Ch. 7: The Nervous System

Created by mf1994 

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Nervous system - organization

CNS: brain, spinal cord
PNS: nerves
Somatic: conscious, voluntary
Autonomic: automatic, involuntary

Nervous system - functions

Sensory/afferent: impulses to CNS from receptors
Motor/efferent: impulses from CNS to effector organs

Central nervous system

Brain and spinal cord
Integrating and command centers
Interpret incoming sensory information and issue instructions

Peripheral nervous system

Nerves
Communication lines
Link all parts of the body by carrying impulses

Astrocytes

Star-shaped with swollen ends
Protect neurons from harmful substances in blood
Help control chemical environment in brain
CNS

Microglia

Spiderlike phagocytes
Dispose of debris and dead brain cells
CNS

Ependymal cells

Circulate cerebrospinal fluid
Protective cushion around CNS
Line cavities of brain and spinal cord

Oligodendrocytes

Flat extensions
Produce myelin sheaths
Wrap around nerve fibers
CNS

Schwann cells

Form myelin sheaths
PNS

Satellite cells

Protective, cushioning cells
PNS

Neurons

Cell body, nucleus, one or more processes
Transmit messages

White matter

Dense myelinated fibers

Gray matter

Unmyelinated fibers and cell bodies

Cerebrum

Most superior
Gyri: elevated ridges
Sulci: shallow groves
Fissures: deeper grooves

Cerebrum - parietal lobe

Somatic sensory area
Posterior to central sulcus
Interprets impulses from sensory recetpros
Recognize pain, coldness, touch

Cerebrum - occipital lobe

Visual

Cerebrum - temporal lobe

Auditory
Olfactory
Borders lateral sulcus

Cerebrum - frontal lobe

Primary motor area
Anterior to central sulcus
Conscious movement of skeletal muscles

Cerebrum - Broca's area

Speech
Base of precentral gyrus

Diencephalon

Interbrain
Sits atop brain stem, enclosed by cerebral hemispheres

Diencephalon - thalamus

Encloses third ventricle
Relay station for sensory impulses

Diencephalon - hypothalamus

Under thalamus
Regulates body temperature, water balance, metabolism
Center for drives and emotions
Pituitary gland: produces hormones
Mammilary bodies: reflex centers

Diencephalon - epithalamus

Roof of third ventricle
Pineal body
Choroid: forms CSF

Brain stem - midbrain

Mammillary bodies to pons inferiorly
Reflex centers for vision and hearing

Brain stem - pons

Rounded structure below midbrain
Mostly fiber tracts
Control of breathing

Brain stem - medulla oblongata

Most inferior of brain stem
Controls heart rate, blood pressure, breathing, swallowing, vomiting
Posterior to pons and medulla, anterior to cerebellum

Cerebellum

Dorsally from occipital lobe
Timing for skeletal muscle activity
Controls balance and equilibrium

Cerebrospinal fluid

Watery broth
Contains less protein, more vitamin C
Watery cushion protects nervous system from blows and trauma

Blood-brain barrier

Least permeable capillaries in body
Separates neurons from bloodborne substances
Useless against fats, respiratory gases, fat-soluble molecules

Meninges - dura mater

Tough mother
Outermost layer
Surrounds brain, attached to inner surface of skull

Meninges - arachnoid mater

Cobweb
Middle layer

Meninges - pia mater

Gentle mother
Innermost layer
Clings tightly to surface of brain and spinal cord

Reflexes - reflex arc

Sensory receptor reacts to stimulus
Effector organ eventually stimulated
Sensory and motor neurons connect the two
Integration center: synapse between sensory and motor neurons

Reflexes - somatic

Stimulate skeletal muscles
Pulling hand away from hot object

Reflexes - autonomic

Activity of smooth muscles, heart, glands
Digestion, elimination, blood pressure, sweating
Secretion of saliva, changes in size of eye pupil

I. Olfactory

Fibers arise from olfactory receptors in nasal mucosa and synapse with olfactory bulbs.
Carries impulses for sense of smell.

II. Optic

Fibers arise from retina of eye and form optic nerve. The two optic nerves from optic chiasma by partial crossover of fibers.
Carries impulses for vision.

III. Oculomotor

Fibers run from the midbrain to the eye.
Supplies motor fibers to four of the six muscles that direct the eyeball, to the eyelid, and to the internal eye muscles controlling lens shape and pupil size.

IV. Trochlear

Fibers run from the midbrain to the eye.
Supplies motor fibers for one external eye muscle.

V. Trigeminal

Fibers emerge from the pons and form three divisions that run to the face.
Conducts sensory impulses from the skin of the face and mucosa of the nose and mouth; also contains motor fibers that activate the chewing muscles.

VI. Abducens

Fibers leave the pons and run to the eye.
Supplies motor fibers to the lateral rectus muscle, which rolls the eye laterally.

VII. Facial

Fibers leave the pons and run to the face.
Activates the muscles of facial expression and the lacrimal and salivary glands; carries sensory impulses from the taste buds of anterior tongue.

VIII. Vestibulocochlear

Fibers run from the equilibrium and hearing receptors of the inner ear to the brain stem.
Vestibular branch transmits impulses for the sense of balance, and cochlear branch transmits impulses for the sense of hearing.

IX. Glossopharyngeal

Fibers emerge from the medulla and run to the throat.
Supplies motor fibers to the pharynx that promote swallowing and saliva production; carries sensory impulses from taste buds of the posterior tongue and from pressure receptors of the carotid artery.

X. Vagus

Fibers emerge from the medulla and descend into the thorax and abdominal cavity.
Fibers carry sensory impulses from and motor impulses to the pharynx, larynx, and the abdominal and thoracic viscera; most motor fibers are parasympathetic fibers that promote digestive activity and help regulate heart activity.

XI. Accessory

Fibers arise from the medulla and superior spinal cord and travel to muscles of the neck and back.
Mostly motor fibers that activate the sternocleidomastoid and trapezius muscles.

XII. Hypoglossal

Fibers run from the medulla to the tongue.
Motor fibers control tongue movements; sensory fibers carry impulses from the tongue.

Spinal nerve plexuses - cervical

C1-C5
Phrenic: diaphragm and muscles of shoulder and neck

Spinal nerve plexuses - brachial

C5-C8 and T1
Axillary: deltoid muscle of shoulder
Radial: triceps and extensor muscles of forearm
Medial: flexor muscles of forearm and some muscles of hand

Spinal nerve plexuses - lumbar

L1-L4
Femoral: lower abdomen, buttocks, anterior thighs, skin of anteromedial leg and thigh
Obturator: adductor muscles of medial thigh and small hip muscles, skin of medial thigh and hip joint

Spinal nerve plexuses - sacral

L4-L5 and S1-S4
Sciatic: lower trunk and posterior surface of thigh
Common fibular: lateral aspect of leg and foot
Tibial: posterior aspect of leg and foot
Superior and inferior gluteal: gluteus muscles of hip

Tract

Collection of nerve fibers in CNS having the same origin, termination, and function

Nucleus

Dense central body in most cells containing genetic material of cell

Ganglion

Group of nerve cell bodies located in PNS

Nerve

Bundle of neuronal processes (axons) outside CNS

ANS - sympathetic

Fight-or-flight
Pounding heart, rapid breathing, cold skin, prickly scalp, dilated eye pupils
Increase heart rate, blood pressure, blood glucose levels

ANS - parasympathetic

Resting-and-digesting
Housekeeping
Normal digestion, elimination of feces and urine, conserving body energy

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