Nervous system 2

Nerve resting potential and impulse action potentialsNerve fibers types and speed of conduction

Resting potential

Potential for a nerve impulse due to polarized state

Relatively negative within nerve

-70 mV inside nerve cells due to 3 Na+ ions transported out of cell for every 2 K+ ions transported in to cell

Nerve impulse

Nerve impulse frequencyLimited by rate of Na+ // K+ repolarizationRefractory period – neuron cannot generate a new impulseAbsolute refractory, 2nd impulse cannot be initiatedRelative refractory, 2nd impulse can be initiated with abnormally strong stimulus

Speed of nerve impulse conductionAffected by:Temperature

Heat increases speed of conductionCold decreases (or stop) speed of conduction

Diameter of fiber; The larger the fiber, the faster the speed of impulse

MyelinationMyelinated nerves much faster speed of conduction

Nerve fiber typesType A

Large diameter, myelinated, short refractory and fast conduction (130 m/sec).Motor (efferent) neurons, touch pressure, temp and proprioception (afferent) receptors

Nerve fiber typesType B

Medium diameter, myelinated, conduction speed not as fast as Type ASmooth muscle and glandular (efferent) innervation and skin and visceral (afferent) receptor

Nerve fiber typesType C

Small diameter, not myelinated.Longer refractory periodSlower speed of conductionSensory (afferent) from skin and ANS efferent to cardiac and smooth muscle

Continuousconduction(slower)

Saltatory conduction(faster)