Nervous System

Question 1

Principal cells of nerve tissue

Answer 1

• schwann cells
• oligodendrocytes
• satellite cells
• microglia
• astrocytes
• ependymal cells

Question 2

The Neuron

Answer 2

• a cell body/soma (perikaryon) containing the nucleus,
• a long cytoplasmic extension called the axon, specialised in
  generating or conducting nerve impulses to other cells that
  terminates in dilations known as end bulbs
• and one or more shorter processes called dendrites specialised in
  receiving stimuli from other cells – the ‘aerial’

Question 3

Axon

Answer 3

Axons are in effect the primary transmission lines of the nervous system, and as bundles they help make up nerves.

Individual axons are microscopic in
diameter - typically about one
micrometre across - but may extend
to 1 metre in length.

*Neurotubules act like conveyor
belts to transport numerous
substances along an axon between
the soma and the axon terminal.

*Neurofilaments are a major
component of the neuronal
cytoskeleton, they provide structural
support for the axon and regulate
axon diameter

Question 4

Myelinated axons

Answer 4

• The myelin sheath is produced by neuroglial cells:
  Schwann cells – peripheral nervous system
  Oligodendrocytes - central nervous system
• Myelin acts as an insulator, allows for faster
  transmission of nerve signals and helps with repair
  of axons.
• Each axon is myelinated along its length by chains
  of glial cells.
• The gap between one such myelinating cell and
  the next = Node of Ranvier

Question 5

Process of myelination

Answer 5

1. schwann cell starts to wrap around a portion of an axon
2. schwann cell cytoplpasm and plasma membrane begin to form consecutive layers around axon
3. the overlapping inner layers of the schwann cell plasma membrane form the myelin sheath
4. eventually, the schwann cell cytoplasm and nucleus are pushed to the periphery of the cell as the myelin sheath is formed

Question 6

CT of peripheral nerve

Answer 6

Individual axon = surrounded by endoneurium
Nerve fascicle (group of axons) = surrounded by
perineurium
Nerve (as seen in gross anatomical specimens) =
surrounded by epineurium

Question 7

Oligodendrocyte

Answer 7

will form the
myelin sheath for several axons insulating the axons and facilitating nerve
impulses

Question 8

Astrocytes

Answer 8

the most numerous cell of the CNS

Two types: Fibrous (located in the white matter) and Protoplasmic (located in the grey matter)

Functions
* Blood brain barrier – end-feet around blood vessels are thought to be basis of control of
the exchange of metabolites between blood and neurons
* Restraint of spread of electrical disturbance by absorption of K+ ions around synapses,
unmyelinated axons and nodes of Ranvier

Question 9

Ependymal cells

Answer 9

low columnar epithelial-like cells, lacking basement
membranes, which line the cavities of the CNS i.e. the central canal of the spinal
cord and the cerebral ventricles

Question 10

Microglia

Answer 10

differ from all other glial cells in originating from
blood monocytes, not from neural tissue precursors; Small elongated cells with
irregular processes. When activated, they become the macrophage cells and antigen-
presenting cells of the CNS mediating immune defence activity

Question 11

Schwann Cells

Answer 11

nclose all axons in nerves
of the PNS, producing myelin sheaths around large-diameter
axons, whose impulse conductivity is augmented at the nodes of Ranvier between
successive Schwann cells

Question 12

Satellite Cells

Answer 12

located within PNS ganglia, aggregated sensory or autonomic
neuronal cell bodies, where they enclose each perikaryon and regulate its
microenvironment.

Question 13

Synapses

Answer 13

Synapses are regions at the end of some axons that transmit the nerve impulse from one neuron to another
They may connect with the dendrites, onto
a cell body, or onto another axon or axon
terminal, as well as into the bloodstream or
diffusely into the adjacent nervous tissue
Synapses can be chemical or electrical
There are numerous synaptic connections
between neurons e.g. Purkinje cells
(cerebellum) have over 200,000

Question 14

Motor End Plates

Answer 14

• A neuromuscular junction (myoneural junction, motor end plate) is a chemical synapse formed by the contact
  between a motor neuron and a muscle fiber.
• It is at the neuromuscular junction that a motor neuron is able to transmit a signal to the muscle fiber, causing
  muscle contraction.
• Toxins that act on neuromuscular junctions:
  Snake venom
  Latrotoxin
  Tetanus toxin
  Nerve gases
  Botulinum toxin

Question 15

Botox

Answer 15

Botulinum toxin (BTX) is a neurotoxin produced by the bacterium
Clostridium botulinum which blocks Acetylcholine release at
neuromuscular junction (inhibits contraction for ~90 days)
Other clinical uses:
* Strabisimus (crossed eyes)
* Hyperhidrosis (excesive sweating)
* Bladder hyperactivity
* Migraine
* Abdominal wall reconstruction