lecture 7/8- neurophysiology I and II Flashcards
nervous system divisions (general)
- CNS
- PNS
CNS divisions (2)
brain and spinal cord
PNS divisions
- afferent (sensory)
- efferent (autonomic and somatic)
efferent divisions
- autonomic –> parasympathetic and sympathetic
- somatic
cells of the nervous system
- neurons
(excitable)
-glial cells (not excitable)
4 types glial cells found in the CNS
-ependymal cells
-astrocytes
-microglia
-oligodenrocytes
2 types of glial cells found in PNS and functions
schwann cells= form myelin sheaths, secrete neurotropic factor
satellite cells= support cell bodies
neuron parts
dendrites= receive signals
cell body (soma)= integrates information
axons= carry info to axon terminal
signal is passed on to next neuron or target cell
what is a nerve?
neuron= 1 cell
nerve= bundle of axons from multiple neurons
what are two diseases caused by demyelination?
MS: multiple sclerosis, degeneration of CNS myelin, progressive
Guillain-Barre syndrome: autoimmune degeneration of PNS myelin, sudden onset, temporary
why does demyelination result in impaired functions?
demyelination causes impaired conduction of electrical signals alonf the axon
loss of function depends on the neurons/nerves affected
what is the resting membrane potential of a neuron
-70mV
what type of channels control the permeability of the neuronal membrane?
gated channels!
-mechanically gated, chemically gated, voltage gates
2 types of electrical signals in neurons
graded potentials
- depolarization or hyperpolarization
(EPSP or IPSP)
electrical signals travel as + or - charges
-lose strength as they travel
action potentials
- all or none
- only depolarization
- amplitude is stable (strength is conserved)
is depolarization excitatory or inhibitory?
excitatory!
Give an overview of neuronal electrical signalling
- signal input in dendrites
- change in ion permeability
- generates graded potential - graded potential spreads through soma
- reaches axon hillock (high density Nav channels)
-if threshold is reaches, AP initiates - AP conducted along axon
- At axon terminal, AP triggers neurotransmitter release
- NT binds to receptors on postsynaptic dendrites/membrane
graded potentials: what happens
if there is more stimulus?
of channel density increases?
more stimulus= more activation of channels
increased channel density= increased sensitivity to stimuli
Ohms law
V= IR
or
I= V/R
current depends on electrochemical gradient of ion and resistance that opposes the flow
two sources of resistance to current flow in cells?
- Rm, membrane resistance
- membrane is normally a good insulator (high Rm)
- open channels allow ion flow (decreases Rm) - Ri, internal resistance of cytoplasm
-inversely related to cell diameter
- larger diameter= lower Ri
do subthreshold graded potential trigger an AP?
NO
do suprathreshold graded potentials trigger an AP?
YES
spatial summation
currents from almost simultaneous graded potentials combine
temporal summation
currents from two graded potentials from one postsynaptic neuron occur close together in time
how does ion permeability change during an AP?
- Na channels open and close faster than K+ channels
-rise in permeability of Na (Pna) drives rising phase of an AP - rise in Pk drives falling phase