Physiology II DIGESTION

Reasons we need food: 1. Fuel: chemical energy/ ATP (cellular respiration).

Most energy is found in lipids, then carbs, then, proteins. When the body takes in more calories than it needs, it stores the excess in the liver and muscles cells as glycogen. Glycogen: polymer of glucose. If glycogen storage areas are full, any excess in calories are stored as fats. Between meals/when exercising, glycogen is first taken out of the liver, then muscles and then from fats weight

loss. Undernourished person’s diet is deficient in calories; in order to fuel the body, the body breaks down its own

proteins causing irreversible damage to the muscles and brain. Overnourished person tends to store excess fats instead of using it for fuel weight gain. Leptin: a hormone made in adipose/fat cells. A lot of adipose tissue/fat= lots of leptin in blood. In theory, leptine is

supposed to tell your brain to decrease you appetite and increase your muscular activity/body heat production. 2. Carbon skeletons: to make the molecules an animal needs to grow, it needs organic sources.

By obtaining carbon from foods like sugar and nitrogen from foods like protein, the animal can a. Break these down b. Rearrange them into new forms that it requires to function properly.

3. Essential nutrients: nutrients the animal must get in a preassemble form. Malnourished person’s diet is missing one or more of the essential nutrients.

4 essential nutrients. 1. Essential amino acids: 20 totals, 8 are essential nutrients/ must come from the diet.

Mostly get from meat, eggs, cheese, corns, and beans. 2. Essential fatty acids: unsaturated fatty acids (double bond) needed for things like phospholipids. 3. Vitamins: organic molecules needed in small amounts, 13 are essential; acts as coenzyme and bind to the active site of an

enzyme enabling it to function. Two types of vitamins:

i) Water-soluble: ex: vitamin C and folic acid ii) Fat- soluble: ex: vitamin A (for good eyesight), vitamin D (for calcium), and vitamins E and K for blood clotting.

4. Minerals: inorganic molecules needed by the body, all are harmful in excess; act as cofactors and bind to the active site of an enzyme. Ex: Ca++ (nerve and muscle), P (ATP and DNA), Fe (hemoglobin), I (thyroid), and Na-K (nerve impulses).

Herbivores eat autotrophs (plants & algae). Carnivores eat other animals Omnivores eat both autotrophs and animals. Most animals are opportunistic and will eat food outside their dietary category when foods are available. 4 ways to feed:

1. Filter/suspension: feeders sift small food particles from water. Ex: baleen whales, clams, and oysters. 2. Substrate: feeders live in or on their food source. Ex: caterpillar on a leaf. 3. Fluid: feeders live by sucking nutrients from their host. Ex: parasites like leech or commensalism situations like when a

bee drinks nectar from a flower. 4. Bulk: feeders eat large pieces of food. Ex: humans and lions.

Food process: ingestion digestion absorption elimination Ingestion: to eat Digestion: using enzymes and water to break down macromolecules into

monomers by hydrolysis reactions. Absorption: take up small molecules form the digestive tract then enter

cells and turned into new molecules by condensation/dehydration reactions.

Elimination: excrete waste. Intra-cellular digestion: takes place in simple animals like paramecium

and sponges involving food vacuole that fuse with lysosomes.

Extra-cellular digestion: takes place in most animals where digestion occurs in compartments. A. Gastrovascular Cavity: pouch with a single opening that functions to digest food and

distribute it throughout the body. B. Complete Digestive Tract or Alimentary Canal: tube with 2 openings that moves to

specialized region to carry out digestion and absorption. Digestion of food begins in the mouth/oral cavity. Chewing/mastication grinds up food into smaller pieces that have a higher surface area. Mouth contains 3 pairs of salivary glands which secrete saliva. Saliva contains:

A. Antibacterial agents: kill bacteria B. Buffers: prevent tooth decay by neutralizing acid in the mouth. C. Mucin: glycoprotein that lubricates the mouth and food for easier swallowing D. Salivary amylase: enzyme that hydrolyzes carbohydrates like starch into

smaller disaccharides. Bolus: chewed up food forms a ball; it travels to the back to the back of the throat

called pharynx. Pharynx leads to a “fork in the road” one path goes to the windpipe/trachea, the

other path is the one food takes the esophagus. When swallow foods, epiglottis (flap of skin above the trachea) closes over the

glottis so food doesn’t enter into the lungs. The act of swallowing is done by voluntary muscle at the top of the esophagus

called the esophageal sphincter. Peristalsis: involuntary smooth muscles take over and contract in rhythmic waves

that push the burger down the food tube all the while, salivary amylase enzyme digesting the carbs.

Cardiac sphincter: a ring of muscle at the end of the esophagus; closes after food passes into the stomach.

If cardiac sphincter weakens, the stomach contents and acid, may return to the esophagus and cause acid reflux/heart burn not connected with the heart.

Stomach: J-shaped organ with accordion-like folds The epithelium that lines the stomach has deep pits that secrete gastric juices. Gastric juices: a mixture of enzymes and HCl having a pH of 2; it denatures

proteins and kills most bacteria that were swallowed with the food. Pepsin: enzyme that digest/hydrolyze protein in the stomach. Protease: any enzyme that digests proteins. In the gastric pits of the stomach, there are 2 types of cells:

1. Chief cells: secrete an inactive-pepsinogen 2. Parietal cells: secrete HCl.

Pepsinogen+ HCl active enzyme pepsin ^ 2 don’t mix until they get into the lumen of the stomach and mucus prevents the

stomach’s lining from being digested. The epithelium of the stomach gets eroded, but mitosis replaces the stomach’s lining every 3 days. If the mucus fails to protect the stomach lining, an ulcer/lesion forms. Most ulcers are caused by bacteria (H. pylori) and can therefore be treated with antibiotics. ~20 seconds, smooth muscle around the stomach involuntarily mixes the stomach’s contents. Stomach empty feel hunger pains. Acid chime: the contents in the stomach form a broth. After being digested and stored for 2-6 hours, the remains of the burger now move out of the stomach via the pyroic

sphincter. Small intestine: 6 meters long, small diameter. Duodenum: top of the small intestine, where most digestion occurs. In duodenum: Carbohydrates- monomers of glucose (monosaccharides): finish getting digested into monomers here with the aid of

enzymes from the pancreas (pancreatic amylase); some of the enzymes include lactase, sucrase, and maltase. The pancreas releases biocarbonate (HCO3-) buffer to offset the acidic chime.

Proteins –amino acids: finish getting digested into amino acids; several proteases are secreted. The pancreas secretes trypsin, chymotrypsin, and carboxypeptidase. The duodenum secretes aminopeptidase.

Nucleic acids-sugar+ phosphate group+ N-base: get digested by a team of enzymes called nucleases. Lipids-glycerol backbone+3 fatty acid tails: liver produces bile salts which then get stored in the gallbladder. These bile

salts are then released into the duodenum and act as “detergents” which break up or emulsify fat into droplets increasing their surface are. Bile is also alkaline so it helps to neutralize the chime, then the enzyme lipase digests the fats.

Humans lack an enzyme to digest the β links of cellulose. Peristalsis moves the digested food to the

remaining regions of the small intestine: the jejunum and the ileum where most of the monomers will get absorbed into the bloodstream.

The lining of the small intestine has a HUGE surface area—characterized by fingerlike projections called villi and microvilli.

Within each villi there are capillaries and a lymph vessel.

Amino acids and glucose are absorbed into the capillaries liver (form glycogen)

Fatty acids and glycerol are absorbed into the lymph vessel drain into veins near the heart

Liver’s main functions: Detoxifies the blood by mixing with bile and

chemically altering toxic substances (ammonia to urea).

Converts glucose to a storage form of energy called glycogen Produce bile salts

Undigested/unabsorbed food move along the large intestine/ colon by peristalsis. Most absorption of water already took place in small intestine. Colon finishes the job forming solid waste or feces. Colon absorbs remaining water, vitamins, minerals, and salts. Cecum: first pouch of the colon. Feces from cecum rectum anus. Appendix: fingerlike extension attached to the colon; part of the lymphatic system. E. coli live in the colon. Their by-products produce vitamins (that can be absorbed into the blood) and gases like methane. Bacterial infection the lining of the colon gets irritated and absorbed less water than normal diarrhea. When we smell food, see, or taste food, the stomach automatically secretes gastric juice. When food does finally enter the stomach, gastrine (hormone) causes the stomach to produce even more gastric juices. Low pH of the chyme that enters the duodenum stimulates the release of the hormone secretin. Secretin: stimulates the pancreas to release bicarbonate buffer. Ccholecystokinin (cck): a hormone is released in response to fatty acids and

amino acids; causes the gallbladder to release bile and the pancreas to release protease.

Dentition: animal’s assortment of teeth. Carnivores have shorter alimentary canals. Herbivores/omnivores have longer alimentary canals since it takes much

longer to digest plant material. Herbivores have either bacteria or protists in their intestines to digest cellulose.

Ex: ruminants like cows and sheep have bacteria in their first stomach called the rumen to digest grass.

1. Mouth/ oral cavity 2. Salivary glands 3. Pharynx 4. Esophagus 5. Cardiac sphincter 6. Stomach 7. Pyroic sphincter 8. Duodenum 9. Jejunum

10. Ileum 11. Liver 12. Gallbladder 13. Pancreas 14. Cecum 15. Large intestine/colon 16. Rectum 17. Anus

HORMONES Hormone: chemical signal that is made in one location then released into body fluids (usually the blood) and communicates a

message somewhere else; it’s either protein or lipids/steroids. While hormones will encounter many cells along their path, they only elicit a response in target cells where they bind to a

specific receptor. 2 internal message systems:

A. Nervous system: conveys fast messages along neurons to elicit a quick response B. Endocrine system: conveys a slow messages with the aid of hormone and is usually long lasting

Endocrine system & nervous system work together to maintain homeostasis in the body. Ex: a baby begins nursing on a mother. Nerve signals sent to the hypothalamus pituitary gland release hormone oxytocin mammary gland to secrete milk.

All organs of the endocrine system are glands—secrete substances 2 types of glands in the body:

A. Exocrine glands: not a part of the endocrine system, secrete products onto a surface or into a cavity. Ex: sweat glands, mucus glands, and digestive glands.

B. Endocrine glands/ductless glands: secrete hormones into intercellular spaces blood target cells. 2 types of feedback:

A. Negative feedback: most common and means the body is trying to get back to homeostasis. Ex: if you don’t have enough glucose in your blood, your body will get it by breaking down glycogen in the liver.

B. Positive feedback: rare and means that when a change occurs to the body, the body amplify that change. Ex: during labor the muscle contractions that push the baby from the birth canal become stronger and stronger by positive feedback thanks to the hormone oxytocin.

Oxytocin: has 2 roles, to increase contractions during labor and stimulate the mammary glands to allow for milk production.

Same hormone can have multiple effects on different target cells.

Invertebrates also rely on the combined efforts of hormones and nerve interactions to know when to grow or when to lay eggs.

Other chemical messages exist that are not hormones. Ex: chemical messages can also occur on a more local scale between cells—local regulators.

Local regulators ex: I. Histamine: causes blood vessels to dilate and become “leaky”

II. Interleukins: causes B and T cells to be activated III. Growth factors: proteins that cause cells to grow and divide. Have cancer lots of growth factor. IV. Prostaglandins: lipids with many roles. Ex: allow for pain sensation, so aspirin blocks this; also involved in smooth

muscle contractions in the female reproductive tract to help bring the sperm to the egg. Pheromones: non-hormone chemical signal is sent from one member of a species to another member of the same species. Ligand: any small molecule that binds to another large one. Chemical signals (hormones, local regulators, or pheromones) all bind to their specific target cell.

^ shows how most proteins bind to their target cell. Proteins bind to a receptor located on the outside of the cell triggers a

response in the target cell.

^ shows how lipids/steroids bind to a receptor located inside the cell to trigger a response in the target cell. shows the actions of a chemical signal called acetylcholine as it binds to different target cells. It has effect on:

A) Skeletal muscle- contract B) Cardiac muscle- relax

Sometimes exact same chemical signal can have different effects in different animals. Ex: estrogen in humans is the main hormone that makes a female undergoes puberty. In birds, estrogen causes a female bird to increase the amount of egg white/albumen.

Sometimes the target cell of a hormone is actually another endocrine gland. Tropic hormone: a hormone is sent from one

endocrine gland to another endocrine gland that hormone. Ex: hypothalamus pituitary gland

Hypothalamus & pituitary gland (in the brain): The hypothalamus receives nerve impulses

from the body causes the release of hormones from the hypothalamus arrives at the pituitary gland release hormone into the blood.

The pituitary has 2 parts to it the posterior (back) and the anterior (front). Posterior pituitary:

1. Function of ADH: reabsorb water primarily from the collecting ducts in the nephron.

2. Function of oxytocin: uterine contraction during labor and milk production.

Anterior pituitary: 1. Growth hormone (GH): not same

as growth factor; it stimulates the growth of bones and cartilage only.

- Gigantism/acromegaly: a disorder when a person has excess amounts of GH.

- Dwarfism (achondroplasia): a disorder when a person has too little GH.

2. Endorphins: “feel good” hormones; block pain perception. Opiate drugs like heroin/morphine mimic the effects of this hormone and bind to the same target cell receptors in the brain.

- Runner’s high: when stress & pain in the body get increased, endorphins kick in, so no pain. - Chocolate triggers the release of endorphins from the brain.

3. MSH (melanocyte stimulating hormone): its target cells are skin cells that contain the black pigment melanin—responsible for moles/beauty marks, freckles, and suntans. And if melanocytes become cancerous they are called melanoma/skin cancer.

Pineal gland (in the brain): Shaped like a pinecone Sensitive to light Releases the hormone melatonin: enables animals like frogs to change their skin color. Melatonin affects biorhythm (a cyclical process or function); biorhythms include the biological clock (having a broad

sense of time/seasons) to having a daily cycle known as a circadian rhythm (having a sense of time during the day, like knowing when it’s time to sleep).

Thyroid gland (in the neck): First signaled by the hypothalamus/anterior pituitary which release TSH

(thyroid-stimulating hormone). TSH then reaches the thyroid gland releases 2 hormone that contain the element iodine (I) into the blood: T3 and T4/thyroxine.

Plays a major role in development and maintain homeostasis in the body. Ex: if a person has too much of these hormones, it leads to hyperthyroidism have high blood pressure, high body temperature, and weight loss. Too little of these hormones leads to hypothyroidism weight gain, lethargy, and intolerance to cold.

Goiter: if a person does not get enough iodine in his diet to make these hormones, then TSH still is sent to the thyroid, but no T3 or T4 is made.

Monitors high levels of Ca++ in the blood. Secretes the hormone calcitonin that causes calcium to go into bones when

Ca+2 levels get too high.

Parathyroid gland (on the thyroid): Monitor when Ca+2 levels in the blood are too low then release hormone PTH (parathyroid hormone) that pulls calcium

from bones. Hormones calcitonin and PTH are considered to be antagonistic hormones: have opposite effects.

Pancreas (below the stomach): Performs both endocrine and exocrine functions (releases biocarbonate & digestive enzymes) 2 types of microscopic cells on the pancreas called the islets of Langerhans secrete hormones:

1. α islets of Langerhans secrete glucagon 2. β islets of Langerhans secrete insulin.

Blood glucose levels are high, the hormone insulin is released to correct this.

Insulin: stimulates the body cells to take in glucose. Blood glucose levels are low; the hormone glucagon

is released to stimulate the liver to hydrolyze glycogen to glucose.

Maintaining proper glucose levels is every important since glucose is the primary fuel for cellular respiration. If your cells aren’t getting enough glucose, you are not creating energy/ATP to fuel metabolic processes.

Diabetes mellitus (honey): an endocrine disorder due to deficient insulin levels. What insulin really does is transport blood glucose into body cells. A diabetic person’s glucose cannot be shuttled into the cells and cellular respiration is hindered. Instead, they excrete the glucose in their urine. Along with glucose excretion, copious amounts of water/urine are excreted as well. As a last resort, the body is forced to break down proteins & lipids to perform cellular respiration.

People with diabetes often crave sugar/have difficulty controlling this disorder since when they eat sugars and the sugars don’t go into body cells; they urinate the sugar out.

Type I diabetes: no insulin, child, autoimmune disease (β cells don’t make insulin). Type II diabetes: no insulin, adult, not enough insulin is made or target body cells don’t recognize insulin.

Adrenal glands (above the kidneys): Release adrenalin/epinephrine and norepinephrine (very similar) in response to positive or negative stress. Positive stress ex: riding a roller coaster Negative stress ex: being attacked Long-term stress:

- Nerve cells get triggered from a long-term stressful situation and alert the hypothalamus/anterior pituitary to release the hormone ACTH (adrenocorticotropic hormone) into the blood.

- ACTH: arrives at the receptor sites on the outside/the cortex of the adrenal glands - Adrenal cortex then releases steroids called corticosteroids - 2 main types of corticosteroids:

1. Mineralocorticoids: have their effects on salts and water balance. When in a long-term stressful situation, the kidneys reabsorb more salts which then cause more water to be reabsorbed as well due to osmosis. More salt and water in the blood high blood pressure. Ex: aldesterone

2. Glucocorticoid: have their effects on glucose metabolism. Under a long-term stressful situation, the body requires more energy. If the liver doesn’t have enough glycogen to fuel the body, glucocorticoids will break down muscle proteins and fats to make more fuel. It also suppresses the body’s immune system. Ex: cortisol

- Cream cortisone could cure inflammation of arthritis, but if used long term can cause high risk of infection. Short-term stress:

- Nervous system releases a chemical called acetylcholine on the middle portion of the adrenal glands called the adrenal medulla.

- The adrenal medulla releases epinephrine and norepinephrine flight or flight hormones. - ^ increase the breakdown of glycogen from the liver then muscle giving your blood a rapid energy boost leads to

high blood pressure. They dilate the bronchioles in the lungs and allow for an increase breathing rate. Precapillary sphincters hunt blood away from the digestive organs and kidneys allowing for an increased blood supply to the heart, brain, and skeletal muscles.

Antagonistic & both operate by negative feedback to regulate the

blood’s glucose levels

Gonads (ovaries and testes): Secrete 3 steroids/lipids hormones in both males and females but in different proportions Hypothalamus anterior pituitary releases gonadotropins called FSH and LH. Testosterone: hormone stimulates the development of the male reproductive system Estrogen: hormone stimulates the development of the female reproductive system Progesterone: in females, it prepares and maintains the uterine lining which supports the growth of an embryo. Birth control pill: increase levels of progesterone (keeps the uterine lining intact or 3 of the 4 weeks) and block

the gonadotropins (FSH & LH) so you don’t ovulate an egg each month. 1. Hypothalamus gland 2. Pituitary gland 3. Pineal gland 4. Thyroid gland 5. Parathyroid gland 6. Thymus gland 7. Adrenal gland 8. Pancreas gland 9. Ovary 10. Testes

NERVOUS SYSTEM

Central Nervous System (CNS) includes the brain and spinal cord.

Brain contains billions of nerve called neurons and trillions of support cells called glia.

Peripheral Nervous System (PNS): includes the nerves of the body. Made up of 2 parts: 1. Somatic Nervous System: carries signals to

skeletal muscles in response to external stimuli. These are voluntary actions.

Autonomic Nervous System: carries signals to smooth and cardiac muscles in response to internal stimuli. These are involuntary actions such as heart rate and contractions in the stomach to churn the food.

Nerve Cells: Neurons: longest cells of the body and are specialized to carry quick “messages” via an electrochemical process. Ex:

sciatic nerve. A neuron consists of:

a. Dendrites: tiny extensions which RECEIVE signals b. Axon: one elongated projection which conveys the nerve impulse. c. Axon hillock: right before the axon and is where the nerve impulse is generated.

Synaptic terminals/terminal branches/terminal buds: branches with specialized endings at the end of the axon that release chemical messengers called neurotransmitters to other cells.

Synapse: the gap between the synaptic terminal and another cell. Support cells: Myelin/ myelin sheath: an insulating layer that

enclose many axons; mostly lipids which act as a poor conductor but great for electrical insulation so it helps to increase the speed of the nerve impulse; made by glia/ support cells.

Comes in 2 varieties: A. Schwann cells: are the myelin sheath of

the PNS and have gaps between them called the nodes of Ranvier

B. Oligodendrocytes: the myelin sheath of the CNS; too have nodes of Ranvier.

Multiple Sclerosis: a disorder that causes the myelin sheath to break down leading to a loss of coordination due to disrupted nerve impulses.

3 Classes of Neurons (all with very different shapes): 1. Sensory neurons/ afferent neurons: communicate info about

both the internal and external world to spinal cord and brain (CNS). Ex: eye/photoreceptors visually sense the world around you. Most sensory neurons make a connection at their synapse to interneuron.

2. Interneuron: take sensory input and transmit that message to motor neurons. Not all nerve impulses require an interneuron. Found entirely in the gray matter of the spine and brain.

3. Motor neurons/efferent neurons: transmit impulses in the opposite direction, away from the brain and spinal cord to effectors cells.

Nerve: a group of axons bundled together like the strands of a cable. Since nerves usually have a white colored myelin sheath around

them, nerves are called white matter. Gray matter gets its color/name from dendrites, cell bodies,

and unmyelinated axons. The simplest neural circuits involve just a sensory neuron to

a motor neuron’s effectors cells (no interneuron) leads to an automatic response called a reflex. Ex: knee-jerk reflex.

Ganglion: group of nerve cell bodies located in the PNS and near to the spinal cord; enables the nervous system to carry out an effect without having to involve the entire system/freeing the brain to focus on more complex problems.

3 types of neural circuits/pathways: 1. Takes info from a single source. Ex: eye brain 2. Takes info from many neurons that all converge at one

postsynaptic neuron. Ex: vision+ touch+ hearing identify an object.

3. Takes info from one neuron to others then back to its source, so a circular path. Ex: memories are processed this way then stored at their source.

Much of what we know of how axons work comes from experiments using the giant axons of squid.

All cells have an electrical charge difference inside and outside of their cells.

The overall charge on the INSIDE of a cell is NEGATIVE due mostly to anion [A-] like some proteins, sulfate (SO4-2), and phosphate (PO4-3). But there are positive ions like K+ inside the cell.

The OUTSIDE of the cell is POSITIVE due mostly to the presence of cation (Na+) ions. But there are negative ions like Cl- outside the cell.

Membrane potential: the difference in voltage between the inside & outside of a cell. All cells have membrane potential, but only nerve and muscle cells can CHANGE their membrane potential’s voltage. They are “excitable” cells that have special channels that let ions enter or leave called gated ion channels. The resting potential: When a neuron is not sending a

signal, it is said to be “at rest” and the inside of the neuron is negative relative to the outside.

The membrane potential is at -70 mV.

Action potential: Na+ gated ion channels open,

letting lots of positively charged Na+ into the cell the inside of the axon to get more positive and is called depolarization.

If depolarization is large enough= enough Na+ enter the axon and gets above the threshold value of -55mV generates an action potential/nerve impulse along the entire length of the axon.

This is an “all-or-none” even and travels in 1 direction only.

After a few milisecs, the neuron will return to its resting state (-70mV) and it is ready to receive another depolarization.

If a depolarization trigger arrived before the neuron returned to this state, no action potential would be generated.

Refractory period: the time required between action potentials. Weak and strong stimuli action potentials are always the same

35 mV, but strong stimuli have a greater frequency of action potentials firing one after another.

A neuron first gets stimulated at the dendrites and cell body leading to the action potential along the axon. The action potential does not actually travel but gets regenerated along each sequence of the axon.

What affects the speed of an action potential? 1. Diameter of Axon: the wider the axon, the faster it travels. 2. Saltatory Conduction (salatatory= “to jump/leap”): if the axon

is myelinated, the myelin is not covering all parts of the axon due to the Nodes of Ranvier, so the nerve impulse jump from node to node.

The synapse: gap junction between either A) 2 neurons or B) A neuron and the cell it controls.

Presynaptic cell: transmitting cell Postsynaptic cell: receiving cell 2 types of synapses:

1) Electrical synapses: more rapid with no loss of signal strength but they are rare. Ex: brains of fish use electrical synapses to escape predators.

2) Chemical signals: much more common. Chemical signals:

1. An electrical impulse arrives at the end of the axon in the presynaptic cell.

2. Ca+2 is then triggered to enter into the end of the axon. 3. Sacs called synaptic vesicles then form that are filled with

neurotransmitters—any substance that is released as a messenger in the synapse.

4. The synaptic vesicles then fuse with the presynatpic membrane releasing neurotransmitters into the synapse.

5. Neurotransmitters then bind to specific protein channels of the postsynaptic cell opening the ion channels. Neurotransmitters act like “keys” to open the ion channels.

6. Specific ions in the synapse such as Na+, K+, Cl- then may cross into the postsynaptic cell. If the voltage can get above the threshold (-55mV), another action potential can fire in the postsynaptic cell.

7. The neurotransmitters quickly get broken down by enzymes and the ion channel closes. Ex: the neurotransmitter acetylcholine gets quickly broken down by the enzyme acetylcholinesterase.

One postsynaptic neuron may receive thousands of signals at its dendrites and cell body.

Some signals will excite the postsynaptic ell by allowing Na+ and K+ to enter the cell pushing the cell towards depolarization.

Others will inhibit the postsynaptic cell by allowing either K+ to exit or Cl- to enter the cell pushing the cell towards hyperpolarization/undershoot.

It is the average/combined effect of all the ions that enter here that the postsynaptic neuron measures.

The part of the postsynaptic neuron measures the combined effect is called the axon hillock. ∴ Synapses close to the axon hillock have a greater effect.

If enough excitatory postsynaptic potential outweigh the inhibitory postsynaptic potentials, the axon hillock opens the gated ion channels along the axon and an action potential is fired.

2 ways to enable the action potential to fire: temporal summation and spatial summation.

2 ways to disable the action potential: subthreshold (no summation) and spatial summation of EPSP and IPSP.

The same neurotransmitter can have different effects on different cells. Ex: acetylcholine—it can cause skeletal muscle to contract and a heart muscle to relax.

Other common neurotransmitters are epi/norepi which functions as hormones too. Dopamine is widespread in the brain and generally speaking is used to excite while serotonin (builds tryptophan=1 of the 20

amino acids) makes one sleepy. Parkinson’s disease: lack of dopamine Schizophrenia: excess of dopamine. Drugs like LSP/acid: produce their hallucinatory effects by binding to the dopamine & serotonin receptors in the brain. Substance P: neurotransmitter for perceiving pain (like prostaglandin) Endorphin: blocks pain GABA: common inhibitory neurotransmitter that lets in the ion Cl- to the postsynaptic cell. Some neurotransmitters are gases like NO (nitric oxide) and CO (carbon monoxide) which act on smooth muscle. Most animals have a nervous system. Cnidarian, like hydra, have nerves that branch throughout the body called a nerve net—no distinction between the CNS and

PNS, impulses are electrical and travel in both directions. Echinoderms, like sea stars, have a radial nerve that extends through each arm this arrangement allows movement

regardless of which arm is leading and stimulates the use of tube feet during feeding.

Centralization: many animals have their nerves primarily in the center of their body. Cephalization: some animals have many neural structures near the head region. ^ This is because the head will most likely encounter food and/or threatening stimulus first. Usually this concentration of neural structures neural structures near the head forms a brain in animals, with a spinal cord

extending longitudinally throughout the body. Central Nervous System: Vertebrate nervous systems are both centralized and cephalized. Notochord back bone Nerve chord spinal cord Cerebrospinal fluid: the fluid of the spine; it brings nutrients, hormones, and WBC’s to different parts of the brain and

acts as a shock absorber to cushion the brain inside the skull. Meninges: layers of tissues that protect the brain and the spinal cord. Bacterial meningitis: bacteria cause inflammation of this tissue near the brain stem.

Peripheral Nervous System: 2 types of nerves:

1. Cranial nerves that come off the brain 2. Spinal nerves that come off the spine

Most contain both sensory and motor neurons, but some cranial nerves just contain sensory (eye and nose).

Ganglia or cell body cluster near the spine. Motor neurons have both autonomic (involuntary) nervous

system (smooth & cardiac muscle) and somatic (voluntary) nervous system (skeletal muscle).

2 divisions of autonomic nervous system: 1. Parasympathetic: autonomic nerve activities that gain or

conserve energy. Ex: slow down the heart rate. 2. Sympathetic: autonomic nerve activities that consume

energy. Ex: accelerate the heart rate. Brain: The vertebrate brain develops from 3 distinct regions:

1. forebrain 2. midbrain 3. Hindbrain.

Cerebellum/ little brain: coordination, balance movement. Pons: aids medulla in some functions like breathing, conducts info between the brain and spinal cord. Thalamus: screens and relays info to and from the cerebrum Medulla oblongata: regulates breathing, heart rate, digestion, and swallowing Cerebrum/cerebral cortex: integrates sensory and motor info, thinking. Hypothalamus: produces hormones, contains the thermostat, hunger, thirst centers, homeostatic regulation. Mid brain: sends sensory info to the forebrain, contains nuclei involved in hearing and vision.

Nerves crisscross in the medulla oblongata left side of the body is controlled by the right half of the brain and vice versa.

Each cerebral hemisphere has an outer covering of gray matter- the cerebral cortex and internal white matter-basal ganglia (nerve cell bodies in brain).

Corpus callosum: a fiber joins right and left hemispheres; made of white matter.

Cerebral cortex has 4 distinct lobes. Primary motor cortex: two functional critical areas which

sends commands to skeletal muscles. Primary somatosensory cortex: receives and partially

integrates signals from touch, pain, pressure, and temperature receptors in the body.

The “special senses”- vision, hearing, smell, and taste are found in the other cortical regions. Electroencephalogram (EEG): record electrical impulses of the brain by placing electrodes on the scalp.

The less mental activity (α), the calmer/more synchronized the brain waves on the EEG.

Reticular formation: group of neurons passes through the brain stem and regulates sleep and alertness. It selects which information goes up to the cortex and filters/ignores certain stimuli like “white noise”.

Left hemisphere: more involved with speech, language, calculation, and processing detailed information.

Right hemisphere: more involved in creativity, music, spatial perception, and overall content.

MUSCLES Muscles: work together in antagonistic pairs. Ex: in flexing the arm, bicep muscle contracts, tricep muscle relaxes; in

extending the arm, bicep muscle relaxes tricep muscles contracts. Vertebrate skeletal muscle is attached to bones and enables an animal to move. Structure of muscle: muscle bundle of muscle fibers single muscle fiber (1

cell) myrofibril sacromere myosin and actin. Each muscle fiber is actually 1 large cell with many nuclei. Actin: thin protein Myosin: thick protein Z lines: the sacromere’s 2

borders; line up and this is why stripes/bands/striations can be viewed when viewing skeletal muscle.

Thin actin filaments attached to the Z line; thick myosin filaments are centered in the sacromere.

When muscles contract, the sacromere’s length from Z-line to Z-line shortens due to the overlapping of the actin filaments.

Thick myosin has little projections coming off of it. To make a sacromere contract, these little

projections first bind ATP. ATP ADP +Pi (hydrolyzed)= “energized” myosin

then attach onto/form a cross bridge with the thin actin.

After the cross bridge forms, the ADP and Pi get released. The releasing is what causes the sliding of actin towards the center.

The little projections coming off of the myosin move from the head position to the tail position.

To get the little projections/cross-bridges to “let go” of actin, another ATP is needed.

This cycle repeats over and over until the sacromere’s length shortens or the muscle cell contracts.

~350 little myosin projections in 1 sacromere. Each projection forms a cross-bridge 5 times/ sec.

Muscle cells only have enough stored ATP energy for a few contractions. ∴

they have to get energy from either glycogen in the liver or muscles. They often get more energy from a substance called creatine phosphate: has

an ample supply of phosphate groups for making ATP. Tropomyosin: a protein that block the sites where the myosin projections

bind to actin when a muscle cell is at rest. For a muscle to contract, the sites must be uncovered by Ca+2. Skeletal muscle contracts when an action potential in a motor neuron

makes a synaptic connection with a muscle cell. Action potential fired release acetylcholine in the synapse acetylcholine

binds to protein receptors on the muscle cell like a key and opens up the receptors let in Ca++ unblocks tropomyosin from the biding sites myosin projections to form cross bridges on actin sacromere to contract.

When the muscle is done contracting, the Ca+2 unbinds form tropomyosin. Duration of a muscle contraction is based on how long Ca+2 stays bound to

tropomyosin. Fast muscle fibers: Ca+2 stays bound to actin for a short amount of time; these are used for rapid, powerful contractions. Ex:

bird flying, sprinting. Slow muscle fibers: Ca+2 stays bound to actin for a long time; these are used to sustain long periods of muscle contraction. Ex:

muscles in the back that maintain posture. Muslce fibers have many mitochondria to create ATP. Some muscle fibers have a lot of protein myoglobin—store a rich supply of O2; contain Fe and give some muscle fibers a

brownish –red color. this is why dark meat in poultry and fish have its color.

2 other kinds of muscles: 1. Cardiac muscle: Found in heart Similar to skeletal muscle in that both have

stripes/striation Main difference between skeletal and cardiac:

cardiac is branded and the ends of the cardiac cells are joined by intercalated discs that relay the signals from cell to cell during a heartbeat.

Can generate an action potential on its own due to the SA node/pacemaker without any input from the nervous system.

2. Smooth muscle: Lacks striations Has a spiral arrangement Cannot generate as much tension as striated

muscle Can contract over much longer lengths Contracts more slowly Found in the walls of hollow organs of the digestive system and in blood vessels