p2: nervous coordination

Question 1

two divisions of nervous system

Answer 1

• CNS: brain and spinal cord
• Peripheral nervous system: nerves from and to the brain and spinal cord

and
- voluntary NS: voluntary conscious control
- autonomic NS: involuntary or subconscious

Question 2

describe how the structure of dendrites enable it to serve its function

Answer 2

• thin extensions on post synaptic membrane
• receives chemical signals
• carries impulses to nerve endings

Question 3

describe how the structure of the myelin sheaths enable it to serve its function

Answer 3

• electrical insulation
• speeds up transmission
• formed from schwann cells

Question 4

describe how the structure of terminal end branches enable it to serve its function

Answer 4

forms a synapse
releases neurotransmitters

Question 5

explain the advantages of simple reflex arcs

Answer 5

• rapid
• protect against damage to body tissues
• dont have to be learnt
• help escape predators

Question 6

as a neurone transmits an impulse, its rate of oxygen consumption increases. explain why.

Answer 6

• ATP required for active transport
• Na+ moved out along the whole length of axon in non myelinated

Question 7

describe how a resting potential is maintained in a neuron

Answer 7

• active transport of sodium ions across membrane
• membrane more permeable to K+ ions
• differential permeability to K+ and Na+ ions
• out of neurone, Na+ concentration higher and K+ conc higher inside neurone
• 3Na+ out and 2K+ in

Question 8

the potential across the membrane is reversed when an action potential is produced

Answer 8

• sodium ion channels protein
• Na+ ions diffuse in

Question 9

how is an action potential generated?

Answer 9

• membrane reaches threshold and becomes depolarised
• reversal of resting potential

Question 10

depolarisation

Answer 10

• stimulus causes membrane to be more permeable to Na+ ions
• if reaches threshold, Na+ ion channel proteins open and inside becomes more positive
• K+ ion channel proteins mainly closed
• high conc of positive ions inside cell = action potential

Question 11

repolarisation

Answer 11

• when reached 40 mV the Na+ channel proteins close
• K+ CHANNEL PROTEINS OPEN
• K+ ions diffuse out down a conc gradient = repolarisation

Question 12

hyperpolarisation

Answer 12

• K+ ion channel proteins remain open longer than needed, so cell more negative (-90mV)
• sodium potassium pump restores back to (-70mV)

Question 13

all or nothing response

Answer 13

• action potential only occurs if all Na+ voltage-gated ion channel proteins opemn
• threshold reached
• subthreshold = no action potential
• action potential size is always the same
• full size action potential always given regardless of size of stimulus

Question 14

define threshold

Answer 14

minimum intensity of stimulus

Question 15

refractory period

Answer 15

• time taken to restore the resting potential
• period of inactivation following transmission of an impulse
• limits number of impulses per second
• maximum frequency of impulse transmission

Question 16

impulse transmission

Answer 16

action potentials act as stimulus to adjacent polarised areas of membrane
- is passed along

Question 17

describe how the speed of conduction could vbe increased ina neurone

Answer 17

• axon is myelinated which provides insulation
• action potential jumps from node of ranvier to node of ranvier (saltatory conduction)
• axon has a large diameter
• so less resistance to flow of ions

Question 18

saltatory conduction

Answer 18

imoulses travel from node of ranvier to node
- depolarisation occurs only at nodes
- less axon needs to be depolarised so increases rate of transmission

Question 19

factor affecting rate of impulse conduction

Answer 19

• myelin sheaths
• temperature, higher KE so increased diffusion of ions
• larger axon diameter greater speed of conuctance and increases number of channel proteins

Question 20

give two reasons why transmission across a cholinergic synapse is unidirectional?

Answer 20

• impulses are unidirectional from pre to post SN
• vesicles containing neurotransmiters only in presynaptic neurone a
• receptor proteins only in post SN

Question 21

where is acetyl choline found?

Answer 21

parasympathetic branch of NS

Question 22

describe the sequence of events leading to the release of acetylcholine and its binding to the post synaptic membrane

Answer 22

• depolarisation of presynaptic membrane
• Ca 2+ ions open and calcium ions enter synaptic knob
• vesicles fuse with presynaptic membrane and release acetyl choline
• acetylcholine diffuses across synaptic cleft
• acetylcholine binds to receptors on the post SN
• sodium ions enter post SN leading to depolarisation

Question 23

when a nerve impulse arrives at a synapse, it causes the release of a neurotransmitter from vesicles in the presynaptic knob. describe how.

Answer 23

• depolarisation causes calcium ion channel proteins to open
• calcium ions enter by faciliated diffusion
• vesicles fuse with preSN

Question 24

neuromuscular junction

Answer 24

• synapse between motor neurone and muscle cell
• uses acetylcholine which binds to nicotinic cholinergic receptors

Question 25

what are the major differences between the cholinergic synapse and the neuromuscular synapse

Answer 25

- in neuro, postSN has lots of folds that form clefts, increase SA so more acetyl enzymes hydrolyse acetyl at a faster rate - postSN has more receptors - action potential always triggers a response in muscle cell

Question 26

the binding of GABA to receptors on postSN membranes causes negatively charged chlorine ions to enter postSN explain how this will inhibit transmission of nerve impulses by postSN neurones

Answer 26

- inside neurone is more negative - not enough Na+ ions to reach threshold - for action potential/depolarisartion

Question 27

myelination affects the rate of conduction of a nerve impulse. explain how.

Answer 27

- myelination provides electrical insulation - action potential jumps between nodes of ranvier - fewer jumps to travel length of axon

Question 28

describe how the inhibition of acetylcholinesterases affects the action of synapses

Answer 28

- acetyl choline not broke down - Na+ ions continue to depolarise/create action potentials

Question 29

summation

Answer 29

build up of neurotransmitters within the synapse

Question 30

spatial summation

Answer 30

- causes release of enough neurotransmitters to reach threshold - causes an axtion potential in postSN - different neurones converge at a single synapse

Question 31

temporal summation

Answer 31

- one presynaptic neuroe but impulses arrive at rapid succession - cumulative effect sufficient to depolarise postSN

Question 32

fatigue

Answer 32

if rate of transmission higher than rate reformed, then fatigued - cant generate an action potential is postSN until transmitter is regenerated

Question 33

excitatory neurotransmitters

Answer 33

- cause an action potential in postSN makes resting potential LESS negative, so less Na+ ions required to reach threshold

Question 34

inhibitory neurotransmitters

Answer 34

- resting potential becomes hyperpolarised - less likely to reach threshold - less likely to generate an action potential

Question 35

effects of drugs on synapses:

Answer 35

- stimulate NS by creating more action potentials - similar shapes to neurotransmitter so bind on postSN and mimic effect - or reduce action potentials so inhibitoty effect - ior ncrease release of neurotransmitters - inhibit enzymes hydrolysing neurotransmitters

Question 36

ao2 examples of drugs

Answer 36

cocaine: prevents hydrolysis of neurotransmitters - codeine: binds to receptors for endorphins - heroin: binds to receptors for endorphins in pain pathways - valium: increases effect of GABA caffeine: reduces threshold for excitation of neurones - botox inhibits release of acetylcholine