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What is a ganglion?
A group, cluster or concentration of nerve cell bodies where many synapses occur
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What is a group of nerve cell bodies called in the CNS?
Nucleus
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What is a group of nerve cell bodies called in the PNS?
Ganglion
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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
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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
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What role do neurofilaments play in neurons?
Provide a structural backbone for dendrites and axons
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What role do microtubules play in axons?
- Transport cargo including vesicles that contain neurotransmitters (both retrograde and anterograde transport)
- Also transport mitochondria.
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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
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Name the six steps of synaptic transmission
- 1) Vesicle transport
- 2) Vesicle-loading
- 3) Depolarization
- 4) Exocytosis
- 5) Binding of NT
- 6) Depolarization
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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)
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Are glia conducting or nonconducting?
Non-conducting
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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
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Which types of nerve fibers use heavily myelinated axons?
- Motor (voluntary)
- Sensory (acute pain)
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What types of nerve fibers use moderate to un-myelinated axons?
- Motor (autonomic)
- Sensory (Chronic pain and pleasure)
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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
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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
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Name four types of glia in the CNS.
- Protoplasmic Astrocyte
- Fibrous Astrocyte
- Microglia
- Oligodendrocyte
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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
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What is the key difference between protoplasmic and fibrous astrocytes?
Protoplasmic occur in grey matter, while fibrous occur in white matter.
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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
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What is the functional role of ependymal cells?
BBB/CSF production
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What is the epineurium?
The connective tissue covering of an entire nerve in the PNS
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What is the perineurium?
The connective tissue covering that segregates different nerve bundles in the PNS.
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What is the endoneurium?
The connective tissue covering that segregates different nerve fibers within a nerve fascicle of a nerve in the PNS
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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
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Describe the connective tissue coverings of the CNS.
- Dura mater
- Arachnoid membrane
- Subarachnoid space filled with CSF
- Pia mater
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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Describe meningitis.
- 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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