Muscle Tissue Flashcards
What is muscle tissue specialized for?
Contraction
When does contraction occur in muscle tissue?
When thin/actin filaments and thick/myosin filaments within cytoplasm slide past one another
List characteristics of skeletal muscle tissue
Contribute to the MSK system
Pull on bones to cause body movement and maintain posture
Striated
Controlled voluntary by the NS
List characteristics of cardiac muscle tissue
Found in the wall of the heart
Striated
Involuntary
Pumps blood through the CV system
List characteristics of smooth muscle
Non-striated
Involuntary
Functions to maintain visceral organ tone and movement
Control blood vessel vasodilation and vasoconstriction
Found lining walls of hollow viscera and blood vessels
List functions of all muscle tissue
Movement of body and body fluids
Maintain posture and body position
Support soft tissues (blood vessels, intestines, urogenital tract, etc)
Sphincters at entrances and exits of certain organ systems
Maintain body temp
Skeletal muscle cells can be referred to as what?
Myocytes, myofibers or muscle fibers
What forms fascicles in skeletal muscle?
Groups of myofibers
What is the endomysium?
CT separating myofibers (skeletal)
What is the perimysium?
CT separating fascicles of skeletal muscle
What is epimysium?
CT layer surrounding the entire skeletal muscle
What are myofibers?
Cylindrical skeletal muscle cells
Describe skeletal muscle nuclei
Multinucleated and located in the periphery of the cell
What is skeletal muscle cell cytoplasm primarily occupied by?
Myofibrils which are composed of thin and thick filaments
What are transverse (t) tubules?
Invaginations of the sarcolemma
What structure stores Ca in skeletal muscle?
Sarcoplasmic reticulum
What are terminal cisternae?
Dilated ends of the SR that release Ca2+ and trigger muscle contraction
What is the skeletal muscle triad?
1 t-tubule and 2 terminal cisternae
When a muscle contracts what happens to the sarcomeres?
Every sarcomere shortens
What is the Z line in a sarcomere?
Anchor site for actin microfilaments
What is the M line in a sarcomere?
Anchor site for thick myosin filaments
What is the I band of a sarcomere?
Only contains actin thin filaments
What is the H zone of a sarcomere?
Contains only thick myosin filaments
What is the A band of a sarcomere?
Overlap of thick and thin filaments plus the H zone
What occurs when a skeletal muscle contracts?
The thin filaments slide past the thick filaments toward the center of the sarcomere brining the Z lines closer together
True or false: every myofibril in a skeletal muscle cell shortens at the same time thus the entire muscle cell contracts
True
During contraction, do thick and thin filaments change lengths?
No - the only thing that changes is their degree of overlap which increases
Muscle shortens, not the filaments
What is the signal to contract driven by in a skeletal muscle cell?
The release of Ca from the SR
Describe the steps of the sliding filament mechanisms
- Ca influx exposes sites on actin allowing the myosin head to bind to actin
- When myosin binds actin the power stroke is invoked
- ATP then binds the myosin and is hydrolyzed generating energy used to release myosin head from actin and re-cock the myosin for another power stroke
- This repeats until the Ca is removed and is transported back into the SR
What is rigor mortis?
Loss of a source of ATP prevents the myosin head from detaching from the actin thereby locking the muscle in place
What is tropomyosin?
Runs in groove formed by F-actin strands and binds to troponin
What are the three types of troponin?
T, I and C
What is troponin T?
Binds to tropomyosin
What is troponin I?
Inhibits the binding of myosin to actin
What is troponin C?
Binds Ca2+
What are the 4 different parts to a chemical synapse between a skeletal muscle and a motor neuron?
Pre-synaptic knob (axon terminal)
Synaptic cleft
Pre- and post synaptic membrane
What are axon terminals?
Ends of nerve fibers that store and release chemical messengers (NTs) at neuromuscular junctions
What is the synaptic cleft?
A space between the axon terminal and skeletal muscle plasma membrane
Describe the steps of the neuromuscular junction/innervation of a skeletal muscle
- Nerve impulses stimulate release of ACh into the synaptic cleft
- ACh binds to receptors on the sarcolemma of muscle cell
- ACh stimulates changes in the membrane that excite the muscle fiber
- Stimulus is carried down the T tubules to stimulate release of Ca from the SR which then initiate muscle fiber contraction
How is ACh removed from the synaptic cleft?
By enzymes such as acetylcholinesterase in the synaptic cleft break down ACh or any leftover ACh is taken up into the axon terminal by receptor mediated endocytosis
Describe cardiac muscle nuclei
Usually cardiac muscle cells have one nucleus but may have two
Centrally located in the cytoplasm
What is unique about cardiac muscle cell contraction?
Can spontaneously contract
Do not need innervation to contract
What is the diad of cardiac muscle cells?
1 t-tubule and 1 SR cisternae found at Z lines and permits uniform contraction of myofibrils within a single cardiomyocyte
What are intercalated discs?
Specialized interdigitating junctions between cardio myocytes that are sites of cell-cell adhesion and low electrical resistance (combination of gap junctions and desmosomes)
What is the function of intercalated discs of cardiac muscle?
Bind cells and transmit forces of contraction to allow for the spread of excitation within the muscle
What are the three types of membrane to membrane contacts of an intercalated disc junction?
Transverse region includes fascia adherens and desmosomes
Longitudinal region includes gap (nexus) junctions
What are fascia adherens of intercalated discs?
Actin filaments at the ends of terminal sarcomeres that insert into the intercalated junction
Transmit contractile forces between cells
Most predominant
What is the purpose of the desmosomes within the intercalated disc junction?
Provide anchorage for the intermediate filaments of the cytoskeleton
What are the gap (nexus) junctions of the intercalated disc junction?
Sites of low electrical resistance that allows for excitation to pass between cardiac muscle cells
Describe smooth muscle cell nuclei
Single elliptical nucleus in center of cytoplasm
Describe smooth muscle cell cytoplasm
No visible striations in cytoplasm but they still use actin/myosin for contraction
What connects smooth muscle cells?
Gap junctions
What innervates smooth muscle cells?
ANS
What controls smooth muscle cell contraction?
Hormones
Describe the smooth muscle contraction apparatus
Contractile apparatus is made up of thin and thick filaments which are anchored to cytoplasmic densities/dense bodies
What are dense bodies comprised of and what is their function?
Desmin and vimentin intermediate filaments
Transmit tension to the cell membrane
True or false: smooth muscle cells contract as one unit
True and they assume a globular shape
