Study Notes for Anatomy/Physiology Chapter 6 Skeletal Muscles
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| Contractility | the ability of skeletal muscle to shorten with force
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| Excitability | the capacity of skeletal muscle to respond to a stimulus
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| Extensibility | the ability to be stretched
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| Elasticity | ability to recoil to their original resting length after they have been stretched
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| Epimysium | connective tissue sheath that surrounds each skeletal muscle
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| Fascia | connective tissue located outside the epimysium that surrounds and separates muscles
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| Fasciculi | numerous visible bundles that compose muscle
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| Perimysium | loose connective tissue that surrounds the fasciculi
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| Fibers | muscle cells
each fiber is a single cylindrical cell containing several nuclei
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| Endomysium | a connective tissue sheath that surrounds each fiber
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| Myofibrils | a threadlike structure that extends from one end of the fiber to the other
fills the cytoplasm of each fiber
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| 2 Major Kinds Of Protein Fibers | 1. actin myofilaments
2. myosin myofilaments
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| Actin Myofilaments | thin myofilaments
they resemble 2 minute strands of pearls twisted together
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| Myosin Myofilaments | thick myofilaments
they resemble bundles of minute golf clubs
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| Sarcomeres | highly ordered units formed by actin and myosin myafilaments
they are joined end-to-end to form the myofibril
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| The basic structural and functional unit of the muscle | The Sarcomere
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| Z line | an attachment site for actin
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| I band | Consists of actin
A light area located on each side of the Z line
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| A band | extends the lenth of the myosin
the darker central region in each sarcomere
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| H zone | Consists only of myosin
a light area in the center of each sarcomere
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| M line | Dark staining band
the center of the sarcomere where myosin myofilaments are anchored
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| Membrane Potential | Resting Membrane Potential
Action Potential
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| 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
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| Action Potential | When a muscle cell is stimulated, the membrane characteristics change briefly
The brief reversal back of the charge
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| Motor Neurons | nerve cells that carry action potential to skeletal muscle fibers
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| Axons | Enter the muscles and branch
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| Neuromuscular Junction (Synapse) | formed near the center of the cell by each branch that connects to a muscle
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| Motor Unit | a single motor neuron and all the skeletal muscle fibers it innervates
Many form a single muscle
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| formed by an enlarged nerve terminal resting in an indentation of the muscle cell membrane | Neuromuscular Junction
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| Presynaptic Terminal | the enlarged nerve terminal
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| Synaptic Cleft | the space between the presynaptic terminal and the muscle cell
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| Postsynaptic Terminal | the muscle fiber
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| Synaptic vesicles | in each presynaptic terminal
secretes a neurotransmitter called acetylcholine
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| Acetylcholine | accumulates in the neurons
causes muscle to contract
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| Acetylcholinesterase | causes the muscle to relax
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| 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
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| Sliding filament mechanism | the sliding of actin myofilaments past myosin myofliaments during contraction
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| Bands that shorten | H bands
I bands
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| Bands that do not change in length | A bands
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| Muscle twitch | a contraction of an entire muscle in response to a stimulus that causes the action potential in one or more muscle fibers
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| Threshold | the level at which a muscle fiber will respond to stimulus
the point the muscle fiber will contract maximally
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| Phenomenon that occurs in the threshold | all-or-none response
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| Lag Phase | the time between application of a stimulus to a motor neuron and the beginning of a contraction
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| Contraction Phase | the time of contraction
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| Relaxation Phase | the time during which the muscle relaxes
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| Tetany | the muscle doesn't have time to fully relax
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| Recruitment | the increase in number of motor units being activated
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| ATP | Adenosine triphosphate
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| ADP | Adenosine diphosphate
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| Adenosine Triphosphate | needed for energy for muscle contraction
produced in the mitochondria
short-lived and unstable
degenearagtes to the more stable ADP plus phosphate
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| Creatine Phosphate | high energy molecule stored when muscle cells are at rest
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| Anaerobic respiration | without oxygen
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| Aerobic respiration | with oxygen
more efficient
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| 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
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| Muscle Fatigue | results when ATP is used during muscle contraction faster than it can be produced in the muscle cells
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| 2 Types of Muscle contractions | Isometric
Isotonic
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| Isometric | equal distance
the length of the muscle does not change, but the amount of tension increases during the contraction process
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| Isotonic | equal tension
the amount of tension produced by the muscle is constant during contraction, but the length of the muscle changes
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| Muscle Tone | refers to constant tension produced by muscles of the body for long periods of time
keeps head up and back straight
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| Fast-twitch Fibers | Contract quickly and fatigue quickly
well adapted to perform anaerobic metabolism
example: white meat of a chicken's breast
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| 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
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| Points of Attachment of Muscles | Origin
Insertion
At these points, the muscle is connected to bone by a tendon
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| Origin | (the head of the muscle)
the most stationary end of the muscle
example: shoulder
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| Insertion | the end of the muscle undergoing the greatest movement
example: elbow
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| Belly | the portion of the muscle between the origin and the insertion
example: arm
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| Synergists | muscles that work together to accomplish specific movements
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| Antagonists | muscles that work in opposition to one another
examples: bicep and tricep
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| Prime mover | among a group of synergists, it is the one muscle that plays the major role in accomplishing the desired movement
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| Occipitofrontalis | raises eyebrows
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| Orbicularis Oculi | closes eyelid
(crows feet)
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| "Kissing muscles" | Orbicularis Oris
Buccinator
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| Orbicularis Oris | Puckers the lips
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| Buccinator | flattens the cheeks
("trumpeter's muscle")
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| Zygomaticus | smiling
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| Levator Labii Superioris | sneering
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| Depressor Anguli Oris | Frowning
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| Mastication | chewing
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| Mastication Muscles | Pterygoids (2pairs)
Masseter (1pair)
Temporalis (1pair)
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| Tongue and swallowing muscles | important in speech and mastication
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| 2 Tongue Muscles | Extrensic Tongue Muscle
Intrinsic Tongue Muscle
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| Extensic Tongue Muscle | moves the tongue
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| Intrinsic Tongue Muscle | changes the shape of the tongue
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| sternocleidomastoid | prime mover lateral neck muscle
rotates and abducts head
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