topic 9

Question 1

what makes up the CNS
what makes up the PNS

Answer 1

the brain and spinal cord
everything outside the CNS

Question 2

What are neurons vs nerves

Answer 2

neurons are individual cells and each one has a nerve fibre that carries the nerve impulse. nerves are a bundle of fibres called axons or dendrons.

Question 3

fibres that transmit the nerve impulse away from the cell body..
fibres that transmit the nerve impulse towards the cell body..

Answer 3

axons
dendrons

Question 4

whats the structure of a myelin sheath

Answer 4

schwann cells wrap itself around the nerve fibres/axon many times to form a myelin sheath. They contain gaps called node of ranvier

Question 5

give 2 reasons as to why a myelin sheath is important

Answer 5

1. protects the nerves from damage
2. speeds up transmission of impulses

Question 6

the speed at which impulses can travel at depend on what 2 things?

Answer 6

1. diameter of nerve fibre - thicker = faster
2. whether it contains a myelin sheath or not

Question 7

whats the difference between a nerve and nerve fibre

Answer 7

a nerve fibre is one single axon, a nerve is a bundle of fibres

Question 8

Membrane permeability of an axon

Answer 8

The axon membrane is impermeable to sodium ions but are permeable to potassium ions

Question 9

When is an axon classed as at rest.
How is the resting potential generated

Answer 9

When it’s not conducting a nerve impulse (resting potential)

Na+/K+ pump, Na+ move out and k+ move in, k+ diffuse out thru k+ channels, membrane is impermeable to sodium ions, Na+ channels closed outside becomes positive and inside becomes negative

Question 10

Because the outside of the cell is positive it makes the inside slightly negative …

What’s the value of resting potential

Answer 10

The membrane is polarised

-70mV

Question 11

What happens In the action potential - depolarisation (membrane becomes less neg)

Answer 11

• a neuron is stimulated the axon membrane increases its permeability to sodium ions
  -sodium ion channels open up allowing Na+ to move into the axon if enough Na+ moved into axon then an action potential / threshold potential is achieved

-as a result the potential diff across the membrane is reversed. The cell = +inside , - outside
pd at this point is +40mV

Question 12

What happens in repolarisation

Answer 12

At the end of depolarisation (the last stage)
the Na+ channels close
-increased permeability of membrane to potassium ions , K+ channels open
-inside of axon is neg again

Question 13

What happens in hyper polarisation

Answer 13

-membrane becomes too negative below -70mv bc K+ channels r slow to close

Question 14

Resting potential restored

Answer 14

sodium potassium pump restores og ion distribution returning membrane to its resting potential

Question 15

what happens during the absolute refractory period
Relative refractory period

Answer 15

sodium ion channels r blocked thus another action potential cant be generated
Can re stimulate action potential but with a very big stimulus

Question 16

what is salatory conduction

Answer 16

where the action potential jumps between gaps in the cells of the myelin sheath called the nodes of ranvier, bc the myelin sheath is impermeable

Question 17

what happens when an impulse arrives at the synaptic knob
1

Answer 17

-Arrival of impulse at
Pre synaptic knob increases permeability of presynaptic membrane to calcium ions, calcium ions move into pre synaptic knob
-synaptic vesicles containing acetylcholine fuse with pre synaptic membrane releasing transmitter substance into synaptic cleft
-mols diffuse across gap and attach to receptor sites at the post synaptic membrane, opening Na+ channels

Question 18

once the neurotransmitter binds to receptor sites what can happen

Answer 18

stimulates opening of Na+ channels enabling Na+ into neuron, membrane depolarises triggering another action potential. this is EPSP excitry post synaptic potential
OR
stimulates opening of Cl- channels, enabling Cl- ions to enter neuron, causing hyperpolarisation of membrane, this makes triggering a new action potential difficult IPSP inhibitory post synaptic potential

Question 19

what effect does nicotine have on the nervous system?

Answer 19

mimics the effect of acetylcholine and triggers the release of dopamine, at high doses nicotine binds to and blocks acetylcholine receptors

Question 20

what effect does lidocaine have on the nervous system?
its used as an anaesthetic which prevents you feeling pain

Answer 20

lidocaine molecules block voltage gated sodium channels preventing the production of an action potential in sensory nerves and preventing you from feeling pain.

Question 21

how does cobra venom have an effect on the nervous system?

Answer 21

toxic, binds to and blocks acetylcholine receptors , prevents transmission pf impulses across synapses, causing paralysis

Question 22

What are cells specialised for the detection of stimuli called

Answer 22

Receptors

Question 23

What are the two types of photoreceptors in the retina called

Answer 23

Cones - which r involved in colour vision
rod - which produce monochromatic vision

Question 24

How do the two photoreceptors differ in their lvl of sensitivity

Answer 24

Cones can only work in bright conditions whereas rods are more sensitive and dim light is sufficient for them .

Question 25

What’s the light sensitive pigment in rod cells called

Answer 25

Rhodopsin which absorbs light energy and splits into retinal and opsin

Question 26

Why aren’t rods stimulated in the dark?

Answer 26

Sodium ions diffuse into the cell thru open sodium channels, not enough rhospsin converted, causing membrane to be depolarised causing release of glutamate (neurotransmitter)

Question 27

What does glutamate do

Answer 27

Works as an inhibitory neurotransmitter,It serves to inhibit the neurons which connect rod cells to the optic nerve and so no info is transmitted to the brain

Question 28

In the presence of light what happens

Answer 28

Rhodopsin splits into retinal and opsin (bleaching) .
Opsin binds to membrane of cells causing Na+ channels to close . W/o affecting transport of Na+ out of cell via active transport , membrane becomes hyperpolarised
-neurotransmitter released into synaptic cleft
-action potential forms and is transmitted to brain via optic nerve

Question 29

What’s the functions of the cerebellum , cerebrum , medulla , hypothalamus

Answer 29

Cerebellum - controls balance and coordination of movement
Cerebrum - initiates movement
Medulla - breathing and heart rate
Hypothalamus- controls thermo and osmoregulation

Question 30

What’s the peripheral nervous system divided into

Answer 30

Voluntary and autonomic nervous system

Question 31

What’s the autonomic nervous system split into

Answer 31

Sympathetic- produces noradrenaline, fight or flight , ganglia close to cns

Parasympathetic - produces acetylcholine, rest & digest, ganglia far from cns

Question 32

What are differences between a sensory and motor neuron

Answer 32

1. Sensory neurons have a longer dendron and shorter axon
2. The cell body is in the middle