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Name some roles of the glial cells?
- Supporting elements
- Form myelin
- Scavenger functions
- Guide migration of neurons
- Induction of and participation in the blood-brain barrier
- Nutritive functions
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What is the function of astrocytes?
- Support
- Protection
- Nourishment
- Glial scar
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What is the function of oligodendrocytes?
Myelnation
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What is the function of microglia?
Phagocytes of the CNS
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What is the function of Ependymal cells?
Lines cavities of CNS
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What are the four information processing operations of neurons?
- Reception
- Analysis/Integration
- Conduction
- Transmission
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What is neuroplasticity?
Recovery of the neuron or reorgaization of undamaged neurons
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Describe the soma
- Metabolic center of neuron
- Nucleus or perikaryon
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Describe dendrites
- Usually several per neuron
- Input units to cell
- Branch-like
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Describe axons
- One per neuron
- Main conducting unit
- arsies from the axon hillock
- diameter 0.2-20 micrometers
- length up 1 meter
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What is the job of the receptive segment?
- Receives the Input
- Typically Dendrites & Cell Body
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What is contained in the Receptive Segment?
Basically proteins. Plasticity is affected by having more or less receptors
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What are Dendritic Spines?
Microspecilizations which contain the post-synaptic density (PSD)
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What affects size and length of dendritic spines?
- Synaptic activity
- Profound spine loss is found in forms of mental retardation
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What is the axon hillock?
A specialized portion of the axon where an action potential is initiated when the critical threshold is reached
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Describe the Integrative Segment
- Receptive segment spreads signals passively to this region
- Begins at the cell body (axon hillock) and ends where the myelin sheath begins
- Potentials are summed and decision is made whether or not to fire (all-or-none)
- AKA - Tigger zone, initial segment, spike generating zone
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Describe the Conductive Segment
- Information conducted from one location in the nervous system to another as action potentials (all or none) along the axon
- Typically the axon
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What is frequency code?
- Each neuron has a spontaneous discharge frequency
- -Increasing information - an increase in discharge frequency
- -Decreasing information - decrease in discharge frequency
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Describe the Transmissive Segment
- Allows communication between neurons
- Typically the presynaptic terminal
- Contain volatge gated Ca2+ which release transmitter
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Describe Synaptic communication
- One-way
- Neurotransmitter release from presynaptic neuron
- Electrical response in post synpatic neuron
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What is the job of first order neurons?
relay information from sensory receptors to CNS
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What is the job of second order neurons?
Cross the midline, relay information to the Thalamus
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What is the job of third order neurons?
Relay information to the cortex
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Where does Divergence occur?
Parallel processing for: sensory systems, input centers, information dispersion
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What are three types of Site of Synapses?
- Axodendritic
- Axosomatic
- Axoaxonic
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What is the purpose of Divergence?
Amplification of weak signals
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What is the purpose of Convergence?
- Good for spatial discrimination
- Uses lateral inhibition that allows the body to pinpoint where the stimulus is located on the body.
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Where are unipolar neurons found?
Found in invertebrate autonomic nervous systems
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Where are pseudo-unipolar neurons found?
First-order sensory neurons
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Where are bipolar neurons found?
2 order neurons in visual & olfactory systems
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Where are multipolar neurons found?
Largest class of cells in vertebrate nervous systems
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What are the three functional classifications of neurons?
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Describe local interneurons
- Process information locally
- rich dendritic arborization
- short axons
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Describe projecting interneurons
- Transmit information between distant locations within NS
- Long axons organized into tracts in SC and brain (2nd order neurons)
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What are some causes of neuronal damage?
- Ischemic, traumatic, toxic, degenerative, abnormal development
- Damage to cell body or axon hillock causes cell death
- Neuronal death causes long-lasting or permanent loss of function
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What is Orthograde Degeneration?
- Also known as Wallerian degeneration
- Distal portion of a damaged axon dies because it is disconnected from the cell body which it sustains it
- Causes denervation hypersensitivity (spasticity)
- Causes muscular atrophy
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What is Retrograde degeneration?
- Begins 2-3 days after injury
- Synaptic retraction
- Atrophy of presynaptic cell
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Name some was neuronal damage can be reversed
- Collateral sprouting from intact neurons
- Reorganization (intact systems assume the lost function, neuroplasticity)
- Wallerian regeneration (functional connections with target cells may be re-established)
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What are three classification types of Peripheral Nerve Injury (PNI)?
- Neurapraxia
- Axontmesis
- Neurotmesis
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What is Transient Neuropraxia?
Due to ischemix block of neuronal conductivity and presents as a rapidly reversible loss of function (arm falling asleep)
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What is Delayed reversible neuropraxia?
Due to demyelination and presents as a loss of function that recovers after a few weeks following re-myelinization (Bell's palsy, Guillian-Barre)
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Define Axonotmesis
Complete interruption of axon with loss of all function suberved by the cell, recovery of function may occur if Wallerian degernartion and regernation occur
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Define Neurotmesis
Complete interruption of entire nerve fiber including cell membrane and myelin sheath, requires surgical re-attachment if recovery of function is to occur.
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Define Neuroma
- Complication of axonotmesis or neurotmesis
- painful and non-painful
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Name some Demyelinating lesions
- Multiple Sclerosis
- Bell's palsy
- Guillian-Barre
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Name 3 factors affecting recovery and sparing of function
- Biological factors (age and sex)
- Characterisics of Lesion (size, momentum)
- Experience (Environmental & training)
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How do "enriched environments" (experience) affect the nervous system?
- Affect cortical depth
- Brain weight
- Dendritic branching,
- Spine development
- Enzyme activity
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"Pre-damage" enrichment is:
Protective
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"Post-damage" enrichment does this:
Improves recovery
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Define Myasthenia Gravis
- Usually an acquired autoimmune disorder
- Body produces antibodies that destroy acetylcholine receptors on the postsynaptic membrane at the myoneural junction
- Blocked receptors cause repetitive contractions to fail
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What are some presentations of MG?
- Double vision
- Difficulty chewing, swallowing and speaking
- Symptoms get worse with fatigue and use
- Ptosis (drooping eye lid)
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