35–1 Human Body Systems

The levels of organization in a multicellular organism include:

•cells

•tissues

•organs

•organ systems

Every cell in the human body is both an independent unit and an interdependent part of a larger community—the entire organism.

Cells

A cell is the basic unit of structure and function in living things.

Individual cells in multicellular organisms are specialized.

Specialized cells are suited to perform a particular function.

Tissues

A group of cells that perform a single function is called a tissue.

There are four basic types of tissue in the human body: epithelial, connective, nervous, and muscle.

Organization of the Body

Epithelial tissue includes glands and tissues that cover interior and exterior body surfaces.

Connective tissue supports the body and connects its parts.

Nervous tissue transmits nerve impulses through the body.

Muscle tissue, along with bones, enables the body to move.

Organs and Organ Systems 

A group of different types of tissues that work together to perform a single function is called an organ.

A group of organs that perform closely related functions is an organ system.

There are eleven organ systems in the body.

Nervous System

Structures: Brain, spinal cord, peripheral nerves

Function: Recognizes and coordinates the body’s response to changes in its internal and external environments

Integumentary System

Structures: Skin, hair, nails, sweat and oil glands

Function: Serves as a barrier against infection and injury; helps to regulate body temperature; provides protection against ultraviolet radiation from the sun

Skeletal System

Structures: Bones, cartilage, ligaments, tendons

Function: Supports the body; protects internal organs; allows movement; stores mineral reserves; provides a site for blood cell formation

Muscular System

Structures: Skeletal muscle, smooth muscle, cardiac muscle

Function: Works with skeletal system to produce voluntary movement; helps to circulate blood and move food through the digestive system

Circulatory System

Structures: Heart, blood vessels, blood

Function: Brings oxygen, nutrients, and hormones to cells; fights infection; removes cell wastes; helps to regulate body temperature

Respiratory System

Structures: Nose, pharynx, larynx, trachea, bronchi, bronchioles, lungs

Function: Provides oxygen needed for cellular respiration and removes excess carbon dioxide from the body

Digestive System

Structures: Mouth, pharynx, esophagus, stomach, small and large intestines, rectum

Function: Converts food into simpler molecules that can be used by the cells of the body; absorbs food; eliminates wastes

Excretory System

Structures: Skin, lungs, kidneys, ureters, urinary bladder, urethra

Function: Eliminates waste products from the body in ways that maintain homeostasis

Endocrine System

Structures: Hypothalamus, pituitary, thyroid, parathyroid, adrenals, pancreas, ovaries (in females), testes (in males)

Function: Controls growth, development and metabolism; maintains homeostasis

Reproductive System

Structures: Testes, epididymis, vas deferens, urethra, and penis (in males), ovaries, Fallopian tubes, uterus, vagina (in females)

Function: Produces reproductive cells; in females, nurtures and protects developing embryo

Lymphatic/Immune Systems

Structures: White blood cells, thymus, spleen, lymph nodes, lymph vessels

Function: Helps protect the body from disease; collects fluid lost from blood vessels and returns the fluid to the circulatory system

Homeostasis is the process by which organisms keep internal conditions relatively constant despite changes in external environments.

Homeostasis in the body is maintained by feedback inhibition.

Feedback inhibition, or negative feedback, is the process in which a stimulus produces a response that opposes the original stimulus.

Systems controlled by feedback inhibition are fully automated and very stable.

An Example of Feedback Inhibition

Thermostat senses temperature change and switches off heating system

Thermostat senses temperature change and switches on heating system

Room temperature increases

Room temperature decreases

Homeostasis In the Body

Maintenance of homeostasis requires the integration of all organ systems at all times.

One example is the maintenance of a stable body temperature.

The hypothalamus monitors the temperature of the skin and the temperature of organs.

If core body temperature drops, the hypothalamus:

• causes blood vessels in the skin to constrict reducing heat loss from skin.

• causes the skeletal muscles to contract involuntarily—to “shiver.”

This causes the body temperature to increase.

If the core body temperature increases, the hypothalamus:

• causes blood vessels in the skin to dilate so heat can escape from the skin.

• the body produces sweat, which cools the body by evaporation.

This causes the body temperature to decrease.

35-2 The Nervous System

The nervous system controls and coordinates functions throughout the body and responds to internal and external stimuli.

Neurons

• The messages carried by the nervous system are electrical signals called impulses.

•The cells that transmit impulses (electrical signals) are called neurons.

Neurons are classified according to the direction in which an impulse travels.

• Sensory neurons carry impulses from the sense organs to the spinal cord and brain.

• Motor neurons carry impulses from the brain and spinal cord to muscles and glands.

• Interneurons connect sensory and motor neurons and carry impulses between them.

Structures of a Neuron

Axon terminals

Myelin sheath

Cell body

Nodes Axon

Dendrites

Nucleus

Neurons

The largest part of a typical neuron is the cell body.

It contains the nucleus and much of the cytoplasm.

Cell body

Neurons

Dendrites extend from the cell body and carry impulses from the environment toward the cell body.

Dendrites

Neurons

The axon is the long fiber that carries impulses away from the cell body.

Axon terminals

Axon

Neurons

The axon ends in axon terminals.

Axon terminals

Axon

NeuronsThe axon is sometimes surrounded by an insulating membrane called the myelin sheath.

There are gaps in the myelin sheath, called nodes, where the membrane is exposed.

Impulses jump from one node to the next.

Myelin sheath

Nodes

The Nerve Impulse

The Resting Neuron 

• When resting, the outside of the neuron has a net positive charge.

• The inside of the neuron has a net negative charge.

• The cell membrane is electrically charged because there is a difference in electrical charge between its outer and inner surfaces.

The Nerve Impulse

The sodium-potassium pump in the nerve cell membrane pumps sodium (Na+) ions out of the cell and potassium (K+) ions into the cell by means of active transport.

As a result, the inside of the cell contains more K+

ions and fewer Na+ ions than the outside.

The Nerve Impulse

• Sodium-Potassium Pump

The Nerve Impulse

More K+ ions leak across the membrane than Na+ ions. This produces a negative charge on the inside and a positive charge on the outside.

The electrical charge across the cell membrane of a neuron at rest is known as the resting potential.

The Nerve Impulse

The Moving Impulse

An impulse begins when a neuron is stimulated by another neuron or by the environment.

movie

The Nerve Impulse

At the leading edge of the impulse, gates in the sodium channels open allowing positively charged Na+ ions to flow inside the cell membrane.

The Nerve Impulse

The inside of the membrane temporarily becomes more positive than the outside, reversing the resting potential.

The Nerve Impulse

This reversal of charges is called a nerve impulse, or an action potential.

The Nerve Impulse

As the action potential passes, gates in the potassium channels open, allowing K+ ions to flow out restoring the negative potential inside the axon.

The Nerve ImpulseThe impulse continues to move along the axon.

An impulse at any point of the membrane causes an impulse at the next point along the membrane.

The Nerve Impulse

Threshold 

• A stimulus must be of adequate strength to cause a neuron to transmit an impulse.

• The minimum level of a stimulus that is required to activate a neuron is called the threshold.

The Nerve Impulse

• A stimulus that is stronger than the threshold produces an impulse.

• A stimulus that is weaker than the threshold produces no impulse.

The SynapseThe Synapse

• At the end of the neuron, the impulse reaches an axon terminal. Usually the neuron makes contact with another cell at this site.

• The neuron may pass the impulse along to the second cell.

• The location at which a neuron can transfer an impulse to another cell is called a synapse.

The Synapse

• A Synapse

movie

The Synapse

The synaptic cleft separates the axon terminal from the dendrites of the adjacent cell.

Synaptic cleft

The SynapseTerminals contain vesicles filled with neurotransmitters.

Neurotransmitters are chemicals used by a neuron to transmit an impulse across a synapse to another cell.

Vesicle

Neurotransmitter

The Synapse• As an impulse reaches a terminal, vesicles send neurotransmitters into the synaptic cleft.

• These diffuse across the cleft and attach to membrane receptors on the next cell.

Receptor

The Synapse

Sodium ions then rush across the membrane, stimulating the next cell.

If the stimulation exceeds the cell’s threshold, a new impulse begins.

The Synapse

Moments after binding to receptors, neurotransmitters are released from the cell surface.

The neurotransmitters may then be broken down by enzymes, or taken up and recycled by the axon terminal.

35-3 Divisions of the Nervous System

The human nervous system has two major divisions:

a. central nervous system

b. peripheral nervous system

The central nervous system relays messages, processes information, and analyzes information.

a.The central nervous system consists of the brain and the spinal cord.

b. Both the brain and spinal cord are wrapped in three layers of connective tissue known as meninges.

Between the meninges and the central nervous system tissue is a space filled with cerebrospinal fluid.

Cerebrospinal fluid acts as a shock absorber that protects the central nervous system.

Cerebrospinal fluid also permits exchange of nutrients and waste products between blood and nervous tissue.

The Brain

a. The brain is the place to which impulses flow and from which impulses originate.

Parts of The Human Brain FIGURE 35-9

Thalamus

Pineal gland

Cerebellum

Spinal cord

Hypothalamus

Pituitary gland

Cerebrum

Brain stemPons

Medulla oblongata

The Cerebrum 

a. The largest and most prominent region of the human brain is the cerebrum.

b. It controls the voluntary, or conscious, activities of the body.

c. It is the site of intelligence, learning, and judgment.

A deep groove divides the cerebrum into hemispheres, which are connected by a band of tissue called the corpus callosum.

Each hemisphere is divided into regions called lobes.

Lobes of the Cerebrum

Each half of the cerebrum deals with the opposite side of the body:

a. The left half of the cerebrum controls the right side of the body.

b. The right half of the cerebrum controls the left side of the body.

The outer layer of the cerebrum is called the cerebral cortex and consists of gray matter.

The inner layer of the cerebrum consists of white matter, which is made up of bundles of axons with myelin sheaths.

The Cerebellum 

a. The second largest region of the brain is the cerebellum.

b.It coordinates and balances the actions of the muscles so that the body can move gracefully and efficiently.

Cerebellum

The Brain Stem

a. The brain stem connects the brain and spinal cord.

b. It has two regions: the pons and the medulla oblongata regulate information flow between the brain and the rest of the body.

c.Blood pressure, heart rate, breathing, and swallowing are controlled in the brain stem.

Pons

Medulla oblongata

Brain stem

The Thalamus and Hypothalamus 

a. The thalamus receives messages from all sensory receptors throughout the body and relays the information to the proper region of the cerebrum for further processing.

a.The hypothalamus controls recognition and analysis of hunger, thirst, fatigue, anger, and body temperature.

b. It controls coordination of the nervous and endocrine systems.

Thalamus

Hypothalamus

The Spinal Cord

a. The spinal cord is the main communications link between the brain and the rest of the body.

b. Certain information, including some kinds of reflexes, are processed directly in the spinal cord.

c. A reflex is a quick, automatic response to a stimulus.

The Peripheral Nervous System

a.The peripheral nervous system is all of the nerves and associated cells that are not part of the brain and the spinal cord.

b. The peripheral nervous system includes cranial nerves, spinal nerves, and ganglia.

c. Ganglia are collections of nerve cell bodies.

The sensory division of the peripheral nervous system transmits impulses from sense organs to the central nervous system.

The motor division transmits impulses from the central nervous system to the muscles or glands.

The motor division is divided into the somatic nervous system and the autonomic nervous system.

The Somatic Nervous System

a.The somatic nervous system regulates activities that are under conscious control, such as the movement of skeletal muscles.

b.Some somatic nerves are involved with reflexes = react to pain.

A reflex arc includes a sensory receptor, sensory neuron, motor neuron, and effector that are involved in a quick response to a stimulus.

a. Reflex Arc

Sensory receptors

Effector (responding muscle)

Interneuron Spinal cord

Sensory neuron

Motor neuron

The Autonomic Nervous System

a.The autonomic nervous system regulates involuntary activities.

b. The autonomic nervous system is subdivided into two parts:

sympathetic nervous system

parasympathetic nervous system

The sympathetic and parasympathetic nervous systems have opposite effects on the same organ system.

These opposing effects help maintain homeostasis.

35–4 The Senses

Neurons that react directly to stimuli from the environment are called sensory receptors.

Sensory receptors react to stimuli by sending impulses to other neurons and to the central nervous system.

Sensory receptors are located throughout the body but are concentrated in the sense organs.

Sense organs include the:

a.eyes

b.ears

c.nose

d.mouth

e.skin

5 categories of sensory receptors:

a.pain receptors

b.Thermoreceptors- heat

c.Mechanoreceptors- pressure

d.Chemoreceptors- chemicals NOSE & TASTE BUDS

e.Photoreceptors- light EYES

Pain receptors are located throughout the body except in the brain.

They respond to chemicals released by damaged cells.

Pain usually indicates danger, injury, or disease.

Thermoreceptors are located in the skin, body core, and hypothalamus.

They detect variations in temperature.

Mechanoreceptors are found in the skin, skeletal muscles, and inner ears.

They are sensitive to touch, pressure, stretching of muscles, sound, and motion.

Chemoreceptors, located in the nose and taste buds, are sensitive to chemicals in the external environment.

Photoreceptors, found in the eyes, are sensitive to light.

Vision

a. The sense organ that animals use to sense light is the eye.

b. The eye has three layers:

the retina

the choroid

the sclera

The retina is the inner layer of eye that contains photoreceptors.

Retina

The choroid is the middle layer of eye that is rich in blood vessels.

Choroid

The sclera is the outer layer of eye that maintains its shape.

The sclera serves as point of attachment for muscles that move the eye.

Sclera

ACTIVE ART

Light enters the eye through the cornea, a tough transparent layer of cells.

Cornea

The cornea helps focus light, which then passes through a chamber filled with a fluid called aqueous humor.

Cornea

Aqueous humor

At the back of the chamber is a disklike structure called the iris, which is the colored part of the eye.

Iris

In the middle of the iris is a small opening called the pupil. Muscles in the iris adjust pupil size to regulate the amount of light that enters the eye.

Pupil

In dim light, the pupil becomes larger.

In bright light, the pupil becomes smaller.

Just behind the iris is the lens.

Muscles attached to the lens change its shape to adjust focus to see near or distant objects.

Lens

Behind the lens is a large chamber filled with a transparent, jellylike fluid called vitreous humor.

Vitreous humor

The lens focuses light onto the retina.

Photoreceptors are arranged in a layer in the retina.

Retina

The photoreceptors convert light energy into nerve impulses that are carried to the central nervous system.

There are two types of photoreceptors: rods and cones.

Rods are sensitive to light, but not color.

Cones respond to light of different colors, producing color vision.

Cones are concentrated in the fovea, which is the site of sharpest vision.

Fovea

There are no photoreceptors where the optic nerve passes through the back of the eye, which is called the blind spot.

Optic nerve

The impulses leave each eye by way of the optic nerve. Optic nerves carry impulses to the brain.

The brain interprets them as visual images and provides information about the external world.

The Ear

a.The human ear has two sensory functions:

hearing

balance

Hearing 

a. Ears can distinguish both the pitch and loudness of those vibrations.

The Human Ear Figure 35-14 pg908

Locate- Tympanum, hammer, anvil, stirrup, & cochlea

Vibrations enter the ear through the auditory canal.

Auditory canal

The vibrations cause the tympanum, or eardrum, to vibrate.

Tympanum

The vibrations are picked up by the hammer, anvil, and stirrup.

Hammer

Anvil

Stirrup

The stirrup transmits the vibrations to the oval window.

Oval window

Stirrup

Vibrations of the oval window create pressure waves in the fluid-filled cochlea of the inner ear.

Cochlea

The fluid-filled cochlea is lined with tiny hair cells that are pushed back and forth by these pressure waves.

In response to the waves, the hair cells produce nerve impulses that are sent to the brain through the cochlear nerve.

Balance 

a. Your ears help you to maintain your balance, or equilibrium.

Within the inner ear, just above the cochlea are three semicircular canals.

Semicircular canals

The canals are filled with fluid and lined with hair cells.

As the head changes position, fluid in the canals changes position, causing the hair on the hair cells to bend.

This sends impulses to the brain that enable it to determine body motion and position.

Smell

a. The sense of smell is actually an ability to detect chemicals.

b. Chemoreceptors in the nasal passageway respond to chemicals and send impulses to the brain through sensory nerves.

Taste

a. The sense of taste is also a chemical sense.

b. The sense organs that detect taste are the taste buds. Most taste buds are on the tongue.

c. Tastes detected by the taste buds are classified as salty, bitter, sweet, and sour.

d. Sensitivity to these tastes varies on different parts of the tongue.

Touch and Related Senses

a. The skin’s sensory receptors respond to temperature, touch, and pain.

b. Not all parts of the body are equally sensitive to touch, because not all parts have the same number of receptors.

c. The greatest density of sensory receptors is found on your fingers, toes, and face.

35–5 Drugs and the Nervous System

A drug is any substance, other than food, that changes the structure or function of the body.

Some drugs, such as cocaine and heroin are illegal. Other drugs, such as penicillin and codeine are prescribed by doctors. Still other drugs, including cough medicines can be purchased over the counter.

All drugs can be harmful if used improperly or abused.

Drugs differ in the ways in which they affect the body.

a. Some kill bacteria and are useful in treating disease.

b. Others affect a particular system of the body.

c. Others cause changes to the brain and synapses.

Stimulants

Stimulants increase heart rate, blood pressure, and breathing rate. In addition, stimulants increase the release of neurotransmitters at some synapses in the brain.

Common stimulants include amphetamines, cocaine, nicotine, and caffeine.

Depressants 

a. Depressants slow down heart rate and breathing rate, lower blood pressure, relax muscles, and relieve tension.

b. Barbiturates, tranquilizers, and alcohol are some examples of depressants.

Cocaine  

a. Cocaine causes the sudden release in the brain of a neurotransmitter called dopamine.

b. Cocaine also acts as a powerful stimulant.

Opiates  

a. Opiates mimic endorphins which normally help to overcome sensations of pain.

b. Common opiates include morphine and codeine.

Marijuana

a. The most widely abused illegal drug is marijuana.

b. Marijuana comes from Cannabis sativa, a hemp plant.

c. Hashish, or hash, is a potent form of marijuana.

d. The active ingredient in marijuana is THC.

Long-term use of marijuana can result in:

a. loss of memory

b. inability to concentrate

c. in males, reduced levels of the hormone testosterone in males

a. Alcohol is a depressant that slows down the rate at which the central nervous system functions.

b. Alcohol slows down reflexes, disrupts coordination, and impairs judgment.

Heavy drinking fills the blood with so much alcohol that the central nervous system cannot function properly.

People who drink a lot of alcohol usually cannot walk or talk properly, and they are not able to safely control an automobile.

Pregnant women who drink alcohol risk having a child with FAS.

Fetal alcohol syndrome (FAS) is a group of birth defects caused by the effects of alcohol on the fetus.

FAS can cause minor to serious brain damage, heart defects, malformed faces, delayed growth, and poor motor development.

Alcohol and Disease

a. People who have become addicted to alcohol suffer from a disease called alcoholism.

b. If a person cannot function properly without satisfying the craving for alcohol, that person has an alcohol-abuse problem.

c. Long-term alcohol use destroys liver cells.

Drug Abuse

a. Drug abuse is the intentional misuse of any drug for nonmedical purposes.

b. Drug abuse can cause psychological dependence or serious physical damage to the body.

Uncontrollable dependence on a drug is called an addiction.

Some drugs cause a strong psychological dependence, or mental craving.

35–1

The type of tissue that holds organs in place and binds different parts of the body together is called

a. muscle tissue.

b. epithelial tissue.

c. connective tissue.

d. skeletal tissue.

35–1

One major function of the integumentary system is to

a. help regulate body temperature.

b. cause the body to move.

c. provide a surface for gas exchange.

d. control growth, development, and metabolism.

35–1

Which of the following is NOT an example of feedback inhibition?

a. shivering to warm the body

b. sweating to cool the body

c. nervous tissue receiving messages

d. turning on the heating system of a house

35–1

The process by which an organism keeps internal conditions relatively constant is called

a. a feedback loop.

b. negative feedback.

c. homeostasis.

d. normal temperature.

Which of the following organ systems transports oxygen, nutrients, and hormones to cells?

a. circulatory system

b. muscular system

c. excretory system

d. nervous system

35-2

Neurons that carry impulses from the brain and spinal cord to the muscles are

a. interneurons.

b. sensory neurons.

c. resting neurons.

d. motor neurons.

35-2

The part of the neuron that carries impulses toward the cell body is the

a. axon.

b. myelin sheath.

c. dendrite.

d. nodes.

35-2

The minimum level of a stimulus that is required to activate a neuron is called its

a. action potential.

b. resting potential.

c. threshold.

d. synapse.

35-2

Chemicals that are used by a neuron to transmit impulses are called

a. neurotransmitters.

b. synapses.

c. axons.

d. inhibitors.

35-2

An action potential begins when

a. sodium ions flow into the neuron.

b. potassium ions flow into the neuron.

c. sodium and potassium ions flow into the neuron.

d. sodium and potassium ions flow out of the neuron.

35-3

The brain stem functions as

a. a location for memory and learning.

b. the control site responsible for heart rate, blood pressure, and breathing.

c. the location where all sensory information is processed and delivered to the cerebrum.

d. an area that recognizes hunger, thirst, and body temperature.

35-3

The left half of the cerebrum largely controls

a. the left side of the body.

b. both the right and left sides of the body.

c. the right side of the body.

d. the right half of the brain.

35-3

The part of the brain that is responsible for coordination and balance is the

a. cerebellum.

b. cerebrum.

c. brain stem.

d. thalamus.

35-3

Reflex arcs are actions that are a part of the peripheral nervous system's

a. sensory division.

b. somatic system.

c. autonomic system.

d. motor division.

35-3

Which of the following is NOT under the control of the autonomic nervous system?

a. heartbeat

b. digestion

c. walking

d. sweating

35–4

The sensory receptor that detects variations in body temperature is a

a. chemoreceptor.

b. mechanoreceptor.

c. thermoreceptor.

d. photoreceptor.

35–4

The part of the eye containing tiny muscles that adjust the size of the pupil is the

a. cornea.

b. iris.

c. lens.

d. retina.

35–4

The part of the ear that produces the nerve impulses sent to the brain is the

a. tympanum.

b. Eustachian tube.

c. cochlea.

d. oval window.

35–4

The structures in your ears that help maintain your sense of balance

a. is the auditory canal.

b. is the hammer.

c. is the tympanum.

d. are the semicircular canals.

35–4

Photoreceptors in the eye that are sensitive to color are

a. rods.

b. cones.

c. rods and cones.

d. the optic nerve.

35–5

35–5

A drug that increases the heart rate and breathing rate is a

a. depressant.

b. opiate.

c. stimulant.

d. barbiturate.

35–5

A powerful stimulant that increases blood pressure and heart rate that can lead to a heart attack is

a. cocaine.

b. opium.

c. marijuana.

d. caffeine.

35–5

Many drugs that affect the brain and behavior do so because they

a. affect organ systems and those changes are detected by the brain.

b. interfere with the normal functioning of neurotransmitters.

c. cause the brain to release endorphins.

d. enter the cell bodies of brain neurons causing them to behave differently.

35–5

True or False? Medically prescribed drugs cannot cause addiction.

a. True

b. False

35–5

Alcohol acts on the brain as a

a. general stimulant of the nervous system.

b. general depressant of the nervous system.

c. pain reliever acting in the cerebrum.

d. stimulant of the brain stem and cerebellum.