Ch 12 - Skeletal Muscle Flashcards
Why is the bicep an example of a flexor muscle?
- Flexor muscles decrease the joint angle when contracted. So when the bicep contracts…like during a curl, the angle of the arm is decreased.
Why are the quads considered an extensor muscle?
- Extensor muscles “extend” the joint angle upon contraction. So when flexing the quads, or doing the quad machine lift at the gym…the angle of the knee joint is increased.
What is the outer most sheath of an entire muscle referred to as?
Epimysium
What are the large subdivisions within the epimysium that house many muscle fibers?
Fascicles
What is the layer of tissue sheath surrounding each fascicle?
Perimysium
Each fascicle is further broken down into many [] cells. These cells are surrounded by their own plasma membrane, referred to as []
Myofibers
Sarcolemma
The sarcolemma (and thus the single myofiber) is enveloped by what tissue layer?
The Endomysium
Muscle fibers fo not pull out of the tendons for what reason?
The tissue layers of the tendon, epimysium, perimysium, endomysium are all continuous.
What do muscles have a striated appearance?
- The striations are caused by light and dark bands
- Light bands are termed - I bands
- Dark bands are termed- A bands
What are the thin “dark” bands that can be seen in the center of the I bands?
Z bands
The specialized region of the sarcolemma of the muscle fiber at teh neuromuscular junction is known as…[]
Motor end plate
T/F
A motor neuron is each somatic motor neuron, together with all of the muscle fibers that it innervates?
False
That is the motor unit
Normally small motor units (innervating a few muscle fibers) are needed for normal movemtns; however, what occurs when a muscle must use larger and larger motor units to produce a strogner contraction?
Motor Unit Recruitment
A sarcomere consists of what? (From Z-band to Z-band)
It is a subunit of the striated muscle. It contains the I -band, A band, and H Band.
What are the even smaller structure within the myofibers called?
Myofilaments
- Myofilaments are composed of two types of filaments.
- What 2 types?
- How do these 2 types effect the striation pattern of a myofiber?
- 2 types
- Thick filament - myosin
- Thin FIlament - actin
- The thick filament gives the fiber its dark color - so these are in the A band. The thin filament gives the fiber its lighter color - so these are in the I band
Why is the central portion of the A band lighter than the outer edges of the A band?
The central portion of the A band is lighter becuase it only contains thick filaments. Whereas the outer edges of the A band have the edges of the thick and thin filaments converging…making it darker.
Where in a sarcomere is the M-Line?
- It is located in the center of the A band, Or in the center of the thick filaments.
- It helps anchor the thick filaments, helping them stay together during a contraction.
- What is the largest protein in the body?
- Where is it located? What does it do?
- Titin - located in the sarcomeres
- It connects to the I-band with a thick springlike structure, and then a longer thin portion runs all the way to the M-Line.
- Becuase of this structure - it contributes to the elastic recoil of muscles that help them return to their resting lengths when relaxed
During a muscle contraction:
A bands shorten?
I Bands shorten?
H Bands shorten?
- Only the I bands shorten during a muscle contraction. The A- band filaments merely move closer together.
- The H bands also shorten! Since the tin filaments are pulled over the thick filaments
Which protein are “cross bridges” a part of?
Myosin
The globular head attached to myosin is known as what enzyme? What does it do?
- myosin ATPase
- It splits ATP into ADP + Pi
What 2 processes must first happen before the myosin can attach to actin?
- ATP –> ADP + Pi
- Pi must then bind to the myosin head, putting the head in the “cocked” position.
What process performs a “power stroke” within a myofiber?
- The myosin head is in the cocked position, and then binds with actin.
- Once bound to actin, the Pi is released causing a conformational change in the myosin head.
- This conformational change causes the power stroke
What process is the force that pulls the thin filaments toward the center of the A band?
The power stroke
What must occur for the myosin head to dettach from the actin, post power stroke?
- After power stroke the myosin head is in the flexed position
- The ADP must release and be replaced with ATP
Splitting of [] is required before a cross bridge can attach to actin
Attachemtn of new [] is needed for the cross brdige to release from actin
ATP (for both)
Is the pulling of myosin/actin power strokes synchronous or asynchronous?
Asynchronous
Which protein rests between the groove of the two actin helical molecules? And usually spans 7 actin subunits.
Tropomyosin
Which protein is bound directly to tropomyosin, instead of actin? And has 3 subunits?
Troponin
Troponin has 3 subunits, what are they and what are their functions?
- Troponin I - inhibits binding of the cross bridges to actin
- Troponin T - binds to tropomyosin
- Troponin C - binds to Ca2+
How must tropomyosin interact with Ca2+ in order for the cross bridges to attach to actin?
Tropomyosin does not interact with Ca2+….troponin does this.
Is the concentration of Ca2+ low or high in the sarcoplasm during contraction?
High
The [] is a modified endoplasmic reticulum, consisting of interconnected sacs and tubes that surround each myofibril within the muscle cell.
Sarcoplastic Reticulum
T/F?
Calcium release channels move calcium into the sarocplastic reticulum from the T-Tubules via active transport?
False
Calcium release channels release calcium, via passive diffusion, out of the sarcoplastic retiuculum and into the cytoplasm of the myofiber
Which narrow membranous “tunnels” are formed from and continuous with the sarcolemma?
Transverse Tubules (T-Tubules)
The transverse tubules are open to the [] environment and are able to conduct {}?
Extracellular environment
Action potentials.
T/F
The Voltage-Gated Calcium Channels have a direct coupling between the calcium release channels in the sarcoplasmic reticulum?
True
T/F
When an AP reaches the T-Tubules, a conformational change in the calcium release channels allows Ca2+ to enter the cytoplasm of the myofiber.
False
The conformational change occurs in the voltage gated caclium channels in the T-Tubules. This change causes the calcium release channels in the Sarcoplasmic reticulum to open and allows Ca2+ to enter the cytoplasm.
The process by which action potentials cuase contraction is termed -
excitation-contraction coupling
Which channel contributes the most (In cardiac muscles but a bunch in normal muscles) to the musle contraction?
Calcium Release Channel (SR)
Voltage-gated Calcium channel (TT)
Ca2+ channels that open in response to a rise in Ca2+ in cytoplasm?
Third option - Ca2+ channels that open in response to a rise in Ca2+ in cytoplasm
What are the pumps that actively pump Ca2+ against is concentration gradient from sarcoplam –> sarcoplastic reticulum?
Sarcoplasmic/endoplasmic reticulum Ca2+ ATPase pumps (SERCA Pumps)
[] - is when a muscle is stimulated enough to cause a contraction and relaxtion period.
Twitch
[] occurs when a 2nd stimulus is delivered to the muscle before it has had a chance to fully relax from the 1st stimulus, thus causing a stronger contraction than the 1st.
Summation
How are skeletal muscle contractions graded?
- A stronger stimulus, increases the frequenceny of APs and concentration of Ca2+ in sarcoplasm.
- The stronger stimulus also recruits more muscle fibers.
- So stronger muscle contraction will require more muscle fibers recruited.
- If the stiimulus is not strong, less fibers will be recruited and vice versa…resulting in graded contractions.
If a muscle is continually stimulted to the point where it reaches its maixumum tension strength for a brief period of time before it begins to fatigue, what is this called?
Does the muscle even relax during this period of time?
Complete Tetanus
Not really, the curve is basically a smooth line up, then plataues…but then fatigues. (It may slightly relax but the curve doesnt show it).
Fill in the Blank -
The [] - velocity curve shows the [] relationship between the force opposing muscle contraction and the [] of muscle shortening
- Force
- inverse
- velocity
How is a muscle, in vivo, able to produce the smooth contractions of a complete tetanus?
Asynchronous activation - muscle fibers of some motor units start ot twich when those of previously activated motor units begin to relax, producing a continuous contraction of the muscle.
What is the staircase effect, or treppe?
- Series of stimulations at a maximal voltage (to produce a contraction) are given to a muscle so that each shock produces a separate twitch.
- Each of these twitches will be successively stronger, up to a higher maximum.
- almost like a muscle warm up
Isotonic contraction
The tension produced by the shortenign of muscles is greater than the force at each value. Therefore the contraction strength is constant at each load.
What kind of contraction occurs when the force is strong enough to inhibit the shortening of a muscle?
Isometric
Concentric vs Eccentric contractions
Use bicep curl as an example
- Concentric - When the muscle tension is greater than the force (Load) and the muscle shortens.
- Eccentric - when the force is greater than the muscle contraction, muscle is stretched by that force.
- Doing a bicep curl = concentric, lowering the dumbbell = eccentric
What are 4 factors that influence the strength of a muscles contraction?
- number of fibers within the muscle that are stimulated to contract.
- Frequency of stimulation
- Thickness of each muscle fiber
- initial length of muscle fibers when they are at rest
At what length does the muscle experience its maximal tension produced?
2.0 - 2.25 um….or 100% - 120% of resting length.
Why does tension increase when the muscle length rises above 2.25um?
- It does not…the tension actually decreases at this point.
- There are fewer intreactions between actin/myosin when the muscle is stretch too far apart.
Why does the muscle tension decrease as its length falls below 2.00 um?
- development of opposing forces - like fluid pressure of sarcoplasm
- Increasing distance between thick and thin filaments of muscle fiber as it gets thicker
- The actin can overlap eachother also…allowing for less interactions.
[]% of ATP consumed by muscles is used by myosin ATPase, []% is used primarily for Ca2+ transport by sarcoplasmic reticulum to allow muscle relaxation.
70%
30%
Where do muscles obtain their energy during…:
Rest-
Exercise-
- Rest - aerobic respiration of fatty acids
- Exercise - muscle glycogen and blood glucose are also incorporated.
What mechanism allows blood glucose to be used by muscles during exercise?
Exercise stimulates the insertion of GLUT4 proteins into the sarcolemma. Specifically in the T-Tubules.
Fill in the blank -
In addition to increased glucose uptake, exercise promotes the inhibition of [] synthesis and the increased uptake and oxidation of [].
glycogen
fatty acids
The [] is the maximum rat eof oxygen consumption (by aerobic) respiration) in the body…
maximal oxygen uptake, or aeorbic capacity
Where does the muscle obtain most of its energy during light exercise?
Aerobic respiration of fatty acids…from fat in adipose tissue.
Once above the lactate threshold (High intensity workout) where does the muscle receive most of its energy?
Stored muscle glycogen and blood plasma
Which high energy compound is used to rapidly restore ATP during short intense bouts of exercise where the ATP is used faster than it can be reproduced through anaerobic metabolism and arobic respiration?
Phosphocreatine, or creatine phosphate
Which concentration is higher in muscle cells…
Phosphocreatine or ATP?
Phosphocreatine
Which enzyme catalyzes the formation and breakdown of phosphocreatine?
CK - Creatine Kinase or creatine phosphokinase, CPK
Skeletal muscle fibers are split into 2 categories based on their contraction speed, what are they?
Slow Twitch (Type I)
Fast Twitch (Type II)
Type I Fibers can also be called [] due to the following factors -
- Slow Oxidative Fibers
- Rich capillary supply
- numerous mitochondria
- aerobic respiratory enzymes
- High concentration of myoglobin
The Type II muscle fibers are not as oxidatively successful, why?
- Less capillary support, less mitochondria, less myoglobin.
- These fibers are adapted to metabolize anaerobically by a large store of glycogen and a high concentration of glycolytic enzymes
- Also called “white fibers”
In humans there are two “sub-types” of fast twitch muscles, what are they called?
- Type IIA Fibers, Fast Oxidative Fibers
- Type IIB/IIX Fibers, Fast Glycolytic Fibers
Why do somatic motor units inneravate Type I and TIIX muscle Fibers?
They do not! A somatic Motor Unit would only innervate 1 type of muscle fiber
Type IIA (fast oxidative fibers) muscle Fibers have the following characteristics -
- Higher oxidative potential (relative to Type II)
- Fast Twitch
- Generates energy through glycolipid metabolism
- Possess a lot of mitochondria
Type IIX/IIB muscle fibers have the following characteristics -
- Lots of ATPase
- Low oxidative capacity
- low myoglobin
- low mitochondria
- Generates energy anaerobically
- Used for weightlifting and sprinting stuff
[] is a reversible, exercise-induced reduction in the ability of a muscle to generate force
Muscle Fatigue
When a muscle completely fatigues - maximal nueral firing and recruitment of motor units - it is though to be an accumulation of extracellular []
K+
What are 4 main causes of muscle fatigue?
- Increased concentration of PO-34, derived from breakdown of phosphocreatine.
- believed to reduce the force developed by cross bridges
- Decline in ATP, around junction of T-Tubes and sarcoplasmic reticulum..hindering actino of Ca2+
- Depletion of myscle glycogen
- may decrease the amount of Ca2+ from sarcoplasmic reticulum
- Increased ADP in cytoplasm.
- Decrease in velocity of muscle shortening
What is it called when we as peolpe get “fatigued” but our muscles are still able to continue working?
Central Fatigue
Endurance atheletes and obese folks both show high levels of intracellular triglycerides…but why do only obese folks get Type 2 diabetes?
- The endurance athlete has adapted ways to oxidize those fatty acids…therefore allowing the insulin to do its job and increase glucose uptake.
- The obese person has a reduced ability to oxidize fatty acids.
[] [] [] are somatic motor neurons with cell bodies in the brain stem and spinal cord and axons that travel within nerves to stimulate skeletal muscle contraction.
Lower Motor Neurons (motoneurons)
[] [] [] interneurons in the brain that contribute axons to descending motor tracts
Upper Motor Neurons
- Lower motor Neurons are influenced by
- 1) [] feedback from muscles and tendons
- 2) facilitory and inhibitory effects from [] []
1) Sensory
2) Upper motor neurons
2 main complexes provide sensory information for nervous system control over skeletal movements, what are these two “structures?”
- Golgi Tendon Organs
- Muscle Spindle Apparatus
This structure acts as a “length” detector in a muscle…
muscle spindle apparatus
What are the 2 types of muscle spindle apparatuses, or intrafusal fibers…
- Nuclear Bag Fibers - nuclei arranged in a loose aggreagte in centrla region of the fibers
- Nuclear Chain Fibers - their nuclei are arranged in rows.
What are the two types of sensory neurons that serve teh intrafusal fibers?
Primary - or annulospiral - sensory endings
Secondary - or flower spray - endings
- These sensory nuerons are located over the contracting poles of nuclear chain fiber…
- What is the other type of sensory neuron that innervates intrafusal fibers? Where does it wrap around the fiber?
- Secondary endings
- Primary - annulosprial - sensory endings
- wrap around teh central regions of the nuclear bag and chain fibers.
T/F
Secondary sensory endings are most stimulated at the onset of a muscle stretch…
- False - primary endings are the most stimulated at the start of a stretch.
- The secondary endings respond in a more “tonic” way to a continued stimulation.
Why does a rapid stimulation only activate Primary Sensory endings?
- It does not! It stimulates both types of endings - causing the reflex contraction to be an even greater response than a gradual stretch.
T/F
- The motor neurons that innervate the extrafusal muscle fibers are called - Gamma motoneurons
- The Motore Neurons that innervate the intrafusal muscle fibers are called - Alpha motoneurons
False
- The motor neurons that innervate the extrafusal muscle fibers are called - Alpha motoneurons
- The Motore Neurons that innervate the intrafusal muscle fibers are called - Gamma motoneurons
How do gamma motoneurons ilicit a muscle contraction?
They don’t. Only stimulation by alpha motoneurons can cause muscle contraction
What kind of contraction does stimulation by gamma motoneurons cause on the spindle fibers?
Isometric. Contraction strength is too weak from spindle fiber to elicit a contraction though.
The stimulation of alpha and gamma motoneurons by 1 upper motor neurons is termed -
Coactivation
Under normal conditions the activity of gamma motoneurons is maintained at a level needed to keep the muscle spindles under proper tension…this is called
Musle Tone
The muscle stretch reflex is what kind of reflex?
Monosynaptic Reflex
Sensory neurons innervating Golgi tendon organs, then synapse with interneurons in the spinal cord…these internuerons are inhibitory or excitatory?
Inhibitory
- What are the 2 synapes in a disynaptic reflex
- What is one example of this?
- The sensory neuron syanpses with an internueron..then the internueron synapses with a motor/efferent/alpha motoneuron.
- The Golgi tendon reflex
- The 2nd synapse here is inhibitory
Reciprocal Innervation is -
What do internuerons use to perform this reciprocal innervation?
- The dual stimulatory and inhibitory activty caused by the stimulation of interneurons in a common stretch reflext
- IPSPs
