Muscle Tissue Characteristics and Structures

Muscle Characteristics

• Electrical excitability: Responsiveness, ability to receive and respond to stimuli
• Contractility: Ability to shorten forcibly when stimulated
• Extensibility: Ability to be stretched
• Elasticity: Ability to recoil to resting length

Muscle Tissue Structures

• Epimysium: Dense irregular connective tissue surrounding an entire muscle
• Perimysium: Fibrous connective tissue surrounding fascicles (groups of muscle fibers)
• Endomysium: Fine areolar connective tissue surrounding each muscle fiber

Sarcomere Structure

• I band: Shortens; contains thin filaments (actin)
• A band: Thick myosin filaments and some actin filaments; dark region within a sarcomere.
• Z disc: Plates delimiting a sarcomere; pulled towards the M line.
• M line: Center of a sarcomere where myosin binds.
• H zone: Only thick myosin filaments, no actin filaments; disappear during contraction.

Skeletal Muscle Fiber Components

• Sarcoplasmic reticulum: Stores and releases calcium ions
• Sarcomere: Smallest contractile unit (functional unit) of a muscle fiber
• Sarcolemma: Muscle fiber plasma membrane

Neurotransmitters & Muscle Action

• Acetylcholine (ACh): Excitatory neurotransmitter at the neuromuscular junction
• Sliding filament theory: Thin (actin) filaments slide past thick (myosin) filaments towards the M-line during contraction.

Energy Production (Respiration)

• Aerobic respiration: Produces 36 ATPs and provides energy for several minutes or longer
• Anaerobic glycolysis: 2 ATPs, lasting 10-30 seconds
• Creatine phosphate: 1 ATP, lasting for about 15 seconds

Muscle Contraction Types

• Isotonic: Muscle shortens because muscle tension exceeds load.
• Isometric: No shortening; muscle tension increases but load is not exceeded.
• Eccentric contraction: Muscle lengthens & generates force
• Concentric contraction: Muscle shortens & generates force.

Muscle Action Types

• Agonist/Prime Mover: Major responsibility for producing specific movement.
• Antagonists: Opposes or reverses particular movement.
• Fixators: Type of synergist that immobilizes a bone or muscle origin to provide a stable base for the prime mover.
• Synergists: Help prime movers.

Muscle Attachment Sites

• Origin: Attachment site on the bone that does not move during muscle contraction.
• Insertion: Attachment site on the bone that moves during muscle contraction.

Skeletal Muscle Function - Control

• Mechanically-gated channels: Open/close in response to a physical distortion in the membrane, a major mechanism underlying touch sensation.
• Action potentials (electrical charges): Propagated across sarcolemma for skeletal muscle. Graded potentials: Signals across short distances. Summation: adding up potentials for stronger contractions
• Somatic system (voluntary) control

Neural System Components

• Central Nervous System (CNS): Brain and spinal cord
• Peripheral Nervous System (PNS): Nerves branching out from the CNS (cranial and spinal nerves).

Cellular components of the nervous system

• Oligodendrocytes, Schwann cells, Astrocytes, Microglia, Ependymal cells

Other muscle/bone information mentioned:

• Rotator Cuff Muscles: Supraspinatus, Infraspinatus, Teres Minor, Subscapularis
• Hamstrings: Biceps femoris, Semitendinosus, Semimembranosus
• Quadriceps: Rectus femoris, Vastus lateralis, Vastus intermedius, Vastus medialis
• List the three types of muscle fibers and describe the function of each, list and describe the major functional divisions of the nervous system.