Muscular System

3 Types of Muscle

Skeletal Muscle (aka "striated“ or "voluntary“) attached to bones and under conscious, willful control. Has the ability to contract (shorten) and thereby bring about movement

I. Muscles and Muscle Fibers Muscles are composed of many fibers that are arranged in bundles called FASCICLES

A muscle also contains 3 different layers of connective tissue: Endomysium Tissue around 1 muscle cell Perimysium Tissue bundle of muscle fibers (fascicle) Epimysium Tissue around an entire muscle belly Muscle fiber (cell) Muscle belly Entire macroscopic organ

How does a muscle cell obtain energy? Fibers contain multiple mitochondria for ATP energy (cellular respiration) Most fibers have multiple nuclei

Muscle Cell (Muscle Fibers) The muscle fiber membrane is called the SARCOLEMMA Muscle fiber cytoplasm is called SARCOPLASM

The muscle fiber membrane is called the SARCOLEMMA and the cytoplasm is called the SARCOPLASM. Within the sarcoplasm are many parallel fibers known as MYOFIBRILS

Human Anatomy 11/2 1. Finish muscle Fatigue Lab 2. Color Muscle Tissue Worksheet 3. On the back of the worksheet, define/describe the terms labeled D-N

Muscle bellyEpimysium Muscle fiber (cell) Sarcomere Fasciclemyofilament

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How do muscle cells contract?

It is important to remember the hierarchy of muscle fibers fasicles Muscle fiber myofilaments actin myosin

Each muscle fiber (cell) is made of many protein filaments called Myofilaments. There are two types: ACTIN – MYOSIN – thin, Actively slide up past myosin thick, does not slide, but moves the actin filaments ? ? ?

The actin and myosin overlap to form dark and light bands on the muscle fiber  A band = d A rk, thick (myosin)  I band = l I ght, thIn (actin) Structure of a SARCOMERE (functional unit of a muscle) In the middle of each I band are Z lines. A sarcomere is one Z line to the other (A band) (I band) Sarcomere

* The arrangement of these sarcomeres next to each other produces the Striations (Z Line) of the skeletal muscle.

SLIDING FILAMENT THEORY The theory of how muscle contracts is the sliding filament theory. The contraction of a muscle occurs as the thin filament slide past the thick filaments. The sliding filament theory involves five different molecules plus calcium ions. The five molecules are: 1.myosin 2.actin 3.tropomyosin 4.troponin 5.ATP

Each Myofibril is surrounded by a network of channels called SARCOPLASMIC RETICULUM. TRANVERSE TUBULES (T Tubule) pass through the fibers.

Include the function of all molecules in #7 of ‘Sliding Filament Theory’ worksheet. The sliding filament theory involves five different molecules. The five molecules are: 1.myosin 2.actin 3.tropomyosin 4.troponin 5.ATP

Any questions? If you don’t ace the next test I will destroy you!!

Cells use electrical impulses to communicate. Muscles use electricity to contract.

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Muscles & Nervous System NEUROMUSCULAR JUNCTION - where a nerve fiber and muscle fiber come together. MOTOR NEURON ENDINGS - nerve fiber caries electrical signal called an action potential that stimulates the muscle fibers

MOTOR END PLATE - specialized part of muscle fiber membrane that transmits neural impulses to the muscle.

1. Neuron Neuromuscular Junction 2. motor end plate 3. Synaptic Vesicle 4. Neurotransmitter Receptor 5. Mitochondria

SYNAPTIC CLEFT - An physical gap or “cleft” which exits between the motor neuron endings and the motor end plate. SYNAPTIC VESICLES - where neurotransmitters are stored in neuron before being released into the synaptic cleft. NEUROTRANSMITTER – chemical substance that transmits signals across a synapse A cleft chin Noradrenaline is a neurotransmitter

The neurotransmitter that crosses the gap is ACETYLCHOLINE. ACETYLCHOLINE - The neurotransmitter that brings about muscle contractions. It is stored in synaptic vesicles. Synaptic Cleft Synaptic Vesicles Neuro- transmitter

Motor Unit The muscle fiber and the motor neuron

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III. Events in Muscle Contraction Nerve impulse stimulates the release of a neurotransmitter (acetylcholine) from synaptic vesicles into synaptic cleft. This stimulates muscle impulse. Impulse spreads across sarcolemma and into fiber along the T-tubules. This impulse causes an increase in the cisternae's permeability to calcium ions. The S.R. has a high conc. of Ca++. Calcium ions diffuse into the sarcoplasm. The Ca++ causes the formation of "cross bridges" between the actin and myosin filaments ' The filaments slide between each other ' this shortens the myofibrils which in turn shorten the muscle fibers, which shortens the muscles

Sliding Filament Handout

IV. Energy Source Provided by ATP from cellular respiration. Occurs in the mitochondria in myofibrils. (requires O 2 and glucose, produces CO 2, H 2 O and ATP) Only 25% of energy produced during cellular respiration is used in metabolic processes - the rest is in the form of HEAT. (This is what produces our body heat and maintains body temperature. More muscle activity = more heat)

Creatine phosphate increases regeneration of ATP

Threshold Stimulus Minimal strength required to cause a contraction Motor neuron releases enough acetylcholine to reach threshold All-or-None Response Fibers do not contract partially, they either do or don't

Motor Unit The muscle fiber + the motor neuron Recruitment more and more fibers contract as the intensity of the stimulus increases Muscle Tone Sustained contraction of individual fibers, even when muscle is at rest

Hypertrophy - muscles enlarge (working out or certain disorders) Atrophy - muscles become small and weak due to disuse

Muscle Fatigue - muscle loses ability to contract after prolonged exercise or strain Muscle Cramp - a sustained involuntary contraction Oxygen Debt - oxygen is used to create ATP, during exercise you may not have enough oxygen - -> this causes Lactic Acid to accumulate in the muscles *See Magic School Bus

Origin and Insertion Origin = the immovable end of the muscle Insertion = the movable end of the muscle **when a muscle contracts the insertion is moved toward the origin The biceps brachii has two origins (or two heads).

Cardiac Muscle Fiber (400x Magnification)

What is rigor mortis? A few hours after a person or animal dies, the joints of the body stiffen and become locked in place. This stiffening is called rigor mortis. Depending on temperature and other conditions, rigor mortis lasts approximately 72 hours. The phenomenon is caused by the skeletal muscles partially contracting. The muscles are unable to relax, so the joints become fixed in place.

What is tetanus? Tetanus causes cholinosterase to not break down the acetylcholine in the synapse. This results in a person's muscles contracting and not relaxing. A tetanus shot must be administered shortly after exposure to the bacteria. Once you develop tetanus, there is no cure.