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83 terms

Muscle

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Action potential
Electrical current conducted along the membrane of a nerve or muscle cell
Excitation-contraction coupling
The series of events linking the electrical signal to muscle contraction
Neuromuscular junction
Region where the motor neuron comes into close contact with the muscle cell
Synaptic cleft
Extracellular space between the neuron terminal and the muscle cell membrane (sarcolemma)
Synaptic vesicles
Small membranous sacs containing a neurotransmitter
Acetylcholine
Neurotransmitter released at the neuromuscular junction
Depolarization
Loss of negative charge inside the cell
Refractory period
The period during repolarizaton when the cell is insensitive to further stimulation
All-or-none response
An action potential, once initiated, ultimately results in full contraction of the muscle cell
Acetyl cholinesterase
An enzyme located on the sarcolemma in the neuromuscular junction which degrades acetylcholine
Motor unit
lower motor neuron that comes from the spinal cord and muscle fibers it stimulates. They can be small or large.
Sarcomere
The smallest functional unit of muscle tissue.
Muscle Fiber
One single muscle tissue cell. Has its own components that make a cell.
Fascicle
Bundle of muscle fibers. Several thousands in a muscle
Sliding Filament Theory
Thin filaments slide over thick filaments
Actin
the protein that is pulled toward the center of the sarcomere by the myosin during contraction
ATP
Energy in the form of what is needed to contract or release a muscle
Thick filament
contains myosin heads that stick out in six different directions to pull thin filaments.
Thin filament
Contains Actin, Tropomyosin, Troponin
Neuromuscular junction
the point at which the motor neuron and muscle connect
Central nervous system
All skeletal muscles are connected with a motor neuron from where?
excitation-contraction coupling
molecular events of a muscle contraction
Step 1a - active site exposure
impulse from CNS, ACh released, diffuses across cleft, stimulates fiber/cell
Step 1b
impulse travels across sarcolemma in all directions, into SR via T-tubules
Step 1c This movement exposes the binding site actin
Ca+2 diffuses out of sarcoplasmic reticulum, binds to troponin, alters its shape and position of tropomyosin
Step 2 Cross bridge attachment
myosin binds to actin binding sites
Step 3 "ratchetting"
"power stroke" myosin cross brindge bends, pulling thin filaments toward center of sarcomere + contraction/muscle fibers shorten
Step 4 Cross-bridge detachment
ATP binds myosin, which breaks the linkage to actin
Step 5a Myosin reactivation
ATPase (enzyme in myosin) breaks down ATP, energy is released (catabolism), myosin uses energy to straighten its cross-bridge
Step 5b
Myosin cross-bridge can now combine with another binding site further down the actin filament and pull again
muscle relaxation
No more ACh = no stiumlation to sarcolemma = SR pumps Ca+2 back inside = no Ca+2 meansactin binding sites are covered
Sarcoplasmic reticulum
storage of Ca+2
ATP
breaking the linkage between actin & myosin requires what?
ATP
reposition/re-energize the myosin head (cross bridge) requires what?
ATP
Pumping Ca+2 back into the sarcoplasmic reticulum requires what?
Rigor mortis
Ca+2 floods ICF from sarcoplasmic reticulum AND extracellular fluid, actin & myosin are binding but no ATP to break the myosin/actin bond
Creatine Phosphate
a quick way to get more ATP, used to convert ADP to ATP. provide ATP before aerobic metabolism only last 15 sec
Aerobic respiration
Yields high amounts of ATP during resting to moderate activity
Tropomyosin & troponin
proteins attached to actin that help control the myosin-actin interactions involved in muscle contraction
converted into lactic acid
What happens to pyruvic acid when there is a lack of oxygen in the muscle?
botulism
causes parlysis of the muscle "botox"
functons of skeletal muscle
maintains posture and moves the body
somatic nervous system
controls muscular system
Frontal lobe
What lobe initiates voluntary movement?
sarcolemma
cell membrane
tropomyosin
polypeptide strands that wrap around the actin to help stabilize it
actin
protein which has active sites for the myosin heads.
Elastic filament
composed of the protein titin. Extends from the z disk to the thin filament and runs with it to attach to the m line
Z discs
anchor the thin filaments.
SR
smooth ER that surround each myofibril. Mitochondria and glycogen granules produce energy during contraction
thin filament
positioned on either side of the sarcomere and are pulled toward the center of the sarcomere during contraction
Transverse tubules
increase surface area
AP
stimulates the release of Ca2+ when it moves across
Small motor units
give fine motor control. 1:10
Large motor units
give gross movements. 1:500
latent
excitation contraction coupling AP-T tubules CA++ release---binding---troponin
contraction
myosin heads in crossbridge cycle
relaxation
CA++ transported back to the SR
warm up effect
Single cell- can experience treppe effect where subsequent twitches can generate more force
Fatigue
run out of synaptic vesicles ACH lactic acid build up.
Recruitment of motor unit
Whole muscle you have many motor units with different thresholds. Recruit more motor units for stronger whole muscle contraction.
tetanus
high frequency of stimulus---fused twitches---sustained contraction
Crossbridge cycle
myosin heads of thick filaments bind and pull the thin filaments
Crossbridge step 1
1. Energized thick filament (give ATP and phosphorus.) Myosin heads in a cocked back position.
Crossbridge step 2 stimulus
2. Stimulus- causes binding sites on actin to be uncovered. Myosin heads bind to actin binding site.
Crossbridge step 3 powerstroke
"ratchetting" of myosin heads---thin filaments are pulled torward the center of the sarcomere. During the powerstroke the ADP & phosphorus leave the myosin head.
Crossbridge step 4
4. Myosin head detaches from the actin thin filament . This occurs when ATP binds to the myosin head.
Crossbridge step 5
5. ATP is hydrolyzed to ADP and inorganic phosphate to energize the myosin head and cock it back again.
Isotonic contraction
"same-length" muscle generates the same force through whole muscle during contraction.
Energy for contraction
ATP- not stored . It is made as it is needed by burning fuel.
ATP supply
1. aerobic- less efficient without 02 (can do for hours) by using glycolysis, Krebs, ETC
ATP supply
2. anaerobic with out oxygen. High intensity, few min, less efficient
Intero sensory receptor
detect muscle stretch and contraction (shortening) Protects from overstretching
Fast-twitch
larger diameter, pailer color (less 02 carrier mypglobin,) faster contracting, less mitochondria, more anaerobic metabolism, can generate more power. Power lifting fatigues fast.
Slow twitch
darker= myoglobin that carries the 02 to mitochondria for aerobic metabolism. High endurance but fairly low power.
Stretch- thin elements of the muscle
titin
Stretch- thin elements of the muscle
endomysium CT around the fiber
Stretch- thin elements of the muscle
perimysium- around fasicles
Stretch- thin elements of the muscle
epimysium around the whole muscle
Stretch- thin elements of the muscle
tendons
myofilaments
proteins inside the myofibril
when does crossbridge formation occur?
When myosin heads bind to actin molecules located on the thin filaments.
The series-elastic component of a muscle must
bind muscle fibers together at the neuromuscular junction,