Neuro Lecture 2
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Neuro Lecture 2
The Cellular Basis of the Nervous System
Name some roles of the glial cells?
Guide migration of neurons
Induction of and participation in the blood-brain barrier
What is the function of astrocytes?
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?
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
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
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
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
"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?
Difficulty chewing, swallowing and speaking
Symptoms get worse with fatigue and use
Ptosis (drooping eye lid)