus and basal cells the precurous of olfactory receptor cells
* basal cells have a lifespan of 2 months
* axons from the olfactor receptor form the olfactory nerve
41
How doest he olfactory nerve work
* CHemicals that can be smelled dissolve in the mucus layer
* Binding of odourant activates G protein and mobilized secondary cAMP that leads to the opening of Na channels to depolarize
* 5 million olfactory receptors in the human nose
* Allows different types of odourant to be able to activate several receptors to create distinct complex cell
42
Does smell have an influence on taste
yes, congested nose can limit taste
* Smell stimulates olfactory receptors to taste and makes it more vibrant
43
44
Give a brief overview on the autonomic nervous system
* Influences vegetative systems through sympathetic and parasympthatic activities
* These two divisions constantly change to maintain homeostasis
* output from the ANS comes from the hypothalamus, brainstem, and spinal cord
* They are sent to pheripher from sympathetic pathways
* Enteric nervous system, reproduction and thermoregulation
SYMPATHETIC NERVOUS SYSTEM
* Constantly active
* Primary role of the stim fight or flight
* During this, adrenal medulla produces epinephrine or norepinephrine
PARASYMPTHATIC
* Rest and digets system
* Responsible for resting and digestive atcivities
* Happens when the body is at rest, during digestion, urination and salivation
45
What is the automic nerve pathway
* 2 neruon chains connecting the CNS to the effector
* Cell body of the first neuron is located within the CNS and its axon is called the preganglionic fiber
* Synapses with the cell body of the second neuron
* The second neuron cell body is located within a cluster of neuronal cells called the ganglio
* The axon of the second neuron is called the postganglionic fiber
* Innervates the effector organ
46
What is the autonomic nerve origin of the sympathetic nervous system
* Fibers orignate in the thoracic cavity
* preganglion fibers are short and terminate at the ganglia
* located in chains down bot hsides of the spinal cord
* Long postganglionic fibers terminate on the effector organs
* Some might pass through the ganglia and terminate in the ganglia
* Located roughly halfway between the CNS and effector organs
47
What is the autonomic nerve origin of the parasympathetic nervous system
* Preganglionic fibers arise from the brain or lower of the spinal cord
* They are long and terminate in the ganglia located close to the effector organ
* Consequently, the post ganglion fibers are very short
48
what are the neurotransmitters of the sympathetic and parasympathetic nervous system
* All **Preganglionic fibers use ACh acetylcholine**
* The postganglionic fibers use different neurontransmitters
* The sympathetic system long postganglionic fibers use NE or Epi
* The short parasympathetctic post ganglionic fibers use ACh
* Mainly norepinephrine for the sympathethic but some may use epinephrine
49
What is autonomic regualtion
* All effector organs recieve input from both the sympathetic and parasympathetic systems
* The concept is reffered as dual innervation
* Some organs such as the kidneys and adrenal glands do not have direct innervation from both systems
* Most Afferent nerve traffic from the visceral organs and visceral activites never reach the level of conscious regulation. They are regulated by autonimic efferent output
50
What is the autonimic innervation of organs
* Sympathetic is excitatory
* Parasympathetic is inhibitory
* There are some examples where this is opposite like in the digestive tract where paraympathetic activity makes it faster
* The main point - both systems have opposite regulatory actions, allows precise regulation of homeostatic parameter
51
What is para and sympatahtic tone
* At any time each system are active to some degree
* One system will dominate over the other at any given time
* When a system increases its firing rate thats when it becomes dominant
SYMPATHETIC DOMINANCE
* Fight or flight response
* prepares the body fro an emergency stressfull activity
* soldier being shot at, automatically increases prepardness
PARASYMPATHETIC DOMINANCE
* Rest and digest
* Active during times of rest
* when the soldier has found somehwere safe they will rest
52
What are the exceptions of Dual innervation
ARTERIOLES AND VEINS
* Most recieve only sympathetic stsims and regualtion is achieved by increasing or decreasing sympathetic activity
*
SWEAT GLANDS
* most only recidve sympathetic innervation
* interestingly, sympathetic postganglionic fibers release ACh and not nor or epi
SALIVARY GALNDS
* recieve dual innervation but interestingly both systems can stimulate it
53
What is the role of adrenal glands in the ANS
* Adrenal medulla functions like a sympathetic ganglion in that it is innervated by sympathetic preganglionic fiber
* Does not give rise to a post hamhlionic fiber, instead upon sympaythetuc stims the adrenal medulla release chemica transmitters
* in this case they qualify as hormones since they are released into circualtion
* 20%of these hormone are norepi, 80% is epi
* Therefore, upon sympathetic stims, the adrenal medulla acts as a global amplifier of the sympatyhetic system
54
what are the two classes of receptors in the ANS
Cholinergic, and adrenergic
55
What are the dif kinds of cholinergic receptors
MUSCARINIC RECEPTOR
* activated my mushroom posion muscarine
* found in effector cell of membranes
* Respond to ACh released by parasympathetic post ganglionic fibers
* bindings of ACh or muscarine, triggers G protein coupled reactions which opens cation channels to depolarize the cell
NICOTINIC RECEPTORS
* activated by tobacco
* found on cell bodies of postganglionic cells in the autonimic ganglia
* bind to ACh released from both sympathetic and parasympathetic preganglionic fibers
* Binding of ACh or nictotine receptors on cation channels lead to opening of the channel leading to the repsonse
56
What are adrenergic receptors
* G protein coupled receptors in the membrane of cells that respond to catchealomines, neurotransmitters
* These are norepi or epi
* truly define how a tissue will respons
* Classified as alpha or beta reeptors
* subclasssifed further
* once activated have different cellular actions
57
what are alpha receptors
* both a1, and a2 have a greater sensitivity to norepinephrine and epinepherine
* all adrengeric receptors activate G proteons
* activation supress the cAMP pathway
* activatation of an a1 receptor activates the Ca2 second messenger system
58
What is a beta receptor
* B2 have a greater affinity for epineprine than B1
* B1 respond equally to norepinephrine and epinephrine
* B3 are only found in adipose
59
How do adrenergic recetorps target tissue selective responses
* Have different cellular actions once they are activated
* Effects of sympathetic stims are determined by the number and type of adnergic receptor in the targe tissues and organs
* A1 receprors are almost all aecitatroy, they are expressed in smooth muscle cells of blood vessels
* Thei stims cause comntraction, in cointrast, the smooth muscle cells of the digestive system primarily express a2 becasue when activated they decrease contractions
* Stims of b1 receptors are found in the heart, stims of b2 receptors are generally inhibitory and douns in the smooth muscle cells of artierioels and respoiratory airways
60
What are drugs that target tissue selective responses
* Stims of B1 are stimulatpory and B2 are inhinitory
* B2 found in smooth muscle cells of artieroles and respiatory airways, bc of this subutamole is an activator of B2 and is a bronchodillator
* Commonly used to treat asthma because it opens airways and have little effect on the heart rate
61
What is the somatic nervous system
* Comprised of axons that innervate the skeletal muscle under voluntary control
* Axons terminate directly on their effectors
* Upon stimulation, they release acetylcholine whcih results in teh contraction of muscles
* Unlike the autonimic system, there is no inhibitory skeletal muscle contractions
* only excitatory
* Relaxation of skeletal muscle occurs by decreasing the excitability of motor neurons
62
What are motor neurons
* Converging point for large amount of sensory input
* Basal nuclei in the cerebellum and brainstem send info to the upper motor neurons
* Recieve sensory input from reflex pathways directly
* Motor neurons accept this collection of both excitatory EPSPs and inhibitory IPSPs signal to ultimately decide whether or not to generation action potentaisl and contrast the muscles through lower motor neurons
* Damage to either upper or lower neurons can cause irreverisble health problems
63
How do neuromsuclar junctions work and what are they
* Terminal end of a motor neurons
* Terminal button is a knob like structure
* Fills a shallow depression
* There is a cleft left between the 2 structures
* Neurotransmitter from the neuron stims the muscle fibers
MECHANISM
* Action potential in a motor neuron is propagated to the axon terminal - the button
* a. Action potential reaches axon terminal.
b. Ca2+ influx triggered by voltage-gated channels prompts Ach release.
c. Ach binds to nicotinic receptors, leading to motor end plate depolarization.
d. Depolarization initiates muscle contraction via voltage-gated Na+ channels.
e. Acetylcholinesterase rapidly deactivates Ach to end contraction signal.
64
How is the neuromusclar system vulnerable
BLACK WIDOW SPIDER
* Causes an explosive release of ACh from all cholinergic sites
* overwhelms acetylchlinoesterase to rapidly inactivate it
* Results in prolonged depoalrization
* During this time, voltage gated ion channels are in theri inactive states and cannot be stimulated
* Should this happen, at the diaphragm contraction could not be initiated and respiratory failure will occur
BOTULINUM TOXIC
* form of food poisioning
* blocks the release of ACh
* Skeletal muscles cannot be excited and respiratory failure will occur
CURARE
* Binds to the same receptor as ACh
* does not cause an end plate potential , preventing ACh from binding
* This prevents skeletal muscles from moving=
* Respiatory failure follow
PHGY216
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