chapter 10 muscle tissue

muscle to bone

1. Bones provide leverage and form the framework of the body, but motion results from alternating contraction (shortening) and relaxation of muscles. 2. Muscular tissue also stabilizes the body's position, regulates organ volume, generates heat, and propels fluids and food through various body systems. 3. Muscular tissue accounts for 40-50 percent of total body mass. 4. The study of muscles is called myology.

cardiac muscle tissue

1. Cardiac muscle tissue is located in the wall of the heart. 2. The cells have the following important characteristics: i. are striated ii. are involuntary iii. some cells have autorhythmicity iv. are branching cylinders that usually contain a single nucleus v. neighboring fibers are connected by intercalated discs that contain: a. desmosomes, which strongly hold the fibers together b. gap junctions, which allow muscle action potentials to spread from one fiber to another fiber vi. compared to skeletal muscle fibers, the sarcoplasm: a. is more abundant and contains thick and thin filaments organized into orderly sarcomeres b. has larger and more numerous mitochondria c. has a less elaborate sarcoplasmic reticulum d. is penetrated by fewer but wider transverse tubules 3. Under normal resting conditions, cardiac muscle tissue rhythmically contracts and relaxes about 75 times per minute; this rhythm may be increased or decreased by nerve or hormonal stimulation. 4. Cardiac muscle tissue has characteristics that permit significant increases in heart rate but prevent the heart from undergoing tetanus. 5. Cardiac muscle fibers can undergo hypertrophy in response to increased workload.

skeletal muscle function

1. Each muscle consists of numerous muscle fibers. 2. Typically, a muscle belly (body) is attached to bones by tendons: - a tendon is a cord of dense connective tissue that attaches a muscle to the periosteum of a bone - some tendons are aponeuroses - an aponeurosis is a broad, flat sheet of connective tissue that attaches a muscle to the periosteum of a bone, another muscle, or the skin 3. Three layers of connective tissue extend from the muscle belly and become continuous with the tendon: i. endomysium surrounds individual muscle fibers ii. perimysium surrounds fascicles (bundles of muscle fibers) iii. outer epimysium encircles the entire muscle belly 4. Various skeletal muscles are grouped together and protected by large connective tissue sheets called fascia.

skeletal muscle fibers

1. Skeletal muscle fibers are not all identical in structure or function: i. Muscle fibers that have a high content of myoglobin, a red oxygen-storing protein (as well as more mitochondria and a rich blood supply), are called red muscle fibers. ii. Muscle fibers that have a low content of myoglobin are called white muscle fibers. iii. Based on structural and functional characteristics, skeletal muscle fibers are classified into three types (see Table 10.4): a. slow oxidative (SO) fibers or type I fibers b. fast oxidative-glycolytic (FOG) fibers or type IIa fibers c. fast glycolytic (FG) fibers or type IIb fibers iv. Most skeletal muscles contain a mixture of all three types of skeletal muscle fibers, but their proportion varies depending on the usual action of the muscle; however, the skeletal muscle fibers in any one motor unit are all of the same type.

two type of smooth muscle tissue

1. Smooth muscle tissue is usually activated involuntarily. 2. There are two types of smooth muscle tissue: i. visceral (single-unit) smooth muscle tissue is the more common type a. located in skin and in the walls of small blood vessels and hollow viscera b. it is autorhythmic; due to presence of gap junctions, entire muscle contracts as a single unit when one fiber is stimulated by neurotransmitter, hormone or autorhythmic signal ii. multiunit smooth muscle tissue a. located in the walls of large arteries, bronchioles, arrector pili muscles, irises of the eyes, and ciliary muscles of the eyes b. each fiber contracts individually upon stimulation

Exercise and Skeletal Muscle Tissue

1. The total number of skeletal muscle fibers and the relative percentages of fast and slow fibers in each muscle is genetically determined and do not change significantly after birth, but the characteristics of the muscle fibers present may be somewhat altered in various ways by various types of exercise. 2. Activities such as proper "warming up", stretching, and strength training are beneficial activities.

fascia

4. Various skeletal muscles are grouped together and protected by large connective tissue sheets called fascia.

Acetylcholine

A neurotransmitter that enables learning and memory and also triggers muscle contraction The effect of acetylcholine is brief because it is rapidly broken down by acetylcholinesterase (AChE) located in the synaptic cleft.

muscle cell membrane

Each muscle fiber has a sarcolemma (plasma membrane) that surrounds the sarcoplasm (cytoplasm); the latter contains an oxygen-binding protein called myoglobin iv. The sarcoplasm contains the sarcoplasmic reticulum (SR) with dilated end sacs called terminal cisterns which store calcium ions via the action of calcium active transport pumps; release of calcium ions into the cytosol triggers muscle contraction

stress relax respond

Most smooth muscle fibers contract or relax in response to neurotransmitters, hormones, autorhythmic signals, stretching or local factors. 5. Smooth muscle tissue exhibits the stress-relaxation response which allows it to be stretched considerably while still retaining the ability to contract effectively.

muscle tone

Muscle tone is a sustained, partial state of involuntary contraction that gives firmness to a relaxed skeletal muscle; in a constantly shifting pattern, a few motor units become active while others become inactive within a skeletal muscle - this is essential for maintaining posture - a muscle becomes flaccid upon loss of muscle tone

smooth muscle division

Smooth muscle fibers can undergo hypertrophy; some smooth muscle fibers can divide and new fibers can be formed from pericytes and, therefore, regeneration can occur to a limited extent.

T tubules

The sarcolemma has tunnel-like invaginations called transverse tubules (T tubules) that penetrate into the muscle fiber at right angles to the myofilaments; these T tubules conduct muscle action potentials which cause the release of calcium ions from the SR.

sarcoplasmic reticulum (SR)

The sarcoplasm contains the sarcoplasmic reticulum (SR) with dilated end sacs called terminal cisterns which store calcium ions via the action of calcium active transport pumps; release of calcium ions into the cytosol triggers muscle contraction

Myofibrils

a. The myofibrils contain numerous parallel (protein) filaments (or myofilaments) called thin filaments and thick filaments that are arranged in functional units called sarcomeres b. Adjacent sarcomeres (see Table 10.1) are separated by Z discs and have regions called the A band, I band, H zone, and M line and a zone of overlap. c. Thick filaments consist of motor proteins called myosin molecules with heads. d. Thin filaments consist of actin molecules plus two regulatory proteins called troponin and tropomyosin. e. Sarcomeres also contain structural proteins (e.g., titin, myomesin, nebulin and dystrophin) which keep the thick and thin filaments properly aligned, give the myofibril elasticity and extensibility and link the myofibrils to Zdiscs and to the sarcolemma.

Microscopic Anatomy of skeletal muscle

i. During embryonic development, a skeletal muscle fiber is formed by the fusion of MYOBLASTS and thus the muscle fibers are multinucleate ii. Growth of a skeletal muscle is achieved primarily by hypertrophy because skeletal muscle fibers do not significantly increase in number (hyperplasia) after birth; skeletal muscle tissue does have limited powers of regeneration due to the presence of SATELLITES cells which can fuse with or replace existing skeletal muscle fibers to a limited extent - if significant skeletal muscle damage or degeneration occurs, skeletal muscle tissue undergoes FIBROSIS, the replacement of muscle fiber by fibrous scar tissue iii. Each muscle fiber has a sarcolemma (plasma membrane) that surrounds the sarcoplasm (cytoplasm); the latter contains an oxygen-binding protein called myoglobin iv. The sarcoplasm contains the sarcoplasmic reticulum (SR) with dilated end sacs called terminal cisterns which store calcium ions via the action of calcium active transport pumps; release of calcium ions into the cytosol triggers muscle contraction.

muscle tissue characteristics

i. Electrical excitability is the ability to respond to certain stimuli by producing electrical signals called action potentials (impulses) ii. Contractility is the ability to shorten, thus developing tension (force of contraction) iii. Extensibility is the ability of the muscle to be stretched without being damaged iv. Elasticity is the ability to return to its original shape after contraction or extension

nerve

i. Nerves typically enter a muscle with the main blood vessels of the muscle as a unit called a neurovascular bundle. ii. Somatic motor neurons send impulses down their axons to stimulate muscle fibers to contract. iii. Blood vessels called capillaries deliver nutrients and oxygen to muscle fibers and carry wastes and heat away from muscle fibers.

type of muscle

i. Skeletal muscle tissue a. moves bones (and, in some cases, skin or other soft tissues) b. striated c. primarily voluntary ii. Cardiac muscle tissue a. forms most of the wall of the heart b. striated c. involuntary d. some cells have autorhythmicity e. regulated by autonomic nervous system and certain hormones iii. Smooth muscle tissue a. located in the walls of hollow internal structures (and arrector pili muscles) b. nonstriated, i.e., smooth c. involuntary d. some cells have autorhythmicity e. regulated by autonomic nervous system and certain hormones

contraction and relaxation of skeletal muscle fibers

i. The junction (or synapse) between a somatic motor neuron and a skeletal muscle fiber is called a neuromuscular junction (NMJ). ii. When a nerve impulse (action potential) arrives at this junction, the synaptic vesicles in synaptic end bulbs (branches of axon terminals) release acetylcholine [ACh] (neurotransmitter molecules) which diffuse across the synaptic cleft and bind to acetylcholine receptor molecules on the junctional folds of the motor end plate; this triggers a muscle action potential that travels along the sarcolemma and ultimately initiates contraction of the muscle fiber. iii. A motor unit consists of a somatic motor neuron plus all the muscle fibers that it stimulates; all fibers in a motor unit therefore contract and relax simultaneously a. the average motor unit contains 150 muscle fibers but there is a wide range that extends from 2-3 muscle fibers per motor unit to 2000-3000 muscle fibers per motor unit b. small motor units provide precise control of movement while large motor units provide greater strength of contraction iv. Muscle contraction is triggered when a muscle action potential is propagated along the sarcolemma through the T tubule system and to the sarcoplasmic reticulum, where it causes the release of calcium ions from the SR's calcium release channels into the cytosol v. Muscle contraction occurs via the sliding filament mechanism: - in the presence of ATP and calcium ions, myosin heads attach to actin molecules to form cross-bridges which pull (i.e., the power stroke) thin filaments toward the center of the sarcomere, resulting in a shortening of the sarcomeres, i.e., excitation-contraction coupling vi. The effect of acetylcholine is brief because it is rapidly broken down by acetylcholinesterase (AChE) located in the synaptic cleft.

smooth muscle characteristics

i. are narrow fibers with two tapering ends ii. have a single nucleus iii. the sarcoplasm: a. contains both thick and thin filaments but they are not arranged into orderly sarcomeres, i.e., nonstriated and therefore called smooth b. contains intermediate filaments attached to dense bodies iv. when a smooth muscle fiber contracts, it turns like a corkscrew v. compared to skeletal muscle, contraction starts more slowly and lasts much longer vi. the prolonged presence of calcium ions in the cytosol provides for smooth muscle tone

3 layer of connected tissue around muscle

i. endomysium surrounds individual muscle fibers ii. perimysium surrounds FACISCLES (bundles of muscle fibers) iii. outer epimysium encircles the entire muscle belly

muscle contraction

i. in an isotonic contraction, tension remains almost constant while the muscle changes its length; there are two subtypes: a) in a concentric isotonic contraction, the tension overcomes the resistance of the object to be moved and therefore the muscle shortens b) in an eccentric isotonic contraction, tension slows the lengthening of the muscle so that the muscle lengthens as it contracts ii. in an isometric contraction, a muscle develops tension but does not shorten because the tension is not great enough to exceed the resistance of the object to be moved; therefore, the muscle length does not change

2 type of muscle contraction

i. in an isotonic contraction, tension remains almost constant while the muscle changes its length; there are two subtypes: a) in a concentric isotonic contraction, the tension overcomes the resistance of the object to be moved and therefore the muscle shortens b) in an eccentric isotonic contraction, tension slows the lengthening of the muscle so that the muscle lengthens as it contracts ii. in an isometric contraction, a muscle develops tension but does not shorten because the tension is not great enough to exceed the resistance of the object to be moved; therefore, the muscle length does not change https://www.youtube.com/watch?v=T3OiOJ6-x34

muscle tissue function

i. producing body movements ii. stabilizing body positions iii. storing and moving substances within the body iv. producing heat

how muscle contraction works

iv. Muscle contraction is triggered when a muscle action potential is propagated along the sarcolemma through the T tubule system and to the sarcoplasmic reticulum, where it causes the release of calcium ions from the SR's calcium release channels into the cytosol

Aponeurosis

strong sheet of tissue that acts as a tendon to attach muscles to bone

What is the cross bridge cycle?

v. Muscle contraction occurs via the sliding filament mechanism: - in the presence of ATP and calcium ions, myosin heads attach to actin molecules to form cross-bridges which pull (i.e., the power stroke) thin filaments toward the center of the sarcomere, resulting in a shortening of the sarcomeres, i.e., excitation-contraction coupling