CNS Cells and Synaptic Transmission Flashcards
What is the CNS organised into
Nuclei, tracts and layers (laminae
Describe white matter tracts
Corticospinal, fascicles (fasiculus= a bundle), cortical medulla, internal capsule and corpus callosum
What is the function of the corpus callosum
To connect the hemispheres
What is a nuclei
A cluster of cell bodies and their dendrites where synapses are made and information is processed
What do nuclei form
The grey matter areas of the brain and the spinal cord
What is white matter
Bundles of myelinated axons which form tracts connecting nuclei
What are supporting cells in the CNS called
Glia
What does white matter connect
Groups of cells
How many layers of the cortex are there in the human brain
6 therefore there is diversity
What are laminae connected by on the same side
Associated fibres
What are laminae connected by on opposite sides
Commissural fibres
What does the reticular arrangement of the CNS around the brainstem mean
There are diffuse connections between neurones
What is the main job of the neuroglia
Myelination
What is the function of oligdendrocytes
Myelination
What is the function of astrocytes
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
What is the function of microglia
Defense, “hoovers”
What is the function of ependyma
Lining ventricular system, very important for CSF
Describe oligodendrocytes
Small, round cell body with about 5 processes that branch and myelinate several axons (10-25)
What do oligodendrocytes determine
Sheath thickness and establishment of Nodes of Ranvier
Describe myelination by oligodendrocytes
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
What does degeneration of myelin sheaths result in
Multiple sclerosis
Describe oligodendrogliomas
Average age of onset 34 years, lead to seizures due to frontal lobe damage
Describe astrocytes
Star-shaped interconnected neuroglial cells that can be visualised with antibodies to GFAP (glial fibrillary acidic protein).
Describe intracellular calcium
Must be kept low
Describe interconnections between glial cells
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
How can astrocytes communicate with eachother
Linked by gap junctions (glial syncitium)
Describe the function of astrocytes in relation to he blood-brain barrier
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
Describe the function of astrocytes in maintaining extracellula potassium ion levels
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
What does elevated K+ lead to
Dyshomeostasis as seen in epilepsy
Describe the function of astrocytes in maintaining extracellular glutamate levels
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
Describe the function of astrocytes in maintaining ion elevels
Regulate concentrations of Ca2+, Cl- and water in the extracellular space
Describe the function of astrocytes in metabolic support
Provide metabolic support for neurones
Describe the function of astrocytes in disease/ pathology
Astrocytomas, astrogliosis (isolation of damaged area, rebuilding BBB, rebuilding new circuitry), epilepsy (rarely epileptic seizures when things go wrong)
Describe the function of astrocytes in control of breathing
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
Why do CNS neurones require protection from pathogens
CNS neurones do not replicate
Describe microglia
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
Describe ependymal cellsq
Ciliated, cuboidal epithelial cells that line the ventricular system of the CNS
What do modified ependymal cells in the choroid plexus do
Produce cerebrospinal fluid
What are ependymomas
Tend to be benign but are space-occupying
What is the tripartite synapse composed of
One presynaptic nerve terminal, two astrocyte processes plus the postsynaptic membrane
What is the major excitatory neurotransmitter in the CNS
Glutamate
Describe glutamate
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
What is the major inhibitory neurotransmitter in the CNS
GABA
Describe cholinergic neurones
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
What are forebrain cholinergic nuclei involved in
Memory
What is ACh metabolised by
Actylcholinesterase (AChE)
What monaime neurotransmitetr originate in the brainstem
Noradrenaline and dopamine
Describe noradrenaline
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
Describe dopamine
Substantia nigra- corpus striatum (Parkinson’s disease). Alterantions in dopamine levels may be involved in schizophrenia
Describe the rahpre nuclei in the midline of the brainstem
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
