NOTES: The Muscular System (Ch 8, part 1) Functions, Characteristics, Types of Muscle Tissue

**Muscles can be voluntary or involuntary** Functions of Muscle: Movement Heat production (thermogenesis)- byproduct of cellular respiration (converting glucose to ATP in the mitochondria of cells) Posture & body/joint support **Muscles can be voluntary or involuntary**

Characteristics of Muscle Tissue In the Tissue Type Handout, you wrote that muscle tissue has: Excitability (irritability): ability to respond to certain stimuli by producing electrical signals called action potentials Stimuli= neurotransmitters or hormones Contractility: ability to shorten & thicken Click for animation Click for animation!

3 Types of Muscle Tissue: Smooth Cardiac Skeletal

1. SMOOTH MUSCLE • Walls of hollow internal organs (ex: arteries, respiratory passages, digestive canals) -Involuntary muscle • Muscle fibers (cells) are joined by electrical junctions which pass messages quickly

2. CARDIAC MUSCLE • Found only in the heart - Involuntary muscle • Cardiac cells are also connected by electrical junctions & pass the “contract” message quickly from cell to cell -Cells don’t get “fatigued” like skeletal muscle cells

3. Skeletal Muscle Attaches to skeleton & is responsible for voluntary body movements Each muscle fiber (cell) is Elongated (length of muscle) Multinucleated has distinct transverse striations (banding pattern)

SKELETAL MUSCLE ACTIONS *The type of movement a skeletal muscle produces depends on the way the muscle attaches on either side of a joint. • Immovable end of a skeletal muscle is called the ORIGIN (may be more than one) • Movable end of a skeletal muscle is called the INSERTION

SKELETAL MUSCLE ACTIONS *when a muscle contracts, its insertion is pulled towards its origin.

Interaction of Skeletal Muscles: Muscles (or muscle groups) that work in opposition to each other are called ANTAGONISTIC Ex: Hamstring muscles & Quadriceps muscles Hamstring muscles contracting causes flexion: acting as the AGONIST (prime mover of the muscle) Quadriceps relaxed: ANTAGONIST

STRUCTURE OF A SKELETAL MUSCLE: *Individual muscles are the organs of the muscular system. They contain skeletal muscle tissue, nervous tissue, blood, and other connective tissues.

Connective Tissue “Covering”: • FASCIA: -connective tissue beneath the skin that covers skeletal muscles -Separates individual skeletal muscles from adjacent muscles (forms compartments) -separates muscles from other internal organs -Binds muscles into their position

MORE CONNECTIVE TISSUES IN THE MUSCLE: -These connective tissues extend throughout the muscular system and all together form the tendon: ● Epimysium: closely surrounds a skeletal muscle (directly under the fascia) ● Perimysium: extends inward from the epimysium and separates the muscle tissue into small compartments called FASCICLES ● Endomysium: surrounds each individual muscle fiber within a fascicle & insulates them from each other -The tendon intertwines with the periosteum in order to attach the muscle to the bone

It’s demo time!

Sarcolemma- plasma membrane of a muscle fiber cell Skeletal muscle fibers have the same structure as most normal cells, although some structures have different names Sarcolemma- plasma membrane of a muscle fiber cell Sarcoplasm- cytoplasm Sarcoplasmic Reticulum- a network of membrane tubules and sacs Similar to the endoplasmic reticulum of other cells Stores & continually pumps calcium ions from the sarcoplasm and stores it in inside the sac Same but different in that muscle fibers: Contain more Mitochondria Have several nuclei per one fiber (cell)  multinucleated

Nucleus

Skeletal muscles also have some different structures than are found in normal cells Myofibrils- make up skeletal muscle fibers Myofilaments- protein fibers that make-up myofibrils Two types of myofilaments: thick and thin fibers Sarcomere- a segment of the myofibril between two Z lines. Also the smallest functioning contractile unit in a muscle Transverse tubules (T- tubules)- allows electrical impulses to travel from the sarcolemma deep into the cell

**TRANSVERSE TUBULES (T tubules) extend inward from the cell membrane and associate with the SARCOPLASMIC RETICULUM (whose membranes surround each myofibril)

Now that we’ve discussed the Anatomy of a Muscle, we need to examine the junction between a nerve and a skeletal muscle. This junction is what “tells” the muscle to contract.

Neuromuscular Junction: MOTOR NEURONS stimulate muscle fibers to contract  In response to a nerve impulse, the end of a motor neuron axon secretes a NEUROTRANSMITTER, which stimulates the muscle fiber to contract

Neuromuscular Junction: One MOTOR NEURON and the MUSCLE FIBERS associated with it constitute a MOTOR UNIT  All muscle fibers of a motor unit contract together!

Excitation and Contraction A motor neuron forms a synapse with a muscle fiber Synapse means “chemical junction” One motor neuron may stimulate many muscle fibers 1) A nerve impulse reaches the end of the motor neuron 2) Synaptic vesicles in the nerve release the neurotransmitter acetylcholine (ACh) 3) ACh diffuses across the synaptic cleft and binds to ACh receptors on the motor endplate of the muscle (part of sarcolemma in contact with neuron) ANIMATION

4) The stimulation of the ACh receptors causes a new impulse to be propagated along the sarcolemma (plasma membrane) and down T-tubules 5) This impulse causes calcium to be released from the sarcoplasmic reticulum 6) The release of calcium starts the sliding filament theory (the contraction of the muscle!) ANIMATION

Another animation!