Cells and Tissues of the Nervous System Flashcards
How is the Nervous system divided?
CNS (Brain & Spinal Cord)
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PNS (Cranial & Spinal Nerves)
PNS:
- Sensory (Afferent) Division
- Motor (Efferent) Division
Motor (Efferent) Division
- Somatic Motor
- Autonomic
Autonomic
- Sympathetic
- Parasympathetic
What are the 2 cell types of the nervous system?
Neurones:
- Structural and functional unit
- EXCITABLE cells
- Impulses carried as ACTION POTENTIALS
Glial Cells:
- Non-excitable supporting cells
- Much smaller than neurones
- Far outnumber neurones
Give some information about neurones structure
E.g. nucleus, cell organelles
Nucleus:
- Loose chromatin
- Prominent nucleolus
Cell organelles:
- Mitochondria
- rER (Nissi bodies)
- Diffuse Golgi apparatus
High metabolic rate
Cytoplasm in the cell body is perikaryon, and the axon is axoplasm
Long living and amitotic
What damage to axons is irreversible?
Axons can grow back but is a neuron cell body is damaged the loss is irreversible
Give some info about myelin sheaths
Increase conduction speed in axons by “Saltatory conduction”
-Nodes of Ranvier between sheaths
Depending on presence or absence of myelin sheath neurones may be:
- Myelinated neurons
- Non-myelinated neurons
Myelin sheath formed by:
- Schwann cells in PNS
- Oligodendrocytes in CNS
How do schwann cells myelinate axons?
Schwann cells wrap around myelinated axons
In myelinated axons a mesaxon is formed
The cytoplasm of Schwann cell gets extruded leaving only the cell membrane.
Why is white matter white?
Cell membrane of Schwann cells wrapping around axon is of multiple layers.
Cell membrane is made of lipids (fat)
White in colour
When you see white matter its because of myelinated sheath
What is a mesaxon?
A pair of parallel plasma membranes of a Schwann cell, marking the point of edge to edge contact by the Schwann cell encircling the axon.
The myelin sheath is of clinical importance in conditions such as Multiple Sclerosis.
Explain this condition
Patchy loss/scarring of myelin sheath (demyelination) -> nerve conduction across affected axons abnormal
Cause unknown (?Viral, ?autoimmune)
MRI shows whitish plaques of demyelination.
Prognosis variable
Scotland has the HIGHEST incidence in the world
What are the 3 types of neurones?
Multipolar
Bipolar
Pseudounipolar
What are multipolar neurones?
Most common
Multiple dendrites and 1 axon
Motor Neurones
Interneurones
What are bipolar neurones?
Most rare
1 axon and 1 dendrite
Olfactory mucosa
Retinal nerve fibres
What are pseudounipolar neurons?
Allows signal to bypass cell body.
Sensory neurones.
Signal goes straight where it wants to go
What PNS glial cells are there?
Satellite:
-Surround Neuronal Cell Bodies
Schwann Cells:
-Myelination
What are the glial cells of the CNS?
Ependymal Cells:
-Line Ventricles
Microglia:
Oligodendrocytes:
Astrocytes:
What is an astrocyte?
Most common CNS glial cell.
Do a lot of things:
- Have end feet surround synapses and capillaries
- –Congregate at synaptic terminals making sure end terminal and dendrite match up
- –Form blood brain barrier
- Help in K+ Buffering
What are Oligodentrocytes?
Myelination of CNS neurones
What are Microglia?
Phagocytes of the nervous system.
-Blood brain barrier prevents phagocytes entering so microglia there to perform role.
- Phagocytosis
- Scar Tissue formation
What do ependymal cells do?
Line ventricles
How are neurones organised?
Neurones are bundles together, or organised; depending on function in different parts of the nervous system.
These bundles of fibres are called tracts
How can you distinguish bundles of myelinated axons from bundles of non-myelinated axons?
Myelin sheath -> made of cell membrane
Cell membrane -> made of lipids
Fats are fellows-white in colour.
So, bundles of myelinated axons together look white.
Neuronal cell bodies/ non-myelinated axons bundled together appear grey.
Describe grey and white matter
Inside CNS:
-Collection of cell bodies + non-myelinated axons form grey matter (if diffuse) or nucleii (if localised)
-Collection of myelinated axons form white matter (diffuse) or tracts (localised)
In the Periphery:
- Myelinated axons form nerves
- Cell bodies form ganglia
What is the very basic topography of the brain?
2 cerebral hemispheres
- Cerebrum = seat of consciousness
- Cerebellum = balance and coordination
- Brainstem = Vital centres (e.g. cardiorespiratory), pathway for fibre tracts
- Diencephalon = holds thalamus and hypothalamus
Describe neural tube formation
When the embryo is 18 days old, it looks like a flat slipper with 3 layers of cells.
The top layer called the surface ectoderm develops a thickening called the neural plate.
This neural plate thickens, folding over and becoming the neural tube.
While this tube was sinking below the surface, some cells in the periphery called neural crest cells migrate and form many other structures and organs
The neural tube went on to form the nervous system
