Lecture 4: SM and Nervous System Flashcards
Function of muscle
creates force for movement
Muscle converts ____ to ______
ATP is converted to mechanical energy
Function of skeletal muscle
Skeletal muscle is voluntary and help with postural stability
Features of skeletal m.
- Striated
- multiple nuclei that are peripherally located
- Strong and quick, thus fatigauble
- Have large cells
What are muscle cells called?
Myofibers
Myocytes
Muscle fibers
What are myofibers made up of?
Myofibrils.
They are surrounded by an endomysium.
What are myofibrils?
Chains of sarcomeres linked together
What is a sarcomere?
Smallest contractile unit of the muscle, made up of actin and myosin myofilaments
A group of myofibers is called what?
Fasicle.
A fasicle is surrounded by what?
A perimysium
Muscles are a group of what, surrounded by what?
Group of fasicles surrounded by an epimysium.
Summary: organization of muscles.
Muscles are surrounded by a fascial covering called a epimysium.
Muscles are made up of fasicles (groups of myofibers), wrapped with perimysium.
Myofibers are made up of myofibrils and are wrapped with endomysium.
Myofibrils are groups of sarcomeres.
1 Sarcomere is measured from
Z-line to Z-line.
Sarcomeres are made up of what?
thin and thick filaments
What are the thick elements of a sarcomere?
Myosin
Describe myosin.
Myosin has 2 heavy chains with globular heads that have actin binding sites with ATPase domains.
They also have 2 light chains,
Connected to the Z-disk by titan.
What is the thin elements of sarcomeres?
Actin.
Describe actin.
Actin is made up of globular actin, to form a monomer fibrillar actin. Two monomer fibrillar actins twist together to form a double strand.
Tropomysoin wraps in between actin strands. On these tropomyosin strands, are troponin. Tropomoyosin blocks the myosin binding sites on actin so that we arent always contracting.
What is the M-line of the sarcomere?
Where myosin attaches
What is the Z-disk?
Z-disks separate sarcomeres. It has attachment sites for actin and titin.
What is the H-band?
Space on either side of the M-line, where there is no actin.
What is the A-band?
Entire length of a single thick filament (from one myosin head to the head of the opposite).
It includes the H band, actin and myosin.
What is the I-band?
Space on either side of the Z-disk, where there is no myosin.
How can we start muscle contraction
For muscle to contract, myosin must bind to actin. However, tropomyodin blocks the myosin binding sites on actin.
Thus, calcium is released from the sarcoplasmic reticulum (SR) and causes a conformational change in the troponin. Tropomyosin moves out of the way and the actin binding sites are now accessible to the heads of the myosin.
What is the sliding filament mechanism?
Thin filaments (actin) and thick filaments (myosin) slide past one another to shorten the sarcomere. The myosin heads will crawl across the actin filaments, bringing the Z-disks closer together.
All of the myofibrils will contract at the same time, making the entire muscle shorten.
Do actin and myosin change in length?
No. They overlap one another.
What are the 3 types of skeletal muscle fibers?
- Type 1
- Type IIA
- Type IIB
Type 1 skeletal muscle fibers
Slow and slow to fatigue because they have many mitochondria. Their contraction is less powerful.
- Has a lot of myoglobin
- Aerobic respiration
Type 2A skeletal muscle fibers
Fast (intermediate) and fatigues intermediately. Thus, it has a powerful contraction
- Has many mitochondria
- Has many myoglobin
- Aerobic respiration (less O2 delivery)
Type 2B skeletal muscle fibers
Fast & fatigues quickly because few mitochondria. Power contraction, though.
- Few myoglobin.
- Anaerobic respiration
What is the sarcolemma?
Sarcolemma is a membrane that surrounds each myofiber.
How are electrical impulses transmitted in skeletal muscle?
Sarcolemma penetrates into the muscle cell to create transverse (T) tubules l to convey AP’s from the sarcolemma–> cell.
What is the sarcoplasm?
The cytoplasm of the muscle cell.
What is the sarcoplasmic reticulum?
A tubular system that acts like the smooth-ER. It stores the Ca2+ that we need for muscle contraction.
Terminal cisternae are flattened sacs of SR on either side of the T-tubule
What are terminal cisternae?
Flattened sacs of SR on either side of the t-tubule.
What is the triad?
2 terminal cisternae + t-tubule. They are connected by end-feet.
What is the end feet?
Connects the t-tubule with the terminal cisternae (SR) to allow Ca2+ to be released.
Excitation-contraction coupling of skeletal muscle
- AP is conducted down the neuron–> axon terminal.
- VGCa2+ will open and cause the influx of Ca2+ into the terminal.
- Ca2+ binds to synaptic vesicles.
- Synaptic vesicles move to the cell membrane and releases ACh into the NMJ via exocytosis.
- ACh will bind to nicotenic cholinergic receptors (Ligand-gated Na+ receptors) in the subneural cleft of the post-synaptic membrane and cause the influx of Na+.
- This will cause localized potentials, which will then activate VGNa+ receptors.
- Because skeletal muscle is so big, they have [t-tubules] to help reach the depths of the muscles. As the AP travels down the T-tubule, it activates DHP receptors, which are coupled to [ryanodine receptors].
- Ryanodine receptors are located on the sarcoplasmic reticulum. - Ca2+ is released from the sarcoplasmic reticulum–> sarcolemma.
- Ca2+ will then bind to Troponin C, causing tropomyosin to shift away from actin binding sites. This allows the myosin heads to interact with the actin binding sites.
- ATP bind to mysoin head (causing it to be active)
- ATP–> ADP + Pi which causes the myosin head to cock back and attach.
- When Pi, leaves, the powerstroke will occur and actin is pulled to the m-line.
- To release, ADP leaves and ATP binds. We are now in the original state
What innervates skeletal muscle?
alpha-motor neurons from the anterior (ventral horn)
Each myofiber is only innervated by 1 nerve, but 1 nerve can innervate many muscle fibers.
Goal of the neuromuscular spindle apparatus
It initiates a reflex to prevent us from overstretching our muscles.
What are the components of the neuromuscular spindle appartus
- Extrafusal muscle fibers
- Intrafusal muscle fibers
- Type 1A sensory nerve fibers
- Alpha-motor nerve fibers
- G-motor nerve fibers
Extrafusal muscle fibers
contract the muscle
Intrafusal muscle fibers
buried inside the [extrafusal m] and sense the length and rate of change of the muscle via [type 1a sensory nerve fibers].
They then control the [alpha-motor nerve AND g-motor nerve]
Type 1A sensory nerve fibers
afferent innervation of intrafusal fibers. They sense they stretch and rate of change of intrafusal fibers.
Alpha-motor nerves
Receive signal from type 1A fibers and cause extrafusal muscle fibers to contract (shorten)
g-motor nerve fibers
Receive signal from type 1A fibers and cause intrafusal muscle fibers to shorten.
They continuously receive signals from higher brain centers to be able to detect changes.
Soma of neuron
contains organelles of the neuron
Nissle substance
High amount of rER in the cytoplasm of the soma
Axon hillock
connects soma and axon.
Summates electrical signals received from dendrites.
Synapse
transfers electrical impulse from neuron–> target tissue.
An axon is wrapped in an
endoneurium
A fasicle (group of neurons) is wrapped in a
perineurium
What is a nerve surrounded by?
Epineurium, wraps all of the fasicles together.
Nerve arrangement
A nerve is made up of fasicles of axons.
Nerve is surrounded by epineurium.
Fasicles are surrounded by perineurium.
Axons are surrounded by endoneuriums.
Multipolar neurons
mulitple dentrites and 1 axon
Bipolar neurons
1 dendrite with multiple extensions and 1 axon
Pseudounipolar neurons
1 cell process with a single dendrite and axon branch
Schwann Cells
mylenate one part of one axon in the PNS
Oligodendrocytes
myelinate one part of many axons in the CNS
Myelin sheath
increases signal conduction.
