The Nervous System

• The NERVOUS SYSTEM controls and coordinates functions throughout the body and responds to internal and external stimuli

NEURONS are cells that transmit messages, called IMPULSES, through the nervous system

The CELL BODY contains the NUCLEUS and most of the cytoplasm, metabolic activity of the cell takes place

here

DENDRITES branch out from the cell body, and they carry impulses from the

environment or from other neurons toward the cell body

The AXON carries impulses away from the cell body. The axon is covered in a membrane called

the MYELIN SHEATH. There are gaps in the myelin sheath, called NODES. The signal can

jump from node to node, increasing the speed of the impulse.

A RESTING NEURON is one that is not transmitting an impulse. Na+/K+ gates pump three Na+ ions out of the cell membrane and two K+ ions

in through the cell membrane, creating a net negative charge inside the cell. This charge

configuration is called the RESTING POTENTIAL of the neuron.

When the neuron receives a signal from the environment or another neuron, the ion gates at the leading edge of the cell open and Na+ is pumped into the the axon, and K+ is pumped out. This creates an ACTION POTENTIAL, which creates a current that moves down the axon.

In order for a neuron to send an impulse in response to a stimulus, the stimulus must overcome the THRESHOLD POTENTIAL, the minimum potential needed in order to create an action potential.

A neuron can transfer a signal to another cell at locations called SYNAPSES. At the synapse, chemicals called NEUROTRANSMITTERS are released, which sends the impulse to receptors in an adjacent cell.

The Nervous System can be broken into two parts:

• The CENTRAL NERVOUS SYSTEM: composed of the brain and the spinal cord

• The PERIPHERAL NERVOUS SYSTEM: composed of all the nerves that aren’t part of the brain or spinal cord

Central Nervous System

• The skull and vertebral column protect the brain and spinal cord

• The brain and spinal cord are protected in three layers of tissue called MENINGES

• The space between the meninges and the brain and spinal cord is filled with CEREBROSPINAL FLUID, which acts as a shock absorber and helps protect the central nervous system.

Parts of the Brain

• CEREBRUM: contains the frontal, parietal, occipital, and temporal lobes

• CEREBELLUM

• BRAIN STEM

• THALAMUS and HYPOTHALAMUS

The Cerebrum

• Folds in the Cerebrum increase the surface area of the brain

• Responsible for voluntary actions, intelligence, learning, and judgment

• Divided into two hemispheres, left and right• Outer Layer – Gray matter composed of nerve

cell bodies• Inner Layer – White matter composed of

bundles of axons with myelin sheaths

The Cerebellum:• Second largest region of the brain• Located in the back of the skull• Responsible for balance and muscle

coordination

The Brain Stem:• Connects the brain to the spinal cord• Regulates the flow of information from the

brain to the rest of the body• Controls basic life functions, such as

heartbeat, breathing, swallowing, etc

Thalamus and Hypothalamus

• Located between the brain stem and the cerebellum

• The THALAMUS receives signals from the body and sends them to the cerebrum to be processed

• The HYPOTHALAMUS recognizes and analyzes hunger, thirst, fatigue, anger, and body temperature.

The Spinal Cord• Communication line

between the brain and the rest of the body

• Made up of bundles of nerves that branch out into the rest of the body

• Processes REFLEXES, quick responses to stimuli

Peripheral Nervous System

• SENSORY DIVISION transmits impulses from the sense organs to the brain

• MOTOR DIVISION transmits impulses from the brain to the muscles or glands

Peripheral Nervous System

• SOMATIC – regulates voluntary impulses

• AUTONOMIC - regulates the involuntary body functions

SIGHT

Light is focused through the LENS onto the RETINA. Images are transmitted from the retina to the brain through the OPTIC NERVE

HEARING – vibrations from noise in the air are sensed by three tiny bones in the ear, the

HAMMER, ANVIL, and STIRRUP. These create pressure waves in the fluid of the COCHLEA,

which contains tiny hairs that wave back and forth. The motion of these hairs produce the nerve

impulses that are sent to the brain

SMELL • SCENT is the detecting

of trace amounts of chemicals

• CHEMORECEPTORS in the lining of the nasal passages detect these chemicals and send an impulse to the brain

• Smell is closely tied to memory and feeling, and can generate responses in people almost immediately

Taste

• Taste is closely related to smell, and taste is the detection of chemicals by chemoreceptors on the tongue

• Tastes are classified as bitter, sour, salty, and sweet

• The human mouth has over 10,000 taste buds, even on the roof!

TOUCH

• Nerve endings in the skin respond to temperature, touch and pain

• The areas that are most sensitive to touch have the highest concentration of nerve endings: the feet, hands, and face

Drugs and the Nervous System

• A DRUG is any substance that changes the structure or function of the body

• STIMULANTS increase the release of neurotransmitters in the brain, they include nicotine, amphetamines, and cocaine

• DEPRESSANTS decrease the rate of functions regulated by the brain. Types of depressants are alcohol, barbituates, and tranquilizers

• OPIATES release endorphins and relieve sensations of pain. Examples are morphine, heroin, and codeine.

ALCOHOL

• Alcohol is a depressant that slows reflexes, disrupts coordination, and impairs judgment

• Alcohol is legal and is the most dangerous and most abused drug in the United States

• Alcohol abuse is responsible for job loss, injuries and fatalities, and destroying families

Alcohol Statistics

• 20% of suicide victims in the U.S. are alcoholics• 14 million people in the U.S. abuse alcohol• 6.6 million American children under 18 live with

an alcoholic parent• 75% of U.S. high school students will consume

alcohol before graduation• An alcoholic will negatively impact the lives of 4

out of 5 Americans (work associates, family, friends) while under the influence

Drinking and Driving

• 30% of all Americans will be involved in alcohol-related motor incidents

• 17,000 alcohol-related traffic fatalities occur per year

• One alcohol-related motor vehicle accident occurs every 30 minutes in the U.S.

• 41% of all traffic fatalities are alcohol related.

Marijuana

• Most widely abused illegal drug in the U.S.

• Results in memory loss and inability to concentrate

• In males, it reduces the levels of testosterone produced

Cocaine• Cocaine is a stimulant that causes a sudden

release of dopamine to the brain• Increases heart rate and blood pressure • The intense high wears off quickly, leaving the

brain depleted of dopamine and the user feeling depressed

ADDICTION is the physical dependence on a drug. Long term use of a drug can lead to

drug-seeking behavior

RISK FACTORS:• Family history of drug/alcohol use• Being male makes you twice as likely to develop

a dependence• Other psychological problems such as

depression, ADHD, PTSD, etc.• Peer Pressure• Anxiety, Depression, Loneliness• Taking a highly addictive drug such as cocaine,

crystal methamphetamine, or heroin

COMPLICATIONS DUE TO ADDICTION:• Health problems• Unconsciousness, coma, death• Depression• Suicide• Family problems• Decreased performance at work or school• Financial problems• Legal problems

THE KEY TO PREVENTING ADDICTION IS TO AVOID DRUGS.

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