Animal Science

Front 1

3 types of muscle cells

Back 1

- skeletal muscle

- cardiac muscle

- smooth muscle

Front 2

Skeletal Muscle

(Voluntary striated muscle)

Back 2

They type that comes to mind when we hear muscle because it moves the bones of the skeleton. It is voluntary because it is under the control of the conscious mind. The striated part comes from its microscopic striped appearance.

Front 3

Tendonds

Back 3

Most skeletal muscles are attached to bones at both ends by tough, fibrous connective tissue bands called tendons that are a continuation of the epimysium.

Front 4

Skeletal Muscle Cells

aka

Muscle Fibers

Back 4

They are large, not very wide but quite long. Skeletal muscles are thin giving them theyre fiberlike shape. Instead of having one nucleus, they have many (100 or more nuclei per cell) located at the edge of the cell beneath the sarcolemma.

Front 5

Sarcolemma

Back 5

Muscle Cell Membrane

Front 6

Myofibril

(Spaghetti)

Back 6

Most of the volume of one skeletal muscle fiber is made up of hundreds or thousands of smaller myofibrils packed together lenthwise, which are themselves composed of thousands of even tinier protein filaments.

Front 7

Sarcoplasmic Reticulum

Back 7

Storage organelle for calcium ions

Front 8

Mitochondria

Back 8

Prominent organelles between the myofibrils in a muscle fiber include many energy producing mitochondria

Front 9

Transverse Tubules

aka

T- tubules

Back 9

A system of tubules that extend in from the sarcolemma (Cell Membrane).

Front 10

Sarcomere

Back 10

One myofibril is made up of a series of protein filaments. These filaments form the contractile units of a myofibril. Each one of these contractile units is called a sarcomere and is the basic contracting unit of skeletal muscle. There are many sarcomeres laid end to end in one myofibril.

Front 11

Z line

aka

Z Disc

Back 11

Each sarcomere has a disc on each end called the Z line. Sarcomeres share discs, so there is one common disc between adjacent sarcomeres.

Front 12

2 types of Myofilaments in skeletal muscle

Back 12

- Actin

- Myosin

Front 13

Actin

Back 13

Thin protein filaments called actin that attach to the z lines and extend toward the center of the sarcomere, but dont meet.

Front 14

Myosin

Back 14

There are also thick protein filaments called myosin that appear to float in the middle of the sarcomere between parallel actin fibers. They do not connect to the z line.

Front 15

I Bands

Back 15

Looking at a myofibril at a higher magnification we can see large light colored bands. These are called I bands and are made up of the thin actin filaments. Each I band extends from one end of the thick myosin filaments in one sarcomere across the z line to the beginning of the myosin fiber in the next sarcomere. In the center of the I band is the dark z disc that is the attachment site for actin filaments.

Front 16

A bands

Back 16

From one z line to the next z line is one sarcomere. Betwen th light I bands are darker bands called A bands. They are areas where the thick myosin filaments and thin actin filaments overlap.

Front 17

Cross bridges

Back 17

Actin fibers are 2 strands of protein twisted together to form a helical structure like DNA. The myosin molecule has a twisted tail attached to two globular heads that form cross bridges to actin and interact with the actin to shorten the sarcomere during muscle contraction

Front 18

Neuromuscular junctions

Back 18

Sites where the ends of motor nerve fibers connect to muscle fibers. However, connect is not accurate because a very small space called the synaptic space exist between the end of the nerve fiber and the sarcolemma of the muscle fiber.

Front 19

Synaptic space

aka

synaptic cleft

Back 19

space between end of nerve fiber and the sarcolemma (cell membrane).

Front 20

Synaptic Vesicles

Back 20

Within the end of a nerve fiber in a neuromuscular junction are tiny sacs called synaptic vesicles that contain the chemical neurotransmitter acetylcholine.

Front 21

Acetylcholine

Back 21

When nerve impulse comes down the motor nerve fiber, it causes the release of acetylcholine, which quickly diffuses across the synaptic space and binds to receptors on the sarcolemma. This starts the process that leads to the contraction of the muscle fiber.

Front 22

Motor Unit

Back 22

Term used to describe one nerve fiber and all the muscle fibers it innvervates. Muscles that must make small movements have only a few muscle fibers per nerve fiber in each motor unit. Large powerful muscles have hundred or more muscles fibers per motor unit.

Front 23

Innervates

(sends impulse to)

Back 23

Each nerve fiber innervates more than one muscle fiber. The number of muscle fibers per nerve fiber determines how small a movement will result from a nerve stimulus.

Front 24

Connective tissue layer

Endomysium

Back 24

Delicate connective tissue layer called endomysium surrounds each individula skeletal muscle fiber (Straw). It is composed of fine, reticular fibers.

Front 25

Fascicles

(bundles of straws)

Back 25

Groups of skeletal muscle fibers, called fascicles are bound together by a tougher connective tissue layer called perimysium, which is composed of reticular fibers and thick collagen fibers.

Front 26

Epimysium

Back 26

Groups of muscle fascicles (the box that holds bundles of straws) are surrounded by epimysium, a fibrous connective tissue layer composed largely of tough collagen fibers. The outer covering of the entire muscle.

Front 27

Connective tissue layer

Back 27

These three connective tissue layers are continuous with the tendon or aponeuroses that connect the muscle to bones or other muscles. They not only hold the components of the muscles together but also help fasten the muscle firmly to its attachment mechanisms. It also contains the blood vessels and nerve fibers that supply the muscle fibers.

Front 28

Initiation of muscle contraction

Back 28

When a nerve impulse travels down a motor nerve fiber and reaches the end bulb at the neuromuscular junction, acetylcholine is released into synaptic space. The acetylcholine molecules bind to receptors on the surface of the sarcolemma which start an impulse that travels along the sarcolemma through the t tubules to the interior of the cell. When the impulse reaches the sarcoplasmic reticulum, it causes the release of stored calcium ions in to the sarcoplasm. As the Ca diffuses into the myofibrils, it turns on the contraction process which is powered by high energy ATP.

Front 29

Initiation of muscle relaxation

Back 29

As soon as the sarcoplasmic reticulum releases its Ca into the sarcoplasm, it begins pumping it back in again. This pulls the Ca out of the myofibrils, and the contraction process shuts down. The elasticity of the muscle fiber then restors it to its original length, relaxing the fiber. Pumping the Ca back into the sarcoplasmic reticulum requires energy, which is also supplied by ATP.

Front 30

Mechanics of Muscle contraction

Back 30

When muscle fiber is in a relaxed state, the actin and myosin filaments overlap only a little. When the fiber is stimulated to contract, the globular heads attached to the tails of the mysoin filaments, which are in contact with the actin filaments, ratchet back and forth and pull the actin filaments on both sides towad the center of the myosin filaments. The sliding of the filaments over each other shortens the sarcomere. The combined shortening of all the end to end sarcomeres in a muscle fiber result in muscle contraction.

Front 31

Characteristics of muscle contraction

Back 31

Small fine movements require only a few muscle fibers to contract. Larger, more powerful movements require the contraction of many muscle fibers. The nervous system is calling the shots; therefore, it must predict how large and powerful a movement needs to be and then it must send the appropriate nerve impulses down to the appropriate muscle fibers in the appropriate muscles. This results in what we refer to as the muscle memory.

Front 32

All or Nothing principle

Back 32

An individual muscle fiber either contracts completely when it receives a nerve impulse, or it does not contract at all.

Front 33

Chemistry of muscle contraction

Back 33

The considerable mechanical work of muscle contraction must be powered by a plentiful supply of energy. The immediate energy source that powers the sliding of the actin and myosin filaments is ATP, which is produced by the many mitochondria in muscle fibers. ATP molecules are like tiny batteries that can release energy and then be recharged so that they can do it again.

Front 34

Creatine phosphate

Back 34

The battery charger that converts ADP back to ATP is another compound in the muscle fiber called CP. When the CP molecule splits, the energy that is released adds a phosphate group to the ADP, converting it back to ATP.

Front 35

Chemistry of muscle contraction

Back 35

The ultimate source of energy used to produce ATP and CP and keep the whole system operating comes from the catabolism (breakdown) of nutrient molecules. The two main components involved are glucose and oxygen. Glucose is a sugar molecule that is the primary source for most body cells. Muscles have a large blood supply that constantly brings new supplies of glucose and oxygen to muscle fibers.

Front 36

Glycogen

Back 36

When the supplies are plentiful and the cells are fairly inactive, muscle fibers can also store glucose and oxygen for future needs. Glucose is stored in the fibers in the form of glycogen

Front 37

Myoglobin

Back 37

Oxygen is stored attached to large protein molecules called myoglobin. Myoglobin is red and can store and release large quantities of oxygen. When strenuous muscle contraction begin to deplete the oxygen supply to a muscle fiber, myoglobin can release its stash of oxygen molecules to resupply the fiber.

Front 38

Aerobic Metabolism

Back 38

As long as the oxygen supply is adequate to keep up with the energy needs of the fiber, the process is known as aerobic metabolism, and the maximum amount of energy is extracted from each glucose molecule.

Front 39

Anaerobic Metabolism

Back 39

Sometimes, particularly during periods of strenuous activity, the need for oxygen exceeds the available supply, and muscle fibers must shift to what is called anaerobic metabolism to produce the energy required for continued activity.

Front 40

Lactic Acid

Back 40

Anaerobic metabolism is not as efficient as aerobic metabolism and results in lactic acid formation as a by product of incomplete glucose breakdown. Lactic acid can accumulate in the muscle tissue and cause discomfort.

Front 41

Cardiac Muscle

(Involuntary Striated Muscle)

Back 41

It is called involuntary because it's contractions are not under conscious control. The striated part of the name is given because under the microscope its cells have the same kind of striped appearance as skeletal muscle cells.

Front 42

Gross Anatomy of Cardiac Muscle

Back 42

Found only in the heart and forms most of the volume of the heart and makes up the majority of the walls of the cardiac chambers. Cardiac muscle cells form elaborate networks around the cardiac chambers

Front 43

Microscopic Anatomy of Cardiac Muscle

Back 43

Cardiac muscles contain many of the same organelles and intracellular structures like skeletal muscles, such as myofibrils. Cardiac muscles are much smaller than skeletal muscle cells and have only one nucleus per cell. They are longer than they are wide and often have multiple branches. They are securely attached to each other end to end to form intricate branching networks of cells.

Front 44

Intercalated discs

Back 44

The firm, end to end attachments between cardiac muscle cells are called intercalated discs. The intercalated discs securely fasten the cells together and also transmit impulses from cell to cell to allow large groups of cardiac muscle cells to contract in a coordinated manner.

Front 45

Physiology of Cardiac Muscle

Back 45

Each cell contracts rythmically with no external stimulation. Each cell would be contracting at a constant rate set by its own internal metronome, some fast and other slow. However, if two cells touch, the slower contracting cell adopts the faster cells contraction rate. C.M contract in a rapid, wavelike fashion

Front 46

2 unique and important things about cardiac muscle

Back 46

1. it contracts without any external stimulation

2. groups of cardiac muscle cells adopt the contraction rate of the most rapid cell in the group.

Front 47

Sinoatrial Node

(SA)

Back 47

The impulse that starts each heartbeat begins in the hearts pacemaker called SA node, located in the wall of the right atrium. The contraction rate of the cardiac muscle cells in the SA node is faster than those in the walls of the atria or ventricals, therefore its rate takes precedence.

Front 48

Nerve Supply

Back 48

Although, It is not needed to initiate the contractions of cardiac muscle, the heart does have a nerve supply that can modify its activity. The nerves to the heart are from both divisions of the autonomic portion of the nervous system; the sympathetic and parasympathetic system.

Front 49

Sympathetic system

Back 49

Sympathetic fibers stimulate the heart to beat harder and faster as part of the fight or flight response that kicks in when an animal feels threatened.

Front 50

Parasympathetic system

Back 50

Parasympathetic fibers do the opposite in that they inhibit cardiac function, thereby causing the heart to bear more slowly and with less force when the body is relaxed and resting.

Front 51

Location of the heart

Back 51

The heart is located in the middle of the thoracic cavity in the mediastinum, the space between the two lungs.

Front 52

Mediastinum

Back 52

The space between the two lungs. In addition to the heart, the mediastinum also contains blood vessels.

Front 53

Base of the heart

Back 53

It has a rounded cranial end (Top part) where the vessels connect. The wide end is the base.

Front 54

Apex of the heart

Back 54

The more pointed caudal end (Bottom). The narrow end is the apex

Front 55

Size and shape of the heart

Back 55

The heart does not sit straight along the median plane in an animal. The base (top) is shifted to the right and faces more dorsally (up). The apex is shifted to the left and sits more ventrally (down).

Front 56

Coverings of the heart

(Pericardium)

Back 56

The heart is contained in a fibrous sac called the pericardium. The pericardium is divided into two parts:

1. Fibrous sac called the pericardial sac

2. Serous pericardium

Front 57

Pericardial Sac

Back 57

The pericardial sac is a little loose so the heart can beat inside it but it is not elastic so it cannot stretch if the heart becomes abnormally enlarged.

Front 58

Serous Pericardium

Back 58

The serous pericardium consists of two membranes. A smooth, moist serous membrane called the parietal layer of the serous pericardium lines the pericardial sac, and the visceral layer of the serous pericardium lies directly on the surface of the heart.

Front 59

Parietal layer

Back 59

It is a smooth moist membrane of the serous pericardium that lines the pericardial sac

Front 60

Visceral layer

Back 60

Of the serous pericardium lies directly on the surface of the heart

Front 61

Pericardial space

Back 61

The are between the two serous membranes. It is filled with pericardial fluid that lubricates the two membranes and prevents friction as they rub together during contractions and relaxations of the heart muscle

Front 62

Wall of the heart

Back 62

Has 3 layers

- Epicardium

- Myocardium

- Endocardium

Front 63

Myocardium

Back 63

The middle and thickest layer is the muscular layer called the myocardium because it is made up of cardiac muscle. Cardiac muscle fibers are joined side to side by multiple branches and end to end by intercalated discs.

Front 64

Autorhythmic

Back 64

Without outside stimulus it can start beating (contracting and relaxing) in a steady rhythm before an animal is born and continue beating through birth.

Front 65

Epicardium

aka

Visceral layer

Back 65

The outermost layer of the heart wall. It is a membrane that lies on the external surface of the myocardium.

Front 66

Endocardium

Back 66

The membrane that lies on the internal surface of the myocardium. It is composed of thin, flat simple squamous epithelium and forms the lining of the heart chambers. The endocardium is continuous with the endothelium that lines blood vessels. The endocardium also covers the valves that seperate the chambers of the heart.

Front 67

Papillary Muscle

Back 67

The inside surface of the myocardium is not smooth. It forms ridges and nipple like projections called papillary muscles that are covered by the endocardium

Front 68

Chambers of the heart

Back 68

There are four chamber in the heart.

Two Atria: (left & right) that receive blood into the heart. Singular is Atrium. Two Ventricles: (left & right) that pump blood out of the heart. The two atria sit on top of the two ventricles and their walls form part of the base of the heart. The two ventricles sit below the two atria and the wall of the left ventricle forms the apex of the heart

Front 69

Interatrial Septum

Back 69

The left atrium and the right atrium are separated by the interatrial septum that is a continuation of the myocardium.

Front 70

Atria

Back 70

The atria receive blood from Lg veins that carry blood to heart. When the atria have filled with blood their walls (composed of myocardium) contract and force blood through one way valves into ventricles. They are at the top of the heart and form the base.

Front 71

Interventricular Septum

Back 71

The left and right ventricles are separated by the interventricular septum, which is a continuation of the interatrial septum.

Front 72

Interventricular groove

Back 72

The area of the interventricular septum and interatrial septum is visible on the outside of the heart as the interventricular groove. The groove contains coronary blood vessels and is frequently filled with fat.

Front 73

Ventricles

Back 73

When the ventricles have received blood from the atria the myocardium of the ventricular walls contract and force blood through one way valves into arteries.

Front 74

Pulmonary Artery

Back 74

The right ventricle pumps blood to the pulmonary circulation through the pulmonary artery. Since blood from the right ventricle doesn't have to go far, the right ventricular wall is thinner than the left ventricular wall.

Front 75

Aorta

Back 75

The left ventricle pumps blood into the systemic circulation through the aorta. The left ventricular wall has the most work to do pumping blood to the rest of the animals body so it has a thicker wall that will contract with greater force. The left ventricular wall makes up the apex of the heart.

Front 76

Auricles

Back 76

The atria are identified on the outside of the heart by their auricles. These are blind pouches that come off the main part of the atria and look like earflaps.

Front 77

Valves of the heart

Back 77

4 one way valves that control blood flow through the heart. Two of the valves are located between the right and left atria and their respective ventricles. The other two are located between the right and left ventricles and the arteries they eject blood into. The valves close at specific times to prevent backflow of blood into the chamber it came from.

Front 78

Atrioventricular Valves

(AV Valves)

Back 78

located between the atria and the ventricles.

Front 79

Tricuspid Valve

Back 79

The right AV valve consists of 3 flaps of endothelium and is called the tricuspid valve. It opens when the pressure from the amount of blood in the right atrium forces it open and allows blood to flow into the right ventricle. When the pressure from the blood in the right ventricle exceeds the pressure of blood in the right atrium the tricuspid valve is forced to shut.

Front 80

Chordae Tendonae

Back 80

The valve is prevented from opening backward into the atrium by collagen fiber cords that are attached to the edge of each cusp and to papillary muscles in the wall of the right ventricle. These cords are called chordae tendonae

Front 81

Bicuspid Valve

aka

mitral valve

Back 81

The left AV valve has only two cusps and is called bicuspid valve. This valve also has attached chordae tendonae.

Front 82

Semilunar valves

Back 82

The two valves that control blood flow out of the ventricles and into arteries are the semilunar valves because they have 3 cusps, each resembles a crescent moon.

Front 83

Pulmonary Valve

Back 83

The right semilunar valve is the pulmonary valve because blood from the right ventricle flows through it into the pulmonary circulation.

Front 84

Aortic Valve

Back 84

The left semilunar valve is the aortic valve because blood from the left ventricle flows through it into the aorta, which is the major artery that is the beginning of the systemic circulation.

Front 85

Skeleton of the heart

Back 85

The skeleton of the heart is located between the atria and the ventricles. It is made up of four dense fibrous connective tissue rings and has 4 primary functions:

1. It separates the atria & ventricles

2. It anchors the heart valves

3. It provides a point of attachment for the myocardium

4. It provides some electrical insulation between the atria and the ventricle.

Front 86

Blood supply to the heart

Back 86

Cells of the heart need nourishment and oxygen brought to them and waste materials carried away.

Front 87

Coronary Arteries

Back 87

Branch off the Aorta just past the aortic valve (left semilunar valve). They continue to branch around the heart until they completely encircle it.

Front 88

Coronary Veins

Back 88

To return blood to the circulation the coronary veins join together near the right atrium and form a channel called the coronary sinus that drains directly into the right atrium.

Front 89

Nerve Supply to the heart

Back 89

Cardiac muscle is autorythmic and can create its own contraction and relaxation through its internal conduction system. The nerve fibers enter the heart and terminate primarily in the right atrium near the are of the cardiac muscle cells that control the cardiac conduction system. The nerve supply to the heart serves a purpose, but is not essential.

Front 90

Blood flow through the heart

Back 90

The entire purpose of the heart is to receive deoxygenated blood from the sytemic circulation (right atrium), send it out to the pulmonary circulation for oxygenation (right ventricle), receive the freshly oxygenated blood back from the pulmonary circulation (left atrium), and put it into systemic circulation (left ventricle).

Front 91

Vena Cava

Back 91

The large vein that brings deoxygenated blood from the systemic circulation to the heart. The vena cava enter the right atrium of the heart.

Front 92

Cardiac cycle

Back 92

Once cycle of atrial and ventricular contraction and relaxation. The cardiac cycle produces one heartbeat

Front 93

Structures of cardiac conduction

Back 93

- SA Node

- AV Node (Atrioventricular node)

- AV Bundle

- AV Valve

Front 94

Atrioventricular Node

Back 94

The impulse generated by the SA node travels through the walls of the atria to the AV node located in the atrioventricular septum that separates the left and right sides of the heart. The only route of conduction the impulse can take from the atria to the ventricles is through AV node.

Front 95

AV Bundle

Back 95

After the delay at the AV Node, the impulse resumes its journey, this time through AV bundle and the purkinje fiber system. The fibers of the bundle travel down the interventricular septum to the apex of the heart.

Front 96

Purkinje fiber system

Back 96

The purkiinje fiber system picks up the impulses, makes a U turn and carries them from the bundle up into the right and left ventrical myocardium. Because the impulse is delivered to the apex more quickly than it can spread from cell to cell, the ventricles actually contract starting from the apex and moving toward the base of the heart. This apex to base direction of ventricular contraction facilitates ejection of blood into the aorta and pulmonary arteries, located at base of heart.

Front 97

Smooth Muscle

aka

(Nonstriated Involuntary Muscle)

Back 97

It is involuntary because its contractions are not under conscious control. The smooth part of the name is because its cells do not have the stripped appearance under the microscope

Front 98

Gross Anatomy of smooth muscle

Back 98

Smooth muscle is found all over the body but not in distinct structures like skeletal muscles and the heart. It is found in two forms:

1. visceral smooth muscle

2. multi unit smooth muscle

Front 99

Visceral smooth muscle

Back 99

Found as large sheets of cells in the walls of some hollow organs

Front 100

Multi unit smooth muscle

Back 100

Found as small, discrete groups of cells.

Front 101

Anatomy of smooth muscle

Back 101

Small and spindle shaped with a single nucleus in the center. Their filaments of actin and myosin are not arranged in parallel myofibrils like in skeletal muscles. Rather, small, contractile units of actin and myosin filaments crisscross the cell at various angles and are attached at both ends to dense bodies that correspond to Z lines in skeletal muscles. When these contractile units shorten, they cause the cell to ball up as it contracts.

Front 102

Visceral smooth muscle

Back 102

Found in walls of many internal soft organs aka viscera. The muscle cells are linked to form large sheets in the walls of organs such as the stomach and intestines, bladder. Fine movements are not possible w/ visceral smooth muscle; rather, it experiences large, rhythmic waves of contraction. No need for external stimulation for contraction.

Front 103

Nerve supply to smooth muscle

Back 103

Visceral smooth muscle has a nerve supply that is not necessary to initiate contraction but serves to modify them. Like cardiac muscle the nerve supply consists of sympathethic and parasympathethic system.

Front 104

Sympathethic stimulation

(Smooth muscle)

Back 104

The effects are reverse in smooth muscle, than cardiac muscle. Sympathethic stimulation decreases visceral smooth muscle activity. Sympathethic stimulation prepares an animal for intense physical activity. Blood is diverted away from the viscera and redirected to the heart and brain to help deal with whatever threat initiated fight or flight response. Decreasing GI motility.

Front 105

Parasympathethic Stimulation

(Smooth Muscle)

Back 105

The effects are reverse in smooth muscle, than cardiac muscle. Parasympathethic stimulation increases visceral smooth muscle activity. When the animal is relaxed and resting, the parasympathetic system predominates and enhances functions such as GI activity to help supply nutrients to the body cells during this down time.

Front 106

Multi Unit Smooth Muscle

Back 106

It is small and delicate. Multi unit smooth muscle is made up of individual smooth muscle cells or small groups of cells. Found where small, delicate contractions are needed, such as the iris and ciliary body of the eye, walls of small blood vessels and passageways to lungs. Contractions are not automatic. They require specific impulses from autonomic nerve contract. The actions of multi unit smooth muscle are specific and carefully controlled.