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What is a ganglion?
A group, cluster or concentration of nerve cell bodies where many synapses occur
What is a group of nerve cell bodies called in the CNS?
What is a group of nerve cell bodies called in the PNS?
What is an autonomic ganglion?
- A cluster of neuronal cell bodies and their dendrites
- A junction between the brain and its autonomic innervation of target organs in the periphery
Describe the structure of a neurofilament.
- 8 tetramers twisted into a single rope-like filament
- 10 nm diameter (smaller than microtubules)
- more stringlike than microtubules
What role do neurofilaments play in neurons?
Provide a structural backbone for dendrites and axons
What role do microtubules play in axons?
- Transport cargo including vesicles that contain neurotransmitters (both retrograde and anterograde transport)
- Also transport mitochondria.
What role does the SER play in neurons?
- Spans the whole neuron from soma to axon terminal
- Occasionally associated with axonal and vesicular membranes
- Conveys molecules or building blocks for membrane assembly
Name the six steps of synaptic transmission
- 1) Vesicle transport
- 2) Vesicle-loading
- 3) Depolarization
- 4) Exocytosis
- 5) Binding of NT
- 6) Depolarization
What are the functions of glia?
- Enhance neuro-transmission
- Structural (Physical support)
- Biochemical (Speed up impulses)
- Nutritive (Growth and maintainence)
- Immune (Scavenge toxins and debris)
Are glia conducting or nonconducting?
Contrast myelinated and unmyelinated neurons.
- Myelinated: more efficient conduction (less leaky)
- Less energy consuming
- Faster impulse velocity
- Unmyelinated: Leak Na+ ions
- Channels must open along entire length
- Slower impulse velocity
Which types of nerve fibers use heavily myelinated axons?
- Motor (voluntary)
- Sensory (acute pain)
What types of nerve fibers use moderate to un-myelinated axons?
- Motor (autonomic)
- Sensory (Chronic pain and pleasure)
Contrast myelination in the CNS vs the PNS.
- PNS: Schwann cells
- Cells wrap around axon many times forming the myelin sheath
- 1 cell per 1-2 mm segment of 1 axon
- Discontiunous- Nodes of Ranvier
- CNS: Oligodendrocytes
- Functional analogue of Schwann Cell
- 1 oligodendrocyte contacts >60 axons
Describe how Schwann cells are involved in unmyelinated axons.
- 10 axons engulfed by a single Schwann cell
- Axons continue to communicate with the extracellular space
Name four types of glia in the CNS.
- Protoplasmic Astrocyte
- Fibrous Astrocyte
What is the functional role of protoplasmic and fibrous astrocytes?
- 1) Contact blood vessels to regulate local blood flow
- 2) Maintain local blood flow
- 3) Scavenge ions and maintain ion homeostasis.
- Summary- metabolic support
What is the key difference between protoplasmic and fibrous astrocytes?
Protoplasmic occur in grey matter, while fibrous occur in white matter.
What is the functional role of microglia?
- 1) Patrol the brain and shield it from injury
- 2) Continually extend and retract their processes
- 3) Stimulated by the release of chemo-attractants
- 4) Processes move towards a site of injury
- Summary: Immune, scavengers
What is the functional role of ependymal cells?
What is the epineurium?
The connective tissue covering of an entire nerve in the PNS
What is the perineurium?
The connective tissue covering that segregates different nerve bundles in the PNS.
What is the endoneurium?
The connective tissue covering that segregates different nerve fibers within a nerve fascicle of a nerve in the PNS
What role do connective tissue coverings play in nerves?
- Provide some protection
- Allow the segregation of different types of afferent and efferent fibers and insulates them from each other
Describe the connective tissue coverings of the CNS.
- Dura mater
- Arachnoid membrane
- Subarachnoid space filled with CSF
- Pia mater
How does the brain maintain homeostasis?
- 1) Capillary Endothelium:
- tight lining of blood vessels (continuous tight junctions)
- Maintain blood brain barrier
- Restricts large molecules and protects the brain from peripheral factors
- 2) Ependymal cells
- Continuous lining of the brain + lining of the ventricular system
- Synthesize, secrete and excrete CSF
- Maintain Blood-CSF barrier
Which substances are able to penetrate the capillary endothelium?
- Astrocytes contact blood vessels
- Lipid-soluble substances pass freely
- Water-soluble substances gain access via membrane-bound pumps to produce CSF
Describe the ventricular system of the brain.
- Comprised of 4 cavities
- Spans the entire CNS
- Circulates CSF (250 mls) @ a rate of 12-36 mls/hr
- Contains nutrients, NTs and waste material
- Acts as a liquid cushion
- Continuous with the sub-arachnoid space
What is the choroid plexus?
- Simple cuboidal epithelium found in the ventricles
- Acts as a barrier, but actively transports small molecules (ions)
- Synthesize/secrete CSF
What is the functional role of the arachnoid villi?
- Pierce through the dura mater, and protrude into the venous cavities
- Allow CSF to exit the brain and into the venous system
What is CSF?
- Cerebrospinal fluid
- Produced by the choroid plexus in the ventricles; flows from the ventricles into the subarachnoid space
- The brain and spinal cord float in the CSF, so the CSF cushions the CNS against impact
Contrast white and grey matter
- White matter: collection of myelinated axons
- tracts (spinal cord) and tracts (CNS)
- Gray matter: Neuronal cell bodies
- horns (spinal cord) and cortices (brain)
Describe multiple sclerosis.
- Primary destructive effect is loss of central myelin
- Death occurs within months to years (>20) of onset
- Incidence ~ 50/100000
- Disease rate shows geographic gradient towards northern latitudes
Describe Amyotrophic Lateral Sclerosis.
- Loss of myelin occurs, but secondary to loss of motor cells and muscle atrophy [skeletal]
- Death occurs within 2-6 years
- Incidence ~ 3-7/100000
- No specific treatment for this disease has been satisfactory
- Caused by inflammation of the coverings of the brain and spinal cord [meninges]
- Develops in response to infection, drug abuse, cancer, or physical injury
- Curable but devastating if left untreated- dementia, death
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