CHAPTER 12: A GLANCE AT THE

NERVOUS SYSTEM

By Shawna Miller

FUNCTIONS AND ORGANS The functions of the nervous system are

to coordinate and control body functions.Receives sensory outputMakes decisionsOrders body responses

The organs of the nervous system are:BrainNervesSpinal cord

NERVOUS TISSUE Consists of two cell types

Neurons- individual nerve cells Dendrite- branched projections, receive impulses Nerve cell body- contains nucleus/other organelles Axon-projection from the nerve cell body, conducts

electrical impulses to destination The point which the axon of one neuron meets the

dendrite of another neuron is called a synapse. The gap between two neurons is called a synaptic cleft. The electrical impulses need help from chemical

messengers caller neurotransmitters. Different neuroglial cells are in nervous tissue

Some produce myelin-a fatty substance which acts like insulation for axons

They do not conduct electrical impulses

CENTRAL NERVOUS SYSTEMReceives impulses from all over the body.The system is made of grey and white matter.Grey matter is uncovered cell bodies and dendrites.White matter is myelinated nerve fibers.The myelin sheath makes the nervous tissue look white.Tracts are bundles of nerve fibers that connect parts of the CNS.Meninges are what the CNS is encased and protected by. There are three of these membranes.

THE BRAIN One of the largest organs in the body.

Center for thought, judgement, memory, and emotion.

Four sections: Cerebrum- largest section in the upper part of the brain. It processes problem solving, language,

thoughts, and memory. It has an outer layer called the cerebral cortex which is made up of folds of grey matter.

Diencephalon- below the cerebrum contains the thalmus and hypothalmus Thalmus- center for relaying impulses for eyes, ears, and skin to the cerebrum. What our pain

perception is controlled by.

Hypothalmus- below thalmus, controls body temperature, sleep appetite, and emotions.

Cerebellum- second largest section, beneath the posterior part of the cerebrum. Helps to maintain body movements and maintain balance.

Brain stem : has three parts Mid brain- acts as pathway between brain and spinal cord

Pons- connects the cerebellum to rest of brain

Medulla oblongata- most inferior portion of the brain; it connects the brain to the spinal cord

A vital are that controls respiration, heart rate, and blood pressure

Site where nerve tracts cross

The brain has four interconnected cavities called ventricles. There is one in each hemisphere of the brain

They contain CSF(cerebral spinal fluid) that protects the brain from shock/sudden movement to brain and spinal cord

A VIEW OF THE BRAIN

SPINAL CORD The spinal cord’s function is to

provide a pathway for impulses traveling to and from the brain

A column of nervous tissue that goes from the medulla oblongata down to the second level of the lumbar vertebra in the vertebral column

Goes down to the center of the spinal cord in the central canal

Outer portion is myelinated white matter- can be either ascending tracts(carrying sensory info to the brain) or descending tracts( carrying motor commands from the brain to a peripheral nerve

MENINGES Three layers of connective

tissue membranes that surround the brain and spinal cord

External to internal: Dura mater(tough mother)- tough

fibrous sac around the CNS Subdural space- actual space

between the dura mater and arachnoid layers

Arachnoid layer(spiderlike)- thin, delicate layer attached to the pia mater by weblike filaments

Subarachnoid space- space between the arachnoid and pia mater layers. It contains cerebrospinal fluid which cushions the brain from the outside

Pia mater(soft mother)- innermost membrane layer which is applied directly to the spinal cord and surface of the brain

PERIPHERAL NERVOUS SYSTEM Includes 12 pairs of cranial nerves and 31 pairs of spinal

nerves Where the nerve originates determines if it is cranial or

spinal The point where either type is attached to the CNS is called

the nerve root Afferent neurons(sensory neurons)- carry sensory info

from a sensory receptor to the CNS Efferent neurons(motor neurons)- carry activity

instructions from the CNS to muscles/glands out in the body Nerves of the peripheral nervous system are subdivided

into two areas: the autonomic nervous system(ANS) and somatic nerves which each serve a different part of the body

The nerve cell bodies of the neurons are grouped together in a knot-like mass, called a ganglion

AUTONOMIC NERVOUS SYSTEM

Involved with control of involuntary or unconscious bodily functions

May increase or decrease activity of smooth muscles

Is divided into two divisions Sympathetic branch- control the

“fight or flight” reaction during stress or crisis. These nerves increase heart rate, dilate airways, increase blood pressure, inhibit digestion, and stimulate adrenaline production

Parasympathetic- counterbalance for sympathetic, the “rest and digest” reaction. They lower heart rate, decrease blood pressure, and stimulate digestion

Somatic nerves- serve the skin and skeletal muscles. Mainly involved with the conscious/voluntary activities of the body. Largest ones found in dermis of skin like touch, pressure and pain. Also carry motor commands to skeletal muscles

COMMON TERMSCerebrospinal, meningitis, analgesia, aphasia, dysphasia, quadriplegia, neuropathy, encephalitis, electroencephalogram

DEFINITIONS Cerebrospinal- pertaining to the

cerebrum and spine Meningitis- meninges inflammation Analgesia- absence of pain or

sensation Aphasia- lack of speech Dysphagia- difficult speech Quadriplegia- paralysis of four Neuropathy- nerve disease Electroencephalogram(EEG)- record

of brain’s activity

TESTS Brain scan-image of the

brain taken after an injection of radioactive isotopes into the circulation

Echoencephalography- record of the ultrasonic echoes of the brain

Myelography- injection of radiopaque dye into the spinal cord

Positron emission tomography- use of positive radionuclides to reconstruct brain sections

TREATMENTSNerve block- injection of regional anesthetic to stop the passage of sensory/pain impulses along a nerve pathLaminectomy- removal of a portion of a vertebra in order to relieve pressure on the spinal nerveTractotomy- surgical interruption of a nerve tract in the spinal cord

MEDICATIONS

Analgesics- non narcotics to treat pain(aspirin, tylenol, aleve, ibuprofen)

Anesthetics- drug that produces a loss of sensation or loss of consciousness( propofol, novocain, lidocaine, nembutal)

Hypnotic- drug that promotes sleep(restoril, seconal, temazepam)

Sedative- drug that has a relaxing or calming effect(amytal, butisol, amobarbital)