Muscles (ch. 10 and a lil 11)

Epimysium

- (connective tissue in skeletal muscle) - Fibrous sheath surrounding entire muscle - Outer surface grades into fascia; inner surface projections form perimysium

Fascia

- (connective tissue in skeletal muscle) - Sheet of connective tissue that separates neighboring muscles or muscle groups from each other and the subcutaneous tissue - wrap around groups of muscles much like a sock encircles your foot

Perimysium

- (connective tissue in skeletal muscle) - Thicker layer of connective tissue that wraps fascicles • Fascicles: bundles of muscle fibers wrapped together - Carries nerves, blood vessels, and stretch receptors

Endomysium

- (connective tissue in skeletal muscle) - Thin sleeve of loose connective tissue around each fiber - Allows room for capillaries and nerve fibers - Provides chemical environment for muscle fiber

Sarcoplasmic reticulum

A fluid‐filled system of membranous sacs that contains calcium ions—released (diffused through cytoplasm) when muscle is stimulated to contract --> Trigger the sliding filament mechanism • The sarcoplasmic reticulum butts up against the transverse tubules from both sides. One transverse tubule and the two terminal cisterns on either side of it form a triad

T tubules

AKA Transverse Tubules, deep invaginations of sarcolemma, become a Triad—T tubule flanked by two terminal cistern • Muscle action potentials propagate along the sarcolemma and through the T tubules, quickly spreading throughout the muscle fiber. This arrangement ensures that all the superficial and deep parts of the muscle fiber become excited by an action potential almost simultaneously.

Describe the two types of muscle contraction

Concentric contraction: muscle shortens to do work Eccentric contraction: muscle generates force as it lengthens

Thin (actin) filaments

Extends from Z disc toward the center of the sarcomere 1. Contains: Actin (contractile), Troponin (regulatory), Tropomyosin (regulatory) 2. On each actin molecule is a myosin‐binding site, where a myosin head can attach

Fast oxidative fibers

Intermediate fibers - Have an intermediate diameter - Contract quickly like fast glycolytic fibers - Are oxygen dependent - Have high myoglobin content and rich supply of capillaries - Somewhat fatigue resistant - More powerful than slow oxidative fibers - contribute to activities such as walking and sprinting.

Origin vs. Insertion

Origin—less movable attachment, the attachment of a muscle's tendon to the stationary bone Insertion—more movable attachment (indirect attachment - tendon), he attachment of the muscle's other tendon to the movable bone

Slow oxidative fibers:

Red slow oxidative fibers - Red color due to abundant myoglobin - Obtain energy from aerobic metabolic reactions - Contain a large number of mitochondria - Richly supplied with capillaries - Contract slowly and resistant to fatigue - Muscles that hold posture or do endurance things like marathon - Fibers are small in diameter

Fast glycolytic fibers

White fast glycolytic fibers - Contain little myoglobin and few mitochondria - About twice the diameter of slow oxidative fibers - Contain more myofilaments and generate more power - Depend on anaerobic pathways - Contract rapidly and tire quickly - quick, powerful movements, such as in lifting and throwing. - The overall result is muscle enlargement due to hypertrophy of the FG fibers.

List the levels of organization in a muscle going from a whole muscle to a myofilament.

Whole muscle -> fascicle -> muscle fiber (cell) -> myofibril -> sarcomere -> myofilaments Fascicle: muscle fiber bundle with dense irregular connective tissue covering called the perimysium

Titin

a springlike molecule that resists overstretching, extend from the Z disc to thick filaments to the M line

Identify the myofilaments responsible for striations.

a. A bands and I bands refract polarized light differently, alternating A and I bands give striated appearance i. A bands—anisotropic ii. I bands—isotropic

Describe a motor unit and its functions: one nerve fiber and all the muscle fibers innervated by it

a. Dispersed throughout muscle b. Produces the action potential that causes muscle fibers to contract in unison c. Produce weak contraction over wide area d. Provide ability to sustain long-term contraction as motor units take turns contracting e. Effective contraction usually requires contraction of several motor units at once f. Average contains 200 muscle fibers, small, fine degree of control (ex: eye, hand) can have 3-6, large strong (calf) can have 1000 muscle fibers per neuron

Distinguish between myofibrils from sarcomere

a. Myofibrils i. Are long rods within cytoplasm ii. Make up 80% of the cytoplasm iii. Are a specialized contractile organelle found in muscle tissue iv. Are a long row of repeating sarcomeres v. Made of contractile, regulatory, and structural proteins b. Sarcomere: i. Functional unit of muscle tissue, filled with microfilaments that make various bands and such

Describe and identify the components of the neuromuscular junction (NMJ)

a. Neuromuscular junction (NMJ)—when target cell is a muscle fiber b. acetylcholine / ACh - transmembrane protein and the neurotransmitter released at the NMJ. c. Synapse—point where a nerve fiber meets its target cell and communication occurs d. One nerve fiber (somatic motor neuron) stimulates the muscle fiber at several points within the NMJ i. Axon terminal AKA terminal bouton—swollen end of nerve fiber ii. Contains synaptic vesicles with ACh e. Synaptic cleft—gap between axon terminal and sarcolemma, the action potential cannot "jump the gap" from one cell to another. Instead, the first cell communicates with the second by releasing a chemical messenger called a neurotransmitter. f. Schwann cell envelops and isolates NMJ

Contractile proteins

actin and myosin - Muscle contracts when myosin binds with actin

H zone

center part of A band where no thin filaments occur

Dystrophin

clinically important protein i. Transfers forces of muscle contraction to connective tissue ultimately leading to tendon ii. Genetic defects in dystrophin produce disabling disease muscular dystrophy

Myomesin

form the M line. The M line proteins bind to titin and connect adjacent thick filaments to one another. Myomesin holds the thick filaments

M line

in center of H zone, Contains tiny rods that hold thick filaments together

I band

region with only thin filaments, Lies within two adjacent sarcomeres

A bands

the entire length of a single thick filament. i. Includes inner end of thin filaments ii. Darker, middle part of sarcomere

Elastic protein

titin: a springlike molecule that resists overstretching i. Two functions 1. Holds thick filaments in place 2. Unfolds when muscle is stretched

Regulatory proteins

troponin and tropomyosin --> In relaxed muscle, myosin is blocked from binding to actin because strands of tropomyosin cover the myosin‐binding site on actin. The tropomyosin strand, in turn, is held in place by troponin molecules. You will soon learn that when calcium ions (Ca2+)bind to troponin; troponin it undergoes a change in shape; this change moves tropomyosin away from myosin‐binding sites on actin, allowing myosin to bind to actin and muscle contraction to begin.

Thick (myosin) filaments

—located in the center of the sarcomere i. Overlap inner ends of the thin filaments ii. Contain ATPase enzymes iii. Myosin (contractile) 1. Heads contain two binding sites (1) an actin‐binding site and (2) an ATP‐binding site. 2. shaped like two golf clubs twisted together. The myosin tail (twisted golf club handles) points toward the M line in the center of the sarcomere

Fixator

• A type of synergist that holds a bone firmly in place EX: pectoralis minor, trapezius, subclavius, serratus anterior muscles (all holding the scapula in place)

List and describe the properties of muscle tissue:

• Excitability (responsiveness): the ability to respond to certain stimuli by producing electrical signals called action potentials (impulses) - To chemical signals, stretch, and electrical changes across the plasma membrane (sarcolemma) - Local electrical excitation sets off a wave of excitation that travels along the muscle fiber • Contractility - Shortens when stimulated - When a skeletal muscle contracts, it generates tension (force of contraction) while pulling on its attachment points. • Extensibility - Capable of being stretched between contractions • Elasticity - Returns to its original rest length after being stretched

• Prime mover (agonist)

• Has major responsibility for a certain movement • Contracts to cause an action • EX: biceps brachii

Explain the sliding filament mechanism of muscle contraction.

• Initiated by release of calcium ions from the sarcoplasmic reticulum • Powered by ATP • Explains concentric contraction o Myosin head attach to thin filaments at both ends of a sarcomere, then pull thin filaments toward the center of the sarcomere o Thin and thick filaments do not shorten

Know the criteria used in naming muscles

• Location of muscle - indicate the bone or body region muscle associated with • Temporalis, intercostals • Shape of the muscle • Trapezius, deltoid • Relative size of muscle • Maximus, minimus, longus (long), brevis (short) • Direction of muscle fibers • Named in relation to a line running the length of the body • Rectus, transverse, oblique • Number of origins (heads) • Bi, tri, and quad • Location of attachments - named according to their points of origin and insertion • Sternocleidomastoid • Origin is always first • Action - named according to the effect of the muscle • Flexor, extensor, adductor

List and describe four functional properties distinguishing muscle tissue from other tissues.

• Movement: Total body movements such as walking and running, and localized movements such as grasping a pencil, keyboarding, or raising your hand • Stability: Skeletal muscle contractions stabilize joints and help maintain body positions, such as standing or sitting. Postural muscles contract continuously when you are awake • Control of openings and passageways - Sphincters: internal muscular rings that control the movement of food, blood, and other materials within body • Heat production: As muscular tissue contracts, it also produces heat, a process called thermogenesis - As much as 85% of our body heat • Glycemic control - Muscles absorb and store glucose which helps regulate blood sugar concentration within normal range

• Antagonist

• Opposes or reverses a movement • EX: triceps brachii

Oxidative fibers

• generate ATP mainly by aerobic (oxygen‐requiring) cellular respiration

• Synergist

• helps the prime mover By adding extra force • By reducing undesirable movements • Synergists are usually located close to the prime mover. • EX: iliacus, psoas major, and rectus femoris

Glycolytic fibers

• produce ATP anaerobically by glycolysis

Four major phases of contraction and relaxation (ESSAY QUESTION)

- Excitation: Process in which nerve action potentials lead to muscle action potentials • Ca^2+ (nerve signal) enters axon terminal • ACh releases • ACh binds to receptor • Opening of ligand-regulated ion gate: creation of end plate potential • Opening of voltage- regulated ion gates; creation of action potentials - Excitation-contraction coupling: Events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them to contract • Action potentials propagated down t tubules (depolarization) • Calcium released from terminal cistern • Binding of calcium tropanin • Shifting to tropomysosin; exposure of active sites on actin - Contraction: Step in which the muscle fiber develops tension and may shorten • Hydrolosis of ATP to ADP + P; activation and cocking of myosin head (recovery stroke) • Formation of myosin- actin cross bridge • Binding of new ATP; breaking of cross bridge • Power stroke; sliding of thin filament over thick filament - Relaxation: When stimulation ends, a muscle fiber relaxes and returns to its resting length • Cessation of nervous stimulation and ACh release • ACh breakdown by acetylcholinesterase (AChE) • Reabsorption of calcium ions by sarcoplasmic reticulum • Loss of calcium ions from toponin • Return of tropomyosin to position blocking active sites actin

Process of a nerve impulse (or nerve action potential) eliciting a muscle action potential

1. Release of acetylcholine: Nerve impulse at the synaptic end bulbs stimulates voltage‐gated channels to open Ca2+ enters the synaptic end bulbs. Voltage‐gated channels (integral membrane proteins) open in response to a change in membrane potential (voltage). The Ca2+ stimulates synaptic vesicles to fuse with the motor neuron's plasma membrane, releasing ACh into the synaptic cleft. The ACh then diffuses across the synaptic cleft between the motor neuron and the motor end plate. 2. Activation of ACh receptors: Binding of two molecules of ACh to the receptor on the motor end plate opens an ion channel in the ACh receptor. Once the channel is open, small cations, most importantly Na+, can flow across the membrane. 3. Production of muscle action potential: The inflow of Na+ triggers a muscle action potential. The muscle action potential then moves along the sarcolemma into the system of T tubules. This causes the sarcoplasmic reticulum to release its stored Ca2+ into the sarcoplasm and the muscle fiber subsequently contracts. 4. Termination of ACh activity: The effect of ACh binding lasts only briefly because ACh is rapidly broken down by an enzyme called acetylcholinesterase (AChE). AChE breaks down ACh into acetyl and choline, products that cannot activate the ACh receptor.

Z disc (Z line)

Boundaries of each sarcomere, Passes through middle of I band

Types of attachment

Direct-Fleshy attachments—CT fibers are short Indirect attachments—CT forms a tendon or aponeurosis Bone markings present where tendons meet bones