nervous coordination 3.6

Question 1

describe the general structure of a motor neurone

Answer 1

cell body
dendrons
axon

Question 2

cell body

Answer 2

contains organelles and high proportion of RER

Question 3

dendrons

Answer 3

branch into dendrites which carry impulses towards cell body

Question 4

axon

Answer 4

long, unbranched fibre
carries nerve impulses
away from cell body

Question 5

describe the additional features of a myelinated motor neurone

Answer 5

Schwann cells
myelin sheath
nodes of ranvier

Question 6

Schwann cells

Answer 6

wrap around axon many times

Question 7

myelin sheath

Answer 7

made from myelin-rich membranes of Schwann cells

Question 8

nodes of ranvier

Answer 8

very short gaps between neighbouring Schwann cells where there is no myelin sheath

Question 9

name three processes Schwann cells are involved in

Answer 9

electrical insulation
phagocytosis
nerve regeneration

Question 10

how does an action potential pass along an unmyelinated neurone

Answer 10

stimulus leads to influx of Na+ ions
first section of membrane depolarises
local electrical currents cause sodium voltage-gated channels further along membrane to open
section behind begins to repolarise
sequential wave of depolarisation

Question 11

explain why myelinated axons conduct impulses faster than unmyelinated axons

Answer 11

saltatory conduction
impulse jumps from one node of ranvier to another
depolarisation cannot occur where myelin sheath acts as electrical insulator
impulse does not travel along whole axon length

Question 12

define resting potential

Answer 12

potential difference across neurone membrane when not stimulated

Question 13

what is the resting potential usually in humans

Answer 13

-70 mV

Question 14

how is resting potential established

Answer 14

membrane is more permeable to K+ than Na+

sodium potassium pump actively transports 3Na+ out of cell and 2K+ into cell

establishes electrochemical gradient
cell contents more negative than extracellular environment

Question 15

name the stages in generating an action potential

Answer 15

depolarisation
repolarisation
hyperpolarisation
return to resting potential

Question 16

what happens during depolarisation

Answer 16

stimulus
fasciliated diffusion of Na+ ions into cell down electrochemical gradient
p.d across membrane reaches threshold potential
voltage gated Na+ channels open
significant influx of Na+ ions reverses p.d to +40mV

Question 17

what is threshold potential

Answer 17

-50mV

Question 18

what happens during repolarisation

Answer 18

voltage gated Na+ channels close
voltage gated K+ channels open
facilitated diffusion of K+ ions out of cell down electrochemical gradient
p.d across membrane becomes more negative

Question 19

what happens during hyperpolarisation

Answer 19

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

Question 20

what is the refractory period

Answer 20

no action potential can be generated in hyperpolarised sections of membrane

Question 21

importance of refractory period (3)

Answer 21

ensures unidirectional impulse
discrete impulse
limits frequency of impulse transmission

Question 22

how does axon diameter affect the speed of conductance

Answer 22

greater diameter = faster

less resistance to flow of ions
less leakage of ions: easier to maintain membrane potential

Question 23

what is the ‘all or nothing’ principle

Answer 23

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

all action potentials have same magnitude

Question 24

name the factors that affect the speed of conductance (3)

Answer 24

myelin sheath
axon diameter
temperature

Question 25

how does temperature affect speed of conductance

Answer 25

higher temperature = faster faster rate of diffusion faster rate pf respiration: more ATP for active transport to re-establish resting potential temperature too high = membrane proteins denature

Question 26

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

Answer 26

student's t test

Question 27

units for the maximum frequency of impulse conduction

Answer 27

Hz

Question 28

how is a larger stimulus detected as larger

Answer 28

raises membrane to threshold potential more quickly after hyperpolarisation therfore greater frequency of impulses

Question 29

what is the function of synapses (3)

Answer 29

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

Question 30

describe the structure of a synapse

Answer 30

presynaptic neuron synaptic knob synaptic cleft postsynaptic neuron

Question 31

postsynaptic neuron

Answer 31

has complementary receptors to neurotransmitters

Question 32

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

Answer 32

wave of depolarisation travels down presynaptic neuron causes voltage gated Ca2+ channels to open vesicles move towards and fuse with presynaptic membrane exocytosis of neurotransmitter into synaptic cleft

Question 33

how do neurotransmitters cross the synaptic cleft

Answer 33

via simple diffusion

Question 34

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

Answer 34

neurotransmitter binds to specific receptor on postsynaptic membrane ligand-gated Na+ channels open if influx of Na+ ions raises membrane to threshold potential action potential is generated

Question 35

why is synaptic transmission is unidirectional

Answer 35

only presynaptic neuron contains vesicles of neurotransmitters only postsynaptic membrane has complimentary receptors impulse always travels presynaptic -> postsynaptic

Question 36

define summation

Answer 36

neurotransmitter from several sub-threshold impulses accumulates to generate action potential

Question 37

what are the two types of summation

Answer 37

temporal spatial

Question 38

define temporal summation

Answer 38

one presynaptic neuron releases neurotransmitter several times in quick succession

Question 39

define spatial summation

Answer 39

multiple presynaptic neurons release neurotransmitter

Question 40

what happens to acetylcholine from the synaptic cleft

Answer 40

hydrolysis into acetyl and choline by acetylcholinesterase acetyl and choline diffuse back into presynaptic membrane ATP is used to reform acetylcholine for storage in vesicles

Question 41

what is the importance of acetylcholinesterase (2)

Answer 41

prevents overstimulation of skeletal muscle cells enables acetyl and choline to be recycled

Question 42

define the structure of a neuromuscular junction

Answer 42

synaptic cleft between a presynaptic neuron and a skeletal muscle cell

Question 43

what is a cholinergic synapses

Answer 43

use acetylcholine as primary neurotransmitter excitatory or inhibitory

Question 44

what happens at an inhibitory synapse

Answer 44

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

Question 45

how might drugs increase synaptic transmission (2)

Answer 45

inhibit acetylcholinesterase mimic shape of neurotransmitter

Question 46

how might drugs decrease synaptic transmission (3)

Answer 46

inhibit release of neurotransmitter decrease permeability of postsynaptic membrane to ions hyperpolarise postsynaptic membrane