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