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Biology A Level 2023 2 > Nervous Coordination > Flashcards

Nervous Coordination Flashcards

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1
Q

describe general structure of a motor neurone

A

cell body : contains organelles and high proportion of rough endoplasmic reticulum

dendrons: branch into dendrites which carry impulses towards cell body

axon: long, unbranched fibre carries nerve impulses away from cell body

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2
Q

describe the additional features of a myelinated motor neurone

A

schwann cells - wrap around axon many times

myelin sheath - made from myeli-rich membranes of schwann cells

nodes of ranvier - very short gaps between neighbouring schwann cells where there is no myelin sheath

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3
Q

3 processes Schwann cells are involved in

A

electrical insulation
phagocytosis
nerve regeneration

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4
Q

how does an action potential pass along an unmyelinated neuron

A
  1. stimulus leads to influx of Na+ ions. first section of membrane depolarises
  2. local electrical currents cause sodium voltage-gated channels further along membrane to open
  3. sequential wave of depolarisation
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5
Q

explain why myelinated axons conduct impulses faster than unmyelinated axons

A

saltatory conduction —> impulse ‘jumps’ from one node of Ranvier to another. depolarisation cannot occur where myelin sheath acts as electrical insulator
so impulse does not travel along whole axon length

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6
Q

what is resting potential

A

potential difference across neuron membrane when not stimulated -50 to -90 mV, (usually about -70 mV in humans)

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7
Q

how is resting potential established

A
  1. membrane is more permeable to K+ than Na+
  2. sodium-potassium pump actively transports 3Na+ out of cell and 2K+ into cell

establishes electrochemical gradient: cell contents more negative than extracellular environment

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8
Q

name the stages in generating an action potential

A

depolarisation
repolarisation
hyperpolarisation
return to resting potential

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9
Q

what happens during depolarisation

A
  1. stimulus – facilitated diffusion of Na+ ions into cell down electrochemical gradient
  2. p.d. across membrane becomes more positive
  3. if membrane reaches threshold potential (-50mV), voltage-gated Na+ channels open
  4. significant influx of Na+ ions reverses p.d. to +40mV
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10
Q

what happens during repolarisation

A
  1. voltage-gated Na+ channels close and voltage-gated K+ channels open
  2. facilitated diffusion of K+ ions out of cell down their electrochemical gradient
  3. potential difference across membrane becomes more negative
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11
Q

what happens during hyperpolarisation

A
  1. overshoot when K+ ions diffuse out = p.d. becomes more negative than resting potential
  2. refractory period: no stimulus is large enough to raise membrane potential to threshold
  3. voltage-gated K+ channels close and sodium-potassium pump re-establishes resting potential
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12
Q

explain the importance of the refractory period

A

no action potential can be generated in hyperpolarised sections of membrane:
- ensures unidirectional impulse
- ensures discrete impulses
- limits frequency of impulse transmission

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13
Q

what is the ‘all or nothing’ principle

A

any stimulus that causes the membrane to reach threshold potential will generate an action potential

all action potentials have same magnitude

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14
Q

name the factors that affect the speed of conductance

A

myelin sheath
axon diameter
temperature

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15
Q

how does axon diameter affect the speed of conductance

A

greater diameter = faster

less resistance to flow of ions (depolarisation and repolarisation)

less ‘leakage’ of ions (easier to maintain membrane potential)

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16
Q

how does temperature affect speed of conductance

A

higher temperature = faster

faster rate of diffusion (depolarisation and repolarisation)

faster rate of respiration (enzyme-controlled) = more ATP for active transport to re-establish resting potential

temperature too high = membrane proteins denature

17
Q

suggest an appropriate statistical test to determine a factor has a significant effect on the speed of conductance

A

students t-test (comparing means of continuous data)

18
Q

suggest appropriate units for the maximum frequency of impulse conduction

A

Hz

19
Q

how can an organism detect the strength of a stimulus

A

larger stimulus raises membrane to threshold potential more quickly after hyperpolarisation = greater frequency of impulses

20
Q

what is the function of synapses

A
  • electrical impulse cannot travel over junction between neurones
  • neurotransmitters send impulses between neurones/from neurons to effectors
  • new impulses can be initiated in several different neurons for multiple simultaneous responses
21
Q

describe the structure of a synapse

A

presynaptic neuron ends in synaptic knob: contains lots of mitochondria, endoplasmic reticulum and vesicles of neurotransmitter

synaptic cleft: 20 - 30 nm gap between neurons

postsynaptic neuron: has complementary receptors to neurotransmitter (ligand-gated Na+ channels)

22
Q

outline what happens in the presynaptic neuron when an action potential is transmitted from one neuron to another

A
  1. wave of depolarisation travels down presynaptic neuron, causing voltage-gated Ca2+ channels to open
  2. vesicles move towards and fuse with presynaptic membrane
  3. exocytosis of neurotransmitter into synaptic cleft
23
Q

how do neurotransmitters cross the synaptic cleft

A

via simple diffusion

24
Q

outline what happens in the postsynaptic neuron when an action potential is transmitted from one neuron to another

A
  1. neurotransmitter binds to specific receptor on postsynaptic membrane
  2. ligand-gated Na+ channels open
  3. if influx of Na+ ions raises membrane to threshold potential, action potential is generated
25
Q

explain why synaptic transmission is unidirectional

A

only presynaptic neuron contains vesicles of neurotransmitter and only postsynaptic membrane has complementary receptors

so impulse always travels presynaptic –> postsynaptic

26
Q

define summation and name the 2 types

A

neurotransmitter from several sub-threshold impulses accumulates to generate action potential:
- temporal summation
- spatial summation

NB no summation at neuromuscular junctions

27
Q

what is the difference between temporal and spatial summation

A

temporal: one
presynaptic neuron releases transmitter several times in quick succession

spatial: multiple
presynaptic neurons release neurotransmitter

28
Q

what are cholinergic synapses

A

use acetylcholine as primary neurotransmitter. excitatory or inhibitory. located at:
- motor end plate (muscle contraction)
- preganglionic neurons (excitation)
- parasympathetic postganglionic neurons (inhibition e.g. of heart or breathing rate)

29
Q

what happens to acetylcholine from the synaptic cleft

A
  1. hydrolysis into acetyl and choline by acetylcholinesterase (AChE)
  2. acetyl and choline diffuse back into presynaptic membrane
  3. ATP is used to reform acetylcholine for storage in vesicles
30
Q

explain the importance of AChE

A

prevents overstimulation of skeletal muscle cells

enables acetyl and choline to be recycled

31
Q

what happens in an inhibitory synapse

A
  1. neurotransmitter binds to and opens Cl- channels on postsynaptic membrane and triggers K+ channels to open
  2. Cl- moves in and K+ moves out via facilitated diffusion
  3. p.d. becomes more negative: hyperpolarisation
32
Q

describe the structure of a neuromuscular junction

A

synaptic cleft between a presynaptic neuron and a skeletal muscle cell

33
Q

cholinergic synapse
- postsynaptic cell
- AChE location
- action potential
- response
- neurons involved

A
  • another neuron
  • synaptic cleft
  • new action potential produced
  • excitatory or inhibitory
  • motor, sensory or relay
34
Q

neuromuscular synapse
- postsynaptic cell
- AChE location
- action potential
- response
- neurons involved

A

-skeletal muscle cell
- postsynaptic membrane
- end of neural pathway
- always excitatory
- only motor

35
Q

how might drugs increase synaptic transmission

A

inhibit AChE

mimic shape of neurotransmitter

Biology A Level 2023 2 (17 decks)

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