Skeletal Muscle and Nerve Tissue Histology Flashcards
Thin actin microfilaments and thick myosin filaments organize into structures called
Myofibrils
Skeletal muscle and cardiac muscle vs smooth muscle
Skeletal and cardiac muscle are striated, smooth muscle is not
Groups of myofibrils make up a
Muscle fiber or myofiber
Groups of muscle fibers/myofibers form a _____ which together, form a ____
Fascicle, which bundle together to form an entire muscle
Myofibers are surrounded by
Endomysium
Fascicles are surrounded by
Perimysium
The entire muscle is surrounded by
Epimysium
Skeletal muscle histological description
Multinucleated cylinders commonly referred to as myofibers. The nuclei are located in the periphery of the cell; the cytoplasm is primarily occupied by myofibrils
What is the basic structural unit of a myofibril (not talking about actin or myosin) and what does it do
Sarcolemma, sleeves around each myofibril and stores calcium
T-tubules
Invaginations of the sacrolemma
Terminal cisternae
Dilated ends of SR that release calcium and trigger muscle contraction
Sarcomere
Extends from one Z-line to the next Z-line
When a muscle cell contracts, every sarcomere shortens
Z-line
Anchor site for actin (thin) filaments
I-band
Only contains actin thin filaments
M-line
Anchor line for thick myosin filaments
H-zone
Contains only thick myosin filaments
A-band
Overlap of thick and thin filaments plus the H-zone
Effect on Z line during contraction
The thin filaments slide past the thick filaments, bringing the Z-lines closer together
Do thin/thick filaments change length in contraction
No, only the degree of overlap between them changes
Tropomyosin
Runs in groove formed by F-actin strands
Binds to troponin complex
Troponin T
Binds the complex to tropomyosin
Troponin I
Inhibits the binding of myosin to actin
Troponin C
Binds calcium
Type I muscle fiber- slow red
Slow oxidative
Contains slow ATPase, red due to high myoglobin
Contractions slower and less powerful
Contract for long periods of time without fatige
Type IIa fibers
Oxidative glycolytic
Largest and most prevalent
Intermediate ATPase and provides power
Primarily aerobic, intermediate fatigue
Type IIb fibers (fast white)
Fast ATPase produces fast contractions
Largely anaerobic
Rapid fatigue
Low myoglobin content
Ganglia vs Nuclei
Neuron clusters in PNS are ganglia
Neuron clusters in CNS are nuclei
Nissl substance
Abundant rough ER that take up the Nissl stain, reflects the need to make lots of neurotransmitters and protein to maintain this large cell
Multipolar neuron
Many dendrites and one axon
Bipolar neuron
One dendrite and one axon
Unipolar neuron
One cell process from which branches a single axon and single dendrite
Satellite cells
Surround the cell body of a neuron in the PNS
Endoneurium
CT between axons
Perineurium
CT surrounding clusters of axons forming fascicles
Epineurium
CT surrounding several nerve fascicles
Presynaptic knob
Axon terminal that contains synaptic vesicles loaded with neurotransmitters
Skeletal vs smooth vs cardiac muscle innervation and axon contact
Every skeletal muscle cell receives an axon terminal but not all cardiac or smooth muscle cells are directly innervated
3 Steps of innervation of skeletal muscle
1- Nerve impulse stimulates release of neurotransmitter into synaptic cleft
2- Neurotransmitter stimulates changes in sarcolemma that excite the muscle fiber. This stimulus is carried down the T-tubules to initiate fiber contraction
3. Enzymes in the synaptic cleft break down neurotransmitter and thus limit its action to a single muscle twitch
Muscle spindle receptors
Monitor changes in length, rate of change and tension of muscle
Intrafusal fibers
Nuclear bag fibers- wrapped at the center by type Ia nerve fibers; detect change in length and degree of tension
Nuclear chain fibers- wrapped at their ends by type II nerve fibers, detect static muscle length
Extrafusal fibers
Muscle fibers outside the spindle, known as alpha motor fibers
Golgi tendon organs
Encapsulated receptors found within myotendinous junctions that sense tension within the tendon
