Chapter 10 A&P muscle tissue

Distribution of Muscle Fiber Types

1. All muscle have some fibers from each type 2. Muscle fiber percentage depends on the function of the muscle 3. For example: a. Muscles of hand and eye - more FG fibers b. Postural muscles of the back - more SO fibers

Contraction of Skeletal Muscle (Organ Level)

1. Contraction of muscle fibers (cells) and muscles (organs) is similar 2. The two types of muscle contractions are a. Isometric contraction b. Isotonic contraction

Muscle Fatigue 2

1. Currently believed to not be due to lack of ATP 2. Currently believed to be due to ion imbalances in the muscle fibers 3. ATP levels are maintained through aerobic cellular respiration in mitochondria

Oxygen Debt

1. Finite amount of oxygen can be delivered to muscle tissue 2. After exercise-hard breathing restores oxygen levels in muscle 3. System must also a. Restore glycogen, ATP and Creatine Phosphate stores b. Convert Lactic Acid to glucose

Graded Muscle Responses

1. Graded muscle responses permit variations in the degree of contraction and fine control of movement 2. Responses are graded by: a. Changing the strength of the stimulus b. Changing the frequency of stimulation

All-or-None Law

1. If a muscle fiber contracts in response to stimulation, it will contract completely (all) 2. If the stimulus is not sufficient, it will not contract (none) 3. The muscle contracts completely or it does not contract

Effects of Exercise

1. Increased exercise=hypertrophy of fibers a. Number of mitochondria b. Glycogen reserves c. Increased ATP synthesis 2. Recent evidence suggests that exercise may show a limited increase in number of muscle fibers 3. Lack of exercise=atrophy a. Decrease in muscle fiber size, tone and power b. Can be reversed unless muscle has been replaced with connective tissue

Crossbridge cycling

1. Increased phosphate ion concentration resulting in interference with phosphate ion release from the myosin head during crossbridge cycling 2. Lower calcium ion availability

Cardiac Muscle

1. Individual cells arranged in thick bundles around the heart 2 Cells branch and are connected by intercalated discs consisting of desmosomes and gap junctions a. Desmosomes b.Gap junctions 3. Simulation via a specialized autorhythmic pacemaker-regulated by autonomic nervous system

Innervation of Smooth Muscle

1. Innervating nerves have bulbous swellings called varicosities 2. Varicosities release neurotransmitters into wide synaptic clefts called diffuse junctions

Excitation at the neuromuscular junction

1. Insufficient free Ca2+ 2. Decreased number of synaptic vesicles to release neurotransmitter

Types of Smooth Muscle: Multiunit

1. Multiunit smooth muscles location: a. In large airways to the lungs b. In large arteries c. In arrector pili muscles d. Attached to hair follicles e. In the internal eye muscles 2. Characteristics include: a. Degree of contraction related to number of innervating neurons

Muscle Fatigue

1. Muscle fatigue - the reduced ability or inability of the muscle to produce muscle tension 2. Causes of muscle fatigue induced by the specific physiological event of muscle contraction: a. Excitation at the neuromuscular junction b. Excitation-contraction coupling c. Crossbridge cycling

Muscle Tone

1. Muscle tone: a. Is the resting tension in a muscle generated by involuntary nervous stimulation of the muscle b. Results in the constant, slightly contracted state of all muscles, which does not produce active movements (protects joints) c. Keeps the muscles firm, healthy, and ready to respond to stimulus 2. Spinal reflexes account for muscle tone by: a. Activating one motor unit and then another in sequence b. Responding to activation of stretch receptors in muscles and tendons

Proportion and Organization of Myofilaments in Smooth Muscle

1. Ratio of thick to thin filaments is much lower than in skeletal muscle 2. Thick filaments have heads along their entire length 3. There is no troponin complex 4. Thick and thin filaments are arranged diagonally, causing smooth muscle to contract in a corkscrew manner 5. Noncontractile intermediate filament bundles attach to dense bodies (analogous to Z discs) at regular intervals

Microscopic Anatomy of Smooth Muscle

1. SR is less developed than in skeletal muscle and lacks a specific pattern 2. T-tubules are absent 3. Plasma membranes have pouchlike infoldings called caveoli (replaces T-tubules) 4. Ca2+ from SR or extracellular space 5. There are no visible striations and no sarcomeres 6. Thin and thick filaments are present

Effects of Aging

1. Slow, progressive loss in muscle mass 2. Size and power of muscles lost 3. Fiber diameters decrease Oxygen storage capacity diminishes 4. Reduce capacity to recover from disease or injury 5. Muscle mass often replaced by dense regular connective tissue 6. Solution: KEEP EXERCISING

Types of Smooth Muscle: Single Unit

1. The cells of single-unit smooth muscle, commonly called visceral muscle a. Contract rhythmically as a unit b. Are electrically coupled to one another via gap junctions c. Are arranged 2-3 sheets d. Innervated by axons and neurotransmitter released at varicosities

Principles of Muscle Mechanics

1. The principles governing contraction of fiber=whole muscle 2. The force on an object=muscle tension a. Opposed by object weight/load 3. A contracting muscle does not always shorten and move the load. 4. A skeletal muscle contracts with varying force and for different periods of time in response to stimuli of varying frequencies and intensities.

Contraction of Smooth Muscle

1. Whole sheets of smooth muscle exhibit slow, synchronized contraction 2. They contract in unison, reflecting their electrical coupling with gap junctions 3. Action potentials are transmitted from cell to cell 4. Some smooth muscle cells: a. Act as pacemakers and set the contractile pace for whole sheets of muscle b. Are self-excitatory and depolarize without external stimuli (through stretch of the muscle-stress/relaxation response

Muscle Twitch

1.The response of a muscle to a single, brief threshold stimulus 2. Phases a. Latent period b. Period of contraction c. Period of relaxation

Motor Unit: The Nerve-Muscle Functional Unit

A motor neuron and all the muscle fibers it supplies: Number of muscle fibers per motor unit can vary from four to several hundred Muscles that control fine movements (fingers, eyes) have small motor units Large weight-bearing muscles (thighs, hips) have large motor units

Nerve supply

A motor neuron supplying multiple muscle cells at the neuromuscular junction Each muscle cell is supplied by one motor neuron terminal branch and is in contact with one or two capillaries Nerve fibers & capillaries are found in the endomysium between individual cells

Muscle Metabolism: Energy for Contraction

ATP is the only energy used directly for contractile activity First source of ATP - ATP stored in the cell (phosphagen system): Sufficient for 4 to 6 sec of activity As soon as available stores of ATP are hydrolyzed, they are regenerated by: Anaerobic glycolysis Aerobic respiration

Muscle: Energy Stores

Abundant mitochondria Myoglobin Creatine phosphate

Muscle contraction depends on two kinds of myofilaments

Actin and myosin

Contractile proteins

Actin and myosin Connect to shorten muscle fibers

Muscle Metabolism: Energy for Contraction

Aerobic mechanism: 1. Provides 95% of energy for muscle activity during rest and light to moderate exercise 2. Occurs in the mitochondria 3. Requires oxygen

Skeletal Muscle Contraction In order to contract, a skeletal muscle must:

Be stimulated by a nerve ending (Ach release) Propagate an electrical current, or action potential, along its sarcolemma (voltage gated Na+ channels) Have a rise in intracellular Ca2+ levels, the final trigger for contraction (release from intracellular stores) Random: Linking the electrical signal to the contraction is excitation-contraction (EC) coupling

Excitation-contraction coupling

Change in ion concentration resulting in inability to conduct an action potential along the sarcolemma

The Proteins of Muscle

Contractile proteins Regulatory proteins Structural proteins

Motor Unit

Definition: a motor neuron and all of the skeletal muscle fibers it innervates Numbers vary depending on muscle size and function Large units found in muscles functioning in "large" movement; ie. walking Small units found in muscle functioning in "fine" movement; ie. hands

Attachment methods

Directly - epimysium of the muscle is fused to the periosteum of a bone Indirectly - connective tissue wrappings extend beyond the muscle as a tendon or aponeurosis

Muscle fibers in bundles-fascicles Connective tissue in 3 layers

Epimysium Perimysium Endomysium

Muscle Fiber Development

Every mature skeletal muscle cell developed from numerous myoblasts that fuse together in the fetus. (multinucleated) Mature muscle cells can not divide Muscle growth is a result of cellular enlargement & not cell division Satellite cells retain the ability to regenerate new cells.

Functional Characteristics of Muscle Tissue

Excitability or irritability Conductivity Contractility Extensibility Elasticity

Blood supply

Extensive supply of blood vessels

Smooth muscle function

Helps maintain blood pressure, and squeezes or propels substances (i.e., food, feces) through organs

Structural proteins

Provide proper alignment, elasticity and extensibility 1. Titin 2. Nebulin 3. Dystrophin 4. Connectin

Skeletal muscles function

Responsible for all locomotion and maintain posture, stabilize joints, and generate heat

Cardiac muscle function

Responsible for coursing the blood through the body

3 muscle tissues

Skeletal Cardiac Smooth

Muscle Function of

Skeletal muscles Cardiac muscle Smooth muscle

skeletal muscle tissue

Structure and characteristics: Long, cylindrical, striated fibers (cells) arranged parallel and unbranched; fibers are multinucleated; fiber is under voluntary control Function: primarily responsible for moving skeleton and selected other components of the body Location: attaches to bones or sometime to skin (e.g., facial muscles)

smooth muscle tissue

Structure and characteristics: Nonstriated cells that are short and fusiform in shape; contain one centrally located nucleus; under involuntary control Function: moves and propels materials through internal organs; controls the size of the lumen Location: walls of hollow internal organs, such as intestines, stomach, airways, urinary bladder, uterus, and blood vessels

cardiac muscle tissue

Structure and characteristics: Short, striated cells typically branching; cells contain one or two centrally located nuclei; intercalated discs between cells; under involuntary control Function: pumps blood through heart Location: Heart wall (myocardium)

Regulatory proteins

Troponin and tropomyosin Turn contraction on and off

Muscle Metabolism: Anaerobic Glycolysis

When muscle contractile activity reaches 70% of maximum: 1. Bulging muscles compress blood vessels 2. Oxygen delivery is impaired 3. Pyruvic acid is converted into lactic acid Lactic acid: 1. Diffuses into the bloodstream 2. Is picked up and used as fuel by the liver, kidneys, and heart 3. Is converted back into pyruvic acid by the liver

Abundant mitochondria

aerobic respiration

Conductivity

an electrical charge travels along the plasma membrane of the skeletal muscle cell

Nebulin

an inelastic protein, helps align the thin filaments; establish thin filament length.

Dystrophin

anchors myofibrils to sarcolemma (muscular dystrophy)

Titin

anchors thick filament to the M line and the Z disc

Endomysium

areolar connective tissue surrounding each fiber

Myoglobin

binds oxygen for aerobic respiration

Gap junctions

communicating junctions

Desmosomes

connecting junctions

Sarcoplasm

cytoplasm of a muscle cell

Epimysium

dense irregular connective tissue around skeletal muscled

Perimysium

dense irregular connective tissue surrounding fascicle

Tendon

dense regular connective tissue attaches muscle to bone, skin, or another muscle; maybe a flattened sheet

Skeletal and smooth muscle cells are?

elongated and are called muscle fibers

Connectin

extends from thick filament core-orientation of filament

Deep fascia

external to epimysium, formed of dense irregular connective tissue; houses nerves, blood vessels, lymph vessels

Creatine phosphate

for anerobic respiration

Sarcolemma

muscle plasma membrane

Prefixes

myo, mys, and sarco all refer to muscle

Repolarization

occurs due to closure of v-gated Na+ channels (inactivation state) and opening v-gate K+ moves out of the cell into the IF and polarity is reversed from positive to negative (+30mV --> -70mV

Depolarization

occurs when threshold (-55 mV) is reached; v-gated Na+ channels open and Na+ enters rapidly, reversing the polarity from negative to positive (-55 mV --> +30 mV)

Hyperpolarization

occurs when v-gated K+ channels stay open longer than the time needed to reach the resting membrane potential; during this time the membrane potential is less than the resign membrane potential of -70mV.

Sarcoplasmic reticulum

smooth ER

Isometric contraction

tension<load=no contraction

Isotonic contraction

tension>load=contraction Shortening—concentric contraction Lengthening-eccentric contraction

Extensibility

the ability to be stretched or extended

Excitability or irritability

the ability to receive and respond to stimuli

Elasticity

the ability to recoil and resume the original resting length

Contractility

the ability to shorten forcibly