Ch. 11. Human Body Systems

Human Body Systems

Structural Hierarchy of Animal Bodies

• Animal bodies are organized into a structural hierarchy:
  • Cell: The fundamental unit of life.
  • Tissues: Groups of similar cells performing a specific function.
  • Organs: Structures consisting of different tissues working together.
  • Organ Systems: Groups of organs coordinating to perform major bodily functions.
  • Organism: The complete, integrated living being.
• Studying these structural levels provides insights into both form and function.
• Form Correlates with Function:
  • Anatomical structures (form) inform our understanding of physiological action (function), and vice versa.

Anatomy vs. Physiology

• Anatomy: The study of the structure of an organism’s body parts (its form).
• Physiology: The study of the functions of those parts.

Organization of the Human Body

• Individual cells are organized into larger working units, progressing from cells to tissues and then to organ systems, eventually forming the entire body.

Major Tissue Types in the Human Body

• Cells work cooperatively as part of a tissue.
• Each tissue consists of similar cells working together to perform a specific function.
• Most animal bodies contain multiple types of tissues.
• Cell: The fundamental unit of life.

Connective Tissue

• Supports, connects, or binds different parts of the body.
• Examples: cartilage, blood, bone.
• Consists of cells scattered throughout an extracellular matrix that helps hold cells together.

Epithelial Tissue (Epithelium)

• Covers the whole surface of the body, including the digestive tract.

Nervous Tissue

• Communicates signals between the brain and the rest of the body.

Muscle Tissue

• Consists of bundles of long cells called muscle fibers.
• Muscle fibers contain specialized proteins that allow them to contract (shorten).
• Types:
  • Skeletal muscle: Attaches to bones.
  • Smooth muscle: Found in the digestive tract and blood vessels.
  • Cardiac muscle: Found in the heart.

Maintaining Internal Conditions

• The animal's internal environment remains relatively constant.
• Your body exchanges chemicals and energy with the environment.
• The body maintains nearly constant internal conditions despite the variability of the external environment.
• Homeostasis: The tendency to maintain a constant internal environment.
• Maintained by negative feedback or, less commonly, positive feedback.

Blood Glucose Levels

• Eating causes blood glucose levels to spike.
• Insulin production lowers blood glucose levels.
• Animal bodies tend to maintain relatively constant blood glucose levels.

Diabetes: Breakdown in Homeostasis

• Diabetes causes blood glucose levels to spike higher.

• Poor insulin production results in a very elevated blood glucose level.

• Type 1:

  • The body doesn’t produce enough insulin.
  • Requires insulin injection.

• Type 2:

  • Cells do not respond normally to insulin.
  • Regularly controlled with diet & exercise.

• Without insulin, the body can’t get enough glucose from the blood, causing levels to spike and drop.

Integumentary System and Temperature Homeostasis

• Integumentary system: skin, hair, nails that protect the body from physical harm.
• Skin structures that aid in temperature regulation:
  • Muscle shivers à heat
  • Fat à insulation
  • Blood vessels near the surface adjust blood flow à adjust heat loss
  • Sweat glands à evaporative cooling
  • Hair follicle & associated muscle à adjust fur coat à adjust insulation

Samples of Skin Structures:

*   Hair
*   Sweat pore
*   Epidermis
*   Oil gland
*   Dermis
*   Muscle
*   Hair follicle
*   Sweat gland
*   Blood vessels
*   Adipose tissue
*   Nerve

Homeostasis and Negative Feedback

• Negative feedback: a form of regulation in which the result of a process inhibits that very process.
• Most concerned with maintaining balance

Examples of Negative Feedback

• Body temperature regulation:
  • When body temperature rises above the normal state (37°C or 98.6°F):
    • Stimulus: Body temperature is above normal state.
    • Response: Sweat is produced, and blood vessels widen.
  • When body temperature drops below the normal state:
    • Stimulus: Body temperature is below normal state.
    • Response: Hairs stand, producing goosebumps, and blood vessels constrict.

Homeostasis and Positive Feedback

• Positive feedback: a form of regulation in which the results of a process intensify that same process.
• Most concerned with causing rapid, powerful changes.
• Example: uterine contractions during birthing.
• Stops with childbirth.

Examples of Positive Feedback

• Uterine contractions during childbirth:
  • Hormones affect the uterus more.
  • Uterus contracts.
  • Placenta makes more hormones.
  • Hormones stimulate more contractions of uterus.
  • Cycle ends once the childbirth is done

Positive-feedback loops are not as common within our bodies as negative-feedback loops.

Food Processing

• Food processing occurs via four stages:
  • Ingestion (eating)
  • Digestion (mechanical and chemical)
  • Absorption (primarily by cells lining the small intestine)
  • Elimination
    *Why chew your food before swallowing it?

Digestion

• Mechanical digestion: the use of physical processes to break down food into smaller pieces.
  • Chewing
  • Churning within in our stomachs
• Chemical digestion: the use of enzymes to perform hydrolysis, chemical reactions that use water to break bonds within large molecules.

Absorption and Elimination

• Absorption: the uptake of small nutrient molecules, primarily by the cells lining the extensive folds of the small intestine.
• Elimination: the disposal of undigested matter from the body.

The Human Digestive System

• The human digestive system is a long tube with specialized organs.
• Your “gut” is called the alimentary canal.
• At each stop along the alimentary canal, specific steps in the processing of food occur.

Alimentary Canal

• The alimentary canal starts at your mouth.
• The mouth, also called the oral cavity, is the site of ingestion & the first stages of digestion.
• At the pharynx, the epiglottis moves to cover the entrance to the trachea, directing food down the esophagus.

Esophagus and Stomach

• Food moves through the esophagus to the stomach via muscle contractions called peristalsis.
• Cells lining the stomach secrete gastric juice, containing enzymes (such as pepsin).

Small and Large Intestine

• Chemical digestion is completed & absorption occurs within the small intestine.
• Within the colon, the main portion of the large intestine, water is absorbed.
• Remaining waste is formed into feces and stored in the rectum.

Elimination of Waste

• Two sphincter muscles, one voluntary and the other not, regulate the opening of the anus.
• When the voluntary sphincter muscle is relaxed, feces are expelled.

Accessory Organs

• Accessory organs secrete specific digestive chemicals into the alimentary canal via ducts.
  • Salivary glands
  • The liver (produces bile that helps process fat digestion)
  • Gallbladder (stores bile)
  • Pancreas (helps neutralize stomach acid)

Human Nutrition

• Proper nutrition provides energy and building materials.
• Food provides energy (fuel).
  • Every cell requires a constant supply of energy in the form of the molecule ATP.
• Food provides the building materials needed for the body’s structures.
  • Essential nutrients are those that cannot be produced by the body itself.
• The potential energy in food is held in molecules like glucose.

Nutrients

• Food as Fuel: The glucose that serves as the input to cellular respiration is obtained by digestion of the food you eat.
• Four categories of essential nutrients:
  • Minerals: minerals are inorganic chemical elements required to maintain health.
  • Vitamins: a vitamin is an organic (carbon-containing) nutrient required in your diet, but only in very small amounts.
  • Essential fatty acids: essential fatty acids are required to build several important lipid-based molecules.
  • Essential amino acids: essential amino acids are required to build proteins.

Digestive System Ailments

• Many illnesses are caused by infection or malfunction of the digestive system.
  • Common ailments include:
    • Acid reflux
    • Appendicitis
    • Cholera
    • Ulcer

Health Problems from Improper Diets

• Obesity
  • Contributes to type 2 diabetes, cancer, and cardiovascular disease.
• Malnutrition
  • Is caused by a diet that lacks sufficient calories or essential nutrients.
• Eating disorders
  • Anorexia nervosa and bulimia can cause nutrient deficiencies and death.

Obesity and BMI

• Body Mass Index is the ratio of weight to height, obesity is an inappropriately high BMI

Gastric Bypass Surgery

• Most common weight loss surgery in US
• Small pouch is created in stomach, the rest is bypassed and small intestine is shortened
• Less absorption and patient fills full faster

The Respiratory System

• The respiratory system exchanges gases: $O<em>2$ into the body and $CO</em>2$ out.
• Due the branching of your airways, there is a tremendous surface area in your lungs.
• Breathing is the alternation of inhalation (in) and exhalation (out) of air from you lungs.

The Human Respiratory System

• Pharynx
• Larynx
• Trachea
• Bronchi
• Bronchioles
• Alveoli
• Diaphragm
• Nasal cavity

Breathing

• Inhalation: Air is inhaled.
  • Rib cage expands.
  • Diaphragm contracts (moves down).
  • Air pressure is higher in the external environment than in the lungs.
• Exhalation: Air is exhaled.
  • Rib cage gets smaller.
  • Diaphragm relaxes (moves up).
  • Air pressure is lower in the external environment than in the lungs.

Oxygen Delivery to the Body

• The circulatory system conveys oxygen from the lungs to body cells.
• Oxygen used as a final electron receptor
• $O<em>2$ à $H</em>2O$
• Air exchange occurs between the lungs and the surrounding blood vessels.

Gas Exchange

• The exchange of gases occurs between blood capillaries and alveoli (tiny air sacs) in your lungs.

Respiratory System Ailments

• Emphysema is often caused by long-term exposure to tobacco smoke or air pollution.
• Bronchitis is most commonly caused by a viral infection of the bronchioles.
• Asthma is a long-term inflammation of the airway.

The Circulatory System

• The circulatory system transports materials throughout the body.
• The heart pumps blood through a series of blood vessels.
• Blood carries nutrients and wastes.
• Your heart and blood vessels working together is your cardiovascular system.

Blood Vessels

• Three types of blood vessels make up the “plumbing” of your circulatory system:
  • Arteries (and smaller arterioles) carry blood away from the heart.
    • Thickest due to highest pressures
  • Veins (and smaller venules) carry blood to the heart.
    • Veins have valves to prevent backflow
  • Capillaries join arterioles to venules and exchange materials in the interstitial fluid.

Cardiovascular Circuits

• The human cardiovascular system can be organized into two circuits:
  • The pulmonary circuit shuttles blood from the heart to the lungs.
  • The systemic circuit shuttles blood from the heart to the rest of the body.

Heart

• The heart is the hub of the human circulatory system.
• Blood enters the heart at the atria, which pumps it a short distance to the ventricles.
• The ventricles then pump it out of the heart to the rest of the body.

Cardiac Cycle

• The cardiac cycle: a rhythmic contraction and relaxation of the heart.
  • Diastole: the heart muscles relax.
    • Low blood pressure value
  • Systole: the heart contracts.
    • High blood pressure value

Heartbeat Timing

• The timing of your heartbeat is set by a natural pacemaker
• The sinoatrial (SA) node is nervous tissue that times heartbeats.
• The SA node causes atria to contract (top down) and sends the signal to the atrioventricular (AV) node to signal the ventricles to contract (bottom up).

Cardiovascular System Ailments

• Hypertension (high blood pressure) increases the risk of heart attack, heart disease, and stroke.
• Heart disease often results from fatty deposits blocking the arteries and is the most common cause of death among Americans.
• Anemia occurs when the blood doesn’t carry enough oxygen.

Coronary Arteries

• If coronary arteries become blocked, heart muscle cells quickly die
• Coronary arteries supply the heart tissues with $O_2$ and energy
• Blockage is called a myocardial infarction, or heart attack. Buildup of fatty deposits, plaque, is usually the result of a gradual process called atherosclerosis.

Blood Composition

• Plasma = 52% water
• Blood = 3% Proteins, electrolytes, & substances being transported (such as $O<em>2$, $CO</em>2$, nutrients, wastes, hormones)
• Cellular elements make up just under half of the volume of blood.
• Blood = 44% Red blood cells
• Blood = 1% White blood cells & platelets
• Your blood consists of many small molecules and several types of cells dissolved in a liquid called plasma.
• Red blood cells transport oxygen using hemoglobin.
• White blood cells fight infections.

Oxygen Transport

• In the lungs, $O_2$ binds to a protein in your red blood cells called hemoglobin. Your blood is red because iron is bound to the heme group in the protein hemoglobin.

Blood Clotting

• Blood contains self-sealing substances that respond to injury
• Almost immediately after damage, platelets form a sticky plug that can seal a minor break.
• Molecules of fibrin cross-link to form a clot which, if on your skin, is called a scab.

Blood Clotting: Positive Feedback

• Damaged endothelial cells secrete chemical signals that attract and activate platelets.
• Clotting begins as activated platelets adhere to the wound site. Activated platelets then secrete more chemical signals.
• These signals attract and activate yet more platelets.
• Cycle ends once the wound is fully sealed.

The Immune System

• The immune system contains many defensive elements.
• Your immune system protects against pathogens using a large number and variety of defenses.
  • These include:
    • External barriers
    • The inflammatory response
    • Complement system proteins
    • White blood cells and the lymphatic system

External Barriers

• External barriers are your first line of defense against infections
  • Skin
    • Forms a protective outer layer that most viruses and bacteria cannot penetrate.
  • Hairs and cilia
    • Sweep particles outward until they can be expelled.
  • Mucous membranes
    • Secrete mucus, a sticky fluid that traps particles.
  • Gastric juice
    • Kills most of the bacteria you swallow.

Inflammatory Response

• The inflammatory response is a nonspecific defense against tissue damage
• The cells of a damaged tissue release chemicals (such as histamine) that trigger the inflammatory response.
• Blood vessels weaken, causing swelling.
• White blood cells called phagocytes engulf and destroy bacteria.

Complement System

• If an invader enters the body, the complement system can provide protection
• Proteins of the complement system assemble on the surface of an invading bacterial cell, forming a hole.
• This causes the bacterial cell to swell and eventually burst.

White Blood Cells

• White blood cells are a key part of your immune system
  • There are two types of white blood cells.
    • Innate cells are pre-made and ready to attack.
    • Lymphocytes are produced after contact with a specific invader.
• Phagocytic cells are innate and engulf foreign invaders.
• $T$ cells are lymphocytes that attack abnormal body cells.

The Lymphatic System

• The lymphatic system kicks into high gear when your body fights an infection
• The lymphatic system is a branching network filled with lymph fluid
  • Consist of Lymph nodes & lymphatic vessels
• Kicks into high gear with an infection
• Invading microbes are swept into lymph nodes, where they are attacked by lymphocytes (white blood cells).

Immune System Attacks

• The immune system mounts highly specific attacks against invaders
• Innate vs. adaptive defenses:
  • Adaptive
    • Slower response (a few days)
    • Invader recognition
    • Repeated exposure to molecules will cause increased responses
  • Innate
    • Immediate, rapid response
    • Physical barriers or inflammation
    • Generalized response, nonspecific

Recognizing Invaders

• Exposure to an antigen (e.g., invading bacteria), a molecule that elicits an immune response, starts your adaptive defenses.
• Your immune system can produce antibodies against millions of antigens
• Then, an activated $B$ cell produces antibodies, proteins that tag antigens.
• First, antigens bind to lymphocytes.$B$ cell
• à tag an invader or an infected cell for attack by other parts of the immune system
• à or can neutralize its target directly (for example, by inhibiting a part of a microbe that is essential for its invasion and survival).

Clonal Selection & Helper $T$ cells

• Clonal selection- Once an antigen activates a particular lymphocyte, it multiplies creating an army of cells when needed
• Helper $t$ cells- lymphocytes that stimulate production of other immune cells
  *Antigen molecules, such as pieces of an invading virus Antigens bind to lymphocytes with complementary receptors.
• This collection of cells can all recognize that particular invader.

Memory Cells

• After a primary immune response, your body produces memory cells.
• If the same invader is encountered again, memory cells instigate a secondary immune response that neutralizes the invader before it causes illness.

Destroying & Remembering Invaders

• $B$ and $T$ CELLS
• MEMORY $B$ AND $T$ CELLS (produced by the first exposure to antigen)
• Subsequent exposure produces more antibody-generating $B$ cells and more memory cells.
• Destroying: Once exposed to an infectious disease, you may have lifetime immunity against it.

Vaccination

• Vaccination (also called immunization) involves purposefully exposing the immune system to an antigen, which stimulates the production of memory cells.
• Modern vaccines are created from killed bacteria or viruses or mRNA or fragments of proteins from these microbes.

Vaccine Success Examples

• Polio Cases in the United States (1912-2001)
• Measles cases in the United States, 1944-2007

Anti-Vaxxers Argument

• Parents are victims of the anti-vax movement, says the pediatrician

Immune System Malfunctions

• Immune system malfunctions cause a variety of disorders
• Stress can reduce the immune response
• Problems can arise when the immune response is too strong.
  • These include:
    • Allergies
    • Autoimmune diseases
    • Organ rejection

Allergic Reactions

• Harmless substances enter the body and $B$ cells make antibodies to it.
• Those bind to mast cells
• On the next exposure, the mast cells release histamine, causing a reaction.
• Problems can also arise when the immune response is not strong enough.
• Genetic or antigen in origin
• These include:
  • Severe combined immunodeficiency
  • Immunodeficiency diseases
    • Including AIDs, brought on by HIV

The Endocrine System

• The endocrine system regulates the body via hormones
• Hormones are chemical signals produced by endocrine tissue that are transported by the bloodstream and affect target cells throughout the body.
• Regulate & coordinate whole-body activities such as metabolism, growth, and reproduction
• A tiny amount of a hormone is often sufficient to influence many cells.

Endocrine System

• Hypothalamus
  • Control center of the endocrine system
• Pituitary
  • Receives signals from the hypothalamus
• Parathyroid glands
  • Helps regulate blood calcium levels
• Thyroid gland
  • Regulates oxygen consumption, metabolism, blood calcium levels, and body temperature
• Pancreas
  • Regulates blood glucose levels through the secretion of hormones
• Adrenal glands
  • Regulates metabolism and responses to stress
• Testes (males) or ovaries (females)
  • Growth and development, promote sexual characteristics, and regulate reproduction

How Hormones Work

• Hormones travel throughout the body, but only cells with receptors for that specific hormone, target cells, are affected.
  • $2$ types of hormones: water-soluble and fat-soluble
• Specificity
• Target cells
• Receptors bind with the hormone

Insulin

• Insulin is a hormone produced in the pancreas that regulates glucose levels.
• The pancreas releases more insulin, which causes body cells to take up and store glucose from the blood.
• The pancreas releases more glucagon, which causes the liver to release stored glucose into the blood.
• Normal blood glucose level Homeostasis

Diabetes Mellitus

• Without proper regulation by insulin, cells cannot obtain enough glucose
• In a person with diabetes mellitus, either the body fails to produce enough insulin (as in type 1) or target cells do not respond normally to insulin (as in type 2).
• Uncontrolled diabetes can cause damage to multiple organs and result in premature death.

The Urinary System

• The urinary system rids the body of nitrogen-containing wastes
• The urinary system disposes of wastes and helps regulate the concentration of water and dissolved substances within the body.
• Osmoregulation is the control of the gain or loss of water and dissolved ions.

Urinary System

• Kidneys (pair)
  • The central organs of the urinary system
• Renal artery and vein
  • Blood supply to and from the kidneys
• Urinary bladder
  • Stores urine
• Ureter
  • Carries urine away from the kidneys
• Urethra
  • A tube through which urine is expelled

Kidneys

• Your kidneys continuously filter your blood, producing urine
• Blood to be filtered enters the kidneys via a renal artery
  • Branches into millions of tiny blood vessels
• The filtering of the blood takes place within the kidney nephrons.
• Filtered blood leaves the kidney via a renal vein.
• Urine exits the kidney via the ureter and collects in the urinary bladder.

Nephron

• A renal artery branch brings blood into the nephron
• Blood pressure pushes water and dissolved molecules out of the blood, through a filter
• Water & valuable solutes reclaimed and returned to the blood via tiny capillaries.
• Filtered blood returns to the bloodstream via the renal vein.
• Concentrated urine travels within the tubules and collecting duct to the ureter

Contents of Urine

• $94\%$ Water
• $3.5\%$ Urea
• $1\%$ Chloride
• $0.5\%$ Sodium
• $0.25\%$ Potassium
• $0.25\%$ Phosphate
• $0.15\%$ Creatinine
• $0.25\%$ Sulphate
• $0.1\%$ Uric acid
• How could one also find glucose in the urine? What would glucose levels in the urine indicate? Is this problematic?

Dialysis

• A person with one functioning kidney can lead a normal life, but if both kidneys fail, the buildup of toxic wastes will lead to certain and rapid death.
• Dialysis is the filtration of the blood by a machine that mimics the action of a kidney.
  • $4-6$ hours 3x week

The Reproductive System

• Males and females both produce, store, and deliver gametes.
• Despite their external differences, both sexes share the following similarities:
  • A pair of gonads, the organs that produce gametes
  • A system of ducts that store and deliver gametes
  • Structures that facilitate copulation (sexual intercourse)

Gonads

• The male gonad is the testis.
• The penis contains erectile tissue that, when filled with blood, produces an erection.
• The scrotum is an external sac that holds the testes and keeps them slightly cooler than body temperature.
• The ovary is the female gonad, where eggs are produced and released.

Male anatomy

• Glans, or head of penis where sperm exits
• Seminal vesicles add fluid to semen
• Vas deferens is duct through which sperm is ejaculated (and target of vasectomy)
• Epididymis is tube in which sperm is matured and stored
• Prostate gland adds fluid to semen
• Urine and sperm are conveyed through a tube called the urethra

Spermatogenesis

• A sperm is a haploid cell formed by the meiotic division of a diploid cell
• Within the testes, diploid cells divide via meiosis to each produce haploid sperm cells (23 chromosomes).
  • Process of spermatogenesis
• Recall that humans have 46 chromosomes.
  • Primary spermatocytes
  • Secondary spermatocytes
  • Sperm

Sperm create in the testes

• Sperm develop in the seminiferous tubules
• Then move to epididymis Maturation & storage
• The tail allows movement

Female anatomy

• The uterus or womb is the site of pregnancy where an embryo develops into a baby.
• The oviduct (fallopian tube) is the site where egg meets sperm.
• The cervix is a narrow neck at the bottom of the uterus, acts as a gateway
• The vagina, or birth canal, is where sperm enters and a baby exits.
• The vulva is the collective name for all of the external female reproductive structures
• The urethra empties the bladder of urine
• CLITORIS, LABIA MINORA, LABIA MAJORA

Oogenesis

• An egg is a haploid cell formed by the meiotic division of a diploid cell
• Within the ovary, during the process of oogenesis, a mature haploid egg called an ovum develops (23 chromosomes).
• = release of secondary oocyte from ovary into oviduct
• develops from ruptured follicle. If the oocyte is not fertilized the corpus luteum degenerates

The Female Reproductive Cycle

• Human menstrual cycle ~28 days
• Ovulation, the release of an egg cell from the ovaries, occurs around day 14.
• Hormones control the formation of the blood rich uterine lining
• Shed with a lack of pregnancy during menstruation

Fertilization

• You, and every human, developed from a single cell
• The time from human fertilization to birth takes about 266 days (38 weeks).
• Fertilization: egg & sperm à Zygote à Cell division & differentiation
• During this time, a zygote develops into an embryo and then into a fetus.
• By day 9 after fertilization, the embryo forms a gastrula, with defined layers that will develop into specific organs and tissues.
• By day 21, the embryo is attached to the wall of the uterus by a placenta.
• By just after week 8, the embryo has developed into a 2-inch-long fetus.

Fetus Development

• The fetus progresses until birth
• First trimester is marked by organ formation.
• Second trimester is a time for growth.
• Third trimester is preparing for birth.
• Childbirth is brought about by labor, a series of uterine muscle contractions.

Reproductive Health

• Issues of reproductive health affect all of us
• Issues of reproductive health can be understood in relation to the anatomy & physiology of the human reproductive system.
  • Including:
    • Contraception
    • Infertility
    • Sexually transmitted diseases (STDs)

Contraception

• Contraception is the deliberate prevention of pregnancy
• Contraception methods vary based on male and female anatomy.
• Female contraception includes preventing the formation of gametes
  • Use of hormonal birth control pills, patches, implants, injections
• Most contraception methods aim to prevent the egg and sperm from joining
  • For female anatomy, these include diaphragm and tubal ligation
  • For male anatomy, these include condom and vasectomy Sperm Egg

Infertility

• About 15% of couples are infertile, that is, they are unable to conceive a child despite one year of trying.
• There are many potential causes of both female and male infertility, and several possible solutions
• Infertility issues affect both males and females, but for different reasons

STDs

• STDs are spread by unprotected sexual contact and represent several organism types
• Herpes. STDs caused by viruses such as herpes, last a lifetime, as there is not cure for viral STDs

STD and Teen Pregnancy Rates

• Teen pregnancy rates and STD rates are highest in states that don’t require contraception education

The Nervous System

• The nervous system receives input, processes it, and sends output
• The nervous system forms a communication and coordination network.
• Your nervous system consist of your brain, spinal cord and many nerves
• Neuron networks enable us to move, perceive our surroundings, learn, and remember

The Brain

• The brain is the hub of the human nervous system
• The nervous system is divided into two major parts:
  • The central nervous system (CNS) includes the brain and spinal cord.
  • The peripheral nervous system (PNS) includes your nerves.
    • Autonomic nerves in internal organs
    • Somatic nerves in skeletal muscle

The Central Nervous System

• The central nervous system receives, processes, and sends out information
• The CNS receives incoming signals from the senses (such as touch) à signal integration à response formulation à transmits signals à reactions, such as moving a muscle
  • Somatic responses:
    • Involve motor output via motor neurons
    • e.g., kicking an incoming ball
  • Autonomic responses:
    • Changes in heart rate, respiratory rate, digestion, sexual arousal, etc.

Components of the Central Nervous System

• Brain
  • Receives and integrates sensory information
  • Maintains body functioning
  • Controls the muscles
  • Center of emotion and intellect
• Spinal cord
  • Central communication conduit between the brain and the body.
  • Initiates reflexes
• The human brain is an incredibly sophisticated system
• Your brain excels at receiving, processing, and communicating information
• The brain acts as the central hub for the nervous system
• The spinal cord acts as the main conduit to the rest of the body
• The peripheral nervous system contains the nerves that covey info into and out of the CNS

Protection of the Central Nervous System

• The CNS is protected by a layer of connective tissue called the meninges
• Both the brain and the spinal cord contain spaces filled with cerebrospinal fluid.
  • Cushions and supplies nutrients, hormones, and white blood cells

Areas of the Brain

• Cerebrum- largest and most complex part; thought, senses, reasoning
• Hypothalamus- hormones, internal temperature, hunger, emotions, internal clock
• Cerebellum- coordinates body movements
• Brainstem- conveys information and helps regulate autonomic functions (breathing & swallowing)
• Thalamus- sorts and relays info to cerebrum

Brain Ailments

• Meningitis- infection of the cerebral spinal fluid (CSP) can lead to an infection of tissues surrounding the CNS, can be very serious
• Concussion- brain impacting the skull causing bruising and swelling of brain tissue
• The nervous system can be negatively impacted by disease and injury
• Disorders of the nervous system are difficult to diagnose and treat because of the complexity of this system
• Some examples include:
  • Depression - $\frac{2}{3}$ of affected are women
  • Alzheimer’s disease - $35\%$ of Americans 80 years and older show symptoms
  • Paralysis
  • Spinal infections