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Title:
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brain & heart .
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Type:
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General .
Brain, portion of the central nervous system contained within the skull.
the brain is the control center for every activity necessary to survival .
Anatomy the adult human brain is made up of approximately 100 billion neurons (nerve cells);
) 엥 𤥓
(
neuroglia (supporting-tissue) cells and other tissues .
ꑓ ( ꑟ ꑓ )
Neurons transmit and analyze all communication within the brain and other parts of the nervous system.
𗨢
Neuroglial cells are twice as numerous as neurons and provide structural support to the neurons.
Neuroglial
Three protective meninges (membranes) cover the brain.
( ) ꑟ
A clear liquid, the cerebrospinal fluid, surrounds the entire brain and protects the internal portion from varying pressures.
䑡
ꥐ
This fluid also transports chemical substances within the nervous system.
𗨢
the brain appears as three connected parts:
:
the cerebrum, the cerebellum, and the brain stem.
쑨
Two other major parts, the thalamus and the hypothalamus, lie above the brain stem underneath the cerebellum.
쑨
Most high-level brain functions take place in the cerebrum.
Its two large hemispheres are divided into five lobes:
: ()拉
the frontal, parietal, temporal, and occipital lobes and the insula.
the cerebrum receives information from the sense organs and sends motor commands (signals that stimulate activity in the muscles
or glands) to other parts of the brain and the body.
) 䐥
( 䤢
Many areas of the cerebral cortex (surface) correspond to specific functions, such as vision, hearing, speech, emotions, thinking, and
remembering.
[] ( )
the cerebellum coordinates body movements.
It is divided into two lobes connected by a bundle of white fibers.
䐤 ()
the cerebellum coordinates voluntary movements by fine-tuning motor commands from the cerebrum.
the cerebellum also maintains posture and balance by controlling muscle tone and sensing limb positions.
the thalamus and the hypothalamus connect the cerebrum to the brain stem .
쑨
the thalamus relays sensory signals to and from the cerebral cortex.
All sensory input to the brain, except the sense of smell, connects to the thalamus.
the hypothalamus lies beneath the thalamus and regulates vital drives and activities, such as eating, drinking, sleep, emotional
behavior, and sexual activity.
ꯑ䤑 []
It also controls the internal organs, interacts closely with the pituitary gland, and helps coordinate brain stem activities.
쑨
the brain stem is responsible for sustaining the basic functions of life, such as breathing and blood pressure.
쑨
[]
It contains relay stations for neurons transmitting signals to the cerebral cortex, as well as many reflex centers- pathways carrying
sensory information and motor commands.
centers- 𥑓
Sensory and motor nerve fibers connecting the brain with the rest of the body cross over to the opposite side in the brain stem.
⯑ 쓑
쑨
the left half of the brain communicates with the right half of the body, and the right half of the brain with the left half of the body.
Twelve pairs of cranial nerves connect the brain with the head and neck .
Some are motor nerves, controlling muscle movement.
Some are sensory nerves, conveying information from the sense organs.
䐥
Others contain fibers for both sensory and motor impulses.
How the Brain works .
the brain functions through nerve cell circuits.
Communication between neurons is both electrical and chemical.
Chemicals called neurotransmitters carry signals from one neuron to another.
One neuron may communicate with thousands of other neurons, and many thousands of neurons are involved in even the simplest
behavior.
Each brain hemisphere is specialized and dominates the other in certain functions.
䤢 dominates
This dominance is related to whether a person is predominantly right-handed or left-handed.
𐖨
In most right-handed people, the left hemisphere processes arithmetic, language, and speech.
the right hemisphere interprets music, complex imagery, spatial relationships, and emotions.
In left-handed people, the pattern of brain organization is more variable.
Brain Disorders Brain disorders have a wide range of causes, including head injury, stroke, bacterial diseases, chemical imbalances,
and changes associated with aging.
After a head injury, a person may be stunned or become unconscious for a moment.
This injury is called a concussion.
A more severe injury may cause headache, dizziness, paralysis, or a convulsion.
䑓
Damage to the cerebrum may cause profound personality changes.
䑓
An injury to a part of the hypothalamus may cause a variety of different symptoms, including loss or increase of appetite,
extraordinary thirst, failure in body-temperature control, and excessive emotionality.
䥐
䑓
If the relationship between the hypothalamus and the pituitary gland is damaged (see Endocrine System), other vital bodily functions
may be disturbed.
)
(
An injury to the brain stem is even more serious, because nerve centers there control breathing and the heart.
쑨
A stroke is damage to the brain due to an interruption in blood flow.
the interruption may be caused by a blood clot (see Embolism;
䑓 Embolism (
Thrombosis), constriction of a blood vessel, or rupture of a vessel accompanied by bleeding.
(
When the blood supply to a part of the brain is interrupted, the cells in that area die, and the function is lost.
A massive stroke can cause one-sided paralysis on the side of the body opposite the brain hemisphere damaged by the stroke.
拉
䑓
Epilepsy is a broad term for a variety of brain disorders involving convulsions.
Cerebral palsy is a broad term for brain damage that permanently affects motor function.
A bacterial infection in the cerebrum (see Encephalitis) or in the coverings of the brain (see Meningitis), an abnormal growth of
healthy brain tissue (see Tumor), or a swelling of the brain can all cause serious brain damage.
( ) (
( Tumor ( ꑓ )
䑓
Some brain diseases, such as multiple sclerosis and Parkinson's disease, are progressive, becoming worse over time.
[]
Problems common in aging include Alzheimer's disease, which damages many areas of the brain.
Brain Imaging .
Several commonly used diagnostic methods give images of the brain without invading the skull.
Magnetic resonance imaging (MRI) provides detailed images of the brain.
( )
Computed tomography (CT) X-rays the brain from many different angles, feeding the information into a computer that produces a
series of cross-sectional images.
㪐 ) CT ( ꐤ
()
CT is particularly useful for diagnosing blood clots and brain tumors.
Ct
Brain imaging studies have provided new insights into sensory, motor, language, and memory processes, as well as into brain
disorders.
()
() ꑟ
Evolution of the Brain .
In vertebrates, the brain is divided into three regions:
: 믑 ()
forebrain, midbrain, and hindbrain.
Brain structure is more complex in highly evolved animals.
Human beings have the most complex brains of all animals .
Evolutionary forces have also resulted in a progressive increase in brain size.
In vertebrates lower than mammals, the brain is small.
In meat-eating animals, particularly primates, the brain increases dramatically in size.
Heart, hollow muscular organ that receives blood from the veins and propels it through the arteries.
propels
In human beings, the heart is located behind the lower part of the breastbone, slightly to the left of center.
얪
Structure and Function .
the heart is a dual pump circulating blood through two separate systems, each consisting of an atrium and a ventricle.
the heart contracts and relaxes the walls of the atria and ventricles to circulate the blood.
atria
Blood is carried to the heart's right atrium through two large veins:
: 拉 ()
the superior vena cava and the inferior vena cava.
the right atrium contracts, transferring the blood to the right ventricle, which sends it to the lungs.
ꨤ
After the blood receives oxygen from the lungs, it returns to the heart's left atrium.
() ꨤ
the left atrium contracts, forcing the blood into the left ventricle and then into the aorta, which passes the blood throughout the body
(see Circulatory System).
() ()
( (
Valves at the openings of the arteries prevent blood from flowing backward.
()
the rate of heartbeat is controlled by the autonomic nervous system.
the heart produces two sounds in each cycle of the beat.
the first, rather dull, coincides with ventricular contraction.
듯 袐
the second, short and sharp, is caused by the sudden closing of the valves.
䑓
Heart Diseases .
Disorders of the heart are caused by birth defects, infection, narrowing of the coronary arteries, high blood pressure, or disturbances
of heart rhythm.
쥐
䑓
A major form of heart disease is atherosclerosis.
In this condition, fatty deposits called plaque build up on the inner wall of the coronary arteries, which supply the blood to the heart
muscle.
鑬 ꐓ
Gradual narrowing of the arteries restricts blood flow.
the plaque may become large enough to obstruct the coronary artery completely, causing a sudden decrease in oxygen supply to the
heart.
拉 鑬
Obstruction can also occur when part of the plaque breaks away and lodges farther along in the artery (see Thrombosis).
鑬
( )
These events are the major causes of heart attacks .
Surgical procedures have been developed to treat heart disease.
In a coronary bypass, a section of vein from the leg is sewn into a blocked coronary artery to form a bridge around the affected area.
() 둨
鐤
In balloon catheterization, a wire with a balloon on the tip is inserted into an artery in the leg and threaded through the aorta into the
coronary artery.
둨 ()
()
When the balloon reaches the blocked area, it is inflated.
This action compresses the plaque and reestablishes normal blood flow.
鑬
In many heart attacks, death follows ventricular fibrillation, also called cardiac arrest, which is rapid ineffective beating of the
ventricles.
fibrillation
A massive electric shock to the chest can often restore a normal heart rhythm.
拉
Severe defects in heart rhythm from other causes can produce dizziness, faintness, and eventually death.
䥐
the most serious of these conditions is called complete heart block.
It can be corrected by inserting an artificial pacemaker, a device that gives timed electric shocks to make the heart muscle contract in
a regular pattern.
쑓
Heart Transplants .
In 1967 South African surgeon Christiaan Barnard performed the first heart transplant surgery, placing a heart from one person into
the body of another.
()
This procedure has become more common as pharmaceutical aids have been developed to reduce the negative response of the
immune system to transplant surgeries.
see Transplantation, Medical .
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