Flashcards in 15. Neuorones, Nerve Fibres and Peripheral Deck (28)
What nerves are in the Brain and how many units of them are there?
Cranial nerves, 12 pairs.
What are the nerves in the spinal cord and its nerves unit?
Segmental or spinal nerves, 31 pairs.
Approximately how many cells make up the nervous system?
What are the two cell types of the nervous system?
Glia (make up 90%) and neurones (make up 10%).
What does the Greek word glia mean?
How can glia be divided?
Into microglia (from bone marrow) and macroglia (from nervous tissues).
How are glia labelled?
By Golgi silver impregnation method.
What neuroglia are found in the CNS?
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.
What neuroglia are found in the PNS?
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.
What are the two main parts that constitute the neurone?
The cell body and the axon.
What does the cell body of neurones contain?
The nucleus (containing the nucleolus), Nissl substance for protein synthesis and the Golgi apparatus for packaging of transmitters into vesicles.
What makes up the grey matter of the brain and why is it grey?
Cell bodies of neurones. It's grey due to their high absorption of incidence light of the microscope.
What is meant by ganglia with cell bodies?
A collection of nerve cell bodies in the PNS.
What are the components of an axon?
Axonal membrane, myelin sheath, node of rancher, atonal terminals, internodal membrane, initial segment and possibly axonal hillock.
Where are action potentials initiated along the axon?
At the initial segment where there is no sheath, next to the cell body.
How can axons vary?
Their thickness and whether or not they are myelinated.
How can the relationship between speed of conduction and axonal myelination be expressed mathematically?
Conduction Velocity = 6 x Fibre Density.
How many times does a Schwann cell wrap itself round an axon on average?
What diseases demyelinate axons?
Multiple sclerosis, Guillain barre, diabetes and polyneuropathies.
When does an axon conduct fast without an axon and when does it conduct faster with an axon?
Faster without an myelination when the axon diameter is less than 1uM but faster with an myelination when the diabetes is larger than 1uM.
How long is a node of Ranvier?
What can nerve fascicles be labelled with?
What makes up the white matter of the nervous system?
Collections of axon as they have reflective shiny whitish appearances due to the myelin sheathing.
What is the order out to writhing of the following?
Epineurium, endoneurium and perineurium.
Epineurium (ensheaths entire nerve), perineurium (ensheaths nerve fascicles) then endoneurium (ensheaths a single cells axon).
What are meninges?
The coverings of the brain and spinal cord.
Which order do dura mater and arachnoid mater go in from outside to in?
Dura mater then arachnoid mater.
How does a neutron react to its axon being severed?
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.