EXAM 3: BIO&251 (Chapter 10: Part 1)

• Cardiac: Found in walls of the heart/pumps blood
• Smooth: Walls of hollow organs/moves eggs, sperm, urine, food, hairs
• Skeletal (most important): Attached to bone or fascia/many functions

• 1. Produce skeletal movement
• 2. Maintain body and posture positions
• 3. Support soft tissues (floor of pelvic cavity)
• 4. Guard entrances and exits (esophagus, external anal sphincter)
• 5. Produce heat - maintain body temperature
• 6. Store nutrient (breakdown release amino acids)

• Three different Connective Tissues present
• 1. Epimysium (outside)
• 2. Perimysium (around)
• 3. Endomysium (inside)

Cell and fiber are the same thing

• Stain darkly (contains lots of proteins)
• Long and Thin
• Striated
• Peripheral nuclei (doesn't interfere with fusing)
• Multinucleated (due to myoblasts fusing together)
• Do not branch

• These are stem cells
• Live in Endomysium
• Function in muscle development (Hyperplasia=more cells, Hypertrophy=large existing cells/happens more often)
• Myoblasts proliferate, differentiate, fuse into multinucleate muscle cells
• Some remain as myosatellite (satellite) cells in skeletal muscle

• Epimysium surrounds entire muscle (DENSE IRREGULAR CT)
• Perimysium defines bundles of muscle fibers (DENSE IRREGULAR CT)
• Endomysium surrounds individual muscle fibers (AEROLAR CT, MYOSATELLITE CELLS [STEM])

All three CT layers contribute to tendons and aponeuroses

• Muscle Cell=muscle fiber=myofiber
• Sarcolemma (cell membrane): Sarco=flesh, lemma=husk
• Sarcoplasm: muslce cell cytoplasm
• Sarcoplasmic Reticulum: modified ER/wraps around contractile proteins to organize them/stores calcium (Higher concentration inside than outside)
• T-Tubules: invaginations of cell membrane
• Myofibrils: contain contractile proteins wrapped by SR
• Sarcomeres: regular arrangement of myofilaments within myofibril

• 
• Resting Muscle: Not permeable to Calcium

• Specialized smooth endoplasmic reticulum
• Wraps around myofilaments (contractile proteins) to form myofibrils

• Stores Calcium in cisternae
• 1.Swellings called terminal cisternae
• 2.Ca²⁺ is continuously pumped into SR from cytoplasm
• 3. SR not very leaky to Ca²⁺ in resting muscle cell

• Flux=PxΔC
• SE contains calcium binding proteins, calsequestrian

• As a result of pumping Ca²⁺ into the SR:
• 1. [Ca²⁺] in SR about 40,000X higher than in the sarcoplasm
• 2. Total [Ca²⁺] = free Ca²⁺ + Ca²⁺ bound to calsequestrian (About 40X more Ca²⁺ bound to calsequestrian than is in the form of free Ca²⁺

During contraction process, SR membrane becomes leaky, Ca²⁺ rapidly enters sarcoplasm

• Invaginations of the sarcolemma (cell membrane)
• Carry action potential deep into cell
• Contain extracellular fluid

• SR wraps around myofilaments
• Organizes them into myofibrils

Myofilaments=proteins

• Types:
• 1. Thin Filament: Actin and other proteins
• 2. Thick Filament: Myosin and Titin

Arranged with myofibrils into sarcomeres

Smallest functional unit of muscle contraction

• *Repeating units along the length of a muscle fiber
• *Regular arrangement causes striated appearance

• Dark=A bands
• Light=I bands

• 
• 1 Sarcomere extends from 1 Z Line to another Z Line
• H Band: Bright Band
• Titin: Green wiggly line
• *Largest known protein and goes all the way through

• 
• Actin: Thin Filament
• Actinin: Makes Titin squiggly

• Z Line
• *Actinin Filaments: Anchors thin filaments between sarcomeres
• *Titin: Attaches here to anchor myosin (largest known protein)

• I Band=isotropic=light in color
• *Thin Filament and titin
• *Shrinks when muscle contracts

• A band=anisotropic=dArk colored
• *Where thick filament is present
• *Does not shrink when muscle contracts

• Contains:
• 1. M Line
• *Myomesin: stabilizes thick filaments
• 2. H Band
• *Thick Filament only
• 3. Zone of overlap
• *Both think and thick filaments

• 
• Head is going to use ATP to move and grab an Actin molecule

• 
• 1. F Actin
• *Composed of 2 strands of G actin subunits
• *Has active sites (myosin-binding sites)

• 2. Nebulin
• *Helps hold G actin subunits together into F actin molecule

• 
• 3. Tropomyosin
• *Covers myosin-binding sites on actin in resting muscle

• 4.Troponin
• *Binds tropomyosin
• *Binds to G-actin and holds tropomyosin in place
• *Has Ca²⁺ binding site

• 5. Dystrophin: Links actin to sarcolemma proteins
• *Transmits force to membrane → tendons

• 
• They are bundles of Myosin filaments around a Titin core
• *Myosin molecules have elongated tail, globular head, and hinge region
• **Heads have ATP-binding site
• **Heads form cross-bridges with actin during contraction

• 
• The I band and the H Zone shrinks.

• 1. Electrical signal (action potential) travels along axon of motor neuron to motor end plate (a.k.a neuromuscular junction)
• 2. Ca²⁺ enters the bouton.
• 3. Neurotransmitter (acteylcholine-ACh) is released into the synapse between nerve and muscle cells.
• 4. ACh diffuses across synapse and binds to ACh receptors on muscle cell surface.
• 5. Receptor changes shape and allows Na⁺ to move down its concentration gradient into muscle cell.
• 6. Action potential spreads over muscle cell surface, including T-Tubules (Excitation).
• 7. Sarcoplasmic reticulum releases Ca²⁺ into cytoplasm (Excitation/Contraction coupling).
• 8. Ca²⁺ interacts with troponin.
• 9. Troponin pulls tropomyosin.
• 10. Myosin-binding sites are uncovered.
• 11. Myosin heads grab and pull on Actin ("power stroke" of contraction).
• 12. Myosin heads bind and split new ATP.
• 13. Myosin heads release Actin and "recock" for another power stroke.

Cross-bridges are formed at different times by individual myosin heads causing a smooth sliding of filaments.

• Graded Potential: Travels along membrane of the synapse.
• Action Potential: Spreads across entire muscle of cell membrane.

This is the link between an action potential on the muscle cell membrane and the beginning of contraction.

• 1. Motor neuron quits firing → no new ACh release
• 2. Acetylcholinesterase (AChE) in synapse is continually breaking down ACh

• Result
• *No new action potential on muscle cell
• **No new Ca²⁺ release from SR
• **Ca²⁺ continually pumped into SR
• **[Ca²⁺] in cytoplasm drops
• *T-T complex covers up myosin-binding sites
• **No interaction between actin and myosin
• **Muscle relaxes passively

• Myosin heads already cocked with ATP
• Ca²⁺ leaks out of SR (ATP required to pump it back in)
• Intracellular [Ca²⁺] rises
• T-T complex binds Ca²⁺ and uncovers myosin-binding sites
• Contraction occurs
• ATP stores become depleted over time
• No ATP available to release myosin from actin and recock heads
• RIGOR MORTIS

• Inhibitory Effects: Block ACh release - Botulinum toxin/Blocks binding of ACh to receptor - Atropine (belladonna), curate
• Excitatory Effects: Block acetylcholinesterase - Neostigmine, DFP (nerve gas)/Increase ACh release - some spider venoms/Mimic ACh - Nicotine