chapter 7 muscles power point

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins

Chapter 7:Muscles


McConnell and Hull: Human Form and Human Function

Chapter Objectives• Overview of Muscle

– List five functions of muscle tissue.

– Compare and contrast skeletal, smooth, and cardiac muscle

• Structure of Skeletal Muscle Tissue

– Using a drawing, identify and describe the special features of a skeletal muscle cell, and explain hoe many such cells, along with connective tissue membranes, are built into skeletal muscle.

• Skeletal Muscle Contraction

– Define sarcomere and explain how muscle contraction results from sarcomere shortening.



Chapter Objectives (cont’d)• Skeletal Muscle Contraction (cont’d)

– Define sarcomere and explain how muscle contraction results from sarcomere shortening.

– Describe the composition of the thin and thick filaments, and label the parts of the sarcomere.

– List all the steps involved in muscle contraction, beginning with an action potential in a neuron and ending with the events of cross-bridge cycling.

– List the steps involved in muscle relaxation.



Chapter Objectives (cont’d)• Muscle Energy

– Identify the used for ATP in muscle contraction.

– Explain the benefits and disadvantages of different energy sources (creatine phosphate, glycolysis, and mitochondrial respiration): compare anaerobic and aerobic metabolism.

– Compare the structure and function of fast glycolytic fibers and slow oxidative fibers.

• Case Study: Muscle Energy Metabolism: The Case of Hammid S.

– List the different causes of muscle fatigue, referring to the case study.



Chapter Objectives (cont’d)• The Mechanics of Muscle Contraction

– Explain how a stronger contraction results from modifying fiber length and/or recruiting additional motor units

– Provide examples of isometric, concentric, isotonic, and eccentric isotonic contractions.

– Discuss the effects of resistance training and endurance exercises on muscles

• Smooth Muscle

– Define the structural and functional differences between skeletal and smooth muscle.

– List the steps involved in smooth muscle contraction, including the different types of stimuli that can induce contraction.



Chapter Objectives (cont’d)• Skeletal Muscle Actions

− Identify the prime mover, synergist and/or antagonist for different body movements at each joint.

• The Major Skeletal Muscles

− For each body region (head, neck, upper limb, torso, and lower limb) label the major skeletal muscles on a diagram and indicate their insertion and origin.



Overview of Muscle

• Functions of muscle

– Move body parts

– Maintain body posture

– Adjust the volume of body structures

– Move substances within the body

– Produce heat

Back to chapter objectives



Overview of Muscle (cont’d)

• There are three types of muscle

– Most important differences relate to four qualities:

• Location

• Microscopic appearance

• Whether or not they are subject to conscious control

• Type of contraction




Overview of Muscle (cont’d)• Types of muscle





• Skeletal muscle moves the skeleton

– Microscopically, skeletal muscle is striated muscle; it has cross stripes (striations)

– Mature muscle cells are long and thin (up to a foot long) and are called muscle fibers

• A muscle fiber is a single mature skeletal muscle cell

– Skeletal muscle is voluntary muscle – it can contract and relax at will.





• Cardiac muscle propels blood through the body

– Cardiac muscle tissue is found only in the heart.

– Microscopically, cardiac muscles are striated.

– Much shorter than skeletal muscle fibers, but they are branched and interconnected

– Cardiac muscle is involuntary muscle – we cannot control its contractions by force of will.





• Smooth muscle powers the actions of viscera

– Found in thick layers in the walls of hollow organs

– Also called visceral muscle

– Adjusts the volume of hollow structures and helps move substances through the body

– Smooth muscle is nonstriated muscle; it has a uniform smooth appearance, without striations

– Involuntary

– Generally do not fatigue





• All muscle tissue is extensive

– All muscle is capable of stretching without tearing, a quality called.

– If muscle did not have this quality, simple actions would cause it to teat.




Overview of Muscle (Review)

• Name two types of striated muscle.




Overview of Muscle (Review)

• Answer: skeletal and cardiac




Structure of Skeletal Muscle Tissue

• The structure of a muscle cell reflects its function

– Sarcolemma – the cell membrane

• Surrounds the cytoplasm but also tunnels deep into the interior of the muscle fiber as a network of T-tubules.

– Action potentials travel down T-tubules and enable coordinated muscle contraction




Structure of Skeletal Muscle Tissue (cont’d)

• The structure of a muscle cell reflects its function

– Sarcoplasm – the cytoplasm of the muscle cell – contains these structures:

• Microfibrils

– Threadlike organelles that accomplish the work of muscle contraction

• Sarcoplasmic reticulum

– Network of fluid-filled tubules similar to the smooth endoplasmic reticulum.





– Sarcoplasm – the cytoplasm of the muscle cell – contains these structures:

• Mitochondria

– Generate ATP that fuels muscle contraction

• Myoglobin

– An iron-containing compound; stores oxygen used to generate energy for muscle contraction




Structure of Skeletal Muscle Tissue (cont’d)• Skeletal muscle cells and muscles





• Connective tissue wraps muscle fibers, fascicles, and whole muscles

– Individual muscle cells are wrapped in a sheath of connective tissue called the endomysium.

– Groups of 100 muscle fibers are formed into structural and functional bundles called fascicles.

• These are wrapped with a thicker, tougher sheath of connective tissue called the perimysium.





– Groups of fascicles form muscles, which are wrapped by a tough layer of connective tissue called the epimysium.

• When formed into a thick, tough cord for attachment at a single point, the epimysium is called a tendon.

• When formed into a sheet for broader, linear attachment, the epimysium is called an aponeurosis.




Structure of Skeletal Muscle Tissue (Review)

• Are tendons examples of epithelial tissue or connective tissue?




Structure of Skeletal Muscle Tissue (Review)

• Answer: connective




Skeletal Muscle Contraction

• A motor unit is a motor neuron and the muscle fibers it controls

– A somatic motor neuron carries a signal that stimulates contraction in skeletal muscle.

– A visceral motor neuron carries a signal to smooth muscle or glands

• The cell bodies of motor neurons are located in the brain or spinal cord and send long cytoplasmic extensions called axons




Skeletal Muscle Contraction (cont’d)

• Motor neurons connect to muscle fibers at the neuromuscular junction

– The neuromuscular junction includes:

• The synaptic bulb of the neuron

• The motor end plate of the muscle fiber

• The synaptic cleft




Skeletal Muscle Contraction (cont’d)• Motor units and the neuromuscular junction





• Chemical synapses use neurotransmitters to transmit a signal between two adjacent cells.

• The basic process is the same in all synapses:

– In response to an action potential in the presynaptic cell, neurotransmitter is released into the synaptic cleft.

– It binds to specific receptors on the postsynaptic cell, altering its electrical activity





• Neuromuscular junction is more specific: an action potential in the presynaptic cell always results in an action potential in the post synaptic cell.

– Every skeletal neuromuscular junction uses the same neurotransmitter (acetylcholine) and the same neurotransmitter receptor (nicotinic cholinergic receptor)

– The receptor is a ligand-gated ion channel





• Events at the neuromuscular junction

1. Electrical signal at the somatic motor neuron

2. Chemical signal (Ach) in the synapse

3. Electrical signal in the sarcolemma

4. A chemical signal (calcium) in the sarcoplasm




Skeletal Muscle Contraction (cont’d)• Events at the neuromuscular junction





• Sarcomere are the functional units of myofibrils

– Each myofibril is a bundle of two types of long myofilaments: thick filaments and thin filaments.

• Thin filaments have Z-discs on one end.

• Thin and thick filaments in alternating rows

– During a muscle contraction the filaments slide past each other

– A single sarcomere is small.

– Sarcomeres lined up end to end produce a myofibril that runs the entire length of a muscle fiber.




Skeletal Muscle Contraction (cont’d)• Pencils can be used to model a sarcomere.





• Myofilaments are composed of contractile proteins

– The molecular structure of thick and thin filaments is essential to the contractile nature of myofilaments.

• Thick filaments are bundles of myosin protein.

– Each molecule of myosin is composed of a long shaft, one end of which terminates in two globular heads

– Each myosin head has two binding sites

• One site for ATP

• One site for thin filaments





– Many myosin molecules with their heads pointing in opposite directions are bundled together to form a thick filament.

– Thin filaments are composed of three proteins, actin, tropomyosin, and troponin.

• Each thin filament contains two long strands of actin molecules that are twisted together

• Each actin molecule contains a binding site for a myosin head

• In the resting state, the binding site is covered with tropomyosin





• Thin filaments

– Troponin is the third constituent–it controls the trypomyosin molecules.

• Keeps them in place over the binding sites in relaxed muscle

• Moves them out of the way for contraction to occur





• Sarcomeres shorten via the cross-bridge cycle

– The Cross-bridge cycle

• Cross-bridge formation

• Power stroke

• Cross-bridge detachment





• The cross-bridge cycle

1. Myosin binding sites on the actin molecules are covered in resting fibers.

2. Action potential releases Ca2+ from the SR.

3. Ca2+ binds troponin. Tropomyosin moves, revealing myosin binding sites.

4. Cross-bridge forms when myosin head binds actin.

5. Myosin head pivots, moving actin. ADP and P dissociate from the myosin head.

6. Myosin head releases actin when a fresh ATP binds.

7. Myosin head binds next actin. ATP is cleaved into ADP and P+, and the cycle repeats.






• The cross-bridge cycle




• Muscle relaxes when cross-bridge cycling ceases

1. Without continued actions in the motor neuron, Ach release ceases.

2. Without ACh, nicotinic receptor channels close; action potentials in sarcolemma cease

3. SR calcium channels close when action potentials cease.

4. As sarcoplasm Ca2+ concentration drops, Ca2+ sissociates from troponin. Tropomyosin resumes its previous position over the myosin binding sites.

5. The thick filaments “lose their grip” on the thin filaments, and the sarcomere returns to its resting length.






• Muscle contraction and relaxation



Skeletal Muscle Contraction (Review)

• What is a motor unit?




Skeletal Muscle Contraction (Review)

• Answer: a somatic motor neuron and the skeletal muscle fibers it innervates




Muscle Energy

• Introduction

– ATP fuels three important aspects of muscle activity:

• Sarcolemma membrane potential

• Cross-bridge cycling

• Muscle relaxation

– ATP + H2O ADP + H2O + PO4 + energy




Muscle Energy (cont’d)

• Different processes can generate ATP

– ATP stores and creatine phosphate provide immediate energy

• Creatine phosphate converts ADP back into ATP

• Unique to muscles

– Glycolysis produces pyruvate and ATP

• Fastest method of generating ATP from nutrients

• Called glycogenolysis

• Occurs in the cytosol of muscle cells

• Does not require oxygen





– Mitochondria break down various nutrients and produce ATP

• Two components

– Citric acid cycle

– Mitochondrial respiration

• Requires oxygen

• Pyruvate or fatty acids + O2 CO2 + H2O + ATP




Muscle Energy (cont’d)• Muscle energy





• Muscle cells contract aerobically or anaerobically

– Muscle cells function aerobically if three conditions are met:

1. The muscle cell containe abundant mitochondria.

2. The muscle cell is supplied with adequate oxygen.

3. The ATP needs of the muscle cell are low or moderate.





– Athletic activities requiring short-lived, powerful contractions are anaerobic – they meet their needs using processes that do not require oxygen.

• Depends on glycogen stores

• Lactic acid produces as a glycolytic end product is metabolized further





– Anaerobic metabolism occurs in three circumstances:

1. Imposed demand

2. Preferentially in glycolytic muscle fibers

3. At the beginning of exercise





• Skeletal muscle fibers are oxidative or glycolytic

– Slow-twitch (oxidative, type I) fibers – optimized for aerobic metabolism

– Fast-twitch (glycolytic, type II) fibers – optimized for anaerobic metabolism

– Most human skeletal muscles are a mixture of slow and fast-twitch muscle fibers.

– The fibers of any given motor unit are all of the same type.




Muscle Energy (cont’d)• Muscle fiber types





• Skeletal muscle experiences fatigue

– When muscle is vigorously exercised for a long time, it loses the ability to respond to nerve stimulation.

• This is known as muscle fatigue.

– The major limit in submaximal endurance exercise is the ability to generate ATP.

– Fatigue in maximal anaerobic exercise is thought to reflect phosphate accumulation.




Muscle Energy (Review)

• Which nutrient generates more ATP per molecule –glucose or fatty acid?




Muscle Energy (Review)

• Answer: fatty acid




Case Study: Muscle Energy Metabolism: The Case of Hammid S.• Understanding how muscle gets its energy supplies is the key to

understanding Hammid’s signs and symptoms.

1. ATP stores and creating phosphate fuel the first few seconds of any contraction.

2. Glycogenolysis followed by glycolysis can also generate energy relatively quickly at the beginning of a contraction.

3. Aerobic metabolism provides a steady supply of ATP over the long term.




Case Study: Muscle Energy Metabolism: The Case of Hammid S. (cont’d)• Hammid does not have the enzyme glycogen phosphorylase,

which breaks down glycogen.

– Hammid has no difficulty initiating muscle contractions.

– His problems arise during sustained activity that exhaust available fuel.

– Lactic acid levels did not rise as they should during normal physical activity.

– Lacks enzyme needed to break down glycogen to supply glucose

– When Hammid’s muscles call for large amounts of fuel, the call goes unanswered; ATP levels fall to dangerously low levels.




Case Study: Muscle Energy Metabolism: The Case of Hammid S. (cont’d)

– Hammid get muscle cramps, creatine levels are elevated in Hammid’s blood.

– Myoglobin stains his urine brown.

• Hammid’s parents were advised to help Hammid with the following:

– Encourage moderate exercise (jogging rather than soccer)

– Consume a candy bar or sugary drink before exercise

– Insist he stop exercising when cramping occurs




Case Study: Muscle Energy Metabolism: The Case of Hammid S. (cont’d)• Hammid’s muscle energy metabolism




Case Study: Muscle Energy Metabolism: The Case of Hammid S. (Review)• Is Hammid suffering from a shortage of ATP, creatine phosphate,

or calcium?




Case Study: Muscle Energy Metabolism: The Case of Hammid S. (Review)• Answer: ATP




The Mechanics of Muscle Contraction• The force an individual muscle exerts depends on:

– The force exerted by each contracting fiber

– The number of motor neurons contracting




The Mechanics of Muscle Contraction (cont’d)• Contractile power depends on muscle fiber length

– At the optimal sarcomere length, all of the myosin heads are positioned to be in contact with actin molecules and form cross-bridges, and the contraction will generate the maximum tension possible (length-tension relationship).

– Short sarcomere lengths contract most forcefully.

– Long sarcomere lengths contract least forcefully.




The Mechanics of Muscle Contraction (cont’d)• Physiological contractions are unfused tetanus

– A single action potential in a muscle fiber results in a weak, transient muscle contraction called a twitch.

– If an action potential occurs before the twitch is finished, the force of the two twitches is summed together.

– Subsequent action potentials result in progressively greater force until incomplete tetanus is reached.

– We do not perceive the partial relaxations because muscle fibers in different motor units alternate contracting and relaxing.




The Mechanics of Muscle Contraction (cont’d)• Determinants of force




The Mechanics of Muscle Contraction (cont’d)• Contractile power depends on number of motor units involved

– As skeletal muscle contracts, first only a few motor units are stimulated, and they are recruited in specific order.

• Slow-twitch fibers are recruited first.

• Fast-twitch fibers are recruited if more force is necessary.

• Even at peak force, not all motor units are active at the same time; they rotate in and out of service.

• Muscle fibers of various units are intermingled, so that motor units throughout the muscle are recruited regardless of the strength of the contraction.




The Mechanics of Muscle Contraction (cont’d)• Muscle fiber contraction may or may not produce movement

– Isotonic contractions are the contractions of everyday movement.

– Two types

• Concentric contractions – shorten the muscle by bring the muscle attachment closer to the origin

• Eccentric contractions – generate a restraining force as the muscle lengthens – more powerful that concentric contractions




The Mechanics of Muscle Contraction (cont’d)– Isometric contractions do not alter the length of the muscle.

• These contractions maintain our body posture.

– Muscle tone is a state of subconscious isometric contraction that occurs even in voluntarily relaxed muscle.

• If the nerve supply to the muscle is interrrupted, the muscle loses its tone and becomes flaccid.

• Complete loss of muscle tone is called flaccid paralysis.

• Spastic paralysis is due to damage to the brain, which impairs control of muscles.




The Mechanics of Muscle Contraction (cont’d)• Isometric and concentric contractions




The Mechanics of Muscle Contraction (cont’d)• Exercise has a positive effect on muscles

– Use it or lose it.

– Muscle power is improved by strength training

– Muscle endurance is improved by aerobic exercise that relies on mitochondrial ATP generation.




The Mechanics of Muscle Contraction (Review)• What is the difference between incomplete and complete tetanus,

and which occurs more frequently?




The Mechanics of Muscle Contraction (Review)• Answer: The muscle fiber relaxes slightly between contractions in

incomplete tetanus but not in complete tetanus. Incomplete tetanus is more common.




Smooth Muscle• Introduction

– Occur in all in the walls of all but the smallest blood vessels and in the walls of hollow organs.

– Takes about 25 times as long to contract as skeletal muscle and consumes 1% as much energy.

– Actin – myosin cross-bridges may latch semipermanently in a latch state.

– Slow, sustaining contractions




Smooth Muscle (cont’d)• Smooth muscle differs structurally from skeletal muscle

– Smooth muscle cells are formed upon a three-dimensional criss-cross structure of noncontractile intermediate filaments.

• Filaments are interconnected by dense bodies

– Dense bodies are the functional equivalent of Z-discs in skeletal muscle.

• Myofilaments are not arranged in perfectly ordered ranks, so the muscle does not appear to be striated.

• Myofilaments inside smooth muscle cells are longer.




Smooth Muscle (cont’d)– Myofilaments of smooth muscle (cont’d)

• Myosin filaments have protruding heads along their entire length, so there is no headless zone.

– The arrangement of smooth muscle cells contributes to its stretchiness.




Smooth Muscle (cont’d)• Structure of smooth muscle




Smooth Muscle (cont’d)• In smooth muscle, calcium acts on myosin, not actin

– Smooth muscle differs in both the source and the role of Ca2+

ions:

• Source: Smooth muscles have very little SR. In smooth muscle, Ca2+ comes though the cell membrane from extracellular fluid.

• Role: Smooth muscle cells contain no troponin, so myosin binding sites are always exposed. Calcium in smooth muscle regulates the activity of the myosin heads on thick filaments.

– Myosin cleaves ATP and moves through the cross-bridge cycle only when Ca2+ is present.




Smooth Muscle (cont’d)• Smooth muscle regulation




Smooth Muscle (cont’d)• Events of smooth muscle contraction

– There is considerable variation, but this is a typical sequence of events:

1. A chemical signal activates calcium channels in the cell membrane or SR.

2. Calcium enters the cytoplasm from the extracellular fluid.

3. The intracellular Ca2+ concentration increases.

4. Through intervening enzymatic steps, calcium activates myosin heads.

5. Activated myosin heads form cross-bridges with actin monecules, the filaments slide, causing muscle contraction.




Smooth Muscle (cont’d)• Smooth muscle contraction is involuntary

– Smooth muscle movement is not subject to conscious control.

– Some smooth muscle is innervated by the autonomic nervous system.

– Other smooth muscles are simulated contract by hormones, or by local chemical signals such as prostaglandins, hydrogen ions, and gases.

– Smooth muscle is also stimulated by mechanical signals, such as stretching.

– The cells in some smooth muscles have unstable membrane potentials, which generate self-stimulating action potentials called pacemaker activity.




Smooth Muscle (cont’d)• Smooth muscle contracts as a single unit

– Groups of smooth muscle contract in unison because the cells are connected by gap junctions.

– Contraction strength in smooth muscle cannot be varied by changing the number of contracting cells.

– The amount of tension generated by individual smooth muscle cells varies according to the amount of calcium allowed into the cell from extracellular fluid.




Smooth Muscle (Review)• True or false: The calcium causing smooth muscle contraction

comes from the extracellular fluid, but the calcium causing skeletal muscle contraction usually comes from the SR.




Smooth Muscle (Review)• Answer: true




Skeletal Muscle Actions• Most muscles cross a joint and act to move one bone in relation

to another

– The end of the muscle that serves as an anchor for the movement is known as the origin.

– The end that moves the body part is the insertion.

• The contraction of a muscle pulls (never pushes) the insertion toward its origin.




Skeletal Muscle Actions (cont’d)• Origin and Insertion




Skeletal Muscle Actions (cont’d)• In producing movement, the actions of different muscles often

complement or oppose each other.

• Types of movements

– Prime mover – the main muscle responsible for a particular movement.

– Antagonist – the muscle that opposes the action of the prime mover

– Synergist – a muscle that assists the action of the prime mover

• Fixators – synergists that prevent the movement of a nearby joint




Skeletal Muscle Actions (Review)• When a muscle contracts, which part moves more – the origin or

the insertion?




Skeletal Muscle Actions (Review)• Answer: insertion




The Major Skeletal Muscles• The human body contains hundreds of muscles.

• Use the illustrations and tables (in the text) to learn the location and shape of major skeletal muscles.

• You can make the task of learning muscle anatomy easier:

– Learn the word parts used to name muscles.

– Perform the actions of muscles as you read about them.




The Major Skeletal Muscles (cont’d)• Superficial muscles (anterior view)




The Major Skeletal Muscles (cont’d)• Superficial muscles (posterior view)




The Major Skeletal Muscles (cont’d)• Muscles of facial expression




The Major Skeletal Muscles (cont’d)• Muscles controlling the jaw and moving the head




The Major Skeletal Muscles (cont’d)• Muscles of the thorax: muscles that move the vertebral column,

abdominal muscles, and respiratory muscles




The Major Skeletal Muscles (cont’d)• Muscles of the perineum




The Major Skeletal Muscles (cont’d)• Muscles that move and stabilize the pectoral girdle




The Major Skeletal Muscles (cont’d)• Muscles that move the arm (humerus) at the shoulder joint




The Major Skeletal Muscles (cont’d)• Muscles that move the forearm, hand, and fingers




The Major Skeletal Muscles (cont’d)• Muscles that move the thigh and leg




The Major Skeletal Muscles (cont’d)• Muscles that move the foot and toes




The Major Skeletal Muscles (Review)• Which muscle strongly flexes the spinal column?




The Major Skeletal Muscles (Review)• Answer: rectus abdominus


chapter 7 muscles power point

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