Neurones- Neuronal communication

Question 1

role of neurones

Answer 1

carry electrical impulses around the body. Impulse always carried away from cell body

Question 2

features found in all neurones

Answer 2

-axon
-cell body containing nucleus
-axon terminal at end of axon containing many nerve endings which allow neurones to connect to other neurones + receive impulses from them= network of communication

Question 3

myelinated vs non myelinated neurones

Answer 3

-myelinated= axon insulated by a myelin sheath (formed by schwann cells) with nodes of ranvier. Electrical impulses jump from node to node= faster communication
-non myelinated= axon is uninsulated, impulse travels slower as it has to go through whole of axon

Question 4

3 main types of neurones and role

Answer 4

sensory-carry impulses from receptors to CNS (brain or spinal cord)
relay- intermediate neurones found in CNS which connect sensory and motor neurones
motor- carry impulses from CNS to effecters e.g muscles or glands

Question 5

features of motor neurones

Answer 5

-large cell body at one end that lies in brain or spinal cord
-nucleus always in cell body
-lots of dendrites extending from cell body, providing large SA for axon terminals of other neurones

Question 6

features of relay neurones

Answer 6

-short, but highly branched dendrites and axons

Question 7

features of sensory neurones

Answer 7

cell body that branches off in middle of cell
no dendrites (confused)

Question 8

resting axon

Answer 8

not transmitting an impulse
inside of axon always has a negative electric potential compared to the outside

Question 9

pd of resting axon

Answer 9

-70mV

Question 10

2 factors for maintaining resting potentials

Answer 10

-active transport of sodium and potassium ions
-differential membrane permeability

Question 11

active transport of sodium and potassium ions

Answer 11

-carrier proteins present in membranes of neurones which use ATP to actively transport 3 sodium ions out of axon for every 2 potassium in
-this creates a larger concentration of positive ions outside the axon= electrochemical gradient

Question 12

differential membrane permeability

Answer 12

protein channels in membrane of neurones are less permeable to sodium ions than potassium which allows potassium to diffuse back down their concentration gradient at a faster rate than sodium ions

Question 13

steps for an AP

Answer 13

-stimulus, depolarisation, repolarisation, hyperpolarisation + return to resting potential

Question 14

stimulus (AP)

Answer 14

-stimulus triggers sodium ion channels to open allowing them to diffuse into the neurone down an electrochemical gradient
-when a large enough stimulus is detected, the RP is converted to an AP
-threshold voltage for AP to be stimulated = -55mV

Question 15

depolarisation

Answer 15

-threshold v reached
-voltage gated sodium ion channels in axon membrane open
-sodium ions flow into axon down a conc gradient
-movement of sodium ions reduces pd across membrane, inside becomes less negative (depolarisation)
-depolarisation causes more sodium channels to open = positive feedback
-AP generated will reach +30mV

Question 16

repolarisation

Answer 16

-1ms after pd has reached +30mV, all sodium channels close
-potassium voltage gated channels open, allowing diffusion of potassium out of the axon, down their conc gradient
-this returns pd to normal (-70mV) =(repolaristion)= negative feedback

Question 17

hyperpolarisation

Answer 17

-potassium ion channels are slow to close= too many potassium ions are outside of the axon
-pd is more negative than normal outside the axon (around -75mV)= short period of hyperpolarisation

Question 18

returning to RP

Answer 18

-once potassium voltage gated channels close, the sodium potassium pump restores the resting potantial