Nervous System 7.6 Nervous system is a complex, highly organized system Coordinates all of the many activities of the body Allows the body to respond and adapt to changes that occur both inside and outside the body

Neuron Also called the nerve cell Basic structural unit of the nervous system Parts of a neuron are the cell body, nucleus inside the cell body, nerve fibers Dendrites carry impulses toward the cell body Axon carry impulses away from the cell body; covered by a myelin sheath Axon lies close to the dendrites of many other neurons and the space between them is the synapse; impulses coming from an axon jump the synapse to get to a dendrite of a neuron that will carry the impulse in the right direction

Nerves Combination of many nerve fibers Located outside of brain and spinal cord Afferent, or sensory nerves carry messages from all parts of the body to the brain and spinal cord Efferent, or motor nerves carry messages from the brain and spinal cord to muscles and glands Associative, or internuncial nerves carry both sensory and motor

Divisions of Nervous System 1. Peripheral Nervous System (PNS) Composed of the nerves Has 2 divisions: somatic nervous system which carries messages between the CNS and body; autonomic nervous system which contains the sympathetic and parasympathetic nervous systems that work together to control involuntary body functions

2. Central Nervous System (CNS) Brain-mass of nerve tissue protected by membranes and the cranium, or skull Cerebrum- largest and highest section of brain, outer part is arranged in folds called convolutions and is separated into lobes Responsible for reasoning, thought, memory, judgment, speech sensations, voluntary body movement

Cerebellum- below the back of the cerebrum, responsible for coordination of muscles, balance, posture, muscle tone Diencephalon is located between the cerebrum and the midbrain; contains the Thalamus and Hypothalamus; Thalamus- relay center that directs sensory impulses to the cerebrum and allow conscious recognition of pain and temperature Hypothalamus- regulates and controls the autonomic nervous system, temp, appetite, water balance, sleep, constriction and dilation of blood vessels, emotions

Midbrain- located below cerebrum at the top of the brainstem, conducts impulses between brain parts and eye reflexes Pons- located below midbrain, conducts messages to other parts of the brain and for chewing, tasting, saliva, respiration Medulla oblongata- lowest part of brainstem, connects with spinal cord, regulates heartbeat, respiration, swallowing, coughing, blood pressure

Spinal Cord- continues down from the medulla oblongata and ends at the first or second lumbar vertebra Surrounded and protected by vertebrae Responsible for many reflex actions Carries sensory (afferent) messages up to brain, and carries motor (efferent) messages from brain to nerves and muscles

Meninges Three membranes that cover and protect the brain and spinal cord Dura matter- thick tough outer layer Arachnoid matter- middle delicate web like layer that is loosely attached to the other meninges to allow space for fluid to flow between the layers Pia matter- innermost layer closely attached to brain and spinal cord, contains blood vessels that nourish the nerve tissue

Ventricles- four hollow spaces located in the brain Filled with a clear colorless fluid called cerebral spinal fluid Fluid circulates continually between the ventricles and through the subarachnoid space to serve as a shock absorber to protect brain and spinal cord Carries nutrients to some parts of brain and spinal cord Helps remove waste

Peripheral Nervous System Consists of the somatic and autonomic systems Somatic: Cranial and spinal nerves 12 pairs of cranial nerves responsible for special senses, sight, hearing, taste, touch, pressure, pain 31 pairs of spinal nerves that carry messages to and from the spinal cord

Autonomic Nervous System Helps maintain a balance in the involuntary functions of the body, but allows the body to react in times of emergency Two divisions that work together to maintain homeostasis Sympathetic- flight or fight mode prepares the body to act in times of emergency, increase heart rate, respiration, blood pressure, slows digestive tract Parasympathetic- counteracts actions of the sympathetic after an emergency, slows heart rate, respiration, blood pressure, increases digestion

Diseases and Abnormal Conditions Cerebral Palsy- disturbance in voluntary muscle action Caused by brain damage due to lack of oxygen or injury during birth or German measles and infections Exaggerated reflexes and seizures, tense muscles, speech impairment, spasms Treatment but no cure

Cerebrovascular Accident (CVA) Also called a stroke or apoplexy Blood flow to brain is impaired, resulting in lack of oxygen and destruction of brain tissue Causes include cerebral hemorrhage resulting from hypertension, aneurysm, or a weak blood vessel, Occulsion or blockage caused by atherosclerosis or a thrombus (blood clot) Loss of consciousness, weakness and vertigo, paralysis on one side of body, visual disturbances, aphasia Immediate treatment is needed, care during the first 3 hours can help prevent brain damage, clot busting drugs, angioplasty, drugs that prevent injury to neurons

Encephalitis- inflammation of the brain caused by a virus, bacteria, or chemical agent, or as a complication of chicken pox or mumps Virus contracted from mosquito bite Fever, weakness, lethargy, headache, vomiting, stiff neck, disorientation, coma Antiviral drugs, fluid and electrolyte balance,

Epilepsy- brain disorder with abnormal electrical impulses in neurons in the brain Brain injury, birth trauma, tumor, toxins such as lead, carbon monoxide, infections Petit mal seizure- mild seizures lasting a few seconds Grand mal- most severe, loss of consciousness lasting several minutes, convulsions with violent shaking, foaming at the mouth

Meningitis- inflammation of the meninges of the brain and spinal cord caused by a bacteria, virus, fungus, or toxins such as lead and arsenic High fever, headache, neck pain, nausea and vomiting, delirium, coma and death if not treated Antibiotics, anticonvulsants, antipyretics

Multiple Sclerosis- chronic, progressive disabling condition resulting from degeneration of the myelin sheath in the CNS Usually occurs between 20 and 40 Cause is unknown but genetics or a viral infection of the immune system is suspected Progresses at different rates and has periods of remission Visual disturbances, weakness, fatigue, poor coordination, tingling and numbness, spasticity of muscles, speech impairment, tremors No cure but physical therapy, steroids, muscle relaxants,

Parkinson’s Disease Chronic progressive condition involving degeneration of brain cells usually in people over 50 Tremor, stiffness, muscular rigidity, loss of facial expression, drooling, shuffling gait Treatment but no cure, Levodopa is used to relieve symptoms, physical therapy

Shingles Acute inflammation of nerve cells Caused by the herpes virus which also causes chicken pox Usually occurs in the thoracic area on one side of body and follows the affected nerve Fluid filled vesicles, severe pain, itching, fever Treatment directed at relieving pain and itching until inflammation subsides usually one to four weeks