Skeletal Muscle and Nerve Tissue Histology Flashcards
What is the main function of skeletal muscle?
generate force for movement by turning ATP into mechanical energy, voluntary movements and postural stability
What are the key characteristics of skeletal muscle?
The muscle is striated and multinucleated, located in the periphery (not center)
What is a sacromere?
a contractile unit of muscle made of actin and myosin myofilaments
What do chains of sacromeres link together form? and what do those form?
Sacromere chains linked together form myofibrils, which form the myofiber (which is the muscle cell)
What fascial covering surrounds myofibrils?
What fascial covering surrounds a group of myofibers (fascicle)?
What fascial covering surrounds a group of fascicles (muscle)?
Endomysium
Perimysium
Epimysium
List from one to four, the formation of muscle
- Groups of sacromeres form myofibrils
- Groups of myofibrils form muscle fiber (myofiber)
- Groups of myofiber form the fascicle
- Groups of fascicles form the Muscle
Myosin are thick filaments, what makes up myosin and what holds it in place?
They have 2 heavy chains with globular heads, which bind to actin with ATPase domains
2 light chains
Myosin is held in place by Titin proteins connected to Z-disk
Actin or thin filaments are made of filamentous actin (f-actin) monomers, which bind to form double stranded chains. The length of the actin filament are determined by nebulin. Where are tropomyosin and troponin located in the Actin?
Tropomyosin strands wrap between the actin strands and troponin sits on tropomyosin strands and covers myosin bindin sites on actin filament so the myosin does not randomly contract
What is the M-line of the sarcomere (myosin and actin together)?
attachment site for myosin (in the middle)
What are z-disk in sarcomeres?
they separate sarcomeres, and is the site of attachment for actin and titin
What is the H-band in sarcomeres?
space on either side of M-line where there is no actin (Hband/zone will shorter with contraction)
What is the A-band in sarcomeres?
distance from the end of one myosin head to the head of the opposite myosin, where actin and myosin overlap
What is the I-band in sarcomeres?
space on either side of the Z-disk where there is no myosin, (I-band will shorten with contraction)
For contraction to occur, myosin must bind to actin, however, troponin blocks the myosin binding sites on the actin filaments, how contraction activated?
Calcium is released from the sarcoplasmic reticulum and binds to troponin
This causes a conformational change which pulls tropomyosin away, exposing the myosin binding sites so myosin and actin can bind
For sliding filament mechanism of muscle contraction, what are key things to remember? (4)
- thin filaments slide past thick filaments
- Z-disks are closer together, H and I bands are smaller
- All myofibrils contract at the same time
- **Actin and myosin do not change in length, they just overlap
What are typical of type I skeletal muscle fibers?
Slow, less powerful contraction
Many mitochondria
Slow fatigability
What are typical of type IIA skeletal muscle fibers?
Intermediate, powerful contraction
Some mitochondria
Intermediate fatigability
What are typical of type IIB skeletal muscle fibers?
Fast, powerful contraction
Few mitocondria
Rapid fatigability (anaerobic respiration)
What is a sarcolemma?
membrane around each muscle cell
What do transverse (T) tubules do?
membrane system penetrating the muscle cell to convey electrical impulses from sarcolemma into cell
What are the sarcoplasm and sarcoplasm reticulum (SR)?
Sarcoplasm is cyotplasm of muscle cell
SR: tubular system acting like smooth ER, which are the terminal cisternae (flattened sac of SR on either side of T tubule) releases Ca to get contraction
What is a triad for electrical impulse transmission?
the T tubule and 2 terminal cisternae
What are the End feet?
connect T tubles with SR to allow Calcium release
How is skeletal muscle innervation and how many nerves per muscle fiber?
they are innervated by peripheral alpha motor neurons from the anterior horn
1 nerve per muscle fiber, >1 muscle fiber per nerve
How do the nerve axons transmit the signal to the muscle?
Release acetocholine into the synaptic cleft, causes end feet to release Ca+ and causing the contraction
What soes the neruromuscular spindle apparatus do?
it has a relfexive response to prevent over stretching of a muscle
What do extrafusal and intrfusal muscle fibers do in neuromuscular spindle apparatus?
Extrafusal contract the muscle
Intrafusal (deep) sense length and rate of chang of the muscle, cause the response
What do type Ia sensory nerve fibers do?
they are the afferent innervation of intrafusal fibers that send signals to the spinal cord
what do alpha motor and gamma motor nerve fibers do?
they are the efferent innervation of extrafusal (alpha) and intrafusal (gamma) muscle fibers
How do the type Ia fibers and alpha and gamma fibers talk to eachother?
Afferent Ia fibers sense stretch in intrafusal fibers and send signal to A and G efferent fibers, causing extra/intrafusal fibers to contract and shorten, relieving the stretch
What makes up a neuron and what do they do?
Soma/body: contains organelles of neurons
Dendrite: receives signals from other neurons
Axon Hillock: connection between some and axon, summates all signals to make action potention
Axon: conveys electrical impulse to synapse
Synapse: transfers impulse from neuron to target tissue
What makes up a nerve?
Axons-> groups of axons = Fasicle -> Nerve =groups of fascicles
What fascia covers each axon, each fascicle and each nerve?
axon: endoneurium
fascicle: perineurium
Nerve: epineurium
What are multipolar neurons?
multiple dendrites and one axon
What are bipolar neurons?
one single dendrite with multiple extensions and one axon with the cell body in the middle
What are pseudounipolar neurons?
one cell process with a single dendrite branch (receives signal) and axon branch (sends signal to muscle), with the cell body connected by a short single process
What is a schwann cell (in PNS)?
surround axon and create myelin sheath in PNS, wrap around one part of one axon
What is an oligodendrocyte?
surround axon and create myelin sheath in CNS, wrap around a part of many axons
What is a myelin sheath?
circumferential layers of myelin allowing for faster signal conduction velocity
