The Motor SystemThe Motor SystemMusclesMuscles

MusclesMuscles Howstuffworks "Cardiac and Smooth Muscle"Howstuffworks "Cardiac and Smooth Muscle"

The 3 main types of Muscles

The body has more then 600 muscles!The body has more then 600 muscles!

MusclesMuscles

3 main types of muscles:3 main types of muscles: 1) Cardiac Muscles1) Cardiac Muscles:: heart muscles heart muscles

Found only in the Found only in the heartheart Involuntary contractionInvoluntary contraction and relaxationand relaxation. Why? It is . Why? It is

controlled by nerves of the autonomic nervous system controlled by nerves of the autonomic nervous system and always has to be pumping in order to pump blood and always has to be pumping in order to pump blood (which contains oxygen, nutrients, and other important (which contains oxygen, nutrients, and other important molecules) to all of the cells of the body. molecules) to all of the cells of the body.

Cardiac MusclesCardiac Muscles-The heart beats non-stop because of these striated muscle cells.

-Cardiac muscle is myogenic, meaning that it is self-excitable stimulating contraction without a required electrical impulse coming from the central nervous system.

-A single cardiac muscle cell, if left without input, will contract rhythmically at a steady rate; if two cardiac muscle cells are in contact, whichever one contracts first will stimulate the other to contract, and so on. This is heavily regulated by the autonomic nervous system

2) 2) Smooth Muscles:Smooth Muscles: found in found in the lining of many organsthe lining of many organs

-Found in the hollow parts of the body, for -Found in the hollow parts of the body, for instance the lining of organs such as: the instance the lining of organs such as: the stomach, esophagus, uterus, and walls of stomach, esophagus, uterus, and walls of blood vessels.blood vessels.-Smooth muscle contractions are required -Smooth muscle contractions are required for such things as: pushing food through for such things as: pushing food through the digestive system or pushing a baby the digestive system or pushing a baby through the vagina.through the vagina.-Similar to cardiac muscles contraction, -Similar to cardiac muscles contraction, smooth muscle contraction is smooth muscle contraction is involuntary involuntary

Smooth MusclesSmooth Muscles

-This type of muscle shows no cross stripes (non-striated muscle cells) under microscopic magnification. It consists of narrow spindle-shaped cells with a centrally located nucleus. Smooth-muscle tissue contract slowly and automatically.

3) 3) Skeletal MusclesSkeletal Muscles:: muscles that are muscles that are attached to boneattached to bone

-Unlike cardiac and smooth muscles, these -Unlike cardiac and smooth muscles, these type of muscles are voluntarily controlledtype of muscles are voluntarily controlled

-These muscles allow you to walk, talk, ride a -These muscles allow you to walk, talk, ride a bike, swim, jump, etc.bike, swim, jump, etc.

-Skeletal muscles attach to bones by -Skeletal muscles attach to bones by tendonstendons

-Skeletal muscles are key in helping you keep -Skeletal muscles are key in helping you keep warm. 80% or all energy used in muscle warm. 80% or all energy used in muscle contraction is lost as contraction is lost as heatheat!!

Skeletal MusclesSkeletal Muscles-Similar to cardiac muscles, Skeletal muscles are striated.

-Like all muscles, skeletal muscles shorten when they contract and lengthen when they relax. The arm bends upwards when muscles contract and pull it upwards.

-The central nervous system sends excitatory or inhibitory nerve impulses to the skeletal muscles which either cause the muscle to contract or relax, never to do both at one time.

Skeletal Muscles Cont….Skeletal Muscles Cont….

Skeletal muscle is composed of many bundles of cells Skeletal muscle is composed of many bundles of cells called called fiberfiber. The fibers are enclosed within a . The fibers are enclosed within a membrane called membrane called sarcolemmasarcolemma

Within the muscle fiber there are many Within the muscle fiber there are many myofilamentsmyofilaments bundles together bundles together There are There are twotwo main types of myofilament which contain main types of myofilament which contain

different contractile units:different contractile units: 1) 1) Thin Myofilament:Thin Myofilament: composed of composed of actin actin (light bands)(light bands) 2) 2) Thick MyofilamentThick Myofilament: composed of : composed of myosin (myosin (dark bands)dark bands) These two types of myofilament overlap to produce a striated These two types of myofilament overlap to produce a striated

(striped) appearance(striped) appearance

Structure of Skeletal MusclesStructure of Skeletal Muscles An individual section of the An individual section of the

myofilament is called a myofilament is called a sarcomeresarcomere

The length of one sarcomere The length of one sarcomere is defined by the is defined by the Z-Line. Z-Line. The Z-lines anchors the actin The Z-lines anchors the actin to each other and to the to each other and to the bone.bone.

The length of the myosin is The length of the myosin is defined by thedefined by the A-Band. A-Band. It It contains both actin and contains both actin and myosin.myosin.

The The I-BandI-Band only contains only contains actin and it is the space in actin and it is the space in between 2 myosin.between 2 myosin.

The The H-Zone H-Zone is the empty is the empty space between 2 actin. space between 2 actin. Myosin is only found in this Myosin is only found in this spacespace

Muscles Contraction (Muscles Contraction (The Sliding Filament The Sliding Filament TheoryTheory))

During each contraction:During each contraction: 1) A neurotransmitter is released from a nerve to the 1) A neurotransmitter is released from a nerve to the

muscles, signaling contractionmuscles, signaling contraction 2) The muscle cell’s endoplasmic reticulum release 2) The muscle cell’s endoplasmic reticulum release

Calcium (CaCalcium (Ca2+2+ ions) ions) near the actin near the actin 3) Calcium ions attach to the actin and this then allows 3) Calcium ions attach to the actin and this then allows

myosin to attach to the actin as well, forming an myosin to attach to the actin as well, forming an ‘‘Actin-Actin-Myosin Cross-BridgeMyosin Cross-Bridge’’

4) The actin and myosin attach and de-attach, over an over. 4) The actin and myosin attach and de-attach, over an over. With each re-attachment of the actin the muscle fibers get With each re-attachment of the actin the muscle fibers get pulled closer together. This carries on until full contraction pulled closer together. This carries on until full contraction of the muscles occurs.of the muscles occurs.

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Calcium ions also start the break down of Calcium ions also start the break down of ATPATP, , which allows the actin to which allows the actin to de-attachde-attach each time from each time from the myosin and also provides the energy for the myosin and also provides the energy for contraction to occur. (contraction to occur. (RecallRecall: when ATP is broken : when ATP is broken down, energy is given off)down, energy is given off)

If no ATP is present, rIf no ATP is present, rigor mortisigor mortis occurs: This occurs occurs: This occurs after death, myosin and actin stay attached, thus after death, myosin and actin stay attached, thus muscles stay fully contracted. The body is stiff as a muscles stay fully contracted. The body is stiff as a board!board!

MuscleAnimationMuscleAnimation

Complications of the muscular Complications of the muscular systemsystem

Muscle soreness, burning, fatigue, tightness, etc., is Muscle soreness, burning, fatigue, tightness, etc., is due to the fact that very little ATP can be stored in due to the fact that very little ATP can be stored in the muscle tissue. As a result, Aerobic Cellular the muscle tissue. As a result, Aerobic Cellular Respiration constantly provides/replenishes most of Respiration constantly provides/replenishes most of the energy (in the form of ATP).the energy (in the form of ATP).

As soon as the ATP is used up and converted back to As soon as the ATP is used up and converted back to ADP, a compound called ADP, a compound called creatine phosphate, creatine phosphate, ensures ensures all ADP is converted back to ATPall ADP is converted back to ATP Creatine is a supplement often used by many sports to Creatine is a supplement often used by many sports to

increase muscle strengthincrease muscle strength Fatigue will only occur if ATP demands can not be Fatigue will only occur if ATP demands can not be

met. Lactic acid begins to build up, muscles tighten met. Lactic acid begins to build up, muscles tighten up, and fatigue takes over.up, and fatigue takes over.

Atrophy:Atrophy: the reduction in size, tone and the reduction in size, tone and power of a muscle due to decreased use and power of a muscle due to decreased use and stimulation, which can eventually lead to stimulation, which can eventually lead to permanent loss of muscle function.permanent loss of muscle function.

Hypertrophy:Hypertrophy: an exercise-induced increase in an exercise-induced increase in muscle mass resulting from an increase in the muscle mass resulting from an increase in the size of individual muscle fibres.size of individual muscle fibres.

Note- neither of these involve a change in the Note- neither of these involve a change in the numbernumber of muscle fibres. of muscle fibres.

Muscle TwitchMuscle Twitch

Muscle twitchMuscle twitch – is a muscle contraction that – is a muscle contraction that lasts a fraction of a second that occurs in three lasts a fraction of a second that occurs in three stages:stages: Latent stage – time between stimulus and initiation Latent stage – time between stimulus and initiation

of the contractionof the contraction Contraction stage – time it takes for the muscle Contraction stage – time it takes for the muscle

fibers to shortenfibers to shorten Relaxation stage – time it takes for the muscle to Relaxation stage – time it takes for the muscle to

return to its regular length.return to its regular length.

Slow twitchSlow twitch – smaller muscle fibers that contract – smaller muscle fibers that contract slowly and resist fatigue because they are surrounded slowly and resist fatigue because they are surrounded by more blood vessels and have by more blood vessels and have more mitochondriamore mitochondria. . i.e. soleus muscle in the leg, postural back musclesi.e. soleus muscle in the leg, postural back muscles

Fast twitchFast twitch– larger muscle fibers that contract – larger muscle fibers that contract quickly to give more power, but depend upon quickly to give more power, but depend upon anaerobic energy production. They are rich in anaerobic energy production. They are rich in glycogen, and have glycogen, and have fewer mitochondriafewer mitochondria and blood and blood vessels surrounding them.vessels surrounding them.i.e. lateral rectus muscle in the eye, bicepsi.e. lateral rectus muscle in the eye, biceps

The effects of exerciseThe effects of exercise Endurance training – Endurance training –

increases the development of increases the development of slow-twitch muscle fibres slow-twitch muscle fibres and has no impact on the size and has no impact on the size of the muscles.of the muscles.

Resistance / strength training Resistance / strength training – thickens fast-twitch – thickens fast-twitch muscles, causing an increase muscles, causing an increase in muscle size.in muscle size.

Tetanus:Tetanus: a state of constant muscle a state of constant muscle contraction. Often caused by bites, or rusted contraction. Often caused by bites, or rusted metals entering the blood stream.metals entering the blood stream.

Muscle spasmsMuscle spasms: involuntary contraction of a : involuntary contraction of a muscle. Often caused by a pinched nerve.muscle. Often caused by a pinched nerve.