the muscular system anatomy & physiology. muscles: the machines of the body skeletal muscle...
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The Muscular System
Anatomy & Physiology
Muscles: the machines of the body
Skeletal Muscle Characteristics Voluntary: move due to a conscious
decision Striated: striped in appearance Multinucleate: Cells long; more nuclei More mitochondria for energy
production 500+ muscles, 40-50% body weight
Skeletal Muscle Extras
Soft and fragile yet TOUGHExerts TREMENDOUS powerPower provided by bundles of muscle fibers wrapped in connective tissueConnective tissue coverings allows for transmission of blood and nerves to muscles & provides support
Functional Characteristics of Skeletal Muscle
Produces movement: for locomotion, manipulation and responding to the external environment; also for expressing emotionsMaintaining posture: works continuously to fight downward pressure of gravity
Functional Characteristics of Skeletal Muscle
Stabilizing joints: muscle tendons stabilize and reinforce joints that have poor articulating surfacesGenerating heat: heat is a by-product of muscular activity; maintains normal body temperature
Skeletal Muscle Interactions
Muscles are arranged in the body to either work together or work in opposition of each otherNumber 1 Rule of Muscle Activity: MUSCLES ONLY PULL*** THEY NEVER
PUSH! In other words, muscle contractions
are caused by SHORTENING of fibers
Skeletal Muscle Interactions
Insertion: the movable attachment of a muscleExamples: biceps tendon attachment to radial tuberosity
Origin: the fixed, immovable point of attachmentExamples: biceps tendon attachment to greater tubercleA muscle contraction involves a muscle’s
insertion moving toward its origin
Origins and Insertions
4 Functional Groups of Skeletal Muscles
1.) Agonists (prime movers): a muscle that provides the major force for providing a specific movement Example: biceps brachii- prime mover
of elbow flexion
4 Functional Groups of Skeletal Muscles
2.) Antagonists: muscles that oppose/reverse a movement; relaxed when the agonist is active; helps regulate action of agonist by providing resistance Can also be agonists Example: the triceps brachii is the
antagonist to the biceps during elbow flexion
4 Functional Groups of Skeletal Muscles
3.) Synergists: “work together”; aids agonist by promoting the same movement or reducing unnecessary movements that might occur as the agonist contracts Example: biceps brachii and
brachioradialis in elbow flexion
4 Functional Groups of Skeletal Muscles
4.) Fixators: a synergist that immobilizes a bone or a muscle’s origin Example: erector spinae (muscles for posture)
All types of muscles work together to provide smooth, coordinated and precise movements. Any one muscle can be in any functional group, dependant on its action
Detailed Skeletal Muscle
Deep fascia: sheet/band of dense connective tissue covering musclesEpimysium: connective tissue covering many fascicles, all bound together
Detailed Skeletal Muscle
Fascicle: a bundle of fibers wrapped in perimysium
Perimysium: connective tissue surrounding a bundle of muscle fibers
Endomysium: connective tissue surrounding each muscle fiber
Aponeuroses: sheetlike epimysia that connects muscle to each other and to cartilage/bone
Detailed Skeletal Muscle
Tendon: cordlike band of epimysia connecting muscles to bones Durable and able
to cross bony projections
Small in diameter to fit in crowded joint spaces
Nervous Stimulation of a Muscle Cell
Skeletal muscle cells possess unique abilities: Excitability: can receive & respond to a
stimulus Contractility: they can shorten Extensibility: lengthen or stretch Elasticity: cells return to resting form after
contracted or stretched
When a skeletal muscle contracts, it is told to do so by the nervous system
Nervous Stimulation of a Muscle Cell
Motor Neuron: nerve extending from spinal cord to muscle fiber Motor Unit: one motor neuron and all the skeletal muscle cells it stimulatesNeuromuscular Junction: where the end of the nerve and the beginning of the muscle fiber meets Synaptic cleft: space between nerve and
muscle fiber
Motor Unit
Nervous Stimulation of a Muscle Cell
Action Potential: an electrical current that can cause a muscular contraction Neurotransmitter: a chemical that carries a signal from the nerve to the muscle; continues the nervous stimulationAcetylcholine (ACh): the neurotransmitter specific to muscles
Nervous Stimulation of a Muscle Cell
The nervous system sends a neural signal to the motor unit. This causes a release of ACh into the neuromuscular junction, where it binds to receptors on the muscle cell. This causes an action potential to run throughout the muscle cell, initiating a muscle contraction.
Synaptic Cleft
Microscopic Anatomy
Microscopic Anatomy of Skeletal Muscle
Muscle cell = muscle fiberSarcomere: contractile units of myofibrils, aligned end-to-endMyofibril: contractile proteins of muscle cells; lie parallel along length of fiber Thin myofilaments: actin Thick myofilaments: myosin
Microscopic Anatomy of Skeletal Muscle
A band: where the myosin filaments are alignedH Zone: less dense portion of A band where thin filaments don’t overlap thick filamentsZ line: separates sarcomeres; where actin filaments attachI band:light bands; where the actin filaments are aligned; extends to tips of myosin filaments
Sarcomere
Graded Responses of Skeletal Muscle Contraction
A graded response: the degree of muscle shortening is dependant on 1. The speed of muscle stimulation 2. The number of muscle cells
stimulated
Speed of Stimulation
Muscle Twitch: a single, brief contraction caused by a mistake of the nervous systemSumming of Contractions: when nervous impulses are delivered to a muscle at a rapid rate so it can’t relax between impulses; the contractions are summed(added) to create a smooth, strong contractionTetanus: no relaxation between contractions; smooth and sustained
Number of Cells Stimulated
Small, weak contractions: few cells initiatedLarge, strong contractions: all motor units are active and all muscle cells stimulated
Types of Skeletal Muscle Contractions
Isotonic: same tone or tension Myofilaments
slide, muscle shortens & movement occurs
Types of Skeletal Muscle Contractions
Isometric: same length Muscles DO NOT
shorten Myosin
myofilaments do not move, tension in the fibers build
Muscle tries to move but cannot
Energy for Muscle Contractions
There are 3 different energy systems in the body that provide for muscle contractionsDefinitions: Creatine Phosphate (CP): high energy molecule
only in muscles which help replenish energy stores
Adenosine Triphoshate (ATP): energy source in the body
Glucose: blood sugar Glycogen: storage form of blood sugar
Energy for Muscle Contractions
Lactic Acid: a byproduct of an anaerobic pathway; causes muscle burningAerobic: using oxygen during activityAnaerobic: not using oxygen during activity
Energy Systems
There are 3 ways energy is utilized for muscular activity: 1. ATP-PC/Rapid Recovery
Anaerobic, lasting no more than 20 seconds ATP production rate is rapid ATP stores broken down rapidly and
resupplied by creatine phosphate (transfers a phosphate to ADP)
More creatine stored in muscles than ATP
Energy Systems
2. Lactic Acid/Anaerobic Breaks down glucose for energy without
using oxygen Muscles are working too fast for oxygen &
glucose to be delivered by aerobic respiration
Results in build up of lactic acid in muscles: promotes muscle fatigue and soreness
Lactic Acid/Anaerobic Continued
Muscle fatigue: when a muscle is unable to contract even though it is still being stimulated.
Oxygen Debt: occurs during prolonged muscle activity; can’t get oxygen fast enough for the muscle’s needs; lactic acid builds up leading to fatigue; repaid by breathing deeply until the muscles receive enough oxygen to get rid of lactic acid and make more ATP and creatine phosphate
Energy Systems
3. Aerobic Respiration During light exercise, ATP stores are
regenerated by using oxygen Can last for hours if glucose supplies are
present Used in endurance activities
Types of Skeletal Muscle Fibers
There are 2 different kinds: 1. Slow twitch
For endurance Speed of contraction is slow Uses aerobic respiration Low glycogen stores-more fats used Slow rate of fatigue
Types of skeletal muscle fibers
2. Fast twitch Explosive movements for short distances Speed of contraction very fast Some aerobic, some anaerobic fibers High glycogen stores but fatigues quickly
The distribution of muscle fibers is not complete until the teenage years. It varies between muscles, within muscles and between people.