cellular neurophysiology

Question 1

what is the cellular anatomy of the nervous system (neruons and glial cells)

Answer 1

neurons = information processing cells, elongated, separated by synapses, electrically active, connected in a network

glia = ‘glue’, for support, some contain insulating myelin

Question 2

what is the purpose of glial cells

Answer 2

provide support to neurons

regulate blood flow and supply of nutrients to neurons

guide development

repair

Question 3

how do action potentials work

Answer 3

1) stimulus causes sodium ion channels to open
2) depolarisation = sodium ion channels open, causing sodium ions to enter the axon
3) repolarisation = sodium ion voltage-gated channels close, stopping flow of Na into axon. Potassium ion channels now open, allowing the diffusion of potassium ions out of the axon
4) Hyperpolarisation = K channels close slowly, so extra K ions exit axon - this is known as the refractory period
5) Na/K pump = this restores the resting potential. This is against the concentration gradient, so requires energy from ATP

Question 4

what is the refractory period

Answer 4

the period of time after a stimulus in which further stimulus has no effect (sort of like a recovery period)

Question 5

what is the excitation threshold and all or none law

Answer 5

• -55 mV
• potential difference from stimulus must reach this in order to trigger depolarisation
• all or none law = a nerve will respond to a stimulus with a complete and maximal response, or no response at all

Question 6

what makes up a neuron?

Answer 6

cell body = contains nucleus

dendrites = receives signals from other neurons

axon = sends signals to other neurons

Question 7

what is the purpose of myelination, and what is saltatory conduction

Answer 7

axons covered in myelin sheath

myelin is a fatty substance that serves as insulation for nerve impulses

each myelin wrapper is a projection from a gial support cell

speeds up nerve conduction

action potential skips from one node of ranvier to the next, which speeds it up - known as saltatory conduction

Question 8

what is a node of ranvier

Answer 8

empty space between myelin sheaths

Question 9

how does the sodium/potassium pump work?

Answer 9

• uses ATP and ADP, as it requires energy to change the shape of the channel
• phospate binds to pump to change shape, allowing K/Na to move against concentration gradient
• phosphate removed from ATP makes ADP

Question 10

what is a h gate?

Answer 10

• in repolarisation, the Na channel is inactive, not closed
• the h gate is what’s blocking the channel

Question 11

how does a synapse work?

Answer 11

neurotransmitters carry signal across synapse, from axon to dendrite

neurotransmitters bind to receptor sites, via lock and key mechanism

this changes the polariastion of the cell

Question 12

what are the types of ion channels

Answer 12

ligand gated ion channels = group of transmembrane ion channel proteins which open in response to the binding of a chemical messenger (a ligand)

voltage gated ion channels = open in response to voltage (when the cell gets depolarised)

Question 13

what are the steps of chemical synaptic transfer

Answer 13

1) action potential arrives at axon terminal
2) voltage gated Ca channels open
3) Ca enters presynaptic neurons
4) Ca signals to neurotransmitter vesicles
5) vesicles move to membranes and dock
6) neurotransmitters released via exocytosis
7) neurotransmitters bind to receptors
8) signal initiated in postsynaptic cell

Question 14

how does electrical synaptic transmission work

Answer 14

there is no synaptic cleft. instead, neurones touch at gap junctions

the two neurons are isopotential (they have the same electrical potential), meaning electrical changes in one are reflected instantaneously in the other

useful when information must be conducted rapidly