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THE NERVOUS SYSTEM I. NERVOUS SYSTEM FUNCTION - “I think; therefore, I am.” (pp. 897-900) Responsible for maintaining _homeostasis_________ in the body by sending and receiving information via _electrical___ impulses. The advantage to an electrical message system is that it is _faster___. II. ORGANIZATION OF THE HUMAN NERVOUS SYSTEM (pp. 787-791) A. The Central Nervous System or _CNS___ Made up of the _brain____ and the _spinal cord__________. The spinal cord acts as a “super highway” connecting the _body____ and _brain_____. There are three means of protection: 1. Bones – _Cranium__ protects the brain; _vertebrae_____ protect the spinal cord 2. Meninges - _3___ layers of tough, elastic tissue that _cushions______ the brain and spinal cord. 3. Cerebrospinal Fluid – Found between the meninges to provide further cushioning B. The Peripheral Nervous System or _PNS____ The PNS is composed of _nerves___, which are bundles of nerve cells. C. The Sensory Organs (pp. 792-795) 1. Touch - Response to a _mechanical____ stimulus. The _skin____ is the largest sensory organ. Sensory receptors detect pressure, pain, heat, cold. 2. Smell - Response to a _chemical_____ stimulus. Sensory receptor cells are bathed in mucus and respond to different chemicals. 3. Taste - Response to a _chemical____stimulus. Sensory receptors called _taste buds____ are located on the _tongue___. Detect sweet, sour, salty, bitter. 4. Vision – Response to a _light___ stimulus. Cornea – Light first passes through the _cornea_____, a transparent, protective covering which begins _focusing___ the light. The light then enters a chamber filled then enters a chamber filled with watery fluid called the _aqueous humor______. _Pupil____ - Hole that light passes through. The size of the pupil is controlled by a ring of muscles known as the _iris___. _Lens____ - Completes focusing of the light ray. There is also a thick jelly-like substance to help maintain the shape of the chamber known as the _vitreous humor______. Retina – Nerve tissue at the back of the eyeball that converts light energy to an _electrical impulse____. Made up of two types of cells: o Rods - Cells that detect _shape & movement______; are stimulated even in _dim___ light. o Cones - Cells that detect _color____; provide a _sharp_____ image; require _bright ____ light for stimulation. Optic Nerve - Transmits the impulse to the _brain___. Additional Structures o Sclera - _”White of the eye”________; continuation of the _cornea____ o Choroid - Layer of blood vessels that _nourish_____ the eye. 5. Hearing - Response to a mechanical stimulation - _sound_____ waves. Sound waves first enter the outer ear and are funneled into the _auditory canal__. Causes vibrations of a membrane known as the _tympanic membrane_______ or _eardrum______. Vibrations are then passed to three tiny bones → o _hammer________________ o _anvil___________________ o _stirrup__________________ The vibrations are transferred from the _stirrup____ to another membrane known as the _oval window_______. Finally, vibrations are converted to an electrical impulse in the _cochlea_______, a snail-shaped sensory structure filled with fluid and tiny hairs. These hairs are pushed back & forth, producing electrical impulses. Nerve impulse is transmitted by way of the _auditory nerve_______ to the _brain_____. The semicircular canals are also found in the ear. They play no role in hearing; instead, they help maintain _balance______. The semicircular canals consist of _3___ fluid-filled canals oriented at different angles to each other. III. NERVE IMPULSE TRANSMISSION The cells that make up the nervous system are known as _neurons_________. They are _specialized______ cells capable of creating an _electrical______ impulse. A. Types of Neurons – There are three types of neurons: Sensory Neurons – Transmit impulses from the _body____ to the _brain_____ and _spinal cord______. Motor Neurons – Transmit impulses from the _brain___ and _spinal cord______ to the _brain______. Interneurons - _Connection______ between sensory and motor neurons. Located in the _brain____ and _spinal cord______ only. B. Structure of a Neuron Dendrite – Short, branched extensions that first receive stimulus; act as _antenna, detectors________ Cell Body – Contains the _nucleus______. Site of _metabolic_____ activity. Receives impulse from _dendrite______. Axon – Transmits impulses _away from the cell body______ to next cell. Usually a long, single fiber with many small tips called _axon terminals_________. Schwann Cells – Wrap around the axons of many neurons to form insulating layers known as a _myelin sheath_______; _insulate______ and _protect_____ the neuron. There are small gaps in the myelin sheath along an axon called _nodes_____. The electrical impulse _hops___ from node-to-node, allowing the impulse to _travel faster____. C. Nerve Impulse Transmission The _electrical____ impulse moves through the neuron in one direction → _dendrite____ → _cell body___ → _axon_____ until it reaches an _axon terminal____. There is a small space between the neuron and the next cell called a _synapse______. Chemicals known as _neurotransmitters_______ are released to carry the impulse across the synapse to the next cell. IV. A CLOSER LOOK AT THE HUMAN BRAIN A. Cerebrum _Largest____ part of the brain Composed of two _hemispheres_____ or sides. _Corpus callosum____________ o Connects the right and left hemispheres o Maintains __communication___ between them Divided into regions called _lobes______; associated with specific functions Controls _conscious activities, intelligence, memory, emotions_________ B. Cerebellum Regulates _posture and balance______ Coordinates _voluntary, skeletal___ muscle movement C. Brain Stem Composed of the _pons, midbrain, and medulla oblongata________. o Pons and midbrain act as _pathways____ connecting different parts of the brain. o Medulla oblongata controls _involuntary____ activities, such as _breathing, heart rate, blood pressure___________ D. Thalamus _”Telephone Operator”___________ Main location for _sensory processing____ E. Hypothalamus Controls many activities relating to _homeostasis____ such as _hunger, thirst, body temperature_________ F. Glands in the Brain Although the following glands are located in the brain, they are not part of the nervous system. They are part of the _endocrine_____ system. Pituitary Gland - _”Master Gland”_____. Releases _hormones___ that regulate other endocrine glands. Pineal Gland – Light-sensitive gland that secretes hormone called _melatonin___; regulates _”internal clock”________. V. DISEASES & CONDITIONS OF THE NERVOUS SYSTEM (pp. 798-799) A. Meningitis – Infection of _meninges_______. Symptoms include severe headache, stiff neck, fever. B. Alzheimer’s Disease – Disease of the elderly in which there is a build-up of protein plaques on neurons in the _cerebrum_______. Results in progressive death of neurons. Symptoms include memory loss, confusion, emotional disturbances. C. Parkinson’s Disease – Disabling disease due to a decrease in _neurotransmitters________ which transmit impulses for movement. Results in tremors, muscle rigidity. D. Multiple Sclerosis – Disease of young adults characterized by destruction of _myelin_____ _sheaths_____ of neurons. Normal nerve function is impaired. Symptoms include numbness, muscle weakness, muscle fatigue, vision problems.