Unit 3 Flash Cards
Muscle
Three types of muscle
skeletal, cardiac, smooth
6 functions of skeletal muscle
1) produce skeletal movement
2) maintain posture
3) support soft tissues
4) guard main entrances and exists
5) maintain body temp
6) store nutrient reserves
Muscle Organizational Terms
Skeletal muscles are striated. Within the msucle you have a fassicle, which is a bundle of muscle fibers. Muscle fibers are individual muscle cells. Inside of those muscle cells you have myofibrils which contain sarcomeres. Those sarcomeres are whereyou have the thick and thin myofilaments
Skeletal Muscle is what system?
SOMATIC nervous system because it’s voluntary movement
Smooth muscle is what system?
AUTONOMIC nervous system because it’s involuntary
sarcolemma
plasma membrane of the muscle fiber
myofibril
shoots of proteins that house sarcomeres
Sarcoplasmic Reticulum (SR)
stores and regulates calcium and their level and also releases/reabsorbs them very fast
Transverse Tubules (T-tubules)
deals w/electrical signals, AP needs to tell the SR to release calcium so that the muscle can contract, shuts off when we want the muscle to relax
Neuromuscular Junction (NMJ)
the first set of steps to control skeletal muscle activity
Steps for neuromuscular junction
1) AP is generated
2) Ca2+ entry via neuron (axon terminal) which stimulates
3) release of acetylcholine (ACh) from vesicles (via exocytosis)
4) Binds to receptor
5) generates AP on sarcolemma
6) runs down T-tubules
7) contraction Occurs
Excitation-Contraction Coupling
basically a component of neuromuscular junction
1) EXCITATION: AP runs down the T-tubules and at the triad, stimulates calcium release into the muscle cell
2) CONTRACTION: contraction occurs– as long as calcium ions stay in the sarcoplasm and are bound to troponin
Steps to INITIATE Muscle Contraction
1) ACh is released: ACh is released at NMJ and binds to ACh receptors on the sarcolemma
2) AP reaches T-Tubule: an AP is generated and spreads across the membrane of the muscle fiber and along T-tubules
3) Sarcoplasmic Reticulum releases Ca2+
4) Active sites exposed and cross-bridges form: calcium ions bind to troponin, exposing active sites on the thin filaments. Cross bridges form when myosin heads bind to those active sites
5) Contraction cycle begins
Contraction Cycle Summarized
1) contraction cycle begins
2) active-site exposure
3) cross-bridge formation
4) myosin head pivoting (power-stroke)
5) cross-bridge detachment
6) myosin reactivation
Steps that END Muscle Contraction
1) ACh is broken down: it’s broken down by acteylocholinesterase (AChE), ending AP generation
2) Sarcoplasmic Reticulum reaborbs Ca2+
3) Active sites covered, and cross-bridge formation ends: without calcium ions, the tropomyosin returns to its normal position and active sites are covered again
4) muscle relaxation occurs
Muscle Relaxation
1) contraction duration depends on: duration of neural stimulus, and number of free calcium ions in sarcoplasm
2) Ca2+ concentrations fall (it’s pumped back into SR)
3) Ca2+ detaches from troponin
4) active sites are re-covered by tropomyosin
Muscle Excitation Events In order
1) ACh is bound to the synaptic cleft
2) Muscle Fiber depolarizes
3) calcium is released from SR
4) Calcium binds to troponin
5) sarcomeres shorten
Statement about muscle contractions that is true:
sarcomere length changes during all types of contractions
Isotonic Contraction
think skeletal muscles changing in length, there are two different subcategories: concentric, and eccentric contractions
example: holding a barbell before doing an arm curl
Concentric Contractions
when muscle tension>load
example: pulling a barbell upwards in an arm curl
Eccentric Contractions
when muscle tension<load
example: extending your arm during an arm curl
ATP used by muscles comes from:
1) creatine phosphate
2) aerobic metabolism
3) glycolysis
Fast muscle fiber
contracts really quickly, has a large diameter and large GLYCOGEN reserves, powerful contraction/fatigues very quickly, anaerobic metabolism
Slow muscle fiber
slow to contract, high oxygen supply, primarily aerobic metabolism, has a small diameter w/more mitochondria, slow to fatigue, and contains myoglobin (protein that binds to oxygen)
Hypertrophy
muscle growth from muscle training activity; increases: diameter of muscle fibers, number of myofibrils (and sarcomeres), also mitochondria and glycogen reserves
Atrophy
lack of muscle activity– reduces muscle size, tone, and power
Tension
when muscles cells contract, they pull on the attached tendon fibers, tension is the pull; it needs energy because it’s an active force
-muscle cells use energy to shorten and generate tension through interactions between thick and thin filaments
-tension production is based on individual muscle fibers
Fiber Resting Length
the time of stimulation (length-tension) relationship
-the number of pivoting cross-bridges depends on: amount of overlap between thick and thin filaments
-optimum overlap produces GREATEST amount of tension
-normal sarcomere length is 75-130% to be optimal
Frequency of Stimulation
a single neural stimulation produces: single contraction twitch (lasts 7-100 msc); sustained muscular contractions (may require repeated stimuli)
Two factors that determine amount of tension produced by whole skeletal muscle:
1) fiber’s resting length (#of cross bridges)
2) frequency of stimulation (how often it receives AP): this is because it determines how much calcium is in the sarcoplasm
Motor Unit
all muscle fibers have 1 single neuron attached to it, but one neuron can be attached to multiple muscle fibers, which is a motor neuron, part of a neuron unit
Relationship between motor unit size and control
the size of the motor dictates how fine the control movement can be
-if you want PRECISE control then you want 4-6 muscle fibers (i.e. like the eye)
-if you want GENERAL control then you want 1,000-2,000 fibers (i.e. your leg)
Myofilaments
contain 2 types of filaments: thin (actin), and thick (myosin)
Thin filaments
1) Actin: active sites bind on actin strands to bind onto mysosin
2) Tropomyosin: prevents actin-myosin interaction
3) Troponin: binds tropomyosin to actin, controlled by Ca2+
Epimysium
an exterior collagen layer, connected to deep fascia, and it separates muscle from surrounding tissue, surrounds skeletal muscle.
Perimysium
surrounds muscle fibers (fascicles), contains blood vessels,
At the level of the sarcomere..
1) what initiates cross-bridge formation: calcium goes from the SR –> the sarcoplasm through ion channels
2) What is preventing myosin from forming a cross-bridge w/actin: tropomyosin bc Ca2+ is bound to troponin
3) Why don’t thin filaments slide backwards when myosin heads detach from actin: there are other myosin heads attached to hold it in place
4) What two roles does ATP play in cross-bridge cycling: it provides energy for the pivot and it causes myosin to detach
5) What must first take place before cross-bridge cycling ends: calcium needs to be removed, uses primary active transport to go up it’s concentration gradient using ATP
