L18: Nervous Tissue II

Question 1

Anatomical divisions of nervous system

Answer 1

• CNS: brain and spinal cord

- PNS: cranial nerves (12 pairs), spinal nerves (31 pairs), plexuses, ganglia (cranial, spinal, autonomic)

Question 2

Gross anatomical divisions within the brain

Answer 2

• Gray matter (cerebral/bellar cortex, nuclei) = cell bodies and neuroglia
• White matter (tracts, fasciculi etc.) = cell axons and neuroglia

Question 3

Where are cell bodies located in the PNS?

Answer 3

• Ganglia (cranial, spinal, autonomic)

Question 4

Where are axons located in the PNS?

Answer 4

• In nerves

Question 5

Where are cell bodies located in the CNS?

Answer 5

• Gray matter (cerebral cortex, cerebellar cortex, nuclei)

Question 6

Where are axons in the CNS located?

Answer 6

• White matter (tracts, fasciculi, lemnisci, commissures, brachii, peduncles)

Question 7

Functional divisions of the nervous system

Answer 7

• Voluntary nervous system: somatic motor: innervation and control of skeletal muscles
• Involuntary nervous system: visceral motor: ANS (SNS thoracolumbar T1-L2/3, PSNS craniosacral – both innervate and control smooth, cardiac muscle and glands) and ENS (controls peristalsis, gland secretions, blood flow through GI)

Question 8

What is a synapse?

Answer 8

• Junction between a neuron and a neuron, muscle cell or gland cell
• Site where an action potential is transmitted from cell to cell

Question 9

Morphological types of synapses

Answer 9

1. ) Axodendritic (most common)
2. ) Axosomatic
3. ) Axoaxonic (less frequent)

Question 10

Functional types of synapses

Answer 10

1. ) Electrical (in cerebral cortex, brainstem and retina; have gap junctions, impulse is rapid)
2. ) Chemical (most common, associated with NTs)

Question 11

Describe morphology of chemical synapses

Answer 11

1. ) Presynaptic component
   - Consists of presynaptic membrane, mitochondria, sER, synaptic vesicles containing NT and presynaptic densities (cone-shaped structures representing the active site of synapse)
2. ) Synaptic cleft
   - Narrow EC space between presynaptic and postsynaptic membranes for NT to diffuse across
3. ) Postsynaptic component
   - Consists of postsynaptic membrane, receptor sites for NT, displays postsynaptic densities (complex of proteins, binding NT receptors), contains ligand-gated Na channels

Question 12

Describe chemical synaptic transmission

Answer 12

• AP reaches presynaptic membrane, causes opening of Ca2+ ion channels
• Ca2+ enter causing synaptic vesicles to approach and attach to inner surface of membrane
• Vesicles fuse, 2 membranes rupture and point of contact and NT is released (kiss and run fusion or collapse fusion)
• NT diffuses across cleft
• NT binds to receptor (transmitter-gated channels) on postsynaptic membrane
• Conformation change occurs at channel proteins, opening of pores
• Influx of Na+ results in local depolarization, which opens up voltage-gated Na+ channels generating impulse

Question 13

Describe choroid plexus – location, composition, function

Answer 13

• Located in ventricles
• Consists of folds of pia mater covered by ependymal cells (simple cuboidal) with these cells held together by zonula occludens (tight junctions). Contain fenestrated capillaries
• Produces CSF. Waste diffuses into CSF of subarachnoid space, reabsorbed by arachnoid villi in superior sagittal sinus, passes into bloodstream. CSF acts as shock absorber

Question 14

3 layers of cerebellar cortex

Answer 14

• Molecular layer (superficial)
• Purkinje layer (middle): Purkinje cells = largest cells of NS, unique to cerebellum
• Granular layer (deepest): contains granule cells (smallest cells of NS)

Question 15

Does regeneration of neurons occur in PNS and CNS?

Answer 15

• only in PNS

Question 16

Two types of changes that occur as a result of injury to neuron

Answer 16

1. ) Anterograde changes: distal to site of injury
   - Segment of axon distal to injury degenerates (known as Wallerian degeneration)
   - Phagocytic cells (from Schwann and monocytes) clean up debris (2 weeks)
   - Schwann cells proliferate and along with their external lamina form tubes and tunnels
2. ) Retrograde rxn and neural regeneration
   - Cell body swells
   - Chromatolysis (1-2 days): Nissl bodies move to soma’s periphery
   - Nucleus moves away from center of cell body
   - Formation of free ribosomes and protein synthesis
   - Axon grows sprouts
   - Schwann cells guide axon growth toward target cell
   - Growing axon grows into endoneurium
   - Aiding in this process: macrophages, fibroblasts, basal lamina and Schwann cells