5.1.3 Neuronal Communication

Question 1

sensory receptor

Answer 1

specialised cells which respond to a specific stimulus by initiating an action potential
a receptor is a transducer as it transforms stimulus energy into electrical responses

Question 2

pacinian corpuscles in skin stimulus

Answer 2

changes in pressure on skin

Question 3

stretch receptor in muscles stimulus

Answer 3

changes in muscle length

Question 4

baroreceptors stimulus

Answer 4

movement

Question 5

osmoreceptors stimulus

Answer 5

solute concentration of blood

Question 6

sensory adaptation

Answer 6

neural or sensory receptors in the brain change/reduce their sensitivity to continuous, unchanging stimuli

Question 7

pacinian corpuscle energy change

Answer 7

kinetic energy to electrical energy

Question 8

baroreceptor energy change

Answer 8

kinetic energy to electrical energy

Question 9

osmoreceptor energy change

Answer 9

chemical energy to electrical energy

Question 10

habituation

Answer 10

Over time, organisms may become more sensitive due to exposure
OPPOSITE OF SENSITISATION

Question 11

stretch receptor energy change

Answer 11

kinetic energy to electrical energy

Question 12

a nerve

Answer 12

an enclosed cable-like bundle of nerve fibres/neurones/cells

Question 13

central nervous system

Answer 13

brain, spinal cord, relay neurones

Question 14

peripheral nervous system

Answer 14

cranial, spinal nerves, containing sensory/motor neurones

Question 15

somatic nervous system

Answer 15

voluntary movements and involuntary reflexes - output to skeletal muscle via motor neurones

Question 16

autonomic nervous system

Answer 16

involuntary - output to smooth muscle or glands or cardiac muscle or internal organs

Question 17

parasympathetic nervous system

Answer 17

relaxing responses - rest and digest
neurotransmitter is acetylcholine and many axons in the vagus nerve

Question 18

sympathetic nervous system

Answer 18

internal alarm
fight or flight responses

Question 19

ganglion

Answer 19

swelling that contains lots of synapses/cell bodies

Question 20

grey matter

Answer 20

synapses, unmyelinated relay neurones, numerous cell bodies

Question 21

white matter

Answer 21

myelinated axons of neurones, relatively few cell bodies

Question 22

threshold value

Answer 22

the minimum receptor potential needed to generate an action potential

Question 23

all-or-nothing response

Answer 23

if the stimulus reaches a certain level, above the threshold, a response will be triggered. if it does not meet the threshold, no response occurs

Question 24

receptor potential

Answer 24

the change in electrical potential caused by a stimulus

Question 25

monosynaptic reflex

Answer 25

one synapse in a reflex arc
e.g sensory to motor

Question 26

reflex arc

Answer 26

responses to changes in environment that do not involve any processing in brain to coordinate movement
same stimulus produces same response every time
allow the body to make involuntary adjustments to changes in external environment to help control internal environment

Question 27

stimulus of an action potential

Answer 27

stimulus triggers stretch-mediated sodium ion channels to open.
sodium ions diffuse into axon, down an electrochemical gradient
potential becomes more positive as ions move in
if enough ions diffuse in to make potential ≥ -55 mV, depolarisation is triggered

Question 28

depolarisation of an action potential

Answer 28

when threshold (-55mV) is met or exceeded, voltage-gated sodium ion channels open and sodium ions diffuse into the axon, down an electrochemical gradient
the inside of the axon becomes less negative as more positive ions diffuse in - reducing potential difference
this triggers more channels to open = more sodium ions diffuse in = more depolarisation
example of positive feedback

Question 29

repolarisation of action potential

Answer 29

after potential difference reaches +40mV, voltage-gated sodium ion channels close = stops further sodium ions diffusing into axon
voltage-gated potassium ion channels open, causing potassium ions to diffuse out of axon, down electrochemical gradient
axon becomes less positive and potential difference returns to -65mV
example of negative feedback

Question 30

hyperpolarisation of an action potential

Answer 30

potential difference undershoots slightly, making axon more negative than at rest
potassium ion channels close too slowly and too many ions diffuse out

Question 31

redistribution of ions to return to an action potential

Answer 31

sodium ion/potassium ion pump restores the normal distribution of ions, restoring the resting potential

Question 32

maintenance of a resting potential

Answer 32

sodium/potassium ion pump: uses ATP to actively transport 3 Na+ OUT of axon, 2 K+ IN. = larger concentration of positive ions outside axon than inside the axon. establishes an electrochemical gradient
differential membrane permeability: selective protein channels allow Na+ and K+ to move across the membrane by facilitated diffusion.
protein channels less permeable to Na+ than K ions = K+ ions can diffuse back down their concentration gradient, out of the axon, at a faster rate than Na+ ions

Question 33

function of a motor neurone

Answer 33

carry impulses from CNS towards effector
short dendrites, long axons
if connected to muscle= motor end plate

Question 34

function of a relay neurone

Answer 34

intermediate neurones
found entirely within the CNS
connect sensory and motor neurones

Question 35

absolute refractory period

Answer 35

during depolarisation
no additional stimulus can produce an action potential - sodium ion conc. is high in axon, sodium ion channels already open

Question 36

relative refractory period

Answer 36

during repolarisation and hyperpolarisation
only a more intense stimulus can produce an action potential

Question 37

refractory period

Answer 37

after an axon transmits an impulse, it cannot transmit another impulse immediately because:
Na+/K+ distribution is to be restored
membrane must be repolarised

Question 38

importance of the refractory period

Answer 38

action potential is only propagated forwards, towards the region which is not in refractory period = 1 direction only
separates action potentials - by the time the second AP is generated, the first has passed further down = sets an upper frequency limit

Question 39

the significance of the frequency of impulse transmission

Answer 39

a neurone will either conduct an action potential or not = all or nothing law.
a more intense stimulus does not cause a larger impulse - causes sensory neurons to produce more generator potentials = more frequent action potentials in sensory neurone
more vesicles released at the synapse, higher frequency of action potentials in the postsynaptic neurone and higher frequency of impulses to the brain

Question 40

roles of synapses

Answer 40

to connect two neurones to pass a signal from one to the other - cell signalling
ensure one-way transmission between neurones
divergence
summation - spatial summation & temporal summation
memory and learning
synaptic fatigue prevents overstimulation
allows weak background stimuli to be filtered out - sensory adaptation e.g. smell of house

Question 41

divergence

Answer 41

one presynaptic neurone might affect many postsynaptic neurones so one AP can be transmitted to several parts of the brain/body
e.g. reflexes - one pathway causes response, one pathway informs brain

Question 42

summation

Answer 42

a type of neural integration whereby all input from several postsynaptic potentials are added together

Question 43

spatial summation

Answer 43

convergence
one postsynaptic neurone could receive potentials from many presynaptic neurones
postsynaptic neurone adds together all stimuli from all presynaptic neurones = producing a coordinated response

Question 44

temporal summation

Answer 44

repeated stimulation of the same synaptic ending in rapid succession may occur until sufficient neurotransmitters are released to allow EPSPs to combine & reach threshold potential to produce AP
ensures only stimulation that’s strong enough is passed on

Question 45

function of myelin sheath

Answer 45

prevents ion movement
saltatory conduction
increases speed of impulse/action potential
insulates axon