Lecture 4: Skeletal Muscle and Nerve Tissue Flashcards
Simply put, how does contraction occur?
Actin (thin filaments) and myosin (thick filaments) slide past each other in myofibrils in the cytoplasm
What is actin made of?
G-Actin Monomers
(globular protiens)
What two chains does Myosin have?
Heavy chain with a globular head
Light chain
How can you differentiate between skeletal, cardiac, and smooth muscle?
Skeletal: Striated and Voluntary
Cardiac: Striated and Involuntary
Smooth: Non-striated and Involuntary
From smallest unit to largest, what are the divisions of a muscle?
Sarcomere -> Myofibrils -> Myocyte (Myofiber) -> Fascicle -> Muscle
What connective tissue separates myofibers?
Endomysium
What connective tissue separates fascicles?
Perimysium
What fascial covering surrounds the entire muscle itself?
Epimysium
What features can be used to identify Skeletal Muscle, especially in a histological slide?
Peripheral nucleii and Striations
Myofibers: Multinculeaded cylinders in the periphery of cell
Myofibrils: In the cytoplasm
What is a sarcomere?
Basic structure of myofibril
What serves as the defined border of a sarcomere?
Z disks
What is the Sarcoplasm?
Cytoplasm of a Muscle Cell
What is Sarcoplasmic Reticulum?
What is stored in there?
Tubular system which acts like smooth ER
-Calcium is stored
What is the Sarcolemma?
The membrane around myocytes that penetrates the muscle cell as T tubules
What are Transverse (T) Tubules?
Invaginations of sarcolemma
What connects the Transverse Tubule to the Terminal Cisternae?
What do they do?
“End Feet”
Allow for calcium release
What does the Terminal Cisternae do?
Dilated ends of Sarcoplasmic Reticulum that releases Calcium to trigger muscle contraction
What is marked here as 1?
What does it contain?
I Band
-only actin thin filaments
What is marked here as 2?
What is found here?
A Band
-Overlap of actin and myosin and H zone
What is marked here as 3?
What is found here?
H Zone
-only myosin thick filaments
What is marked here as 4?
What is found here?
M Line
-anchor site for myosin thick filaments
What is marked here as 5?
What is found here?
Z Line
Anchor site for actin thin filaments
What attaches to the Z disk?
Actin and Titin (which in turn holds myosin)
What holds the Myosin to the Z disk, thus holding Myosin in place?
Titin protiens
What all is contained within the H Zone?
Myosin fibers and the M line
What is contained within the I band?
Actin
The Z Disk
(straddles sarcomeres)
What is defined as the A band?
Distance from end to end of myosin within one sarcomere.
Does the A Band shorten during contraction?
No. Only the H Zone and the I band shorten
Where are myosin going one direction attached to the myosin going the other direction?
M line / M disc
What two regions of a Myofibril shorten during muscle contraction?
The H Zone and the I Band
What does Tropomyosin do?
Wraps between actin strands and holds troponin
What keeps the muscles from contracting all the time?
Tropomyosin blocks the myosin binding sites
What does Calcium do to incite muscle contraction?
It binds to Troponin, which then causes Tropomyosin to change conformation, and no longer block the Myosin binding sites on the Actin Filament
What are the basic characteristics of Type 1 muscle fibers?
- Slow ATPases
- Slow Contractions and low power (e.g. muscles in back)
- Low fatigability
- Many mitochondria and very aerobic
- Abundant Myoglobin for O2 (gives red color)
What is a Type IIa Muscle Fiber?
- Largest and most prevalent (seen in most of body)
- Intertmediate ATPase that provides power
- Primary aerobic
What are the basic characteristics of Type IIb Muscle Fibers?
- Fast ATPase and largerly anaerbic
- Rapid Fatigue
- Low myoglobin content
What are the major parts of a neuron?
- Cell Body: processes electrical information
-
Cell Processes
- Dendrites: carries electrical signals toward cell body
- Axons: carries electrical signals away from cell body
- Synapse: Transfer of electric signals from axon terminal of one nerve to an effector cell
What is the Nissl substance?
Rough ER that makes a lot of neurotransmitters and protein to maintain neurons
What is the function of the Axon Hillock?
Sums up all of the action potentials from the dendrites, and sends a signal down the axon if it is sufficient.
What is this type of neuron?
How many dendrites and axons for this neuron?
Multipolar Neuron
-Multiple dendrites, one axon
What is this type of neuron?
How many dendrites and axons for this neuron?
Bipolar Neuron
-Single dendrite (with multiple extensions) and one axon
What is this type of neuron?
What are the characteristics of this neuron?
Unipolar Neuron
A cell body connected to a cell process with a dendrite branch and an axon branch
Do Schwann cells wrap around parts of single axons or many axons together?
Parts of a single axon in the PNS
Do Oligodendrocytes wrap around parts of single axons or many axons together?
Many axons together in the CNS
What connective tissue layer wraps a single myelinated or unmyelinated axon?
It is connective tissue between axons
Endoneurium
What connective tissue layer wraps a fascicle of nerve fibers together?
Perineurium
What is the connective tissue layer surrounding the outside of the entire spinal nerve?
Epineurium
In broad terms, how does the chemical synapse work?
Step 1: Synpatic vessels in the presynaptic knob release a NT into the synpatic cleft via exocytosis.
Step 2: NT binds to a receptor on the postsynpatic membrane
Step 3: Postsynpatic cell is now stimulated
How does the neuromusclar junction work?
Step 1: Acetylcholine is released into synaptic cleft
Step 2: Acetylcholine stimulates sarcolemma and excites the muscle fiber. This stimulus is carried to T tubules to initiate contraction
Step 3: Acetylcholine is broken down in synpatic cleft, ending its signal.
What is an intrafusal muscle fiber?
What are its two compartments?
Specialized fibers inside muscle spindle
Nuclear Bag Fibers: Detect change in length and degree of tension
Nuclear Chain Fibers: Detect static muscle length
What is an extrafusal muscle fiber?
Muscle fiber outside muscle spindle under voluntary control,
-In charge of contracting the muscle fibers
What is the function of Alpha-Motor nerve fibers?
Sends the signal to contract to a muscle to extrafusal fibers
Why is it important to have electrical impulses shuttled into the cell?
So that the myocyte can contract all at once, instead of from the outside in.
