human body

HUMAN HUMAN BODYBODY

I. The Human Body A. Introduction Humans are the most complex organisms on Earth, and every

cell in the human body must work together to keep functioning. There are many levels of organization:

• 1. Cell - basic unit of structure and function in ALL living things and usually are specialized

for a particular function.• 2. Tissues- group of cells that perform a single

function.

4 types of tissue

a. Epithelial

• covers body surfaces, lines cavities, organs, vessels. May contain glands for secretions or cells with cilia. Examples include thyroid gland, epicardium of heart, arteries & veins.

Epidermis small intestine kidney

b. Connective• the most abundant and widespread tissue in

the body. Used for support, transport, storage, and as connectors. Has a network of non-living material called a matrix. Ex. Bone, blood, cartilage.

c. Muscle

• able to generate electrical signals that create force and movement. Ex. Skeletal muscle, cardiac muscle, & smooth muscle.

d. Nerve

• specialized to generate and transmit electrical signals to transfer information. Examples include tissues of the brain and spinal cord.

PNS – ganglion Blue stained Myelin sheath with red nuceli

3. Organ - group of tissues

working together for a

particular function.

4. Organ system - Group of

organs working together

to perform a function.

B. Organ Systems• All the parts of the body work together to maintain the internal

conditions inside of a human.

1. Nervous system - Receives, processes, and responds to sensory

information: coordinates all body functions

2. Endocrine System - regulates homeostasis with chemicals called

hormones.

3. Skeletal System - protects and supports body parts.

4. Muscular System - produces movement.

5. Integumentary System- physical barrier against injury, dehydration,

pathogens.

6. Circulatory system - transports O2 and CO2, nutrients, and wastes.

7. Respiratory system - responsible for the exchange of O2 and Co2

8. Lymphatic System - destroys pathogens, fights infection.

9. Digestive System - breaks down food into absorbable monomers.

10. Urinary System - washes or cleans the blood; regulates blood volume.

11. Reproductive System – produces gametes; development of embryo in female

• Organ systems work together in the body to maintain homeostasis.

• Homeostasis - the process by which organisms keep internal and physical conditions constant, or in internal harmony. This harmony is accomplished by negative feedback mechanisms.

• Negative feedback - the process in which a stimulus produces a response that opposes the original stimulus. (ex. House hold heater or AC(pg. 896) & thyroid hormones)

• This process is fulfilled by the endocrine and nervous systems working together.

• Endocrine system - may take hours to couple of days to affect the body. • Nervous system - quick and rapid transmission to the body

Nervous System

“I think, therefore, I am”

II. Nervous System

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

A. Neurons

• Neurons are cells that transmit nerve impulses. Impulses are electrical signals. These signals contain information of what is happening to the body, what is going on in the body, and how the body should respond.

2. Structure of a Neuron• All neurons have the same basic structure.

Structure of a Neuron cont.a. Cell Body - contains the nucleus and the rest of

the organelles. Site of metabolic activity; it receives the impulses from the dendrites.

b. Dendrites - short, branched extensions that receive a stimulus and carry that information to the cell body; they act as detectors or antennae.

Structure of a Neuron cont.

c. Axon - a long, single fiber that branches into many swellings known as axon terminals. The axon transmits impulses away from the cell body and out through the terminals.

Structure of a Neuron cont.

2. Structure of a Neurond. Schwann cells - specialized cells that cover the

axons of many larger neurons. The phospholipid bilayer of the cell membranes of these cells have a higher than usual concentration of lipids. Schwann cells wrap around the neuron to form insulation layers known as the Myelin sheath, which protects and insulates the neuron.

• e. Nodes of Ranvier - nodes are small gaps in the myelin sheath. The electrical impulses can hop from node to node, allowing the impulse to travel faster and in one direction.

Neurons in the hippocampus

3. Synapse• The small space between a neuron and any other cell is

called the synapse. When an impulse reaches the end of an axon, the impulse must be carried across the synapse by chemicals called neurotransmitters.

• Neurotransmitters are stored in vesicles in the axon terminals of a neuron. When an impulse reaches the axon terminal, the vesicles containing the neurotransmitters are released into the synapse by exocytosis.

• The chemicals diffuse across the synapse and stimulate the sodium channels to open in the adjacent cell, stimulating the next cell to go from resting potential to action potential. The neurotransmitters are then broken down and recycled. Examples of Neurotransmitters are Dopamine, Serotonin, Acetylcholine

4. All or Nothing response • The transmission of a nerve impulse is an all

or nothing response which means that either the stimulus will produce an impulse or it will not produce an impulse; therefore the strength of an impulse is always the same. The minimum level of a stimulus required to activate a neuron called the threshold. Because all nerve impulses have the same intensity, the intensity of the stimulus (or response) is reflected in the number of neurons stimulated and the frequency of stimulation.

III. Organization of the Human Nervous System

A. Central Nervous System (CNS) The CNS is made up of the brain and the spinal cord.

A. Central Nervous System (CNS)1. Protection of the CNS - These organs are vital importance and are

therefore, well protected. Three means of protection: a. Bones - Cranium protects the brain; vertebrae protect

the spinal cordb. Meninges - 3 layers of tough, elastic connective tissue

that cushion the brain and spinal cord.c. Cerebrospinal Fluid - fluid between the meninges; acts

as additional cushion

2. Spinal Cord • Column of nerve tissue extending from the

brain through the vertebrae. Serves as the main communication link between the brain and the rest of the body

3. Brain • It is the control center of the entire nervous

system. Although it makes up only about 2% of the body’s mass, it uses about 25% of the body’s oxygen. The human brain is folded into convolutions to increase surface area.

Parts of the brain:

a. Cerebrum

b. Cerebellum

c. Brain Stem

d. Thalamus

e. Hypothalamus

a. Cerebrum 1. Cerebrum- Largest part of the brain; it is composed

of 2 hemispheres or sides - right & left. It controls the conscious activities, intelligence, memory, language, sense, judgment, movement, emotions, personality

2.Corpus Calleosum - connects the right and left cerebral hemispheres and maintains the communication between them.

b. Cerebellum

• located in the back of the brain. Regulates posture, balance, muscle tone, & coordinates the voluntary movement.

c. Brain Stem Composed of the medulla oblongata, pons, &

midbrain.

1 & 2. Pons & midbrain - act as pathways that connect the different parts of the brain.

3. Medulla oblongata - controls involuntary activities such as breathing, heart rate, and blood pressure

d. Thalamus• “telephone operator” for the brain it is the

main site of sensory processing; sorts out sensory information – ex: smell, taste, etc.

e. Hypothalamus• Controls many

activities relating to homeostasis such as body temp, breathing rate, feeling of hunger, thirst, sex drive. Works closely with medulla oblongata.

B. Peripheral Nervous System (PNS)

The PNS relays messages from the body to the brain and transmits commands from the brain to the body. The PNS is composed of nerves which are bundles of sensory and

motor neurons. The PNS is subdivided into:

1.Autonomic Nervous System

2.Somatic Nervous System

1. Autonomic Nervous System

• Network of nerves that regulate activities not under conscious control. The ANS is under the control of the medulla oblongata.

2. Somatic Nervous System

• Regulates activities under conscious control, such as the movement of skeletal muscles. Sometimes a stimulus will result in an automatic, unconscious response within the somatic system. This is called a reflex. Most impulses received by the spinal cord are sent to the brain for processing and interpretation. A reflex is processed directly in the spinal cord. It is a quick and automatic response, although the brain becomes aware after the reflex has occurred.

IV. Sensory Organs

• A. Vision

• B. Hearing

• C. Smelling and Taste

• D. Touch & related senses

A. Vision

• The eyes contain sensory receptors that respond to light. The light energy is then converted to an electrical impulse and transmitted to the brain.

A. Vision - cont 1. Light first passes through the cornea - transparent,

protective covering which begins to focus the light onto the back of the eye. The light then enters a chamber filled with watery fluid called the aqueous humor.

2. The amount of light entering eye is controlled by the iris which consists of tiny muscles arranged in a ring.

3.Light enters through the opening in the center of the iris called the pupil.

4. The beam of light passes through the lens. There are small muscles attached to the lens to change its shape and complete the focusing of the light. There is a chamber behind the lens filled with a jellylike fluid call the vitreous humor.

A. Vision- cont 5. The lens focuses the light onto a delicate tissue called the

retina where the light energy is converted to an electrical impulse. The retina is nerve tissue made up of 2 types of cells: A. rods - cells that detect shape and movement; are stimulated even in dim light.

B. cones - cells that detect color; require bright light for stimulation.

6. The retinal tissue comes together to form the optic nerve which transmits the impulse to the thalamus and then to the cerebrum

7. Sclera - the “white of the eye” and is a continuation of the cornea. It encases and protects the eye

8. Choroid - a layer of blood vessels that nourish the eye.

Pathway of Light Through the Eye

• Cornea pupil lens retina

optic nerve thalamus cerebrum

B. Hearing 1. Sound waves first enter the outer ear and are

funneled into the auditory canal.2. Those sound waves cause vibrations of a

membrane called the tympanic membrane or eardrum which passes those vibrations to the middle ear.

3. The tiny bones in the middle ear begin vibrating. They are the malleus, incus, and stapes. Each bone stimulates the next to vibrate.

4. The bones transmit the vibrations to a thin membrane called the oval window.

B. Hearing5. Vibrations are then passed to the cochlea, a snail

shaped sensory structure filled with fluid and tiny hairs. These hairs are pushed back and forth, producing nerve impulses.

6. Nerve impulses are transmitted through the auditory nerve to the thalamus and cerebrum.

7. Semicircular canals are also found in the ear. They play no role in hearing, instead, they help maintain balance. They consist of 3 fluid-filled canals at different angles to each other.

Pathway of Sound Through the Ear

• Auditory canal - tympanic membrane - malleus - incus - stapes - oval window - cochlea - auditory nerve - thalamus - cerebrum

C. Smelling and Taste

• Response to a chemical stimulus. Smell sensory receptor cells are bathed in mucus and respond to different chemicals. Taste buds are located on the tongue and detect sweet, sour, salty, and bitter.

D. Touch & related senses• Response to a mechanical stimulus. The skin

is the largest sensory organ and it detects pressure, pain, heat, cold.

V. Glands

• These glands are in the brain, but are not part of the nervous system and they are not made up of nerve tissue.

• They are a part of the endocrine system• Pituitary gland - “Master gland” releases hormones

that regulate other endocrine glands• Pineal gland - light sensitive gland that regulates

daily (circadian) rhythms and reproductive cycles

VI. Diseases & Conditions of the Brain

A. Meningitis

B. Alzheimer’s Disease

C. Parkinson’s Disease

D. Multiple Sclerosis

E. Stroke

F. Addiction

A. Meningitis• Infection of the meninges. Usually caused by

a bacteria or virus.

• Symptoms include a severe headache, fever, stiff neck, nausea.

B. Alzheimer’s Disease • Disease of the elderly in which

there is a buildup of protein plaques on the neurons of the cerebral cortex (cerebrum) resulting in progressive death of neurons.

• This leads to loss of memory, confusion, emotional disturbances, cognitive deterioration

• Cause is unknown• Find it by blood tests and

neuroimaging, memory, and cognitive tests

C. Parkinson’s Disease

• Disabling disease due to a decrease in neurotransmitters which transmit impulses for movement.

• Result in tremors, muscle rigidity

D. Multiple Sclerosis

• Disease of young adults characterized by destruction of myelin sheaths of neurons.

• Normal nerve function impaired.

• Symptoms include numbness, muscle weakness, muscle fatigue, vision problems

E. Stroke

Blockage of blood flow to the brain resulting in lack oxygen to those cells

F. Addiction Neurological change resulting in an

uncontrollable compulsive seeking and using a drug despite the negative health and social consequences.