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Phys Lect 11

3 ways of classifying muscles 1.Control mode (Voluntary or Involuntary). 2.Histological (Straited or Smooth). 3.Anatomic (Skeletal, cardiac, smooth).
Important functions of smooth muscles 1.Sphincter control. 2.Vascular tone. 3.Peristalsis. 4.Birthing contractions
Properties of Skeletal muscle 1.Velocity: Rapid. 2.Duration: Relatively long. 3.Fatigability: variable.
Properties of Cardiac muscle 1.Velocity: Rapid. 2.Duration: Short. 3.Fatigability: No fatigue (can't have the heart getting tired).
Properties of Smooth muscle 1.Velocity: Slow. 2.Duration: Long. 3.Fatigability: No fatigue.
Electrical Excitation of Skeletal muscle Comes from a motor nerve
Electrical Excitation of Cardia muscle MYOGENIC: it generates its own electrical excitation which then travels through the myocardia via gap junctions.
Electrical Excitation of Smooth muscle Varies, can either come from a motor nerve or move via gap junctions.
What ion is directly responsible for initiating contraction in all 3 muscle types? [Ca2+]. A rise in concentration triggers a contraction. *At rest: 10^-7. *Contractoin: 10^-6
Thick and Thin myofilaments Thick: Myosin. Thin: Actin
Myosin Structure Consists of: 1. 2 Globular head (important for contraction). 2.tail (flexible to allow movement for the head).
2 major binding sites on the myosin head 1.ATP binding site. 2.Actin binding site.
Components of the Troponin Complex? 1.Troponin T (binds to tropomyosin). 2.Troponin I (binds to actin, inhibits Actin-myosin interaction). 3.Troponin C (responds to Ca2+).
A-band Width of the myosin filaments. Includes actin overlap.
I-band Actin filaments without and Myosin overlap. Contain the Z-LINES which come closer together during sarcomere shortening.
H-zone Contain just the myosin without any actin overlap. Contains the M-LINE in the middle of the sarcomere
What happens during a contraction: A-band STAYS THE SAME b/c the myosin filaments aren't changing in length.
What happens during a contraction: I-band DECREASES, bringing the Z-lines closer together
What happens during a contraction: H-zone DECREASES
Describe the steps of Cross-bridge cycling 1.Myosin head is bound by ADP + Pi, ready to bind to Actin. 2.Ca2+: myosin head binds to actin. 3.Power stroke: the myosin head moves. ADP + Pi are released. 4.ATP: myosin head detaches from actin. 5.ATP hydrolysis creates a new ADP + Pi
[Ca2+] control which process of Cross-Bridge Cycling? The binding of Myosin head to actin filament. **Ca+ binds to Troponin C, which then shifts tropomyosin and Troponin I so the myosin binding site on the actin filament is now exposed.
What happens if striated muscle is suddenly deprived of ATP? The myosin head is stuck bound to the actin filament. (stuck contracted). **Rigormortis**
Myosin Light Chain Kinase Phosphorylates the myosin head in SMOOTH muscle so that it can actively hydorlyze ATP. **It is ACTIVATED by INCREASED Ca2+**
Myosin Light Chain Phosphatase Dephosphorylates the myosin head in SMOOTH muscle which prevents it from hydrolyzing ATP/contracting.
Ca2+ role in smooth and striated muscle contraction 1.Smooth muscle: stimulates contraction via activating Myosin Light Chain Kinase. 2.Striated muscle: stimulates contraction via binding to Troponin C and moving tropomyosin to expose actin
Dystrophin Connects the myofilaments to the cell membrane, allowing the tension/force created by smooth muscle shortening. **Problematic in MD, leads to rupturing of cell membranes and difficulty generating force due to a lack of connection
Muscular Dystrophy Loss of Dystrophin, defect in cytoskeletal connection between myofilaments and muscle membrane. **Pt will present with muscle weakness, delayed coordination. Evident muscle breakdown followed by hypertrophy (as the body attempts to compensate).
Created by: WeeG