Muscle Tissue - Chiropractor Manhattan
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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.
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 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.