Muscle I Flashcards
What is the primary function of all muscle
Generate force and/or movement in response to physiological stimulus
What are 7 functions of muscle
- body movement
- maintenance of posture
- respiration
- productions of body heat
- communication
- constrictions of organs and vessels
- heart beat
What does all generation of force depend on
Conversion of chemical energy (ATP)
What are characteristics of skeletal muscle?
- primarily voluntary by somatic motor neurons
- striated and multinucleated
- attached to bone or attached to other skeletal muscle that is attached to bone
What is another word for muscle cell
Muscle fiber
Why is muscle striated
Arrangement of thick and thin filaments
Characteristics of cardiac muscle
- generates force to create pressure gradient that drives blood flow
- primarily involuntary; spontaneous electrical activity (doesn’t need neuronal input)
- can be altered by autonomic NS, hormones
- striated and uninucleated
Characteristics of smooth muscle
- primarily involuntary: autonomic control, spontaneous, hormones, paracrines or autocrines
- non-striated and uninucleated
What does smooth muscle provide mechanical control of?
- digestive tract
- urinary tract
- reproductive tract
- blood vessels
- airways
How is skeletal muscles attached to bone
Tendons
What is origin
Closest to trunk or to more stationary bone
What is insertion point
More distal or more mobile attachment
What are antagonistic muscle groups
- when movement is around a joint
- flexor-extensor pairs
- flexor: brings bones together
- extensor: moves bones away
How much of total body weight is skeletal muscle and how much of daily energy expenditure does it use
40%
Based on activity level 15-60%
What is a muscle cell membrane
Sarcolemma
What is a muscle cytoplasm
Sarcoplasm
What is a muscles modified endoplasmic reticulum
Sarcoplasmic reticulum
How long are muscle fibers
Can extend entire length of muscle
- sartorius ~30cm
What is components of skeletal muscle from largest to smallest?
Muscles fascicles and connective issue and nerve and blood vessels -> muscle fibers -> sarcolemma (t-tubules) and sarcoplasm and nuclei -> SR and myofibrils and mitochondria and glycogen -> troponin, actin, tropomyosin, myosin, titin, nebulin
How many muscle fibers in a muscle fascicle
20-60
How many myofibrils in a single muscle fiber
1000+
What are myofibrils composed of
Sarcomeres stacked end to end
What is a sarcomere
Basic functional unit of skeletal muscle
Made of long myofibrils
Where is force generated
At level of individual sarcomere
What are the contractile proteins
Thick filament: myosin
Thin filament: actin
What is dark on a sarcomere
Thick filament doesn’t let light through (myosin)
Z-disk is dense protein structure
What is the model of a sarcomere
Z disk to z disk
What are the thin filaments
F-actin, tropomyosin, troponin complex
What is F-actin
Back bone of thin filaments
- double stranded alpha helical polymer of G-actin molecules
- contains binding site for myosin
What is tropomyosin
- two identical alpha helictites that coil around each other and sit in the two grooves formed by actin strands
- regulated actin-myosin binding
- when active sit over myosin binding sites
What is the troponin complex
Heterotrimer (3 protein structures) consisting of:
1. Troponin T (TNT) : binds to a single tropomyosin
2. Troponin C (TnC): Ca2+ binding site
3. Troponin I (TnI): under resting conditions is bound to actin inhibiting contraction
Where is troponin complex situated
~ every 7 actin molecules
- holds tropomyosin over myosin binding site
What are the thick filaments
Bundle of myosin molecules
- two intertwined heavy chain
- each heavy chain contains two light chains
- regulatory light chain
- essential light chain
What does the myosin head contain
Region for binding actin as well as site for binding and hydrolyzing ATP (ATPase)
What does regulatory light chain regulate
ATPase activity of myosin
- controls speed and movement
What does essential light chain stabilize
The myosin head
What are the accessory proteins in the sarcomere
Titian and nebulin
What is titin
Very large protein extending from m-line to z line
- appears to be involved in stabilization of thick filaments and elastic recoil of muscle (pulls sarcomere back to resting length)
What is nebulin
Large protein that interacts with thin filaments
- believed to regulate length of thin filaments and contribute to structural integrity of myofibrils
What are the 5 bands of the sarcomere
Z disk, I bands, A band, H zone, M line
What is the z disk
Zigzag protein structure that is the attachment site for thin filaments
What are I bands
Lightest band of sarcomere, occupied only by thin filaments
- considered 2 with z disk in middle
What is A band
Darkest band, encompasses entire eight of thick filament, including area where thin and thick overlap
What is H zone
Central region of A band, consists only of thick filaments
What is M line
Proteins form attachment site for thick filaments, equivalent to z disk for thin filaments
What are the transverse tubules
Continuation of sarcolemma into middle of muscle fiber
What is a muscle triad
T-tubule with 2 adjacent terminal cisternae
What is a terminal cisternae
Portion of SR that interacts with t-tubules (most of calcium storage)
What is Sarcoplasmic reticulum
Modified endoplasmic reticulum that serves Ca2+ storage for contraction
What is the sliding filament model
- sarcomere shortens
- actin and myosin do not change length but slide past one another
What is muscle tension
Force generated by contracting skeletal muscle
When muscle is contracted which band remains constant
A band doesn’t change while H zone and I band shorten
