CNS cells and Synaptic Transmission

Question 1

white matter fibres tend to run along certain pathways together - what are these called?

Answer 1

tracts

Question 2

what are white matter tracts made up of?

Answer 2

Made up of axons – the long extensions from the neuron’s cell body, that terminate in synapses.

Question 3

tracts can be described as either:

Answer 3

projection (afferent or efferent)
OR
association (connect areas in the same hemisphere)
OR
commissural (connect areas in different hemispheres)

Question 4

when laminae are connected on the same side, it’s called?

Answer 4

Association fibres

Question 5

when laminae are connected on opposite side, it’s called?

Answer 5

Commissural fibres

Question 6

name the 4 neuroglial cell types

Answer 6

Oligodendrocytes
Astrocytes
Microglia
Ependyma

Question 7

what about Oligodendrocytes

Answer 7

Responsible for myelination in the CNS
they are small, round cell bodies with about 5 processes that branch and myelinate several axons
they determine myelin sheath thickness and the establishment of Nodes of Ranvier
Therefore, properly functioning conduction of action potentials is due to the activity of oligodendrocytes

Question 8

what are Astrocytes involved in

Answer 8

blood-brain barrier and blood flow
extracellular K+
extracellular Glutamate
ATP-induced Ca2+ uptake
growth factors
neuronal migration
synapse formation (forming neural circuitry)
neurogenesis
glial scars
astrocytomas

Question 9

what are ependyma involved in

Answer 9

lining ventricular system

Question 10

what are microglia involved in

Answer 10

defence

Question 11

as you get older, what happens to myelin sheaths

Answer 11

Myelin sheaths shown signs of deterioration as you get older

Question 12

what is the cause of multiple sclerosis

Answer 12

Degeneration of myelin sheaths (demyelinating disease) is the cause of multiple sclerosis

Question 13

what are astrocytes

Answer 13

Star-shaped, interconnected neuroglial cells that can be visualised with antibodies to GFAP (glial fibrillary acidic protein)

Question 14

Calcium ions regulate almost all intracellular processes (but not action potentials).

what are the immediate effects of Ca2+?

Answer 14

exocytosis
modulation of ion channels
contraction

Question 15

Calcium ions regulate almost all intracellular processes (but not action potentials).

what are the delayed effects of Ca2+?

Answer 15

modulation of intracellular enzymes which can result in the regulation of intracellular metabolism
regulation of gene expression (this can also occur via the modulation of intracellular enzymes)
the regulation of gene expression can lead to long-term adaptive changes

Question 16

what about Interconnections between glial cells – the ‘glial syncytium’

Answer 16

Focus on astrocytes whose processes are coupled by gap junctions which have pores in them
The pores allow diffusion of the following molecules:
second messengers
nucleotides
other large molecules
AND
ions – electrical coupling

Question 17

how are extracellular K+ levels maintained by astrocytes

Answer 17

Extracellular potassium ion levels MUST be kept around 2.0 – 2.5mM Astrocytes

1: Directly take up K+ from extracellular space by K+ pumps
2. Redistribute K+ within the glial syncitium for subsequent discharge into the extracellular/perivascular space

Question 18

why are extracellular K+ levels maintained by astrocytes

Answer 18

Elevated K+ leads to dyshomeostasis as seen in epilepsy

Question 19

Extracellular glutamate levels MUST be kept around…? and why must they be maintained at this?

Answer 19

Extracellular glutamate levels MUST be kept around 3mM and must be maintained because Excess glutamate is highly TOXIC to neurones

Question 20

astrocytes are involved in regulating what in extracellular space

Answer 20

Astrocytes are involved in regulating the
concentrations of Ca2+, Cl- and water in the
extracellular space

Question 21

Astrocytes provide metabolic support for neurones. how?

Answer 21

astrocytes converts glucose to lactate which is released into EC (extracellular) space and taken up by neurones.
(this MAY be the ultimate source of the BOLD contrast measured by fMRI.)

Question 22

Roles of astrocytes in disease/pathology

Answer 22

Astrocytomas
Astrogliosis (isolation of damaged area, rebuilding blood brain barrier, rebuilding new circuitry)
Epilepsy

Question 23

what is the direct role of astrocytes in the control of breathing?

Answer 23

Astrocytes in the chemosensory areas of the brainstem are highly sensitive to pH. They release ATP to stimulate chemosensitive neurones that cause increases in breathing

Question 24

what about microglia?

Answer 24

Microglia - ‘the immune system of the brain
microglia are normally resting cells that become activated by brain injury
(infection, inflammation, trauma, hypoxia etc.)

As CNS neurones do not replicate, they require protection from pathogens hence microglia

Question 25

what are ependymal cells

Answer 25

Ciliated, cuboidal epithelial cells that line the ventricular system of the CNS

Question 26

what produces cerebrospinal fluid (CSF)?

Answer 26

Modified ependymal cells in the choroid plexus produce CerebroSpinal Fluid (CSF)

Question 27

The Tripartite synapse is composed of:

Answer 27

ONE presynaptic nerve terminal TWO astrocyte processes Plus the postsynaptic membrane

Question 28

The major EXCITATORY neurotransmitter in the CNS is

Answer 28

GLUTAMATE

Question 29

The major INHIBITORY neurotransmitter in the CNS is

Answer 29

GABA (γ-aminobutyric acid)

Question 30

what is acetylcholine (ACh) metabolised by

Answer 30

ACh is metabolised by acetylcholinesterase (AChE)

Question 31

what are the 2 main groups in the pons whose axons run rostrally and terminate in specific regions?

Answer 31

The Axons Running to the Substantia Nigra & Subthalamic Nucleus (Involved in Stereotyped Movements) The Forebrain Cholinergic Nuclei (Involved in Memory)

Question 32

the locus coeruleus (LC) produces Noradrenaline (norepinephrine). LC's neurons in the pons that project to?

Answer 32

entire cerebral and cerebellar cortex thalamus spinal cord

Question 33

lateral tegmental nucleus (LTN) is a cluster of neurons located in the tegmentum of the pons and midbrain. the lateral tegmental nucleus sends projections to?

Answer 33

spine (spinal projection for urinary continence) hypothalamus to control releasing factors

Question 34

alterations in dopamine may be involved in?

Answer 34

schizophrenia

Question 35

substantia nigra produces dopamine. substantia nigra projects to what?

Answer 35

corpus striatum (a key part of the basal ganglia)

Question 36

The raphé nuclei in the midline of the brainstem contains what?

Answer 36

Contain the vast majority of neurones in the CNS that contain and use serotonin (5-HT) as their neurotransmitter

Question 37

what is spinal projection involved in?

Answer 37

analgesia in dorsal horn of spinal cord bladder control (promotes continence)

Question 38

what is rostral projection involved in?

Answer 38

Rostral projections to hypothalamus and cerebral cortex - modulates sleep/wake states’ - possibly involved in schizophrenia

Question 39

For managing cognitive symptoms like memory loss in Alzheimer's disease, what medications are prescribed?

Answer 39

donepezil, rivastigmine, galantamine, and memantine are commonly used, with donepezil being the most prescribed

Question 40

mechanism of action of donepezil

Answer 40

Donepezil binds reversibly to acetylcholinesterase, the enzyme that breaks down acetylcholine. Increased Acetylcholine Availability: By inhibiting acetylcholinesterase, donepezil prevents the breakdown of acetylcholine, leading to a higher concentration of acetylcholine at the synapses (the junctions between nerve cells). Enhanced Cholinergic Transmission: The increased availability of acetylcholine enhances cholinergic neurotransmission, which is the process by which nerve cells communicate using acetylcholine.