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Ch.6 Muscles

Contractility The ability of skeletal muscle to shorten with force
Excitability The capacity of skeletal muscle to respond to a stimulus
Extensibility The ability to be stretched
Elasticity Ability to recoil to their original resting length after they have been stretched
Epimysium A connective tissue sheath that surrounds each skeletal muscle
Fascia Another connective tissue located outside the epimysium. Surrounds and separates muscles
Perimysium Loose connective tissue that surrounds muscle fasciculi (fascicle)
A muscle is composed of... Numerous visible bundles known as muscle fasciculi (fascicle)
The fasciculi are composed of... Fibers
Fibers Single muscle cells
Endomysium A connective tissue sheath that surrounds each fiber
Myofibrils... Fill the cytoplasm of each fiber
Myofibrils A threadlike structure that extends from one end of the fiber to the other
2 major kinds of protein fibers that myofibrils consist of Actin myofilaments, myosin myofilaments
Actin myofilaments Thin myofilaments
Myosin myofilaments Thick myofilaments
Form highly ordered units called sarcomeres Actin and myosin myofilaments
Sarcomere is the... Basic structural & functional unity of the muscle
Resting membrane potential The charge difference across the membrane
Action potential The brief reversal back of the charge
Motor neurons Nerve cells that carry action potentials to skeletal muscle fibers
Each branch that connects to the muscle forms a ___________ _________ or ________ near the center of the cell. Neuromusclular junction or synapse
Motor unit A single motor neuron & all the skeletal muscle fibers it innervates
Presynaptic terminal Enlarged nerve terminal
Synaptic cleft The space between the presynaptic terminal & the muscle cells
Postsynaptic terminal Muscle fiber
Each presynaptic terminal contains... Synaptic vesicles
Synaptic vesicles that secrete a neurotransmitter called... Acetylcholine
Every muscle fiber Cylindrical cell
Each muscle fiber... contains several nuclei
Muscles help... produce heat essential for maintenance of normal body temperature.
Action potential reaches nerve terminal Synaptic vesicles releases acetylcholine into synaptic cleft (by exocytosis)
Acetylcholine diffuses across Synaptic cleft
Acetylcholine binds to receptor molecules in the muscle cell membrane (sarcolemma)
Combination of acetylcholine with its receptor Influx of sodium ions into the muscle fibers
The influx of sodium ions into the muscle fibers initiates Action potential in muscle cell
Acetylcholinesterase The acetylcholine released into the synaptic cleft between the neuron & muscle cell is rapidly broken down by enzymes
Name 2 things the enzymatic breakdown ensures 1. One action potential in the neuron yields only one action potential in the skeletal muscle. 2. Only one contraction of the muscle cell
Muscle contraction Occurs as actin & myosin myofilaments slide past one another causing the sarcomeres to shorten.
Sarcomeres shorten muscle shortens
Sliding filament mechanism Sliding of actin myofilaments past myosin myofilaments during contraction
H and I bands Shorten
A bands Do not change in length
Muscle twitch Contraction of entire muscle
Muscle fiber won't respond to stimulus until that stimulus reaches a level called... Threshold
Once the stimulus reaches threshold... Muscle fiber will contract maximally
Reaching threshold and muscles contract maximally known as... All-or-none response
Lag phase Time between application of a stimulus to a motor neuron & the beginning of contraction
Contraction phase Time of contraction
Relaxation phase Time during which the muscle relaxes
Tetany The muscle remains contracted without relaxing
Recruitment The increase in number of motor units being activated
ATP is needed for Energy for muscle contraction
ATP is produced In mitochondria
ATP is Short-lived and unstable
ATP stands for Adenosine triphosphate
Creatine phosphate When at rest they can't stockpile ATP but they can store another high-energy molecule
Anaerobic respiration Without oxygen
Aerobic respiration With oxygen (more efficient)
Oxygen debt Amount of oxygen needed in chemical reactions to convert lactic acid to glucose & replenish the depleted stores of creatine phosphate stores in muscle cells
Muscle fatigue ATP is used during muscle contraction faster than it can be produced in the muscle cells
2 types of muscle contractions Isometric & Isotonic
Isometric (equal distance) Length of the muscle does not change, but the amount of tension increases during the contraction process
Isotonic (equal tension) Amount of tension produced by the muscle is constant during contraction, but the length of the muscle changes
Muscle tone Refers to constant tension produced by muscles of the body for long periods of time.
Fast- twitch fibers Contract quickly and fatigue quickly. Well adapted to perform anaerobic metabolism
Slow-twitch fibers contract more slowly & are more resistant to fatigue. Better suited for aerobic metabolism
Points of attachment of each muscle Its origin & insertion
At the attachment points the muscle is connected to Bone by a tendon
Origin (head) Most stationary end of the muscle
Insertion End of the muscle undergoing the greatest movement
Belly Portion of the muscle between the origin and the insertion
Some muscles have Multiple origins or head
I band Light area on each side of Z line. Consists of actin
A band Darker central region in each sarcomere. Extends the length of the myosin
H zone Center of the sarcomere (another light area.) Consist of only myosin
M line Dark staining band. Myosin myofilament are anchored in the center of the sarcomere
Created by: syerrawilson
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