The Mammalian Nervous System

Question 1

What 2 divisions is the nervous system made up of

Answer 1

Central nervous system
Peripheral nervous system

Question 2

What is the CNS and PNS made up of

Answer 2

CNS - brain and spinal cord
PNS - pairs of nerves which originate from either the brain or spinal cord

Question 3

What are the 2 divisions of the PNS

Answer 3

Voluntary nervous system - impulses under voluntary or conscious control
Autonomic nervous system - carries impulses to smooth muscle, glands and cardiac muscles (involuntary)

Question 4

What are the 2 divisions of the autonomic nervous system

Answer 4

Sympathetic (speeds up)
Parasympathetic (slows down)

Question 5

Difference in function of the sympathetic and parasympathetic

Answer 5

Sympathetic - produces noradrenaline, involved in fight or flight, activated when stressed or active
Parasympathetic - slower + more inhibitory, produces acetylcholine, maintains normal functioning of the body

Question 6

Structure of sensory neurone

Answer 6

Cell body in the middle, myelinated

Question 7

Structure of relay neurone

Answer 7

Cell body in middle, non myelinated

Question 8

Structure of motor neurone

Answer 8

Cell body at beginning, myelinated

Question 9

Myelination formation and purpose

Answer 9

Wrapped in a specialised cell called a Schwann cell
This cell forms a fatty layer around the neurone known as myelins sheath
Myelin sheath protects nerve from damage and speeds up impulse (saltatory conduction)

Question 10

Is resting potential

Answer 10

When the inside of an axon is negatively charged compared to the outside (polarised) at around -70mV

Question 11

What is an action potential

Answer 11

A wave of depolarisation (inside of axon turns positive) which occurs when a neurone sends information from its cell body down its axon

Question 12

What are the stages of an action potential

Answer 12

Depolarisation
Depolarisation
Hyperpolarisation

Question 13

How is resting potential maintained

Answer 13

Na - K pump that pumps 3Na+ out and 2K+ in using active transport (most Na+ channels are closed and most K+ channels are open)

Question 14

What is the charge of an action potential

Answer 14

+40mV

Question 15

Steps of an action potential

Answer 15

Na+ channels open reacting to stimuli
Na+ diffuse rapidly into the axon
Positive feedback happens so more Na+ move in
Axon is +40mV (threshold)
Na+ gates close
Na-K pump pumps excess sodium ions out
K+ channels open
Too many move out resulting in hyperpolarisation
Gates K+ channels close
Inside of to axon returns to resting potential (-70mV)

Question 16

What is the refractory period

Answer 16

The recovery time of an axon

Question 17

What is the purpose of a refractory period

Answer 17

Ensures that action potential were propagated in one direction only
Produces discrete impulses (action potentials are separated from each other)
Limits the number of action potential

Question 18

What is a synapse

Answer 18

The gap between two neurones

Question 19

What are the events at a synapse

Answer 19

Action potential arrives at the presynaptic nob
Calcium channels open and Ca+ moves in
Triggers vesicles to fuse to ore synaptic membrane
Neurotransmitter is released into the synaptic cleft
NT diffuses across cleft
NT binds to specific protein receptors on the Na+ channel on the post synaptic membrane
Causes Na+ channels to open and Na+ diffuses in
Excitatory response is set up in the post synaptic nob

Question 20

What is an inhibitory post synaptic potential (IPSP)

Answer 20

A synaptic potential that makes a post synaptic neurone less likely to generate a potential
Different ion channels open allowing negative ions to diffuse in
Post synaptic nob is more negative that normal rest in potential making an action potential less likely to occur

Question 21

Breakdown of neurotransmitters

Answer 21

NTs are broken down by hydrologic enzymes
They then move back across the cleft and back into the synaptic nob (recycled)

Question 22

What is acetylcholine

Answer 22

A NT that binds to receptors and is broke down by acetylcholinesterase
Hydrolyses acetylcholine into acetate and choline
Acetylcholine and choline diffuse back across cleft to be recycled

Question 23

What are the 2 main types of synapse

Answer 23

Adrenergic - sympathetic, noradrenaline
Cholinergic - parasympathetic, acetylcholine

Question 24

Nicotine on the synapse

Answer 24

Mimics effects of acetylcholine
Triggers an action potential in postsynaptic membrane but receptors remain unresponsive for a while
Triggers release of dopamine (pleasure)
Has stimulating effects but too much can be lethal

Question 25

Lidocaine on the synapse

Answer 25

Used as a local anaesthetic by dentists Blocks voltage gated Na+ channels preventing action potential,s Can be used to prevent heart arrhythmias as it prevents early or extra action potentials

Question 26

Cobra venom in the synapse

Answer 26

Binds reversible to acetylcholine receptors so prevents trans,issue. Of impulses across the synapse Muscles aren’t stimulated to contract so the person becomes paralysed

Question 27

What is transduction

Answer 27

Converts light into nerve impulses (takes place in the retina)

Question 28

Rod cells

Answer 28

Spread evenly across the retina (except fovea) More numerous than cone cells Provides image in black and white as they can’t distinguish between wavelengths Detect light at a very low intensity Certain threshold must be met for a generator potential to occur Have low visual acuity

Question 29

Generator potential rod cells

Answer 29

Generated in bipolar cell which they are connected to as rod cells are 3:1 (retinal convergence) This makes threshold more likely to be reached during summation

Question 30

Rod cells - low light

Answer 30

Rhodopsin pigment must be broken down to create a generator potential Low light intensity has enough energy to break this down

Question 32

Cone cells

Answer 32

Tightly packed at the fovea 3 different types of cone cells responding to different wavelengths of light 1:1 with bipolar neurone Only respond to high light intensity as summation can’t occur Brain can distinguish between seperate sources of light

Question 33

Cone cells - high light

Answer 33

Contain iodopsin which requires a higher intensity of light to be broken down Contain different types of iodopsin which respond to different wavelengths of light

Question 34

What is the fovea

Answer 34

Part of the retina that light is focused upon Receives the greatest intensity of light so cone cells are found here

Question 35

How does rhodopsin work

Answer 35

Formed from opsin and retinal Retinal exists as cis retinal and trans retinal In dark all retinal is cis form When a photon hits rhodopsin it converts from cis to trans Thus puts strain on opsin and retinal Retinal exists, bond g breaking up the molecule This is known as bleaching

Question 36

What is bleaching

Answer 36

Red cells are usually permeable to Na+ ions When rhodopsin is bleached it causes Na channels to close making it less permeable The Na pump continues to work This makes the rod cells more negative than normal This is generator potential

Question 37

Calculation for cardiac output

Answer 37

Cardiac output = stroke volume x heart rate

Question 38

Which part of the brain controls heart rate

Answer 38

Medulla oblongata

Question 39

Chemoreceptor and baroreceptor

Answer 39

Chemoreceptor (carotid artery) - detects a change in chemicals (CO2 + pH) Baroreceptor (aorta and carotid artery)- detects a change in pressure (blood pressure)

Question 40

High CO2 / low pH

Answer 40

Chemoreceptor detects change and sends impulse to medulla along sympathetic Noradrenaline binds to receptors on SAN increasing heart rate

Question 41

Low CO2 / high pH

Answer 41

Chemoreceptor detects change and sends impulse to medulla along parasympathetic Acetylcholine binds to receptors in SAN and heart rate decreases to norm

Question 42

Low blood pressure

Answer 42

Detected by baroreceptor which sends impulse along sensory neurone (sympathetic) to medulla Secretes noradrenaline which binds to receptors in SAN increasing heart rate

Question 43

High blood pressure

Answer 43

Detected by baroreceptors which send impulses to medulla along parasympathetic Secretes acetylcholine which binds to receptors on SAN decreasing heart rate to norm