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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 _very fast!_. 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 _brain_____ and _body__. There are three means of protection: Bones – _Cranium____ protects the brain; _Vertebrae____ protect the spinal cord Meninges - _3___ layers of tough, elastic tissue that _cushion______ the brain and spinal cord. Cerebrospinal Fluid – Found between the meninges to provide _additional cushioning__________ B. The Peripheral Nervous System or _PNS_______ The PNS is composed of _nerves_____, which are bundles of nerve cells. There are 2 divisions in the peripheral nervous system. Somatic PNS – Regulates activities under _conscious_______ control, meaning _brain_____ is involved. However, sometimes a response must occur very quickly. This is known as a _reflex______. A reflex is processed directly in the _spinal cord_____, although the brain becomes aware after the response has taken place. Autonomic PNS – Regulates activities that are not under conscious control such as _breathing, heart rate, blood pressure_________________________. 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______ of 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 _sharper________ 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 _tympanum___________. Vibrations are then passed to three tiny bones → o _malleus (hammer)______ o _incus (anvil)___________ o _stapes (stirrup)________ The vibrations are transferred from the _stapes______ to another membrane known as the _oval window__________. Finally, vibrations are converted to an electrical impulse in the _cochlea______, a snailshaped sensory structure filled with fluid and tiny hairs. These hairs are pushed back & forth, producing electrical impulses. A 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 _spinal cord___ and _brain______. Motor Neurons – Transmit impulses from the _brain__ and _spinal cord____ to the _body______. 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-tonode, 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.