Signalling in the nervous system

Question 1

Neuronal signaling definition

Answer 1

The transfer of information along and between neurones.

Question 2

Electrical signalling definition

Answer 2

Cell body communicated with its terminuss using electrical impulses.
Action potential causes depolarization of the terminal and release of neurotransmitter.

Question 3

Major ions that contribute to membrane potential

Answer 3

Na+
K+
Cl-
A- (Large anions)

Question 4

Resting membrane potential

Answer 4

Cell membranes are impermeable to Na+.
Na+ is pumped out of the cell by Na+/K+ ATPase.
2 K+ ions pumped in for every 3 Na+ pumped out.
Na+ is concentrated outside the cell.
K+ is concentrated inside the cell.

Question 5

Where are large anions (A-) found?

Answer 5

Trapped in the cell

Question 6

What forces Cl- to stay out of the cell?

Answer 6

Electrical gradient.

Question 7

What forced K+ to stay inside the cell?

Answer 7

Electrical gradient and Na+/K+ ATPase

Question 8

At resting membrane potential where are the ions?

Answer 8

Na+ and Cl- are outside of the cell.

K+ and A- are inside of the cell.

Question 9

The action potential - Movement of ions

Answer 9

If the membrane is slightly depolarized (-55mV), voltage-gated Na+ channels open so Na+ floods in. Voltage-gated K+ channels also open so K+ floods out. After 1ms Na+ channels inactivate (close) and K+ channels open and inactivate more slowly.

Question 10

Propagation

Answer 10

Small area of membrane is depolarized.
Na+ moves into cell and is lost from external medium (less positive outside).
Local currents in adjacent sections.
Membrane reaches threshold for AP (-55mV).
Propagation of AP down the axon.
At axon hillock.
Na+ channels become inactivated, after being activated they are refractory.
Na+ channel cannot reopen again immediately.
Only propagates in one direction.

Question 11

Neurotransmission - Physiological importance

Answer 11

Communication between neurones (Short distance/slow).

Complex signalling

Question 12

Neurotransmission - Pharmacological importance

Answer 12

Site for drug action

Question 13

Neurotransmitters: Monoamines

Answer 13

Noradrenaline (NA)
Dopamine (DA)
5-HT (5-hydroxytryptamine)
Acetylcholine (Ach)

Question 14

Neurotransmitters: Amino acids

Answer 14

Glutamate

GABA (y-aminobuutyric acid)

Question 15

Neurotransmitters: Synthesis

Answer 15

Synthesized from precursors by the action of enzymes.

EG DA synthesised from tyrosine by tyrosine hydroxylase and DOPA decarboxylase.

Question 16

Neurotransmitter: Storage

Answer 16

Stored in vesicles ready for release. Protected from metabolic enzymes.

Question 17

Neurotransmitter: Release

Answer 17

Depolarization of the terminal causes Ca2+ dependent exocytosis.
Voltage sensitive Ca2+ channels open.
Vesicles fuse with presynaptic membrane and empty into synaptic cleft.

Question 18

Neurotransmitter: Termination (Re-uptake)

Answer 18

High affinity re-uptake removes transmitter from synaptic cleft.
Intraneuronal metabolism then inactivates transmitter.
Monoamines and amino acids.
Metabolica enzymes

Question 19

Neurotransmitter: Termination (Metabolism)

Answer 19

Extraneuronal metabolism inactives transmitter, choline is recycled.
Metabolic enzymes.
Ach

Question 20

Receptors used in neurotransmission.

Answer 20

Excitatory / inhibitory
Ligand-gated ion channels
G-protein coupled receptors

Question 21

Neurotransmission (PHARMACOLOGY) - Synthesis

Answer 21

Transmitter synthesis may be increased or decreased by drugs.
False transmitter.
Precursor availability.
Enzyme inhibitors.

Question 22

Neurotransmission (PHARMACOLOGY) - Storage and release

Answer 22

Vesicle disrupts causing initial increase in release, then a decrease.
Releasing agents cause non-impulse dependent release.
Inhibitors of intraneuronal metabolism enzymes can increase transmitter in each vessicle.

Question 23

Neurotransmission (PHARMACOLOGY) - Interaction with target cell.

Answer 23

Receptor agonists, antagonists and modulators.
Each transmitter has many different receptor (sub)types.
These have different distributions and mediate different effects.
Neurotransmission is specialised at the receptor level.
Pharmacology can exploit this.

Question 24

Neurotransmission (PHARMACOLOGY) - Termination

Answer 24

Blockage of uptake causes a build up of transmitter in the synaptic cleft.
Inhibitors of metabolism cause increase in level of transmitter in synaptic cleft.