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Musculoskeletal System

Our muscles and skeletons, the effectors that produce movement.

Skeletal muscle

Striated muscle, voluntary movements, cells are muscle fibers

Cardiac muscle

heartbeat, involuntary movements, striated, cells are smaller than skeletal muscle and only have one nucleus. Cells branch and form meshwork. Made of pacemaker and conducting cells.

Smooth muscle

involuntary movement of internal organ (stimulated by movement of food). Under control of autonomic nervous system. Cells are arranged in sheets and connected through gap junctions. Can be stimulated by hormones and does not involve troponin.

Muscle fibers

Multinucleate cells of the skeletal muscle, formed from fusion of embryonic muscle cells (myoblasts). One muscle consists of many muscle fibers bundled together by connective tissue.


Each muscle fiber has multiple bundles of myofibrils where the contractile proteins are found. Consist of sarcomeres.

Contractile proteins

Actin and myosin. The interaction of the filaments allows for muscle contraction.


Thin filament contractile proteins. Repeating units of actin monomers. Have myosin binding sites.


Thick filament contractile protein. Tons of myosin molecules.


The units of contraction. Made up of overlapping filaments of actin and myosin. Distinct banding pattern within. Win they contract the z lines come towards each other.


Protein that holds myosin filaments in place. It is down the length of the myofibril.

z line

The boundary of a sarcomere, it is where the actin filaments attach

h zone

The region with no actin filaments.

A band

The entire length of the myosin filaments

Sliding filament theory

When a sarcomere shortens the actin and myosin slide along each other. The z lines move closer and the h zone becomes smaller. When the sarcomeres shorten muscle fibers shorten.

Myosin binding sites

The myosin filaments can interact with the actin filaments. In a relaxed muscle the sites are blocked.

Myosin molecule

Two long polypeptide chains twisted together with a globular head on one end.

Myosin head

They bind to specific sites on the actin molecules. The myosin changes shape and causes the actin filament to slide 5-10 nm, and this continues until the muscle is contracted.

Muscles contract

Action potentials from motor neurons initiate muscle contraction.

Motor unit

All of the muscle fibers activated by a single motor neuron. All the muscle fibers contract at the same time. The more motor units that are activated the stronger the muscle contraction will be.

Muscle cells

Can generate action potentials. They are initiated by motor neurons. Action potential is conducted to all points on the surface of the muscle fiber.

T tubules

System of tubules in the sarcoplasm of the muscle fiber.

Sarcoplasmic reticulum

Closed compartment that surounds every myofibril. Stores calcium until the muscle cell is stimulated.


Part of an actin filament. 3 subunits. One binds with actin one binds with tropomyosin and one binds with calcium


blocks myosin binding sites on actin in resting fiber

T Tubules in action

As a result of firing an action potential they contract. An action potential arrives at the axon terminal and Acetylcholine is released. As the action potential spreads down the T tubules it opens up calcium channels and calcium is released into the sarcoplasm and in amongst the myofibrils. Released calcium stimulates muscle contraction.

part 2

Calcium is released from the sarcoplasmic reticulum and it binds to Troponin. Troponin changes shape and exposes myosin binding sites on actin. Myosin heads are attached to an ADP and a phosphate and the heads bind to actin as soon as the sites are exposed. The phosphate is released. Myosin changes shape and pulls actin filament over top of the myosin filament. The molecule of ADP gets replaced with ATP ATP breaks the bond between myosin and actin. The myosin head goes back to normal.

Intercalated disks

mechanical adhesions between adjacent cells

Gap junction

form cytoplasmic connections between cells

pacemaker and conducting cells

do not contract initiate and coordinate rhythmic contractions of the heart. P(creates signal to beat) C(carry information from the pacemaker to the ventricles.


Generated by the muscle itself. Pacemaker can maintain the heartbeat without info from the CNS. Based on the cns' info of blood levels it can increase or decrease the heart rate.

Gap junctions of smooth muscle

Electrical connection, action potential in one cell in a sheet can spread to all other cells.

Plasma membranes in smooth muscle

They are sensitive to stretch. Stretched cells depolarize and fire action potentials.

Smooth muscle contraction

Calcium influx to sarcoplasm is stimulated by stretching action potentials or hormones. Calcium binds with calmodulin. It activates myosin kinase which phosphorolates myosin heads. Myosin can bind and release actin.


Minimum unit of contraction. Generated by single action potential. Force generated depends on how many muscle fibers are in the motor unit. Tension generated depends on motor units available and the frequency at which they are firing.


Action potentials are so frequent that calcium never cleared from the sarcoplasm. So there is a continuous contraction. Depends on a supply of ATP. ATP is needed to break the actin myosin bond and "re-cock" the myosin head. To maintain contraction the cycle has to continue.

Muscle tone

Many muscles of the body maintain a low level of tension when the body is at rest. Activity of a small but changing number of motor units.

Slow-twitch fibers

have more mitochondria. Oxidative or red muscle. Contains myoglobin. Maximum tension is low and develops. Highly resistant to fatigue. Have good reserves of fuel so they can maintain ATP production.

Fast-twitch fibers

Glycolitic or white muscle. Very little myoglobin. Maximum tension is high and develops quickly. Fatigues rapidly. Fibers cannot replenish ATP fast enough to sustain contraction for long periods of time. Good for short term work.

Anaerobic exercise

Increases strength. The bigger the muscle the stronger the muscle. Weight lifting repeatedly contracts specific muscles under heavy loads until fatigued. Minor tissue damage. Muscle fibers get bigger


Increases endurance. Increases the oxidative capacity of the muscle. Increases the number of mitochondria and myoglobin.

Skeletal systems

Provide rigid supports against which muscles can pull.


An internal scaffolding to which the muscles attach. Advantage is that it grows with the animal. Humans have 206 bones.

Axial skeleton

the part of the skeleton that includes the skull and spinal column and sternum and ribs

Apendicular skeleton

Everything but the skull spinal column sternum and ribs


Tough rubbery mix of polysaccharides and proteins. Stiff and resilient but somewhat flexible. Joints, ear, larynx and nose.


Extracellular matrix of calcium phosphate. Made of osteoblasts and osteoclasts.


build up and lay down new bone.


Osteoblasts that get trapped in the material that gets laid down


Break down the bone, they reabsorbe and erode bone, forming cavities and tunnels.

Membraneous bone

Outer bones of skull

cartilage bones

forms 1st as cartilage then slowly ossifies. limbs

Bone structure

compact or cancellous

compact bone

solid and hard


appears spongy

Bone stops growing when...

The outer cites and the center sites fuse.

Haversian bone

Compact bone centered around haversian canals. The osteoblasts lay the bone down in rings.


Flexor and extensor. Muscles exert force in only one direction. Muscles work in agnostic pairs.


The muscle that bends a joint


The muscle that straightens a joint.


Bands of connective tissue that holds bones together at the joints.


Connective tissue straps that attach muscles to bones.

Respiratory Gases

Oxygen, carbon dioxide, exchanged by diffusion.

Barometric pressure

Pressure exerted by the atmosphere. At sea levels its 760mm of Hg. In a vacuum the pressure is zero.

Partial pressures

concentration of different gases in a mixture. O2 makes up 20.9% of atmosphere

Amount of oxygen

20.9% of atmosphere. There is no change in the amount of oxygen in the atmosphere at any height.

Fick's law of diffusion

The variables that have an effect on the rate of diffusion of a substance. Increase surface area (A) increase diffusion rate. Increase distance (L) decrease diffusion rate.

Water vs. Air

O2 content of air is higher. It diffuses 8,000 times faster from air than in water and it takes more energy to move water over the respiratory surfaces than it does air.

Air breathing water problems

Mitochondria are bathed in water containing solutions, hard to get O2. Because we are filled with water its hard to diffuse oxygen and we have specialized respiratory systems with large surface areas to get more O2.

Ocean creatures

Flat worms have no respiratory systems but their body is so flat that the distance between their cells and body surface is so small that they can exchange gases.

High temp. problems

Most water breathers are ectothermic so they need more O2 as temperatures increase. Warm water holds less o2 than cold water.

Increase in altitude

At all altitudes O2 makes up 20.9% of atmosphere but the barometric pressure decreases. Diffusion of O2 depends on partial pressure differences.


Is lost by diffusion as O2 diffuses in. Rate of diffusion depends on the partial pressure gradient. Amount of CO2 in the atmosphere is very low. Makes up .03% of atmosphere.

Maximize gas exchange

Increase in surface area, maximize partial pressure gradients, minimize diffusion differences.

Circulatory system

Some animals do not have circulatory systems. Open and closed.

Open circulatory system

No distinction between blood and tissue fluids. Arthropods. They do have heart that pumps blood through the vessels but it eventually mixes with the fluid.

Closed circulatory system

Blood and tissue fluids are separate. Heart pumps blood through the system.

Advantages of closed circulatory system.

Blood moves more rapidly. Blood can be directed to specific tissues. Diverting blood flow to things that are working. Large molecules remain inside vessels, don't loose important proteins or RBC in tissues. Supports higher levels of activity.

Vertebrate Circulatory systems

Closed Circulatory systems and hearts with 2+ chambers. Increased separation of oxygenated and deoxygenated blood. Two different circuits, pulmonary and systemic.

Oxygenated blood

Blood thats going to tissues, filled with O2

Deoxygenated blood

blood thats returning from tissues, O2 is mostly gone.


having to do with the lungs


relating to the whole body rather than only a part


blood vessels that carry blood away from the heart


small vessels that receive blood from the arteries


blood vessels that carry blood back to the heart


tiny, thin-walled blood vessels that allow the exchange of gases and nutrients between the blood and the cells of the body


small vessels that gather blood from the capillaries into the veins

Blood flow

Arteries > arterioles > capillaries > venules > veins

Fish Circulation

2-chambered heart, single atrium and ventricle, very little separation of oxygenated and deoxygenated blood. Low pressure in capillaries which is a disadvantage.

Lungfish circulation

3 chambered heart, still mixing of oxygenated and deoxygenated blood but they are separated in the heart. Have the ability to bypass the gills and have the blood go through the lungs.

Amphibian Circulation

3 chambered heart, 2 atria and a ventricle. Still mixing of the blood but there is a separation of pulmonary and systemic circuit. Maintains the two under different pressures. They can also absorb oxygen across their body surface.

Crocodilian Circulation

4 chambered heart. Complete separation of blood and systemic and pulmonary. They can control when they breathe, they can bypass circulation in their lungs by increasing pressure so it goes through to the systemic.

Birds and Mammals

4 chambered heart, Complete separation.

Advantages of separate circuit

No mixing of oxygenated and deoxygenated blood. Maximal respiratory gas exchange. The two circuits can operate at different pressures.

Human Heart

Right side - deoxygenated. Left side - oxygenated. Valves.

Atrioventricular Valve

A valve in the heart between each atrium and ventricle that prevents a backflow of blood when the ventricles contract.

Pulmonary Valve

prevents blood from flowing back into the right ventricle after it has entered the pulmonary artery

Aortic Valve

prevents blood from flowing back into the left ventricle after it has entered the aorta

Pulmonary Vein

carries oxygenated blood from the lungs to the heart

Optimizing partial pressure gradients

Minimize the diffusion path length. Ventilation and perfusion.


Exposes the gas exchange surfaces regularly to a fresh respiratory medium. PO2 high and PCO2 low.


Circulating blood over the internal side of the exchange surfaces. PO2 low and PCO2 high.

Gas exchange system

A gas exchange system consists of the organisms gas exchange surfaces plus the ventilation and perfusion systems


System of air tubes that provide all cells of the body with an ample supply of oxygen. Tracheae branch into tracheoles and these branch into air capillaries. This allows insects to remain small. O2 is brought into the insect by spiracles.

Fish Gas Exchange.

The fish gills provide a very large surface for gas exchange between the water and the internal environment of the fish. There is a unidirectional flow of water over the gills. The gills are protected by opercular flaps.


Each gill consists of hundreds of gill filaments, each gill filament has rows of folds called lamellae that serve as gas exchange surfaces.

Countercurrent flow

Blood flows in the opposite direction of water. This is more efficient and the blood will eventually reach a point of almost 100% saturation. The water is always more saturated than the blood so there is a gradient of oxygen.

Bird lungs

Birds maintain high levels of activity. They have smaller lungs than mammals and they have a unidirectional flow of air through the lungs. Their lungs expand during exhalation and contract during inhalation. Fresh air never mixes with stale air. A

Air flow in Birds

During inhalation the air is taken not directly into the lungs but first into the posterior air sacs. During exhalation the air sacs contrat and push the air into the lungs. During the next inhalation the air flows into the anterior air sacs. In the next exhalation the air is expelled.

Tidal Volume

The amount of air that moves in and out per breath.

Inspiratory reserve volume

The amount of air you can take in thats above and beyond the normal tidal volume.

Expiratory reserve volume

The amount of air you can breathe out above and beyond the normal tidal volume.

Residual Volume

Volume of air that is always present in the lungs. It is the air that makes up the difference of vital and total lung capacity.


The sights of gas exchange in the human lungs there are 300 million alveoli in the human lungs and the combined surface area of all of them is about 70 m^2. They are surrounded by networks of capillaries that also have very thin walls.


the smallest tubes of the bronchus. Coming from the bronchi that contain clusters of alveoli at each end.


Collects dirt and microorganisms that are inhaled. Mucus elevator.

Mucus elevator

interior surfaces of the airways down to the respiratory bronchioles are lined with ciliated epithelial cells. Mucus coating traps particles in the air. Beating of the cilia push particles up to the pharynx where they are swallowed.


Reduces the surface tension of alveoli walls. Premature babies do not have this.

Transporting O2 and CO2

Transported by the blood (perfusion). The blood plasma only holds small amounts of O2. Hemoglobin binds to 4 molecules of O2.


iron-containing protein in red blood cells that transports oxygen from the lungs to the tissues of the body. The ability of hemoglobin to bind to or release O2 depends on the partial pressure of O2 in the environment.

Hemoglobin composition

alpha, beta or gamma chains. 2 alpha and 2 beta in adults, 2 alpha and 2 gamma in fetal humans.

Affinity of Hemoglobin

Changes in environment have an affect. When the pH is more acidic the hemoglobin releases more O2 into the tissues. When there is BPG in the blood it binds with hemoglobin and lowers the affinity for O2 so more oxygen goes to the tissues and not lungs.


O2 binding molecule found in muscle cells. Higher affinity for O2 than hemoglobin. Provides muscle cells with a reserve supply of O2. Diving mammals have high concentrations so that their muscles do not get starved of oxygen when they go underwater.

Transporting CO2

CO2 can decrease pH of blood stream. CO2 is diffused from cells into the plasma. Some CO2 remains carried in the plasma some binds to hemoglobin but the majority is converted to bicarbonate ions. CO2+H20 > H2CO3 > HCO3- +H+. In the lungs these processes are reversed. CO2 goes out of the bloodstream into the lungs and it is exhaled.

Buffer CO2

It maintains ph in the solution. Can either bind to excess H+ or increase H+ as needed.

Breathing regulation

Controlled in brain stem. Pons regulates normal breathing. When the brain chord is severed above the medula the person breathes irregularly. The pons can change breathing in respons to increasing levels of CO2.

Asexual reproduction

Does not require mating
Little genetic diversity
Mostly sessile.
Takes a lot less energy than sexual reproduction. Much more efficient.
Three types of asexual reproduction are budding, regeneration, and parthenogenesis.


offspring grow as a bud off the parent as a completely new organism. And it grows until it is ready to be independent, sometimes even to the full size of the parent.


Usually thought of as a re-growing of a leg but some can create a whole new organism. A starfish can grow into a new organism if a leg is cut off as long as it contains part of the central disk.


The development of offspring from unfertilized eggs.
- May determine the sex of the offspring.
--Ones that develop are usually males and then females will develop as the fertilized egg.

Females can act as males in some species

-Depends on cyclic hormonal states (estrogen and progesterone).
--Act of mating is still sometimes needed in these organisms. Initiates the production of eggs even if they do not get fertilized.

Sexual Reproduction

Two parents produce specialized cell types (gametes) that fuse (fertilization) to form a new individual.
Promotes genetic diversity
- crossing over (crossing over of their information) and independent assortment (chromosomes separate independently of one another)
3 steps: gametogenesis (production of gametes), mating (brings gametes together) and fertilization (gametes fuse together)


Specialized type of cell division called meiosis. (End up with half genetic information in daughter cell.)
Gametes have half the number of chromosomes

Gametogenesis occurs in

Testes in males; gametes are small, motile sperm.
Ovaries in females; (much larger than sperm) gametes are non-motile ova, or eggs.
Gametes are produce from germ cells. Germ cells give rise to pregametes which go through meiosis to the sperm or eggs.


Continuous process in human adult males.
Primary spermatocytes undergo meiosis to form 4 spermatids


Mature in testes to form sperm

Rigid between spermatids

they remain connected because the x chromosome only gets put into half the spermatids, the other half has a y chromosome. The information from the x is needed for the final maturation of the sperm.


the production, growth, and maturation of an egg, or ovum. A discontinuous process in human females.
Primary oocytes are formed during fetal development.

Primary oocytes

Females are born with every oocyte they will ever have. Sit arrested in the first stage of meiosis until puberty. (can stay in that stage from weeks to years). After puberty: each month a few oocytes are triggered to continue through meiosis.
Only one completes meiosis and is released as the ovum (menstrual cycle)

Oogenesis 2

Primary oocytes undergo meiosis to form 1 ovum and 2 polar bodies
1◦ oocyte 2◦ oocyte + polar body
2◦ oocyte ovum + polar body


very large, large amount of cytoplasm, surrounding matrix for protection


Union of a haploid sperm and a haploid egg. Creates a single diploid cell, called a zygote

Fertilization steps

-Sperm has to find and recognize the egg
-Sperm penetrates matrix surrounding the egg
-Plasma membranes fuse
-Egg blocks entry of additional sperm (changes it's plasma membrane)
-Egg activation (going through second meiotic division)
-Egg and sperm nuclei fuse

Acrosome reaction

Acrosome in head of sperm ejects contents. Enzymes allow penetration through protective matrix.

Sperm and Egg Interactions

Recognition occurs through receptors on the surface of sperm and egg, Acrosome reaction, Fusion of egg and sperm membranes

Sperm and Egg Recognition

Species and cell type specific. (Organisms that use external fertilization the sperm has to make sure that the egg is the same species)

Fusion of Egg and Sperm

Allows sperm nucleus to enter egg cytoplasm

Fast Block to Polyspermy

Not seen in mammals. Rapid electrical depolarization of membrane potential (bunch of sodium atoms changes the environment in the egg)

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