Nerve impulse

Question 1

Nerve impulse

Answer 1

Message carried along a nerve fibre

Question 2

Parts of the nerve impulse

Answer 2

Polarisation, Depolarisation, Repolarisation, Hyperpolarisation

Question 3

Membrane potential

Answer 3

Difference in ion concentration between inside and outside the neuron which creates a potential difference across the membrane of a neuron

Question 4

Polarisation

Answer 4

When the neuron is at rest, charge of -70mV (resting membrane potential), sodium gates are closed- concentration of Na+ is about 10 times higher outside, potassium gates are open- concentration of K+ is about 30 times higher inside, sodium-potassium pump maintains resting potential, stays polarised as the membrane isn’t equally permeable to all ions

Question 5

Depolarisation

Answer 5

Nerve impulse received, sufficiently stong stimulus (15mV) is applied to the nerve fibre, sodium gates open, K+ moves out, becomes positive, all or nothing response

Question 6

Movement of a nerve impulse along the neuron

Answer 6

As one Na+ gate opens, the next opens and the ones behind it close

Question 7

Repolarisation

Answer 7

Neuron trying to reset as it can’t receive another impulse unless polarised, tries to get rid of K+, Neuron is repolarised by the closure of the Na+ gates and the potassium pump removes potassium from the neuron

Question 8

Action potential

Answer 8

Nerve impulse, depolarisation followed by repolarisation

Question 9

Hyperpolarisation

Answer 9

Return to polarised or negative state, Period directly after repolarisation, Sodium potassium pump actively pumps out sodium, Sodium potassium pump overcompensates meaning the neuron is more negatively charged than resting

Question 10

Refractory period

Answer 10

Time during and just after an action potential (nerve impulse) in which the neuron cannot respond to another stimulus (as it’s in another phase)

Question 11

Conduction in an unmyelinated fibre

Answer 11

Action potential (nerve impulse) simply moves along the length of the fibre, 2 m/sec

Question 12

Conduction in a myelinated fibre

Answer 12

Myelin insulates the neuron membrane so that ions cannot diffuse through it, saltatory conduction occurs instead, 140 m/sec

Question 13

Saltatory conduction

Answer 13

Impulse leaps from one Node of Ranvier to another (doesn’t have to open every gate)

Question 14

Transmission across the synapse

Answer 14

Nerve impulse reaches the axon terminal and changes from an electrical impulse to an electro chemical impulse, Depolarisation of pre-synaptic knob (axon terminal button) causes calcium gates to open and Ca 2+ to rush in, Rush of Ca 2+ results in the release of neurotransmitter from vesicles through exocytosis, Neurotransmitters diffuse across the synapse and increase Na+ permeability of the post synaptic membrane (dendrite) which initiates depolarisation of the next neuron

Question 15

Neurotransmitters

Answer 15

Acetylcholine, Adrenaline, Dopamine, Histamine