Lecture 19 - Nervous System Structure & Function

Question 1

What 2 parts can the nervous system be divided into?

Answer 1

1) CNS - Brain & SC

2) PNS - Cranial, Spinal & Peripheral Nerves

Question 2

Where can white & grey matter be found?

What do they consist of?

Answer 2

Grey = peripheral in brain, central in SC (H shape) - make sure you can recognise on a picture. Consists of nerve cell bodies, dendrites, axon terminals and neuroglia.

White = central in brains, peripheral in SC. Consists of myelinated material

Question 3

Describe the structure of a section of spinal cord

Answer 3

• Grey matter in middle in H/butterfly shape
• Top is dorsal horns (posterior technically) and bottom in ventral horns (anterior technically).
• White matter contains nerve fibres which form ascending and descending tracts.
• Surrounded by the Pia mater, can notice the ventral fissure at the bottom of the section, and spinal canal in the middle too.

Question 4

What is myelin on axons composed of in the CNS and PNS?
Where is the main body/proximal part of the axon found?
Where is the distal part/arborisations of the axon found?

Answer 4

In CNS - Oligodendrocytes
In PNS - Schwann cells
- In the CNS (soma, dendrites, proximal part)
- In the PNS (distal part to skeletal muscle)

Question 5

What is the location & function of the 4 types of axon? (motor, sensory, integrative and anaxonic)

Answer 5

1) Motor - CNS to periphery. Sends signals to effector tissues.
2) Sensory - Periphery to CNS. Sends signals to integrative center.
3) Integrative - In CNS, collates all information
4) Anaxonic - retina, acts as a relay

Question 6

Which direction is anterograde and retrograde in regards to an axon?
How to vesicles move in these directions from the soma to synapse and back?
Where are unipolar, bipolar and postsynaptic autonomic neurone cell bodies located?
Where are purkinje and pyramidal cells restricted to?

Answer 6

• Anterograde is towards the synapse, retrograde towards the soma (cell body).
• Along a microtubule “shuttle” system.
• Outside the CNS
• The CNS

Question 7

What are the different kinds of synapse?

Answer 7

1) Axosomatic - axon synpases on another neurone
2) Axodendritic - axon terminal synpases with dendritic spine
3) Axoaxonic - axon synpases with another axon
5) Denro-dendritic
4) Axo-axonal

Question 8

What are the 4 connective tissue layers that surround nerves?

Answer 8

1) Endoneurium - loose connective tissue surrounding single nerve cells.
2) Perineurium - loose connective tissue surrounding clusters of axons (fascicles)
3) Epineurium - dense irregular connective tissue filling space between fascicles
4) Paraneurium - separates nerves from surrounding structures.

Question 9

What 2 things makes conduction in a nerve faster?

Answer 9

1) Larger diameter of the axon

2) Presence of myelin - allowing for saltatory conduction

Question 10

Compare and constrast the size, speed, location, function, myelination and internodal distance of A, B and C fibres.

Answer 10

Size = thickest, medium, thinnest
Speed = Fastest, medium, slowest
Location = CNS, viscera, periphery
Function = Motor, sensory, sensory
Myelination = Myelinated, myelinated, unmyelinated
Internodal distance = Largest, smallest, NONE.

Question 11

What are the 4 main support cells found in the CNS?

Answer 11

1) Oligodendrocytes
2) Astrocytes
3) Microglial cells
4) Ependymal cells

Question 12

What is the role of oligodendrocytes in the CNS?

Answer 12

Same as Schwann cells in the PNS, wrap around axons to myelinate them. Difference to Schwann cells is that they wrap around more then 1 axon simultaneously.

Question 13

What is the structure and 2 main roles of astrocytes in the CNS?

Answer 13

• Star like shape with perineurial feet that contain gap junctions (for transport of nutrients from blood to nerve cells).
• They also regulate nerve impulses but releasing GABA , and contribute to the BBB.

Question 14

Where are satellite cells found and what is their function?

Answer 14

Only found in sensory neurone cell bodies (specifically dorsal root ganglion) therefore in the PNS, and have functions similar to an astrocytes.

Question 15

Describe the structure and function of microglial cells in the CNS.

Answer 15

• Large cells with elongates (flattened) nucleus
• Resident macrophage of the CNS, removes damaged nerve cells. Also thought to digest protein tangles associated with dementia and Alzheimers.

Question 16

Where are ependymal cells found?
What is their structure?
What is their function?

Answer 16

• They line the spinal canal (small hole in centre of SC cross-section)
• They look similar to columnar epithelial cells and are derived from the neural crest and epithelial tissue. They have both cilia and microvilli on their surface.
• Synthesise/secrete CSF in the ventricles, cilia moves CSF through ventricles into SC. Microvilli absorb CSF for removal of pathogens.
• Modified tight junctions between ependymal cells control fluid release into the brain.

Question 17

What is the cause and symptoms of multiple sclerosis?

Answer 17

• Relapsing/remitting disease that is degenerative, caused by autoimmune degradation of myelin in the CNS
• Fatigue, vision problems, slurred speech, paraesthesia, muscle spasms, constipation. Symptoms caused by loss of conduction velocity.