Musculoskeletal Flashcards
Skeletal muscles is composed of ……. which are attached by ….. to the skeletal system
Myofibers (multinucleated, surrounded by sarcolemma)
tendons
The shortening of the skeletal muscle results from increase of ………. towards the center of the …… . This method is called …..
the extent of thin-thick filaments overlap
sarcomere
the sliding filament mechanism
When the actomyosin complex is formed, the head undergoes ……..
conformational change displacing the thin filament toward the center of the sarcomere
In skeletal muscle contraction, Power stroke means ………
the dissociation of Pi from the ADP, which leads to the acceleration of the tilting step
* The molecular event in this cycle is driven ty the hydrolysis of ATP
See P. 516 if not clear
In skeletal muscle contraction, the dissociation of ADP from the tilted head leads to …..
attachment of a new ATP from the cytoplasm, and the dissociation of the head
In skeletal muscle contraction, the final step involves …..
the hydrolysis of ATP, and repositioning of the myosin head for another cycle
In skeletal muscle contraction, if ATP runs out, this leads to ……
trapping of the myosin head in the tilted state, also know as rigor state
* Example is rigor mortis
Excitation contraction coupling means ………
the mechanism by which an AP by a motor neuron leads to skeletal muscle contraction
AP in the myofiber leads to the release of ….. from the …..
Ca, sarcoplasmic reticulum
Both troponin and tropomyosin are located on ……. . State the subunits with their functions
the actin filament
* Troponin is a complex of subunits T,I,C.
C binds Ca, while T binds to tropomyosin, and I binds to T and inhibits its action
* Binding of Ca to subunit C shifts the position of the tropomyosin in respect to the actin filament, exposing the myosin binding site
* Ca-ATPase of the sarcoplasmic reticulum depletes Ca and restores the inactivation state of actin
In skeletal muscle contraction, a single AP results in ….
a single muscle twitch, that occurs 2 miliseconds after depolarization (during repolarization)
Define
- Isometeric contraction
- Isotonic contraction
- Dynamic contraction
- muscle length is fixed, tension increases
- muscle length shorten, tension constant
- both length and tension change. It is two types, Concentric (muscle shortens) & eccentric (muscle pulled out)
Ryanodine receptor is …..
located on the sarcoplasmic reticulum. When activated by Ca, leads to release of more Ca from the sarcoplasmic reticulum (Ca induced Ca release).
* Succinylcholine (general anesthetic) causes inhibition of this receptor and release of large amount of Ca, and subsequent overheating (malignant hyperthermia).
In isometric contraction, the tension developed depends on ……
the length of the muscle
* There is an optimal length for the development of maximum muscle tension
The total force generated by many sarcomeres acting in series is the same as that of one sarcomere. T/F??
True
because the forces act in opposing direction on both side of the Z line and cancel each other
* This means that sarcomeres in the same myofibril do not generate additive force
* The more sarcomeres arranged in series, the faster the shortening of the muscle
The force that the muscle generates is proportional to …..
the cross sectional area of the contractile material.
In isotonic contraction, the velocity of contraction is inversely proportional to the ……….
load
* At zero velocity, the contraction becomes isometric. This is the maximum active force of the muscle at this point
What is difference between fast & slow muscle fibers??
- Fast: white, large in diameter, less mitochondria, depends on anaerobic glycolysis, high myosin ATPase, and high in SR and T tubules content. Allow finer movements.
- Slow: Red (myoglobin), high mitochondria, small diameter, oxidative phosphorylation used for energy, low myosin ATPase, and low in SR and T tubules content, smaller motor end plates, high capillary content
Muscles with less sarcoplasmic reticulum contracts slowly because …..
less Ca is released, and contraction takes longer because of the slower removal of Ca
The motor unit consists of …… & ……
all muscle fibers & a single alpha motor neuron axon
* Excitation of the alpha motor neuron results in contraction of all the fibers in the motor unit
Changing the firing rate of an alpha motor neuron leads to ……
change in the muscle type (fast or slow)
* If the nerve is destroyed,, all related muscle fibers atrophy
Length and tension in a skeletal muscle depends on ……
rate of firing of the motor neuron
* All motor neuron inputs are excitatory & reach threshold
Neuronal cell bodies of the alpha motor neuron are located in …….
the ventral horn of the spinal cord gray matter
* Alpha motor neurons are myelinated
Initiation of contraction for the skeletal muscle occurs in …… & ……
cerebral cortex and the cerebellum
Before tension in a skeletal muscle is exerted, stretching of ……..
all elastic element in the muscle (tendons, CT) must occur.
Tension in skeletal muscles does not build in a single twitch because …..
by the time the slack is removed, the single twitch begin to decline
Tetanus is …….
summation of all muscle contractions during repetitive stimuli within a short time.
Ca availability will be increased from repeated contractions
* Tetanus can continue until fatigue is developed due to lactic acid accumulation
Graded tension forces in skeletal muscles can be developed by ……
increasing the number of motor units and increase firing rate
What are the two types of skeletal muscles receptors??
- Muscle spindles: located between the fibers (intrafusal)
2. Golgi tendon organ: in the tendons, arranged in series with the muscle fibers
Muscle spindles consist of two parts, …. & ….
Nuclear bag & nuclear chain (depending on the arrangement of the nuclei in their equatorial region)
What is the innervation of the muscle spindles?
- Gamma motor neuron (efferent): controls the tone and contraction of the muscle spindles during activity. Input is from the CNS
- Ia fibers (primary, annulospiral, afferent): fast, innervate nuclear bag & chain. Detect dynamic Δ in muscle length.
- II fibers (secondary, flower spray, afferent): slower, innervate the nuclear chain only. Detect the static Δ in muscle length
Golgi tendon fires when ……….
the muscle contracts, stretching the tendons
* GTO responds to muscle tension, while muscle spindles respond to change in length
Golgi tendons are supplied by …… afferents, with their function being …….
type Ib
* These fibers synapse on inhibitory interneurons, which inhibit alpha motor neurons to prevent damage to the skeletal muscle
Both skeletal muscle afferents fire if …….
the muscle is stretched
- If the stretched muscle contract, spindles cease its discharge, while GTO increases.
- Muscle spindles are arranged in parallel, while the GTO are in series with the myofibers
Smooth muscles are usually …….. than skeletal muscles, and have less …. & ….
smaller & uninucleated
myofibrils per cell
myosin
* Also, no T tubules and sparse SR
The analogous to Z line in the smooth muscle is …..
Dense bodies
- it is the site of actin insertion
- Also located in the cell membrane, so it causes deformation of the cell during contraction
Excitation-Contraction coupling in smooth muscles is mediated by …… because
myosin kinase, because there’s no troponin
What is the function of satellite cells???
Regeneration of muscle cells
Each sarcomere has …… T-Tubules
two
Ca enters the smooth muscle and binds to ….., which it activates the …..
calmodulin
myosin kinase
* Phosphorylation of myosin enables it to interact with actin.
* Each contraction cycle requires 1 ATP
……. are located at the junction of the I & A band
T tubules
