Week 5 Physiology - Neurophysiology

Question 1

Electrical signal

Answer 1

From one end of the neuron to the other

Question 2

Chemical signal

Answer 2

From neuron to neuron (or effector)

Question 4

Resting membrane potentials

Answer 4

• All cells have a resting membrane potential
• Potential - electric charge due to movement of ions across a membrane
• Constant flow of ions across the membrane at rest (sodium and potassium)
• Membrane is polarised - one side is different to the other (outside=+, inside=-)
• Resting membrane potential is approximately -70mV

Question 5

Leakage channels

Answer 5

• Constant permeability
• Respond to the binding of a neurotransmitter
  Channels:
• Potassium leakage channel
• Sodium leakage channel
• Sodium-potassium pump

Question 6

Depolarisation

Answer 6

• When membrane potential reaches 30mV
• Due to sodium ions moving into the cells
• Inside of the cell is more positive than outside

Question 7

Hyperpolarisation

Answer 7

• When membrane potential reaches -90mV
• Due to potassium ions moving out of cell
• Inside of cell is more negative than outside

Question 8

Types of signals

Answer 8

Depolarising and hyperpolarising changes in membrane potential are used by neurons and muscle cells as signals
* Graded potentials
* Action potentials

Question 9

Graded potentials

Answer 9

• Small deviation from the resting membrane potential that makes the membrane either more polarised or less polarised
• Occur in dendrites and cell bodies
• Are local, short lived and spread in all directions
• Set up for action potential
• Travel only short distances
• Occur in response to the opening of:
  
  • Mechanically-gated channels - respond to stimulation that comes from touch, pressure, vibration, soundwaves, found more in sensory neurons, allows passage of cations (e.g. sodium, calcium) to depolarise cell
  • Ligand-gated channels - respond to another chemical (e,g, acetylcholine), allows passage of ions (e.g. sodium, chloride) to depolarise or hyperpolarise cell

Question 10

Action potentials

Answer 10

• Occurs when the membrane potential of a cell rapidly rises and falls, initiated by the graded potential
• Occurs in axon of neuron or axon terminal
• Are self-sustaining and travel in one direction
• Travel long distances
• Involve:
  
  • Voltage-gated sodium channels - two gates (activation - opened by voltage change, inactivation - not sensitive to voltage), cycle through closed, open, inactive stages
  • Voltage-gated potassium channels - one gate (opened by voltage change), cycle through closed, open stages

Question 11

Action potential graph

Answer 11

• At rest - both voltage-gated channels closed, membrane potential is -70mV
• Depolarising phase - when membrane reaches threshold (-55mV in muscle or nerve) voltage-gated channel opens, membrane potential up to 30mV
• Repolarising phase - voltage-gated sodium channel inactive, voltage-gated potassium channel open, membrane potential continues toward resting membrane potential (-70mV) and potentially goes further to -90mV (hyperpolarised due to slow gate close)
• Back to rest - both voltage-gated channels close, sodium-potassium pump used to help membrane potential return to rest (-70mV)

Question 11

Refractory periods

Answer 11

• Absolute refractory period
• Relative refractory period

Question 12

Absolute refractory period

Answer 12

• Cannot initiate another action potential
• Means action potential can only travel in one direction
• Utilises inactivation gates

Question 13

Relative refractory period

Answer 13

Can only initiate another action potential with a greater stimulus