Transcript Why is Our Immune System Important?

WHY IS OUR IMMUNE SYSTEM IMPORTANT?
One of the best known examples of the importance of the immune system is the “Bubble Boy” or David Vetter.
David was born on September 21, 1971.
Even before he arrived, his parents and physicians were making extraordinary arrangements for his life. David
had an older brother who died of Severe Combined Immune Deficiency (SCID) before David was born. SCID is a
complete absence of an immune system. After the birth and death of one son with SCID, the Vetters opted to
try a new approach to ensure David's well-being until an effective scientific option to reconstitute his immune
system became available.
They agreed to place David into a specially designed plastic-enclosed environment immediately after birth.
The bubble was complete with filtered air and strict antiseptic precautions to ensure no germs could enter and
infect David. The plastic incubator (later replaced by a plastic-enclosed "room") became popularly known as
David's "bubble," and David was thus referred to as "the Bubble Boy."
INTRODUCTION TO PROTECTION & CONTROL
• What if diseases from all over the world were to attack your body and
your body was not about to fight them? You would probably die within
seconds or minutes.
• However, there is no reason to worry about such an occurrence because
our body has a highly specialized mechanism called the immune system,
which declares war on all disease causing organisms called pathogens.
The structure of our immune system is divided into two specially unique
defense armies.
• These are the Non-Specific defenses and the Specific defenses.
NON-SPECIFIC DEFENSE MECHANISMS
• The Non-Specific defense mechanisms is a defensive action that works against
a wide variety of invaders. Some apparent symptoms relating to this response
are redness, heat, swelling, and pain.
• These are the defence mechanisms that we are born with...that come
standard in our bodies. These include the barrier formed by our skin;
chemicals in perspiration, skin oil, saliva, tears, etc.; the hairs in our nostrils;
the ciliary escalator (the cilia and mucus that clean out dust and debris from
our lungs and trachea) in our respiratory tracts; the inflammatory response
which is the dilation of blood vessels and accumulation of WBCs at the site of
an injury (the signs of which are that the area is red, hot, and swollen); and
fever, a raised body temperature to inhibit the growth of pathogens.
• Note that a fever is caused by your body to inhibit the growth of bacteria,
etc., not by the “germs” themselves, per se.
There are four main strategies of non-specific defence mechanism:
1. Mechanical defence
• Nasal hairs filter the air that is drawn into the upper airways.
• Cilia which line the airways, sweep bacteria and other
particles away from the lungs.
2. Physical defence
• The skin made up of squamous epithelium forms a tough
impermeable barrier which normally keeps out bacteria and
viruses.
• Normally keeps out bacteria and viruses.
• The mucous membranes that line the entry points of the body
such as nose, eyes, mouth opening, airways, genital openings and
anus produce fluids and/or sticky mucus. This traps
microorganisms and stops them attacking the cells underneath.
3. Chemical defence
• Fluids such as sweat, saliva and tears contain chemicals that
create harsh environments for microorganisms. Sweat contains
lactic acid and the enzyme lysosome, both of which slow down
bacterial growth.
• Stomach acid kills many microorganisms that manage to get this
far.
• When we are injured, blood clots at the injury site, sealing the
breach to prevent entry of bacteria.
4. Biological defence
• Normally a vast number of non-pathogenic bacteria live
on skins and mucous membranes, also called as normal
microflora.
• These organisms do not harm the body but rather crowd
out harmful bacteria preventing them from gaining a foot
hold from launching a full- scale infection.
SPECIFIC DEFENSE MECHANISMS
• In cases where microorganisms get through the primary deterrents, there
is a back-up system: the specific defense mechanisms.
• This reaction is also referred to as the inflammatory response. Its purpose
is to comprise a specific defense measure against a pathogen.
• The specific defense system is not made up of actual organ structures, but
it is made up of billions of cells. Thus, the specific defense system is
known as a functional system, as opposed to an organ system.
• When microorganisms penetrate the skin or the epithelium lining
the respiratory, digestive, or urinary tracts, it results in
inflammation.
• Damaged cells release chemical signals such as histamine that
increase capillary blood flow into the affected area (causing the
areas to become heated and reddened).
• The heat makes the environment unfavorable for microbes and
raises the mobility of white blood cells. It also increases the
metabolic rate of nearby cells.
• Capillaries pass fluid into interstitial areas, causing the
infected/injured area to swell. Platelets move out of the capillary
to seal the wounded area.
INFLAMMATORY RESPONSE & IMMUNE RESPONSE
• When microorganisms penetrate the skin or the epithelium lining the
respiratory, digestive, or urinary tracts, it results in inflammation. This reaction
is called the inflammation response.
• Damaged cells release chemical signals such as histamine that increase capillary
blood flow into the affected area (causing areas to become heated and
reddened.) The heat makes the environment unfavorable for microbes and
raises the mobility of white blood cells.
• It also increases the metabolic rate of nearby cells. Capillaries pass fluid into
interstitial areas, causing the infected/ injured area to swell. Platelets move out
of the capillary to seal the wounded area.
The main symptoms of the inflammatory response are as follows:
• The tissues in the area are red and warm, as a result of the large
amount of blood reaching the site.
• The tissues in the area are swollen, again due to the increased
amount of blood and proteins that are present.
• The area is painful, due the expansion of tissues, causing
mechanical pressure on nerve cells, and also due to the presence
of pain mediators.
HOW DOES THE INFLAMMATORY RESPONSE END?
• Obviously, the inflammatory response should only last for
as long as the infection exists. Once the threat of infection
has passed, the area should return to normal existence.
• The actual process by which the inflammatory response
ends is now only beginning to be understood. The key
element is a phenomenon known as "Apoptosis".
THE IMMUNE RESPONSE
• The immune system also generates specific responses to specific invaders,
such as bacteria, viruses, and substances that appear foreign and harmful
to the body. A specific defense mechanism builds up resistance against a
specific pathogen or antigen.
• This system is more effective than the nonspecific methods as it has a
memory component that improves response time when an invader of the
same type (or species) is again encountered. Specific defenses are tailored
to an individual threat. Two types of specific defenses are antibodymediated and cell-mediated responses.
CELL-MEDIATED IMMUNITY
• Cell-mediated Immunity requires direct physical contact with antigens.
• It is provided by T cells and does not involve the secretion of antibodies.
• T cells are involved in the attacking of certain bacteria, viruses, fungi and
immunity to cancer cells.
1. macrogphages engulf invaders
2. antigens appear on macrophage surface
3. Helper T-cells bind to macrophage surface sending out
chemical messages
4. T-cells multiply and get specific Killer T-cells to come help
5. T-cells attaches to infected cell and kills them with chemicals
6. Killer T-cells move them on to additional targets
ANTIBODY-MEDIATED (HUMORAL) IMMUNITY
• Antibody-Mediated (Humoral) Immunity results from the production
of antibodies specific to a given antigen (antibody-generators, located
on the surface of an invader).
• Antibodies bind to the antigens on invaders and kill or inactivate
them in several ways. Most antibodies are themselves proteins or are
a mix of protein and polysaccharides.
• Antigens can be any molecule that causes antibody production.
• Antibody-mediated immunity is provided by the B cells (a specific type of
white blood cell called macrophages). Within a few days after an infection, an
antigen causes the production of large amounts of the antibody capable of
interacting with it.
• Stages in this process are:
1. antigen detection
2. pathogen activates specific B cells
3. macrophages activate helper T cells
4. B cells and T cells meet and B cells produce antibodies or memory cells
5. antibody's "tag" invaders for further elimination
• Each stage is directed by a specific cell type.
Killer T-Cells
• Defends the body by destroying foreign,
infected, and cancerous cells.
• A cell infected with a virus will display viral
antigens on its membrane.
• Killer T-cells recognize the viral antigens
and attach to that cell's plasma membrane.
• The T-cells secrete proteins that punch
holes in the infected cell's plasma membrane.
• The infected cell dies.
Helper T-Cells
• Regulate immune responses
• Enabling the other T-cells and B-cells to perform their functions by
secreting messenger proteins or by direct contact with other cells.
• It is this cell that is destroyed by the HIV virus in patients with Acquired
Immune Deficiency Syndrome (AIDS)
Memory Cells
• Remain in the body awaiting reintroduction of the antigen.
VACCINATION
• Vaccination is a term derived from the Latin vacca (cow, after the cowpox
material). A vaccine stimulates the antibody production and formation of
memory cells without causing the disease.
• Vaccines are made from killed pathogens or weakened strains that cause
antibody production but not the disease. Vaccines exist for all sorts of
diseases, both viral and bacterial: measles, mumps, whooping cough,
tuberculosis, smallpox, polio, typhoid, etc.
Vaccination Schedule
2, 4, 6 months
12 months
18 months
4-6 years
Grade 5
Grade 9
Yearly
Every 10 years
Diphtheria, whooping cough, lockjaw, polio, influenza type B,
pneumococcal infections
Measles, mumps, German measles, chickenpox, meningitis
Two booster needles to continue protection
Diphtheria, tetanus, whooping cough, polio, measles, mumps,
rubella
Hepatitis B, Human Papillomavirus (girls only), meningitis
Diphtheria, tetanus, whooping cough, HPV (girls only),
meningococcal conjugate
Influenza (high risk groups)
Booster dose: tetanus, diphtheria
TYPES OF IMMUNITY
Active Immunity
• Active Immunity develops after an illness or vaccine. Vaccines are weakened
(or killed) viruses or bacteria that prompt the development of antibodies.
Passive Immunity
• Passive Immunity is the type of immunity that is short-lived, usually only lasting
a few weeks. It is given to combat a specific disease. Examples include:
• A mother's breast milk contains antibodies received by the baby. These only
last several weeks
• Gamma Globin shot is purely an injection of antibodies to provide temporary
immunity. You might receive a Gamma Globin shot if you travel outside the
country.
ALLERGIES
• An allergy is an abnormal high sensitivity reaction to an ordinarily harmless substance. The
immune system of an allergic person reacts when an allergen (antigen that triggers the allergic
reaction) is absorbed into the body, treating the substance as a harmful invader, causing the
white blood cells to being producing antibodies.
The most common allergies include:
• pollens
• molds
• insect stings
• household dust mites
• animal dander
• foods
• medication
• insect droppings
• An extreme, life-threatening allergic reaction usually to food,
medication or insect bites is called an anaphylactic reaction.
• It can result in breathing problems, dizziness, hives, a sudden drop in
blood pressure, an asthma attack, or unconsciousness. It can be fatal.
• It must be treated promptly. An emergency kit containing epinephrine
(adrenaline) is usually used by patients prone to these attacks.
• It counters the fatal effects by working directly on the cardiovascular
and respiratory systems. It also rapidly constricts blood vessels, relaxes
muscles in the lungs to improve breathing, reverses swelling, and
stimulates the heartbeat.
THE LYMPHATIC SYSTEM
• The lymphatic system can be thought of as a secondary circulatory system.
• The lymph vessels contain a clear, colorless fluid called lymph, which is
derived from a network of capillaries which collect this clear fluid as it
filters through the capillaries of the blood.
• The lymphatic system provides our immune defenses, filters foreign
substances and cell debris from the blood and destroys them; and
produces a type of white blood cells known as lymphocytes, which
circulate in the blood and lymph vessels.
• Lymph passes from tiny capillaries to lymph vessels and flows through
lymph nodes that are located along the course of these vessels.
• Cells of the lymph nodes phagocytize, or ingest bacteria, old red blood
cells, and toxic and cellular waste.
• Finally, the lymph flows into either the thoracic duct, a large vessel that
runs parallel to the spinal column, or into the right lymphatic duct, both of
which transport the lymph back into veins of the shoulder areas where is
re-enters the general circulation.
• All lymph vessels contain one-way valves, like the veins, to prevent
backflow.
• In an infection, the lymph nodes occasionally become enlarged with lymph
and white blood cells and become palpable (can be felt by an examiner).
These can be felt most easily at the neck, in infections of the neck and
head; in the axillary region (the armpit), in infections of the breast or arm;
and in the inguinal region (the groin), in infections of the pelvis or lower
extremities.
• The tissues of the lymphatic system include the spleen, thymus, bone
marrow, and aggregates of lymphatic tissue located in the tonsils and
intestines.
• The spleen, thymus, and bone marrow manufacture
lymphocytes, which are the major cell type of the system.
• Lymphocytes arise from by mitosis of stem cells in the bone
marrow.
• Stem cells differentiate into the major players in the immune
system (granulocytes, monocytes, and lymphocytes).
• The spleen is also involved in the
destruction of old cells and other
substances by phagocytosis and
plays a role in immune responses.
• The thymus is considered the central
organ that controls lymphocyte
production and antibody formation.
• Lymphocytes can be classified as
T cells (thymus-derived) or B cells
(bone-marrow-derived). Other cells
of the lymphatic system include
monocytes, which function to ingest
foreign substances. Monocytes are
believed to originate from
lymphocytes.
BLACK
GREEN
YELLOW
BROWN
PINK
WHITE
RED
BLUE
PURPLE
ORANGE
BLACK
GREEN
YELLOW
BROWN
PINK
WHITE
RED
BLUE
PURPLE
ORANGE
You probably noticed that it is rather tough to say the
names of the colors very fast, since your brain is also
reading the text, which is almost unavoidable...The right
half of your brain is trying to say the colors, the left half is
trying to say the word itself.
THE NERVOUS SYSTEM
• Your nervous system coordinates and controls the essential functions in
your body. It receives and relays information about activities within your
body and monitors and responds to internal
and external changes.
• You can think of your nervous system as a communication system by with
the various cells and parts of your body interacting with the outside world.
• Without your nervous system you would be incapable of responding to
changes inside and outside your body. In other words, you would be
unable to maintain homeostasis
CNS
• The Central Nervous System consists of the Brain and Spinal Cord. It
contains millions of neurons (nerve cells).
• If you slice through some fresh brain or spinal cord you will find some areas
appear grey whilst other areas appear rather white. The white matter
consists of axons, it appears white because it contains a lot of fatty material
called myelin.
• The myelin sheath insulates an axon from its neighbours. This means that
nerve cells can conduct electrical messages without interfering with one
another.
• The grey matter consists of cell bodies and the branched dendrites which
effectively connect them together.
• Different areas of the brain are concerned with different functions. For
example, you "see stars" when you bang your head and stir up the visual
centre which is at the back of your brain.
• There are areas of the brain which deal with speech, hearing, smell, sight,
movements, salivating, and so on.
• Some of these centres are concerned with the information coming into the
brain (sensory areas) and others are concerned with making something
happen (motor centres).
• What do you do when you bite into a ripe apple? Do you wiggle your toes
or salivate?
• Some responses are very simple and everyone makes the same response:
e.g. we all sneeze when our noses are tickled.
• Other stumuli are much more complicated and we do not all react or
respond in the same way.
PNS
• The Peripheral Nervous System consists of all the sensory nerves (these
feed information into the spinal cord and brain) and the motor nerves
(these carry messages to other parts of the body from the brain and spinal
cord).
• Sensory nerves contain sensory neurones. Motor nerves contain motor
neurones. Mixed nerves contain both sensory and motor neurones.
• Sensory neurones are usually connected to motor neurones by
intermediate neurones (sometimes called inter neurones).
• Sensory, intermediate and motor nerves have gaps between them called
synapses.
• The Central Nervous System is divided into the somatic nervous system
and the autonomic nervous system.
• The somatic nervous system controls skeletal muscle as well as external
sensory organs such as the skin. This system is said to be voluntary because
the responses CAN be controlled consciously.
• Reflex reactions of skeletal muscle however are an exception. These are
involuntary reactions to external stimuli.
• The autonomic nervous system controls involuntary muscles,
such as smooth and cardiac muscle.
• This system is also called the involuntary nervous system.
• The autonomic nervous system can further be divided into the
parasympathetic and sympathetic divisions.
• The parasympathetic division controls various functions which
include inhibiting heart rate, constricting pupils, and contracting
the bladder.
• The nerves of the sympathetic division often have an opposite
effect when they are located within the same organs as
parasympathetic nerves.
• Nerves of the sympathetic division speed up heart rate, dilate
pupils, and relax the bladder.
• The sympathetic system is also involved in the flight or fight
response.
• This is a response to potential danger that results in accelerated
heart rate and an increase in metabolic rate.
THE BRAIN
The Cerebrum
• The cerebrum or cortex is
the largest part of the
human brain, associated
with higher brain function
such as thought and action.
The Cerebellum
• The cerebellum, or "little brain", is
similar to the cerebrum in that it
has two hemispheres and has a
highly folded surface or cortex. This
structure is associated with
regulation and coordination of
movement, posture, and balance.
Medulla Oblongata
• This structure is the "tail"
part of the brain stem,
between the pons and
spinal cord. It is
responsible for maintaining
vital body functions, such
as breathing and heart
rate.
Pons
• Part of the hindbrain. It is
involved in motor control
and sensory analysis. It
has parts that are
important for the level of
consciousness and for
sleep.
Corpus Callosum
• Is a bundle of axons which
connects the two
hemispheres.
Frontal Lobe- associated
with reasoning, planning,
parts of speech, movement,
emotions, and problem
solving
Parietal Lobe- associated
with movement, orientation,
recognition, perception of
stimuli
Occipital Lobe- associated
with visual processing
• Temporal Lobe- associated
with perception and
recognition of auditory
stimuli, memory, and
speech
RIGHT-BRAINED & LEFT-BRAINED
• The term was coined by psychologist Julian Jaynes, who presented the idea
in his 1976 book The Origin of Consciousness in the Breakdown of the
Bicameral Mind.
• The right hand and eye could name an object, such as a pencil, but the
patient could not explain what it was used for.
• When shown to the left hand and eye, the patient could explain and
demonstrate its use, but could not name it.
• Further studies showed that various functions of thought are physically
separated and localized to a specific area on either the left or right side of
the human brain. This functional map is consistent for an estimated 70 to
95 percent of us.
NERVE IMPULSES
• One of the basic life functions of all living things is the ability
to respond to a stimulus. There are many stimuli to which an
organism must respond: a change in air temperature, a
change in carbon dioxide level in the blood, contact with a hot
or sharp object, the itch at the end of your nose, the hardness
of your chair, the cramp in your leg, a feeling of hunger, and
many more that have not been mentioned.
• There are three main types of structures related to stimuli
and responses. Each has a specific function in relation to
the others.
• The three structures are receptors, neurons, and
effectors.
• A receptor is a kind of sensor that picks up information about an
organism's internal or external environment.
• Receptors may be neurons themselves, or they may be organs
that are specialized for detecting stimuli.
• A receptor picks up a certain kind of stimulus. For example, the
eye is a receptor that is sensitive to light, but not to odour.
• A neuron is a specialized cell that transmits
electrochemical messages, or nerve impulses, from the
receptors to the effectors.
• An effector is a structure that responds when it is
stimulated by nerve impulses.
• The principal effectors are muscles and glands. Muscles
respond by contracting; glands respond by secreting.
• The human nervous system is made up of 10 to 12 billion nerve
cells called neurons.
• Some neurons, such as those in the brain, are a fraction of a
centimeter in length. Others, such as those that run through the
legs, are as long as a meter, going from the toes to the spinal
cord.
• A neuron has several distinct parts, as shown below.
• The cell body of the neuron contains the nucleus and most of the
cytoplasm known as soma. Soma flows into the extensions. The shape of
the cell body varies. Some are round, while others resemble a diamond or
are irregular in shape.
• Nerve fibers extend from the cell body. These fibers contain one long fiber,
the axon, and one or more short fibers, the dendrites. A neuron can have
as many as 200 dendrites. While the dendrites are shorter than the axon,
they branch extensively because their function is to pick up impulses,
either from receptors or other neurons in the vicinity, and conduct them
toward the cell body.
• The axon carries the impulses away from the cell body, passing it on to
other neurons or cells.
• The axons of many neurons are covered with a white, fatty protein known
as myelin sheath.
• The main function of this sheath is to insulate the axon, preventing the loss
of chemical ions that are present in the nerve fiber. Since these ions are
necessary for the transmission of impulses along a nerve cell, the presence
of a myelin sheath increases the speed of transmission.
• The myelin sheath is formed of flat Schwann cells, which are wrapped
around the axon like a jellyroll. In myelinated axons, gaps that are not
covered with the myelin sheath are called nodes of Ranvier.
• Nerve impulses jump from node to node, resulting in transmission up to 20
times faster than in nonmyelinated axons.
• Biologists classify neurons according to their function. There are
sensory neurons, associative neurons, and motor neurons.
• Sensory neurons transmit impulses from receptors to the brain or
spinal cord. These pick up the stimuli of sight, smell, sound, taste,
and touch. Sensory neurons are important in carrying messages
about a person's internal or external environment.
• Associative neurons, (also called interneurons or association
neurons) found only in the brain, ganglia, or spinal cord, are
responsible for coordinating nervous activity (they “decide” what
to do) and relaying the messages from the sensory neurons to the
proper motor neurons to effect an appropriate action by the
effectors (muscles and glands).
• Motor neurons receive messages from the associative
neurons in the brain and spinal cord and activate the
muscles and glands (the effectors).
• A nerve is a bundle of nerve fibers (axons) bound together by a sheet of
connective tissue.
• Nerves consist primarily of axons of neurons.
• The cell bodies of those neurons are gathered together into groups.
• A group of cell bodies that is located outside the brain or spinal cord makes
up a ganglion.
• A group of cell bodies that is inside the brain or the spinal cord is referred
to as a nerve center.
• Within the brain and spinal cord, the myelinated fibers form areas referred
to as white matter. The cell bodies of the neurons and unmyelinated fibers
make up the gray matter of the brain and spinal cord.
The Synapse
• Because one neuron does not touch
another, there is no contact between
them, and the electrochemical impulse
cannot pass directly from one nerve
cell to another. The microscopic space
that exists between the axon of one
neuron and the dendrite of another is
called a synapse.
• An axon ends in many small fibers. The endings of axons (synaptic
knobs) have cytoplasmic vesicles called synaptic vesicles inside
them.
• These tiny sacs are filled with compounds called transmitter
substances (also known as neurotransmitters).
• Neurotransmitters include the following compounds:
acetylcholine, noradrenalin, dopamine and serotonin.
• When an impulse reaches the end of an axon, it stimulates the
synaptic vesicles to release their transmitter substance into the
synapse.
• The substance, acetylcholine, for example, diffuses across the synapse
to the dendrite of the adjacent neuron.
• The acetylcholine combines with the receptor molecules in the cell
membrane of the dendrite or cell body of the next neuron, increasing
the permeability of the membrane at that point on the second neuron
to sodium ions, and reversing the polarization of the membrane.
• The electrochemical impulse starts on its way along that neuron.
• Transmission of acetylcholine from a motor neuron axon to a muscle
cell (across a neuromuscular junction) stimulates the muscle cell to
contract.
• Enzymes destroy the transmitters shortly after they are released
into the synapses and neuromuscular junctions.
• Acetylcholinesterase, for example, digests acetylcholine to acetic
acid and choline. These compounds diffuse back into the axon
where they are used again in the synthesis of acetylcholine.
• If the excess transmitter substances were not broken down by
enzymes, they would continue to initiate impulses in dendrites
indefinitely and cause muscles to contract continuously.
• When an effector responds to an impulse as described previously, the
response is called a reflex act.
• A reflex act is an automatic or involuntary action, which is always the same
when a particular stimulus is involved.
• The closing of the pupil of the eye in response to bright light or the rapid
withdrawal of the hand after touching something hot, are both examples of
the reflex act.
• Reflex activity is predictable; it provides a rapid reaction protecting the
body from harm. Reflex acts occur in a fraction of a second, before a
person has time to think consciously about what appropriate action is
required.
• A reflex arc is initiated by stepping upon a sharp stone. Impulses,
started by receptors in the toe, travel along sensory neurons to
the spinal chord, where associative neurons are stimulated.
• The impulses are "switched" to other neurons—among them
motor neurons that stimulate leg muscles to contract and move
the foot away from the rock.
• Impulses going from the injured toe to the spinal cord result in
reflex movement, but also travel up nerve pathways to the brain.
• Associative neurons in the brain are activated. Impulses may pass
from the brain to many parts of the body, leading to voluntary
movement.
• The reflex arc consists of five parts, which usually involve three
neurons (two or more than three are quite common). The reflex
arc requires:
• Receptor. The receptor recognizes some change in the
environment, whether heat, light, sound, or some other factor.
The receptor is stimulated to initiate a nervous impulse.
• Sensory neuron. The sensory neuron conducts the impulse from
the receptor to the spinal cord.
• Associative neuron. The associative neuron directs the impulse
from the sensory neuron to the motor neuron. It allows the
impulse to be routed into a number of possible pathways.
• Motor neuron. The motor neuron carries the impulse to the
appropriate organ (usually a muscle) to produce the response.
• Effectors. The effector is the muscle or organ that will contract or
otherwise respond appropriately to the stimulus.
• When a doctor wants to check your reflexes, he
sometimes strikes the tendon just below the knee cap
with his little rubber hammer. He watches to see if your
lower leg moves forward immediately. If it does, all is well.
• This forward movement of the lower leg is a reflex act and
happens involuntarily.
• The rubber hammer strikes the tendon, pulling it down, and
stretches the muscles in the upper thigh.
• The stretch receptors, being embedded in the thigh muscles, pick
up the stimuli. Let us follow the path of an impulse generated by
only one receptor through the reflex arc to one effector.
• Provided the stimulus has exceeded the receptor's threshold, an
impulse will be initiated there and propagated along a sensory
neuron.
The impulse travels to the spinal cord. At this point, the synaptic
knobs on the axon's end fibers stimulate their synaptic vesicles to
release acetylcholine into the synapse between them and the
dendrites of associative neurons (sometimes called interneurons).
One associative neuron takes the impulse to the brain; a second,
using the same method of impulse transfer as related above, takes
the impulse directly to a motor neuron's dendrites. The impulse
propagates itself along the axon of the motor neuron. When the
impulse reaches the motor end plates at the end of the neuron,
they are stimulated and cause contraction of the upper thigh
muscle (the effector), which moves the lower leg forward. Because
of this quick responding reflex act, your leg responds to the tap of
the hammer even before you are aware of the pain.
THE ENDOCRINE SYSTEM
• As we have learned, the nervous system communicates
information about activities within your body and monitors and
responds to internal and external changes. The endocrine system
is the system of the body that deals with chemical communication
by means of hormones, the ductless glands that secrete the
hormones, and those target cells that respond to hormones. The
foundations of the endocrine system are the hormones and
glands.
• The endocrine system functions in maintaining the basic functions of the
body ranging from metabolism to growth.
• Both systems are essential in the maintenance of homeostasis.
• The nervous system acts very quickly, but its effects are short-lived.
• The endocrine system reacts more slowly to a change in the body, but its
effects last longer.
Hormones
• Hormones are chemical messengers released by specialized
endocrine cells or specialized nerve cells.
• They transfer information and instructions from one set of cells to
another. Although many different hormones circulate throughout
the bloodstream, each one affects only the cells that are
genetically programmed to receive and respond to its message.
• Hormone levels can be influenced by factors such as stress,
infection, and changes in the balance of fluid and minerals in
blood.
• A gland is a group of cells that produces and secretes, or gives off,
chemicals.
• A gland selects and removes materials from the blood, processes
them, and secretes the finished chemical product for use
somewhere in the body.
• Some types of glands release their secretions in specific areas. For
instance, exocrine glands, such as the sweat and salivary glands,
release secretions in the skin or inside of the mouth.
• Endocrine glands, on the other hand, release more than 20 major
hormones directly into the bloodstream where they can be
transported to cells in other parts of the body.
The Neuroendocrine System
• The endocrine system and the nervous system are so closely
associated, that they are collectively called the neuroendocrine
system.
• Neural control centres in the brain control endocrine glands. The
main neural control centre in the brain is the hypothalamus.
• Suspended from the hypothalamus by a thin stalk is the pituitary
gland.
• The hypothalamus sends messages to the pituitary gland, which
then releases hormones that regulate body functions.
Pituitary Gland
• The pituitary gland is found on a small stalk at the base of the brain. It
controls the action of all other endocrine glands and is therefore often
referred to as the “master gland”.
• It is composed of two separate halves: the posterior lobe which is derived
from brain tissue and the anterior lobe which is derived from epithelial
tissue of the roof of the mouth.
• The posterior lobe of the pituitary gland secretes two hormones which are
manufactured by specialized neurons of the hypothalamus and stored in
the posterior lobe.
• These hormones are oxytocin and antidiuretic hormone (ADH), also
known as vasopressin.
• Oxytocin causes contractions of the smooth muscle in the uterus during
childbirth. It is also important in the transport of milk from the glands to
the nipple. In males, it is needed to stimulate muscles of the sperm duct to
propel the sperm out of the body.
• Antidiuretic hormone (ADH) controls the elimination of water from the
kidneys. If water concentration in the body decreases, the amount of ADH
released into the bloodstream increases.
• More water is reabsorbed by the kidneys and retained in the body. If the
hypothalamus does not produce ADH in sufficient quantities, a condition
called diabetes insipidus results as the body eliminates too much water.
ADH also influences blood pressure by causing the small arteries to
contract.
Nervous System
Endocrine System
How It
Communicates
Impulse across synapses
Hormones in blood
Response Speed
Responds very rapidly
Responds slowly
How Long It Lasts
(Duration)
Short-term and reversible
effects
Longer lasting effects
Where Does It
Go?
Signal runs through nerves
to specific cells
Hormones broadcast
to target cells
everywhere
What Does It
Do?
Causes glands to secrete or
muscles to contract
Causes changes in
metabolic activity
Protecting Your Head!
• Sports injuries that affect the central and peripheral nervous
system are responsible for thousands of deaths or permanent
peripheral damage in Canadian youth.
• A concussion is caused by the brain being subjected to a trauma
where it twisted. Often both brain cells and blood vessels that
feed the brain are affected. Blood flow to the brain is restricted by
the increase in pressure due to swelling. This results in an "energy
crisis" in the brain that can last for weeks.
• The brain floats in cerebrospinal fluid and is encased in the skull. These
protections allow it to withstand many of the minor injuries that occur in
day to day life.
• However, if there is sufficient force to cause the brain to bounce against the
rigid bones of the skull, then there is potential for injury.
• It is the acceleration and deceleration of the brain against the inside of the
skull that can cause the brain to be irritated and interrupt its function. The
acceleration can come from a direct blow to the head or face, or from
other body trauma that causes the head to shake
• If a second concussion occurs before the brain recovers from the
first one, the energy-starved cells in the brain are likely to die, and
individuals may experience a life-threatening swelling of the
brain, referred to as second impact syndrome (SIS).
• Half of individuals with SIS die, and it is most common in male
adolescents and young adults. The long term effects of
concussions vary from negligible to cognitive and behavioural
impairments, and may depend on the number of concussions.