15. Neuorones, Nerve Fibres and Peripheral

Question 1

What nerves are in the Brain and how many units of them are there?

Answer 1

Cranial nerves, 12 pairs.

Question 2

What are the nerves in the spinal cord and its nerves unit?

Answer 2

Segmental or spinal nerves, 31 pairs.

Question 3

Approximately how many cells make up the nervous system?

Answer 3

1 trillion.

Question 4

What are the two cell types of the nervous system?

Answer 4

Glia (make up 90%) and neurones (make up 10%).

Question 5

What does the Greek word glia mean?

Answer 5

Glue

Question 6

How can glia be divided?

Answer 6

Into microglia (from bone marrow) and macroglia (from nervous tissues).

Question 7

How are glia labelled?

Answer 7

By Golgi silver impregnation method.

Question 8

What neuroglia are found in the CNS?

Answer 8

Astrocytes - assist in the transfer of nutrients and waste products between the neurone and blood, constitute the blood brain barrier, provide physical support for neurone and have phagocytise functions.
Oligodendrocytes - myelination, myelinated up to 250 different axons at one time.
Ependyma - line the ventricles and central canal of spinal cord for circulation of CSF.
Microglia - immunity and inflammation.

Question 9

What neuroglia are found in the PNS?

Answer 9

The Schwann cell - insulates peripheral nerve axons to speed impulse conduction, 1 Schwann cell per axon.
The Sattelite cells - physical support of neurones.
Microglia - immune and inflammatory functions.

Question 10

What are the two main parts that constitute the neurone?

Answer 10

The cell body and the axon.

Question 11

What does the cell body of neurones contain?

Answer 11

The nucleus (containing the nucleolus), Nissl substance for protein synthesis and the Golgi apparatus for packaging of transmitters into vesicles.

Question 12

What makes up the grey matter of the brain and why is it grey?

Answer 12

Cell bodies of neurones. It’s grey due to their high absorption of incidence light of the microscope.

Question 13

What is meant by ganglia with cell bodies?

Answer 13

A collection of nerve cell bodies in the PNS.

Question 14

What are the components of an axon?

Answer 14

Axonal membrane, myelin sheath, node of rancher, atonal terminals, internodal membrane, initial segment and possibly axonal hillock.

Question 15

Where are action potentials initiated along the axon?

Answer 15

At the initial segment where there is no sheath, next to the cell body.

Question 16

How can axons vary?

Answer 16

Their thickness and whether or not they are myelinated.

Question 17

How can the relationship between speed of conduction and axonal myelination be expressed mathematically?

Answer 17

CV=6FD

Conduction Velocity = 6 x Fibre Density.

Question 18

How many times does a Schwann cell wrap itself round an axon on average?

Answer 18

10 times.

Question 19

What diseases demyelinate axons?

Answer 19

Multiple sclerosis, Guillain barre, diabetes and polyneuropathies.

Question 20

When does an axon conduct fast without an axon and when does it conduct faster with an axon?

Answer 20

Faster without an myelination when the axon diameter is less than 1uM but faster with an myelination when the diabetes is larger than 1uM.

Question 21

How long is a node of Ranvier?

Answer 21

1uM

Question 22

What can nerve fascicles be labelled with?

Answer 22

Sudan black.

Question 23

What makes up the white matter of the nervous system?

Answer 23

Collections of axon as they have reflective shiny whitish appearances due to the myelin sheathing.

Question 24

What is the order out to writhing of the following?

Epineurium, endoneurium and perineurium.

Answer 24

Epineurium (ensheaths entire nerve), perineurium (ensheaths nerve fascicles) then endoneurium (ensheaths a single cells axon).

Question 25

What are meninges?

Answer 25

The coverings of the brain and spinal cord.

Question 26

Which order do dura mater and arachnoid mater go in from outside to in?

Answer 26

Dura mater then arachnoid mater.

Question 27

How does a neutron react to its axon being severed?

Answer 27

The proximal segment of the axon seals up the damage to prevent leakage of cell contents.
A nerve stump is formed and the cell body puffs up with increased contents.
The distal segment is cut off from nutritional support of the cell body.
The distal segment of the axon dies.
The distal segment of axons undergo Wallerian degeneration.
The nucleus has been displaced from its former central position to the peripheral margins (chomatolysis).
The axon usually regrows.

Question 28

What three basic units make up the nervous system?

Answer 28

Brain, spinal cord and nerves.