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88 Cards in this Set

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What are the 3 types of muscle?
skeletal, cardiac, and smooth
What two kinds of myofilaments are necessary for muscle contraction?
actin and myosin
Sarcolemma
muscle plasma membrane
Traits of Skeletal Muscle
-Packaged in skeletal muscles that attach to and cover the bony skeleton
-Has obvious stripes called striations
-Is controlled voluntarily (i.e., by conscious control)
-Contracts rapidly but tires easily
-Is responsible for overall body motility
-Is extremely adaptable and can exert forces ranging from a fraction of an ounce to over 70 pounds
Traits of Cardiac Muscle Tissue
Occurs only in the heart
Is striated like skeletal muscle but is not voluntary
Contracts at a fairly steady rate set by the heart’s pacemaker
Neural controls allow the heart to respond to changes in bodily needs
Traits of Smooth Muscle Tissue
Found in the walls of hollow visceral organs, such as the stomach, urinary bladder, and respiratory passages

Forces food and other substances through internal body channels

It is not striated and is involuntary
Functional Characteristics of Muscle Tissue
Excitability, or irritability – the ability to receive and respond to stimuli

Contractility – the ability to shorten forcibly

Extensibility – the ability to be stretched or extended

Elasticity – the ability to recoil and resume the original resting length
Muscle Functions
Skeletal muscles are responsible for all locomotion

Cardiac muscle is responsible for coursing the blood through the body

Smooth muscle helps maintain blood pressure, and squeezes or propels substances (i.e., food, feces) through organs

Muscles also maintain posture, stabilize joints, and generate heat
Endomysium –
fine sheath of connective tissue composed of reticular fibers surrounding each muscle fiber
Perimysium –
fibrous connective tissue that surrounds groups of muscle fibers called fascicles
Epimysium –
an overcoat of dense regular connective tissue that surrounds the entire muscle
How many nerves, arteries and veins in each muscle?
Each muscle is served by one nerve, an artery, and one or more veins
How are nutrients delivered?
Contracting fibers require continuous delivery of oxygen and nutrients via arteries
What happens when Skeletal muscles contract?
When muscles contract the movable bone, the muscle’s insertion moves toward the immovable bone, the muscle’s origin
Direct Attachment
epimysium of the muscle is fused to the periosteum of a bone
Indirect Attachent
connective tissue wrappings extend beyond the muscle as a tendon or aponeurosis
Microscopic Anatomy of a Skeletal Muscle Fiber
Each fiber is a long, cylindrical cell with multiple nuclei just beneath the sarcolemma.

Fibers are 10 to 100 m in diameter, and up to hundreds of centimeters long

Each cell is a syncytium produced by fusion of embryonic cells
What is in a Muscle Fiber?
Fibers contain the usual organelles, myofibrils, sarcoplasmic reticulum, and T tubules
What is in Sarcoplasm?
Sarcoplasm has numerous glycosomes and a unique oxygen-binding protein called myoglobin
What are Microfibrils?
Myofibrils are densely packed, rodlike contractile elements
How are Microfibrils arranged?
The arrangement of myofibrils within a fiber is such that a perfectly aligned repeating series of dark A bands and light I bands is evident
What is a sarcomere?
The smallest contractile unit of a muscle
Where are Sarcomeres found?
The region of a myofibril between two successive Z discs
what is the banding pattern of a sarcomere?
Thick filaments – extend the entire length of an A band

Thin filaments – extend across the I band and partway into the A band

Z-disc – coin-shaped sheet of proteins (connectins) that anchors the thin filaments and connects myofibrils to one another
Why are M lines darker?
M lines appear darker due to the presence of the protein desmin
What are T Tubules?
T tubules are continuous with the sarcolemma

They conduct impulses to the deepest regions of the muscle

These impulses signal for the release of Ca2+ from adjacent terminal cisternae
In order to contract, a skeletal muscle must:
Be stimulated by a nerve ending

Propagate an electrical current, or action potential, along its sarcolemma

Have a rise in intracellular Ca2+ levels, the final trigger for contraction
Linking the electrical signal to the contraction is:__________
excitation-contraction coupling
Skeletal muscles are stimulated by?
motor neurons of the somatic nervous system
Each axonal branch forms a neuromuscular junction with:
a single muscle fiber
When a nerve impulse reaches the end of an axon at the neuromuscular junction:
Voltage-regulated calcium channels open and allow Ca2+ to enter the axon

Ca2+ inside the axon terminal causes axonal vesicles to fuse with the axonal membrane
What is Action Potential?
A transient depolarization event that includes polarity reversal of a sarcolemma (or nerve cell membrane) and the propagation of an action potential along the membrane
What is depolarization?
Initially, this is a local electrical event called end plate potential

Later, it ignites an action potential that spreads in all directions across the sarcolemma
A motor unit is?
a motor neuron and all the muscle fibers it supplies
Muscles that control fine movements (fingers, eyes) have:
small motor units
How are muscle fibers distributed in motor units?
Muscle fibers from a motor unit are spread throughout the muscle; therefore, contraction of a single motor unit causes weak contraction of the entire muscle
Muscle tone is:
the constant, slightly contracted state of all muscles, which does not produce active movements
Muscle tone serves what purpose?
Keeps the muscles firm, healthy, and ready to respond to stimulus
How do spinal reflexes account for muscle tone?
Activating one motor unit and then another

Responding to activation of stretch receptors in muscles and tendons
isotonic contraction
In isotonic contractions, the muscle changes in length (decreasing the angle of the joint) and moves the load
What are the two types of isotonic contractions?
concentric and eccentric
Concentric contractions –
the muscle shortens and does work
Eccentric contractions –
the muscle contracts as it lengthens
Isometric Contractions
Tension increases to the muscle’s capacity, but the muscle neither shortens nor lengthens

Occurs if the load is greater than the tension the muscle is able to develop
What is the source of muscle energy?
ATP is the only source used directly for contractile activity
As soon as available stores of ATP are hydrolyzed (4-6 seconds), they are regenerated by:
The interaction of ADP with creatine phosphate (CP)

Anaerobic glycolysis

Aerobic respiration
What happns during Anaerobic Glycolysis
When muscle contractile activity reaches 70% of maximum:

Bulging muscles compress blood vessels

Oxygen delivery is impaired

Pyruvic acid is converted into lactic acid
During Anaerobic Glycolysis lactic acid:
Diffuses into the bloodstream
Is picked up and used as fuel by the liver, kidneys, and heart
Is converted back into pyruvic acid by the liver
Muscle fatigue –
the muscle is in a state of physiological inability to contract
Muscle fatigue occurs when:
ATP production fails to keep pace with ATP use

There is a relative deficit of ATP, causing contractures

Lactic acid accumulates in the muscle

Ionic imbalances are present
For a muscle to return to a resting state:
Oxygen reserves must be replenished

Lactic acid must be converted to pyruvic acid

Glycogen stores must be replaced

ATP and CP reserves must be resynthesized
How much energy released in muscle activity is useful as work
Only 40% of the energy released in muscle activity is useful as work
How much is heat?
The remaining 60% is given off as heat
Aerobic exercise results in an increase of:
Muscle capillaries
Number of mitochondria
Myoglobin synthesis
Resistance exercise (typically anaerobic) results in:
Muscle hypertrophy
Increased mitochondria, myofilaments, and glycogen stores
Smooth Muscle lacks...
the coarse connective tissue sheaths of skeletal muscle, but have fine endomysium
Smooth Muscle is organized in ____ layers of ______ fibers.
Organized into two layers (longitudinal and circular) of closely apposed fibers
Smooth muscle is found in the wall of _____ _______. (Except the _____)
hollow organs (except the heart)
Peristalsis –
alternating contractions and relaxations of smooth muscles that mix and squeeze substances through the lumen of hollow organs
How does smoth muscle contact?
When the longitudinal layer contracts, the organ dilates and contracts
When the circular layer contracts, the organ elongates
Smooth muscle lacks ________ junctions.
neuromuscular
Innervating nerves have bulbous swellings called ________.
varicosities
Varicosities release neurotransmitters into wide synaptic clefts called ___________ junctions.
diffuse junctions
Microscopic Differences of Smooth Muscle from skeletal muscle.
SR is less developed than in skeletal muscle and lacks a specific pattern

T tubules are absent

Plasma membranes have pouchlike infoldings called caveoli

There are no visible striations and no sarcomeres
In smooth muscle there is no:
Troponin complex
Smooth muscles are ______ and ________ without external stimuli
self-excitatory depolarize
Unique characteristics of smooth muscle include:
Smooth muscle tone
Slow, prolonged contractile activity
Low energy requirements
Response to stretch
stress-relaxation response
Smooth muscle responds to stretch only briefly, and then adapts to its new length

The new length, however, retains its ability to contract
Certain smooth muscles can divide and increase their numbers by undergoing ___________.
hyperplasia
The cells of single-unit smooth muscle, commonly called _______ muscle
visceral
Traits of visceral muscle:
Contract rhythmically as a unit
Are electrically coupled to one another via gap junctions
Often exhibit spontaneous action potentials
Are arranged in opposing sheets and exhibit stress-relaxation response
Multiunit smooth muscles are found:
In large airways to the lungs
In large arteries
In arrector pili muscles
In the internal eye muscles
Muscle tissue develops from embryonic mesoderm called ______.
myoblasts
Multinucleated skeletal muscles form by _______ of myoblasts
fusion
Cardiac and smooth muscle myoblasts do not fuse but develop _______ _________ at an early embryonic stage
gap junctions
As muscles are brought under the control of the somatic nervous system, the numbers of ____ and ______ fibers are also determined
fast and slow fibers
can cardiac and skeletal muscle reproduce through mitosis?
Cardiac and skeletal muscle become amitotic, but can lengthen and thicken
How does muscle development occur?
Development occurs head-to-toe, and proximal-to-distal
Peak natural neural control of muscles is achieved by ___________.
mid-adolescence
Women’s skeletal muscle makes up ___% of their body mass
36%
Men’s skeletal muscle makes up ___% of their body mass
42%
The difference between men and women's muscle mass is due primarily to the male sex hormone _________.
testosterone
By age 80, _____% of muscle mass is lost (sarcopenia)
50% of muscle mass is lost
With age, Muscles become ______ and more ________.
stringier and more sinewy
Sarcopenia can be reversed by _______ _______
Regular exercise
_______________may block distal arteries, leading to intermittent claudication and causing severe pain in leg muscles
Atherosclerosis
Atrophic Muscular Diseases
muscular dystrophies
post poliomyelitis syndrome
Infections of the muscles
HIV, tetanus, Lyme’s, influenza
trichinosis, gangrene(myopathic)