4: The Nervous System

Question 1

Discuss nerve tract organisation

Answer 1

In CNS, axons of the same type may be bundled into tracts.

Cell bodies of axons in the same tract = nuclei

Question 2

What are the four main glial cells?

Answer 2

Astrocytes – nourish neurons, form blood-brain barrier

Ependymal cells – line ventricles of brain, produce cerebrospinal fluid

Microglia – phagocytic cells that ingest, break down waste products and pathogens

Oligodendrocytes [CNS] and Schwann cells [PNS] produce myelin sheaths around axons

Question 3

Define temporal summation and spatial summation

Answer 3

Temporal - multiple signals integrated in short space of time
Spatial - signals in many different places

Question 4

What is saltatory conduction?

Answer 4

Signal hopping from one node of ranvier to the next

Question 5

Discuss three ways in which neurotransmitters are removed from the synaptic cleft

Answer 5

• • neurotransmitters broken down by enzymes, e.g. acetylcholinesterase
• • Reuptake carriers in presynaptic neuron
• • Simple diffusion out of synaptic cleft, e.g. NO

Question 6

What is a supraspinal circuit?

Answer 6

A nerve

Question 7

What is a supraspinal circuit?

Answer 7

A neural circuit that goes via the brain, unlike reflexes

Question 8

What kind of reflex arc do we observe in:

• knee-jerk reflex
• withdrawal reflex

Answer 8

Knee-jerk = monosynaptic arc
Withdrawal = polysynaptic arc