The Human Body

Ch. 35 Nervous System

Organization of the Body

• 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

• Homeostasis -the process of keeping internal conditions relatively constant despite changes in the external environment

Maintaining Homeostasis

• 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

• The nervous system controls & coordinates functions throughout the body & responds to internal & external stimuli

Neurons

• 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

• 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

• 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

• 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

• 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

• The brain consists of the cerebrum, cerebellum, & brain stem

Brain

• Cerebrum - the largest region of the human brain• It is responsible for the voluntary, or conscious,

activities of the body

Brain

• 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

• 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

• 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

• 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

• 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

• 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

• The autonomic nervous system regulates activities that are automatic• Ex.) Heart rate increases as you run

• Overall, the PNS transmits impulses from sense organs to the CNS & back to muscles or glands

The Senses

• 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

• 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

• Thermoreceptors are found in the skin, body core, & hypothalamus• They also detect variations in temperature

The Senses

• Mechanoreceptors are found in the skin, skeletal muscles, & inner ears• They are sensitive to touch, pressure, stretching

of muscles, sound, & motion

The Senses

• 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

• 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

• 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

• 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

• Ears contain structures that help your CNS maintain your balance, or equilibrium; they monitor your head in relation to gravity

Smell & Taste

• Taste buds - sense organs that detect taste• Chemoreceptors found in the taste buds are

sensitive to chemicals in food

Touch & Related Senses

• 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

• Drug - any substance, other than food, that changes the structure & function of the body

Drugs That Affect the Nervous System

• 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

• 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

• 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

• Opiates mimic natural chemicals in the brain known as endorphins, which normally help to overcome sensations of pain• The first doses produce feelings

of pleasure & security

Drugs That Affect the Nervous System

• 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

• 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

• 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

• Drug abuse - the intentional misuse of any drug for nonmedical purposes

• Addiction - an uncontrollable dependence on a drug