CH 8 - The Muscular System Flashcards
Muscular tissue 3 types:
Skeletal, cardiac, smooth
Skeletal muscle
Attached to bones Volunary Contract/relax by conscious control Limited capacity of regeneration Has striations
Elongated cells make up muscle fibers, multinucleated and peripherally placed
Cardiac muscle
Found ONLY in the heart
Forms the bulk of the heart wall
Involuntary
Contraction not under conscious control
Fibers are branched,striated, has a single centrally located nucleaus, intercalated discs, gap junctions
Can regenerate under certain conditions
Smooth Muscle
Located in walls of hollow internal structures
(Blood vessels, airways, stomach, intestine)
Participates in internal processes such as digestion and regulation of BP
Fibers are spindle shaped, single oval nucleaus, non striated, involuntary, can regenerate
Functions of muscular tisshue
Body mmts - walking/running
Body positions - stabilize jnts
Heat - when a muscle contracts it produces heat
Involuntary contraction - shivering
Skeletal muscle contraction - return blood in veins to heart
Storing/moving substances - sphincters
Temporary storage of food - stomach/urine
Cardiac muscle contractions - pump blood through vessels
Smooth muscle contractions - move food/substances through the body
3 layers of connective tissue
Whats the role of connective tissue
Protect and strengthen skeletal muscles
Epimysum - wraps entire muscle
Perimysium - surrounds bundles of 10-100 fibers
Endomysium - wraps individual fibers
Tendon
Cord of dense connective tissue composed of parallel bundles of collagen fibers
Attach muscle to bone
Achilles tendon
Skeletal muscles are supplied with
Nerves and blood vessels
ATP is required for what
Muscle contraction
Prolonged muscle action depends of a blood supply to deliver nutrients/oxygen and remove waste products
How do muscles contract
The artery and vein that accompany each nerve penetrates a skeletal muscle and the fibers make contact with the terminal portion of the neuron
Muscle action potential is
An electric signal when a skeletal muscle fiber is stimulated before it contracts
Motor end plate
The region of the sarcolemma near the axon terminal
Motor neuron
Nerve cell that delivers the muscle action potential
Motor unit
Single neuron along with all the muscle fibers it stimulates
Axon terminals
When the axon of a motor neuron enters a skeletal muscle
Divides into branches
Approach but do not touch the sarcolemma of the muscle fiber
Synaptic end bulbs
Enlarged swellings at the ends of the axon terminals
Synaptic vesicles
In the synaptic bulbs
Synaptic cleft
Space bt the axon terminal and sarcolemma
Neurotransmitters
Chemicals that fill the synaptic vesicles
Neuromuscular junction (NMJ)
The synapse formed between the axon terminals of the motor neuron and the motor end plate of a muscle fiber
Muscle fibers are covered by
Sarcolemma - the plasma membrane
Sarcolplasm
The cytoplasm of the muscle fiber
Contains many mitochondria
Produce lg amts of ATP
Sarcoplasmic reticulum stores calcium ions required for muscle contraction
Transverse tubules (T Tubles) are tunnels from the surface toward the center of each muscle fiber
How does a motor neuron excite a skeletal muscle fiber
Release of acetylcholine
Activation of Ach receptors
Generation of muscle action potential
Release of acetylcholine
Arrival of nerve impulse at the synaptic end bulbs as triggers release of the neurotransmitter acetylcholine (Ach)
activation of Ach receptors
The binding of Ach to its receptor in the motor end plate opens ion channels that allow sodium ions to flow across the membrane
Generation of muscle action potential
Inflow of sodium generates a muscle action potential which travels along the sarcolemma and through the T tubules
In breakdown of Ach, what happens
It only lasts breifly because the neurotransmitter is rapidly broken down in the synaptic cleft by an enzyme called acetylcholinesterase (AchE)
Myoglobin are
A number of molecules in the sarcoplasm that stores oxygen until it is needed by the mitochondria to generate ATP
Two protein filaments in the myofibrils include
Thin filaments (actin) Thick filaments (myosin)
A band
Dark area
I band
Light area
Sarcomere
Functional unit of striated muscle fibers
Z discs
Zig zagging zones of dense protein material that separates the sarcomeres from one another
H zone contains
Only thick filaments
Actin is the protein component in
Thin filament
Myosin is
The binding site in each actin molecule is where the myosin head attaches
Tropomyosin and troponin are
2 other proteins in thin filaments
Myosin is the protein in
Thick filaments
Shaped like 2 golf clubs twisted together
Myosin tails are arranged
Parallel to each other
Myosin heads are
The projecting ends from outward from the surface of the shaft
Sliding filament theory
Myosin heads of thick filaments pull on thin filaments causing the thin filaments to slide toward the center of a sarcomere
This leads to muscle contraction
Only occurs when the level of calcium ions is high enough and ATP is available
Whats needed for muscle contraction
Calcium ions and energy in the form of ATP
Contraction cycle is
The repeating sequence of events
1) splitting ATP into ADP
2) forming cross-bridges
3) power stroke
4) binding ATP
Relaxation from contraction has 2 changes
Acetylcholine is broken down by acetylcholinerase (AChE)
Calcium ions are rapidly transported from the sarcoplasm into the sarcoplasmic reticulum and tropomyosis slikds over myosis binding sites on actin, then the thin filaments slip back to their relaxed positions
Muscle tone
A process when a whole muscle is not contracting, a small number of its motor units are involuntarily activated to produce a sustained contraction
Flaccid
When muscle tone is lost and neurons are damaged/cut
Creatine
A small AA that is made in the liver, kidneys, & pancreas derived from (milk, red meat, fish)
Muscle fibers have 3 sources of ATP production
1) creatine phosphate
2) anaerobic glycolysis
3) aerobic respiration
Creatine phosphate is what
An energy rich molecule that is unique to muscle fibers
Anaerobic glycolysis is a process when
Oxygen levels are low
Vigorous muscle activity
Pyruvic acid converted to lactic acid
Occurs w/o using oxygen
Aerobic cellular respiration is a
Series of oxygen requiring rxns that produce ATP in the mitochondria and muscle activity that lasts longer than half a min
Muscle fibers have 2 scs of oxygen
1) oxygen that diffuses into them from the blood
2) oxygen released by myoglobin in the sarcoplasm
Myoglobin is
An oxygen binding protein found only in muscle fibers
Binds oxygen when oxygen is plentiful and releases it when its less
Muscle fatigue
Inability of the muscle to contract forcefully after prolonged activity
Caused by lowered release of calcium ions from sarcoplasmic reticulum resulting in decline of calcium level in sarcoplasm
Oxygen debt
The added oxygen over and above the oxygen consumed at rest that is taken into the body after exercise
3 ways the extra oxygen is used to restore metabolic conditions
1) convert lactic acid back into glycogen stores in the liver
2) resynthesize creatine phosphate and ATP
3) to replace the oxygen removed from myoglobin
Recovery oxygen uptake
The elevated use of oxygen after exercise
Control of muscle tension results from
1) single muscle action potential
2) a muscle twitch has a smaller force than a maximum force or tension
The total tension of a muscle fiber depends on
The rate at which nerve impulses arrive at its neuromuscular junction
Twitch contraction is a
Brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron
Myogram
Recording of a muscle contraction
Latent period
A brief delay between the application of the stimulus and the beginning of the contraction
Contraction period
The second phase
Upward tracing
Repetitive power strokes
Relaxation period
Third phase
Downward tracing
Power strokes cease
Frequency of stimulation
If a second stimulus arrives before a muscle fiber has completely relaxed the second stimulation will be stronger than the first because the second contraction begins when the fiber is at a higher level of tension already
Wave stimulation
A larger contraction
Unfused (incomplete) tetanus
Wavering contraction when a skeletal muscle fiver is stimulated at a rate of 20-30x/sec
Fused (complete) tetanus
Sustained contraction
80-100x/second
Motor unit recruitment
The process in which the number of contracting motor units is increased
3 types of skeletal muscle fibers
Slow oxidative fibers (SO) - postural muscles of neck, back, leg -lg amt of myoglobin and mitochondria - resistant to fatigue -prolonged sustained contractions (Long distance walking)
Fast oxidative-glycolytic fibers (FOG) -leg muscles -high resistance to fatigue -lg amt of myoglobin and glycogen -anaerobic glycolysis (Running, swimming)
Fast glycolytic fibers (FG) -shoulder/arm -fatigue quickly -anaerobic glycolysis -low myoglobin -lg amt of glycogen (Wt lifting, sprinting)
Cardiac muscle tissue is found only where
In the heart Single centrally located nucleus Involuntary Contraction is not under conscious control Can regenerate under certain conditions
Intercalated discs are what
Irregular transverse thickenings of carcolemma
Gap junctions allow muscle action potentials to do what?
Spread quickly from one cardiac muscle fiber to another
Has endomysium, perimysium but lacks epimysium
The heart beats because some of the cardiac muscle fibers act as a
Pacemaker to initiate each cardiac contraction
What increases and decreases the heart rate?
Several hormones and neurotransmitters
Under resting conditions what should the BPM be
75x/min
Mitochondria in the cardiac muscle fibers do what?
Produce most of the needed ATP via aerobic cellular respiration
Cardiac muscle fibers can use lactic acid to do what
Make ATP
Smooth muscle tissue is found where?
Internal organs and blood vessels
Involuntary
Not under conscious control
Contains thick, thin, and intermediate filaments
2 types of smooth muscle:
Visceral
Multi-unit
Visceral (single unit) are found where
Walls of blood vessels, stomach, intestine, uterus, urinary bladder
Multi unit smooth muscle fibers consist of
Where are they found?
Individual fibers w/ motor nerve endings
Found in walls of lg arteries, lg airways to lungs, arrector pili muscle of skin, and internal eyemuscles
Dense bodies are similar to what
Where are they found in
Similar to Z discs in striated muscle to where the thin filaments are attached
Found in sarcoplasm and sarcolemma
Most smooth muscle fibers contract and relax in response to nerve impulses from what?
ANS
Hormone epinephrine is released by what and causes what?
Released by adrenal medulla
Causes relaxation of smooth muscle in the airways and blood vessels walls
Around 30 yrs old what happens
Humans undergo a slow progressive loss of skeletal muscle mass which is replaced by fibrous and adipose tissue
Origin
Attachment of a muscle by means of a tendon to the stationary bone
Insertion is
The other end of the muscle attached by means of a tendon to the movable bone at a point
Group actions
When muscles are moving and acting in groups
Prime mover or agonist
This is the leader muscle that causes an action
Antagonist
Is a muscle that relaxes while the prime mover contracts
Synergists are
Muscles that help the prime mover function
Fixaters are
Groups of muscles that stabilize the origin of the prime mover
Myopathy
Disease/disorder of the skeletal muscle
Neuromuscular dz
Disease/disorder of the skeletal musle to any of the components of a motor unit
Myasthenia gravis
Autoimmune dz that causes chronic progressive damage of the neuromuscular junction (face and neck)
Muscular dystrophy refers to a group of what
Inherited muscle - destroying dz that cause progressive degeneration of skeletal muscle fibers
DMA - duchenne muscular dystrophy
Fibromyalgia
Non articular rheumatic d/o that usually appears bt ages 25-30
Severe fatigue, poor sleep, headaches, depression
Electromyography (EMG)
Study of electrical changes that occur in musculature tissue
Hypertonia
Increased muscle tone - muscle stiffness
Hypotonia
Decreased/lost muscle tone
Myalgia
Pain in associated muscles
Myoma
Tumor consisting of muscular tissue
Myomalacia
Softening of muscle tissue
Myositis
Inflammation of muscle fibers (cells)
Myotonia
Increased muscular excitability and contractility
