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Lecture 6

BSC 283 Lecture Notes - Lecture 6: Threshold Potential, Internal Resistance, Positive Feedback

Biological Sciences
Course Code
BSC 283
Wolfgang Stein

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Neuron Function
Organization of the Nervous System
o Peripheral and central nervous systems
o Basic control pathway: sensory input (PNS) integrative center (CNS) motor
output (PNS)
CNS: brain and spinal cord
PNS: sensory and efferent divisions
o Efferent division: autonomic and somatic motor neurons
o Autonomic neurons: sympathetic and parasympathetic
Neuron Anatomy
o Several anatomical types based on dendrites and axons: pseudounipolar,
bipolar, anaxonic and multipolar
o Neuron structures and function: dendrites (input); cell body (integration); axon
(conduction); terminal and synapse (pre- and post- and cleft; transmission); some
neurons have myelin along axons (aids electrical conduction)
Axonal Transport
o Specialized cellular function of neurons
o Fast: 400 mm/day; two directions anterograde (towards terminal; synaptic
vesicles and mitochondria) and retrograde (towards cell body; old components for
recycling and signaling)
o Slow: 0.2 to 2.5 mm/day; towards terminal; enzymes and cytoskeleton proteins
Glial Cells (Glia)
o CNS: ependymal cells (line ventricles; stem cells); astrocytes (regulate extracellular
fluid composition, secrete neurotropic factors, form blood brain barrier, and
provides ATP substrates); oligodendrocytes (form myelin, multiple cells on one
axon); microglial cells (immune)
o PNS: Schwann cells (form myelin; one cell on one axon); satellite cells (support
cell body)
Membrane Potential
o Nernst equation (mV)
o Goldman-Hodgkin-Katz equation (mV)
o Pion: membrane permeability to an ion (leak channels)
o At rest: Pk >> Pcl >>> Na; cell dominated by PK, Vm close to EK
o Neurons change Vm by changing Pion: accomplished by opening and closing
gated channels (voltage, ligand, mechanical)
Graded and Action Potentials in Neurons
o Graded potential: “passive”, graded, amplitude reflects stimulus strength; degraded
its distance; can be summed; created by local current flow
o Current obeys Ohm’s Law
I = V / R
I: current (ion flow)
V: voltage (charge difference)
R: resistance (to ion flow)
o Action potential: “active”, travel long distances without degradation; cannot be
summed; frequency (or pattern) reflects stimulus strength
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