Bundles of up to 150 muscle fibers; found under the epimysium
Connective tissue surrounding the fasiculi.
Connective tissue surrounding each muscle fiber; is continuous with the sarcolemma
Muscle fiber's membrane
The junction between a motor neuron and the muscle fibers it innervates; AKA motor end plate
A motor neuron and the muscle fibers it innervates
The cytoplasm of the muscle fiber; contains contractile components
Contain the apparatus that contracts the muscle cell; hunderds of myofibrils dominate the sarcoplasm
Thick filament about 16 nm in diameter that contain up to 200 myosin molecules
Globular heads protruding away from the myosin filament at regular intervals
Thin filaments about 6nm in diameter; consist of 2 strands arranged in a double helix
Smallest contractile unit of skeletal muscle; average about 2.2 micrometers in length in a relaxed fiber and are repeated the entire length of the muscle fiber.
Dark; corresponds with the alignment of the myosin filaments
Light, corresponds with the areas in two adjacent sarcomeres that contain only actin filaments
The middle line of the I-band and appears as a thin, dark line running longitudinally through the I-band
The area in the center of the sarcomere where only myosin filaments are present
Intricate system of tubules parallel to and surrounding each myofibril that terminates as vesicles in the vicinity of the Z-lines; store calcium ions
Run perpendicular to the sarcoplasmic reticulum and terminate in the vicinity of the Z-line between two vessicles; AKA transverse tubules
Pattern of a T-tubule spaced between and perpendicular to two sarcoplasmic reticulum vessicles
An electrical nerve impulse
Sliding Filament Theory
Actin filaments at each end of the sarcomere slide inward on myosin filaments, pulling the Z-lines toward the center of the sarcomere and thus shortening the muscle fiber.
A protein that is situated at reular intervals alond the actin filament and has a high affinity for calcium ions; calcium ions released from the sarcoplasmic reticulum bind with troponin
Protein molecule that runs along the length of the actin filament in the groove of the double helix
Resting Phase of Sliding-Filament Theroy of Muscular Contration
Little calcium is present in the myofibril, so very few of the myosin cross-bridges are bound to actin; no tension is developed in the muscle
Excitation-Contraction Coupling Phase of Sliding-Filament Theroy of Muscular Contration
Sarcoplasmic reticulum is stimulated to release calcium ions, which bind with troponin, causing a shift in the tropomyosin. Mysoin cross-bridge head now attaches more reapidly to actin filament
Contraction Phase of Sliding-Filament Theroy of Muscular Contration
The energy for cross-bridge flexion comes from hydrolysis of ATP to ADP and phosphate, which is catalyzed by ATPase. Another ATP molecule must replace ADP on the myosin cross-bridge head in order for the head to detach from the active actin site and recock.
Recharge Phase of Sliding-Filament Theroy of Muscular Contration
Measurable muscle shortening transpires only when the binding of calcium to troponin, coupling of the mysoin cross-bridge with actin, cross-bridge fexion, dissociation of actin and myosin, and recocking of the mysosin cross-bridge head is repeated over and over throughout the muscle fiber.
Relaxation Phase of Sliding-Filament Theroy of Muscular Contration
Occurs when the stimulation of the motor neuron stops. Calcium is pumped back into the sarcoplasmic reticulum, which prevents the link between the actin and myosin filaments. Brought on by the return of actin and myosin filaments to their unbound states
Neurotransmitter released by the arrival of the action potential at the nerve terminal, which diffuses across the neuromuscular junction, causing excitation of the sarcolemma
All-or-None Principle of Muscle
There is no such thing as a motor neuron stimulus that causes onle some of the fibers to contract. Similarly, a stronger action potential cannot produce a stronger contraction.
The brief contraction that results from an action potential traveling down a motor neuron, activating the muscle fibers
When stimuli are delivered at so high a frequency that the twitches begin to merge and eventually completely fuse
Fast-twitch Motor Unit
One that develops force and also relaxes rapidly and thus has a short twitch time.
Slow-twitch Motor Unit
One that develops force and relaxes slowly and has a long twitch time
Type I fibers
Slow-twitch; generally fatigue resistant and have a high capacity for aerobic energy supply, but limited potential for raped force development
Type II Motor Units
Fast-twitch; characterized as inefficient and fatigable and having low aerobic power, rapid force development, high actomyosin myofibrillar ATPase activity, and high anaerobic power.
Means of vaying skeletal muscle force involving an increase in force through varying the number of motor units activated.
Structure and Function of the Muscular, Neuromuscular, Cardiovascular, and Respiratory Systems