Neuro Lecture 2
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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
What is the function of astrocytes?
- Glial scar
What is the function of oligodendrocytes?
What is the function of microglia?
Phagocytes of the CNS
What is the function of Ependymal cells?
Lines cavities of CNS
What are the four information processing operations of neurons?
What is neuroplasticity?
Recovery of the neuron or reorgaization of undamaged neurons
Describe the soma
- Metabolic center of neuron
- Nucleus or perikaryon
- Usually several per neuron
- Input units to cell
- One per neuron
- Main conducting unit
- arsies from the axon hillock
- diameter 0.2-20 micrometers
- length up 1 meter
What is the job of the receptive segment?
- Receives the Input
- Typically Dendrites & Cell Body
What is contained in the Receptive Segment?
Basically proteins. Plasticity is affected by having more or less receptors
What are Dendritic Spines?
Microspecilizations which contain the post-synaptic density (PSD)
What affects size and length of dendritic spines?
- Synaptic activity
- Profound spine loss is found in forms of mental retardation
What is the axon hillock?
A specialized portion of the axon where an action potential is initiated when the critical threshold is reached
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
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
What is frequency code?
- Each neuron has a spontaneous discharge frequency
- -Increasing information - an increase in discharge frequency
- -Decreasing information - decrease in discharge frequency
Describe the Transmissive Segment
- Allows communication between neurons
- Typically the presynaptic terminal
- Contain volatge gated Ca2+ which release transmitter
Describe Synaptic communication
- Neurotransmitter release from presynaptic neuron
- Electrical response in post synpatic neuron
What is the job of first order neurons?
relay information from sensory receptors to CNS
What is the job of second order neurons?
Cross the midline, relay information to the Thalamus
What is the job of third order neurons?
Relay information to the cortex
Where does Divergence occur?
Parallel processing for: sensory systems, input centers, information dispersion
What are three types of Site of Synapses?
What is the purpose of Divergence?
Amplification of weak signals
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.
Where are unipolar neurons found?
Found in invertebrate autonomic nervous systems
Where are pseudo-unipolar neurons found?
First-order sensory neurons
Where are bipolar neurons found?
2 order neurons in visual & olfactory systems
Where are multipolar neurons found?
Largest class of cells in vertebrate nervous systems
What are the three functional classifications of neurons?
Describe local interneurons
- Process information locally
- rich dendritic arborization
- short axons
Describe projecting interneurons
- Transmit information between distant locations within NS
- Long axons organized into tracts in SC and brain (2nd order neurons)
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
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
What is Retrograde degeneration?
- Begins 2-3 days after injury
- Synaptic retraction
- Atrophy of presynaptic cell
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)
What are three classification types of Peripheral Nerve Injury (PNI)?
What is Transient Neuropraxia?
Due to ischemix block of neuronal conductivity and presents as a rapidly reversible loss of function (arm falling asleep)
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)
Complete interruption of axon with loss of all function suberved by the cell, recovery of function may occur if Wallerian degernartion and regernation occur
Complete interruption of entire nerve fiber including cell membrane and myelin sheath, requires surgical re-attachment if recovery of function is to occur.
- Complication of axonotmesis or neurotmesis
- painful and non-painful
Name some Demyelinating lesions
- Multiple Sclerosis
- Bell's palsy
Name 3 factors affecting recovery and sparing of function
- Biological factors (age and sex)
- Characterisics of Lesion (size, momentum)
- Experience (Environmental & training)
How do "enriched environments" (experience) affect the nervous system?
- Affect cortical depth
- Brain weight
- Dendritic branching,
- Spine development
- Enzyme activity
"Pre-damage" enrichment is:
"Post-damage" enrichment does this:
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
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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