Excitation - the process of eliciting the action potential.

Question 1

intro

Answer 1

• minimum value of depolarisation that must be reached
• in order for a neurone to begin an action potential
• most neurones is around -55mV

Question 2

mechanism - step 1

Answer 2

resting membrane potential

• neurone is at rest
• around -70mV
• unequal distribution of na+/k+ ions
• selective permeability to these ions to sodium/ potassium

Question 3

mechanism - step 2

Answer 3

initiation of action potential

• neurotransmitter binds to cell membrane receptor
• resting potential -70mV to critical threshold -55mV

Question 4

mechanism step 3

Answer 4

depolarisation

voltage gated sodium channels open + sodium ions enter due to electrochemical gradient

value inside = +30mV

Question 5

mechanism - step 4

Answer 5

repolarisation

sodium has reached peak value so now voltage sodium channel close

voltage gated potassium channels open + potassium ions exit

Question 6

mechanism - step 5

Answer 6

hyperpolarisation

voltage potassium ions remain inside longe than necessary making MP more negative

Question 7

mechanism - step 6

Answer 7

resting state

-70mV membrane potential as potassium channel closes

sodium-potassium pump restores original ion balance

Question 8

propagation of action potential

Answer 8

= movement of AP from axon to synapatic terminal

• influx of sodium causes local positive charge
• depolarises adjacent cell membrane
• voltage gated sodium ion channels open

Question 9

myelinated neurones - structure 1

Answer 9

mylein sheath = fatty layer of schwann cells in CNS/PNS
- prevents ion leakage
- insulating layer
- maintains electrical signal

Question 10

myelinated neurones - structure 2

Answer 10

nodes of ranvier = gaps in myelin sheath
- focus points for voltage gated ion channels to concentrate

Question 11

myelinated neurones - characteristic - 1

Answer 11

SPEED (2)

• saltatory conduction = AP jumping from node of ranvier 1 to node of ranvier 2
• myelin sheath = increases speed of AP

Question 12

myelinated neurones - characteristic - 2

Answer 12

ENERGY
- less energy required for ion exchange
- less energy needed for propagation

Question 13

myelinated neurones - characteristic - 3

Answer 13

PROPAGATION
- high speed 120m/s
- more efficient over long distances

Question 14

unmyleinated neurones - structure

Answer 14

• no myeline sheath
• no nodes of ranvier

Question 15

unmyleinated neurones - characteristic 1

Answer 15

SPEED

• no saltatory conduction only continuous conduction
• • no myelin sheath = slow

Question 16

unmyleinated neurones - characteristic 2

Answer 16

ENERGY
- more energy needed as ion exchange occurs along full length of axon
- more energy needed to maintain ion conc gradient

Question 17

unmyleinated neurones - characteristic 3

Answer 17

PROPGATION
- low speed 1m/s
- less efficient for long distances

Question 18

refractory period - absolute

Answer 18

no matter how strong the stimulus is it cannot begin a new AP

depolarisation (start) -> repolarisation (end)

voltage gated sodium channels get inactive they cannot reopen until repolarisation is finished

needed
- prevent backward flow nerve impulse from neurone along axon

Question 19

refractory period - relative

Answer 19

occurs after absolute refractory period

stimulus can only occur if it reaches a threshold bigger than the original one

cause
- repolarisation
- hyperpolarisation

allows neurone to fire AP timely

Question 20

classification of nerve fibres

Answer 20

by erlanger + gasser into A,B,C

Question 21

classification of nerve fibres - group 1a

Answer 21

Aα fibers

largest diameter (15μm)
fastest conduction (120m/s)

motor to skeletal muscles/ proprio-ception

Question 22

classification of nerve fibres - group 1b

Answer 22

Aβ fibers
touch/ pressure sensation

Question 23

classification of nerve fibres - group 1c

Answer 23

Aγ fibers
motor to muscle spindles

Question 24

classification of nerve fibres - group 1d

Answer 24

Aδ
- pain and temp sensations

Question 25

classification of nerve fibres - group 2

Answer 25

B fibres

primary preganglionic fibres

Question 26

classification of nerve fibres - group 3

Answer 26

C fibres

primary postganglionic fibres