Muscle Anatomy and Physiology

Structure of Muscle Tissue

• Each muscle is supplied with:
  • A nerve (motor unit)
  • An artery
  • Several veins for nutrient supply and waste removal
• ATP is required for muscle function and must be recycled via veins to facilitate muscle contractions.

Types of Muscle Contractions

• Isotonic Contraction:
  • The muscle contracts and changes length, thereby producing movement.
• Isometric Contraction:
  • The muscle contracts but does not change length, resulting in tension without movement.

Skeletal Muscle Actions

• Origin: The immovable end of a muscle.
• Insertion: The movable end of a muscle.
• Muscle Actions:
  • Agonist (Prime Mover)
  • Primarily responsible for movement.
  • Synergists:
  • Assist the agonist in performing a movement.
  • Antagonists:
  • Resist the actions of the agonist and cause movements in the opposite direction.
  • Example: During arm flexion, the biceps brachii acts as the agonist and the triceps brachii acts as the antagonist.

Muscle Attachment Mechanics

• Attachment of Muscle to Bone:
  • Muscles attach to bones through tendons.
  • Individual muscle groups are wrapped in fascia.
• Tendon fibers may intertwine with:
  • Periosteum of bone
  • Adjacent muscle tissue to form a sheet-like aponeurosis.

Muscle Anatomy and Functions

• Muscle Fibers (Cells):
  • Each muscle fiber contains myofibrils.
• Myofibrils shorten to contract muscle fibers.
• The basic contractile unit is the sarcomere:
  • Composed of proteins actin and myosin.
• Sarcoplasmic Reticulum (SR):
  • A web that encases the muscle cell.
  • Associated with T-tubules wrapping around the cell membrane.

Neuromuscular Junction and Muscle Contraction

• Neuromuscular Junction:
  • The site where nerves connect to muscle tissue.
  • A nerve impulse or action potential exchanges concentrations of Na⁺ and K⁺ ions across the membrane.

Acetylcholine (ACh) and Muscle Control

• Destruction of Acetylcholine:
  • ACh that is bound to its receptors is quickly broken apart by the enzyme acetylcholinesterase.
  • This process prevents continued muscle fiber contraction in the absence of additional stimuli.
  • ACh components are recycled and reused by the neuron.
• Effects of Pesticides (e.g., Malathion):
  • Prolongs the effect of ACh leading to involuntary muscle spasms.
• Myasthenia Gravis:
  • A neuromuscular disease where ACh receptors are defective, leading to muscle weakness.

Toxins Influencing Muscle Activity

• Animal Toxins and Venoms:
  • Contain acetylcholinesterase or block ACh receptors, inducing paralysis and potentially death.
• Botulism:
  • Caused by the bacterium Clostridium botulinum.
  • Produces neurotoxins that hinder the release of neurotransmitters, causing paralysis.

Smooth Muscle Characteristics

• Contains actin and myosin, but no troponin.
• Each cell contains one nucleus, and there are no neuromuscular junctions:
  • Nerves innervate directly releasing neurotransmitters.
• Contractions are slower and prolonged.
• Calcium interacts with calmodulin (a protein) to activate myosin heads for contraction.