Practical Exam 2 - AOIs and Muscles Flashcards
Sartorius AOI
Action: Flexion of thigh and lateral rotation of femur
Origin: Anterior superior iliac spine
Insertion: Proximal shaft of tibia
Adductor Magnus AOI
Action: Adduction and extension of thigh
Origin: Pubis and Ischium
Insertion: Gluteal tuberosity and linea aspera (femur)
Adductor Longus and Brevis AOI
Action: Adduction of thigh
Origin: Body and inferior ramus (pubis)
Insertion: Linea aspera
Rectus Femoris (quadriceps) AOI
Action: Extension of leg; Flexion of thigh
Origin: Anterior inferior iliac spine
Insertion: Patella and tibial tuberosity
Vastus Lateralis (quadriceps) AOI
Action: Extension of leg
Origin: Greater trochanter (femur)
Insertion: Patella and tibial tuberosity
Vastus Medialis (quadriceps) AOI
Action: Extension of leg
Origin: Intertrochanteric line and linea aspera (femur)
Insertion: Patella and tibial tuberosity
Vastus Intermedius (quadriceps) AOI
Action: Extension of leg
Origin: Anterolateral shaft of femur
Insertion: Patella and tibial tuberosity
Tensor Fascia Latae AOI
Action: Flexion, abduction, and medial rotation of thigh
Origin: Anterior superior iliac spine
Insertion: Iliotibial tract
Gluteus Medius AOI
Action: Abduction of thigh
Origin: Ala (ilium)
Insertion: Greater trochanter (femur)
Gluteus Maximus AOI
Action: Extension, lateral rotation, and abduction of thigh
Origin: Ala (ilium); Sacrum; Coccyx
Insertion: Gluteul tuberosity (femur)
Biceps Femoris (hamstrings) AOI
Action: Flexion of leg; Extension of thigh
Origin: Ischial tuberosity
Insertion: Head of fibula
Semitendinosus AOI
Action: Flexion of leg; Extension of thigh
Origin: Ischial tuberosity
Insertion: Proximal shaft of tibia
Semimembranosus AOI
Action: Flexion of leg; Extension of thigh
Origin: Ischial tuberosity
Insertion: Medial condyle (tibia)
Fibularis (Peroneus) Tertius AOI
Action: Dorsiflexion and eversion of the foot
Origin: Fibula; Interosseus membrane
Insertion: Metatarsal V
Fibularis (Peroneus) Brevis AOI
Action: Plantar flexion and eversion of foot
Origin: Distal shaft of fibula
Insertion: Metatarsal V
Fibularis (Peroneus) Longus AOI
Action: Plantar flexion and eversion of foot
Origin: Proximal shaft of fibula
Insertion: Metatarsal I; Medial cuneiform
Gastrocnemius (medial and lateral head) AOI
Action: Plantar flexion of foot; Flexion of leg
Origin: Medial and lateral condyles (femur)
Insertion: Calcaneus
Plantaris AOI
Action: Plantar flexion of foot; Flexion of leg
Origin: Distal shafts of tibia and fibula
Insertion: Calcaneus
Soleus AOI
Action: Plantar flexion of foot
Origin: Proximal shafts of tibia and fibula
Insertion: Calcaneus
Flexor Digitorum Longus AOI
Action: Plantar flexion and inversion of foot; Flexion of toes II-V
Origin: Mid-shaft of tibia
Insertion: Distal phalanges II-V
Anterior View of Thigh (Muscles found and what they are)
- Sartorius
- Adductor magnus
- Gracilis
- Rectus femoris
- Vastus lateralis
- Vastus medialis
- Vastus intermedius
- Tensor fasciae latae
https://imgs.search.brave.com/8ZUPeQNZTfc-LSdCQ92cWW002TBZ0bjmG4kBYUvhNcs/rs:fit:860:0:0:0/g:ce/aHR0cHM6Ly93d3cu/ZWFydGhzbGFiLmNv/bS93cC1jb250ZW50/L3VwbG9hZHMvMjAx/Ny8wNy9hbnRlcmlv/ci10aGlnaC5qcGc
https://assets.coursehero.com/study-guides/lumen/images/ap1x94x1/muscles-of-the-hips-and-thighs/Thigh-anterior-muscles-855x10242.png
Posterior View of Thigh (Muscles found and what they are)
- Gluteus maximus
- Gluteus medius (only cat)
- Biceps femoris (hamstrings)
- Semitendinosus
- Semimembranosus
https://upload.wikimedia.org/wikipedia/commons/thumb/7/70/Posterior_Hip_Muscles_3.PNG/250px-Posterior_Hip_Muscles_3.PNG
https://www.physio-pedia.com/images/0/02/Hamstring_tendons.png
Anterior View of Lower Leg (Muscles found and what they are)
- Tibialis anterior
- Fibularis longus
- Extensor digitorum longus
- Extensor hallucis longus (only cat)
- Fibularis brevis (only human)
https://imgs.search.brave.com/cQ05gH0fFdMptCMFjPloPTQvgV6MlWzcIxiOJtwnF7k/rs:fit:500:0:0:0/g:ce/aHR0cHM6Ly9zaW1w/bGVtZWQuY28udWsv/aW1hZ2VzL0FudGVy/aW9yX0xlZ19NdXNj/bGVzLmpwZw
https://imgs.search.brave.com/1i1uVybwfijgL6GGX0bJIzNMLUTYenzSZQuiO69tkic/rs:fit:500:0:0:0/g:ce/aHR0cHM6Ly9jZG4u/bGVjdHVyaW8uY29t/L2Fzc2V0cy9BbnRl/cmlvci12aWV3LW9m/LXRoZS1sZWctZmVh/dHVyaW5nLXRoZS1t/dXNjbGVzLW9mLXRo/ZS1hbnRlcmlvci1j/b21wYXJ0bWVudC1h/bmQtdGhlaXItcmVs/YXRpb25zLXdpdGgt/b3RoZXItbXVzY2xl/cy1hbmQtZWFjaC1v/dGhlci5wbmc
Posterior View of Lower Leg (Muscles found and what they are)
- Gastrocnemius
- Plantaris (only cat)
- Soleus
- Flexor digitorum
- Flexor hallucis longus (only cat)
https://teachmeanatomy.info/wp-content/uploads/Muscles-in-the-Superficial-Layer-of-the-Posterior-Leg-600x632.jpg.webp
https://teachmeanatomy.info/wp-content/uploads/Muscles-in-the-Deep-Layer-of-the-Posterior-Leg-600x739.jpg.webp
Skeletal muscle components
Each muscle is made of individual muscle fibers (muscle cells) organized by fascicles;
Epimysium surrounds muscle bundles of fascicles; Perimysium surrounds individual fascicles; Fascicles made of individual muscle fibers; Endomysium surrounds individual muscle fibers
Muscle components: Smallest to largest
Myofilament
Sarcomere (series of myofilaments in a specific pattern)
Myofibril (bundle of sarcomeres)
Muscle fiber or myocyte (contains multiple myofibrils)
Fascicle (bundle of muscle fibers)
Skeletal muscle (composed of multiple fascicles)
Upper motor neuron lesions
Strokes damaging neurons in the brain leading to a loss of motor function
Excitability
An electric charge differential which can be changed upon stimulation (such as through neurotransmitter binding) to ultimately produce an intracellular muscle response; All muscle cell membranes possess this
Contractility
All muscle cells shorten when stimulated
Extensibility
All muscle cells can be stretched, sometimes more than their resting length
Elasticity
All muscle cells, after being stretched, can recoil to the resting cell length
An entire skeletal muscle (like the gastrocnemius) is an…
An entire skeletal muscle (like the gastrocnemius) is an organ that contains nerves, blood vessels, and connective tissue, as well as muscle fibers
Where do blood vessels enter the muscle
Blood vessels enter the muscle near its centre and then branch throughout the muscle running through the connective sheaths (epimysium, perimysium, and endomysium)
Tendons
Connective tissues that attach muscle to bone; Connective tissue sheaths of muscle are continuous with each other and with tendons to transfer the force of contracting muscle fibers to the structure to be moved; Cylindrical shaped or rope-like
Insertion
The bone or structure that is moving
Origin
The bone or structure that mostly does not move
Direct attachment
If periosteum (membrane surrounding bones) or perichondrium (connective tissue surrounding cartilage of developing bone) is fused with the muscles epimysium
Indirect attachment
More durable, smaller, and more common; A tendon or aponeurosis
Aponeurosis
Flat, tendon-like connective tissue that connects muscles to other muscles, skin, or bones
Tendons vs aponeurosis
Tendons: Mostly collagen; rope-like extensions of a muscles connective tissue
Aponeurosis: Sheet-like extension that connects to other muscles
Antagonistic
Two or more muscles usually work antagonistically; As one muscle contracts and shortens, its antagonist relaxes and elongates
Ex: Curling a dumbbell towards you contracts your biceps as your triceps relax, and bringing your arm away from you contracts your triceps as your biceps relax
Muscle cell components
Large multinucleated cells; Contains sarcolemma, sarcoplasm, myoglobin, glycosomes
Sarcolemma
Plasma membrane of a muscle fiber
Sarcoplasm
Cytoplasm of a muscle fiber
3 ways to refer to a muscle cell
Myocyte
Myofiber
Skeletal muscle cell
Myoglobin
Muscle cells contain a lot of myoglobin; Stores oxygen
Glycosomes
Muscle cells contain a lot of glycosomes; Granules of glycogen that ca be broken down to supply ATP from glucose for energy
Myofibril
Repeating units of sarcomeres; Takes up most of the intracellular volume; Organelles of skeletal muscles
Sarcomere
Smallest “atomic” contractile units of skeletal muscle fibers
Why are skeletal muscles straited?
Dark A bands and light I bands within sarcomeres that are perfectly lined beside one another
Sarcomere contains:
I-band
A-band
H-band
Z-line
M-line
I-band
Lightest areas of sarcomere; Only made of thin filaments composed of actin
A-band
Darkest areas of sarcomere; Composed of myosin and actin
H-band
Area within A-band; Composed of only thick filaments made of myosin
Z-line
Defines boundary of sarcomere and bisects I-band and neighboring sarcomeres; Sarcomere runs from Z-line to Z-line
M-line
Center of sarcomere to which myosin bind
Thick filaments
Contain protein myosin and run the length of the A band; M-line connects thick filaments; Thick filaments only have myosin heads in areas where actin proteins of the thin filament and the myosin heads of the thick filament overlap; Each thick filament contains over 300 myosin molecules
Myosin heads
Myosin proteins contain protruding globular heads and each head associates with two light chains; When a muscle contracts, the globular myosin heads link the thick and thin filaments together making cross bridges and swivel as motors to create force that shortens the sarcomere
Thin filament
Consists of a helix of two actin subunit strands and the proteins tropomyosin and troponin; Each actin subunit is a globular actin and contains active sites where myosin heads attach
What do troponins three globular polypeptides do
Each have a different function
1) Binds actin
2) Binds tropomyosin
3) Calcium ions bind with the last; Sandwiched between the other two troponin polypeptides
Elastic filaments
Composed of the protein titin; Run from the Z-line to the thick filaments to hold them in place and provide flexible recoil to the sarcomere as it contacts, relaxes, and stretches; When titin reaches its normal extension, it stiffens and resists further over-stretching of the muscle
Sarcoplasmic reticulum
Smooth endoplasmic reticulum; Interconnects and surrounds each myofibril; Forms terminal cisterns; Highly abundant mitochondria and glycogen granules found near; Controls calcium levels within the sarcoplasm and stores and releases calcium to control muscle fiber contraction
Terminal cisterns
Large perpendicular cross channels formed by the sarcoplasmic reticulum at the A band I band junction; Always found in pairs
T tubules
Elongated tubular extensions of the sarcolemma dive deeply into the cell; Found at A band I band junctions
Triad
T tubule with terminal cisterns on both sides
Electrical signals and t tubules
When a nerve stimulates a muscle, an electrical signal travels down the sarcolemma, and since T tubules are tubular extensions of the sarcolemma, the electrical signal can be carried deep into the muscle to every sarcomere; Electrical signal causes the release of calcium from the terminal cisterns which leads to contraction
Integral proteins of t tubules and terminal cisterns
Both t tubules and the terminal cisterns have integral membrane proteins that protrude into the space between these structures; Integral proteins of t tubules function as voltage sensors while the integral proteins of the terminal cisterns create gated channels for the release of calcium
Polarization
Inside of the cell is more negative relative to the outside; All plasma membranes of all human cells carry this and resting charge
Step 1 of the initiation and propagation of muscle cell action potential
Acetylcholine binds to its receptor opening chemical ligand-gated ion channels for sodium; These events transiently make the inner surface of the sarcolemma less negative (depolarization) and is termed the End Plate Potential
Step 2 of the initiation and propagation of muscle cell action potential
Voltage-gated sodium channels on the surrounding sarcolemma respond to the change in charge and open allowing positive sodium to enter down its electrochemical gradient; Once a threshold potential is achieved, the voltage change in the membrane becomes sufficient to open further voltage-gated sodium channels and spread the signal in the form of depolarization wave along the sarcolemma termed a Muscle Action Potential
Step 3 of the initiation and propagation of muscle cell action potential
Once the voltage becomes sufficiently positive, the voltage-gated sodium channels close, and the voltage-gated potassium channels open; The membrane then becomes more negative (repolarizes) as positive potassium exits the cell down its concentration gradient; Once the membrane becomes sufficiently negative again, this change in charge closes the voltage-gated potassium channels
Gradient differences for sodium and potassium are restored by…
Gradient differences for sodium and potassium are restored by a sodium potassium ATPase pump that moves sodium out and potassium in
Refactory period
While repolarizing, the cell cannot be stimulated again until the membrane is sufficiently negative
Electrical signal vs muscle contraction
The electrical events leading to muscle contraction happens in about 1 millisecond, but the consequential contraction may last for more than 100 times the duration of the electrical signal
Summary of entire action potential process
Action potential travels down sarcolemma and down t tubules where depolarization causes voltage-sensitive tubule proteins to undergo a change in shape which leads to the opening of calcium release channels in the terminal cisterns
Calcium moves into sarcoplasm where it removes inhibitory action of tropomyosin as calcium binds to troponin causing the troponin to change shape which moves tropomyosin away to expose the binding active sites for myosin on the actin thin filaments
Myosin binds and cross-bridge cycling commences
When the membrane repolarizes, the voltage sensitive tubule proteins regain their resting configuration which consequently closes the calcium release channels of the terminal cisterns
Calcium is actively pumped back into the sarcoplasmic reticulum by ATP dependent calcium pumps embedded within the terminal cistern membrane
Once calcium levels drop, the inhibitory effect of tropomyosin is restored such that actin and myosin no longer cross bridge, leading to muscle relaxation
Excitation-contraction coupling
A physiological process that links the electrical stimulation of a muscle fiber to its mechanical contraction; While muscle contraction is the ultimate outcome of ECC, the process itself involves a complex series of events that occur at the molecular and cellular levels; Events of the contraction of the muscle
1) Action potential generation
2) Electrical stimulation
3) Depolarization
4) Calcium release
5) Calcium binding to troponin
6) Cross-bridge cycling
7) Relaxation
Tropomyosin vs troponin
Tropomyosin: Blocks binding active sites on actin so myosin cant bind
Troponin: Calcium binds with troponin causing it to change shape and move tropomyosin away to expose binding sites
Calcium
Depolarization: Calcium release channels open in terminal cisterns and calcium moves into sarcoplasm
Binding: Calcium binds with troponin causing tropomyosin to expose actin binding sites for myosin heads
Repolarization: Calcium release channels close and Calcium is pumped back into sarcoplasmic reticulum by ATP dependent calcium pumps within terminal cistern membrane
Levels drop: Once calcium levels drop, inhibitory effect of tropomyosin is restored, halting cross bridging and leading to muscle relaxation
Cross bridge cycling
Occurs multiple times during a singular muscle contraction;
1) Binding: Tropomyosin physically blocks myosin binding active sites on actin when intracellular calcium is low; As calcium rises intracellularly, it binds to troponin; Once two calcium ions bind to troponin, it changes shape which forces tropomyosin to change position into actin helix groove thus unblocking the myosin binding sites on actin
2) Power Stroke: Power stroke occurs where inorganic phosphate and ADP are released from myosin head allowing myosin to switch to low energy state; This pulls actin filament towards M line
3) Detaching: ATP binds with myosin head causing myosin head to detach
4) Cocking: Hydrolysis of ATP into ADP and inorganic phosphate repositions myosin head in its high energy configuration
When nerve impulses arrive at muscle in rapid succession, intracellular calcium quickly elevates and is sustained leading to another contraction before the muscle was completely relaxed; Next contraction will be stronger and/or more sustained
Power Stroke
Phosphate and ADP are released from the myosin head when myosin binds to actin; Results in the myosin to swivel or stroke from its high energy configuration to a low energy state; This pulls the actin filament toward the M line
Muscle tension
The force exerted by a contracting muscle on an object
Load
The opposing force applied on the muscle by the mass of the object being moved
Each individual muscle fiber is innervated by
Each individual muscle fiber is innervated by a branch of a motor axon
Neuronal action potential
Activates all of the muscle fibers innervated by the motor neuron and its axonal branches
Motor unit
The motor neuron combined with all of the individual muscle fibers it innervates; Smaller the motor unit, the finer the control of movement in that muscle; Thus, the muscles controlling the movements of fingers and eyes have small motor units, whereas those controlling the large limb muscles may have very large motor units
Regardless of the number of muscle fibers controlled within a motor unit, a specific motor unit contains…
Regardless of the number of muscle fibers controlled within a motor unit, a specific motor unit contains only one neuron
The muscle fibers from a single motor unit are typically…
The muscle fibers from a single motor unit are typically spread throughout the entire muscle (not clustered together) thus allowing graded control of the entire muscle and not just a small portion of it
The activation process of motor neurons involves…
The activation process of motor neurons involves the initiation of an action potential along with the axon of a neuron; The axon can branch many times, with each branch synapsing with each muscle fiber controlled by that particular neuron; This causes nearly simultaneous activation of all synapses and thus nearly simultaneous contraction of all muscle fibers
Sliding Filament Model of Contraction
During a muscle contraction, the thick and thin filaments do not change length; Instead thin filaments are pulled past the stationary thick filaments by the power stroke; Since the thin filaments are directly attached to the z-lines, the z-lines of each sarcomere are pulled toward the M-line, thus shortening the sarcomere
Occurs as myosin power strokes, releases, attaches again, and then repeats these steps
Overlapping within muscles
Relaxed muscle fiber: Thich and thin filaments overlap only at the ends of A bands
Contraction: Overlap increases past the ends of A bands at the expense of the H zone and the I bands; This pulls Z lines towards M line, however the A bands do not change in length
How are sliding filaments for contraction accomplished
Accomplished upon nervous stimulation of the muscle leading to increased sarcoplasmic calcium concentrations and latching of the thick filaments to myosin-binding sites of thin filament actin
Skeletal muscles contract when
Skeletal muscles contract when a motor nerve stimulates an electrical action potential that propagates along the sarcolemma leading to brief rises in intracellular calcium resulting in completion of excitation-contraction coupling
Somatic motor nuerons
Activate skeletal muscle; Cell bodies are located in the brain or spinal cord; Axons are usually bundled together to form a nerve and extend to the muscle they innervate; Once an axon from a nerve enters a muscle, it divides into several axonal branches which service the muscle fibers
Neuromuscular junction
A chemical synapse between a motor neuron and a muscle fiber that allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction; Each muscle fiber has only one neuromuscular junction, or motor end plate, about halfway down the muscle fiber, where the nerve communicates to the muscle; Sarcolemma at neuromuscular junction is greatly folded to increase surface area for an abundance of acetylcholine receptors
Synaptic end bulb
Axon terminal; End of the axon; Contain an abundance of synaptic vesicles that are filled with the neurotransmitter (ACh)
Synaptic cleft
The space between the axon terminal and the muscle fiber; Filled with extracellular fluid containing collagen fibers and glycoproteins
Nerve action potential leads to
1) When a nerve action potential traverses the axon and reaches the axon terminal, depolarization of the axon terminal membrane leads to a calcium influx in the axon terminal which, in turn, leads to the synaptic vesicles fusing with the axon terminal membrane to release acetylcholine into the synaptic cleft; The electrical signal traveling down the nerve is converted to a chemical signal
2) The acetylcholine then diffuses across the synaptic cleft to bind to the acetylcholine receptors on the junctional folds of the sarcolemma; Activation of the acetylcholine receptors opens channels that allow sodium influx into the muscle fiber depolarizing the sarcolemma and causing a muscle action potential; The chemical signal is converted back to an electrical signal
3) The depolarization travels down the sarcolemma in all directions from the neuromuscular junction and down the t tubules leading to the calcium release from the sarcoplasmic reticulum causing muscle contraction
Acetylcholinesterase
Found in synaptic cleft; Breaks down acetylcholine to acetic acid and choline to terminate the signal allowing for fine control of muscle activation
Contraction
Refers to the activation of actin-myosin cross bridges; Does not always shorten the muscle; Can either be isotonic or isometric
Isotonic
During isotonic exercises, the muscles contract but joints do not move and muscle fibers maintain a constant length; Exercises are performed against an immovable surface; During isotonic exercises, a body part is moved and the muscle fibers shorten or lengthen; Isotonic contractions help to maintain an upright balanced posture and stabilize joints
Isometric
In isometric contractions, the thin filaments do not move while the cross bridges form to generate force; Muscle tension remains constant but the muscle length changes
Concentric
Isotonic contractions are concentric if the muscle length decreases; Example would be the biceps when curling a barbell
Eccentric
Isotonic contractions are eccentric if muscle length increases during contraction; Example would be uncurling the barbell by extending your arm from original curled position
What happens at neuromuscular junction
Action potentials arriving at axon terminal trigger the release of acetylcholine into the synaptic cleft of the neuromuscular junction; Acetylcholine diffuses through junctional cleft and binds to acetylcholine gated receptors on motor end plate; Bound receptors open cation-selective ion channels, which depolarizes the muscle end plate and leads to the release of calcium from the sarcoplasmic reticulum; Increases cytosolic calcium sets in motion the biochemical events that underlie contraction
Acetylcholine
Rapidly hydrolyzed by acetylcholinesterase
EMG
Electromyogram; Extracellular recording of electrical activity in a whole muscle; Activation of one or more motor units in a muscle produces an electrical event that is often sufficiently large to be detectable with electrodes applied to the skin surface
CMP
Compound muscle potential; Observed in an EMG; The sum of the electrical activity of many individual muscle fibers, all firing at once
Magnitude of CMP
Reflects the number and size of motor units that are active
Muscle twitch
A motor units reaction to a single action potential of its motor neuron; Made of three parts or periods: Latent period, period of contraction, and period of relaxation
Period of latency
First part of of a muscle twitch; Excitation-coupling occurs; Cross bridges are beginning to form, but measurable tension is not yet achieved; The greater the load that is applied to a muscle, the longer the latent period will be
Period of contraction
Lasts once tension is measurable until tension peaks; During this time, cross bridges are cycling; The muscle will shorter as the force is being generated by the contraction exceeds the resistance applied to the muscle
Period of relaxation
Occurs when calcium levels drop in the sarcoplasm; Number of cycling cross bridges decreases and tension declines; A muscle can contract rapidly but will relax more slowly in comparison
Why do some muscles twitch and relax more rapidly than other muscles?
Due to differences in the enzyme composition and metabolic properties of different muscles in the body; Example: lateral rectus eye muscle twitches and relaxes more rapidly than the slower soleus muscle
How do axons control movement
A whole muscle is controlled by firing up to hundreds of motor axons; These axons control movement in a variety of ways to produce smooth strength graded muscle responses: Recruitment, Henneman’s size principle, and frequency of action potentials
Recruitment
A way the nervous system controls a muscle; Adjusts the number of motor axons firing, thus controlling the number of twitching muscle fibers
Henneman’s size principle
Central nervous system signals small motor units to be recruited first followed by larger and larger motor units as the stimulus increases until all motor units are recruited; As stimulus strength increases so does the muscle contraction until a maximum contraction is reached at which a maximal stimulus stimulates the muscle to contract with as much force as possible and higher stimuli do not increase the strength of contraction; Explains how the same muscle can control fine delicate movements and also perform powerful heavy maneuvers
Low threshold vs high threshold motor neurons
Henneman’s size principle; Low threshold, easily excitable motor neurons control small motor units, and high threshold, least excitable motor neurons control large motor units
Frequency of action potentials
Nervous system controls muscle contraction by varying the frequency of action potentials in the motor axons; Stimulation intervals greater than 200ms, between 200 and 75ms, higher stimulation frequencies, and even higher stimulation frequencies
Stimulation interval greater than 200ms
Intracellular calcium is restored to baseline levels between action potentials and contraction consists of separate twitches
Stimulation intervals between 200 and 75ms
Calcium in muscle is still above baseline levels when next action potential arrives; Muscle fiber is not completely relaxed and the next contraction is stronger than normal; Summation
Unfused or incomplete tetanus
Higher than 75ms; Degree of summation increases leading to sustained graded contractions that can increase in size and length
Complete tetanus
Even higher than 75ms; Muscle has no time to relax at all between successive stimuli leading to a smooth contraction many times stronger than a single twitch; Tetanic contraction
Baseline tone
Skeletal muscle maintains a baseline tone where relaxed muscle will be in a state of higher contraction; This does not give rise to movements but keeps muscles healthy, firm, and primed to respond
Electromygraphy
A technique that measures the electrical activity of muscles and nerves controlling the muscles; Data recorded is an EMG; Size and shape of waveform measured provides information about ability of muscle to respond when nerves are stimulated; Used when people have symptoms of weakness and examination shows impaired muscle strength; Can also help to differentiate muscle weakness caused by neurological disorders from other conditions
Function of EMG
Provides a depiction of the timing and pattern of muscle activity during complex movements; Raw surface EMG signal reflects the electrical activity of the muscle fibers active at that time; Motor units fire asynchronously and it is possible to detect the contributions of individual motor units to the EMG; As strength of muscle contraction increases, intensity of action potentials increase and the raw signal may represent the electrical activity of thousands of individual fibers
Coactivation
A phenomenon in which contraction of the muscle leads to some minor contractile activity in the antagonist muscle; Likely helps to stabilize the joint and generate smooth contractions and relaxations against the load on the muscle
ATP generation mechanisms
1) Creatine phosphate directly phosphorylating ADP to ATP
2) Anaerobic glycolysis
3) Aerobic respiration
Creatine phosphate
Interacts with ADP to transfer a phosphate and energy to the ADP to form ATP and creatine; Muscles store up to 3 times more creatine phosphate than ATP; Stored ATP and creatine phosphate can power a muscle for only about 10 seconds during very vigorous activity; Creatine pathway reaction is readily reversible so during periods of rest the muscle will regenerate creatine phosphate by reversing the reaction; Surges of intense activity rely on stored ATP and creatine phosphate
Anaerobic glycolysis
Glycogen from muscle stores will be broken down to glucose and further broken down with glucose from the blood to provide ATP; Glycolysis is first phase of glucose break-down; Does not require oxygen for completion; Glucose is broke down to pyruvate molecules and forms 2 ATP per glucose; At about 70% of maximal contraction, a muscle will become too bulged so it will compress blood vessels decreasing oxygen delivery; When this happens, pyruvate is converted back to lactic acid, which exits the muscle and can be converted by the liver back to glucose; Slightly longer duration but high intensity exercises are powered by mostly anaerobic glycolysis
Aerobic respiration
If sufficient oxygen is available, the pyruvate from the glycolysis will enter the TCA cycle and oxidative phosphorylation in the mitochondria to produce more ATP; Completely breaks down glucose to produce carbon dioxide, water, and about 34 ATP per glucose; Slow because of all steps and intermediates required, but produces many ATP; As long as oxygen is available, muscles will perform aerobic pathways
Anaerobic metabolism
Very fast but does not produce much ATP; Can power muscle for about 40 seconds; Fatty acids can be burned and are a major energy source, especially after 30 minutes of contractile activity; When activity in muscle creates a demand that exceeds the speed that oxidative pathways can be completed, metabolism will switch to anaerobic pathways
Aerobic endurace
The amount of times a muscle can contract using aerobic pathways
Anaerobic threshold
The point at which metabolism in the muscle switches to anaerobic glycolysis
Fatigue
In isolated muscles, depletion of energy and metabolite stores result in fatigue; Ionic imbalances across the muscle cell membranes can also lead to fatigue; Example: potassium accumulation in t tubules can change the membrane potential and disturb calcium release from the terminal cisterns; lactic acid accumulation can also lead to fatigue; Fatigue occurs in muscles faster when have a lower capacity for oxidative metabolism; Fatigue can also occur because the motor drive from the brain is reduced, rather than as a result of an appreciable depletion of the muscle energy reserves
Force of muscle contraction is affected by
The more motor units recruited, the greater the force of contraction; The larger the size of a muscle fiber (greater diameter), the greater the force; Exercise can increase the force of contraction because exercise causes muscle fibers to hypertrophy (increase in size or volume due to enlargement of cells); Contraction summation due to increased stimulation frequency will also increase force of contraction; Extent of stretch to the muscle will also determine contractile strength
Optimal length-tension relationship
At the optimal length-tension relationship, the muscle will be slightly stretched so that the overlap of the thick and thin filaments is optimal; The body joints usually prevent a muscle from being stretched beyond degree at which the thick and thin filaments can overlap
Slow vs fast muscle fibers
Muscles vary in how fast and for how long they can contract before fatigue sets in; The difference between slow and fast fibers is partially determined by the responsiveness of their motor neurons but is largely due to the speed at which myosin ATPases can split ATP in the three muscle fiber types; Contraction duration will be influenced by how fast a muscle type can pump calcium back into the sarcoplasmic reticulum
Oxidative vs glycolic muscle fibers
Muscle fibers can be classified by the metabolic pathway they mainly use during contraction; Oxidative fibers rely mostly on aerobic pathways and glycolic fibers mainly rely on anaerobic glycolysis and creatine phosphate
Muscle fibers are either
Slow oxidative fibers, fast oxidative fibers, or fast glycolic fibers
Fatigue when contracted for prolonged periods of time
Fatigue is correlated with depletion of ATP, nutrients, and oxygen in muscle fibers, but is also due to perception of conditions in the muscle by the brain; The perception of fatigue can be influenced by verbal encouragement
