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Muscle Functions
• (1). Maintaining posture
• (2). Stabilizing joints
• (3). Generating heat
• (4). Storing and Moving – Smooth muscle (peristalsis)
Functional Characteristics of Muscle• (1). Excitability and Irritability
• (2). Contractility– Ability to shorten
• (3). Extensibility– Ability to be stretched
• (4). Elasticity– Ability to recoil and resume original shape
Skeletal Muscle Tissue1. Function
2. Voluntary
3. Large Cells
– 10 to 100 um diameter
– 30 cm length
4. Multinucleated
5. Striated
6. Functional Syncyntium
Smooth Muscle Tissue 1. Functions
2. Locations
– Hollow organs
– “Visceral”
3. Uninucleated
– Spindle-shaped cells
4. Non-striated
5. Involuntary
– Peristalsis
Cardiac Muscle Tissue 1. Function – Location
2. Involuntary
3. Striated
4. Intercalated discs
– Specialized gap junctions
Skeletal Muscle Gross Anatomy
Organization Level – Muscles
Connective Tissue Sheaths
Deep Superficial- Hypodermis
Epimysium Perimysium
Endomysium
Somatic Motor Neurons-part of Peripheral Nervous System motor division
VeinsBlood Returns to the Heart
Contractile Regulatory
Structural
Ultrastructure of Myofilaments
• Sliding Filament Model
• Exitation-Coupling
• Link (ch.7-myofilament and sarcomere contraction)
Relaxed Fully Contracted
What Causes a Muscle Contraction to Occur?
• Muscle Contractions – Nerve Stimulation– Neuromuscular Junction
• Nerves contain Neurotransmitters– Muscle contraction – Acetylcholine (ACh)
• NT bind to sarcolemma of muscle (Receptor Sites)
• Causes a nerve impulse (Action Potential)
• Stimulates the Sarcoplasmic Reticulum to release Ca++ • Stimulates the muscles to contract
Neuromuscular Junction
Generation of an Action Potential
Excitation-Contraction Coupling
• 1. Tropomyosin blocks binding site (low Ca levels)
• 2. As Ca levels rise, binds to TnC of troponin
• 3. Troponin undergoes a transformation change- moves tropomyosin away from binding site
• 4. Attachment of myosin head
Events in Muscle Fiber Contraction
Events in the Sliding of Thin Filaments During Contraction
Links for Action Potential and Coupling
• Link (ch. 7 – action potential)• NHC (sliding filament)
Muscle Twitch
Treppe: Initial contractions are not as strong as later contractions caused by the same amount of stimulus. Why? Increasing availability of Ca in the SR; Increasing Ca increase the number of troponin binding sites open; muscles warm up and liberate heat making them more pliable