BIOL 212 SI Section 1

Exam 4 Review

Sensory Systems

Subdivisions of the nervous systemo The central nervous system is made up of the brain and spinal cordo The peripheral nervous system is made up of all of the nerves

The afferent nervous system transmits sensory information to the CNS via sensory neurons

The efferent nervous system transmits motor information from the CAN via motor neurons

The somatic nervous system is responsible for voluntary movement and response

The autonomic nervous system is responsible for involuntary responses

o The parasympathetic division is responsible for relaxation and digestion

o The sympathetic division is responsible for responses associated with the fight or flight response

The human braino The cerebellum is responsible for coordination of complex motor patternso The diencephalon is responsible for relay of information to the cerebellumo The brain stem is responsible for relay of information to the spinal cord and

autonomic control of the heart, lungs, and digestive systemo The cerebrum is responsible for conscious thought and processing of sensory

information. Made up of four lobes: the parietal, occipital, temporal, and frontal lobes

o How do animals transform stimuli into signals?

o Each type of sensory information has a specific type of receptor that makes a synapse with a sensory neuron. This process is called transduction.

Mechanoreceptors respond to changes in pressure

Chemoreceptors respond to specific molecules Photoreceptors respond to wavelengths of light Electroreceptors detect electrical fields Magnetoreceptors detect magnetic fields Thermoreceptors detect changes in temperature Nocireceptors sense harmful stimuli like injury

o The signal must be amplified. The stronger the stimulus, the stronger the greater response from the

receptor, the more action potentials produced.

o The final step is transmission of the signal to the central nervous system.

The brain can interpret sensory information because receptor cells are highly specific, and each sensory neuron sends information to a different part of the brain.

For example: different sensors are used to detect different pitches of sound

Mechanoreception o Land animals use hearing organs to detect pressure changes in air, or sound.

Aquatic animals detect pressure changes in water through a lateral line system.o Both land and animals use structures called hair cells for mechanoreception.

They have stiff outgrowths called stereocilia that are reinforced by actin filaments.

Many also have a kinocilium, which is an arrangement of microtubules. Pressure on these cells results in depolarization or hyperpolarization.

o If the stereocilia are bent in the direction of the kinocilium, K+ channels open,

causing ions to rush in and depolarize the membrane. Hair cells are covered by an extracellular fluid with a high concentration

of K+, so it is still moving down the concentration gradient. Depolarization causes calcium ion channels to open, increasing the

amount of neurotransmitter released between the hair cell and sensory neuron. Because of this, more action potentials are fired.

If the stereocilia are bent in the other direction, ion channels close, hyperpolarizing the hair cell.

o The mammalian ear is made up of three sections: The outer ear: the ear canal funnels sound into the ear, vibrating the

tympanic membrane. The middle ear: the tympanic membrane vibrates against the three ear

ossicles. The last one vibrates against the oval window to produce waves of fluid inside the inner ear.

The size of the oval window is very important. If it is too big, it doesn’t vibrate correctly. If it is too small, it can’t vibrate enough to produce strong waves in the cochlea.

The inner ear: The cochlea is a coiled tube with three chambers. One of

those holds the hair cells sandwiched between the basilar and tectorial membrane.

Each segment of the basilar membrane vibrates in response to different frequencies.

o Bats and elephants

Bats can detect high ultrasounds needed in order to echolocate. A large area of their basilar membrane is specialized for detecting high frequencies of the returning echoes.

Elephants can detect low infrasounds needed for long-distance communication. Wild elephants can communicate even when they are miles apart!

o The lateral line system in aquatic amphibians and fish is made up of hair cells embedded in gel-like structures called cupulae inside a canal running along the length of the body.

Some nocturnal predatory catfish were experimented on to see if they

relied on their lateral line system for foraging. One group had the lateral line system removed and the other removed their chemoreceptors. The latter saw little change in hunting success, but the former had much less success.

Photoreceptiono Pupil shape and eye type correlates to the environment and behavior of the

animal. Vertical pupils are usually used by small ambush predators Round pupils are usually used by large predators Horizontal pupils are usually used by prey animals living in open habitat

o Many insects have compound dyes made up of thousands of ommatidiam, each with a lens and four receptor cells. These are good for detecting movement.

o Simple eye structure

The outermost layer of the eye is the sclera The front of the sclera forms a transparent sheet of connective tissue

called the cornea The iris is a pigmented, round muscle that controls how much light enters

the eye Light enters the pupil and passes through a curved, clear lens The retina contains the photoreceptors, bipolar cells, and ganglion cells.

o Rods are sensitive to dim light and only detect black and white. Cones can detect

different wavelengths of light, or colors. Rods and cones have membranous discs with large amounts of the

transmembrane protein opsin. Each opsin is associated with a molecule called retinal. In rods these two

form a complex called rhodopsin. When exposed to light, retinal changes from the cis conformation to the

trans conformation, activating the opsin.

o In rods, the membrane is depolarized when in the dark. The molecule cGMP

opens the ligand-gated sodium channels.

When exposed to light, rhodopsin is activated, leading in a reduction of

cGMP concentration. With less cGMP, sodium channels close and the membrane hyperpolarizes.

o Color vision and color blindness

Humans have three different types of cones, each with a different type of opsin that respond to different wavelengths: S, M, and L.

Red-green color blindness occurs when there is a defect in M/L opsin. The L allele is functional, but the M allele is defective, so the green-sensitive cones are not present.

This is more common in males because the gene for M opsin is located on the X chromosome. If females have a defective M, another M can compensate for it. Males only have one X chromosome, so they do not have another to compensate for a defective M.

The types of opsin present depends on the behavior and habitat. Chemoreception

o The senses of gustation and olfaction originate in the chemoreceptors.o A taste bud is made up of 100 spindle-shaped taste cells that make a synapse

with sensory neurons.

Saltiness is detected when an excess of sodium ions depolarizes the cell

membrane of certain taste cells. Sourness is detected when hydrogen ions from citric acid depolarize the

membrane of certain taste cells. Bitterness is detected by a suite of transmembrane receptor proteins.

Bitterness is extremely important because it usually indicates toxicity. Sweetness is detected by three closely related transmembrane receptor

proteins. One detects umami while the other two taste for sweetness. One sweet receptor has binding sites for multiple types of sweet compounds.

o For olfaction, odor molecules must diffuse into a mucosal layer of the nasal cavity and bind to membrane-bound receptors, activating olfactory neurons.

Each olfactory neuron has a different receptor and goes to a distinct region of the olfactory bulb.

o Many animals use thermoreceptors to detect changes in temperatures and relay that information to the hypothalamus.

Pit vipers have extremely sensitive thermoreceptors in pits under their nostrils that are used for hunting small mammals.

All animals give off electrical impulses, so many fish like sharks use electroreception to detect predators or prey.

o Sharks have pores called the ampullae of lorenzini. Bacteria, fungi, invertebrates, and many vertebrates have been found to be able to

detect magnetic fields.o Birds use magnetoreceptors in their beaks and eyes for navigation.

A pheromone is a chemical that is secreted and affects the behavior and physiology of others of the same species.

o Bombyx mori females secrete BOMBYKOL to attract male moths.o Bees will use them to alert others of an intruder.o Female rodents will signal to a male when they are ovulating.o Tetrapods have the vomeronasal organ on the roof of their nasal cavity to detect

pheromones.

Animal Movement

Locomotion is the movement of an entire animal in relation to its environment There are three types of muscles in vertebrates

o Skeletal muscle is attached to bone or exoskeleton for voluntary control. o Smooth muscle surrounds hollow tubes and cavities, under involuntary control.o Cardiac muscle is found only in the heart and under involuntary control.

Muscle structureo Skeletal and cardiac muscle is made up of long, slender cells called muscle fibers.o The muscle fiber is made up of many contractile strands called myofibrils.o Myofibrils are striated, having dark and light bands. These areas are called

sarcomeres. The light bands are made up of actin The dark bands are made up of myosin

o The muscle contracts when that sarcomere gets shorter.

o How do muscles contract?

o The shortening of sarcomeres occurs because myosin pulls actin towards the middle. The actin and myosin do NOT get shorter. This is called the sliding filament model.

oo The actin-myosin interaction has 4 steps. This is also called the cross-bridge cycle

We start with myosin bound to actin. ATP binds to the myosin head, releasing it from the actin ATP is hydrolyzed, causing the myosin head to change shape and bind to

a different spot on the actin. The Pi is released, causing the myosin head to change shape again,

moving the actin filament. The ADP is released, and the cycle repeats as long as Ca+ is present

Regulation of muscle activityo When muscles are relaxed, tropomyosin and troponin work together to block the

myosin binding sites on actin

oo Contraction begins when calcium ions bind to troponin, moving the complex and

exposing the binding sites. How do neurons initiate contraction?

o The brain receives the signal, integrates it, and triggers an AP to the motor neurons.

o When action potential reaches the end of the motor neuron, Ca+ channels open and trigger the release of the neurotransmitter acetylcholine

o Acetylcholine binds to the ligand-gated channels on the cell membrane of the muscle fiber, propagating an action potential.

o That action potential travels to the T tubules.o The Ca+ channels in the sarcoplasmic reticulum open, releasing Ca+ into the

muscle.

oo During relaxation, Ca+ is pumped back into the sarcoplasmic reticulum.

Rigor Mortiso After death, the sarcoplasmic reticulum deteriorates, and cellular respiration

stops. How does this cause rigor mortis?o The sarcoplasmic reticulum stores calcium, so if it deteriorates, Ca+ is dumped

into the muscle cell, causing troponin to expose the binding sites on actin. ATP is already present on the myosin, so the myosin goes through the cross-bridge cycle. However, without ATP, myosin cannot detach from actin. The muscle thus stiffens and cannot relax until the actin and myosin break down.

Characteristics of muscle types

o Smooth Muscle Single nucleus Unstriated and has no sarcomeres Unbranched Innervated by autonomic motor neurons Activated by acetylcholine and inhibited by norepinephrine and

epinephrineo Cardiac Muscle

1 or 2 nuclei Striated and has sarcomeres Branched with intercalated disks between cells Innervated by autonomic motor neurons Activated by norepinephrine and epinephrine and relaxed by

acetylcholineo Skeletal Muscle

Multinucleated Striated and has sarcomeres Unbranched Innervated by somatic motor neurons Stimulated by acetylcholine

What factors affect force output of skeletal muscle?o The relative proportion of different fiber typeso The organization of fibers within the muscleo How the muscle is used

Skeletal fiber typeso All fibers are present but in different amountso Myoglobin is an iron-containing pigment that binds to oxygeno Slow Fibers (Red)

High myoglobin concentration Derive ATP from aerobic respiration Many mitochondria Start slow but take long to fatigue

o Fast Fibers (White)

Low myoglobin concentration Derive ATP from glycolysis

Few mitochondria Start fast but fatigue quickly

o Intermediate Fibers

High myoglobin concentration Derive ATP from glycolysis and aerobic respiration Many mitochondria Intermediate

Muscle fiber organization

o Length and cross-section of a fiber influences its contractile propertieso Parallel fibers: long chains of sarcomeres along the length. Have a long length

but a large cross section, so they are fast but not strong.o Pennate fibers: sarcomeres are lined up diagonally to a tendon. They have a

large cross section but are shorter, so they are strong but not as fast.

o Hydrostatic Skeletons

o Hydrostatic skeletons use pressure of internal fluids to support the body.o Found in sea anemones, jellyfish, mollusks, worms. Hydrostats is also used in

tongues, penises, and tube feet of starfish.o Earthworms use their hydrostatic skeleton for locomotion

They have two types of muscles: longitudinal muscles that run down the side of the body and circumferential muscles that run around the body like rings.

The circumferential muscles contract, increasing the pressure of the fluid, extending the relaxed longitudinal muscles.

The longitudinal muscles then contract, increasing the pressure of the fluid, extending the relaxed circumferential muscles.

These two are an example of an antagonistic muscle group. Endoskeletons

o A series of rigid structures inside the bodyo The vertebrate endoskeleton is a system of rigid levers and articulations that

allow limbs to swivel, hinge, or pivot. o Bone is made up of cells embedded in an extracellular matrix made up of calcium

phosphate with calcium carbonate and collogen.o Cartilage is made up of cells scattered in an extracellular matrix of

polysaccharides and proteinso Ligaments are bands of connective tissue like collagen that binds bones together

and stabilizes jointso Tendons are bands of connective tissue that attach bones to skeletal muscleo Antagonistic muscles groups work together but opposite in order to perform

movement. The flexors decrease the angle between bones, pulling them closer

together. The extensors increase the angle of the joint, pull them further away

from each other. Its important to know that muscles do not extend on their own, they

need another muscle to pull them back into place.

o Bone is living tissue that is used to maintain blood calcium levels.

Ostoblasts build the calcium matrix in bone, decreasing blood calcium levels.

Osteoclasts break down the calcium matrix of bone, increasing blood calcium levels.

Exoskeletonso Encloses and protects the body of animalso Found in arthropodso Insects have chitinous ingrowths of their exoskeleton called apodemes where

muscles attach.o Exoskeletons do not grow with the animal, so it must be occasionally molted

Chemical Signals in Animals

A hormone is a chemical signal that originates in a cell and circulates through the body fluids to reach and affect a distant target cell

How are electrical signals and chemical signals different functionally?o Action potentials have short-term effects on a set of cellso Chemical signals are produced in low concentrations but have enormous and

lasting effects on target cells.o They are used together to coordinate activities throughout the body.

Categories of chemical signals in animalso Autocrine signals act on the same cell that secretes them

Example: interleukin2

o Paracrine signals diffuse locally and act on nearby cells

Example: insulin, glucagon, cytokines

o Endocrine signals are carried between cells by blood or other body fluids

Example: hormones

o Neural signals diffuse a short distance between neurons Example: neurotransmitters

o Neuroendocrine signals are released from neurons and travel through the blood

to target cells Example: neurohormones like anti-diuretic hormone

Hormone signaling pathways

o All hormone pathways are regulated via negative feedback, meaning that the end response inhibits the production of the chemical signal.

o The endocrine pathway sends hormones directly from endocrine cells to effector cells

o The neuroendocrine pathway releases neuroendocrine signals that act directly

on effector cells

o In the neuroendocrine-to-endocrine pathway, the neuroendocrine signals

stimulate cells in the endocrine system, which produce an endocrine signal that acts on effector cells

o Hormones of the human endocrine system

The hypothalamus The pineal gland The pituitary gland with an anterior and posterior region. Located right

below the hypothalamus The thyroid gland is in the neck The four parathyroid glands are ebedded in the thyroid gland The adrenal glands sit on the kidneys The pancreas is located in the abdominal cavity The testes and ovaries

o The exocrine glands deliver their secretions through ducts into a space other than the circulatory system.

Examples include salivary glands, digestive glands in the pancreaso There are three different types of hormones

Polypeptides are chains of amino acids. They bind to receptors on the surface of the cell

Amino acid derivatives bind to receptors on the surface of the cell Steroids bind to receptors on the inside of the cell

o Steroid hormones travel throughout the body and enter the cells to bind to

receptors inside the cell. The receptor-hormone complex then binds to DNA to trigger transcription.

o Lipid insoluble hormones like epinephrine trigger a signal transduction cascade

When the hormone binds to the receptor, it activates the G protein to split and activate adenylyl cyclase, which converts ATP to cyclic AMP.

This cAMP then triggers a phosphorylation cascade, further amplifying a signal.

When activated by epinephrine, the response is the breakdown of glycogen into glucose.

Hormones coordinate activities in development, growth, and reproduction

o Metamorphosis in amphibians is driven by the hormone T3, or thyroxineo Metamorphosis in insects is driven by two hormones: juvenile hormone and

ecdysone. In the larval stage, both are in equal levels. When JH decreases in levels, the body goes through complete remodeling.

o In vertebrates, genes on the sex chromosomes are the primary determinate factor on sex.

The male and female gonads produce testosterone and estradiol respectively.

The surges of sex hormones associated with puberty are signaled by growth hormone

Hormones respond to environmental changes

o In mammals, photoreceptors in the eye send signals to the pineal gland, which releases melatonin to relay information to the hypothalamus.

Changes in photoperiod (seasons) are associated with changes in sex hormone releases in species with breeding seasons.

o Many day-active lizard species have a parietal eye, or a small hole covered by membrane at the top of the skull containing photoreceptors

Hormones are involved in the maintenance of homeostasis o Homeostasis is the maintenance of relatively constant physical and chemical

conditions inside the bodyo Homeostatic systems depend on three components

A sensory receptor that monitors a condition An integrator that processes information and compares it to a set point Effector cells that return conditions to that set point

o Examples: Insulin and glucagon regulate blood glucose andidiuretic hormone and aldosterone regulate water and electrolyte

balance erythropoietin regulates oxygen availability by stimulating red blood cell

productiono Hypothalamic-pituitary axis

The pituitary is directly connected to the hypothalamus. This connection is the basis of the connection of the central nervous system and endocrine system.

To get the adrenal cortex to release cortisol in response to stress, the hypothalamus releases corticotropin releasing hormone (CRH) to stimulate the pituitary to release adrenocorticotropic hormone (ACTH), which triggers the adrenal cortex to release cortisol. Cortisol in turn inhibits those original signals.

Circulation and Gas Exchange

Five essential steps for gas exchangeo Ventilation occurs when air or water moves through a gas exchange organ like

gills or lungso Diffusion takes place when CO2 and O2 diffuse between the air or water and the

ventilatory surfaceo Circulation occurs, and CO2 and O2 are circulated through the body dissolved in

bloodo Diffusion takes place when CO2 and O2 diffuse between the blood and the cellso In cellular respiration, O2 is used to produce ATP while CO2 is released as a

byproduct

o How do O2 and CO2 behave in air?

o Partial pressure is the pressure of a particular gas in a mixture of gaseso According to Dalton’s law, the partial pressure of a gas is the sum of partial

pressures of all gases in the mixtureo Gasses diffuse from areas of high partial pressure to areas of low partial pressureo To calculate partial pressure, multiply the fraction of air that gas comprises by

the total atmospheric pressure. Oxygen comprises 21% of air, what is the partial pressure at 760 mmHg?

PO2 = 0.21 x 760 mmHg = 160 mmHg What is the partial pressure at 250 mmHg?

PO2 = 0.21 x 250 = 53 mmHg As you increase in elevation, it becomes harder to breath because

the external partial pressure of oxygen is lower How do O2 and CO2 behave in water?

o There is less oxygen available in water than in air and water is much more dense and thus flows less easily

o Factors that affect the amount of O2 and CO2 in water Solublity of a gas in water Temperature of gas in water: cold water contains more oxygen Presence of other solutes: more oxygen in fresh water Partial pressure of gas in contact with water

The activity of inhabiting organisms: photosynthetic organisms increase oxygen, decomposers decrease oxygen

Surface area and mixing increases oxygen Fick’s Law of Diffusion

o There are three parameters that allow animals to maximize rate of diffusiono A – a large surface area for gas exchangeo P2-P1 – A high gradient of partial pressuerso D – a low thickness of the surfaceo Solubility of the gas and the temperature are in the constant K

o Insect tracheal system

o Spiracles on the body surface lead to tracheae that branch into trachioles that terminate near the body cells.

o These are very efficient, being able to support insect flight muscles with a high metabolism

o The tracheae are compressed and dilated for ventilation, similar to how we use our diaphragm

o Gills are outgrowths of the body surface or throat used for gas exchange in aquatic

animalso Gills allow for an extremely large surface area and have an extremely thin

epitheliumo Gill structure is very diverse, being either internal or external depending on the

specieso Fish gills work via a countercurrent system

The flow of the capillaries is opposite to the flow of water over the gills

This exchange system creates a large partial pressure difference and keeps them from reaching equilibrium.

Very efficient for exchange of both oxygen and carbon dioxide

Lung structures

o Air enters through the mouth and nose, into the trachea and bronchi, and into the alveoli

o Alveoli are thin-walled structures with capillaries. They facilitate gas exchange by having a thin barrier and a large surface area.

Negative Pressure ventilationo The air pressure inside the body cavity is slightly lower than the atmospheric

pressure. This keeps the lungs from collapsing when we breath out.o To inhale, the diaphragm flexes and increases volume in the body cavity. This

decreases pressure in the lungs, pulling in air.o To exhale, the diaphragm relaxes and decreases volume in the body cavity. This

increases pressure in the lungs, forcing air out. o Only seen in mammals

o Positive pressure ventilation

o Frogs draw in air by increasing the volume of the oral cavity. o The nasal passages are closed, and the air is pushed into the lungs by decreasing

the volume of the oral cavity.

o How is ventilation used to maintain homeostasis?

o When exercising, O2 is used and CO2 is produced. When CO2 enters the blood, it is converted into bicarbonic acid, decreasing the pH of blood.

CO2 + H2O H2CO3 H+ + HCO3o The brain senses this change in pH and sends a signal to the respiratory system

to increase breath rate. Blood is a connective tissue made up of mostly liquid plasma and the rest is made up of

formed elementso The formed parts are platelets, white blood cells, and red blood cells

Hemoglobin is a tetramer, or made up of four polypeptide chains, each with a heme group.

o These heme groups contain one Fe++ atom each, which can bind to an oxygen molecule

oo Oxygen diffuses from blood to tissues due to the partial pressure gradient

Oxygen dissociation curve/hemoglobin saturation curveo This graph plots the percent saturation of O2 in hemoglobin, or the affinity of

hemoglobin to O2, versus the partial pressure of oxygen within the tissues.o Low partial pressure in tissue, low affinity of hemoglobino High partial pressure in the tissue, high affinity of hemoglobin

o Hemoglobin exhibits cooperative binding, meaning that the binding of oxygen increases

the affinity of it to bind to more oxygen. This is why the graph is a sigmoidal curve.o If this did not occur, the change of O2 release between rest and exercise would

not be as great.

o During exercise, the change in pH causes the graph to shift to the right, causing oxygen

to unload faster. This is called the Bohr shift. Fetal hemoglobin has a higher affinity, shifting the graph to the left. This allows the fetus

to get oxygen from the mother.

o When CO2 enters the red blood cell, the enzyme carbonic anhydrase converts it to

bicarbonate. The excess proton is taken up by hemoglobin to decrease pH.