nerves

Question 1

what is the peripheral nervous system composed of?

Answer 1

spinal nerves, cranial nerves and their roots and branches

Question 2

what is the central nervous system composed of?

Answer 2

the brain and spinal cord

Question 3

give the general reflex arc

Answer 3

stimulus–> sensory neurone–>relay neurone–>motor neurone–>effector (muscle/gland)

Question 4

whats the difference between endocrine and nervous responses?

Answer 4

endocrine responses are slower but last longer, it involves hormones being released into the bloodstream (affecting target organs)

Question 5

why is the white matter white?

Answer 5

contains myelinated neurones, lipids

Question 6

why is the grey matter grey?

Answer 6

contains many nuclei, cell bodies and non-myelinated neurons

Question 7

what is the middle of the spinal cord called?

Answer 7

central canal

Question 8

what is the swelling called before the white matter, that contains a cell body (and what’s it called on the lower side)?

Answer 8

dorsal root ganglion, ventral root

Question 9

what does the dorsal root ganglion hold?

Answer 9

cell bodies of the sensory neurones

Question 10

give an example of a nerve net

Answer 10

hydra

Question 11

give some characteristics of hydra

Answer 11

• sensory receptors respond to a limited range of stimuli
• number of effectors is small
• contains one type of nerve cell
• signal travels in many directions
• unmyelinated

Question 12

what is the degree of response in hydra dependent on?

Answer 12

the strength of the stimulus and how many receptors are stimulated

Question 13

name parts of the motor neurone starting from the cell body

Answer 13

cell body, dendrites, myelin sheath, axon, nodes of Ranvier, synaptic end bulb (axon terminals)

Question 14

what value is resting potential?

Answer 14

-70mV

Question 14

how is potential difference measured?

Answer 14

oscilloscope

Question 15

describe resting potential

Answer 15

• sodium potassium pump using ATP actively transporting 3 Na+ out of the neurone and 2 K+ into the neurone.
• potassium ion channels are leaky and K+ ions pass out of the axoplasm by facilitated diffusion
• sodium ion channels are closed so sodium ions remain outside

Question 16

what makes the neurone -70mV?

Answer 16

• large plasma proteins and organic phosphates in the cytoplasm (negative)
• ion movement (3 Na+ out and 2K+ in)

Question 17

what happens after a stimulus is applied to the axon?

Answer 17

the permeability of the membrane to sodium ions increases = sodium ions open

Question 18

what’s the result of the sodium ion channels being opened by a stimulus?

Answer 18

sodium ions diffuse into the axon through the channels (reducing the potential difference)

Question 19

what value is threshold?

Answer 19

-55mV

Question 20

what happens to the sodium ion channels once passed threshold?

Answer 20

all sodium ion channels open = full action potential is generated = sodium ions RAPIDLY diffuse into the cell

Question 21

what happens if the threshold (-55mV) is not reached?

Answer 21

the sodium ion channels close and resting potential restores quickly

Question 22

what’s the value for depolarisation?

Answer 22

+40mV

Question 23

describe what happens in depolarisation

Answer 23

sodium ions rapidly diffuse into the cell, which changes the potential difference from -70mV to +40mV

Question 24

describe the all or nothing law

Answer 24

the action potential is either generated if the threshold level is reached or not if it isn't

Question 25

how are different strengths of stimuli differentiated?

Answer 25

number of action potentials per second (not by size)

Question 26

what's it called when you return to resting potential from the action potential (depolarisation)?

Answer 26

repolarisation

Question 27

what occurs in repolarisation?

Answer 27

potassium ions leave the axoplasm by facilitated diffusion (travel down concentration gradient and potential difference falls quickly)

Question 28

what is the overshoot after repolarisation called?

Answer 28

hyperpolarisation

Question 29

what occurs in the refractory period?

Answer 29

hyperpolarisation (potential difference lower than resting potential) -- keeps the transmission from travelling in one direction

Question 30

why does the refractory period make the transmission travel in one direction?

Answer 30

during an action potential & repolarisation, further action potentials are not possible = keeps the transmission along the axon moving in one direction as the part of the membrane immediately behind an action potential is still repolarising and cannot be stimulated to respond

Question 31

what type of conduction can occur in myelinated neurones?

Answer 31

saltatory conduction

Question 32

explain saltatory conduction

Answer 32

due to the Schwann cells, the action potentials are only generated at the nodes of Ranvier, so the action potential 'jumps' from one node to the next

Question 33

give 2 advantages of myelinated vs unmyelinated

Answer 33

- faster conduction (100m/s vs 1m/s) - sodium potassium pump only operates at the nodes, so less ATP is used in myelinated neurons

Question 34

give 3 factors that affect transmission rates in axons

Answer 34

- diameter of the axon (wider=less resistance therefore faster) - higher temperatures - myelination

Question 35

what is the synapse?

Answer 35

where 2 neurons meet/ motor neurone meets an effector

Question 36

name the parts of the synapse (generally)

Answer 36

synaptic knob, mitochondria for ATP, presynaptic neurone, vesicles containing transmitters, post synaptic neuron, synaptic cleft

Question 37

describe the first step in synapse transmission with acetylcholine

Answer 37

when a wave of depolarisation reaches the axon terminal which has calcium ion channels in the membrane of the synaptic knob

Question 38

what happens in synapse transmission when a wave of depolarisation reaches the axon terminal?

Answer 38

the calcium ions stimulate the vesicles containing neurotransmitter to move to the presynaptic membrane and fuse with it

Question 39

what happens in synapse transmission when Ca2+ ions stimulate the vesicles containing neurotransmitter to move to the presynaptic neurone?

Answer 39

neurotransmitter is released into the synaptic cleft by exocytosis (requires ATP)

Question 40

what does the neurotransmitter do after it diffuses across the synaptic cleft?

Answer 40

binds to ligand gated receptors on the post synaptic membrane = sodium ion channels open on the post-synaptic membrane so sodium ions diffuse into the cell = depolarisation

Question 41

what do the enzymes do in the synaptic cleft? (in synapse transmission)

Answer 41

it breaks down the neurotransmitter and take the products back to the synaptic knob (to be resynthesised and packaged into vesicles)

Question 42

what prevents the simultaneous transmission of impulses (3 things)

Answer 42

- enzymes (transport of products back to synaptic knob) - active transport of calcium ions out of the synaptic knob (prevents vesicles releasing neurotransmitter simultaneously) - reabsorbing the neurotransmitter back into the synaptic knob

Question 43

give 4 ways in which antagonists may work

Answer 43

- preventing calcium ion channels opening - preventing exocytosis - blocking receptors - causing hyperpolarisation of post-synaptic membranes (so it's harder to reach threshold)

Question 44

give 3 way in which agonists may work

Answer 44

- inhibiting the enzymes (like acetylcholinesterase) that break down neurotransmitter - causing more exocytosis; preventing uptake of neurotransmitter from the cleft - mimicking the effect of neurotransmitter by linking to the receptors

Question 45

what's the enzyme called in the example of synapses (acetylcholine)?

Answer 45

acetylcholinesterase