Chapter 10: The Muscle Tissue
Motion results from
Alternating contraction (shortening) & relaxation of muscles
The scientific study of muscles
Myology
Skeletal muscle tissue
Cardiac muscle tissue
Smooth (visceral) muscle tissue
The four functions of muscle tissue
The characteristics of muscle tissue
Excitiability (irritability)
The ability to respond to certain stimuli by producing action potentials (impulses)
Action potentials
Electrical signals
Contractility
The ability to shorten & thicken (contract), generating force to do work
Extensibility
The ability to be extended (stretched) without damaging the tissue
Elasticity
The ability to return to original shape after contraction or extension
The term fascia
Applied to a sheet or broad band of fibrous connective tissue underneath the skin (superficial fascia) or around muscles & organs of the body (deep fascia)
Other connective tissue components covering the entire muscle
Epimysium
Perimysium
Covering fasciculi
Endomysium
Covering individual muscle fibers
Tendons & aponeuroses
Extensions of connective tissue beyond muscle cells that attach the muscle to bone or other muscle
Tendon (synovial) sheaths
Enclose certain tendons & allow them to slide back and forth more easily
Tensosynovitis
Inflammation of the tendon sheaths and synovial membranes of certain joints, especially those of the wrists, shoulders, elbows, fingers, and ankles
Nerves (containing motor neurons)
Motor neuron & the muscle fibers it stimulates form
Motor unit
Single motor unit may innervate as few as 10 or as many as
2,000 muscle fibers
Neuromuscular Junction (NMJ)
Refers to an axon terminal of a motor neuron and the portion of the muscle fiber sarcolemma in close approximation with motor end plate
Acetylcholine (ACh)
Released by the synaptic vesicles of a motor neuron, triggers a muscle action potential
Skeletal muscle consists of
Fibers (cells) covered by a sarcolemma
Fibers (cells) that are covered by a sacolemma contains
Myofibrils that consist of thin & thick filaments (myofilaments)
The filaments are compartmentalized
Sarcomeres
Thin filaments are composed of
Thick filaments consist
Mostly of myosin
Actin & myosin
Two contractile proteins in muscle
Tropomyosin & tropin
Muscle's regulatory proteins
Projecting myosin heads that contain actin and ATP binding sites are called
Cross bridges
Elastic filaments help
Stabilize the position of thick filaments
Sliding of thin filaments; Activated cross bridges attach to actin & a change in orientation of the cross bridges occurs
Power stroke
Rigor mortis
State of muscular rigidity following death, results from a lack of ATP to split myosin-actin cross bridges
If body temperature decreases
Shivering can help elevate it to normal
All-or-nothing principle
Individual muscle fibers contract to their fullest extent; they do not partially contract
Twitch contraction
Brief contraction of all the muscle fibers in a motor unit in response to a single action potential
Record of a muscle contraction
Myogram
Myogram includes three periods
The refractory period
Time when a muscle has temporarily lost excitability
Skeletal muscles have
Short refractory period
Cardiac muscles have
Long refractory period
Wave (temporal) summation
Increased strength of a contraction from resulting from the application of a second stimulus before the muscles has completely relaxed after a previous stimulus
Sustained muscle contraction that permits partial relaxation between stimullus
Incomplete (unfused) tetanus
Sustained contraction that lacks even partial relaxation between stimuli
Complete (fused) tetanus
In treppe (staircase effect)
Each of the first few contractions is a little stronger than the last
Muscle fibers develops its greatest tension when
There is an optimal overlap between thick & thin filaments
Recruitment (multiple motor unit summation)
The process of increasing the number of active motor units that prevents fatigue and helps provide smooth muscular contraction rather than a series of jerky movements
Muscle tone
Sustained partial contraction of portions of a relaxed skeletal muscle results in a formness known as
Refers to decreased or lost muscle tone; such muscles are said to be flaccid
Hypotonia
Hypertonia
Refers to increased muscle tone and may be expressed as either spasticity (stiffness) or rigidity
Active tension
Tension generated by contractile elements (thick & thin filaments) is called
Passive tension
Tension generated by elastic elements and is not related to muscular contraction is called
Isotonic contractions
Occurs when a constant load is moved through the range of motion possible at a joint & include concentric contractions and eccentric contractions
Isometric contraction
The muscle does not shorten but tension increases
Muscular atrophy
Wasting away of muscles & may be caused by disuse or severing of the nerve supply
Muscular hypertrophy
Refers to an increase in the diameter of muscle fibers resulting from very forceful, repetitive muscular activity
On demand, skeletal muscle fibers can
Step up ATP production
Creatine phosphate (phosphocreatine) and ATP
Constitute the phosphagen system
The AEROBIC partial catabolism of glucose to generate ATP and can provide enough energy for about 30-40 seconds of maximal muscle activity occurs in
The glycogen-lactic acid system
Muscular activity lasting more than 30 seconds depends increasingly on AEROBIC system (reactions requiring oxygen) and system of ATP production involves the complete oxidation of glucose
Cellular respiration (biological oxidation)
Muscle tissue has two sources of oxygen
The aerobic system will provide
Enough ATP for prolonged activity so long as sufficient oxygen and nutrients are available
Elevated oxygen use after exercise
Recovery oxygen consumption
The inability of a muscle to maintains its strength of contraction or tension and occurs when a muscle cannot produce enough ATP to meet its need
Muscle fatigue
Microscopic muscle damage appears to be a major contributing factor to
Muscle soreness that follows bouts of strenous exercise
All skeletal muscle fibers are not identical in
Structure and function
Color caries according to the content of
Myoglobin
Myoglobin is an
Oxygen storing reddish pigment
Red muscle fibers have
A high myglobin content while the myoglobin content of white muscle fibers is low
Fiber diameter varies as do the
Cell's allocations of mitochondria, blood capillaries, and sarcoplasmic retifulum
Contraction veolcity and resistance to fatigue also
Differ between fibers
Skeletal muscle fibers are classified as
Type I (slow oxidative)
Type IIA (fast oxidative)
Type IIB (fast glycolytic)
The use of anabolic steriods by athletes
Increase muscle size, strength, and endurance has been shown to have serious side effects, some of which are life-threatening
Cardiac muscle tissue
Found only in the heart and is striated ad involuntary
Compared to skeletal muscle, cardiac muscle tissues have
The fibers branch
Freely and are connected via gap junctions
Intercalated discs
Provide strength and aid in conduction of muscle action potentials by way of communicating junctions located in the discs
Unlike skeletal muscle tissue, cardiac muscle tissue
Cardiac muscle can contract
Without extrinsic (outside) stimulation and can remain contracted longer than skeletal muscle tissue
Cardiac muscle has
Long refractory period that allows tie for the heart to relax between beats and which prevent tetanus