Studied by 13 people
What are the three types of muscle tissue is the muscular system?
Skeletal, Cardiac, and Smooth
What is skeletal muscle?
Attached to bones of skeleton
Voluntary (consciously controlled)
What is cardiac muscle?
Makes up most of the wall of the heart
Involuntary (non-consciously controlled)
Responsible for pumping action of the heart
What is smooth muscle?
Found in walls of internal organs, such as those of digestive tract.
Involuntary (non-consciously controlled)
Skeletal muscles
Over 600 skeletal muscles in the body
Attached to bones, and skin of face
Under conscious control (voluntary)
Are organs of the muscular system
What is skeletal muscle composed of?
Skeletal muscle tissue
Nervous tissue
Blood
Connective tissue
What is Fascia?
Thin covering of connective tissue around a muscle.
What are tendons?
Cord-like mass of connective tissues that connect muscles to a bone.
What is Aponeurosis?
Sheet-like mass of connective tissue that connects a muscle to bone, skin, or another muscle.
What does the Epimysium surround?
Surrounds whole muscles; lies beneath fascia.
What does the Perimysium surround?
Surrounds fascicles within a muscle.
What does the Endomysium surround?
Surrounds muscle fibers (cells) within a fascicle.
What is a compartment?
Space containing groups of muscles, blood vessels, and nerves enclosed by fascia.
What is Compartment Syndrome?
It’s fluid accumulation with a compartment which results in the increase of pressure in the compartments.
It leads to deficiency of oxygen and nurtients.
Also causes severe pain.
Fascia
Fascia of each muscle is part of network of fasciae
Portion surrounding muscles is deep fascia, which connects to subcutaneous fascia under skin
Network also connects to subserous fascia of serous membranes
Skeletal muscle fiber (cell) are…
Multinucleated
What is sarcolemma?
Cell membrane of muscle fiber
What is the sarcoplasm?
Cytoplasm of muscle fiber
Myofribils consist what?
Thin actin filaments and thick myosin filaments.
What is sarcomeres?
Units that connect end-to-end, to make up myofibrils. (Functional unit of the muscular system)
What is the Sarcoplasmic reticulum (SR) and what does it store?
It is the endoplasmic reticulum of muscles and it stores calcium.
What is the transverse (“T”) tubule responsible for?
It relays electrical impulses to the SR.
What does the Triad consist of?
1 T tubule and 2 SR cisternae
What does myofibrils consist of that connect from end-to-end?
Sarcomeres
How are Striation patterns made?
They’re made by the arrangement of myofilaments in the myofibrils.
The A sarcomere consists of what structures?
I band- Light band; composed of thin actin filaments
A band- Dark band; composed of thick myosin filaments with portions overlapped with thin actin filaments.
H zone- Center of A band; composed of thick myosin filaments.
Z line (Z disc)- Sarcomere boundary; in center of I band which anchors filaments in place.
M line- Center of sarcomere and A band; anchors thick filaments
Thick filaments
Composed of myosin proteins
Heads form cross-bridges with thin filaments
Thin filaments
Composed of actin protein
Associated with troponin and tropomyosin, which prevent cross-bridge formation when muscle is not contracting.
Heavy chains and light chains form what?
Heavy chains intertwine to form myosin tail
Light chains form myosin globurlar head
Actin filaments made up of what?
G actin (globular) subunits
G actin subunits bears active sites for myosin head attachment during contraction.
G actin subunits link together to form what?
Long fibrous F actin (filamentous)
____ F actin strands twist together to form a thin filament.
Two
What does tropomyosin and troponin do?
They regulate proteins bound to actin.
Contraction of a skeletal muscle fiber
Requires interaction from several chemical and cellular components.
Results from a movement within the myofibrils, in which the actin and myosin filaments slide past each other, shortening the sarcomeres
Muscle fiber shortens and pulls on attachment points.
Neuronmuscular Junction (NMJ)
A type of Synapse
Also called a myoneural junction
Site where an axon of motor neuron and skeletal muscle fiber interact
Skeletal muscle fibers contract only when stimulated by a motor neuron
Parts of a Neuromuscular Junction consist of..
Motor neurons
Motor end plates
Synaptic Cleft
Synaptic vesicles
Neurotransmitters
Motor neuron
Neuron that controls skeletal muscle fibers
Motor end plate
Specialized folded portion of skeletal muscle fiber, where fiber binds to neurotransmitter.
Synaptic Cleft
Space between neuron and muscle fiber, across which neurotransmitter travels.
Synaptic vesicles
Membrane-bound sacs containing neurotransmitters
Neurotransmitters
Chemical released by motor neuron to deliver message to muscle fiber
Steps for contraction at neuromuscular junction
Action potential arrives at the end of a motor neuron
Action potential sends an electrical signal which opens a voltage channel
Calcium rushes into end of motor neuron and stimulates release of ACh from synaptic vesicles
ACh diffuses arcross synaptic cleft and bind to receptors
AcH receptors open a channel where Na ions enter and K ion exits.
A change occurs in the membrane potential called the end plate potential
Generations of an Action Potential Across the Sarcolemma
Resting sarcolemma is polarized, meaning a voltage exists across membrane
Action potential is caused by changes in electrical charges
Three steps of action potential across the sarcolemma.
End plate potential- generated at the neuromuscular junction
Depolarization- generating and propagating an action potential
Repolarization- restoring the sarcolemma to its initial polarized state (negative inside, positive outside)
Refractory period
Muscle fiber cannot be stimulated for a specific amount of time, until repolarization is complete.
What is excitation-contractions coupling?
Connnection between muscle fiber stimulation and muscle contraction.
During muscle relaxation:
Calcium ions are stored in sarcoplasmic reticulum
Troponin-tropomyosin complexes cover binding sites on actin filaments
Upon muscle stimulation:
Muscle impulses travel down the T-tubules causes SR to release
Calcium ions binds to troponin to change its shape
Each tropomyosin is held in place by a troponin molecule; change in shape of troponin alters the position of tropomyosin
Binding sites on actin are now exposed
Myosin heads bind to actin, forming cross-bridges
Cross-Bridge Cycling in order
Myosin head attaches to actin binding site, forming cross-bridge
Myosin cross-bridge pulls thin filaments towards center of sarcomere
ADP and Phosphate are released from myosin
New ATP binds to myosin
Linkage between actin and myosin cross-bridge break
ATP splits
Myosin cross-bridge goes back to original position, ready to bind to another binding site on actin.
Relaxation
Acetylcholinesterase rapidly decomposes ACh remaining the synapse
Muscle impulse stops when ACh is decomposed
Stimules to sarcolemma and muscle fiber membrane ceases.
Calcium pumps calcium ions back into sarcoplasmic reticulum
Troponin-tropomyosin complex again covers binding sites on actin.
Myosin and actin binding are now prevented.
Muscle fiber relaxes.
Sliding Filament Model of Muscle Contraction:
When sarcomeres shorten, thick and thin filaments slide past each other
H zones and I bands narrow (some texts state the H zones will disappear and I bands shorten)
Z lines move closer together (pulled toward M line)
A bands move closer to each other
Thin and thick filaments do not change length
Overlap between filaments increases
Myasthenia Gravis (MG)
An autoimmune disorder, which antibodies attack acetylcholine receptors on skeletal muscle fibers (motor end plates) in neuromuscular junctions.
Person may have only one-third normal number of ACh receptors
May lead to widespread muscle weakness and muscle fatigue
Treatments for it include drugs that inhibit acetylcholinesterase and immunosuppressant drugs
Muscular Dystrophy
Deficiency or abnormality/mutation in scarce muscle protein called dystrophin.
Dystrophin binds to internal side of muscle cell membrane, and holds them together during contraction.
In absence of normal dystrophin, cells lose normal structure and die.
Clostridium Botulinum
Anaerobic bacteria that produces a toxin that caused food poisoning.
Grows in food that is not properly preserved
Causes digestive, muscular, and respiratory symptoms.
Treated with an antitoxin
Used in small doses as Botox to smooth wrinkles, treat mirgraines. Blocks the release of Ach causing paralysis.
ATP reserves
First source of energy for muscle contraction
Muscle cells store only a small amount-must be able to regenerate ATP
Creatine Phosphate
Initial source of energy to regenerate ATP from ADP and P.
Stores energy in phosphate bond
Cellular respiration
Must be used to fuel longer periods of muscle contraction
Breaks down glucose to produce ATP
Glucose stored as glycogen in muscle cells
Types of phases of cellular respiration:
Anaerobic Phase
Aerobic Phase
Anaerobic (does NOT require O2) Phase
Glycolysis
Occurs in cytoplasm/cytosol
Produces little ATP- 2 ATP
Aerobic Phase
Citric acid cycle and electron transport chain system
Occurs in the mitochondria
Produces the most ATP (max is 30 in a muscle cell)
What does myoglobin do?
It stores extra oxygen in muscles (increases the amount of oxygen available in the muscle cells to support aerobic respiration.
Important because blood flow may decrease when contracting muscle fibers compress blood vessels.
Oxygen Debt
The amount of oxygen needed by liver cells to convert the accumulated lactic acid to glucose, and to restore muscle ATP and creatine phosphate concentrations.
Anaerobic (Lactic Acid) Threshold
Shift in metabolism from aerobic to anaerobic, during strenuous muscle activity, when the above systems cannot supply the necessary O2
Lactic acid is produced which goes to the liver to be converted to glucose. (Requires ATP)
Muscle Fatigue
Inability to contract muscles (For example, during prolonged exercise)
Common causes of muscle fatigue
Decreased blood flow
Ion imbalances across the sarcolemma
Loss of desire to continue exercise (psychological)
Accumulation of lactic acid (controversial)
Muscle Cramp
Not fully understood
Sustained, involuntary muscle contraction
May be caused by changes in electrolytes concentration in extracellular fluids in the area
Sodium
Chlorine
Magnesium
Potassium
Calcium
Heat production
Heat is a byproduct of cellular respiration in active cells. In other words, active cells generate heat.
Muscle contraction will release heat
Muscle cells are a major source of body heat. Muscle tissue is a large portion of body mass.
More than half the energy release in cellular respiration becomes heat; less than half is transferred to ATP.
Blood transports heat throughout body core.
Threshold Stimulus
Minimum strength of stimulation of a muscle fiber required to cause contractions
What is a twitch?
A contractile response of a single muscle fiber to a single impulse
Twitches vary in strengths (contributing factors):
Development of fatigue
Length to which fiber is stretched before stimulation
Period of times associated with a twitch
Latent period- Delay between stimulation and start of contraction (approximately 2 milliseconds)
Period of contraction- Fiber pulls at attachments
Period of relaxation- Pulling forces decrease
What does a myogram do?
It records events of a muscle twitch.
Length-Tension Relationship
The length of muscle fiber before stimulation determines the amount of force it can develop.
Optimum starting length is resting length of the fiber which allows the greatest force to develop.
Stretched muscle fiber develop less force, since some myosin heads cannot reach binding sites on actin.
Shortened muscle fiber also develop less force, since compressed sarcomeres cannot shorten further.
Whole muscle contraction
The actions we perform usually require the contribution of multiple muscle fibers simultaneously.
We can electrically stimulate the whole muscle which contracts the muscle.
When contracted muscles will pull on levers (bones).
Summation
Process by which the force of individual muscle fiber twitch combine, when frequency of stimulation increases.
Produces sustained contractions and can lead to partial or complete tetanic contractions
What are the types of Tetanus?
Partial Tetany and Complete Tetany
What is Partial Tetany and Complete Tetany?
Partial Tetany
Occurs at higher frequencies of stimulation
Time spent in relaxation between twitches become very brief
Complete Tetany
Occurss at very high frequencies of stimulation
Does not occur in body, only in laboratories
Forceful sustained contraction has no relaxation between twitches.
What is a motor unit?
A motor neuron plus all of the muscle fibers it controls.
(Most muscle fibers have only one motor end plate)
A whole muscle consists of many motor units
Precise movements of motor units
Produced with fewer muscle fibers in a motor unit.
Example: the motor unit of the muscle that moves the eye including fewer than 10 muscle fibers per motor unit and can produce very slight movements
Coarse movements of motor units
Produced with large numbers of fibers in a motor unit
Motor units of the large muscle in the back may include a hundred or more muscle fibers. Movements are larger scale than the eye.
Sustained contractions
Smaller motor units (smaller diameter axons)- recruited first
Large motor units (larger diameter axons)- recruited later and with greater force
Summation and recruitment can produce sustained contractions of increasing strength
Whole muscle contractions are smooth movements. Individuals twitches do not normally occur. Partial or tetanic contractions of muscle fibers are common.
What is muscle tone (tonus)?
Continuous state of partial contractions in resting muscles.
Contributes to maintaining posture
Taught neck, head, trunk, and lower limbs enable a person to sit up, stand, hold up head etc.
Lose consciousness and the body collapses
What happens in isotonic contractions?
Muscle contracts and changes length. (Means equal force)
Types of Isotonic contractions
Concentric- shortening contraction; occurs when lifting an object
Eccentric- lengthening contraction; occurs when force not sufficient to lift object (lowering a hand weight)
Isometric contractions
Muscle contracts but does NOT change length
Means “equal length”
Tension develops, but parts attached to muscle do not move (no movement-holding object in place)
Muscles vary in the following ways:
Contraction speed: Slow or Fast
Method of ATP production: Oxidatively or Glycolytically
Three types of muscle fibers found in human:
Slow Twitch fibers (Type I)
Fast-twitch fatigue-resistant fibers (Type IIa)
Fast-twitch glycolytic fibers (Type IIb)
Slow-twitch fibers (Type I) (Will be on test)
Always oxidative
Resistant to fatigue (due to high ATP production)
Red fibers (High myoglobin)
Abundant myoglobin (stores oxygen in muscles)
Good blood supply
Many mitochondria
Slow ATPase activity; slow to contract
Fast-twitch fatigue-resistant fibers (Type IIa) (Might be on test so still know it)
Intermediate twitch fibers
Intermediate oxidative capacity
Intermediate amount of myoglobin
White fibers (have less myoglobin)
Resistant to fatigue
Rapid ATPase activity
Fast-twitch glycolytic fibers (Type IIb) (Will be on test)
Anaerobic respiration (glycolysis)
White fibers (less myoglobin)
Poorer blood supply than slow-twitch fibers
Fewer mitochondria than slow twitch
More SR than slow-twitch (SR to store and absorb calcium ions)
Susceptible to fatigue
Fast ATPase activity; contract rapidly
What is hypertrophy and atrophy?
Hypertrophy- enlargement of skeletal muscle that is exercised
Atrophy- decrease in size (actin and myosin filaments) and strength of skeletal muscle that is unused. Can happen if neurons no longer supply a signal.
What does Aerobic and Forceful exercise stimulate?
Aerobic exercise simulates slow-twitch fibers; in response, fibers increase their capillaries and mitochondria
Forceful exercise simulates mainly fast-twitch fibers; in response, fibers produce new actin and myosin filaments, and the muscle enlarges.
Smooth muscle
Compared to skeletal muscle fibers, smooth muscle fibers are:
Shorter
Single, centrally located nucleus
Elongated with tapering ends (tissue looks like spindles)
Myofilaments randomly organized (so they have actin, myosin, and myofibrils)
Lack striations
Lack transverse tubules
Sarcoplasmic reticulum (SR) not well developed
Smooth muscle SIMILARITIES to skeletal muscle
Mechanisms reflect reactions to actin and myosin
Triggered by membrane impulses and release of calcium ions
Both use energy from ATP molecules (have mitochondria)
Neurotransmitters: acetylcholine
Smooth muscle DIFFERENCES to skeletal muscle
Does not have troponin; instead has calmodulin-binds to calcium activating contraction
Calcium needed diffuses into the cell from extracellular fluid not SR
Neurotransmitters: norepinephrine SO SMOOTH MUSCLE HAS BOTH ACETYLCHOLINE AND NOREPINEPHRINE
What are the two types of smooth muscle?
Multi-unit smooth muscle
Visceral smooth muscle
Multi-unit smooth muscle
Cells are less organized
Function as separate units
Fibers function independently
Iris of eye, walls of blood vessels
Stimulated by neurons, hormones
What role does hormones play in multi-unit smooth muscles?
It can stimulate or inhibit contractions or may alter the degree of response to neurotransmitters.
Visceral smooth muscles
Single-unit smooth muscle; cells respond as a unit
Sheets of spindle-shaped muscle fibers
Fibers held together by gap junctions
Exhibit rhythmicity
Conduct peristalsis
Walls of most hollow organs (intestines, stomach, etc.)
More common type of smooth muscle
Smooth muscle contractions RESEMBLE skeletal muscle contractions in the following ways:
Interaction between actin and myosin
Both use calcium and ATP
Both are triggered by membrane impulses
Smooth muscle contractions DIFFER from skeletal muscle contraction in the following ways:
Smooth muscle lacks troponin; used calmodulin instead
Two neurotransmitters affect smooth muscle: Acetylcholine (Ach) and norepinephrine (NE)
Hormones can stimulate or inhibit smooth muscle
Stretching can trigger smooth muscle contractions
Smooth muscle slower to contraction and relax
Smooth muscle more resistant to fatigue
Smooth muscles can change length without changing tautness.
Cardiac Muscle
Located only in the heart
Striated muscle cells
Muscle fiber joined together by intercalated discs
Fibers branch, contains a single nucleus; has many mitochondria
Network of fibers contracts as a unit (syncytium)
Self-exciting and rhythmic
Does not require stimulation from neurons
Longer refractory period (muscle fiber cannot be stimulated until repolarization is complete) than skeletal muscle.
No sustained or tetanic contractions
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