Transcript 18-Nervous System - Jamestown Public Schools

The Human Body
Ch. 35 Nervous System
Organization of the Body
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The levels of organization in a multicellular
organism include cells, tissues, organs, &
organ systems.
There are 11 distinct human body systems.
(see pages 892-893 in text)
Cells
-A cell is the basic unit of structure & function
in living things
-Specialized cells - cells uniquely suited to
perform a particular function
Tissues
• There are 4 basic types of tissue in the human
body: epithelial, connective, nervous, & muscle
• Epithelial tissue - includes glands & tissues that
cover interior & exterior body surfaces
Tissues con’t
• Connective tissue - provides support for the
body & connects its parts
• Nervous tissue - transmits nerve impulses
throughout the body
• Muscle tissue - along with bones, enables the
body to move
Maintaining Homeostasis
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Homeostasis -the process of keeping
internal conditions relatively constant
despite changes in the external environment
Maintaining Homeostasis
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Negative Feedback - when a stimulus
produces a response that opposes the
original stimulus
• Ex.) Thermostat regulating room temp,
Pancreas releasing insulin
Negative Feedback
The Nervous System
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The nervous system controls & coordinates
functions throughout the body & responds
to internal & external stimuli
Neurons
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Messages carried by the nervous system are
electrical signals called impulses
Neurons - cells that transmit impulses
Cell Body - largest part of a neuron,
contains the nucleus & most of the
cytoplasm, where the metabolic activity of
the cell takes place
Neurons
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Dendrites - short, branched extensions, that
carry impulses from the environ. or from
other neurons toward the cell body
Axon - long fiber that carries impulses away
from cell body
Myelin sheath - insulating membrane that
surrounds the axon
Neurons
The Synapse
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Synapse - the location where 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
Divisions of the Nervous System
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The peripheral nervous system (PNS) receives
info. from the environ. & relays commands from
the CNS to organs & glands
The central nervous system (CNS) relays
messages, processes information, & analyzes
information
The CNS is the control center of the body,
includes the brain & spinal cord
The Central Nervous System
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Meninges - layers of connective tissue that
are wrapped around the brain & spinal cord
Cerebrospinal fluid - bathes the brain &
spinal cord & acts as a shock absorber that
protects the CNS
Brain
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The brain consists of the cerebrum,
cerebellum, & brain stem
Brain
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Cerebrum - the largest region of the human
brain
• It is responsible for the voluntary, or conscious,
activities of
the body
Brain
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Cerebellum - the 2nd largest region of the
brain
• It is located at the back of the skull
• The cerebellum coordinates & balances the
actions of the muscles so that the body can
move gracefully & efficiently
Brain
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Brain stem - connects the brain & spinal
cord
• It is located below the cerebellum, it includes 2
regions: the pons & the medulla oblongata
• Each of these regions regulates the flow of info.
between the brain & the rest of the body
• Controls important functions like: blood
pressure, heart rate, breathing, & swallowing
Brain
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The thalamus & hypothalamus are found
between the brain stem & the cerebrum
Thalamus - receives messages from all of
the sensory receptors throughout the body
& then relays the info. to the proper region
of the cerebrum for further processing
Brain
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Hypothalamus - the control center for
recognition & analysis of hunger, thirst,
fatigue, anger, & body temperature
• It also controls the coordination of the nervous
& endocrine systems
The Spinal Cord
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Certain kinds of info., including some kinds
of reflexes, are processed directly in the
spinal cord
Reflex - a quick, automatic response to a
stimulus; it allows your body to respond to
danger immediately, without spending time
to think about a response
• Ex.) sneezing & blinking
The Peripheral Nervous System
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The sensory division of the PNS transmits
impulses from sense organs to the CNS
The motor division transmits impulses from
the CNS to the muscles or glands
The somatic nervous system regulates
activities that are under conscious control,
such as movement of the skeletal muscles
The Peripheral Nervous System
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The autonomic nervous system regulates
activities that are automatic
• Ex.) Heart rate increases as you run
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Overall, the PNS transmits impulses from
sense organs to the CNS & back to muscles
or glands
The Senses
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Sensory receptors - neurons that react to a
specific stimulus such as light or sound by
sending impulses to other neurons, &
eventually to the CNS
There are 5 general categories of sensory
receptors: pain receptors, thermoreceptors,
mechanoreceptors, chemoreceptors, &
photoreceptors
The Senses
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Pain receptors are found throughout the
entire body, except the brain, & respond to
chemicals released by damaged cells
• Pain usually indicates danger, injury, & disease
The Senses
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Thermoreceptors are found in the skin, body
core, & hypothalamus
• They also detect variations in temperature
The Senses
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Mechanoreceptors are found in the skin,
skeletal muscles, & inner ears
• They are sensitive to touch, pressure, stretching
of muscles, sound, & motion
The Senses
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Chemoreceptors are found in the nose &
taste buds, & are sensitive to chemicals in
the external environ.
Photoreceptors are found in the eyes, & are
sensitive to light
Vision
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Eyes are sense organs used to detect light
The iris is the colored part of the eye
The pupil is in the middle of the iris
Muscles in the iris regulate the amount of
light that enters the eye
Vision
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Lens - located just behind the iris, muscles
attach to the lens to change its shape, to
help you adjust your eyes’ focus to see near
or distant objects
Retina - where light is focused onto from
the lens; here, light energy is converted into
nerve impulses that are carried to the CNS
Vision
Hearing & Balance
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Sound is nothing more than vibrations in the
air around us
The ears are the sensory organs that can
distinguish both the
pitch &
loudness of
those
vibrations
Hearing & Balance
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Ears contain structures that help your CNS
maintain your balance, or equilibrium; they
monitor your head in relation to gravity
Smell & Taste
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Taste buds - sense organs that detect taste
Chemoreceptors found in the taste buds are
sensitive to
chemicals in
food
Touch & Related Senses
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The sense of touch is not found in just 1
place
All of the regions of the skin are sensitive to
touch
Skin is the largest sense organ of the body
It contains sensory receptors that respond to
temp., touch, & pain
Drugs & the Nervous System
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Drug - any substance, other than food, that
changes the structure & function of the
body
Drugs That Affect the Nervous
System
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Stimulants - drugs that increase the actions
regulated by the nervous system
• They increase heart rate, blood pressure, &
breathing rate
• Includes: amphetamines, cocaine, nicotine, &
caffeine
Drugs That Affect the Nervous
System
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Depressants - drugs that decrease the rate of
functions regulated by the brain
• They slow down heart rate & breathing rate,
lower blood pressure, relax muscles, & relieve
tension
• Includes: Barbiturates, & tranquilizers
Drugs That Affect the Nervous
System
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Cocaine causes the sudden release in the
brain of a neurotransmitter called dopamine
• Its normally released when a need such as
hunger or thirst, is fulfilled
• By fooling the brain, cocaine produces intense
feelings of pleasure & satisfaction
Drugs That Affect the Nervous
System
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Opiates mimic natural chemicals in the
brain known as endorphins, which normally
help to overcome sensations of pain
• The first doses produce
of pleasure & security
feelings
Drugs That Affect the Nervous
System
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Marijuana produces a temporary feeling of
euphoria & disorientation
• Smoking marijuana is more destructive to your
lungs than smoking tobacco
• Long-term use can result in memory loss;
inability to concentrate; & in males, reduced
levels of the hormone testosterone
Drugs That Affect the Nervous
System
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Alcohol is a depressant that slows down the
rate at which the CNS functions
• It slows down reflexes, disrupts coordination,
& impairs judgment
Drugs That Affect the Nervous
System
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Fetal alcohol syndrome - a group of birth
defects caused by the effects of alcohol on
the fetus
• Babies born with FAS can suffer from heart
defects, malformed faces, delayed growth, &
poor motor development
Drug Abuse
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Drug abuse - the intentional misuse of any
drug for nonmedical purposes
Addiction - an uncontrollable dependence
on a drug