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
Describe vesicle formation
Top end of neural tube forms brain.
Rest forms spinal cord.
Soon as neural tube is formed it divides into 3 primary vesicles (week 4)
- Forebrain
- Midbrain
- Hindbrain
Secondary vesicles (week 5):
- Forebrain divides into Telencephalon and Diencephalon
- Midbrain stays
- Hindbrain divides into Metencephalon and Myelencephalon
What are the derivatives of the secondary vesicles?
Telencephalon:
- cerebral cortex
- basal ganglia
Diencephalon:
- thalamus
- hypothalamus
Mesencephalon:
-Midbrain
Metencephalon:
- Pons
- Cerebellum
Myelencephalon:
-Medulla
How do the ventricles of the brain form?
Cavity of neural tube forms the ventricles of the brain.
- Telencephalon = lateral ventricles
- Diencephalon = 3rd ventricle
- Mesencephalon = cerebral aqueduct
- Rhombencephalon = 4th ventricle
Explain the ventricles
The lateral ventricles are C-shaped cavities which lie in the cerebral hemispheres.
The inter ventricular foramen connects them with the 3rd ventricle (the cavity within the diencephalon)
The cerebral aqueduct lies in the midbrain
The diamond-shaped 4th ventricle lies in the hindbrain
What are the 3 meninges covering the CNS?
Pia mater:
- Innermost layer
- Thin and vascular
- Dips into fold of brain
Arachnoid mater:
- Middle layer
- Spider-weblike
Dura Mater:
- Outer layer
- Tough, fibrous and has dural folds
CSF lies between the Pia mater and the arachnoid mater
What is the subdural space?
Potential space which is traversed by blood vessels penetrating into the CNS
What is CSF?
Cerebrospinal Fluid
The fluid inside the cavity of brain (i.e. the ventricles) and central canal of spinal cord.
To some extend responsible for the maintenance of the “intracranial pressure”
Is also present surrounding the brain and spinal cord in between the layers of meninges which are coverings of the brain (between pia and arachnoid)
Where is CSF present?
Inside ventricles
Between pia and arachnoid
Where is CSF formed?
By choroid plexus in each ventricle
Lateral ventricles the largest and produces the most CSF
Where is CSF absorbed?
By arachnoid villi into saggital sinus (venous channel in brain)
How does the CSF circulate?
Through the roof of the 4th ventricle which has a thin membrane.
3 holes (2 lateral, 1 medial) allows the CSF to enter subarachnoid space.
Flows around the brain making brain float.
Drains by arachnoid villi
What are dural folds?
Protect the brain
Exist between cerebellum folds and other folds in the brain.
Fix the brain relative to the skull
Means the brain doesn’t get thrown about the head
What is the blood brain barrier?
A protective mechanism that helps maintain a stable environment for he brain and prevents harmful amino acids and ions present in the bloodstream and blood cells from entering the brain.
- Endothelium (tight junction)
- Thick basal lamina
- Foot processes of astrocytes
Why is the blood brain barrier present?
Capillaries are usually fenestrated.
You don’t want that in areas of the brain because a lot of proteins (from food) act as neurotransmitters.
Brain needs very constant environment which is unlike the constantly changing nature of the rest of the bodies blood.
Only things that can pass are water, lipid soluble molecules and O2.
Hypothalamus can detect stuff your body doesn’t like from the blood and therefore cause you to throw up.
