Nervous System
o Cellular Organization
Input region: composed of dendrites and cell body (soma) where sensory signals
are received
Trigger zone: located between input region and conductile region, site where
synaptic signals are generated
Conductile region: myelinated axon of the cell that is responsible for carrying
synaptic signal from input region to output region
Output region: axon terminal where signal triggers release of neurotransmitters
into the synaptic cleft
“Computation system”
Sensory in=peripheral nervous system
Integration=central nervous system (spinal cord and brain)
Motor Out=peripheral nervous system
o Axoplasmic Transport: discovered by injecting radioactive amino acids to input
region and watching proteins assembled from amino acids travel down the axon at
different speeds
Protein synthesis confined to soma-cell body
Transported to axon terminal from cell body in vesicles attached to kinesin
(+ end directed=anterograde)
Transported to cell body from axon terminal in vesicles attached to dynein
(- end directed=retrograde)
Slow axoplasmic transport: includes cytoplasmic proteins (cytoskeletal subunits,
cytosolic proteins, glycolytic enzymes)
Moves 0.5-2 mm/day
Move at fast rates intermittently (hitchhiker moving long distances)
Fast axoplasmic transport: includes vesicular proteins/membrane bound proteins
- Moves 200-400mm/day
, o Resting Membrane Potential
Anions (A-): large, negatively charged ions that are trapped inside the cell
membrane (generally amino acids/proteins)
K+: small, permeable cation
Travels across the membrane through K+ leak channels
Equilibrium: the tendency of K+ to leave the cell (travelling down its
concentration gradient) is balanced by the force of the electrical potential exerted
by the negatively charged A- on the positively charged K+ ions
- Equilibrium potential: electrical potential where equilibrium is reached
- Represented by EK=RT/ZF(ln[Koutside]/[Kinside])
- R=gas constant
- T=temp in Ko
- Z=charge of ion
- F=Faraday #
- EK is measured in volts
- Resting Membrane
- Membrane Potential seeks equilibrium potential for ion whose
permeability is dominant
- Resting Membrane Potential=equilibrium potential for K + leak channels
- Around -70 mv
o Capacitance: storage of charge across an insulating layer (phospholipid bilayer)
- Phospholipid bilayer is thin (6-7nm thick), so charges can interact on opposite
sides
o Ion Concentrations (Banana in the Ocean):
- K+
- [K+ outside of the cell]=4-5mm
- [K+ inside of the cell]=110mm
- Na+
- [Na+ outside of cell]=130-140mm
- [Na+ inside of cell]=10mm
- Ca2+
- [Ca2+ outside of cell]=2-3mm
- [Ca2+ inside of cell]=0.1mm
- Cl-
- There is a greater [Cl-] outside the cell than there is inside the cell
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