Musculoskeltal System Flashcards
The Human Body Contains How many Skeletal Miscles
Greater Than 600
What are the 4 Functions of Skeletal Muscle
- Force production for locomotion and breathing
- Force Production for Posture Support
- Heat Production during cold stress
- Endocrine organ that plays a role in regulating other organ systems
Flecked
Decrease joint angle
Extensions
Increase joint angle
The connective Tissue Covering Skeletal Muscle
- epimysium
- Perimysium
- Endomysium
- Basement Membrane
- Sarcolemma
Epimysium
Surrounds entire muscle
Perimysium
Surrounds bundles of muscle fibers
Fascicles
Bundles of muscle fibers
Endomysium
Surrounds individual muscle fibers
Basement Membrane
Just below endomysium providing another protective layer
Sarcolemma
Muscle cell membrane that surrounds the muscle fiber
Satellite cells play a role
in muscle growth and repair
Strength Training causes growth enhancement by
Dividing and increasing the number of nuclei to the existing muscle fiber
More Nuclei Allow for
Greater protein synthesis for muscle growth
Myonuclear domain
The volume of cytoplasm surrounding each nucleus
Each nucleus can support
A limited myopic lead domain
A single nucleus can sustain the necessary gene expression for the production of proteins only for
A limited area of cell volume therefore to maintain a constant myonuclear domain new nuclei are added to muscle fibers during growth
Beneath the sarcolemma lies the
Sarcoplasm which contains cellular proteins organelles and myofibrils
Myofibrils
Contain contractile proteins - actin and myosin
Actin
Thin filament - contain the proteins troponin and tropomyosin which play a key role in the contractile process
Myosin
Thick filament
Sarcomere (subdivision of a myofibril)
Includes:
- Z line
- M line
- H zone
- A band
- I band
Z line
Divided each sarcomere
M line
The fine line in the middle of the H zone
H zone
Myosin filament with no overlap of actin located in the center of a sarcomere
A band
Dark portion of a sarcomere where myosin filaments are located
I band
Light region of the sarcomere where actin is primarily located
Sarcoplasmic Reticulum
- Membranous channels that surround each myofibril
- Storage site for calcium
- Terminal Cisternae (lateral sacs) enlarged portion of SR
Transverse Tubules
Extend from sarcolemma to SR and runs completely through the muscle fiber. Lies between the terminal Cisternae.
Neuromuscular Junction
Is the junction between the motor neuron and muscle fiber
Motor Unit
Motor neuron and all fibers it innervates
Motor Neurons extends
Outward from spinal cord
Motor end plate
Pocket formed around motor neuron by sarcolemma
Neuromuscular Cleft
Short gap between neuron and muscle fiber
Synaptic Cleft
Neuromuscular Cleft
Acetylcholine is released from
The motor neuron
Acetylcholine causes
An increase in the permeability of the sarcolemma to sodium which results in an end plate potential - depolarization of muscle
End Plate Potential
Muscle depolarization
The sliding Filament Model
Muscle shortening occurs due to the movement of the actin filament over the myosin filament causing muscle shortening and tension development which causes the formation of cross bridges between actin and myosin and the reduction in the distance between Z lines of the sarcomere
Power Stroke
Formation of cross bridges between actin and myosin filaments
Swinging lever arm model
Sliding filament model
Calcium binding to troponin causes
Tropomyosin to be removed from the active binding site on actin leading to cross bridge attachment
ATP is required for
Muscle contraction
Myosin ATPase
Breaks down ATP as fibers contract
Myosin ATPase is located
On the head of the myosin cross bridge
ATP breakdown leads to
Muscle shortening by energizing myosin cross bridges
EC coupling
Depolarization of motor end plate in coupled to muscular contraction by
- action potential travels down the transverse tubules and causes release of calcium from the SR
- Calcium binds to troponin causing a position change in tropomyosin and exposing the active sites on actin
- Strong binding state formed btw actin and myosin
- contraction occurs
Excitation
- Nerve signal arrives at synaptic knob
- Ach is released into synaptic cleft and bonds to receptors on motor end plate, which open ion channels allowing sodium to enter the muscle fiber
- Sodium influx causes depolarization that is conducted down transverse tubules
Contraction
- Depolarization of T-Tubules causes release of calcium from the SR
- Calcium binds to troponin causing a shift in tropomyosin to uncover myosin binding sites on actin
- Myosin binds to actin to form cross bridges
- Pi is released from myosin and cross bridge movement occurs
- New ATP attaches to myosin breaking the cross bridge. Then ATP is broken down which energizes myosin
Relaxation
- Motor Neuron Stimulation ends, Ach is no longer released and muscle fibers repolarizes
- Calcium is pumped back into SR and tropomyosin returns to original position covering myosin binding sites on actin and muscle relaxation occurs
Cross Bridges Require
ATP
After the inorganic phosphate leaves the cross bridge the myosin head moves producing the
Power stroke
Muscle Fatigue
A decline in muscle power output by a decrease in force generation and a decrease in shortening velocity
Muscle fatigue is caused by
Disturbances in the CNS and peripheral factors within skeletal muscles
CNS fatigue from long duration exercise
A decrease in excitatory neurotransmitters in the motor cortex reduces motor neuron activation to skeletal muscle.
Current Research Suggests that fatigue is due to both
Central and peripheral factors
Peripheral Factors related to muscle fatigue
Peripheral factors disrupt cross bridge formation at high intensity ( ~60 seconds) and long duration (2-4 hours)
High intensity exercise leads to muscle fatigue when
There is an accumulation of lactate, hydrogen ions, ADP, inorganic phosphate, and free radicals which diminishes cross bridges bound to actin which decreases force production.
Long Duration Exercise leads to muscle fatigue when
There is an accumulation of free radicals, an electrolyte imbalance or glycogen depletion
Source of ATP
Oxidative Phosphorylation
PC-ATP system
Glycolysis
Fatigue is characterized by
A reduction in muscle force production and a decreased contraction time
Muscle Cramps Are
Spasmodic involuntary muscle contractions
Two theories of muscle cramps
Electrolyte and dehydration theory
And the altered neuromuscular control theory
Electrolyte depletion and dehydration theory
Water and sodium loss via sweating causes spontaneous muscle contraction which causes motor nerve terminals to spontaneously discharge
Altered neuromuscular control theory
Muscle fatigue causes abnormal activity in muscle spindle (increased activity) and golgi tendon organ (decreased activity) which leads to increased involuntary firing of motor neurons located in the spinal cord which causes muscle contractions or cramps
Muscle cramps can be relieved by
Passive stretching
Passive stretching relieves cramps by
Stretching activates Golgi tendon organs which inhibit motor neurons in the spinal cord resulting in muscle relaxation
Inverse stretch reflex
Stretching activates Golgi tendon organs which inhibit motor neurons in the spinal cord resulting in muscle relaxation
Inverse stretch reflex provides support
That impaired neuromuscular control is present in exercise induced muscle cramping
Percentage o fiber types in skeletal muscle is related to
Genetics, blood levels of hormones and the exercise habits of the individual
Biochemical properties of skeletal muscle
Oxidative Capacity
Type of Myosin ATPase
Abundance of contractile proteins within the fiber
Oxidative Capacity
Number of capillaries, mitochondria and amount of myoglobin
Fatigue resistance
Type of Myosin ATPase
Speed of ATP degradation
Results in high speed of muscle shortening
High ATPase activity
High ATP breakdown capability
Abundance of contractile proteins within the fiber
Large amounts of actin and myosin relate to being able to produce more force
Contractile Properties of skeletal Muscle
- Maximal Force Production
- Speed of Contraction
- Maximal Power Output
- Muscle Fiber Efficiency
Maximal Force Production
Force per unit of cross sectional area
Speed of contraction
Myosin ATPase activity
Vmax is determined by
The rate of cross bridge cycling
Maximal Power Output
Determined by force generation and shortening velocity
Muscle Fiber Efficiency
Measure of muscle fiber economy
- the less ATP used to produce a greater force the more efficient it is
Muscle Fiber Efficiency Formula
ATP uses/Forced Produced
Muscle Biopsy
Small piece of muscle is removed
Staining for types of myosin ATPase
Type I fibers are the lightest and appear blue
Type IIa appear intermediate and are green
Type IIx appear the darkest and are black
Dystrophin appears red
Immunogistological staining
Selective antibody binds to a unique myosin proteins fiber types are differentiated by color difference
Gel electrophoresis allows you to identify
Myosin isoforms specific to different fibers types
Dystrophin
Protein in sarcolemma
Type 1 fibers
Slow twitch/Slow Oxidative
High # of mitochondria High Resistance to Fatigue Aerobic Respiration dominates Low ATPase activity Low Vmax Highly efficient Moderate specific Tension
Type IIa
Intermediate Fibers/Fast Oxidative -Glycolytic Fibers
High/moderate # of mitochondria High/moderate Resistance to Fatigue Aerobic and Anaerobic Respiration High ATPase activity High Vmax Moderately Efficient High specific tension
Type IIx
Fast twitch/Fast Glycolytic
Low # of mitochondria Low Resistance to Fatigue Anaerobic Respiration dominates High ATPase activity High Vmax Not efficient High specific Tension
Type 1 fibers have less
Contractile proteins than type 2 for a specific area
Fast fibers exert more force
Than type 1 fibers because they contain more myosin cross bridges per cross sectional area
Type 1 fibers have low Vmax capabilities
Due to low myosin ATPase activity
Non-athletes have
Half slow and half fast fibers
Power athletes
Have a high percentage of fast fibers
Endurance athletes have
A higher percentage of slow fibers
Muscle Action Describes
The process of force development
Isometric action
Static exercise
The muscle exerts force with out changing length
Examples of isometric action
Pulling against an immovable object
Postural muscles during sitting or standing
Dynamic action
Isotonic exercise
Can be concentric or eccentric
Concentric action
Muscle shortens during force production
Eccentric Action
Muscle produces force but length increases
Eccentric action is associated with
Muscle fiber injury and delayed onset muscle soreness
Muscle Twitch
Contraction as the result of a single stimulus like electrical shock
Consisting of a
Latent Period immediately after stimulus and lasting approximately 5 ms
Contraction Period where tension is developed lasting approximately 40 ms
Relaxation period where the muscle returns to the original length lasting approximately 50 ms
Speed of shortening is greater in
Fast fibers because
SR releases Calcium at a faster rate and higher ATPase activity
Force exerted during muscle contraction is dependent on 3 factors
Type and number of motor units recruited
Initial muscle length
Nature of the neural stimulation of motor units
Types and number of motor units recruited
More motor units = greater force
More Fast Motor Units = greater force
Initial muscle length
Increased cross bridge formation at ideal length
Neural stimulation
Simple twitch
Summation
Tetanus
Summation
Addition of successive twitches causes increased force
Tetanus
Increasing stimuli so rapidly so that the individual contractions blend into a single sustained contraction
As the frequency of neural stimulation increases
The force developed increases
Force velocity relationship
At any absolute force the speed of movement is greater in muscles with higher percentages of fast twitch fibers
The maximum velocity of shortening is greatest
at the lowest force
The peak power increases with velocity up to movement spee doc
200-300 degrees/second
Power decreases beyond this velocity because force decreases with increasing movement speed - that is because rapid shortening restricts the number of cross bridges between actin and myosin limiting force production
Mykonos
Small signaling molecules released by skeletal muscle. They act as hormones or hormone messengers that affect a variety of other tissues
Skeletal muscle produces my planes when it
Contracts stimulating glucose uptake and fatty acid oxidation
Promoting blood vessel growth in muscle
Promoting liver glucose production and TGA breakdown
IL-6
Principle myofibril produced during exercise
Pro and anti inflammatory
Inhibits TNF a and other antionflammatories
Regular exercise
Promotes antionflammatory environment
Proprioceptors
Provide CNS with information about body position
They are located in joints and muscles
Kinesthesia
Related to conscious recognition of the body parts with respect to one another and to limbs movement rates
Joint Propioceptors
- Free nerve endings sensitive to touch and pressure - initially strongly stimulated at the beginning of movement and then become less sensitive
- Golgi type receptors - found in ligaments and around joints
- Pacinian Receptors
In tissues and around joints
Detect the rate of joint rotation
Muscle Proprioceptors
Provide sensory feedback to the nervous system concerning relative muscle length and tension development by muscle
- Muscle spindle
- Golgi tendon organ
Muscle Spindle
Respond to changes in muscle length that require the finest degree of control
Muscle spindles consist of
Intrafusal Fibers
Gamma Motor Neurons
Sensory Nerve Endings
Intrafusal Fibers
Run parallel to normal muscle fibers and insert into connective tissue with in muscles
Intrafusal fibers are composed of
Several thin muscle cells
Extrafusal Fibers
Normal muscle fibers
Gamma Motor Neurond
Stimulate intrafusal fibers to contract simultaneously with extra feudal fibers stimulated by alpha motor neurons
Sensory nerve endings
Provide the CNS with continuous information about static muscle length
Stretch Reflex
Rapid stretch on muscle causes reflex contraction
Muscle Spindle Action
- Muscle spindle detects stretch of the muscle
- Sensory neurons conduct action potential to the spinal cord
- Sensory neurons synapse with alpha motor neurons
- Muscle contracts and resists being stretched
GTO
Results in reflex relaxation of muscle
