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Chapter 6 Muscles

Study Notes for Anatomy/Physiology Chapter 6 Skeletal 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 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
Created by: Harmon.jpaige