Chapter 11 - Muscle Tissue Flashcards
What is skeletal muscle?
Voluntary striated muscle that is usually attached to one or more bone. The CT tissues of the muscles are continuous with the collagen of the tendons which are continuous with collagen of the bone.
What are the universal characteristics of muscle?
- Responsiveness (excitability) - when stimulated muscle cells respond with electrical changes across the plasma membrane.
- Conductivity - stimulation of a muscle cell triggers a wave of excitation that travels along the cell.
- Contractility - muscle cells shorten when stimulated.
- Extensibility - muscle cells are able to stretch again between contractions.
- Elasticity - muscle cells stretch and recoil when released.
What are the types of skeletal muscle?
a. Striations - alternating light and dark bands that result from overlapping arrangements of the internal contractile proteins.
b. Voluntary - usually subject to conscious control.
c. Involuntary - usually not under conscious control.
What are muscle fibers (myofibers)?
Skeletal muscle cells
What are the sarcoplasm (cytoplasm) contents?
a. Myofibrils - long protein cords (myofilaments) in the sarcoplasm.
b. Glycogen - starch-like carbohydrate that provide energy.
c. Myoglobin - red pigmented molecule which stores oxygen.
d. Multiple nuclei press against the sarcolemma (plasma membrane).
e. Sarcoplasmic reticulum (SR) - smooth ER, a reservoir of Ca2+.
f. Terminal cisternae - dilated ends of the SR.
g. Transverse (T) tubules - infoldings of the sarcolemma extending from one side to the other, convey electrical signals from the surface to the interior.
What are myofilaments?
Complex of contractile protein molecules
What are the types of myofilaments?
- Thick filaments - bundle of myosin proteins.
- Thin filaments - two intertwined strands of fibrous actin made of globular (G) protein actin.
- Elastic filaments - proteins that anchor each filament to Z disc and M line.
- Dystrophin - protein between the outer actin and the first linking protein that pulls on CT leading to the tendon when the actin moves.
What are the characteristics of thick filaments?
a. Shaft-like tail of two intertwined chains.
b. A double globular head projecting from the tail at an angle.
What are the characteristics of striations?
- A band - dark band formed by parallel thick filaments that overlap thin filaments.
- H band - lighter region of an A band that contains thick filaments only.
- M line - line in the middle of an H band where thick filaments are linked.
- I band - light band of thin filaments only.
- Z disc - dark line in the middle of the I band where thin filaments and elastic filaments are anchored.
- Sarcomere - from one Z disc to the next (the contractile unit).
- A muscle shortens because its sarcomere shortens and pull the Z discs closer to each other, dystrophin with the linking proteins pulls the sarcolemma.
What are motor neurons and motor units?
- Skeletal muscle never contracts unless it is stimulated by a nerve.
- Somatic motor neurons - nerve cells with cell bodies in the brainstem and spinal cord that innervate skeletal muscle.
- Somatic motor fiber - axon from a neuron that branches out to a number of muscle cells and stimulates each one.
- Motor unit - a neuron and all the muscle cells it innervates.
What are the types of motor units?
a. Small motor unit - 3 to 6 muscle cells per neuron, for finer control.
b. Large motor units - 1,000 muscle cells per neuron, for strength.
c. To prevent fatigue, motor units are able to work in shifts, thus the muscle as a whole can sustain long-term contractions.
What makes up the nerve-muscle relationship?
A. Motor Neurons and Motor Units
B. Neuromuscular Junction
C. Electrically Excitable Cells - muscle fibers and neurons
What is synapse?
The point where a neuron meets its target cell (neuromuscular junction or motor end plate for muscles)
What makes up the synapse?
a. Synaptic knob - dilated tip of an axon.
b. Synaptic cleft - gap between knob and muscle fiber.
c. A Schwann cell envelops the junction and isolates it.
d. Synaptic vesicles - vesicles in knob that contain and release ACh.
e. ACh - neurotransmitter that crosses the synaptic cleft.
f. ACh receptors - proteins in the sarcolemma that bind ACh.
g. Acetylocholinesterase (AChE) - enzyme in the cleft that breaks down ACh after the cell has been stimulated.
What are the characteristics of electrically excitable cells?
- In a resting cell there are anions on the inside of the cell and more cations on the outside, thus the plasma membrane is polarized or charged.
- In a resting cell Na+ are in the ECF and K+ are in the ICF with the anions.
- Resting membrane potential - the voltage across the plasma membrane of a resting cell (-90 mv).
What are the actions of stimulation?
a. Depolarization - Na+ gates open and Na+ diffuse in causing the inside to be positive.
b. Action potential - a rapid voltage change in the plasma membrane that is accomplished by depolarization and is self-propagating.
c. Repolarization - K+ gates open and K+ diffuses out returning the inside of the cell to negative.
d. Na+-K+ pumps exchange Na+ inside for K+ outside to prepare for another stimulation.
What are the behaviors of skeletal muscle fibers?
A. Excitation B. Excitation-Contraction Coupling C. Contraction D. Relaxation E. The Length-Tension Relationship and Muscle Tone