Chapter 11 - Nervous System

Question 1

What is the nervous system responsible for? What does it enable?

Answer 1

Controlling most body functions

- Enables the organism to receive and respond to stimuli form their external and internal environments

Question 2

How quickly do these signals travel within the nervous system?

Answer 2

100m/s

Question 3

What is the nervous system composed of? What do they do?

Answer 3

1) Neurons: Specialized nervous tissue
2) Neuroglia: Cells that support/protect the neurons

• They work together to form major organs of the nervous system (brain, spinal cord, complex organs)

Question 4

How is the nervous system grouped?

Answer 4

1) Central Nervous System (CNS)

2) Peripheral Nervous System (PNS)

Question 5

Describe the structure of a neuron:

• What do they do?
• What do they consist of?

Answer 5

Neurons are the functional units of the nervous system and are used to convert the electrochemical signals and conduct them throughout the body

They consist of:

• Dendrites: cytoplasmic extensions that receive info and transmit it toward the body
• Cell body (soma): contains nucleus and controls metabolic activity of the neutron
• Axon: long cellular process that transmits impulses (AP) away from the cell body
• Myelin: prevents leakage of signal from axons and allows for faster conduction of impulses
• Nodes of Ranvier: gaps between segments of myelin - where the AP propagates
• Synaptic terminal: axons end in swellings

Question 6

What is myelin produced from? How do they differ from the CNS to PNS?

Answer 6

Glial cells

• CNS: Oligodendrocytes
• PNS: Schwann cells

Question 7

What are neurotransmitters?

Answer 7

They are released from the synaptic terminals into synapse (synaptic cleft) which is the gap between the axon terminals of one cell and the dendrites of the next cell

Question 8

What is the function of neurons?

Answer 8

Specialized to receive signals from sensory receptors or from other neurons in the body
- Signals create action potentials which travel the length of the axons to invade the nerve terminal and causing the release of the neurotransmitter into the synapse

Question 9

Describe the resting potential:

• At rest? Due to?
• How many millivolts at RP? Meaning?
• What is the difference between inside/outside cell due to?
• How many Na/K pumped in/out? Results in?
• What is the cell more permeable to?

Answer 9

At rest, a neuron is polarized due to unequal distribution of ions between the inside and outside of the cell

• 70mV - meaning the inside is more negative than the outside
• The difference is caused by selective ion permeability of the neuronal cell membrane and is maintained by the active transport of ions by the Na/K pump
• 3Na out and 2K in which results in negative internal environment
• More permeable to K; allows some to move back out via facilitated diffusion

Question 10

Describe the action potential:

• What happens if the cell is excited (depolarized)?
• When does an AP begin?
• What happens when AP reaches the terminal?
• What happens after the signal has been propagated through a segment of axon?
• What does this accomplish together?
• What is hyper polarization and refractory period?

Answer 10

• The inside of the cell is less negative and more positive, allowing the cell to reach threshold potential then the voltage-gated channels located in the nerve cell membrane open in response
• An AP begins when the voltage gated Na channels open to respond to depolarization, allowing Na to rush into the cell causing rapid depolarization (continuous process) toward the terminal
• Once the AP reaches the terminal, a final voltage-gated channel specific for Ca opens and allows Ca to rush in triggering the exocytosis of synaptic vesicles containing neurotransmitters
• After the signal has been propagated through a segment of axon, the high voltage causes voltage-gated K channels to open allowing K to rush out of the cell - at this point Na channel close and the Na/K pump begins to pump Na out
• Together these processes return the cell to its negative potential (repolarization)
• Hyperpolarization occurs when the neurons voltage shoots past the resting potential and becomes even more negative inside than normal due to K being free to leave the cell which results in the refractory period, a time after an AP during which a new AP is difficult/impossible to occur (this allows time for neuron to regenerate neurotransmitter and that AP moves in forward direction)

Question 11

What is the all or none response?

- What is stimulus intensity coded by?

Answer 11

If and only if the threshold membrane potential is reached, an AP will occur (fire maximally or not at all)
- Stimulus intensity is coded by frequency of AP and not their magnitude

Question 12

Describe impulse propagation:

• How is info transferred? Why?
• How is speed increased?

Answer 12

Although axons propagate AP bidirectionally, info transfer only occurs in one direction (dendrite to synaptic terminal) because of the refractory period
- Speed is increased by an increase in diameter of the axon and increase in the myelinated segments of the axon such that the membrane is permeable to ions only in the nodes of Ranvier - “hops from node to node”

Question 13

Describe the synapse:

• What is it?
• What does the nerve terminal contain? What occurs here?
• When are neurotransmitters removed?

Answer 13

The synapse is the gap between the axon terminal of one neutron (pre-synaptic) and the dendrites of another neutron (post-synaptic); they can communicate with other cells than neurons i.e. muscle cells (effector cells)
- Nerve terminals contain thousands of membrane-bound vesicles full of chemical messengers (neurotransmitters); when the AP arrives at the nerve terminal (depolarization), the synaptic vesicles fuse with the pre-synaptic membrane and released the neurotransmitter into the synapse which diffuses across and acts on a receptor embedded on the post-synaptic membrane - the release of this neurotransmitter leads to depolarization

They are removed in many ways:

1) Taken back up via nerve terminal (reused/degraded)
2) Degraded by enzymes in the synapse (Act)
3) Diffuse out of synapse

Question 14

Describe the effect of the drug curare:

Answer 14

Blocks post-synaptic nicotinic acetylcholine receptors (i.e. on muscles) so acetylcholine is unable to interact with them

• Muscle relaxation and/or paralysis
• Blocks the ability to constrict muscles

Question 15

Describe the effect of the drug botulinum toxin:

Answer 15

Prevents the release of acetylcholine from pre-synaptic membrane
- Paralysis

Question 16

Describe the effect of the drug anti-cholinesterases:

Answer 16

Used as nerve gas and in the insecticide parathion

• Substance inhibits activity of the acetylcholinesterase enzyme that is responsible for degrading acetylcholine released into the synapse
• Results in acetylcholine unable to be degraded and takes affect on post-synaptic membrane
• No coordination of muscle contractions can occur

Question 17

Describe the different types of neurons:

• Afferent
• Efferent
• Interneurons
• Plexus
• Ganglia

Answer 17

1) Afferent neurons carry sensory info about the external/internal environment to the brain or spinal cord
2) Efferent neurons carry motor commands from the brain or spinal cord to various body parts

3) Interneurons participate only in local circuits
- Links sensory and motor neurons in the brain and spinal cord
- Cell bodies and nerve terminals are in same location

4) Plexuses are a network of nerve fibers

5) Ganglia are clusters of neuronal cell bodies (PNS)
- Called nerve in the CNS

Question 18

How is the nervous system organized?

Answer 18

• Nervous system is broken down in the the CNS and PNS
• The CNS is then broken down into the brain and spinal cord
• The PNS is then broken down into somatic and autonomic
• The autonomic part of the PNS is further broken down into sympathetic and parasympathetic

Question 19

What does the CNS consist of?

Answer 19

The brain and spinal cord

Question 20

What is the brains purpose? What does it consist of? How is it organized?

Answer 20

It is a mass of neurons that resides in the skull that functions to interpret sensory info, form motor plans, and cognitive function

• Consists of outer portion of cell bodies (gray matter) and and inner portion of myelinated axons (white matter)
• The brain is divided into the forebrain, midbrain, and hind brain

Question 21

Describe the forebrain:

- What does it consist of?

Answer 21

1) Telencephalon
- Major component is the cerebral cortex which is highly convoluted gray matter on the surface of the brain
- This part processes and integrates sensory input and motor responses
- Important for memory and creative thought
- Olfactory bulb is centre for reception and integration of olfactory input (smell)

2) Diencephalon
- Contains that thalamus and hypothalamus
- Thalamus: Relay and integration center for spinal cord and cerebral cortex
- Hypothalamus: Controls visceral functions (i.e. hunger, thirst, sex drive, water balance, BP, temp regulation) and is important for endocrine system control

Question 22

Describe the midbrain:

Answer 22

It is a relay enter for visual and auditory impulses

- Play important role in motor control

Question 23

Describe the hindbrain:

• What does it consist of?
• Together, what do they constitute?

Answer 23

1) Cerebellum
- Modulate motor impulses initiated by cerebral cortex
- Maintenance of balance, hand-eye co-ordination, and timing of rapid movements

2) Pons
- Relay center to allow the cortex to communicate with the cerebellum

3) Medulla
- Vital functions (i.e. breathing, HR, GI activity)

• Together = the brainstem

Question 24

Describe the spinal cord:

• What is it and what does it do?
• What is it structure?
• What is the dorsal horn?
• What is the ventral horn?

Answer 24

The spinal cord is elongated extension of the brain that acts as the conduit for sensory info to the brain and motor info from the brain; it can integrate simple motor responses by itself (reflexes)

• Cross sections shows outer white matter area containing motor/sensory axons, and an inner gray matter containing nerve cell bodies
• Sensory info enters spinal cord through dorsal horn
• Motor info exits spinal cord through ventral horn

Question 25

What would be utilized for simple reflexes?

Answer 25

Sensory fibers entering the dorsal root ganglion

Question 26

What would be utilized for other reflexes?

Answer 26

Interneurons between sensory/motor fibers that allow for processing within the spinal cord

Question 27

Describe the PNS:

Answer 27

Consists of nerves and ganglia - Sensory nerves enter CNS and motor nerves leave CNS as part of PNS - PNS further subdivided into somatic and autonomic nervous system; each having motor and sensory components

Question 28

What is the somatic nervous system?

Answer 28

Innervates skeletal muscle and responsible for voluntary movement as well as reflex arcs

Question 29

What is the autonomic nervous system? What does it include? What does it innate? Why is it important?

Answer 29

Also called involuntary* Regulated body's internal environment without aid of conscious control - Includes both sensory and motor fibers - Innervates cardiac and smooth muscle - Important for BP control, GI excretion, respiration, reproduction

Question 30

Describe the two parts of the autonomic system

Answer 30

1) Sympathetic: Flight or Flight - Responses that ready the body for action in emergency situation - Increases BP, HR, blood flow to skeletal muscles, and decreases gut motility - Uses NE as main neurotransmitter 2) Parasympathetic: Rest and Digest - Conserve energy and restore the body to resting activity levels after exertion - Lower HR and increase gut motility - Vagus nerve is important because it innervates many of the thoracic and abdominal viscera - Uses ACh as main neurotransmitter

Question 31

What are special senses?

Answer 31

Human body has number of organs that are specialized receptors adapted to detect stimuli

Question 32

Describe the eye: - What does it do? - What is the structures and functions?

Answer 32

The eye detects light energy (photons) and transmits info about intensity, colour, and shape to the brain Structures and functions: 1) Sclera: Eyeball covered by thick, opaque layer (white) 2) Choroid: Beneath sclera which helps to supply retina with blood; dark, pigmented area that reduces reflection 3) Retina: Inner most part which contains photoreceptors to sense light 4) Cornea: Front of the eye bends and focuses light rays 5) Pupil: Rays travel through this opening whose diameter is controlled by pigmented muscular iris 6) Iris: Responds to light internist 7) Lens: Shape and focal length which is controlled by ciliary muscles, focuses image on retina 8) Photoreceptors: Are in the retina that transduce light into AP - Cones: High intensity illumination, sensitive to colour, 3 pigments absorbed (red, green, blue) - Rods: Low intensity illumination, night vision, rhodopsin pigment only absorbs a single wavelength - Photoreceptors synapse onto bipolar cells which synapse onto ganglion cells - Axons of ganglion bundle to form optic nerves which conducts visual info the the brain 9) Fovia: Small area of retina above the blind spot that is densely packed with cones and important for high acuity vision 10) Vitrous humour: Maintains shape of eye and optical properties 11) Aqueous humour: Watery substate that fills space between lens an cornea

Question 33

Why do blind spots exist?

Answer 33

The point at which the optic nerve exits the eye is the blindspot - Photoreceptors are not present here

Question 34

Describe 5 eye disorders:

Answer 34

1) Myopia: Near-sightedness - when the image is focused infront of the retina 2) Hypermyopia: Far-sightedness - when the image is focused behind the retina 3) Astigmatism: Caused by irregular shaped cornea 4) Cataracts: Develop when lens becomes opaque, light cannot enter eye, and blindness results 5) Glaucoma: Increase in eye pressure in the eye because of blocking of the outflow of the aqueous humour, resulting in optic nerve damage

Question 35

Describe the ear: - What does it do? - Structure and function (processes of hearing)

Answer 35

The ear transduce sound energy (pressure waves) into impulses perceived by the brain as sound which then ass through three different regions of the ear: 1) Outer ear: Consists of the auricle (external ear) and auditory canal 2) Middle ear: Consists of the tympanic membrane (ear drum) at the end of the auditory canal - Three bones (ossicles), the malleus, incus, and stapes) amplify the stimulus and transmit it through oval window which leads to the fluid-filled inner ear 3) Inner ear: Consists of the cochlea and vestibular apparatus - Involved in maintaining equilibrium - Vibration of ossicles exerts pressure on fluid in cochlea, stimulating hair cells in basilar membrane to transduce the pressure into AP which travel via the auditory (cochlear) nerve to the brain for processing