Transcript Muscle Tissue - Chiropractor Manhattan

Muscle Tissue
Types of Muscle Tissue
 Skeletal muscle tissue
 Cardiac muscle tissue
 Autorhythmicity - pacemaker
 Smooth muscle tissue
Functions of Muscle Tissue
 Producing body movements
 Stabilizing body positions
 Storing and moving substances within the body
 Sphincters – sustained contractions of ringlike bands
prevent outflow of the contents of a hollow organ
 Cardiac muscle pumps nutrients and wastes through
 Smooth muscle moves food, bile, gametes, and urine
 Skeletal muscle contractions promote flow of lymph and
return blood to the heart
 Generating heat - thermogenesis
Properties of Muscle Tissue
 Electrical excitability
 Produces 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
 Elasticity
 Ability 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 organs
 Superficial fascia (subcutaneous layer) – separates
muscle from skin
 Deep fascia – holds muscles with similar functions
together
 Epimysium – outermost layer – encircles whole
muscles
 Perimysium
 Surrounds groups of 10 – 100 individual muscle fibers
separating them into bundles called fascicles
Connective Tissue
Components
 Endomysium
 Separates individual muscle fibers within the fascicle
 Tendon
 All 3 CT layers may extend beyond the muscle to
form a cord of dense regular CT that attaches
muscle to the periosteum of bone
 Aponeurosis
 A broad, flat layer of CT
Nerve and Blood Supply
 Skeletal 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 fiber
 Contains 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 Hypertrophy
 Muscular atrophy – wasting away of muscles
 Disuse
 Denervation
 Muscular hypertrophy – an excessive increase in the
diameter of muscle fibers
Filaments and the Sarcomere
 Filaments – structures within the myofibril
 Thin
 Thick
 Sarcomere – basic functional unit of a myofibril
 Z discs – separate one sarcomere from the next
Filaments and the Sarcomere
 A band – predominantly thick filaments
 Zone of overlap at the ends of the A bands
 H zone – contains thick, but no thin filaments
 I band – thin filaments
 M-line – middle of the sarcomere
Muscle Proteins
 Contractile proteins – generate force
 Myosin
 Actin
 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 Contraction
 An increase in calcium ion concentration in the cytosol
initiates muscle contraction and a decrease in calcium
ions stops it.
Rigor Mortis
 After 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 ATP
 1. 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 ATP
 2. Anaerobic cellular respiration.
 Glucose undergoes glycolysis, yielding ATP and 2
molecules of pyruvic acid.
 Does not require oxygen.
Production of ATP
 3. 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 Fatigue
 Muscle 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 Units
 A 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 Contraction
 A 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 Period
 A period of lost excitability during which a muscle fiber
cannot respond to stimulation.
Motor Unit Recruitment
 The 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 Tone
 Even 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.
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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.
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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 Fibers
 Most 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 Fibers
 Muscles 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 Tissue
 The 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 Tissue
 Activated 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.