Muscle Tissue. Types of Muscle Tissue Skeletal muscle tissue Cardiac muscle tissue Autorhythmicity -...
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Transcript of Muscle Tissue. Types of Muscle Tissue Skeletal muscle tissue Cardiac muscle tissue Autorhythmicity -...
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.