WHAT IS THE NERVOUS SYSTEM?

Your nervous system consists of the brain, spinal cord, and nerves that run throughout your body. The nervous system carries messages to your muscles and organs. These messages tell your body what to do.

Your spinal cord is made of bundles of nerves. It starts in your neck and goes down your back. Nerves go out from the spinal cord to other parts of your body. Nerves from the spinal cord extend to the tips of your fingers and toes. Your spine, or backbone, protects your spinal cord.

How Nervous System works???

Nervous tissue is made up of two principal types of cells

Supporting cells is non-excitable cells that provide structural support or that serve important physiological and immunological functions in the nervous system. Also called glial cells.

Neurons, also called nerve cells, are highly specialized to transmit messages (nerve impulses) throughout the body.

• Astrocytes - star shape cells that account for nearly half of the neural tissue.

- They form a barrier between capillaries and neurons, protect the neurons in the blood and maintain chemical environment in the brain.

• Microglia – spiderlike phagocytes that dispose debris (dead brain cells and bacteria).

• Ependymal cells – glial cells line the cavities of the brain and the spinal cord. Helps circulate the cerebrospinal fluid and forms protective cushion around the CNS.

• Oligodendrocytes – produce fatty insulating coverings called myelin sheaths.

Types of supporting cells

Types of Sensory receptors

a. Pain and pressure receptors

b. Meissners corpuscles (touch receptors)

c. Pacinian corpuscles (deep pressure receptors)

d. Golgi tendon organ (proprioceptor)

e. Muscle spindle (proprioceptor)

Example of touch pressure receptor

Structural Classification of Neurons

Functional Classification of Neurons

The central nervous

consists of the brain and spinal cord, which occupy the dorsal body cavity and act as the integrating and command centers of the nervous system. They interpret incoming sensory information and issue instructions based on past experience and current conditions.

The central nervous system (CNS) represents the largest part of the nervous system, including the brain and the spinal cord.

The brain is the largest and most complex mass of the nervous tissue in the body, its four major regions – cerebral hemispheres, diencephalons, brain stem and cerebellum.

Your brain is made of about 100 billion nerve cells. It looks like a lump of pinkish-gray jelly. Your brain is protected by bone called your skull. Liquid and skin like tissues also protect your brain.

The Major Regions of the Brain

Sensory and motor Functions

Brain Dysfunction

nervous disorder, neurological disease, neurological disorder - a disorder of the nervous system

epilepsy - a disorder of the central nervous system characterized by loss of consciousness and convulsion

apraxia - inability to make purposeful movements

paralysis agitans, Parkinson's, Parkinson's disease, Parkinson's syndrome, Parkinsonism, shaking palsy - a degenerative disorder of the central nervous system characterized by tremor and impaired muscular coordination

cerebral palsy, spastic paralysis - a loss or deficiency of motor control with involuntary spasms caused by permanent brain damage present at birth

agraphia, anorthography, logagraphia - a loss of the ability to write or to express thoughts in writing because of a brain lesion

acataphasia - a disorder in which a lesion to the central nervous system leaves you unable to formulate a statement or to express yourself in an organized manner

aphasia - inability to use or understand language (spoken or written) because of a brain lesion

agnosia - inability to recognize objects by use of the senses

CJD, Creutzfeldt-Jakob disease, Jakob-Creutzfeldt disease - rare (usually fatal) brain disease (usually in middle age) caused by an unidentified slow virus; characterized by progressive dementia and gradual loss of muscle control

Reye's syndrome - acquired encephalopathy following acute viral infections (especially influenza or chicken pox) in young children; characterized by fever, vomiting, disorientation, coma, and fatty infiltration of the liver

Wernicke's encephalopathy - inflammatory degenerative disease of the brain caused by thiamine deficiency that is usually associated with alcoholism

Spinal CordThe spinal cord

functions in the transmission of ascending impulses to the brain and of descending impulses from the brain to the cord.

Thus, it conveys to higher centers information brought to it by peripheral nerves from many parts of the body; in addition, it is acted on by impulses from the brain itself. The spinal cord relays impulses also to the muscles, blood vessels, and glands by means of outgoing nerves, either in response to incoming stimuli or to signals from higher levels.

The PNS consists of all other nerves and neurons that do not lie within the CNS. The large majority of what are commonly called nerves (which are actually axonal processes of nerve cells) are considered to be PNS. The peripheral nervous system can be further classified either by direction of neurons and by function.

Three types of directions of the Neuron:

Sensory system by sensory neurons, which carry impulses from a receptor to the CNS

Efferent system by motor neurons, which carry impulses from the CNS to an effector

Relay system by relay neurons, which transmit impulses between the sensory and motor neurones. However, there are relay neurons in the CNS as well.

Spinal nerve Plexuses

Cervical plexus

serves the head, neck and shoulders

Brachial plexus

serves the chest, shoulders, arms and hands

Lumbar plexus serves the back, abdomen, groin, thighs, knees, and calves

Sacral plexus serves the pelvis, buttocks, genitals, thighs, calves, and feet

Solar plexus serves internal organs

Anatomy of Autonomic Nervous System

Effects of the Sympathetic and Parasympathetic divisions to Autonomic Nervous System

Target organ/system

Parasympathetic effects Sympathetic effects

Digestive system Increases smooth muscle mobility (peristalsis) and amount of secretion by digestive system glands; relaxes sphincters

Decreases activity of digestive system ad constricts digestive system sphincters

Liver No effect Causes glucose to be released to blood

Lungs Constricts bronchioles Dilates bronchioles

Urinary bladder/ urethra Relaxes sphincters (allows voiding)

Constricts sphincters (prevent voiding)

Kidneys No effect Decreases urine output

Heart Decreases rate; slows and steadies

Increases rate and force of heartbeat

Blood vessels No effect on most blood vessels Constricts blood vessels in viscera and skin ; increases blood pressure

Glands – salivary, lacrimal Stimulates; increases production of saliva and tears

Inhibits; result is dry mouth and dry eyes

Eye (iris) Stimulates constrictor muscles; constricts pupils

Stimulates dilator muscles; dilates pupils

Eye (ciliary muscle) Stimulates to increase bulging of lens for close vision

Inhibits; decreases bulging of lens; prepares for distant vision

Adrenal medulla No effect Stimulates medulla cells to secrete epinephrine and norepinephrine

Sweat glands of skin No effect Stimulates to produce perspiration

Arrector pili muscles attached to hair follicles

No effect Stimulates; produces “ goose bumps”

Penis Causes erection due to vasodilation

Causes ejaculation (emission of semen)

Cellular metabolism No effect Increases metabolic rate; increases blood sugar levels; stimulates fat breakdown