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Nervous System Functions of the Nervous Systems Your nervous system controls all of your body’s actions and functions. It senses changes not only within your body but also outside of it in your environment Enables you to respond within fractions of a second. Structure of the Nervous System: Two main divisions: Central Nervous System (CNS) Peripheral Nervous System (PNS) PNS gathers information from inside and outside your body CNS receives and analyzes this information and initiates responses. PNS then picks up and carries the response signal o This information is transmitted throughout your body by means of electrical charges or impulses. o These impulses travel at speeds up to 280 miles per hour. o The messengers and receivers of these transmissions are neurons, or nerve cells. Functions of Neurons: Three main types: Sensory Neurons Motor Neurons Interneurons Sensory neurons carry signals from sense receptors in the CNS Motor neurons carry signals from the CNS to muscles or glands Interneurons form all the electrical connections within the CNS itself Unlike other cells, neurons cannot replace themselves. If the cell body of neuron is damaged or degenerates, the cell dies. Each neuron is made up of three basic parts: Cell body: Consists of a nucleus o Control center of the cell o In a sack of fluid contained within a outer skin called the cell membrane o Nucleus receives and sends nerve impulses. o It also regulates the amount and type of proteins made in the cell Dendrites: o Are branching projections of the cell body o Receive and carry impulses toward the cell body Axons: o Every neuron has threadlike extension o Carries impulses away from the cell body o Branches at its end to form terminals though which signals are sent to targets cells, such as the dendrites of other neurons, muscles cells, or glands o Vary in length from a fraction of an inch to several feet. o Most axons have a coating or sheath of fatty material call myelin. o The myelin sheath insulates the nerve fiber and speeds the transmission of impulses The Central Nervous System Made up of two main parts Spinal Cord: Cylinder of nerve tissue about 18 inches long and about as thick as your index finger Runs down the central canal in the spine Downward extension of the brain Protected by cerebrospinal fluid that acts like a shock absorber. Protected by three layers of connective membranes called the spinal meninges. Brain: Largest, most complex part of your nervous system. Helps you receive and process messages Weighs about three pounds. Contains 100 billion neurons Uses more then 20 percent of the oxygen you inhale. Protected by 8 cranial bones Protected by three layers of membranes called cranial meninges. Brain has three main divisions: Cerebrum: Most complex part of the brain Site of most conscious and intelligent activities Outer layer, or cortex, is where conscious thought takes place. Divided into two halves called the cerebral hemispheres o Right hemisphere controls the muscular activities of and receives sensory input from the left half of the body o Right hemisphere is concerned with imagination and visual thinking artistic activities, and emotional responses such as color appreciation. o Left hemisphere does the same for right half of the body. o Left hemisphere is mainly responsible for language, logic, arithmetic calculation, analysis, and critical thinking. Each hemisphere has four lobes. The frontal lobe controls voluntary movements and also has a role in the use of language. The prefrontal areas of this lobe are believed to be involved with intellect and personality. The parietal lobe is involved with a wide variety of sensory information: heat, cold, pain, touch, and body position in space The occipital lobe contains the sense of vision. The temporal lobe contains the senses of hearing and smell as well as memory, thought, and judgment. Cerebellum: Second largest part of the brain Located beneath the occipital lobes of the cerebrum Divided into two hemispheres Concerned mainly with maintaining posture, balance, and coordinating skeletal muscle movement. Receives impulses from the balance organs of the inner ear and from muscles. After receiving this information, the cerebellum refines the orders sent to muscles from the motor cortex in the cerebrum to ensure smooth, coordinated movements and balance. Brain Stem: 3 inches long Acts partly as a pathway from messages traveling between other parts of the brain and spinal cord. Connects with 10 of the 12 pairs of the cranial nerves and controls basic functions such as breathing, heartbeat, and eye reflexes. Brain stem consists of three main parts: Medulla Oblongata: Lowest part of the brain stem Contains vital controls centers that regulate: Heartbeat Breathing Blood pressure Digestion Swallowing Vomiting Sneezing Coughing Relays taste sensations from the tongue and is involved in speech and in tongue movements Pons: Above the medulla Serves mainly as a pathway for nerve impulses passing to and from the cerebrum Relays sensory information from the ear, face, and teeth as well as the signals that move the jaw and adjust facial expressions. Midbrain: Shortest part of the brain Contains the nuclei of the two pairs of cranial nerves that control eye movement and pupil size Reflexive response of turning your head when you hear an unexpected loud noise Thalamus and hypothalamus are closely associated with the brain stem o Thalamus: Receives information from different sense organs such as the eyes and ears. o Hypothalamus: Controls body temperature, stimulates appetite, and regulates sleep. The Peripheral Nervous System: Means located away from the center Consisted of nerves that fan out from the central nervous system to the muscles, skin, internal organs, and glands. PNS carries messages between the CNS and the rest of the body. Consists of 12 pairs of cranial nerves that branch from the brain and 31 pairs of spinal nerves that branch from the spinal cord. PNS is composed of two subdivisions: Autonomic Nervous System (ANS) Is responsible for controlling the involuntary functions of the body, such as sweating, digestion, and heart rate. Consists of a network of nerves divided into 2 parts o Sympathetic Nervous System o Parasympathetic Nervous System Sympathetic Nervous System: Responds to the body’s needs during increased activity and in emergencies (Fight or Flight response) Parasympathetic Nervous System: Opposes the actions of the sympathetic system by slowing body functions Somatic Nervous System: Includes cranial and spinal nerves that transmit impulses from the CNS to the skeletal muscles. Voluntary responses; responses that are under your control. Reflex Action: Occurs automatically, without conscious thought or effort. Care of the Nervous System: You need to exercise regularly Proper Nutrition Adequate rest and sleep Avoid using alcohol and other drugs Problems of the Nervous System: Head and spinal cord injuries o Paraplegic: Paralysis of the lower body o Quadriplegic: Paralysis of both arms and legs Degenerative Diseases o Parkinson’s disease: caused by degeneration of the nerve cells within the brain that modify nerve impulses transmitted from the motor area of the brain. o Multiple Sclerosis: It involves the destructions of the myelin sheath that surrounds nerves fibers o Alzheimer’s Disease: General mental deterioration. Patients gradually lose their memory and powers and judgments. o Epilepsy: Is a disorder of the nervous system that is characterized by recurrent seizures. Grand Mal Seizures: Usually last about 2-5 minutes and fall to the floor, unconsciousness. Petit Mal Seizures: Often pass unnoticed; usually people have a blank stare for about 30 seconds. o Cerebral Palsy: Disorder that are the result of damage to the brain before birth, during birth, in the newborn period, or in early childhood