Question | Answer |
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 | connective tissue sheath that surrounds each skeletal muscle |
Fascia | connective tissue located outside the epimysium that surrounds and separates muscles |
Fasciculi | numerous visible bundles that compose muscle |
Perimysium | loose connective tissue that surrounds the fasciculi |
Fibers | muscle cells
each fiber is a single cylindrical cell containing several nuclei |
Endomysium | a connective tissue sheath that surrounds each fiber |
Myofibrils | a threadlike structure that extends from one end of the fiber to the other
fills the cytoplasm of each fiber |
2 Major Kinds Of Protein Fibers | 1. actin myofilaments
2. myosin myofilaments |
Actin Myofilaments | thin myofilaments
they resemble 2 minute strands of pearls twisted together |
Myosin Myofilaments | thick myofilaments
they resemble bundles of minute golf clubs |
Sarcomeres | highly ordered units formed by actin and myosin myafilaments
they are joined end-to-end to form the myofibril |
The basic structural and functional unit of the muscle | The Sarcomere |
Z line | an attachment site for actin |
I band | Consists of actin
A light area located on each side of the Z line |
A band | extends the lenth of the myosin
the darker central region in each sarcomere |
H zone | Consists only of myosin
a light area in the center of each sarcomere |
M line | Dark staining band
the center of the sarcomere where myosin myofilaments are anchored |
Membrane Potential | Resting Membrane Potential
Action Potential |
Resting Membrane Potential | The outside of most cell membranes is positively charged compared to the inside of the cell membrane, which is negatively charged
It is the charge difference across the membrane |
Action Potential | When a muscle cell is stimulated, the membrane characteristics change briefly
The brief reversal back of the charge |
Motor Neurons | nerve cells that carry action potential to skeletal muscle fibers |
Axons | Enter the muscles and branch |
Neuromuscular Junction (Synapse) | formed near the center of the cell by each branch that connects to a muscle |
Motor Unit | a single motor neuron and all the skeletal muscle fibers it innervates
Many form a single muscle |
formed by an enlarged nerve terminal resting in an indentation of the muscle cell membrane | Neuromuscular Junction |
Presynaptic Terminal | the enlarged nerve terminal |
Synaptic Cleft | the space between the presynaptic terminal and the muscle cell |
Postsynaptic Terminal | the muscle fiber |
Synaptic vesicles | in each presynaptic terminal
secretes a neurotransmitter called acetylcholine |
Acetylcholine | accumulates in the neurons
causes muscle to contract |
Acetylcholinesterase | causes the muscle to relax |
Muscle Contraction | occurs as actin and myosin myofilaments slide past one another causing the sarcomeres to shorten
when sarcomeres shorten, it causes the muscle to shorten |
Sliding filament mechanism | the sliding of actin myofilaments past myosin myofliaments during contraction |
Bands that shorten | H bands
I bands |
Bands that do not change in length | A bands |
Muscle twitch | a contraction of an entire muscle in response to a stimulus that causes the action potential in one or more muscle fibers |
Threshold | the level at which a muscle fiber will respond to stimulus
the point the muscle fiber will contract maximally |
Phenomenon that occurs in the threshold | all-or-none response |
Lag Phase | the time between application of a stimulus to a motor neuron and the beginning of a contraction |
Contraction Phase | the time of contraction |
Relaxation Phase | the time during which the muscle relaxes |
Tetany | the muscle doesn't have time to fully relax |
Recruitment | the increase in number of motor units being activated |
ATP | Adenosine triphosphate |
ADP | Adenosine diphosphate |
Adenosine Triphosphate | needed for energy for muscle contraction
produced in the mitochondria
short-lived and unstable
degenearagtes to the more stable ADP plus phosphate |
Creatine Phosphate | high energy molecule stored when muscle cells are at rest |
Anaerobic respiration | without oxygen |
Aerobic respiration | with oxygen
more efficient |
Oxygen debt | the amount of oxygen needed in chemical reactions to convert lactic acid to glucose and replenish the depleted stores of creatine phosphate stores in muscle cells |
Muscle Fatigue | results when 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
the length of the muscle does not change, but the amount of tension increases during the contraction process |
Isotonic | equal tension
the 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
keeps head up and back straight |
Fast-twitch Fibers | Contract quickly and fatigue quickly
well adapted to perform anaerobic metabolism
example: white meat of a chicken's breast |
Slow-twitch Fibers | Contract more slowly and are more resistant to fatigue
they are better suited for aerobic metabolism
example: the dark meat of a duck's breast of the legs of a chicken |
Points of Attachment of Muscles | Origin
Insertion
At these points, the muscle is connected to bone by a tendon |
Origin | (the head of the muscle)
the most stationary end of the muscle
example: shoulder |
Insertion | the end of the muscle undergoing the greatest movement
example: elbow |
Belly | the portion of the muscle between the origin and the insertion
example: arm |
Synergists | muscles that work together to accomplish specific movements |
Antagonists | muscles that work in opposition to one another
examples: bicep and tricep |
Prime mover | among a group of synergists, it is the one muscle that plays the major role in accomplishing the desired movement |
Occipitofrontalis | raises eyebrows |
Orbicularis Oculi | closes eyelid
(crows feet) |
"Kissing muscles" | Orbicularis Oris
Buccinator |
Orbicularis Oris | Puckers the lips |
Buccinator | flattens the cheeks
("trumpeter's muscle") |
Zygomaticus | smiling |
Levator Labii Superioris | sneering |
Depressor Anguli Oris | Frowning |
Mastication | chewing |
Mastication Muscles | Pterygoids (2pairs)
Masseter (1pair)
Temporalis (1pair) |
Tongue and swallowing muscles | important in speech and mastication |
2 Tongue Muscles | Extrensic Tongue Muscle
Intrinsic Tongue Muscle |
Extensic Tongue Muscle | moves the tongue |
Intrinsic Tongue Muscle | changes the shape of the tongue |
sternocleidomastoid | prime mover lateral neck muscle
rotates and abducts head |