Neuronal communication 5.3

Question 1

what are transducers

Answer 1

convert the energy of the stimulus to electrical energy by creating an electrochemical gradient

Question 2

what is the ‘all or nothing principle’

Answer 2

action potential only happens if the stimulus is strong, if its weak no action potential is produced.

Question 3

what is the first step of generation and transmission of signal

Answer 3

stimulus
triggers opening of Na+ channels
Na+ diffuses INTO neurone
inside of neurone is less negative
(electrochemical gradient)

Question 4

what is the second step of generation and transmission of a signal

Answer 4

depolarisation
if P.D reaches threshold value -50 mV
voltage gated sodium ion channels open
more sodium ions diffuse in
(positive feedback)

Question 5

what is the third step of generation and transmission of a signal

Answer 5

repolarisation
at P.D of +30mV
sodium ion channels close
voltage gated potassium ion channels open
permeablity to K+ ions increase
K+ ion diffuse OUT
(negative feedback)

Question 6

what is the fourth step of generation and transmission of signals

Answer 6

hyperpolarisation
P.D overshoots because K+ ion channels are slow to close
too many potassium ions diffuse out
at less than - 70 mV

Question 7

what is the final step of generation and transmission of signals

Answer 7

resting potential
original P.D is restored
non-excited state

Question 8

how does the pacinian corpuscle work

Answer 8

pressure deforms the membrane
sodium ion channels open
sodium ions diffuse into neuron
depolarisation creates generator potential
if there’s enough sodium ions it reaches threshold potential

Question 9

what is the node of Ranvier?

Answer 9

gap in the myelin sheath in axon

Question 10

what is a schwann cell

Answer 10

a cell wrapped around the axon forming the myelin sheath

Question 11

where is the cell body of the motor/relay/sensory neuron at

Answer 11

cns/cns/pns

Question 12

what does the motor neuron connect

Answer 12

CNS to effector

Question 13

what does the relay neuron connect

Answer 13

sensory to motor

Question 14

what does the sensory neuron connect

Answer 14

PNS to relay

Question 15

what is the refractory period

Answer 15

• when both sodium and potassium ions closed
• axon membrane is in a period of recovery and is unresponsive

Question 16

what is a synapse

Answer 16

junction between two or more neurons

Question 17

what is the synaptic cleft

Answer 17

gap between neurons

Question 18

what is the presynaptic bulb

Answer 18

axon end of first bulb

Question 19

what is the postsynaptic membrane

Answer 19

on next neuron has receptors and binds to neurotransmitter

Question 20

describe the transmission across the synapse (6 marks)

Answer 20

1️⃣ Action potential arrives at pre-synaptic bulb → Ca²⁺ channels open
2️⃣ Ca²⁺ influx causes synaptic vesicles to release ACh into synaptic cleft
3️⃣ ACh binds to receptors on post-synaptic membrane
4️⃣ Na⁺ channels open → Depolarization → New action potential
5️⃣ ACh broken down by acetylcholinesterase (AChE) to stop signal

Question 21

what is a cholinergic synapse

Answer 21

uses the neurotransmitter acetylcholine.

Question 22

what are the advantages of myelinated neurons

Answer 22

transmit action potential quicker so can reach the end of the neuron faster
they can be longer too so carry impulses at longer distances

Question 23

what is summation

Answer 23

when several EPSPs are added together

Question 24

what happens if a neurone is subjected to both stimulation form IPSPs and EPSPs? (6 marks)

Answer 24

• if EPSPs > IPSPs → Membrane reaches threshold → Action potential fires
• If IPSPs > EPSPs → Membrane stays hyperpolarized → No action potential
• If EPSPs ≈ IPSPs → No significant change, neuron remains at resting potential

Question 25

role of acetylcholinesterase

Answer 25

enzyme hydrolyses acetylcholine into ethanoic acid and choline stops transmission of signals

Question 26

why do impulses travel in one direction

Answer 26

- from receptors to effector - cannot go the opposite way

Question 27

types of sensory neurons and their function

Answer 27

- mechanoreceptors : pressure and movement e.g pacinian corpuscle - chemoreceptors: chemical e.g olfactory receptors in nose - thermoreceptors: temperature e.g hypothalamus - photoreceptors: light e.g rods and cones

Question 28

describe the sensory neurone

Answer 28

- Carry impulses from receptors to CNS - Dendron → carries impulse to cell body - Axon → carries impulse away from cell body

Question 29

describe the relay neuron

Answer 29

- Found in CNS – connect sensory & motor neurons - Short & highly branched for fast communication

Question 30

describe the motor neuron

Answer 30

- Carry impulses from CNS to effectors - Cell body at one end (in CNS) - Long axon to transmit impulses to effectors

Question 31

myelinated Vs unmyelinated

Answer 31

- myelinated = faster impulse - has myelin sheath - saltatory conduction - vice versa

Question 32

temporal Vs spatial summation

Answer 32

🔹 Temporal Summation → One neuron fires multiple times quickly 🔹 Spatial Summation → Multiple neurons release neurotransmitters simultaneously

Question 33

excitatory Vs inhibitory

Answer 33

E: - increase chance of action potential - Acetylcholine (ACh) in cholinergic synapses I: - Reduce chance of action potential - GABA

Question 34

stronger stimulus means?

Answer 34

Higher frequency of action potentials (not higher voltage)

Question 35

what does resting potential mean

Answer 35

voltage across a membrane when it is not being stimulated

Question 36

how can resting potential be established

Answer 36

sodium-potassium pump 3 Na+ in 2 K+ out by active transport inside is more negative than outside

Question 37

why is the refractory period important

Answer 37

- stops action potentials from merging into eachother so they are distinct from eachother - temporarily blocks backwards movement so that it forces impulses to travel in one direction