Muscle Tissue

Types of Muscle TissueSkeletal muscle tissue

Cardiac muscle tissueAutorhythmicity - pacemaker

Smooth muscle tissue

Functions of Muscle TissueProducing body movements

Stabilizing body positions

Storing and moving substances within the bodySphincters – sustained contractions of ringlike bands

prevent outflow of the contents of a hollow organCardiac muscle pumps nutrients and wastes throughSmooth muscle moves food, bile, gametes, and urineSkeletal muscle contractions promote flow of lymph

and return blood to the heart

Generating heat - thermogenesis

Properties of Muscle Tissue

Electrical excitabilityProduces electrical signals – action potentials

Contractility Isometric contraction – tension without muscle

shortening Isotonic contraction – constant tension with muscle

shortening

Properties of Muscle Tissue

Extensibility – ability of a muscle to stretch without being damaged

ElasticityAbility of a muscle to return to its original length

Connective Tissue Components

Fascia – a sheet of fibrous CT that supports or surrounds muscles and other organsSuperficial fascia (subcutaneous layer) – separates

muscle from skinDeep fascia – holds muscles with similar functions

together

Epimysium – outermost layer – encircles whole muscles

PerimysiumSurrounds groups of 10 – 100 individual muscle

fibers separating them into bundles called fascicles

Connective Tissue Components

EndomysiumSeparates individual muscle fibers within the

fascicle

TendonAll 3 CT layers may extend beyond the muscle

to form a cord of dense regular CT that attaches muscle to the periosteum of bone

AponeurosisA broad, flat layer of CT

Nerve and Blood SupplySkeletal muscles are well supplied with nerves

and blood vessels

Neuromuscular junction – the structural point of contact and the functional site of communication between a nerve and the muscle fiber

Capillaries are abundant – each muscle fiber comes into contact with 1 or more

Sarcolemma, T Tubules, and Sarcoplasm

Sarcolemma – the plasma membrane of a muscle cell

T (transverse) tubules – Propogate action potentials – extend to the outside of the muscle fiber

Sarcoplasm – cytoplasm of the muscle fiberContains myoglobin – protein that binds with

oxygen

Myofibrils and Sarcoplasmic Reticulum

Myofibril – the contractile elements of skeletal muscle

Sarcoplasmic reticulum (SR) – encircles each myofibril – stores CA2+ (its release triggers muscle contractions)

Atrophy and HypertrophyMuscular atrophy – wasting away of muscles

DisuseDenervation

Muscular hypertrophy – an excessive increase in the diameter of muscle fibers

Filaments and the Sarcomere

Filaments – structures within the myofibrilThinThick

Sarcomere – basic functional unit of a myofibril

Z discs – separate one sarcomere from the next

Filaments and the Sarcomere

A band – predominantly thick filamentsZone of overlap at the ends of the A bandsH zone – contains thick, but no thin filaments

I band – thin filaments

M-line – middle of the sarcomere

Muscle ProteinsContractile proteins – generate force

MyosinActin

Regulatory proteins – switch contraction on and off

Structural proteins

Sliding Filament Mechanism

Muscle contraction occurs because myosin heads attach to the thin filaments at both ends of the sarcomere and pull them toward the M line.

The length of the filaments does not change; However, the sarcomeres shorten, thereby shortening the entire muscle.

Role of Ca2+ in ContractionAn increase in calcium ion concentration in the

cytosol initiates muscle contraction and a decrease in calcium ions stops it.

Rigor MortisAfter death the cellular membranes

become leaky.

Calcium ions are released and cause muscular contraction.

The muscles are in a state of rigidity called rigor mortis.

It begins 3-4 hours after death and lasts about 24 hours, until proteolytic enzymes break down (digest) the cross-bridges.

Neuromuscular Junction (NMJ)

Muscle action potentials arise at the NMJ.

The NMJ is the site at which the motor neuron contacts the skeletal muscle fiber.

A synapse is the region where communication occurs.

Neuromuscular Juntcion (NMJ)

The neuron cell communicates with the second by releasing a chemical called a neurotransmitter.

Synaptic vesicles containing the neurotransmitter acetylcholine (ach) are released at the NMJ.

The motor end plate is the muscular part of the NMJ. It contains acetylcholine receptors.

The enzyme acetlycholineesterase (AChE) breaks down ACh.

Production of ATP1. From creatine phosphate.

When muscle fibers are relaxed they produce more ATP than they need. This excess is used to synthesize creatine phosphate (an energy rich compound).

Production of ATP2. Anaerobic cellular respiration.

Glucose undergoes glycolysis, yielding ATP and 2 molecules of pyruvic acid.

Does not require oxygen.

Production of ATP3. Aerobic cellular respiration.

The pyruvic acid enters the mitochondria where it is broken down to form more ATP.

Slower than anaerobic respiration, but yields more ATP.

Utilizes oxygen.2 sources of oxygen.

Diffuses from bloodstream.Oxygen released from myoglobin.

Muscle FatigueMuscle fatigue is the inability of a muscle to

contract forcefully after prolonged activity.

Central fatigue – a person may develop feelings of tiredness before actual muscle fatigue.

Oxygen Debt or Recovery Oxygen Uptake

Added oxygen, over and above resting oxygen consumption, taken in after exercise.

Used to restore metabolic conditions.1. To convert lactic acid back into glycogen

stores in the liver.2. To resynthesize creatine phosphate and

ATP in muscle fibers.3. To replace the oxygen removed from

hemoglobin.

Motor UnitsA motor unit consists of the somatic motor

neuron and all the skeletal muscle fibers it stimulates.

A single motor neuron makes contact with an average of 150 muscle fibers.

All muscle fibers in one motor unit contract in unison.

Twitch ContractionA twitch contraction is the brief contraction of all

the muscle fibers in a motor unit in response to a single action potential.

A myogram is a record of a muscle contraction and illustrates the phases of contraction.

Refractory PeriodA period of lost excitability during which a

muscle fiber cannot respond to stimulation.

Motor Unit RecruitmentThe process in which the number of active

motor units increases.

The weakest motor units are recruited first, with progressively stronger units being added if the task requires more force.

Muscle ToneEven at rest a muscle exhibits a small amount of

muscle tone – tension or tautness.

Flaccid – when motor units serving a muscle are damaged or cut.

Spastic – when motor units are over-stimulated.

Isotonic and Isometric Contractions

Concentric isotonic contraction – a muscle shortens and pulls on another structure.

Eccentric isotonic contraction – the length of a muscle increases during contraction.

Isometric contraction – muscle tension is created; However, the muscle doesn’t shorten or lengthen.

Types of Skeletal Muscle Fibers

Slow oxidative (SO) fibers.Smallest of the fibers.Least powerful.Appear dark red – much myoglobin and many

capillaries.Resistant to fatigue.

Types of Skeletal Muscle Fibers

Fast oxidative-Glycolytic (FOG) fibers. Intermediate in diameter.Appear dark red – much myoglobin and many

capillaries.High level of intracellular glycogen.Resistant to fatigue.

Types of Skeletal Muscle Fibers

Fast Glycolitic (FG) fibers.Largest in diameter.Contain the most myofibrils, therefore more

powerful contractions.Appear white – low myoglobin and few

capillaries.Large amounts of glycogen – anaerobic

respiration.Fatigue quickly.

Distribution and Recruitment of Different

Types of FibersMost skeletal muscles are a mixture of all three

types.

The continually active postural muscles have a high concentration of SO fibers.

Distribution and Recruitment of Different

Types of FibersMuscles of the shoulders and arms are used

briefly and for quick actions, therefore they have many FG fibers.

Muscle of the legs support the body and participate in quick activities, therefore they have many SO and FOG fibers.

Cardiac Muscle TissueThe principle tissue in the heart is cardiac

muscle tissue.

Cardiac muscle fibers have intercalated discs, which connect the ends of the cardiac muscle fibers together.

Cardiac muscle tissue remains contracted 10 to 15 times longer than skeletal muscle.

Requires a constant supply of oxygen and contains larger and more numerous mitochondria.

Smooth Muscle TissueActivated involuntarily.

Two types.Visceral (single-unit) smooth muscle.

Walls of small blood vessels and walls of hollow organs (I.E. Stomach, intestines, uterus, and urinary bladder).

Multi-unti smooth muscle.Walls of large ateries, in the airways of lungs, in

arrector pili muscles.