Lecture 26

Question 1

Nervous system =

Answer 1

CNS + PNS

Question 2

Dendrites are:

Answer 2

a short branched extension of a nerve cell, along which impulses received from other cells at synapses are transmitted to the cell body. There can be multiple dendrites but only one axon.

Question 3

Axon is:

Answer 3

the long thread-like part of a nerve cell along which impulses are conducted from the cell body to other cells.

Question 4

Soma is:

Answer 4

Cell body

Question 5

Synaptic inputs are:

Answer 5

Input from other neurons recieved on the dendritic tree and the soma.

Question 6

Action potentials are:

Answer 6

Axon conducted messages away from the soma to the axon terminals (synaptic boutons)

Question 7

Electric signals:

Answer 7

Dendrites, cell body, axon

Question 8

Chemical signals:

Answer 8

synapses

Question 9

Resting Membrane Potential of the cytoplasm compared to the extracellular space:

Answer 9

50 to 70 mV lower (i.e. more negative)

Question 10

RMP is:

Answer 10

the electrical potential difference across the cell membrane which results from seperation of charge. There is more negative charges inside the cell than outside.

Question 11

The potential outside the cell is defined as:

Answer 11

zero.

Question 12

The RMP is a result of: (x3)

Answer 12

• Unequal concnetrations of Na+ and K+ inside and outside of the cell.
• Unequal permeability of the cell membrane to these ions.
• Electrogenic action of the Na-K pump - only a small contribution.

Question 13

How are concentration gradients for K+ and Na+ maintained?

Answer 13

-By the Na/K pump

Question 14

How is unequal permability of the cell membrane to diff ions explained?

Answer 14

• By the two types of ion channeks in neurons:
  1. Non-gated leak channels (open at rest)
  2. Gated channels (closed at rest)
• In cell membrane of neurons, there are many leak K+ channels, but very few leak Na+ channels. At rest: Pk+/PNa+ = 40/1

Question 15

In cell membrane of neurons, there are many leak ___ channels, but very few leak __ channels

Answer 15

many K+, few Na+

Question 16

How does unequal concnetration and unequal cell membrane permeability to Na+ and K+ result in a negative RMP?

Answer 16

-At intracellular potential at which the net flow of ions is zero, in spite of a conc gradient and permeability

Question 17

Nernst equation:

Answer 17

Eion = 61.5 mV x log [ion]o / [ion]i

-Only applies to a situation when a cell membrane is permeable to only one ion. eg. Glia cells

Question 18

Rule: The higher the permeability of the cell membrane to a particular ion, ___

Answer 18

the greater the ability of this ion to shift the RMP towards its equilibrium potential

Question 19

At rest, in neuron the permeability is much higher to ___

Answer 19

K+ than Na+. Thus the RMP is closer to the eq potential for K+ than Na+