L21) Nervous tissue structure and function

Question 1

Define the CNS and PNS
* Describe the structure of grey and white matter (in CNS and PNS)
* Describe the structure of the neuron (and its variations)
* Describe the structure and function of the synapse (and its variations)
* Describe the structure and function of neuroglial cells (glial cells) * PNS-Schwanncells
* CNS - astrocytes, oligodendrocytes, microglia, ependymal cells * Astrocytesandtheblood-brainbarrier
* Summarise the function(s) of nerves
* Electrical conduction, neurotransmitter production, and release, etc.
* Describe the signs, symptoms and cause of multiple sclerosis

Question 2

Name the two nervous system divisions?

Answer 2

• CNS - central nervous system
• PNS -peripheral nervous system

Question 3

What does the CNS consist of?

Answer 3

Composed of:
* Brain
* Spinal cord
Contains:
* Relay neurons

Question 4

What does the PNS consist of?

Answer 4

Composed of:
* Cranial nerves
* Spinal nerves
* Peripheral nerves
Contains:
* Sensory neurons
* Motor neurons

Question 5

Where is the grey matter in (a) the brain? (b) the spinal cord?

Answer 5

(a) peripheral in brain - ‘nuclei’
(b) central in spinal cord - H or butterfly shaped

Question 6

what does the grey matter consist of?

Answer 6

• nerve cell bodies
• dendrites
• axon terminals
• non-myelinated axons
• neuroglia (support cells)

Question 7

where is the white matter in (a) the brain? (b) the spinal cord?

Answer 7

(a) central in brain
(b) peripheral in spinal cord

Question 8

what does the white matter consist of?

Answer 8

• myelinated material

Question 9

what are the anterior and posterior prongs of the grey matter referred to as in the spinal cord? and what are they connected by?

Answer 9

• ventral horns (VH) and dorsal horns (DH) respectively
• connected by the grey commisure (GC)

Question 10

what does the white matter of the spinal cord contain? what is visible in this section?

Answer 10

• contains nerve fibres that form ascending and descending tracts
• blood vessels of the pia matter, ventral fissure and some dorsal roots of spinal nerves are visible

Question 11

d

Question 12

what is the difference between the axon myelination in the CNS vs the PNS?

Answer 12

• in CNS, myelin produced by and part of an oligodendrocyte
• in PNS, myelin produced by and part of schwann cell

Question 13

What are the four different types of neurones?

Answer 13

• motor
• sensory
• integrative
• anaxonic

Question 14

what is the location and function of a motor neuron?

Answer 14

• location: CNS to periphery
• function: to seend signals to effector tissues

Question 15

what is the location and function of a sensory neuron?

Answer 15

• location: periphery towards CNS
• function:to send environmental signals to integrative centre

Question 16

what is the location and function of a integrative neuron?

Answer 16

• location: CNS
• function: collate all information

Question 17

what is the location and function of a anaxonic neuron?

Answer 17

• location: retina (some parts of the CNS)
• function: act as relays

Question 18

sss

Question 19

how is a neurotransmitter synthesised?

Answer 19

• immature vesicle contains only enzyme in its membrane
• as it travels the length of the axon, it starts to synthesise the neurotransmitter
• after neurotransmitter release, the vesicles has two fates: (1) recycled through clanthrin-coated endocytosis. (2) lost to neurolemma

transport in done through microtubules

Question 20

what are the five different types of synapses?

Answer 20

1. (a) axosomatic - direct to the plasma membrane of nerve or cell
2. (b) axodendritic - axon terminal synapses with dendritic spine
3. (c) axoaxonic - synapse at the axonic bouton
4. (d) dendro-dentritic
5. (e) axo-axonal - impinging dendritic/axonal synapse usually inhibits other inputs

axoaxonic may enhance or inhibit axodendritic/somatic synapse

Question 21

what nerve fibres are present in the peripheral nerves? what are they seperated by?

Answer 21

• sensory
• integrative
• motor
• seperated by connective tissue layers

Question 22

state the hierarchy of connective tissue in the peripheral nerves

Answer 22

Endoneurium
* loose connective tissue
* surrounds single nerve cells/axons
Perineurium
* specialised connective tissue - transports proteins
* maintains ionic composition
* surrounds clusturs of axons (fasicle)
Epineurium
* dense irregular connective tissue
* seperates different types of nerves and fills spaces between fasicles
Paraneurium
* fascia that seperates nerves from surrounding structures

Question 23

clinical correlate - myeline

Answer 23

Damage to myelin:
* in the CNS - cause of MS (multiple sclerosis)
* in the PNS - cause of Guillain-Barre syndrome

Question 24

how does myelination occur?

Answer 24

1. axon sitting in a groove is surrounded by a schwann cell
2. the mesaxon membrane initiates myelination by surrounding the embedded axon
3. a sheet like extension of the mesaxon membrane then wraps successively around the axon, forming multiple membrane layers
4. cytoplasm is extruded from between the two apposing plasma membranes of the schwann cell, which then become compacted to form myelin

Question 25

what distinguishes the role of an oligodendrocyte from that of a shwann cell?

Answer 25

• does the same thing as a schwann cell but in the CNS
• cytoplasmic processes from the oligodendrocyte form flattened cytoplasmic sheaths that wrap around each of the axons
• difference: wraps around more than one axon simultaneously

Question 26

name the support cells in the CNS -glia?

Answer 26

• oligodendrocytes
• astrocytes
• microglial cells
• ependymal cells

Question 27

describe an astrocyte

Answer 27

• star-like structure
• have perineural feet that contain gap junctions - (biochem support for endo cells; transport nutrients from blood to nerve cells)
• regulate nerve impulses by releasing glutamate (near node of Ranvier)
• contribute to the blood brain barrier
• calcium regulation?

Question 28

describe a microglial cell?

Answer 28

• large cells
• elongated nucleus
• relatively fewer processes emanating from cell body
• found throughout CNS
• resident macrophage
• thought to digest protein tangles in senile dementia and alzheimers

resident = immune function; remove damaged nerve cells; sense increased K+ ions

Question 29

where are ependymal cells found?

Answer 29

• line the spinal canal
• just posterior to ventral median fissure

Question 30

describe the structure of an ependymal cell

Answer 30

• derived from neural crest and neural tissue
• look like columnar epithelial lining the canal and ventricles of the brain
• joined by junctional complex (JC) - seperates the lumen of the canal from lateral intercellular space
• apical surface has both cilia (C) and microvilli (M)

Question 31

describe the function of ependymal cells

Answer 31

• synthesise and secrete CSF (cerebrospinal fluid) in ventricles (choroid plexus)
• cilia move CSF through ventricles to spinalcord
• microvilli absorb CSF for pathogen removal - present pathogens to microglial and astrocytes
• modified tight junctions between epithelial cells contril fluid release into brain

Question 32

clinical correlate - MS
what is the most common type?

Answer 32

• remitting-relapsing
• degenerative
• caused by autoimmune degradation of myelin