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Nervious System Vocb. -Bio

Terms

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Neurons
Classified into 3 different types according to the direction in which an impulse travels Cells that transmit these impulses or electrical signals
Cell Body
The largest part of a typical neuron Contains the nucleus and much of the cytoplasm Most of the metabolic activity of the cell takes place here
Dendrites
Short, branched extensions Carry impulses from the environment of from other neurons toward the cell body
Axon
The long fiber that carries impulses away from the cell body Ends in a series of small swellings Neurons may have dozens of these
Myelin sheath
The membrane that the axon is surrounded by Leaves may gaps called node where the axon membrane is exposed
Resting neuron
Has a positive charge on the outside and the inside is negative
Resting potential
The electrical charge across the cell membrane of a neuron in its resting state Its not really "resting" because it must produce a constant supply of ATP to fuel active transport
Action Potential
Reversal charges from negative to positive Also called a nerve impulse The membrane temporally becomes more positive than the outside reversing the resting potential
Threshold
The minimum level of a stimulus that is required to activate a neuron Any stimulus stronger than this will produce an impulse
Synapse
The location at which a neuron can transfer an impulse to another cell
Neurotransmitters
Chemicals used by a neuron to transmit an impulse across a synapse to another cell
Cerebrospinal Fluid
Bathes the brain and spinal cord and acts as a shock absorber that protects the central nervous system Also allows for the exchange of nutrients and waste products between blood and nervous tissue
The Brain
Contains approx. 100 billion neurons Mass: 1.4 kilograms The main switching unit of he central nervous
The Cerebrum
Largest and most prominent region Responsible for the voluntary, or conscious, activities of the body The site of intelligence, learning and judgment
The Cerebellum
The second largest region Located at the back of the skull Coordinates and balances the actions of the muscles
The Thalamus
Receives messages from the sense organs Relays information in the proper region of the cerebrum for further processing
The Brain Stem
Connects the brain and the spinal cord Located just below the cerebellum Includes tow regions - pons and the medulla oblongata
The Hypothalamus
The control center for recognition and analysis of hunger, thirst, fatigue, anger, and body temperature
The Spinal Cord
Lime a major telephone line that carries thousands of calls at once the spinal cord id the main communications link between the brain and the rest of the body
Reflex
Is a quick automatic response to a stimulus Allows the body to respond to danger immediately without thinking about response
Meninges
Connective tissue that the brain and the spinal cord is wrapped in
The Central Nervous System
Consists of the brain, and the spinal cord
Drug
Any substance, other than food, that change the structure or function of the body Some drugs, such as cocaine and heroin, are so powerful and dangerous that their possession illegal They differ in the was in which they affect the body
Stimulants
Increase the actions regulation by the nervous system Increase heart rate, blood pressure and breathing reate. In crease the release of neurotransmitters at some synapses in the brain
Depressants
Decrease the rate of functions regulated by the brain Slow down heart rate and breath rate, lower blood pressure, relax muscles, and relive tension Enhance the effects of neurotransmitters that prevent some nerve cells from starting action potentials
Cocaine
Obtained from the leaves of coca plants Causes the sudden release on the brain of a neurotransmitter called dopamine
Opiates
Mimic natural chemicals in the brain known as endorphins, which normally help to overcome sensation of pain The first does of these drugs produce strong feelings of pleasure and security, but the body quickly adjusts to the higher levels of endorphins
Alcohol
Is a depressant that slows down the rate at which the central nervous system functions Slows down reflexes, disrupts coordination, and impairs judgment
Drug Abuse
The intentional misuse of any drug for nonmedical purposes Causes serious physical damage to the body
Addiction
An uncontrollable dependence on a drug
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Sensory receptors
React to a specific stimulus such as light or sound by sending impulses to other neurons, and eventually to the central nervous system Located through out the body
There are 5 general categories of sensory receptors:
Pain Thermoreceptors Mechanoreceptors Chemoreceptors Photoreceptors
Pupil
Small opening in the middle of the iris Through which light enters the eye
Lens
Transparent object behind the iris Changes shape to help adjust the eye's focus to see near of distant objects
Retina
Innermost layer of the eye; contains photoreceptors
Rods
Extremely sensitive to light, but they do not distinguish different colors
Cones
Less sensitive than rods Do respond to light of different colors Produce color vision
Cochlea
Fluid-filled part of the inner ear Sends nerve impulses to the brain
Semicircular canals
1 of 3 structures within the inner ear that help monitor the position of the body

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