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CH 9.1 Types of Muscle Tissue
Muscle Functions
1. Muscles make up half of body mass
2. Transforms chemical energy (ATP) into mechanical energy
3. Homeostatic Heat Production
a. Consumes most energy from muscle contraction
Muscle Types
1. Skeletal Muscle
a. Produces movement by acting on the skeleton
b. Maintains posture
c. Stabilize joints control internal movement
d. Generates heat
e. Contains
i.
Connective Tissue Layers
1. Epimysium
2. Perimysium
3. Endomysium
ii.
Blood Vessels and Nerves
1. Enter the CT and branch in the cell
2. Cardiac Muscle
a. Found on the heart wall
b. Pumps blood through the circulatory system
3. Smooth Muscle
a. Found in the skin
i.
Associated with hair follicles
b. Internal Organs
c. Blood Vessels
i.
Critical component to regulate blood pressure
d. Internal Passageways
i.
Eg. Peristalsis in the intestines
Skeletal Muscle Organization (basic levels)
1.
2.
3.
4.
5.
6.
7.
Tendon
Fascicle
Muscle Fiber (Cell)
Myofibril
Sarcomere
Microfilament
Actin and Myosin
Skeletal Muscle Layers with CT (superficial to deep)
Long, multi nucleated cells. Connective tissue layers highlighted.
1. Epimysium Connective Tissue
a. Outer covering of fascicles
2. Fascicles
a. Bundles/groups of muscle fibers
3. Perimysium Connective Tissue
a. Covers each fascicle bundle
4. Endomysium Connective Tissue
a. Covers each muscle fiber (muscle cell)
5. Muscle Fibers (muscle cells)
a. Many fibers makes up a single fascicle
b. Nuclei are found here
c. Many myofibril makes up a single muscle fiber
d. Surrounded by sarcolemma
e. Filled with sarcoplasm
6. Myofibrils
a. Mitochondrion found here
b. Sarcoplasmic reticulum
i.
Surrounds the myofibril
ii.
Form of endoplasmic reticulum
iii.
Many actin and myosin filaments make up a myofibril
7. Myosin and Actin filaments
a. Creates banding striations
b. Forms the sliding filament mechanism
Excitability
1. Plasma membranes change electrical states
a. Polarized to depolarized
2. Sends an action potential along the membrane
3. Influenced by
a. Nervous system
i.
Cardiac and skeletal muscle
b. Hormones and local stimuli
i.
Can also influence cardiac and skeletal muscle
Muscle Basic Characteristics
Skeletal Muscle
1.
2.
3.
4.
5.
6.
Contractions for body movement
Voluntary
Long, cylindrical, striated cells
Multi nucleated
Contracts rapidly, tires easily
Smooth Muscle
1.
2.
3.
4.
5.
In walls of organs and blood vessels
Involuntary
Spindle-shaped, non-striated cells
Mono nucleate
Slow, sustained contractions
Cardiac Muscle
1.
2.
3.
4.
5.
6.
7.
In heart wall
Amitotic
Involuntary
Striated, branching cell
Mono or binucleate
Intercalated discs
Self-initiating contractions
CH 9.2-3 Physiologic Functions of Muscle
Major Physiologic Functions of Muscle
1. Movement
a. Molecular motors cause movement of fibers
b. Causes movement of cells and bones
i.
Changes bone position
c. Moves material through tubes
i.
Peristalsis
2. Heat Production
a. All energy not converted to mechanical energy
b. Much converted to heat
c. Large amounts of muscle in the body, creates large amounts of heat
3. Communication
a. Muscles control
i.
Facial expression
ii.
Gesturing
iii.
Writing
iv.
Typing
v.
Speaking
Muscle Power Efficiency
1. Power comes from ATP
a. Generated by cellular metabolism
2. Biochemical efficiency for movement is 25-40%
a. Balance of energy produced during contraction released as heat
CH 9.4 Muscle Properties
Major Muscle Properties
1. Contractibility
a. Ability to shorten its length
b. Requires energy
c. Skeletal muscle contractions
i.
Pulls bones through attached tendons
d. Smooth muscles contractions
i.
Generates pressure
ii.
Capable of forcing liquids through hollow structures (blood vessels)
2. Elasticity
a. Capacity to return stretched muscle to original length
3. Excitability
a. Capacity of muscle to respond to a stimulus to contract
b. Skeletal
i.
Responds to nervous system
c. Smooth and cardiac
i.
Affected by nervous system
ii.
Also responds to physical stimulations and hormones
4. Extensibility
a. Ability to return to its original length
i.
Still responds to stimulus
b. Returns by
i.
Elastic recoil
ii.
Actions of other muscles
iii.
Gravity
iv.
Fluid under pressure within a vessel
Muscle Contraction Process (basic)
1. Skeletal and Cardiac (striated muscles)
a. Protein fibers: Actin is pulled by Myosin when
i.
Specific binding sites shielded by proteins troponin and tropomyosin
ii.
Exposed in response to interactions between calcium ions and proteins
2. Smooth Muscle
a. Protein fibers: Actin is pulled by Myosin when
i.
Calcium ions activates enzymes
ii.
Enzymes activates myosin heads to pull actin fibers
3. All muscles require ATP to continue process of contraction
4. All muscles relax when calcium ions are removed and actin binding sites are re-shelided
Differences Among Three Muscle Types
1. Actin and Myosin protein arrangement
a. Skeletal and Cardiac Muscle
i.
Regular protein arrangement creating a pattern: Striations
b. Smooth Muscle
i.
Irregular protein arrangement
ii.
Uniform, non-striated appearance
2. Nuclei
a. Skeletal
i.
Multinucleated
b. Cardiac
i.
One or two nuclei per cell
c. Smooth
i.
Single nucleus
3. Connections between cells
a. Cardiac
i.
Physically and electrically connected to each other
ii.
Entire heart contracts at once
b. Skeletal and Smooth Muscle
i.
Not connected to pass electrical impulses
CH 9.5 Skeletal Muscle
Skeletal Muscle
1. Ability to contract and cause movement
a. Produces movement
b. Stops movement
i.
Resists gravity to maintain posture
2. Holds the body upright
a. Small, constant adjustments
3. Prevents excess movement of the bones and joints
a. Preventing damage to joints (misalignment)
b. Keeps joints stable
4. Located at openings of internal tracts
a. Anus, mouth
b. Controls movement of various substances for voluntary control
i.
Swallowing
ii.
Urination
iii.
Defecation
5. Protects internal organs
a. Abdominal and Pelvic organs
b. Acts as external barrier to shield from trauma
c. Supports weight of organs
6. Contributes to homeostasis
a. Generates heat when ATP is broken down
b. Exercise causes body temp to rise
c. Extreme cold causes shivering
i.
Random skeletal muscle movement to generate heat
7. Richly supplied by blood vessels
a. Nourishment and oxygen delivery
b. Waste removal
8. Somatic Motor Neuron Innervation
a. Each muscle supplied by an axon branch of a motor neuron
b. Signals the muscle to contract
c. Only way to contract is through the nervous system (unlike cardiac and smooth)
9. Contains various integrated tissues
a. Muscle fibers (cells)
b. Blood vessels
c. Nerve fibers
d. 3 layers of Dense Irregular Connective Tissues
3 layers of Dense Irregular Connective Tissues (-mysia)
1. Epimysium
a. Outer most CT layer, surrounding the entire muscle
b. Allows the muscle to contract powerfully while maintaining the structural integrity
c. Separates the muscle from other tissues and organs
i.
Allows the muscle to move Independent of the surrounding tissues
2. Perimysium
a. Middle CT layer, surrounding individual fascicles (fiber bundles)
b. Arrangement allows for the nervous system triggering of a specific movement of a subset of
fibers
3. Endomysium
a. Inner most CT layer, covering individual muscle fibers (cells)
b. Thin CT layer of collagen and reticular fibers
c. Contains the extracellular fluid: Sarcoplasm
d. Contains cellular nutrients supplied via the blood
Tendons and Muscles
1.
2.
3.
4.
Skeletal muscles work with tendons to pull on bones for movement
Collagen fibers in all 3 CT layers (mysia) intertwined with collagen of a tendon
Opposite end of tendon fuses with periosteum of the bone
Tension from movement transferred through mysia to pull the bone
Aponeurosis
1. Broad tendon-like sheet that fuses with mysia
2. e.g. Lower back: latissimus dorsi fuses is an example of aponeurosis
Fascia
1. Connective tissue between the skin and bones
Skeletal Muscle Organization
1.
2.
3.
4.
5.
6.
7.
Tendon
Fascicle
Muscle Fiber (Cell)
Myofibril
Sarcomere
Microfilament
Actin and Myosin
CH 9.6 Skeletal Muscle Fibers (cells)
Skeletal Muscle Fibers (Muscle Cells)
A skeletal muscle fiber is surrounded by a plasma membrane called the sarcolemma, which contains
sarcoplasm, the cytoplasm of muscle cells. A muscle fiber is composed of many fibrils, which give the cell
its striated appearance.
1. Long and cylindrical
2. Large for human cells
a. Up to 100mcm in diameter
b. Up to 30cm (11.8 in) in the Sartorius of upper leg
3. Terminology
a. Sarco: FLESH
4. Sarcolemma
a. Plasma membrane of muscle fiber (cell)
5. Sarcoplasm
a. Cytoplasm of the muscle fiber (cell)
6. Sarcoplasmic Reticulum (SR)
a. ER of the muscle fiber
b. Stores, released and retrieves calcium ions
7. Sarcomere
a. Functional unit of the muscle fiber
b. Highly organized arrangement of contractile myofilaments
i.
Actin (thin) filaments
ii.
Myosin (thick) filaments
Embryonic Development
1. Embryonic myoblast cells, each with single nucleus fuse with up to 100's of other myoblasts
forming a multinucleated skeletal muscle fiber (cell)
2. Multiple nuclei
a. Contain multiple copies of genes
b. Allows for large amounts of protein and enzyme production
i.
Needed for muscle contraction
CH 9.7 The Sarcomere
The Sarcomere
The region from one Z-line to the next Z-line, is the functional unit of a skeletal muscle fiber.
1. Functional unit of the muscle fiber (cell)
2. Striated appearance due to arrangement of myofilaments
a. Actin (thin)
b. Myosin (thick)
3. Myofilaments situated in sequential order from one end of the fiber to another
4. Sarcomeres are bundled to make up a myofibril, running the length of the fiber
5. Myofibril (in-line sarcomere group) contraction is muscle contraction
6. Each sarcomere is 2mcm in length
7. Z-discs (or Z-lines)
a. End borders of sarcomere
8. Actin filaments
a. Thin strands
b. Has a troponin-tropomyosin complex
c. Anchored to end border Z-discs
d. Project inward from ends
9. Myosin filaments
a. Thick strands with multiple heads
b. Projects from the center of the sarcomere
CH 9.8 The Neuromuscular Junction
Neuromuscular Junction
1.
2.
3.
4.
Site where a motor neuron's terminal end meets the muscle fiber (cell)
Region where muscle fiber responds to nervous stimuli
Every skeletal muscle is innervated by a motor neuron at the NMJ
Excitation signal from neuron is only way to activate fiber to contract
CH 9.9 -11 Excitation-Contraction Coupling
Excitation-Contraction Coupling
The initiation of a muscle contraction by a neural stimulus (Excitation), to initiate an action potential
(wave of electrical signal along the sarcolemma/membrane). This is Coupled to a muscle Contraction by
the release of calcium ions from the Sarcoplasmic Reticulum, facilitating the contraction and release of
actin and myosin proteins within the Sarcomere. The calcium ions interact with shielding proteins,
troponin and tropomyosin, moving them aside to expose actin binding sites. With the binding sites
available, the myosin heads can attach and pull the actin filaments in towards the center of the
sarcomere, causing the muscle fiber to shorten.
1. Membrane Potentials/Electrical Gradients
a. Inside of cell is usually -60 to -90 relative to outside (multipolar motor -70)
i.
Electrical differences created by ions
2. Membrane potential used to generate electrical signals
a. Movement of ions across the membrane channel proteins
i.
Channels open and close
b. Creates electrical current
3. Forms the basis of neural signaling to muscle contraction
Action Potential
1. Special type of electrical signal that travels along a cell membrane
2. Allows signal to be quickly transmitted over long distances
Acetylcholine (ACh)
1. Neurotransmitter or chemical messenger
Resting Membrane Potential
1. Normal voltage between sides of the sarcolemma (membrane)
Depolarize
1. Becomes less negative
a. Muscle fiber has a RMP of -70mV and moves closer to zero
Graded Summation / All-or-none AP
1. Depolarization of +15mV to threshold of -55mV (from RMP of -70mV)
Sarcolemma
1. Phospholipid bilayer of the muscle fiber (cell)
T-Tubules
1. Periodic invaginations of the sarcolemma
a. Occasional entryways into the cell
Triad
1. Arrangement of T-tubule with SR on either side
a. Surrounds the myofibril
Sarcomere
1. Cylindrical structure of the myofibril
2. Contains actin and myosin filaments
a. Sliding mechanism in 6:1 ratio
Tropomyosin
1. Protein that winds around the chains of the actin filament
2. Prevents binding of the myosin head
Troponin
1. Part of the troponin-tropomyosin complex
2. Troponin has a binding site for Ca2+
a. Ca2+ causes movement of the complex, exposing the actin binding site for the myosin head
to attach
Motor End-Plate and Innervation
The Generation of an Action Potential
Across a Neuro Muscular Junction
1. The nerve receives a stimulus that generates an action potential to propagate along the axon.
2. The AP reaches the axon terminal
a. Depolarization of the axon membrane opens Na+ and Ca2+ voltage gated channels.
b. Ca2+ influx into the axon terminal from the surrounding extracellular fluid
3. Ca++ ions promote the fusion of synaptic vesicles containing acetylcholine (ACh) with the axon
terminal membrane
4. Synaptic vesicles release the ACh into the synaptic cleft by exocytosis
a. ACh diffuses across the synaptic cleft to bind to ACh receptors on the motor end plate
b. Leftover ACh is degraded by the enzyme acetylcholinesterase (AChE)
i.
Prevents unwanted extended muscle excitation
5. Binding of Ach to Ach receptors on the sarcolemma opens chemically gated Na+ channels
a. Na+ ions diffuse rapidly into the cell causes a change in the membrane potential (voltage) to
become less negative
b. Resting membrane potential (RMP)decreases= depolarization at motor end plate
c. Meanwhile, sodium potassium pumps (Na+ K+) restore ion concentration between
membrane sides back to RMP
6. Propagation of the action potential
a. Waves spreads along the sarcolemma to adjacent areas opening more Na+ voltage gated
channels
7. Repolarization occurs immediately after the depolarization wave passes
a. Na+ channels close (preventing the increase of voltage inside the cell)
b. K+ diffuses out of the cell
c. Polarized state of the membrane is restored to RMP
8. Action potential continues down the T-tubules, deep into the muscle
a. This is the depolarization/repolarization wave
9. Action potential triggers release of Ca2+ ions from the terminal cisternae into the sarcoplasm
The Sliding Filament Mechanism
Continuation of the Action Potential from the Nero Muscular Junction
10. Newly available Ca2+ ions from the SR, binds to troponin
a. Troponin is attached to tropomyosin and blocks the attachment site for myosin filament
heads to attach. This is known as the troponin-tropomyosin complex
b. The troponin changes shape and moves the tropomyosin, exposing the actin binding site
11. Activated myosin heads attach to actin binding sites
a. This is in preparation for the power stroke
12. Myosin heads pivot = Power Stroke
a. High energy to low energy release
i.
ADP and Pi (inorganic phosphate) are released
b. Actin filament is pulled toward the center of the sarcomere at the M Line
13. New ATP molecule binds to myosin head
a. Causes detachment from actin
14. Myosin head prepares for next stroke
a. ATP hydrolysis into ADP + Pi
b. High-energy state or "cocked" position
End of Muscle Contraction
1. Stops when signaling from motor neuron ends
a. Sarcolemma and T-Tubules repolarize (decrease in voltage to RMP)
b. Voltage gated Ca2+ channels in the Sarcoplasmic Reticulum close
i.
Ca2+ ions pumped back into the SR
c. Lack of Ca2+ causes re-shielding of the actin binding sites
i.
Shielded by the troponin-tropomyosin complex
2. Stops upon ATP depletion
a. Muscles fatigue
3. Stops upon death
a. Lack of ATP prevents myosin head release
i.
Rigor mortis: permanent muscle contraction
CH 9.11 Sources of ATP
Sources of ATP
1.
2.
3.
4.
ATP is the energy source for muscle contraction
Directly involved in the cross-bridge cycle of the sliding filament mechanism
ATP provides energy to power the active transport Ca2+ pumps in the SR
ATP storage in muscle is low
a. Only a few seconds worth of contractions
Mechanisms for ATP regeneration
1. Creatine Phosphate
a. Molecule with energy storage in phosphate bonds
b. Resting muscles stores excess ATP by transfer to creatine
i.
Produces ADP and creatine phosphate
c. Acts as energy reserve to quickly create ATP
d. When ATP is needed
i.
Creatine phosphate transfers phosphate back to ADP to form ATP
ii.
Reaction catalyze by enzyme creatine kinase
e. Quick reaction time powers first few seconds of muscle contraction: up to 15 seconds
worth of energy
2. Glycolysis
a. Anaerobic process: non-oxygen dependent
b. Initiated when ATP is depleted from creatine phosphate
i.
Glycolysis results in a slower rate of ATP availability than CP
c. Breaks down glucose as energy source
i.
Glucose provided by blood
ii.
Can metabolize glycogen stores in muscle?
d. One glucose molecule yields:
i.
Two ATP molecules
ii.
Two pyruvic acid molecules
1. Can be used in aerobic respiration if oxygen is available
2. If no oxygen is available, then converts to lactic acid
a. Lactic acid contributes to muscle fatigue
3. Conversion of pyruvic acid to lactic acid allows recycling of NAD+ enzyme from
NADH
a. Necessary for glycolysis to continue
b. Occurs during strenuous/high energy exercise with low oxygen delivery to
muscles
e. Glycolysis can only sustain approximately 1 minute of muscle activity
f. Useful in short bursts of high-intensity output
3. Aerobic Respiration
a. Breakdown of glucose in the presence of sustained supply of oxygen
i.
Muscles store O2 in myoglobin proteins as compensation mechanism
b. Produces ATP, CO2 and water
c. Approximately 95% of the ATP required for resting or moderate activity takes place in the
mitochondria
d. Inputs for aerobic respiration
i.
Glucose from the blood stream
ii.
Pyruvic acid from glycolysis
iii.
Fatty acids
e. One glucose molecule yields:
i.
36 ATP
f. Aerobic training increases efficiency of the circulatory system in order to deliver more O2
quickly
Muscle Fatigue
Occurs when muscle can no longer contract from neural signaling
1. Depleted ATP reserves decrease muscle function
2. Lactic acid buildup
a. Lowers intracellular pH
i.
Affects enzyme and protein activity
3. Excessive membrane depolarization
a. Causes Na+ and K+ imbalances
i.
Results in disruption of Ca2+ flow from
4. Long periods of sustained exercise
a. May damage SR and sarcolemma
i.
Impairs Ca2+ regulation
Oxygen Debt
Amount of oxygen needed to compensate for ATP production without oxygen during muscle
contraction: Glycolysis and Creatine Phosphate mechanisms
1. Oxygen is required to restore ATP and creatine phosphate levels
2. Oxygen converts lactic acid to pyruvic acid
3. Oxygen converts lactic acid into glucose or glycogen in the liver
These combined processes result in an increased breathing rate that remains elevated during and after
exercise until the oxygen debt has been met.
CH 9.12 Relaxation
Relaxation of a Skeletal Muscle
1. Relaxation begins with the motor neuron
a. Stopes the release of ACh into the synapse at the NMJ
2. Repolarization of the muscle fiber occurs
a. Muscle fiber again becomes more negative
i.
Muscle goes back to its RMP of about -70mV
b. Ca2+ gates in the SR close
3. Active (ATP driven) pumps moves Ca2+ out of the sarcoplasm back into the SR
4. Re-shielding of the actin binding sites occurs with the lack of available Ca2+
a. Troponin-Tropomyosin complex blocks these sites
5. Lack of ability to form cross-bridges between actin and myosin causes lack of tension and
subsequently relaxation
Muscle Strength
1. Number of muscle fibers in a muscle is determined by genetics
2. Muscle strength is directly related to amount of myofibrils and sarcomeres within each fiber (cell)
3. Hypertrophy: Increased mass in skeletal muscle
a. Increased production of sarcomeres and myofibrils
b. Caused by
i.
Hormones
ii.
Stress
iii.
Artificial anabolic steroids
4. Atrophy: Decreased mass in skeletal muscle (muscle fibers numbers remain intact)
a. Decreased sarcomeres and myofibrils
b. Caused by
i.
Decreased use
Muscle Contraction Concept Review
1.
2.
3.
4.
5.
6.
7.
8.
9.
Sarcomere is the smallest contractile portion of the muscle
Myofibrils are complex of thick and think (myosin and actin) filaments
Troponin and tropomyosin are regulating proteins that block actin binding sites
Sliding filament mechanism is directly responsible for contraction
Ach is a neurotransmitter that binds to receptors at the NMJ to initiate depolarization (becomes
less negative), starting the Action Potential
The action potential released Ca2+ from the SR
Ca2+ causes the un-shielding of the acting binding sites to facilitate cross-bridging of the myosin
and actin fibers
The Power Stroke occurs once the myosin heads attach to the actin fiber binding sites, followed by
a ratcheting movement powered by ATP
Sarcomeres, Myofibrils and Muscle Fiber shortening, define a contraction to produce movement
CH 9.12 Nervous Control of Muscle Tension
Nervous System Control of Muscle Tension
1. Muscle Tension
a. The force generated by the contraction of the muscle
i.
Shortening of the sarcomere
2. Isotonic and Isometric Contractions
a. Contractions against a load that does not move
b. Most actions of the body are a combination of Isotonic and Isometric Contractions
Isotonic Contractions
1. Constant muscle tension throughout the contraction
2. Two types of isotonic contractions
a. Concentric Contraction
i.
Muscle shortens to move the load (lifting up)
ii.
e.g. Biceps brachii muscle contracting in a curl lift
1. Angle of the elbow joint decreases as forearm is moved closer to the body
b. Eccentric Contraction
i.
Muscle lengthens and tension diminishes (lifting down)
ii.
e.g. Biceps brachii muscle lengthens
1. Angle of the elbow joint increases as forearm is extended
2. e.g. Weight is slowly lowered
Isometric Contractions
1.
2.
3.
4.
Muscle produces tension without changing the angle of a skeletal joint
Involves sarcomere shortening and increased tension
Does not move a load
Active in maintaining posture and bone and joint stability
a. Holding the head upright under normal conditions
CH 9.13 Motor Units & Length Tension
Motor Units: GROUP of muscle fibers in a muscle innervated by a single motor neuron
Motor neuron axons will BRANCH to form synaptic connections at their individual NMJ's
1. Muscle contraction depends on innervation by the axon terminal of a motor neuron
2. Each muscle fiber (cell) is innervated by one motor neuron
3. Size of a motor unit depends on the nature of the muscle
a. Small motor units
i.
Single motor neuron supplies a SMALL number of muscle fibers
ii.
Permits fine motor control
1. e.g: extraocular eye muscle (eyeball movement)
iii.
Each muscle has thousands of muscle fibers
1. Single motor neuron supplies about every six muscle fibers by individual
branches stemming from a single axon
b. Large motor units
i.
Single motor neuron supplies a LARGE number of muscle fibers
ii.
Axon splits into thousands of branches
iii.
Concerned with simple or gross movements
iv.
e.g: Back or thigh muscles
Motor Units Wide Range of Control Over the Muscle
1. Combinations of small and large motor units gives a wide range of control
2. Recruitment: Increasing activation of motor units
3. Small motor units
a. More excitable firing because of a lower threshold
b. Fires first to the smaller fibers
c. Results in a small degree of strength/tension
4. Large motor units
a. Fires when more strength is needed
b. Bigger muscles with a higher threshold
5. Recruitment
a. Nervous system uses recruitment as an efficiency mechanism
b. Increasing activation of motor unites produces an increase in power
c. Contraction grows stronger with increased recruitment
d. Some large motor units will produce 50x more power than small
i.
Allows for soft and strong function from the same muscle
e. Maximum Muscle Force
i.
Max amount of motor units recruited simultaneously for max force
ii.
Short timespan due to energy requirements
iii.
Generally, not all motor units fire at once
1. Prevents completes complete fatigue
Length-Tension Range of a Sarcomere
Sarcomere length directly effects the force generated upon shortening
1. Cross-bridges (myosin head/actin fibers connection) can only occurs where there are actin/myosin
overlap within the sarcomere
2. Ideal sarcomere length to produce max tension is at 80%-120% of its resting length
3. 100% of Length is when the medal edges of the myosin and actin fibers are even
a. This length maximizes overlap of actin-binging sites with myosin heads
4. Beyond 120% filaments do not overlap sufficiently
5. Under 80% has a reduced overlap range
a. H Zone is reduced in length
CH 9.13 Motor Neuron Frequency
Muscle Twitch
An isolated, muscle contraction from a single action potential from a motor neuron
1. A twitch can last from a few to 100 milliseconds depending on muscle
2. Tension produced can be measured by a myogram
a. Instrument that measures tension over time.
3. Each Twitch undergoes 3 phases
a. Latent Period
i.
Action Potential propagates along sarcolemma
ii.
Ca2+ ions released from SR
iii.
Excitation and contraction coupling
1. No contraction yet
b. Contraction Phase
i.
Ca2+ ions in the sarcoplasm have bound to troponin
ii.
Tropomyosin has shifted exposing actin binding sites
iii.
Sarcomeres are shortening to max tension
c. Relaxation Phase
i.
Tension is decreasing as contraction stops
ii.
Ca2+ ions are pumped back in the SR
iii.
Cross-Bridge cycling stops
iv.
Muscle fibers return to resting state
Graded Muscle Response
Allows for a variation in muscle tension
1. Twitch does not produce significant muscle activity
2. Graded Muscle Response
a. A Series of sustained action potentials to the muscle fibers
b. Necessary to produce work
c. Can be modified by the nervous system, producing various amounts of force
d. Frequency of AP and number of transmitting motor neurons affect the tension produced in
skeletal muscle
Wave Summation
Overlapping muscle fiber stimulation produces a stronger contraction
1. Fibers are stimulated as a previous twitch is occurring
2. The second twitch is the stronger of the two
a. Motor signaling is SUMMED
b. Additional Ca2+ ions becomes available to the sarcomeres
3. Summation results in greater contraction of the motor unit.
Tetanus
The fusion of contractions, producing a single contraction
1. Increased frequency of motor unit signaling continues until it peaks
2. Incomplete tetanus
a. This tension is 3-4 times greater than a single twitch
b. Muscle has quick cycles of contraction/relaxation
3. Complete tetanus
a. Results what stimulus frequency is high enough that relaxation disappears completely
b. Contraction becomes continuous
c. Increased Ca2+ contractions allows all sarcomeres to form cross bridges and shorten
d. Continues until muscle fatigues
Treppe (aka: Staircase effect)
1.
2.
3.
4.
5.
Muscle has been dormant for extended amount of time is activated
Initial contractions are half the force of subsequent contractions
Increased in a graded matter resembling stairs
Increased concentration of Ca2+ with steady stream of APs
Maintained with adequate ATP
CH 9.14 Muscle Tone & Fiber Types
Muscle Tone
The maintenance of contractile proteins produce tension to stabilize joints and maintain posture
1. Skeletal muscles are rarely relaxed
2. Small contractions maintain contractile proteins: muscle tone
3. Accomplished by interaction between the nervous system and skeletal muscles
a. Activation of few motor units at a time in a cyclical manner preventing fatigue
i.
Some recover, while others are active
Hypotonia or Atrophy
1. Can result from CNS damage
a. Cerebellum damage
b. Loss of innervation to a skeletal muscle
i.
e.g. Poliomyelitis
c. Muscles display flaccid appearance
d. Functional impairments like weak reflexes
Hypertonia (excessive muscle tone)
1. Accompanied by hyper-reflexia
a. Excessive reflex response
2. Often results of damage to upper motor neurons in the CNS
3. Muscle rigidity
a. e.g: Parkinson's disease
4. Spasticity
a. Phasic change in muscle tone
b. Limb snaps back from passive stretching
i.
Seen in some strokes
CH 9.14 Skeletal Muscle Fiber Types
Classifying Muscle Fiber Types
1. Speed of contraction
a. Dependent on how quickly myosin's ATPase hydrolyzes ATP to produce the cross-bridge
action
i.
ATP causes detachment of myosin head to actin after the power stroke
2. How ATP is produced / Primary metabolic pathway
a. Aerobic Respiration - Oxidative
i.
Glucose and Oxygen
ii.
More ATP produced in each cycle
1. More mitochondria than glycolytic fibers
a. ATP produced here with oxygen
iii.
More resistant to fatigue
b. Anaerobic Respiration - Glycolytic
i.
Glycolysis
ii.
Less ATP produced in each cycle
iii.
Fatigue at a quicker rate
Three Types of Skeletal Muscle Fibers
Most skeletal muscle contains all three types in varying proportions.
(Shown in order of least to most fatiguing and slow to fastest fibers)
1. Slow Oxidative (SO) Fiber
a. Aerobic Respiration to produce ATP
i.
Glucose and Oxygen
b. Slow Contractions
c. Fatigues least of all fibers
2. Fast Oxidative (FO) Fibers
a. Aerobic Respiration to produce ATP (primary source)
i.
Glucose and Oxygen
b. May switch to Anaerobic Respiration for ATP
i.
Glycolysis
c. Fast Contractions
d. Fatigues faster than SO fibers
3. Fast Glycolytic (FG) Fibers
a. Anaerobic Respiration (primary source) of ATP
b. Fastest contractions (fast or fastest?)
c. Fatigues faster than SO and FO
Slow Oxidative (SO)Fibers
1. Useful in:
a. Maintaining posture
b. Producing isometric contractions
c. Stabilizing bones and joints
2. Sustained muscle activity over long periods of time
3. Fibers have a small diameter
4. Does not produce large amount of tension
5. Capable of contracting for long periods (less fatigue) due to large ATP amount
6. Oxidative (SO) fibers have more mitochondria than in glycolytic fibers
a. Produces the most ATP per cycle
7. Extensively supplied with blood capillaries for oxygen requirement
8. SO fibers store Myoglobin
a. Oxygen carrying molecule
b. Give SO fibers a Red Color
Fast Oxidative (FO) Fibers
1. Useful in:
a. Walking
b. Functions more than posture, but less than sprinting
i.
More tension than SO fibers
ii.
More fatigue resistant than FG fibers
2. Also called Intermediate Fibers
a. Characteristics between slow and fast fibers
3. Produce ATP more quickly than SO fibers
4. Primarily Aerobic, but also used Anaerobic metabolic pathways
5. Producing high amounts of tension
6. Does not have significant amount of Myoglobin
a. Gives FO fibers a lighter color than SO fibers
Fast Glycolytic (FG)Fibers
1. Useful in sprinting and quick, and short movements
a. Rapid forceful contractions
b. Fatigues quickly
2. Primarily use Anaerobic Respiration (Glycolysis) as ATP source
3. Large diameter fibers
4. High levels of tension
5. High amounts of glycogen
a. Used in glycolysis to quickly produce ATP
6. Insignificant amounts of mitochondria and myoglobin
a. Gives FG fibers a lighter color than FO fibers
Slow Oxidative
Fast Oxidative
Fast Glycolytic
Metabolic Pathway
Aerobic
Aerobic/Anaerobic
Anaerobic
Contraction Speed
Slow.
Fast.
Fastest.
Strength/Tension
Low.
Med.
High.
Endurance
High.
Med.
Low.
Fiber Size
Small.
Med.
Large.
Myoglobin/Color
Red
Pink
White
CH 9.14 Smooth Muscle
Smooth Muscle
1.
2.
3.
4.
5.
6.
Named due to lack of striations
Spindle shaped (thin-wide-thin)
Single nucleus
Produce endomysium CT
30 to 200 mcm (1000's times shorter than skeletal fibers (cells)
Stimulated by:
a. Pacesetter cells by the autonomic NS
b. Hormones
c. Spontaneously
d. Stretching
7. Some smooth muscle cells have latch-bridges
a. Slow-cycle cross-bridges
b. No need for ATP
8. Present in:
a. Walls of hollow organs
i.
Urinary bladder
ii.
Uterus
iii.
Stomach
iv.
Intestines
b. Walls of passageways
i.
Arteries
ii.
Veins of the circulatory system
c. Tracts of:
i.
Respiratory system
ii.
Urinary system
iii.
Reproductive system
d. Eyes
i.
Changes size of iris
ii.
Alters shape of the lens
e. Skin
i.
Erects hair for fear / temperature
Smooth Muscle Cell Makeup
1. Actin and Myosin filaments are present, not in striated patterns
a. Thin and thick contractile proteins present in random order
2. Dense bodies anchor thin actin filaments at ends
a. Analogous to Z-Discs of a sarcomere in skeletal and cardiac muscle
3. Calveoli: SR membrane indentations
a. Calcium ions supplied by SR from extracellular fluid through calveoli
4. Calmodulin
a. Regulatory protein controls the cross-bridge formation
b. Troponin is absent in smooth muscle
Smooth Muscle Fiber Contractions
1. Ca2+ ions pass through calcium channels in the sarcolemma
a. Additional Ca2+ released from SR
2. Ca2+ binds to Calmodulin
3. Calcium-Calmodulin Complex
a. Activates Myosin Kinase
4. Myosin (light chain) Kinase
a. Activates Myosin heads
i.
Converts ATP to ADP and Pi
ii.
Pi attaches to the myosin head
5. Myosin head attached to actin binding sites and pulls actin filaments
6. Actin filaments (attached to dense bodies), are pulled center
a. Dense bodies are tethered to the sarcolemma
7. Entire muscle fiber is contracted by ends pulled center
a. Midsection bulges center in corkscrew motion
Single Unit Smooth Muscle
1. Contains Gap Junctions
a. Synchronizes membrane depolarization
b. Muscle contracts as a single unit
2. Permits muscle to stretch, contract and relax as the organ expands
3. Found in:
a. Walls of the viscera (visceral muscle). Organs
Multiunit Smooth Muscle
1. Cells DO NOT have Gap Junctions
2. Contracting does not spread between cells
CH 9.15 Interactions of Skeletal Muscles
Interactions of Skeletal Muscles
1. Skeleton movement is created by the contraction of muscle fibers (cells)
2. Skeletal muscles have an origin and an insertion
3. Tension is transferred from muscle to tendons to move bone
a. Tendons are strong bands of dense regular CT
b. Attaches muscle to bone
4. Most skeletal muscles must be attached to a fixed part of the skeleton
5. Facial muscles (produce facial expressions) do not attached to bone
a. Insertions and Origins are in the skin
b. Muscles contract to:
i.
Smile or frown
ii.
Form sounds and words
iii.
Raise the eyebrows
6. Other skeletal muscles that do not move the skeleton
a. Tongue
b. External urinary sphincter
c. External anal sphincter
d. Diaphragm
i.
Contracts and relaxes to change the volume of air
ii.
Does not move the skeleton
Key Terms for Skeletal Muscle Movement
1. Insertion
a. Moveable end of muscle, attached to the bone being pulled
2. Origin
a. End of muscle that is fixed / stabilized to a bone
3. Prime Mover / Agonist
a. Principal muscle used in movement
i.
Multiple muscles can be involved in a movement action
4. Synergist
a. Assists the Agonist
5. Fixator
a. A synergist that makes the insertion site more stable
b. Stabilizes a bone that is the attachment point for the prime mover
Antagonist
a. Muscle with the opposite action of the prime mover
b. e.g.: extending the knee
i. Quadriceps are activated = Agonist
1. Pulls lower leg straight at the knee
ii. Hamstrings are activated = Antagonist
1. Releases tension keeping the leg bent
c. Antagonist play two roles
i. Maintains body or limb position
1. Holding the arm out
2. Standing erect
ii. Control rapid movement
1. Shadowboxing without landing a punch
2. Ability to check the motion of a limb
Muscle Compartmental Organization
Skeletal muscle is enclosed by CT at three levels:
1. Endomysium
a. Covers each muscle fiber (cell)
2. Perimysium
a. Covers each fascicle (bundled group of muscle fibers)
b. Fascicle
i.
Bundled group of muscle fibers
ii.
Fascicle arrangement is correlated to the force generated by the muscle
iii.
Affects the range of motion of the muscle
3. Epimysium
a. Covers the entire muscle
Classifications of Common Fascicle Arrangements
Each arrangement has its own range of motion and ability to do work
1. Parallel
a. Fascicles arranged in the same direction of the muscle of the long axis
b. Majority of skeletal muscles are arranged in this fashion
c. e.g. Sartorius
i.
Fusiform / belly
1. Central Body
a. Plump with a large mass in the middle between insertion and origin
b. Ends are tapered
2. Circular (sphincters)
a. Concentrically arranged bundles
b. When relaxed, opening size is increased
c. When contracted, opening shrinks to closure
i.
e.g. Orbicularis oris (mouth)
1. Contracts: oral opening is smaller (pucker, whistle)
ii.
e.g. Orbicularis oculi (eye)
1. Surrounds each eye
3. Convergent
a. Widespread, expanded muscle, at a smaller common attachment
b. Attachment points: tendon, aponeurosis (flat, broad tendon), or a raphe (slender tendon)
i.
e.g. Pectoralis major (large chest muscle)
1. Converges on the greater tubercle of humerus via tendon
ii.
e.g. Temporalis of the cranium
4. Pennate (feathers)
a. Fascicles blend into a central tendon that runs the length of the muscle
b. Muscle fibers can only pull at an angle, only allowing a small movement
c. Holds more muscle fibers, producing more tension for its size
d. 3 Sub types:
i.
Unipennate
1. Fascicles located on one side of central tendon
a. e.g. Extensor digitorum (forearm)
ii.
Bipennate
1. Fascicles on both sides of central tendon
iii.
Multipennate
1. Muscle fibers wrap around the tendon, forming individual fascicles
2. Allows for movement in multiple directions
a. e.g. Deltoid
i.
Fibers cover the shoulder, but have a single tendon insertion on the
deltoid tuberosity of the humerus
ii.
Deltoid abducts
iii.
Deltoid abducts and flexes when anterior fascicles are stimulated:
abducts and flexes (arm raises and moves anteriorly)
5. Triangular
Lever System of Muscle and Bone Interactions
1. Muscles are arranged in pairs based on functions
2. Muscle to bone connection depends on:
a. Force
b. Speed
c. Range of motion
CH 9.16 Naming Skeletal Muscles
Naming Skeletal Muscles
1. Named based on
a. Location and size
i.
e.g. Gluteus maximus and gluteus minimus
b. Bone association and location in the body
i.
e.g. Tibialis anterior
c. Fascicle direction
i.
e.g. Abdominal muscles
1. Rectus (straight) abdominis
2. Oblique (angle) abdominis
3. Transverse (across) abdominis
d. Origin/how many origins
i.
Biceps brachii
1. Bi: muscle has two origins
ii.
Triceps brachii
1. Tri: muscle has three origins
e. Insertion
i.
Pectoralis major
f. Shape
i.
Orbicularis
g. Length
i.
Brevis: short
ii.
Longus: long
h. Position relative to the midline
i.
Lateralis: outside of midline
ii.
Medialis: toward the midline
i. Location of a muscles attachments
i.
Origin is always named first, then insertion
1. Sternocleidomastoid
a. Dual Origin: Sternum and Clavicle
b. Insertion: Mastoid process of the temporal bone
j. Movement
i.
Flexor
1. Decreases angle at joint (flexes)
ii.
Extensor
1. Increases angle at joint (extends)
iii.
Abductor
1. Moves bone away from the body
iv.
Adductor
1. Moves bone toward the midline
k. Groups, Number of muscles
i.
Quadriceps
1. Group of 4 muscles in the anterior thigh
Mnemonic Device for Latin
Roots
Example
Latin or Greek
Translation
Mnemonic Device
ad
to; toward
ADvance toward your goal
ab
away from
n/a
sub
under
SUBmarines move under water.
ductor
something that moves
A conDUCTOR makes a train move.
anti
against
If you are antisocial, you are against engaging in
social activities.
epi
on top of
n/a
apo
to the side of
n/a
longissimus
longest
“Longissimus” is longer than the word “long”
longus
long
Long
brevis
short
Brief
maximus
large
Max
medius
medium
“Medius” and “medium” both begin with “med”
minimus
tiny; little
Mini
rectus
straight
To RECTify a situation is to straighten it out
multi
many
If something is MULTI-colored, it has many
colors
uni
one
A UNIcorn has one horn
bi/di
two
If a ring is DIcast, it is made of two metals
tri
three
TRIple the amount of money is three times as
much
quad
four
QUADruplets are four children born at one birth
externus
outside
External
internus
inside
Internal