CNS Cells and Synaptic Transmission

Question 1

What is the CNS organised into

Answer 1

Nuclei, tracts and layers (laminae

Question 2

Describe white matter tracts

Answer 2

Corticospinal, fascicles (fasiculus= a bundle), cortical medulla, internal capsule and corpus callosum

Question 3

What is the function of the corpus callosum

Answer 3

To connect the hemispheres

Question 4

What is a nuclei

Answer 4

A cluster of cell bodies and their dendrites where synapses are made and information is processed

Question 5

What do nuclei form

Answer 5

The grey matter areas of the brain and the spinal cord

Question 6

What is white matter

Answer 6

Bundles of myelinated axons which form tracts connecting nuclei

Question 7

What are supporting cells in the CNS called

Answer 7

Glia

Question 8

What does white matter connect

Answer 8

Groups of cells

Question 9

How many layers of the cortex are there in the human brain

Answer 9

6 therefore there is diversity

Question 10

What are laminae connected by on the same side

Answer 10

Associated fibres

Question 11

What are laminae connected by on opposite sides

Answer 11

Commissural fibres

Question 12

What does the reticular arrangement of the CNS around the brainstem mean

Answer 12

There are diffuse connections between neurones

Question 13

What is the main job of the neuroglia

Answer 13

Myelination

Question 14

What is the function of oligdendrocytes

Answer 14

Myelination

Question 15

What is the function of astrocytes

Answer 15

Blood-brain barrier, maintaining extracellular potassium, maintaining extracellular glutamate levels, regulating concentrations of Ca2+ Cl- and water, provide metabolic support for neurones, development of the CNS, neurogenesis, glial scars, astrocytomas

Question 16

What is the function of microglia

Answer 16

Defense, “hoovers”

Question 17

What is the function of ependyma

Answer 17

Lining ventricular system, very important for CSF

Question 18

Describe oligodendrocytes

Answer 18

Small, round cell body with about 5 processes that branch and myelinate several axons (10-25)

Question 19

What do oligodendrocytes determine

Answer 19

Sheath thickness and establishment of Nodes of Ranvier

Question 20

Describe myelination by oligodendrocytes

Answer 20

Post-natally in humans takes several months and adds about 1 kilo to brain weight (myelination responsible for 40-50% of brain weight); myelin sheaths show no sign of deterioration as you get older

Question 21

What does degeneration of myelin sheaths result in

Answer 21

Multiple sclerosis

Question 22

Describe oligodendrogliomas

Answer 22

Average age of onset 34 years, lead to seizures due to frontal lobe damage

Question 23

Describe astrocytes

Answer 23

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

Question 24

Describe intracellular calcium

Answer 24

Must be kept low

Question 25

Describe interconnections between glial cells

Answer 25

Glial syncitium- focus on astrocytes whose processes are coupled by gap junctions which have pores in them. A pair of astrocytes is coupled by about 200 gap junctions. The pores allow molecules of

Question 26

How can astrocytes communicate with eachother

Answer 26

Linked by gap junctions (glial syncitium)

Question 27

Describe the function of astrocytes in relation to he blood-brain barrier

Answer 27

Some mechanisms of transport are active, some passive. In the BB possible to use pulse ultrasound to target specific areas of the brain with drugs. Astroglial regulation of local blood flow link neural activity to the local circulation by releasing vasodilators and vasoconstrictors

Question 28

Describe the function of astrocytes in maintaining extracellula potassium ion levels

Answer 28

Extracellular potassium ion levels must be kept around 2.0-2.5 mM. Astrocytes directly from the extracellular space by K+ pumps, redistribute K+ within the glial syncitium for subsequent dischatge into the extracellular/ perivascular space

Question 29

What does elevated K+ lead to

Answer 29

Dyshomeostasis as seen in epilepsy

Question 30

Describe the function of astrocytes in maintaining extracellular glutamate levels

Answer 30

Extracellular gluatamate levels must be kept around 3mM as excess glutamare is highly toxic to neurones and results in cytotoxic cell death. Excess glutamate is absorbed by astrocytes, repackaged and sent back to the neurone

Question 31

Describe the function of astrocytes in maintaining ion elevels

Answer 31

Regulate concentrations of Ca2+, Cl- and water in the extracellular space

Question 32

Describe the function of astrocytes in metabolic support

Answer 32

Provide metabolic support for neurones

Question 33

Describe the function of astrocytes in disease/ pathology

Answer 33

Astrocytomas, astrogliosis (isolation of damaged area, rebuilding BBB, rebuilding new circuitry), epilepsy (rarely epileptic seizures when things go wrong)

Question 34

Describe the function of astrocytes in control of breathing

Answer 34

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 35

Why do CNS neurones require protection from pathogens

Answer 35

CNS neurones do not replicate

Question 36

Describe microglia

Answer 36

Immune system of the brain. Normally resting cells that become activated by brain injury (infection, inflammation, trauma, hypoxia etc.). When activated they clear up (phagocytose). They migrate to different sites of damage

Question 37

Describe ependymal cellsq

Answer 37

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

Question 38

What do modified ependymal cells in the choroid plexus do

Answer 38

Produce cerebrospinal fluid

Question 39

What are ependymomas

Answer 39

Tend to be benign but are space-occupying

Question 40

What is the tripartite synapse composed of

Answer 40

One presynaptic nerve terminal, two astrocyte processes plus the postsynaptic membrane

Question 41

What is the major excitatory neurotransmitter in the CNS

Answer 41

Glutamate

Question 42

Describe glutamate

Answer 42

Found in 80% of cortical neurones, all neurones from one region of the brain to the other use glutamate whether they are carrying an excitatory or inhibitory action

Question 43

What is the major inhibitory neurotransmitter in the CNS

Answer 43

GABA

Question 44

Describe cholinergic neurones

Answer 44

Two main groups in the pons whose axons run postrally and terminate in the substantia nigra and subthalamic nucleus and are involved in stereotypes movements

Question 45

What are forebrain cholinergic nuclei involved in

Answer 45

Memory

Question 46

What is ACh metabolised by

Answer 46

Actylcholinesterase (AChE)

Question 47

What monaime neurotransmitetr originate in the brainstem

Answer 47

Noradrenaline and dopamine

Question 48

Describe noradrenaline

Answer 48

Locus coeruleus- pons projecting to entire cerebral and cerebellar cortex, thalamus and spinal cors. Lateral tegmental- spinal projection (urinary competence) hypothalamus to control releasing factors

Question 49

Describe dopamine

Answer 49

Substantia nigra- corpus striatum (Parkinson's disease). Alterantions in dopamine levels may be involved in schizophrenia

Question 50

Describe the rahpre nuclei in the midline of the brainstem

Answer 50

Only neurones in the CNS that contain and use seretonin (5-HT) as their neural transmitter. Spinal projections- analgesia in dorsal horn, bladder control (promotes continence). Rostral projection- to hypothalamus and cerebral cortex, modulates sleep/wake states, possibly involved in schizophrenia and very recently cot death