Neuro

Question 1

T/F - Entry of Na+ into the nerve cell during an action potential, causes further Na+ to enter the cell in a positive feedback loop

Answer 1

TRUE

Graded potentials = multiple small stimuli, which result in Na+ influx

Summation of these graded potentials allows the cell membrane to reach threshold potential.

Upon reaching threshold potential, this stimulates instant opening of VG-Na+ channels and further Na+ influx into the cell

Question 2

T/F - A nerve cell membrane is charged at rest, with negative charges aligned along the outside of the nerve cell membrane

Answer 2

FALSE

The resting membrane potential refers to the potential difference that exists across the cell membrane when the cell is in an unexcited state.

Determined by the concentration and ionic charge of the ions that are present on either side of the cell membrane

Question 3

T/F - Propagation of an nerve action potential is unidirectional along the conducting nerve fibre

Answer 3

TRUE

Action potential propagation is unidirectional, because the membrane that was recently depolarised will be in its refractory period (and thus unable to be activated)

Question 4

T/F - Saltatory conduction refers to conduction of the action potential in unmyelinated nerve fibres

Answer 4

FALSE

Saltatory conduction refers to action potentials jumping from point to point along a nerve. This only happens in myelinated nerves at the nodes of Ranvier,.

Nodes of Ranvier

• Located between fatty layers of myelin from Schwann cells
• Characterised by a high concentration of VG Na+ channels

Myelin

• Increases the resistance and reduces the capacitance of the membrane
• Action potentials can only fire off at the nodes
• Local, electronic currents are responsible for depolarising the next node along the axon to threshold potential

Question 5

T/F - During the absolute refractory period, a supra maximal stimulus is required to elicit an action potential

Answer 5

FALSE

During the absolute refractory period, it is impossible to evoke another action potential

• Occurs when the outer m gate is open (following activation) but the inner h gate has closed (mediating inactivation)
• h gate closure is a time-dependent process but occurs slower than m gate opening