BMSC 207: Module 7 - 13

What are contractile filaments?

the basic contractile units of muscle; thick and thin filaments

What is contraction?

the shortening of muscle which results in the generation of force and/or movement

What is cross-bridge cycling (contraction relaxation cycle)?

the sequence of events that occur at the level of the thick and thin filaments resulting in the shortening of skeletal muscle and the generation of force and/or movement

what is excitation-contraction coupling?

the generation of an action potential in a skeletal muscle fibre and subsequent increase in intracellular Ca2+ that initiates contraction

What is motor unit?

a single alpha motor neuron and all the muscle fibres that it innervates

what is muscle fibre?

one individual muscle cell

What is neuromuscular junction?

the specialized synapse between an alpha motor neuron terminal and individual muscle fibre

what is the primary function of all muscles?

to generate force and/or movement in response to a physiological stimulus

What are some examples of some primary functions of muscles?

- body movement
- maintenance of posture
- respiration
- production of body heat
- communication
- constriction of organs and vessels
- heartbeat

what does the generation of force depend on in all muscle types?

the conversion of chemical energy (ATP)

what are striation caused by?

due to arrangement of thick and thin filaments

what are some functions of skeletal muscles?

- respiration
- helps circulatory system
- move skeleton

what is the stimulus source for skeletal muscles?

somatic motor neurons

True or False. skeletal muscles are striated and uninucleated.

False, they are striated and multinucleated

is the skeletal muscles primarily voluntary or involuntary?

voluntary

what is the stimulus for cardiac muscle?

spontaneous electrical activity

is the cardiac muscle primarily involuntary or voluntary?

involuntary

True or False. Cardiac muscle is striated and uninucleated.

True

what can the cardiac muscle be altered by?

autonomic NS, hormones

what is the stimulus for smooth muscle?

- autonomic control
- spontaneous
- hormones
- paracrines or autocrines

is the smooth muscle primarily involuntary or voluntary?

involuntary

True or False. Smooth muscles are striated and uninucleate.

- False, they are non-striated and uninucleate

what does smooth muscle provide mechanical control of?

- digestive tract
- urinary tract
- reproduction tract
- blood vessels
- airways

what is the main role of smooth muscles?

- movement of substances into, out, or throughout the body

what is the origin of skeletal muscles?

the closest to the trunk or to more stationary bone

how are the skeletal muscle attaches to bones?

by tendons

what is the insertion of skeletal muscles?

more distal or more mobile attachment

what are the antagonistic muscle groups in skeletal muscles?

flexor-extensor pairs

what is the flexor?

brings bones together

what is the extensor?

moves bones away

what percent is skeletal muscle of the total body weight?

40%

what is the muscle fiber?

It is a muscle cell.

what is the sarcolemma?

muscle cell membrane

what is the sarcoplasm?

cytoplasm of a muscle cell

what is the sarcoplasmic reticulum?

the modified endoplasmic reticulum

what is the muscle fasicle?

bundle of muscle fibers

arrange the muscle components from largest to smallest: muscle fibre, myofibril, fasicle, muscle, sarcomere

muscle > fasicle > muscle fibre > myofibril >sarcomere

what do striations correspond to?

the ordered arrays of thick and thin filaments within myofibrils

What is the thin myofilament?

actin

What is F actin made of?

back bone of thin filaments, double stranded alpha helical polymer of G-actin molecules.

what does F-Actin contain?

binding site for thick filaments (myosin)

what is Tropomyosin?

two identical alpha helicies that coil around each other and sit in the two grooves formed by actin strands, regulates the binding of myosin to actin

what is the troponin complex?

heterotrimer situated every 7 actin molecules

what does the troponin complex consist of?

- troponin T (TnT)
- troponin C (TnC)
- troponin I (TnI)

what is troponin T (TnT)?

binds to a single molecule of tropomyosin

what is troponin C (Tnc)?

Ca2+ binding site

what is Troponin I (TnI)?

under resting condition is bound to actin inhibiting contraction

What do thick myofilaments consist of?

myosin

what does the myosin molecule consist of?

2 intertwined heavy chains, each heavy chain contains 2 light chains

what do myosin heads contain?

a region for binding actin as well as a site for binding and hydrolyzing STP (ATPase)

what is the regulatory light chain?

chain regulates ATPase activity of myosin

what is the essential light chain?

chain stabilizes myosin head

what is titin?

a very large protein extending from M line to Z line, appears to be involved in stabilization and the elastic recoil behavior of muscle

what is nebulin?

a large protein that interacts with the thin filaments, believed to regulate the length of thin filaments and contribute to the structural integrity of myofibrils

What is the Z-disk of the sarcomere?

zigzag protein structure that is the attachment site for the thin filaments

What are I bands of the sarcomere?

lightest band of sarcomere, region occupied only by thin filaments

What is the A Band of a sarcomere?

darkest band of sarcomere, encompasses entire length of the thick filament, including very dark area where thin and thick filaments overlap

What is the H zone of a sarcomere?

central region of A band, consists only of thick filaments

What are M-lines in sarcomeres?

proteins form the attachment site for he thick filaments, equivalent to z disk for thin filaments

what is the mitochondrion needed for in muscle fibre?

to produce ATP depending on type of muscles

what is the function of sarcoplasmic reticulum?

store and release calcium

what is glucose stored as within the sarcoplasm?

glycogen

what is the function of transverse tubules?

to deliver action potential to the interior of the muscle fiber

what is the function of terminal cisternae?

swollen regions of sarcoplasmic reticulum, stores and release Ca2+

what is muscle tension?

the force generated by a contracting skeletal muscle is referred to as muscle tension

what regions of the sarcomere shorten during contraction?

H zone and I band shorten, while A band remains constant

what is neuromuscular junction?

point of synaptic contact between somatic motor neuron and individual muscle fibre

What is excitation-contraction coupling?

an action potential initiated in the skeletal muscle fibre results in an increase in intracellular (sarcoplasmic) calcium

what regions are involved in voluntary movement?

- basal ganglia
- premotor cortex (motor association)
- thalamus
- midbrain
- cerebellum

where do upper motor neurons travel?

from primary motor cortex to spinal cord (output signal)

what is the corticospinal tract?

descending tract (ventral and interior lateral white matter)

what is upper motor neuron?

brain to spinal cord, carried in descending tract, crosses over at medulla to synapse with alpha motor neuron

what is alpha (lower) motor neuron?

spinal cord to muscle

what is a motor unit?

a single motor neuron and all the muscle fibres it innervates

what are the characteristics of alpha motor neurons?

large diameter, myelinated axon, 15-120 m/sec

True or False. One muscle fiber will only ever have synaptic input by one neuron.

True

what is amyotrophic lateral sclerosis (ALS)?

neurodegenerative motor neuron disease that degenerates upper and/or lower motor neurons leading to muscle atrophy and weakness from disuse

what happens in ALS?

upper and/or lower motor neurons degenerate leading to muscle atrophy and weakness from disuse

what are three components of neuromuscular junction?

- presynaptic motor neuron filled with synaptic vesicles
- the synaptic cleft
- the postsynaptic membrane of the skeletal muscle fibre

what is the motor end plate?

region of sarcolemma at the neuromuscular junction

what do junctional folds do?

on sarcolemma increases surface area

what do motor neuron vesicles contain?

acetylcholine

What does muscle sarcolemma contain?

nicotinic acetylcholine receptors

what is the extracellular matrix?

meshwork of proteins and proteoglycans

what does the sarcolemma of muscle fibre contain?

nicotinic acetylocholine receptors

what are monovalent cation channel?

member of cys-loop receptor family of ligand gated ion channels (permeable to Na+ and K+

what is required to open the ACh receptor?

requires two acetylcholine molecules

what is myasthenia gravis?

- means severe weakness of muscle
- disorder of neuromuscular transmission

what is autoimmune?

body produces antibodies that bind to ACh receptors

what are DHP receptor?

L-type Ca2+ channel (voltage sensitive)

what is RyR?

ryanodine receptor (Ca2+ release channel on SR)

what is ATP binding?

ATP binds to the head of myosin heavy chain reducing affinity of myosin for actin

What is ATP hydrolysis?

ATP is broken down to ADP and inorganic phosphate (Pi) resulting in the myosin head pivoting around hinge into cocked state. the cocked head is now aligned with and binds to a new actin molecule on thin filament

What is the powerstroke?

dissociation of Pi from myosin head strengthens bond between actin and myosin and triggers power stroke, a conformational change in which the myosin head returns to its un-cocked state and while doing so pulls the actin filaments generating force and motion

what is the ADP release?

dissociation of ADP from myosin causes myosin to remain bound to actin until ATP initiates the cycle again

what does the termination of contraction require?

removal of Ca2+

how can Ca2+ be removed to the extracellular space?

by the Na-Ca exchange or by the Ca2+ pump which uses ATP

what is rigor mortis?

development of rigid muscles several hours after death

what happens when ATP is stopped by rigor mortis?

- Ca2+ cannot be removed (SERCA pump is ATP powered)
- ATP needed to release myosin head from actin, remains in latched cross bridge formation until muscles begin to deteriorate

what is the timing of E-C coupling?

- slight delay between motor neuron AP and muscle fibre AP (synaptic release)
- delay between muscle fibre AP and contraction (latent period) time when Ca2+ is being released and binding troponin