Class 16 - Muscle Tissue Flashcards
Characteristics of ALL muscle cells (5)
- Excitability - to outside stimuli (chemical signals, stretch, electrical changes across plasma membrane)
- Conductivity - Local electrical excitation sets off wave of excitation that travels along muscle fiber.
- Contractility - shortens when stimulated
- Extensibility - capable of being stretched between contractions
- Elasticity - Ability to “bounce back” to original testing length after stretching
4 characteristics of collagen in muscle (4)
- Stretches slightly under tension and recoils when released
- Resists excessive stretching, protecting from injury
- Returns muscle to resting length
- Contributes to power output and muscle efficiency
Components of a muscle fiber (7)
- Sarcolemma - plasma membrane of a muscle fiber
- Sarcoplasm - cytoplasm of a muscle fiber
- Myofibrils - Long protein cords occupying most of sarcoplasm
- Glycogen - carbohydrate stored to provide local energy for exercise
- Myoglobin - red pigment; provides some local oxygen for immediate muscle activity
- Many mitochondria
- Nuclei - 30 to 80 per mm. Help fiber repair
Sarcoplasmic reticulum
smooth ER that forms network around each myofibril
Terminal cisterns
dilated end-sacs of SR which cross muscle fiber. Act as calcium reservoir. Calcium bound to calequestrin.
Transverse (T) tubules
Tubular infoldings of the sarcolemma which penetrate through cell and emerge on other side.
Each has two terminals cisterns associated with it on either side
Myoblasts
Muscle stem cells that fused to form each muscle fiber early in development, each contributing one nucleus
Satellite cells
Unspecialized myoblasts remaining between the muscle fiber and endomysium.
Help regenerate damaged skeletal muscle tissue
What are myofibrils composed of? + 3 types
Muscle filaments (myofilaments)
- Thick filaments
- Thin filaments
- Elastic filaments
Thick myofilaments
Made of several hundred myosin (motor protein) molecules
Each molecule shaped like golf club: two chains intertwined to form tail and globular head
Heads direct outward with bare zone in between
Thin myofilaments + 3 composing proteins
- Fibrous (F) actin - two intertwined strands of globular (G) actin subunits, each with an active site that can bind to head of myosin molecule
- Tropomyosin - each blocks six or seven active sites on G actin subunits
- Troponin - calcium-binding protein on each tropomyosin molecule
Elastic myofilaments
Made of huge springy protein called titin.
Runs thru core of thick filament and anchors it to Z disc at M line.
Helps stabilize and position thick filament
Prevents overstretching and provides recoil
What are the two contractile proteins and two regulatory proteins of myofilaments?
Contractile: Myosin and actin
Regulatory: Tropomyosin and troponin (binds calcium, moves tropomyosin off actin active sites)
Dystrophin
Protein which links actin in outermost myofilaments to membrane proteins that link to endomysium
Transfers forces of muscle contraction to connective tissue and ultimately tendon
Genetic defects produce muscular dystrophy
A band + 2 components
Darkest part where filament thick filaments overlap hexagonal array of thin filaments
- H-band - less dark, middle of A band. Thick filaments only.
- M line - dark, transverse protein in middle of H band
I band + 1 component
Light band of striations.
Z disc - protein complex that provides anchorage for thin filaments and elastic filaments.
Sarcomere
Segment from Z disc to Z disc. Functional contractile unit of muscle fiber.
Muscle contraction process
Muscles shorten because individual sarcomeres shorten - Z discs are pulled together as thick/thin filaments slide past each other.
Dystrophin and linking portions also pull extracellular proteins, pulling extracellular tissue
Denervation atrophy
Shrinkage of paralyzed muscle when nerve remains disconnected
Nerve stimulation is ESSENTIAL to muscle contraction
Somatic motor neurons + somatic motor fibers
Nerve cells whose cell bodies are in the brain stem/spinal cord while their axons (somatic motor fibers) lead to skeletal muscle
Each nerve fiber branches out to multiple muscle fibers, but each muscle fiber is supplied by only one motor neuron
Motor unit + 4 characteristics of their muscle fibers
One nerve fiber and all the muscle fibers innervated by it
Muscle fibers are:
1. dispersed throughout the muscle
2. contract in unison
3. Produce weak contraction over wide area
4. Require other motor units to take turns with to sustain long-term contractions
Avg motor unit fibers/fascicles + 2 types
Avg motor unit contains 200 muscle fibers in up to 100 fascicles
- Small motor unit - provides fine degree of control (hand or eye muscles controlled by units with only 3-5 fibers each)
- Large motor units - provide more strength than control (quadriceps femoris and gastrocnemius controlled by motor units with ~1,000 fibers)
3 components of neuromuscular junction
- Synapse/NMJ - point where nerve fiber meets target cell; each terminal branch of nerve fiber within NMJ has separate synapse with muscle fiber
- Axon terminal - swollen end of nerve fiber. Contains synaptic vessels with acetylcholine
- Synaptic cleft - narrow gap between axon terminal and sarcolemma
Postsynaptic membrane folds
Increase surface area of the neuromuscular junction, maximizing the number of ACh receptors.
Basal lamina
Encloses entire NMJ. Thin layer of collagen and glycoprotein separating muscle fiber and nerve endings from surrounding connective tissue
Passes thru synaptic cleft
Acetocholinesterase (AChE)
Enzyme that breaks down ACh, allowing for muscle relaxation
Found in sarcolemma, lamina, and synaptic cleft.
Electrophysiology
Study of electrical activity of cells
Electrical activity depends on concentration differences in ions of ICF and ECF
Polarized membrane and normal K+ Na+ concentrations
Contains a net negative charge
Normal resting cell:
More K+ inside (ICF), more Na+ outside (ECF)
Electrical potential/voltage and resting membrane potential
Electrical potential - Any difference in charge between two points
RMP - the natural state of the plasma membrane with a polarized negative charge
2 actions of a stimulated cell + action potential definition
- Ion channels open, allow Na+ into cell, causing depolarization (increased positive charge in cell)
- Additional ion channels allow K+ out of cell, causing repolarization
Action potential - voltage shift of cell membrane
Cholinesterase inhibitors, tetanus, flaccid paralysis, botulism
Cholinesterase inhibitors - Found in some pesticides. Bind to acetocholinesterase and prevent degradation of ACh causing spastic paralysis (continual contraction)
Tetanus - form of spastic paralysis where glycine of spinal cord ceases to prevent motor neurons from producing unwanted contractions
Flaccid paralysis - state in which muscles are limp and cannot contract. Curare competes for ACh receptor sites
Botulism - food poisoning which causes blockage of ACh release, causing flaccid paralysis
