9 MUSCLES & MUSCLE TISSUE

PART I MUSCLES & MUSCLE TISSUE OVERVIEW OF MUSCLE TISSUES

a. Types of muscle tissue Skeletal Cardiac Smooth Structure Striated/Nonstriated? Location Where is this muscle tissue found in the body? Function Voluntary/Involuntary? What is its function? Striated (striped) Striated (striped) Nonstriated Packaged in skeletal muscles that attach to and cover the bony skeleton Occurs only in the walls of the heart Walls of hollow visceral organs (e.g. stomach, urinary bladder, uterus, blood vessels) Voluntary (consciously controlled) Overall body mobility Involuntary (unconsciously controlled) Pump blood Involuntary (unconsciously controlled) Force substances through internal body channels

i. Overview of muscle tissues B. Types of Muscle Tissue Muscle contraction depends on two kinds of myofilaments – actin and myosin Muscle Terminology Prefixes – myo, mys, and sarco all refer to muscle Myo-, mys-: muscle Sarco-: flesh

b. Functional Characteristics of Muscle Tissue Excitability/Irritability – ability to receive and respond to stimuli Contractility – ability to shorten forcibly Extensibility – ability to be stretched or extended Elasticity – ability to recoil and resume the original resting length after being stretched

Stabilize Joints – stabilize and strengthen joints of the skeleton c. Muscle Functions Produce Movement – locomotion, coursing blood through the body, propulsion of substances through organs and tracts Maintain Posture – erect or seated posture despite downward pull of gravity Stabilize Joints – stabilize and strengthen joints of the skeleton Generate Heat – muscles generate heat as they contract and maintain normal body temperature Skeletal muscles are responsible for all locomotion Cardiac muscle is responsible for coursing the blood through the body Smooth muscle helps maintain blood pressure, and squeezes or propels substances (i.e., food, feces) through organs

Which of the following is not a prefix used to refer to muscle? mys myo sarco lemma Answer: d. lemma

all of these muscle types are subject to conscious control Of the following muscle types, which is the only one subject to conscious control? smooth skeletal cardiac all of these muscle types are subject to conscious control Answer: b. skeletal

skeletal muscle is the only striated muscle type Which two types of muscle appear striated when examined under a microscope? smooth and skeletal smooth and cardiac cardiac and skeletal skeletal muscle is the only striated muscle type Answer: c. cardiac and skeletal

PART II ANATOMY OF SKELETAL MUSCLE MUSCLES & MUSCLE TISSUE

i. Skeletal muscle Gross Anatomy of a Skeletal Muscle Each skeletal muscle is a discrete organ, made up of skeletal muscle fibers, blood vessels, nerve fibers, and connective tissue. Connective Tissue Sheaths In an intact muscle, the individual muscle fibers are wrapped and held together by several different connective tissue sheaths. These connective tissue sheaths support each muscle fiber and reinforce the muscle as a whole, preventing muscles from bursting during exceptionally strong contractions.

1. Connective tissue sheaths Endomysium – surrounds each individual muscle fiber Perimysium – surrounds each fascicle (groups of endomysium-wrapped muscle fibers) Epimysium – surrounds the whole muscle

The connective tissue that covers each muscle fiber is the ________. epimysium perimysium sarcolemma endomysium

A. Gross anatomy of skeletal muscle Attachments Most skeletal muscles span joints and are attached to bones in at least two places. When a muscle contracts, the muscle’s insertion (movable bone) moves toward the muscle’s origin (immovable or less movable bone). Muscle attachments, whether origin or insertion, may be direct or indirect.

2. attachments Direct Attachments – epimysium of muscle is fused to periosteum of bone Indirect Attachments – muscle’s connective tissue wrappings extend beyond the muscle and anchor the muscle to bone Tendon – ropelike connective tissue; attaches muscle to bones Aponeurosis – connective tissue sheet; attaches muscle to bones

A sheet like extension of the epimysium is called ________. direct attachment indirect attachment tendon aponeurosis both 1 and 3 both 2 and 3 both 1 and 4 both 2 and 4

B. Microscopic Anatomy of a Skeletal Muscle Fiber Each skeletal muscle fiber is a long cylindrical cell with multiple nuclei arranged underneath its sarcolemma, or plasma membrane. The sarcoplasm, or cytoplasm, of a muscle fiber contains unusually large amounts of glycosomes (granules of stored glycogen – to be used to make ATP in cellular respiration) and myoglobin (a red pigment that stores oxygen – to be used to make ATP in cellular respiration).

B. Microscopic Anatomy of a Skeletal Muscle Fiber Myofibrils Each muscle fiber contains many rod-like myofibrils. The myofibrils contain the contractile elements of skeletal muscle cells.

b. Microscopic anatomy of skeletal muscle fiber Striations, Sarcomeres, and Myofilaments Each myofibril is composed of two types of myofilaments. Myosin – thick protein filaments Actin – thin protein filaments Actin and myosin overlap to form light and dark bands. The alternation of these light and dark bands form striations.

The thin filaments of muscle fibers are comprised of which of the following components? titin troponin actin myosin Answer: b. titin

2. striations, sarcomeres, and myofilaments These striations are actually bands, zones, and lines. A Band – overlapping myosin and actin (dark bands) H Zone – within an A band; myosin only I Band – actin only (light bands)

2. striations, sarcomeres, and myofilaments M Line – within H Zone; where 2 myosin protein filaments join Z Disc – within I Band; where 2 actin protein filaments join; forms sarcomere boundary Sarcomeres are the basic units of contraction. They extend from Z Line to Z Line.

Thick filaments are found in the ________ of the sarcomere. Z-disc I-band A-band all of the above contain thick filaments

The basic unit of contraction of a muscle fiber is the __________. myofibril sarcomere fascicle myofilament Answer: a. sarcomere

C. ULTRASTRUCTURE AND MOLECULAR COMPOSITION OF THE MYOFILAMENTS Thick Filament Components Myosin – protein with heads that form cross bridges between thick and thin filaments

C. ULTRASTRUCTURE AND MOLECULAR COMPOSITION OF THE MYOFILAMENTS Thin Filament Components Actin – protein with active sites to which the myosin heads attach during contraction Tropomyosin – rope-like protein wrapped around thin filaments; block myosin binding sites on actin in a relaxed muscle fiber Troponin – binds calcium during muscle contraction

c. Ultrastructure and molecular composition of myofilaments  

d. Sarcoplasmic reticulum and t-tubules The sarcoplasmic reticulum stores calcium and releases it on demand when the muscle fiber is stimulated to contract. Elongated tubes, called T-tubules, extend from the sarcolemma and penetrate deep into the muscle cell. They conduct impulses deep into the muscle cell and allow for uniform and synchronous contraction of the muscle.

The thin filaments are not comprised of which of the following components? actin titin troponin tropomyosin Answer: b. titin

Calcium ions will bind to ________ when present in the sarcoplasm. myosin heads ATP myosin binding sites troponin

What is the major function of the sarcoplasmic reticulum? store sodium ions store potassium ions expel calcium ions from the cell store calcium ions Answer: d. store calcium ions

The t-tubules are an extension of the ___________. sarcomere sarcoplasmic reticulum sarcolemma endomysium

PART III MUSCLES & MUSCLE TISSUE SLIDING FILAMENT THEORY OF CONTRACTION

ii. Sliding filament model of contraction Sliding Filament Theory of Contraction During contraction, the thin filaments slide past the thick filaments so that the actin and myosin filaments overlap.

the A-bands get shorter During a muscle contraction, the sliding filament theory would be apparent in a sarcomere because __________. the I-bands get longer the A-bands get shorter the H zone becomes less obvious and the Z-discs move closer together the Z-discs get pulled closer toward the I-bands and the H zone becomes more obvious Answer: c. the H zone becomes less obvious and the Z-discs move closer together

ii. Sliding filament model of contraction Mechanism Muscle contraction requires calcium and energy, in the form of ATP, in order for the thick and thin filaments to slide past each other. The steps are:

B. Mechanism Relaxation Prior to muscle contraction, the myosin binding sites on the actin molecule are physically blocked by tropomyosin. In addition, ATP is bound to the myosin heads. As a result, the myosin heads of the thick filaments cannot attach to the thin filaments.

B. Mechanism Contraction Arrival of an action potential causes release of Ca2+ from the sarcoplasmic reticulum. The Ca2+ binds to troponin, which changes shape and removes the blocking action of tropomyosin so that the myosin binding sites on the actin filament become exposed.  

B. Mechanism Contraction Cross Bridge Formation: ATP turns into ADP, releasing energy and allowing the myosin heads to attach to the binding sites on the actin filament, forming ‘cross bridges’.

B. Mechanism Contraction Power Stroke: The myosin heads push on the thin filament, sliding it toward the center of the sarcomere.

B. Mechanism Contraction Cross Bridge Detachment: Fresh ATP attaches to the myosin heads, releasing them from the binding sites on the actin and re-priming them for a repeat movement.

2. contraction These cross bridge attachments are formed and broken several times during a contraction. As this occurs simultaneously in myofibrils throughout the cell, the muscle cell shortens.

In a resting muscle cell the myosin binding sites are blocked by ________. actin myosin troponin tropomyosin

When a muscle cell is at rest most of the intracellular calcium is found in the ___________. sarcoplasm t-tubule sarcoplasmic reticulum myosin heads

Calcium is released from the sarcoplasmic reticulum in response to ______. ATP calcium pumps an action potential troponin

What substance must bind to myosin heads in order for the heads to detach from the thin filaments? calcium ATP troponin sodium

PART IV EXCITATION-CONTRACTION COUPLING MUSCLES AND MUSCLE TISSUE

Excitation-Contraction Coupling & Sliding Filament Mechanism of Contraction Presentation WHO: Groups of 2 students WHAT: Using the paper model, present the steps involved in Excitation-Contraction Coupling & Sliding Filament Mechanism of Contraction HOW: Begin with an action potential propagating down the axon of a neuron. End with relaxation of the muscle fiber and release of calcium. Be sure to include the following concepts/terms in your presentation: Ca2+ synaptic vesicle Acetylcholine Na+ sarcolemma T-tubule sarcoplasmic reticulum troponin tropomyosin myosin head actin Sliding Filament Theory contraction relaxation

a release of calcium ions from the sarcoplasmic reticulum At the neuromuscular junction, the muscle contraction initiation event is ______. a release of calcium ions from the sarcoplasmic reticulum conduction of an electrical impulse down the t-tubules binding of acetylcholine to membrane receptors on the sarcolemma sliding of actin and myosin filaments past each other Answer: c. binding of acetylcholine to membrane receptors on the sarcolemma

In a muscle fiber, the key intracellular event that stimulates muscle contraction is known as ________. polarization depolarization repolarization potential Answer: b. depolarization

During depolarization, the sarcolemma is most permeable to _______. sodium ions potassium ions calcium ions chloride ions Answer: a. sodium ions

What is calcium’s function during muscle contraction? Calcium binds to troponin, changing its shape and removing the blocking action of tropomyosin. Calcium binds to troponin to prevent myosin from attaching to actin. Calcium depolarizes the muscle fiber. Calcium flows down the t-tubules to stimulate the influx of sodium from the sarcoplasmic reticulum. Answer: a. Calcium binds to troponin, changing its shape and removing the blocking action of tropomyosin.

Corpses usually exhibit rigor mortis because __________. ATP hydrolysis stimulates myosin head attachment to actin ATP hydrolysis promotes myosin head detachment from actin calcium stores become deficient corpses are non-living humans Answer: b. ATP hydrolysis promotes myosin head detachment from actin

How does calcium re-enter the terminal cisternae after muscle contraction is finished? diffusion active transport filtration rings the doorbell

PART V MUSCLES AND MUSCLE TISSUE CONTRACTION OF A SKELETAL MUSCLE

i. Contraction of a skeletal muscle The force exerted by a contracting muscle on an object is called muscle tension, and the opposing force exerted on the muscle by the weight of the object to be moved is called the load.

i. Contraction of a skeletal muscle The Motor Unit Each muscle is served by at least one motor nerve. A motor neuron and all the muscle fibers it supplies is called a motor unit. Muscles that exert fine control have small motor units. Large, weight-bearing muscles, whose movements are less precise, have large motor units.

i. Contraction of a skeletal muscle The Muscle Twitch The response of a motor unit to a single action potential of its motor neuron is called a muscle twitch. Graded Muscle Responses Healthy muscle contractions are relatively smooth and vary in strength as different demands are placed on them. These variations are referred to as graded muscle responses.

A single contraction in response to a single threshold stimulus is defined as _________. summation tetany treppe twitch

i. Contraction of a skeletal muscle Graded Muscle Responses Muscle contraction can be varied in two ways: Change frequency of stimulation Change strength of stimulus

i. Contraction of a skeletal muscle Isotonic and Isometric Contractions Isotonic Contractions (iso = same; tonic = tension) Muscle length changes; load moved; tension constant Isometric Contractions (iso = same; metric = measure/length) Muscle tension changes; muscle length constant; load does not move; load > force muscle can generate

Which type of muscle contraction occurs when the muscle neither shortens nor lengthens during contraction? isotonic concentric eccentric isometric

Isometric contractions come into play when an individual is ________. jumping walking up-hill lifting a heavy object maintaining an upright posture Answer: d. maintaining an upright posture

Providing Energy for Contraction ii. MUSCLE METABOLISM Providing Energy for Contraction As a muscle contracts, ATP provides the energy for cross bridge movement and detachment and for operation of the calcium pump. Surprisingly, muscles store very limited reserves of ATP, about 4-6 seconds’ worth at most. Since ATP is the only energy source used for contraction, it must be regenerated as fast as it is broken down if contraction is to continue.

The energy source that is used directly for muscle contraction is ______. ATP glucose creatine phosphate fatty acids

Creatine Phosphate + ADP  Creatine + ATP Muscle metabolism ATP Regeneration After ATP is broken down to ADP and P, it is regenerated by three pathways: Direct Phosphorylation of ADP by Creatine Phosphate Equation: Creatine Phosphate + ADP  Creatine + ATP

B. Anaerobic Mechanism: Glycolysis and Lactic Acid Formation Equation: Glucose  Lactic Acid + ATP Huge amounts of glucose are used to produce relatively small amounts of ATP; accumulating lactic acid contributes to muscle fatigue and muscle soreness during intense exercise.

Glucose + Oxygen  Carbon Dioxide + Water + ATP c. aerobic respiration Equation: Glucose + Oxygen  Carbon Dioxide + Water + ATP Aerobic respiration provides a high yield of ATP, but it is relatively slow because of its many steps and it requires continuous delivery of oxygen and nutrients keep it going.

Muscle soreness may be due in part to which pathway of ATP production? phosphorylation aerobic respiration anaerobic glycolysis oxidation

A. Providing energy for contraction Muscle Fatigue: physiological inability to contract even though the muscle still may be receiving stimuli; different from psychological fatigue in which the muscle can still contract but we feel tired Oxygen Debt: extra amount of oxygen that the body must take in for restorative processes muscle needs in order to return to resting state

A. Providing energy for contraction Heat Production Only 40% of energy is used to do work – the rest is lost as heat. Heat buildup is prevented from reaching dangerous levels by sweating. Shivering occurs when muscle contractions are used to produce more heat.

PART VI MUSCLES AND MUSCLE TISSUE EFFECT OF EXERCISE ON MUSCLES

All of the following can occur during exercise except: oxygen levels decrease ATP levels decline inorganic phosphate levels decrease calcium levels decrease