Muscle Flashcards
Skeletal Muscle - Function
moves skeleton + other structures
Ex. precise eye movements
Skeletal Muscle - Embryology
Somites
Each somite provides skeletal muscle for different levels of body
Skeletal Muscle - Mechanism of Action for functions
Skeletal Muscle - Potential Diseases
Skeletal Muscle - Contraction Method
Stimulus is initiated within a neuron in spinal cord + impulse is brought down spinal cord w/long nerve fiber
Cardiac Muscle - Function
propels blood through the heart and lungs into the aorta (2 paths)
Cardiac Muscle - Embryology
Cardiac Muscle - Mechanism of Action for Function
Cardiac Muscle - Potential Diseases
Cardiac Muscle - Contraction Method
impulse contraction initiated at SA node of the heart which is then fine-tuned by the vagus nerve
Smooth Muscle - Function
contraction of blood vessels, viscera, intrinsic muscle of eye
(does so by changing the shape + size)
Smooth Muscle - Embryology
Smooth Muscle - Mechanism of Action for Functions
Smooth Muscle - Potential Diseases
Smooth Muscle - Contraction Method
Mechanical Impulses (Passive stretch) Electrical depolarization ( neural stimulation) Chemical Stimuli (hormones; 2nd messenger pathways)
Skeletal Muscle - Characteristics
- Cross striations (alternating dark + light bands)
What provides polarity in the embryo?
notochord
What is the dermamyotome comprised of?
dorsal dermis (dermatome) + skeletal muscle (myotome)
Skeletal Muscle - cells become elongated by…
…fusion
Why are contractile proteins made in muscle cells but not spleen cells?
Contractile proteins genes are transcribed in muscle cells
*the transcription is regulated by transcription factors
define trans-activators
proteins expressed during specific stages of development
bind to specific regions of genes
intimate transcription of specific genes
(EX. MyoD in skeletal muscle)
What does the basic region of MyoD bind to?
promoter of DNA
What does the Helix-Loop-Helix region of the MyoD bind to?
transcription factors (+ or -)
(+) - unregulated transcription
( - ) - inhibits transcription
What does the up-regulation of myogenin de-regulate?
Pax7
What do high levels of Pax7 indicate?
Proliferation
What do satellite cells always express?
Pax7
What does a high level of myogenin expression do?
upregulates transcription of contractile protein genes
What is the sarcolemma comprised of?
plasma membrane + basal lamina
What is responsible for myofiber contraction?
myofilament interaction
Myosin - Functions
- form thick filaments
- hydrolyze ATP
- interact with F-actin (receptor located at the head)
Troponin C Function
Binds to calcium => intimate contraction process
Troponin T Function
Binds complex of tropomyosin
Troponin I Function
Inhibits binding of myosin to actin
Tropomyosin
double helix of 2 polypeptides (lies in groove between actin molecules)
Titin
protein that stabilizes and centers myosin containing thick filaments
*allows certain amount of stretch + prevents tearing
Neuromuscular Junction (aka Motor End Plate)
Contact between axon and muscle fiber
Motor Unit
Motor neuron w/axonal branches + muscle cells they contact
Synaptic Cleft
Space left on muscle fiber if axon was removed
What happens to acetylcholine after it is released?
it binds to receptors on the muscle cell membrane
what happens after acetylcholine binds to receptors on the muscle cell membrane?
the membrane becomes permeable to sodium ions
what happens after the membrane becomes permeable to sodium ions?
depolarization of muscle cell membrane
what does the depolarization of the muscle cell membrane result in?
depolarization (action potential) transmitted throughout the muscle
How is the action potential transmitted throughout the muscle
T-Tubule system
What happens after the action potential is transmitted to the muscle?
Acetylcholine is degraded
Clinical Significance: Myasthenia Gravis - Cause
Patient produces antibodies against AcH receptors; ultimately preventing acetylcholine from binding
Clinical Significance: Myasthenia Gravis - Symptoms
Patients have weak muscle contractions and droopy eyelids + mouth
T-tubule
invagination of the plasma membrane
Triad Location
A-I junction in skeletal muscle
Terminal Cisterna
Specialized ends of the SR where networks meet
Sarcoplasmic Reticulum
repeating network around myofibrils
*extends from one A-I junction to the next A-I junction
Neuromuscular Spindle - Function
- allow for coordination
- senses stretch and communicates to CNS
Muscle Cell Components in Neuromuscular Spindle
Connective Tissue Capsule + Intrafusal Muscle Fibers + Stretch Receptor
How is a damaged muscle repaired?
Satellite Cells
Terminally differentiated cells (definition and example)
Defined: cannot divide any further
Ex. myotube satellite cells + cardiac cells
What does the force of contraction vary by?
Organization of fibers
Three basic type of fibers in muscles
Type 1, 2A and 2B
Contractile Speed
determines how fast the fiber can contract and relax
What does enzymatic velocity of myosin ATPase determine?
The rate at which the enzyme is capable of breaking down ATP during the contraction cycle
Metabolic Profile
capacity for ATP production by oxidative phosphorylation or glycolysis
Type 1 Fiber - Characteristic
Slow Oxidative
Abundance of Mitochondria
Seen as Red (strong staining of succinic dehydrogenase) + Small on images
Type 2A Fibers - Characteristic
Fast Oxidative
Medium/Large with Pale Staining
Fibers 2B Characteristics
Fast Glycolytic
Medium/Large with Pale Staining
Which muscle fibers have high myoglobin content?
Type 1 + 2A
Intercalated Discs - Function
allow electrochemical coupling between cells => communicate impulse for contraction from one cell to another
Purkinje Fibers - Function + Location
brings down the impulse to ventricles
Location: below endothelium
Purkinje cells - Characteristics
- Large cells
- fibrils pushed towards periphery
- bi-nucleated
- connect via gap junctions
Cardiac Muscle - Characteristics
- Intercalated discs
- Striated
- Centrally located nuclei
- Branching
Connections in Intercalated Discs
- fascia adherens (transverse component)
- gap junctions (lateral component)
- desmosomes (throughout)
Intercalated Discs - Gap Junctions (Function)
ionically couple one cell to the next
Intercalated Discs - Fasciae Adherentes (Function)
- Hold cardiac muscle cells at their ends
- Site where thin filaments of terminal sarcomere attach to plasma membrance
Diad
- Cardiac Muscle
- similar to Triad in skeletal muscle
- Location: Z-line
Cardiac Hypertrophy - Common Causes
- High BP
- heart valve stenosis
What is Cardiac Hypertrophy?
thickening of the myocardium (heart muscle)
Smooth Muscle Location
- Viscera
- Vascular System
- Arrector Pili muscle in the skin
- Intrinsic muscle of the eye
Single Unit Smooth Muscle
unit/group of cells work together, connected by gap junctions
allow ions + small molecules to pass b/w cells
whole sheet contracts together
(Ex. GI Tract)
Multiunit Smooth Muscle
Individual smooth muscle cells are independently innervated fibers
controlled by signals from nerves
Ex. Eye
Smooth Muscle Cell - Characteristics
- No visible sarcomeres or striations
- No T-Tubules
- Thin filaments attached to dense bodies
- Bindle or sheets of elongated cells
- Closely packed
- Tapered ends
Myosin Filament arrangement in Smooth Muscle
- one direction on one side and the opposite direction on the other side
- no bare zone
advantage of no bare zone in myosin filaments?
contraction lasts a long time
Clinical Significance: Asthma/ Allergic Reactions
SMOOTH MUSCLE of bronchi contract + airways narrow
Clinical Significance: Fibrosis
- excess myofibroblasts
- Occurs in liver (response to alcohol abuse)
- Occurs in lungs (response to smoking abuse)
