C2.2 Neural Signalling

Question 1

Features of nervous system (4)

Answer 1

central nervous system - brain + spinal cord protected by bone

receives + processes bodily information + activity

composed of neurons that carry electrical impulses

peripheral nervous system - non-CNS nerves - connects CNS to organs, muscles, sensors

Question 2

Structure of a neuron (4)

Answer 2

cell body/soma

dendrites (one or more)

long axons

axon terminal (synaptic) knobs

Question 3

Features of the cell body/soma for neurons (2)

Answer 3

nucleus + cytoplasm

neurons do not multiply - have no centrioles

Question 4

Features of dendrites for neurons (2)

Answer 4

short + branched nerve fibers from cell surface

make connection with other neurons - have increased SA

Question 5

Features of the axon hillock in neurons (2)

Answer 5

connects cell body to axon

site where action potential generated

Question 6

Features of the axon for neurons (2)

Answer 6

long single fibre away from cell body

covered by Schwann cells/a myelin sheath

Question 7

Features of axon terminal (synaptic) knobs

Answer 7

axon terminal (synaptic) knobs - end of nerve where impulse leaves

Question 8

3 Types of neurons

Answer 8

Sensory neurons

Motor Neurons

Relay Neurons

Question 9

Define sensory neurons (2)

Answer 9

long axons

transmits nerve impulses from sensory receptors to CNS

Question 10

Define motor neurons

Answer 10

long axons

transmit nerve impulses from CNS to effectors

Question 11

Define Relay neurons

Answer 11

smaller cells with more interconnections

Question 12

Define resting potential of a neuron (4)

Answer 12

membrane potential when a neuron is not transmitting a signal

more Na+ outside, more K+ inside

potential difference - voltage is at -70 mV

sodium-potassium pump - pumps 3 Na+ out and 2 K+ in

channels - K+ ions flow out at faster rate than Na+ ions flow in

Question 13

Features of sodium-potassium pump (2)

Answer 13

uses ATP

3 Na+ pumped out, 2K+ pumped in

Question 14

Role of Sodium Potassium Pump for maintaining resting potential for Na+ ions (4)

Answer 14

few Na+ channels –> Na+ ions diffuse at slower rate

no pump –> more Na+ ions will enter cell due to diffusion

more Na+ ions –> more positive = depolarisation

pump - actively removes Na+ ions

Question 15

Role of Sodium-Potassium pump for maintaining resting potential for K+ ions (4)

Answer 15

diffusion - K+ ions will leave cell (more inside)

electropotential gradient - K+ ions will re-enter (because insides is more negative from diffusion)

diffusion force > electropotential gradient (gradient charge less negative hence weaker)

pump - pumps K+ ions in to maintain resting potential

Question 17

Factors which impact speed of nerve impulse (3)

Answer 17

amount of myelinaton

diameter of axon

temperature

Question 18

Myelinated neurons as a factor which impacts speed

Answer 18

prevents leakage of neurons into the axon

Question 19

Diameter of axons as a factor which impacts speed

Answer 19

wider surface area

for charges to hop from sections in resting potential

Question 20

Temperature as a factor which impacts neuron speed

Question 21

myelination

Answer 21

action potential hop between gaps of myelin sheath

called nodes of ranvier

Question 22

Pre-synaptic neuron (2)

Answer 22

carries impulse towards synapse

“sender”

Question 23

Post-synaptic neuron (2)

Answer 23

carries impulse away from synapse

receiver

Question 24

Synaptic transmission (3)

Answer 24

neurotransmitter binds to neuroreceptors in post-synaptic membrane

ligand-gated sodium channels open - sodium ions flow in

creates depolarisation - may initiate action potentials if threshold reached

Question 25

Break-down of neurotransmitters in synaptic transmission

Answer 25

specific enzyme breaks down neurotransmitter broken-down products reabsorbed by the pre-synaptic neuron

Question 26

Acetylcholine (2)

Answer 26

nuerotransmitter that triggers muscle contraction promotes parasympathetic responses (relaxing body after stress)

Question 27

How is acetylcholine made

Answer 27

made in axon terminal combines chlorine with acetate group from Acetyl CoA

Question 28

Where acetylcholine is made (3)

Answer 28

stored in vesicles in axon terminal performs exocytosis in response to nerve impulse activates post-synaptic cell by binding to specific receptor

Question 29

Breakdown of Acetylcholine (4)

Answer 29

must be continually removed from synapse - may lead to fatal convulsions + paralysis broken down by enzyme acetylcholinesterase (AChE) enzyme released into presynaptic neuron or embedded onto membrane of post-synaptic neuron

Question 30

Neuromuscular Junction (4)

Answer 30

specialised synapse between motor neuron + muscle fiber motor neuron releases acetylcholine binds to receptors on plasma membrane of muscle fiber --> initiates muscle contraction causes depolarisation of muscle membrane + release of calcium

Question 31

Neuroglandular junction (2)

Answer 31

synapses between neurons + glandular cells regulate secretory activities

Question 32

Excitatory synapses (2)

Answer 32

depolarises the local membrane potential of post-synaptic cell makes cell more prone to firing

Question 33

Inhibitory synapses (2)

Answer 33

hyperpolarises (more negative) the local membrane potential of postsynaptic cell less prone to firing

Question 34

Explain repolarisation (3)

Answer 34

voltage gated sodium- ion channels close voltage-gated potassium ion channles open when 40+ reached K+ ions rush out of cell --> membrane is repolarised then hyperpolarised

Question 35

Factors which determine strength of action potential (2)

Answer 35

amount of neurotransmitter released --> more neurotransmitter = more channels open time neurotransmitter is in area

Question 36

Explain excitatory postsynaptic potential (4)

Answer 36

opening of channels --> leads to depolarisation + increases chances of action potential happening inside of post-synaptic cell becomes less negative Na+ channels (come in) Ca2+ comes in

Question 37

Explain inhibitory postsynaptic potential (5)

Answer 37

opening of ion channels --> leads to hyperpoarisation makes action potential less likely inside of psot-synaptic cell becomes more negative influx of Cl- efflux of K+