Introduction to the Nervous System

Question 1

What is a neuron?

Answer 1

A fundamental cellular unit of the CNS and PNS

Question 2

What are the types of Glial cells?

Answer 2

Schwann cell - peripheral myelinating glia
Oligodendrocytes - CNS myelinating glia
Microglia - function as phagocytes in the CNS
Astrocytes - metabolic support and regulation of the BBB

Question 3

What are the basic neuron types?

Answer 3

Multipolar neuron (motor neuron)
Bipolar neuron (interneuron, i.e. bipola cell of retina)
Pseudo-unipolar neuron (sensory neuron, i.e. ganglion cell of dorsal root)
Unipolar neuron

Question 4

Describe how the conduction of action potentials takes place

Answer 4

1. In an unmyelinated axon, action potentials travel along the whole axolemma
2. in a myelinated axon, action potentials jump between gaps in the myelin known as Nodes of Ranvier (this is known as saltatory conduction)

NB: myelination increases conduction velocity. Diameter is also important in speed of action potential propagation (larger the diameter, faster the conduction)

Question 5

What are the various definitions of a neurotransmitter?

Answer 5

1. A substance synthesised and stored in a presynaptic neuron
2. A substance released on stimulation of the presynaptic neuron
3. Application of the substance to the postsynaptic cell should reproduce the effects of normal neurotransmission
4. The action of the substance on the postsynaptic cell and synaptic transmission should be susceptible to competitive blockade by the same agents
5. An enzyme capable of destroying the substance should exist in the vicinity of the synapse

Question 6

What are the ways in which the nervous system has its effect on effector tissues?

Answer 6

• Neurotransmission at a synaptic cleft may be excitatory or inhibitory
• Excitatory postsynaptic potential (EPSP) = Neurotransmission depolarises the membrane of the postsynaptic neuron. If threshold potential is reached (typically -55mV), then an action potential is propagated
• Inhibitory postsynaptic potential (IPSP) = Neurotransmission hyperpolarises the membrane of the postsynaptic neuron. Greater excitation is needed in order to rech threshold potential.