The Nervous SystemPart: 3

Ms. Herrera

Spinal CordExtends from the foramen magnum of the

skull to the first or second lumbar vertebraComprised of 31 pairs of spinal nerves

8 cervical12 thoracic5 lumbar 5 sacral1 coccygeal

Extends from the foramen magnum of the skull to the first or second lumbar vertebra

Spinal Cord AnatomyInternal gray matter is mostly cell bodies

Dorsal (posterior) hornsAnterior (ventral) horns Gray matter surrounds the central canal

Central canal is filled with cerebrospinal fluid

Exterior white mater—conduction tractsDorsal Column: contains sensory (afferent)

tracts Lateral & Ventral Column: Contains both

ascending and descending (motor: efferent tracts)

Peripheral Nervous System (PNS)Comprised of nerves and ganglia (neuronal cell

bodies) that are outside the CNSMixed nerves

Both sensory and motor fibersAll spinal nerves are mixed

Sensory (afferent) nervesCarry impulses toward the CNSFound in sensory structures

Motor (efferent) nervesCarry impulses away from the CNSArise in CSN and include nerves from Somatic and

Autonomic division

Cranial Nerves There are a total of 12 that are identified by

name and numberMostly serve the head and neckMost are mixed nerves, but three are sensory

only

Peripheral Nervous System (PNS)

PNS: Spinal NervesThere is a pair of

spinal nerves at the level of each vertebrae for a total of 31 pairs

Formed by the combination of the ventral and dorsal roots of the spinal cord

Named for the region from which they arise

PNS: Spinal NervesSpinal nerves divide

soon after leaving the spinal cordDorsal rami—serve

the skin and muscles of the posterior trunk

Ventral rami—form a complex of networks (plexus) for the anterior

PNS: Spinal Nerves

PNS: Autonomic Nervous SystemA.K.A. involuntary nervous systemMotor subdivision of the PNS

Consists only of motor nervesActions:

Regulates activities of cardiac and smooth muscles and glands

Two subdivisionsSympathetic divisionParasympathetic division

PNS: Differences Between Somatic and Autonomic Nervous Systems

Somatic AutonomicNerves

one motor neuron

Effector organsskeletal muscle

Neurotransmittersalways use acetylcholine

Nervespreganglionic and

postganglionic nerves

Effector organssmooth muscle, cardiac

muscle, and glandsNeurotransmitters

use acetylcholine, epinephrine, or norepinephrine

Anatomy of the Autonomic Nervous System

PNS: Autonomic Functioning

Sympathetic ParasympatheticA.K.A. “fight-or-flight”

responseResponse to unusual

stimulusTakes over to increase

activitiesRelease acetycholineRemember as the “E”

division Exercise, excitement,

emergency, and embarrassment

“housekeeping” activitiesConserves energyMaintains daily

necessary body functions

Release norepinephrineRemember as the “D”

division digestion, defecation,

and diuresis