Nervous tissues

Question 1

3 types of neurone

Answer 1

• multipolar; motor/efferent
• bipolar; relay/special sense
• pseudo-unipolar; sensory/afferent

Question 2

Soma (cell bodies)

Answer 2

Most are found in the CNS or in ganglia (PNS). They house the usual organelles ie. nucleus, mitochondria, ER, golgi, ribosomes etc.

Question 3

Nissl bodies

Answer 3

The active sites of protein synthesis ie. rough ER and ribosomes, only found within the cell body. They are basophilic acidic granules, so can be stained using dyes such as cresyl violet.

Question 4

Axon

Answer 4

Responsible for the propagation of action potentials from the axon hillock (where the AP is generated) down the neurone to the terminal bouton. The axoplasm contains mitochondria, microtubules and neurofilaments, allowing bidirectional travel. It contains no RER and therefore does not exhibit Nissl staining.

Question 5

Synapses

Answer 5

Minute gaps between cells of the nervous system can occur:
-with effectors (muscles/glands)
-with other neurones (axosomatic, axodendritic, axoaxonic)
The synaptic cleft follows the terminal bouton at the distal end of the presynaptic axon.

Question 6

Location of cell bodies

Answer 6

• found in the grey matter of the CNS, on the inside of the spinal cord and the outside of the brain eg. ventral horn grey matter
• found in the ganglia of the PNS eg. dorsal root ganglia

Question 7

Function of glia

Answer 7

• provide structural, survival and functional support to neurones
• 1:1 ratio with neurones
• occupy extracellular space
• create an ideal microenvironment for neurones
• smaller than neuronal cell bodies

Question 8

Types of glia

Answer 8

• ependymal cells
• astrocytes
• microglia
• oligodendrocytes
• Schwann cells

Question 9

Astrocytes

Answer 9

• most common glial cell
• bind to capillaries and meninges
• involved in metabolic exchange between neurons and the blood, contributing to the blood brain barrier
• provide structural support for neurones
• help cells migrate in development

Question 10

Microglia

Answer 10

• immune function and aid in repair
• provide immunosurveillance and phagocytose microbes and cellular debris
• mobile within the CNS
• morphology changes when active

Question 11

Ependymal cells

Answer 11

• ciliated epithelium-like cells (no basement membrane)
• line the ventricles and canal of the spinal cord
• found in the choroid plexus, which filters the blood to produce CSF

Question 12

Oligodendrocytes

Answer 12

• myelinate neurones in the CNS

- one oligodendrocyte myelinates many adjacent axons (~50)

Question 13

Schwann cells

Answer 13

• myelinate neurones in the PNS

- one Schwann cell myelinates one axon (can be many per axon)

Question 14

Myelin sheath

Answer 14

Increases the speed of nerve impulses via saltatory conduction. Myelin is made of concentric layers of glial cell membrane, and has a slightly different composition between oligodendrocytes and Schwann cells. Gaps in the myelin sheath are called Nodes of Ranvier.

Question 15

Myelination

Answer 15

1) axon invaginates into the glial cell and comes together to form a sheet of internal membrane (mesaxon)
2) internal membrane fuses
3) glial cell wraps many times around the axon, cell membranes can fuse
4) cytoplasm is pushed to the outside

Question 16

Unmyelinated axons

Answer 16

In both the CNS and PNS, some smaller axons can be unmyelinated. However, axons in the PNS are always supported by Schwann cells, which may ensheath but not wrap around them.

Question 17

Anatomy of a nerve

Answer 17

Numerous axon bundles (fascicles) are surrounded by three protective layers of connective tissue:

• endoneurium
• perineurium
• epineurium