The muscular systemThe muscular system

Muscle tissue factsMuscle tissue facts

Muscles make up Muscles make up half of your body half of your body weight.weight.

Lines the insides of Lines the insides of hollow organs.hollow organs.

They take chemical They take chemical energy (ATP) and energy (ATP) and directly convert it directly convert it to mechanical to mechanical energy.energy.

Important prefixesImportant prefixes

Mys or myo- muscleMys or myo- muscle Sarco- flesh (referring to muscle)Sarco- flesh (referring to muscle)

Types of Muscle tissuesTypes of Muscle tissues

There are three types of muscle There are three types of muscle tissues:tissues:• SkeletalSkeletal• CardiacCardiac• SmoothSmooth

Skeletal Muscle TissueSkeletal Muscle Tissue

Skeletal muscle tissue is bundled to Skeletal muscle tissue is bundled to create skeletal muscle, which are create skeletal muscle, which are organs that attach directly to the organs that attach directly to the skeleton.skeleton.

They have obvious stripes called They have obvious stripes called striations.striations.

Often are muscles that can be Often are muscles that can be voluntarily controlled. The only voluntarily controlled. The only muscle type that has voluntary muscle type that has voluntary control.control.

*Key words to remember: *Key words to remember: • Skeletal: striated, voluntarySkeletal: striated, voluntary

Cardiac Muscle TissueCardiac Muscle Tissue

Found only in the heart.Found only in the heart. Striated, but involuntary.Striated, but involuntary. contracts normally at a steady rate contracts normally at a steady rate

set by the hearts pacemaker set by the hearts pacemaker depending on the situation.depending on the situation.

Key words to remember:Key words to remember:• Cardiac: striated, involuntaryCardiac: striated, involuntary

Smooth muscle tissueSmooth muscle tissue

Found in the walls of hollow visceral Found in the walls of hollow visceral organs (like stomach). It has the role organs (like stomach). It has the role of forcing fluids and other substances of forcing fluids and other substances through internal body channels.through internal body channels.

No striationsNo striations Slow sustained contractions.Slow sustained contractions. Key words to remember:Key words to remember:

• Visceral, nonstriated and involuntaryVisceral, nonstriated and involuntary

Special characteristics of muscle Special characteristics of muscle tissuetissue

Irritability: able to respond to the Irritability: able to respond to the outside environment. Usually outside environment. Usually responds to chemical and electrical responds to chemical and electrical impulses. impulses.

Contractility: is the ability to shorten Contractility: is the ability to shorten forcibly when stimulated.forcibly when stimulated.

Extensibility: the ability to stretch or Extensibility: the ability to stretch or extend.extend.

Elasticity: the ability for muscle to Elasticity: the ability for muscle to recoil to its original shape after recoil to its original shape after stretching.stretching.

General Muscle FunctionsGeneral Muscle Functions

Producing movement.Producing movement. Maintaining posture and body Maintaining posture and body

Position.Position. Stabilizing joints.Stabilizing joints. Generating heat.Generating heat. Protection (skeletal muscle)Protection (skeletal muscle)

Skeletal MusclesSkeletal MusclesGross AnatomyGross Anatomy

Skeletal muscleSkeletal muscle

Each muscle in skeletal muscle is its Each muscle in skeletal muscle is its own discrete organ. Each is made up own discrete organ. Each is made up of several kinds of tissues.of several kinds of tissues.

Nerves and blood supplyNerves and blood supply

In general, each muscle is served by In general, each muscle is served by at least one nerve, one artery, and at least one nerve, one artery, and one or more veins.one or more veins.

Skeletal muscles tend to be highly Skeletal muscles tend to be highly vascularized, because they expend a vascularized, because they expend a lot of energy when they contract.lot of energy when they contract.

Connective tissue sheathsConnective tissue sheaths

Each muscle fiber is wrapped in an Each muscle fiber is wrapped in an individual sheath to support the individual sheath to support the entire muscle. This is important entire muscle. This is important since this will help prevent muscles since this will help prevent muscles from bursting, except for when a from bursting, except for when a contraction is too strong.contraction is too strong.

Sheath typesSheath types

Epimysium-dense overcoat that Epimysium-dense overcoat that surrounds the whole muscle.surrounds the whole muscle.

Perimysium and fascicles- fascicles Perimysium and fascicles- fascicles are groups of muscle cells that look are groups of muscle cells that look like a bundle of sticks. Each fascicle like a bundle of sticks. Each fascicle is connected by dense fibrous tissue is connected by dense fibrous tissue called the perimysium.called the perimysium.

Endomysium- a sheath of connective Endomysium- a sheath of connective tissue that surrounds each individual tissue that surrounds each individual muscle fiber. Consists of dense muscle fiber. Consists of dense connective tissue.connective tissue.

RememberRemember

Muscles span over joints. The less Muscles span over joints. The less moveable part of a muscle is called moveable part of a muscle is called the origin, and the more moveable the origin, and the more moveable area is the insertion.area is the insertion.

Muscles can attach directly, where Muscles can attach directly, where muscle is fused directly to bone, or muscle is fused directly to bone, or indirectly, where muscle attaches to indirectly, where muscle attaches to bone through a tendon.bone through a tendon.

Skeletal MusclesSkeletal MusclesMicroscopic AnatomyMicroscopic Anatomy

Inside skeletal muscle tissueInside skeletal muscle tissue

Sarcoplasm- cytoplasm of muscle Sarcoplasm- cytoplasm of muscle cells that contains high amounts of cells that contains high amounts of glycosomes, which store glucose for glycosomes, which store glucose for situations of high activity.situations of high activity.

Myoglobin- a red pigment that stores Myoglobin- a red pigment that stores oxygen. *very similar to hemoglobin.oxygen. *very similar to hemoglobin.

myofibrilsmyofibrils

Rod-like fiber that run parallel to the Rod-like fiber that run parallel to the muscle fibers. There are hundreds of muscle fibers. There are hundreds of thousands in each muscle cell.thousands in each muscle cell.

StriationsStriations

Striations Are repeating series of dark and Striations Are repeating series of dark and light bands in the muscle tissue. light bands in the muscle tissue.

Dark bands are called Dark bands are called A bandsA bands Light bands are called I Light bands are called I bandsbands

H zone, M line, and Z discH zone, M line, and Z disc

H zone- light region in the middle of H zone- light region in the middle of an A band.an A band.

M line- bisection of the H zoneM line- bisection of the H zone Z disc- dark interruption in the I Z disc- dark interruption in the I

band.band.

SarcomereSarcomere

Sarcomere- the smallest functional Sarcomere- the smallest functional unit of the muscle tissue.unit of the muscle tissue.

Thicker parts of the of tissue contain Thicker parts of the of tissue contain myosin, which runs down the length myosin, which runs down the length of the I band.of the I band.

Thin filaments contain actin, which Thin filaments contain actin, which extends through the I band and extends through the I band and partly into the A band.partly into the A band.

Sarcoplasmic reticulumSarcoplasmic reticulum

A type of smooth ER that A type of smooth ER that interconnects each myofibril.interconnects each myofibril.

Sliding Filaments Model of Sliding Filaments Model of ContractionContraction

During muscle contraction, thin and During muscle contraction, thin and thick filaments begin to over lap thick filaments begin to over lap greatly. greatly.

There is very little overlap in the There is very little overlap in the thick and thin filament when the thick and thin filament when the tissue is relaxed.tissue is relaxed.

For a skeletal muscle fiber to For a skeletal muscle fiber to contractcontract

1. It must be stimulated by a nerve 1. It must be stimulated by a nerve ending.ending.

2. It must generate an electrical current 2. It must generate an electrical current called an action potential through the called an action potential through the sarcolemma (thin membrane that covers sarcolemma (thin membrane that covers the muscle fiber).the muscle fiber).

3. a quick moment of calcium ions spike 3. a quick moment of calcium ions spike and act a trigger for muscle contraction to and act a trigger for muscle contraction to occur.occur.

Nerve stimulus of muscle Nerve stimulus of muscle contractioncontraction

Nerve cells in skeletal muscle are Nerve cells in skeletal muscle are called somatic motor neurons. The called somatic motor neurons. The place where somatic motor neurons place where somatic motor neurons join to a muscle through large join to a muscle through large branches the axon of the nerve cell is branches the axon of the nerve cell is called a neuromuscular junction.called a neuromuscular junction.

The nerves do not connect with each The nerves do not connect with each other and are separated by a space other and are separated by a space called a synaptic cleft. The cleft is called a synaptic cleft. The cleft is filled with a gel like substance that filled with a gel like substance that contains acetylcholine (a contains acetylcholine (a neurotransmitter, abbreviated Ach).neurotransmitter, abbreviated Ach).

Acetylcholine (Ach) will land on the thick Acetylcholine (Ach) will land on the thick parts of the sarcolemma that contain large parts of the sarcolemma that contain large Ach receptors.Ach receptors.

When Ach diffuses across the membrane, When Ach diffuses across the membrane, it causes a change in electrical potential in it causes a change in electrical potential in the membrane.the membrane.

The enzyme acetylcholesterase will break The enzyme acetylcholesterase will break down acetylcholine so that it does not down acetylcholine so that it does not continue muscle fiber contraction when continue muscle fiber contraction when not necessary. not necessary.

Channels involved in muscle Channels involved in muscle contractioncontraction

Calcium channels trigger the release of Ach.Calcium channels trigger the release of Ach. Ach binds to Ach receptors to open sodium-Ach binds to Ach receptors to open sodium-

potassium channels. High sodium influx causes potassium channels. High sodium influx causes electrical potential.electrical potential.

The influx of sodium depolarizes other sodium The influx of sodium depolarizes other sodium channels and further depolarizes the sarcolemma channels and further depolarizes the sarcolemma and creates an action potential.and creates an action potential.

Transmission of action potential along T-tubules Transmission of action potential along T-tubules causing a conformation change in voltage causing a conformation change in voltage sensitive proteins which cause calcium channels sensitive proteins which cause calcium channels to release calcium into cytosol.to release calcium into cytosol.

Muscle fiber contraction:Muscle fiber contraction:cross bridge activitycross bridge activity

The attachment of myosin to actin is The attachment of myosin to actin is called cross bridge formation. It requires called cross bridge formation. It requires calcium to occur. When intracellular calcium to occur. When intracellular calcium is low, muscle is relaxed. calcium is low, muscle is relaxed.

Myosin has a special blocking molecule Myosin has a special blocking molecule called tropomyosin. As calcium levels rise, called tropomyosin. As calcium levels rise, tropomyosin will be removed by troponin. tropomyosin will be removed by troponin. Troponin will not move the tropomyosin Troponin will not move the tropomyosin unless it binds to calcium ions to itself. unless it binds to calcium ions to itself.

This acts as the go ahead to move This acts as the go ahead to move tropomyosin by guaranteeing enough tropomyosin by guaranteeing enough calcium is present.calcium is present.

Contraction of Skeletal MuscleContraction of Skeletal MusclePrinciples of Muscle MechanicsPrinciples of Muscle Mechanics

The principles of skeletal muscle The principles of skeletal muscle contraction and general muscle contraction and general muscle contraction are basically the same.contraction are basically the same.

The force exerted by a muscle on an The force exerted by a muscle on an object is called muscle tension.object is called muscle tension.

The weight of the object is called the The weight of the object is called the load.load.

Contracting muscle does not Contracting muscle does not always shorten and move a load.always shorten and move a load.

If you develop muscle tension and If you develop muscle tension and the load does not move, this is the load does not move, this is referred to as isometric contraction.referred to as isometric contraction.

If you develop muscle tension and If you develop muscle tension and the load you are attempting to lift or the load you are attempting to lift or move does in fact move, it is referred move does in fact move, it is referred to as an isotonic contraction.to as an isotonic contraction.

Motor unitsMotor units

The functional unit of a motor neuron The functional unit of a motor neuron and all of the muscles it supplies is and all of the muscles it supplies is called a motor unit.called a motor unit.

When the motor neuron fires, all of When the motor neuron fires, all of the muscles it associates with will the muscles it associates with will contract simultaneously.contract simultaneously.

The number of muscle fibers to The number of muscle fibers to motor units tends to vary depending motor units tends to vary depending on the location and how precise on the location and how precise control needs to be.control needs to be.

The motor unit to muscle fiber ratio The motor unit to muscle fiber ratio would be small when a fine muscle is would be small when a fine muscle is required to move like an eyelash.required to move like an eyelash.

Motor units and the muscles they Motor units and the muscles they control are not necessarily right next control are not necessarily right next to each other. to each other.

This is important because a single This is important because a single motor neuron will not cause a strong motor neuron will not cause a strong contraction in a single area of a contraction in a single area of a muscle, but a weak contraction over muscle, but a weak contraction over the entirety of the muscle.the entirety of the muscle.

Muscle twitchMuscle twitch

The response of a motor unit to an The response of a motor unit to an action potential of its motor neuron is action potential of its motor neuron is called muscle twitch.called muscle twitch.

It consists of three stages:It consists of three stages:• The latent periodThe latent period• The period of contractionThe period of contraction• The period of relaxationThe period of relaxation

The latent periodThe latent period

Muscle tension increases but no Muscle tension increases but no response is seen. Lasts only a few response is seen. Lasts only a few milliseconds.milliseconds.

Contraction periodContraction period

Cross bridges activate. If the build of Cross bridges activate. If the build of tension is greater than the load being tension is greater than the load being lifted, then muscle will shorten.lifted, then muscle will shorten.

Last from 10-100 Last from 10-100

milliseconds.milliseconds.

Period of relaxationPeriod of relaxation

Calcium reenters the sarcoplasmic Calcium reenters the sarcoplasmic reticulum. Muscle contraction reticulum. Muscle contraction declines. Muscle relaxes and returns declines. Muscle relaxes and returns to latent state.to latent state.

Muscle MetabolismMuscle Metabolism

Muscle metabolismMuscle metabolism

Muscles use ATP when they contract to Muscles use ATP when they contract to perform the cross bridge movement, and perform the cross bridge movement, and for the operation of the calcium pumps of for the operation of the calcium pumps of the sarcoplasmic reticulum. the sarcoplasmic reticulum.

They can get that ATP from three different They can get that ATP from three different means:means:• Direct phosphorylation of creatine phosphate.Direct phosphorylation of creatine phosphate.• glycolysis (anaerobic)glycolysis (anaerobic)• Aerobic respirationAerobic respiration

Direct phosphorylationDirect phosphorylation

Reaction of creatine phosphate and ADP.Reaction of creatine phosphate and ADP. creatine creatine

kineasekinease Creatine phosphate + ADP Creatine phosphate + ADP creatine + ATP creatine + ATP

Stats:Stats:• Oxygen use: noneOxygen use: none• Products: 1 ATP per CP, creatineProducts: 1 ATP per CP, creatine• How long energy lasts: 15 seconds.How long energy lasts: 15 seconds.

Anaerobic respiration: GlycolysisAnaerobic respiration: Glycolysis

Forms ATP without oxygen, forming lactic acid in Forms ATP without oxygen, forming lactic acid in the process. Energy source is glucose.the process. Energy source is glucose.

Glucose breaks down through glycolysis to create Glucose breaks down through glycolysis to create pyruvic acid, which is then broken down into pyruvic acid, which is then broken down into pyruvic acid and released in the blood.pyruvic acid and released in the blood.

Stats:Stats:• Oxygen use: NoneOxygen use: None• Products: 2 ATP per glucose, lactic acidProducts: 2 ATP per glucose, lactic acid• How long it lasts: ~60 secondsHow long it lasts: ~60 seconds

Aerobic respirationAerobic respiration

Uses glucose and oxygen to produce Uses glucose and oxygen to produce ATP.ATP.

Glucose + oxygen Glucose + oxygen carbon dioxide + water + ATP carbon dioxide + water + ATP

Stats:Stats:• Oxygen Use: Yes (required)Oxygen Use: Yes (required)• Products: 32 ATP per glucose, carbon Products: 32 ATP per glucose, carbon

dioxide and waterdioxide and water• How long it lasts: hoursHow long it lasts: hours

What is used during sports What is used during sports activities?activities?

The length of time a muscle can The length of time a muscle can undergo aerobic respiration without undergo aerobic respiration without tiring is called tiring is called aerobic enduranceaerobic endurance..

At the point where a muscle can no At the point where a muscle can no longer continue to support itself longer continue to support itself under just aerobic respiration, it will under just aerobic respiration, it will reach its reach its anaerobic thresholdanaerobic threshold. .

Muscle FatigueMuscle Fatigue

Muscle fatigue is the physiological inability Muscle fatigue is the physiological inability for a muscle to contract. Several things for a muscle to contract. Several things cause this including mineral imbalances.cause this including mineral imbalances.

Contracture- the complete loss of ATP Contracture- the complete loss of ATP which prevents rapid muscle contraction.which prevents rapid muscle contraction.

Permanent contracture= rigor mortisPermanent contracture= rigor mortis Temporary contracture= writerTemporary contracture= writer’’s cramp.s cramp.

Oxygen DeficitOxygen Deficit

For a muscle to return to normal, For a muscle to return to normal, oxygen levels must be restored, oxygen levels must be restored, lactic acid must be converted back to lactic acid must be converted back to glucose or glycogen, and ATP and glucose or glycogen, and ATP and creatine phosphate must be creatine phosphate must be resynthesized.resynthesized.

An oxygen deficit is the oxygen An oxygen deficit is the oxygen needed to begin the healing process.needed to begin the healing process.

Force of Muscle ContractionForce of Muscle Contraction

The force of a muscle contraction is The force of a muscle contraction is affected by four things:affected by four things:

1. The number of muscle fibers 1. The number of muscle fibers stimulated.stimulated.

2. The relative size of the fibers.2. The relative size of the fibers. 3. The frequency of stimulation.3. The frequency of stimulation. 4. The degree of muscle stretch.4. The degree of muscle stretch.

1. Number of stimulated muscle 1. Number of stimulated muscle fibersfibers

More fibers= bigger contractionMore fibers= bigger contraction

2. The size of muscle fibers2. The size of muscle fibers

The bulkier the The bulkier the muscle, the more muscle, the more tension it can have.tension it can have.

Regular resistance Regular resistance exercise will lead exercise will lead to hypertrophy to hypertrophy (bigger muscles)(bigger muscles)

3. Frequency of Fire3. Frequency of Fire

Force generated by cross bridges is called Force generated by cross bridges is called internal tension. internal tension.

Internal tension stretches the connective Internal tension stretches the connective tissue sheaths (called contractile tissue sheaths (called contractile components).components).

They become tight and transfer tension They become tight and transfer tension called external tension to the load and called external tension to the load and when the contraction ends the when the contraction ends the noncontractile components help return the noncontractile components help return the muscle to itmuscle to it’’s original shape.s original shape.

4. Degree of muscle stretch4. Degree of muscle stretch

The degree of muscle stretch in The degree of muscle stretch in relationship to the amount of force relationship to the amount of force produced is called the length tension produced is called the length tension relationship.relationship.

Velocity and duration Velocity and duration of muscle fibersof muscle fibers

Speed of contraction:Speed of contraction:• slow fiber- high aerobic rate, low slow fiber- high aerobic rate, low

anaerobic rate, slow movement, long anaerobic rate, slow movement, long endurance. endurance.

• fast fiber- high anaerobic rate, low fast fiber- high anaerobic rate, low aerobic rate, fast movement, low aerobic rate, fast movement, low endurance.endurance.

Major pathways of forming ATP:Major pathways of forming ATP:• Oxidative fibers- rely on oxygen and ATP Oxidative fibers- rely on oxygen and ATP

generationgeneration• Glycolytic fibers- relies on anaerobic Glycolytic fibers- relies on anaerobic

glycolysis to form ATP.glycolysis to form ATP.

So……So……

So you can classify skeletal muscle So you can classify skeletal muscle fibers as:fibers as:• Slow oxidative fibersSlow oxidative fibers• Fast oxidative fibersFast oxidative fibers• Fast glycolytic fibersFast glycolytic fibers

To learn these, refer to the velocity To learn these, refer to the velocity of the muscle fiber, and the of the muscle fiber, and the pathways for forming ATP.pathways for forming ATP.

Muscle Adaptation to exerciseMuscle Adaptation to exercise

Aerobic/endurance exercise will (over Aerobic/endurance exercise will (over time) increase the number of time) increase the number of capillaries in the muscle, causing a capillaries in the muscle, causing a slight increase in muscle size, slight increase in muscle size, however…however…

If you are looking for bulging muscle If you are looking for bulging muscle than anaerobic processes like weight than anaerobic processes like weight lifting will increase muscle size and lifting will increase muscle size and give you that ripped look.give you that ripped look.

That ripped lookThat ripped look

Overuse injuriesOveruse injuries

Muscles do not heal over night. Muscles do not heal over night. Prolonged and extended use Prolonged and extended use repeatedly under high intensity can repeatedly under high intensity can cause muscle to tear, causing cause muscle to tear, causing intense pain and temporary loss of intense pain and temporary loss of muscle function.muscle function.

Smooth MuscleSmooth Muscle

Smooth muscleSmooth muscle

Lines the walls of hollow organs (like Lines the walls of hollow organs (like the intestines). The only major the intestines). The only major exception is the heart, which is made exception is the heart, which is made up of cardiac tissue.up of cardiac tissue.

Microscopic anatomyMicroscopic anatomyof smooth muscleof smooth muscle

In smooth muscle there is no sheath In smooth muscle there is no sheath that covers all of the smooth muscle, that covers all of the smooth muscle, however, there is a small amount of however, there is a small amount of connective tissue (endomysium) that connective tissue (endomysium) that is found between smooth muscle is found between smooth muscle tissue.tissue.

Smooth muscle fibers will alternate Smooth muscle fibers will alternate contraction and relaxation in the contraction and relaxation in the tissues. When muscle contracts, the tissues. When muscle contracts, the organs will dilate and shorten, organs will dilate and shorten, pushing substances (like food) pushing substances (like food) downward. downward.

This action is This action is

known as peristalsis.known as peristalsis.

Smooth muscle is autonomic Smooth muscle is autonomic (automatic) and is involuntarily (automatic) and is involuntarily controlled.controlled.

Myosin arrangement in smooth Myosin arrangement in smooth musclemuscle

Myofilaments in the smooth muscle have Myofilaments in the smooth muscle have four major differences when comparing four major differences when comparing them to skeletal muscle.them to skeletal muscle.

They are:They are:• 1. Thick filaments are fewer but have myosin 1. Thick filaments are fewer but have myosin

heads along their entire length.heads along their entire length.• 2. No troponin complex within the filaments.2. No troponin complex within the filaments.• 3. Thick and thin filaments are arranged 3. Thick and thin filaments are arranged

vertically, which cause muscle contraction to vertically, which cause muscle contraction to move in a cork screw like manner.move in a cork screw like manner.

• 4. Smooth muscle fibers contain a lattice-like 4. Smooth muscle fibers contain a lattice-like arrangement of noncontractile intermedeiate arrangement of noncontractile intermedeiate filaments that resist tension.filaments that resist tension.

Smooth muscle contractionSmooth muscle contraction

Smooth muscle is able to contract in Smooth muscle is able to contract in a a ““smoothsmooth”” and synchronized fashion and synchronized fashion due largely to the fact that there are due largely to the fact that there are gap junctionsgap junctions that link the cells in the that link the cells in the smooth muscle tissue together smooth muscle tissue together allowing for an action potential to allowing for an action potential to move across the tissue easily.move across the tissue easily.

Contraction of smooth muscle is Contraction of smooth muscle is similar to that of skeletal muscle in similar to that of skeletal muscle in that:that:• 1. Actin and myosin interact by the 1. Actin and myosin interact by the

sliding filament mechanism.sliding filament mechanism.• 2. The final trigger for contraction is a 2. The final trigger for contraction is a

rise of intracellular calcium.rise of intracellular calcium.• 3. The sliding process is energized by 3. The sliding process is energized by

ATP.ATP.

Regulation of ContractionRegulation of Contraction

Two major factors regulate Two major factors regulate contraction of smooth muscle. They contraction of smooth muscle. They are:are:• 1. Neural regulation- just like skeletal 1. Neural regulation- just like skeletal

muscle. AP is generated by muscle. AP is generated by Neurotransmitter bindingNeurotransmitter binding Increase in Increase in intracellular calciumintracellular calcium Ach diffusion Ach diffusion through musclethrough muscle

2. Hormones and local chemical 2. Hormones and local chemical factors- smooth muscles that have factors- smooth muscles that have no nerve supply will rely on a change no nerve supply will rely on a change in chemicals or hormones to signal in chemicals or hormones to signal contraction.contraction.

Types of Smooth MuscleTypes of Smooth Muscle

Single unit smooth muscle- lines the Single unit smooth muscle- lines the walls of hollow organs except the walls of hollow organs except the heart. heart.

Multiunit smooth muscle- lines the Multiunit smooth muscle- lines the insides of the lungs and in large insides of the lungs and in large arteries, eye muscles, and arrector arteries, eye muscles, and arrector pilli muscles. pilli muscles.

Developmental Aspects Developmental Aspects

of Muscleof Muscle

Muscle tissue progenitorMuscle tissue progenitor

Most all muscle tissue cells are Most all muscle tissue cells are produced by a cell called a myoblast.produced by a cell called a myoblast.

When myoblast become innervated, When myoblast become innervated, they release a growth hormone they release a growth hormone called agrin is released.called agrin is released.

The imbedded neurons in the The imbedded neurons in the myoblast will help determine the myoblast will help determine the type of muscle tissue.type of muscle tissue.