Membrane potenital

Question 1

The neuron, a single nerve cell, has what main parts?

Answer 1

The cell body which contains a nucleus.
Dendrities come of the cell body. It is the dendrites and cell body that act as the input zone.
The axon hillock is the neck of the cell body, the trigger zone. The signal is then past down the axon, the conducting zone where it reaches the axon terminals.

Question 2

What are the directions of movement for K+, Na+, CL- and Ca2+

Answer 2

K+ moves from intracellular to extracellular = efflux

Na+, Cl- and Ca2+ move from extracellular to intracellular = influx

Question 3

What is the resting membrane potential due to?

Answer 3

90% due to passive diffusion of K+ and Na+ down their conc gradients.
10% due to Na/K+ (Active transport). 3na+ out and 2 K+ in

Question 4

What is a graded potential and how does it occur

Answer 4

A localised stimulus applied directly to a segment of axon causes a localised graded potential. The change in membrane potential is the result of the opening of a small number of voltage gated Na+ channels in the axonal membrane.

Question 5

What causes an action potential to occur

Answer 5

When the graded potentials that cause membrane potentials to reach threshold, so the graded potentials acts as a triggering event.

Question 6

Anterograde axonal transport provides what?

Answer 6

Supplies axon terminals with organelles, metabolic components, synaptic vesicles and receptors

Question 7

What is the basis of signalling by neurons?

Answer 7

Electrical potentials across the cell membrane

Question 8

What establishes the resting membrane potential of neurons?

Answer 8

Ion Channels

Question 9

What channels are responsible for the action potential and release of neurotransmitters?

Answer 9

Voltage gated ion channels

Question 10

What type of channels dominate on the

1) soma and dendrites
2) Axon and its terminals

Answer 10

1) Ligand gated channels that cause membrane depolarisation or hyperpolarisation
2) Voltage gated channels

Question 11

Conductance of the membrane is what?

Answer 11

Reflects the ease with which ions flow across the membrane, greater the conductance the greater the flow of ions.. Conductance is the inverse of resistance .Well insulated neurons have larger length constants

Question 12

How are the action potentials continuously generated over the long distanced axon?

Answer 12

Via the nodes of ranvier. These nodes allow the action potential to be replicated with little decay in magnitue or frequency. If the space between each node was too small then this would slow down the deliverance of the signal as it would require each signal to be regenerated however if they were too far apart then the signal may lose its magnitude to reach action potential threshold at the next node. The nodes allow the action potential to be above threshold potential so that the next node can continue the action potential

Question 13

How does an action potential occur?

Answer 13

Rapid activation of voltage gated Na channels followed by its inactivation alongside the delayed opening of the voltage gated K channels. K channels open more slowly than Na channels. K channels are active near the peak of the action potential whilst na channels open early in the action potential timecourse resulting in rapid depolarisation

Question 14

What part of the neuron must depolarise to threshold for the activation of voltage gated sodium channels?

Answer 14

Axon hillock

Question 15

Absolute refractory period is what?

Answer 15

When something cannot be stimulated because it is depolarising. its the part before the curve goes into hyperpolarisation

Question 16

What is relative refractory period?

Answer 16

The section during and after hyperpolarisation. When the membrane requires a greater than normal stimulus

Question 17

Axon diameter and myelination affect what? How?

Answer 17

Speed of propagation, speed of the signal.
Larger diamter axons have less cytoplasmic reisstance to current flow. Thicker muelination increases the resistance of the axonal membrane.

Question 18

What needs to enter the axon terminal to allow the release of neurotransmitters?

Answer 18

Calcium via voltage gated channels

Question 19

Describe how positive and negative equilibrium potential is described?

Answer 19

The charge inside the cell soooo if the negative ion is at high conc inside the cell then the cell is a positive equilibrium potential to attract the ions into the cell.

Question 20

In order for a neuron to communicate a stronger signal, which factor needs to be altered?

Answer 20

Action potential firing frquency, AP frequency is an essential component of coding information, higher the frequency the stronger a signal.