Muscular System

Muscular System

Chapter 10 Muscular Tissue Lecture slides prepared by Curtis DeFriez, Weber State University Copyright John Wiley and Sons, Inc. All rights reserved. Functions of Muscular Tissue Like nervous tissue, muscles are excitable or "irritable they have the ability to respond to a stimulus Unlike nerves, however, muscles are also:

Contractible (they can shorten in length) Extensible (they can extend or stretch) Elastic (they can return to their original shape) Copyright John Wiley and Sons, Inc. All rights reserved. Functions of Muscular Tissue Muscle makes up a large percentage of the bodys weight

Their main functions are to: Create motion muscles work with nerves, bones, and joints to produce body movements Stabilize body positions and maintain posture Store substances within the body using sphincters Copyright John Wiley and Sons, Inc. All rights reserved. Three Types of Muscular Tissue Location Skeletal

Function movement, skeleton heat, posture Cardiac Visceral (smooth

muscle) heart G.I. tract, uterus, eye, blood vessels Appearance Control

striated, multinucleated (eccentric), fibers voluntary parallel pump blood striated, one

involunta continuously central nucleus ry Peristalsis, blood no striations,

pressure, one central pupil size, nucleus involunta ry

erects hairs Copyright John Wiley and Sons, Inc. All rights reserved. Three Types of Muscular Tissue (a) Skeletal muscle (b) Cardiac muscle (c) Visceral smooth muscle Copyright John Wiley and Sons, Inc. All rights reserved.

Skeletal Muscle Location Skeletal Function movement, skeleton heat, posture

Cardiac heart Visceral G.I. tract, (smooth uterus, eye,

muscle) blood vessels Appearance Control striated, multinucleated

voluntar (eccentric), fibers y parallel pump blood striated, one

involunta continuously central nucleus ry Peristalsis, blood no striations,

pressure, one central pupil size, nucleus involunta ry

erects hairs Copyright John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle Copyright John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle Skeletal muscle fibers are very long cells next to neurons (which can be over a meter long), perhaps the longest in the body The Sartorious muscle contains

single fibers that are at least 30 cm long A single skeletal muscle fiber Copyright John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle The terminal processes of a motor neuron in close proximity to the sarcolemma of a skeletal muscle fiber Motor neuron

Sarcolemma Copyright John Wiley and Sons, Inc. All rights reserved. Organization of Muscle Tissue The epimysium, perimysium, and endomysium all are continuous with the connective tissues that form tendons and ligaments (attach skeletal muscle to bone) and muscle fascia (connect muscles to other muscles to form groups of muscles)

Copyright John Wiley and Sons, Inc. All rights reserved. Organization of Muscle Tissue Epimysium Perimysium Organization of a single muscle Copyright John Wiley and Sons, Inc. All rights reserved. Organization of Muscle Tissue

Organization of a fasciculus Copyright John Wiley and Sons, Inc. All rights reserved. Organization of Muscle Tissue Organization of a muscle fiber Copyright John Wiley and Sons, Inc. All rights reserved. Organization of Muscle Tissue

A muscle, a fasciculus, and a fiber all visualized Copyright John Wiley and Sons, Inc. All rights reserved. Organization of Muscle Tissue In groups of muscles the epimysium continues to become thicker, forming fascia which covers many muscles

This graphic shows the fascia lata enveloping the entire group of quadriceps Copyright John Wiley and Sons, Inc. All rights reserved. Organization of Muscle Tissue Many large muscle groups are encased in both a

superficial and a deep fascia Real Anatomy, John Wiley and Sons Copyright John Wiley and Sons, Inc. All rights reserved. Organization of Muscle Tissue An aponeurosis is Epicranial essentially fascia that

aponeurosis a thick Frontal belly of the connectsoccipitofrontalis m. two muscle bellies. This epicranial aponeurosis connects the muscle bellies of the

occipitalis and the frontalis to form one muscle: The Copyright John Wiley and Sons, Inc. All rights reserved. Organization of Muscle Tissue Veins, arteries, and nerves are located in the deep fascia between muscles of the thigh.

Copyright John Wiley and Sons, Inc. All rights reserved. The Skeletal Muscle Fiber Beneath the connective tissue endomysium is found the plasma membrane (called the sarcolemma) of an individual skeletal muscle fiber The cytoplasm (sarcoplasm) of skeletal muscle fibers is chocked full of contractile proteins arranged in myofibrils

Copyright John Wiley and Sons, Inc. All rights reserved. The Skeletal Muscle Fiber You should learn the names of the internal structures of the muscle fiber Sarcolemma Sarcoplasm Myofibril T-tubules Triad (with terminal cisterns

Sarcoplasmic reticulum Sarcomere Copyright John Wiley and Sons, Inc. All rights reserved. The Skeletal Muscle Fiber Increasing the level of magnification, the myofibrils are seen to be composed of filaments Thick filaments Thing filaments Copyright John Wiley and Sons, Inc. All rights reserved.

The Skeletal Muscle Fiber The basic functional unit of skeletal muscle fibers is the sarcomere: An arrangement of thick and thin filaments sandwiched between two Z discs A scanning electron micrograph of a sarcomere Copyright John Wiley and Sons, Inc. All rights reserved.

The Skeletal Muscle Fiber Muscle contraction occurs in the sarcomeres The Z line is really a Z disc when considered in 3 dimensions. A sarcomere extends from Z disc to Z disc. Copyright John Wiley and Sons, Inc. All rights reserved. Muscle Proteins Myofibrils are built from three groups of proteins Contractile proteins generate force during

contraction Regulatory proteins help switch the contraction process on and off Structural proteins keep the thick and thin filaments in proper alignment and link the Copyright John Wiley and Sons, Inc. All rights reserved. Muscle Proteins The thin filaments are comprised mostly of the structural protein actin, and the thick filaments are comprised mostly of the structural protein myosin

However, in both types of filaments, there are also other structural and regulatory proteins Copyright John Wiley and Sons, Inc. All rights reserved. Muscle Proteins In the thin filaments actin proteins are strung together like a bead of pearls In the thick filaments myosin proteins look like golf clubs bound together Copyright John Wiley and Sons, Inc. All rights reserved.

Muscle Proteins In this first graphic, the myosin binding sites on the actin proteins are readily visible. The regulatory proteins troponin and tropomyosin have been added to the bottom graphic: The myosin binding sites have been covered Copyright John Wiley and Sons, Inc. All rights reserved.

Muscle Proteins In this graphic the troponin-tropomyosin complex has slid down into the gutters of the actin molecule unblocking the myosin binding site Myosin binding site exposed The troponin-tropomyosin complex can slide back and forth depending on the presence of Copyright John Wiley and Sons, Inc. All rights reserved.

Muscle Proteins Ca2+ binds to troponin which changes the shape of the troponin-tropomyosin complex and uncovers the myosin binding sites on actin Copyright John Wiley and Sons, Inc. All rights reserved. Muscle Proteins Besides contractile and regulatory proteins, muscle contains about a dozen structural

proteins which contribute to the alignment, stability, elasticity, and extensibility of myofibrils Titan is the third most plentiful protein in muscle, after actin and myosin - it extends from the Z disc and accounts for much of the elasticity of myofibrils Copyright John Wiley and Sons, Inc. All rights reserved. The Sliding-Filament Mechanism With exposure of the myosin binding sites on

actin (the thin filaments)in the presence of Ca2+ and ATPthe thick and thin filaments slide on one another and the sarcomere is shortened Copyright John Wiley and Sons, Inc. All rights reserved. The Sliding-Filament Mechanism The sliding of actin on myosin (thick filaments on thin filaments) can be broken down into a 4 Copyright John Wiley and Sons, Inc. All rights reserved.

Step 1: ATP hydrolysis Step 2: Attachment Copyright John Wiley and Sons, Inc. All rights reserved. Step 3: Power Stroke Step 4: Detachment Copyright John Wiley and Sons, Inc. All rights reserved.

The Sliding-Filament Mechanism Copyright John Wiley and Sons, Inc. All rights reserved. Contraction and Movement Overview Interactions Animation Contraction and Movement You must be connected to the internet to run this animation. Copyright John Wiley and Sons, Inc. All rights reserved.

Length-Tension Relationship Sarcomere shortening produces tension within a muscle Compress ed thick filaments Limited contact between

actin and myosin Copyright John Wiley and Sons, Inc. All rights reserved. Excitation-Contraction Coupling We will come back to the term excitationcontraction coupling in a little bit Before we can describe the entire process, from thinking of moving a muscle to actual contraction of sarcomeres, we must

first explore the processes that occur at the neuromuscular junction Copyright John Wiley and Sons, Inc. All rights reserved. Neuromuscular Junction Excitation-Contraction coupling (EC coupling) involves events at the junction between a motor neuron and a skeletal muscle fiber Copyright John Wiley and Sons, Inc. All rights reserved. Neuromuscular Junction

An enlarged view of the neuromuscular junction The presynaptic membrane is on the neuron while the postsynaptic membrane is the motor end plate on the muscle cell. The two membranes are separated by a space, or cleft Copyright John Wiley and Sons, Inc. All rights reserved. Neuromuscular Junction Conscious thought (to move a muscle) results in

activation of a motor neuron, and release of the neurotransmitter acetylcholine (AcCh) at the NM junction The enzyme acetylcholinesterase breaks down AcCh after a short period of time Copyright John Wiley and Sons, Inc. All rights reserved. Neuromuscular Junction The plasma membrane on the far side of the

NMJ belongs to the muscle cell and is called the motor end plate The motor end plate is rich in chemical (ligand) gated sodium channels that respond to AcCh. Another way to say this: The receptors for AcCh are on the ligand-gated sodium channels on the motor end plate Copyright John Wiley and Sons, Inc. All rights reserved. Neuromuscular Junction The chemical events at the NMJ transmit the electrical events of a neuronal action potential

into the electrical events of a muscle action potential Copyright John Wiley and Sons, Inc. All rights reserved. Neuromuscular Junction Interactions Animation Neuromuscular Junctions You must be connected to the internet to run this animation. Copyright John Wiley and Sons, Inc. All rights reserved.

Muscle Action Potential The muscle AP is propagated over the surface of the muscle cell membrane (sarcolemma) via voltage (electrical)-gated Na+ and K+ channels Copyright John Wiley and Sons, Inc. All rights reserved. Muscle Action Potential By placing a micropipette inside a muscle cell, and then measuring the electrical potential across the cell membrane, the phases of an

action potential (AP) can be graphed (as in this figure) Copyright John Wiley and Sons, Inc. All rights reserved. Muscle Action Potential The behavior of the Na+ and K+ channels, at various points in the AP, are seen in this graphic

Na+ gates open during the depolarization phase K+ gates open during the repolarization phase Copyright John Wiley and Sons, Inc. All rights reserved. Generating An Action Potential The flow of ions through cell a membrane looks a lot like a "piece" of electricity flowing through a wire (but not as fast) Generating an AP on the muscle membrane involves the transfer of information from an

electrical signal (down the neuron), to a chemical signal (at the NMJ), back to an electrical signal (depolarization of the sarcolemma) Copyright John Wiley and Sons, Inc. All rights reserved. Excitation-Contraction Coupling Copyright John Wiley and Sons, Inc. All rights reserved. Excitation-Contraction Coupling EC coupling involves putting it all together

The thought process going on in the brain The AP arriving at the neuromuscular junction The regeneration of an AP on the muscle membrane Release of Ca2+ from the sarcoplasmic reticulum Sliding of thick on thin filaments in sarcomeres Generation of muscle tension (work) Copyright John Wiley and Sons, Inc. All rights reserved. Excitation-Contraction Coupling Copyright John Wiley and Sons, Inc. All rights reserved.

Excitation-Contraction Coupling Role Players in E-C The brain coupling The motor neuron Regenerate AP The T-tubules Acetylcholine (ACh)

The SR Acetylcholinesterase Ca2+ release enzyme Troponin/ Ach receptors on the

Tropomyosin motor endplate ATP Na+-K+ channels on the Myosin binding sarcolemma

Filaments slide Na+ flow Muscles contract Copyright John Wiley and Sons, Inc. All rights reserved. Contraction of Sarcomere Interactions Animation Contraction of a Sarcomere You must be connected to the internet to run this animation.

Copyright John Wiley and Sons, Inc. All rights reserved. Sources of Muscle Energy Stored ATP 3 seconds Energy transferred from stored creatine phosphate 12 seconds Aerobic ATP production Anaerobic glucose use

30-40 seconds Copyright John Wiley and Sons, Inc. All rights reserved. Sources of Muscle Energy Copyright John Wiley and Sons, Inc. All rights reserved. Sources of Muscle Energy Copyright John Wiley and Sons, Inc. All rights reserved. Sources of Muscle Energy

Copyright John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle Metabolism In a state of homeostasis, muscle use of O2 and nutrients is balanced by the production of manageable levels of waste products like CO2 Heat - 70-80% of the energy used by muscles is lost as heat - muscle activity is important for maintaining body temperature Lactic acid (anaerobic)

Copyright John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle Metabolism Oxygen Debt, or "Excess Post-Exercise Oxygen Consumption" (EPOC) is the amount of O2 repayment required after exercise in skeletal muscle to: Replenish ATP stores Replenish creatine phosphate and myoglobin stores Convert lactic acid back into pyruvate so it can be used in the Krebs cycle to replenish

Copyright John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle Metabolism Copyright John Wiley and Sons, Inc. All rights reserved. Muscle Metabolism Muscle Metabolism You must be connected to the internet to run this animation. Copyright John Wiley and Sons, Inc. All rights reserved.

Cardiac and Smooth Muscle Metabolism In response to a single AP, cardiac muscle contracts 10-15 times longer than skeletal muscle, and must continue to do so, without rest, for the life of the individual To meet this constant demand, cardiac muscle generally uses the rich supply of O2 delivered by the extensive coronary circulation to Copyright John Wiley and Sons, Inc. All rights reserved.

Cardiac and Smooth Muscle Metabolism Like cardiac muscle, smooth muscle (in your deep organs) is autorhythmic and is not under voluntary control (your heart beats and your stomach digests without you thinking about it). Unlike cardiac (and skeletal muscle) however, smooth muscle has a low capacity for generating ATP and does so only through Copyright John Wiley and Sons, Inc. All rights reserved.

The Motor Unit Motor Unit is composed of a motor neuron plus all of the muscle cells it innervates High precision Fewer muscle fibers per neuron Laryngeal and extraocular muscles (2-20) Low

precision Many muscle fibers per neuron Thigh muscles (2,000-3,000) Copyright John Wiley and Sons, Inc. All rights reserved. The Motor Unit Florescent dye is used to show the terminal processes of a single neuron which terminate on a few muscle fibers

Copyright John Wiley and Sons, Inc. All rights reserved. The Motor Unit Activities requiring extreme precision (like the subtle and rapid movements of the eye) involve muscles with very small motor units (1-4 muscle fibers/neuron) Copyright John Wiley and Sons, Inc. All rights reserved. The Motor Unit All-or-none principle of muscle contraction When an individual muscle fiber is stimulated

to depolarization, and an action potential is propagated along its sarcolemma, it must contract to its full forceit cant partially contract Also, when a single motor unit is recruited to contract, all the muscle fibers in that motor unit must all contract at the same time Copyright John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle Fiber Types Skeletal muscle fibers are not all alike in

appearance or function. By appearance: Red muscle fibers (the dark meat in chicken legs) have a high myoglobin content, more mitochondria, more energy stores, and a greater blood supply White muscle fibers (the white meat in chicken breasts) have less myoglobin, mitochondria, Copyright John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle Fiber Types Slow oxidative fibers (SO) are small, appear dark red, are

the least powerful type. They are very fatigue resistant Used for endurance like running a marathon Fast oxidative-glycolytic fibers (FOG) are intermediate in size, appear dark red, and are moderately Copyright John Wiley and Sons, Inc. All rights reserved. Skeletal Muscle Fiber Types Copyright John Wiley and Sons, Inc. All rights reserved.

Skeletal Muscle Fiber Types Most skeletal muscles are a mixture of all three types of skeletal muscle fibers; about half the fibers in a typical skeletal muscle are slow oxidative (SO) fibers Within a particular motor unit all the skeletal muscle fibers are the same type The different motor units in a muscle are recruited in a specific order depending on the Copyright John Wiley and Sons, Inc. All rights reserved. Tension in a Muscle

There is a brief delay called the latent period as the AP sweeps over the sarcolemma and Ca 2+ ions are released from the sarcoplasmic reticulum (SR) During the next phase the fiber is actively contracting This is followed by relaxation as the Ca2+ ions are re-sequestered into the SR and myosin binding sites are covered by tropomyosin Temporary loss of excitability is call the refractory period All muscle fibers in a motor

Copyright John Wiley and Sons, Inc. All rights reserved. Tension in a Muscle A twitch is recorded when a stimulus that results in contraction (force) of a single muscle fiber is measured over a very brief millisecond time frame Copyright John Wiley and Sons, Inc. All rights reserved. Tension in a Muscle Applying increased numbers of action potentials

to a muscle fiber (or a fascicle, a muscle, or a muscle group) results in fusion of contractions (tetanus) and the performance of useful work Copyright John Wiley and Sons, Inc. All rights reserved. Tension in a Muscle Two motor units, one in green, the other in purple, demonstrate the concept of progressive activation of a muscle known as recruitment Recruitment allows a muscle to accomplish increasing gradations of contractile strength

Copyright John Wiley and Sons, Inc. All rights reserved. Muscle Tension Interactions Animation Control of Muscle Tension You must be connected to the internet to run this animation. Copyright John Wiley and Sons, Inc. All rights reserved. Muscle Contraction

Isotonic contractions results in movement Concentric isotonic is a type of muscle contraction in which the muscle shorten while generating force Eccentric isotonic is a contraction in which muscle tension is less than the resistance (the muscle lengthens) Isometric contractions results in no movement Copyright John Wiley and Sons, Inc. All rights reserved. Muscle Contraction

Copyright John Wiley and Sons, Inc. All rights reserved. Imbalances of Homeostasis Exercise-induced muscle damage After intense exercise electron micrographs reveal considerable muscle damage including torn sarcolemmas and disrupted Z-discs Blood levels of proteins normally confined only to muscle (including myoglobin and the enzyme creatine kinase) increase as they are released from damaged muscle

Copyright John Wiley and Sons, Inc. All rights reserved. Imbalances of Homeostasis Spasm A sudden involuntary contraction of a single muscle within a large group of muscles usually painless Cramp Involuntary and often painful muscle contractions Caused by inadequate blood flow to muscles

(such as in dehydration), overuse and injury, Copyright John Wiley and Sons, Inc. All rights reserved. Imbalances of Homeostasis Disease States and Disorders Fibrosis (myofibrosis) Replacement of muscle fibers by excessive amounts of connective tissues (fibrous scar

tissue) Myosclerosis Hardening of the muscle caused by calcification Both myosclerosis and muscle fibrosis occur Copyright John Wiley and Sons, Inc. All rights reserved. Imbalances of Homeostasis Aging

In part due to decreased levels of physical activity, with aging humans undergo a slow, progressive loss of skeletal muscle mass that is replaced largely by fibrous connective tissue and adipose tissue Muscle strength at 85 is about half that at age 25 Compared to the other two fiber types, the Copyright John Wiley and Sons, Inc. All rights reserved.

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