Nervous System Histology and Physiology

the nervous system (NS) is branched into the ______ NS and the _______ NS

central, peripheral

the central nervous system is composed of the

brain and spinal cord

brain

interprets and stores information and sends orders to muscles, glands, and organs

spinal cord

pathway connecting the brain and the peripheral nervous system

peripheral nervous system

transmits information to and from the central nervous system

the two branches of the peripheral nervous system are the _______ NS and the _______ NS

autonomic, somatic

the two divisions of the autonomic nervous system are the _______ division and the _______ division

parasympathetic, sympathetic

the two branches of the somatic nervous system are the _____ systems and the ______ systems

sensory, motor

autonomic nervous system

automatically regulates glands, internal organs and blood vessels, pupil dilation, digestion, and blood pressure

somatic nervous system

carries sensory information and controls movement of the skeletal muscles

parasympathetic division

maintains body functions under ordinary conditions; saves energy (REST AND DIGEST)

sympathetic division

prepares the body to react and expend energy in times of stress (FIGHT OR FLIGHT)

sensory system (afferent)

carries messages from senses to CNS

motor system (efferent)

carries messages from CNS to muscles and glands

dendrites

extrude from cell body; receive signals

cell body

control center

axon hillock

controls initiation of action potential

axon

conduction of nerve signal (action potential)

axon terminal

signal output; forms junction with next neuron (synapse)

multipolar neuron

-one axon

-multiple dendrite

-MOST COMMON (composes most neurons of brain and spinal cord)

bipolar neuron

-one axon

-one dendrite

-found in olfactory cells, some neurons of retina, sensory neurons in ear

pseudo-unipolar neuron

-one process from cell branches into a T shape

-carries signals to spinal cord for touch and pain

epineurium

connective tissue layer that surrounds ENTIRE NERVE

epineurium histology

fascicle (middle black box in picture)

bundle of nerve fibers

fascicle histology

perineurium

connective tissue layer that surrounds the FASCICLE

perineurium histology

endoneurium

connective tissue layer that surrounds INDIVIDUAL AXON

endoneurium histology

myelination

Axons are covered in myelin sheath for insulation and to speed up electrical signals.

nodes of ranvier

gaps in the myelin sheath

nerve histology (longitudinal section)

nerve histology (cross-section)

dorsal root ganglion

dorsal root ganglion (higher objective)

action potential

-firing of a neuron

-brief, transient reversal of membrane potential (voltage) that sweeps along the membrane of a neuron

resting membrane potential (RMP)

- -70 mV

-voltage across the membrane in neuron that is NOT FIRING

-2 K+ IN and 3 Na+ OUT

threshold potential

- -55 mV

-point at which voltage-gated ion channels begin to open

depolarizing phase

- -55 to +40 mV

-the membrane potential rapidly INCREASES as Na+ FLOWS IN

repolarizing phase

- +40 mV to -70 mV

-membrane potential rapidly DECREASES as K+ FLOWS OUT

hyperpolarization phase

- -70 to -80 mV

-the membrane potential rapidly DECREASES as K+ FLOWS OUT

return to RMP

membrane potential rises again to RESTING (-70 mV)

absolute refractory period

-nerve CANNOT BE STIMULATED due to Na+ FLOWING IN no matter how great the stimulus

-occurs during DEPOLARIZATION AND MOST OF REPOLARIZATION

relative refractory period

-interval of time in which 2nd action potential CAN be initiated

-BUT stimulus must be GREATER THAN BEFORE

-Na+ are CLOSED

-K+ flows OUT

-membrane becomes more NEGATIVE

compound nerve

A nerve composed of several neurons, each having different properties with respect to irritability and conduction velocity

compound nerve action potential

cumulative action potentials of all the neurons in the nerve

AXON SIZE

Large axons have _______ threshold

lower

DISTANCE FROM ELECTRODE

The ________ axon will reach threshold first

closer