Neurophysiology. Regions of the Brain and Spinal Cord White matter – dense collections of...
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Transcript of Neurophysiology. Regions of the Brain and Spinal Cord White matter – dense collections of...
Neurophysiology
Regions of the Brain and Spinal Cord
• White matter – dense collections of myelinated fibers• Gray matter – mostly soma and
unmyelinated fibers
Neuron Classification
• Structural: –Multipolar — three or more
processes (99%)–Bipolar — two processes (axon and
dendrite) (eye and olfactory)–Unipolar — single, short process –
ganglia in PNS as sensory
PLAYPLAY InterActive Physiology ®: Nervous System I: Membrane Potential
Resting Membrane Potential (Vr)• potential difference (–70 mV) across the
membrane of a resting neuron• generated by different concentrations of Na+,
K+, Cl, and protein anions (A)• Ionic differences are the consequence of:– Differential permeability of the neurilemma to Na+
and K+
– Operation of the sodium-potassium pump
Resting Membrane Potential
Figure 11.7
Resting Membrane Potential (Vr)
Figure 11.8
Changes in Membrane Potential
–Depolarization – the inside of the membrane becomes less negative –Repolarization – the membrane returns to
its resting membrane potential–Hyperpolarization – the inside of the
membrane becomes more negative than the resting potential
Graded Potentials
• Short-lived, local changes in membrane potential
• Decrease in intensity with distance• Magnitude varies directly with the strength of
the stimulus• Sufficiently strong graded potentials can
initiate action potentials
Action Potentials (APs)• brief reversal of membrane potential with a
total amplitude of 100 mV• only generated by muscle cells and neurons• Do not decrease in strength over distance• principal means of neural communication• action potential in the axon of a neuron is a
nerve impulse
Absolute Refractory Period
• The absolute refractory period:–Prevents the neuron from generating an
action potential– Ensures that each action potential is
separate– Enforces one-way transmission of nerve
impulses
Saltatory Conduction
• only at the nodes of Ranvier• Voltage-gated Na+ channels are concentrated
at these nodes• Action potentials jump from one node to the
next• Much faster than conduction along
unmyelinated axons
Saltatory Conduction
Figure 11.16