Animal Muscles

• Cytoskeleton

  • Dense and complex network of fibres
  • Helps maintain cell shape by providing structural support
  • Not a static structure like scaffolding used at construction sites
  • Its fibrous proteins move and change to alter the cell’s shape, shift its contents, and even more the cell itself
  • Three types of cytoskeletal elements: actin filaments (microfilaments), intermediate filaments, microtubules
• Actin Filaments (Microfilaments)

  • Smallest cytoskeletal elements
  • Formed by polymerization of individual actin molecules into long strands
  • Two strands coil around each other
  • Grouped together into long bundles or dense networks
  • Usually found just inside plasma membrane
  • Two distinct ends are referred to as plus and minus ends
  • Movement, with the motor protein myosin
  • Uses ATP to change shape and do work:
  • Muscle contraction
• Cytokinesis - diving cytoplasms during cell division
• Cytoplasmic streaming - flow of cytoplasm
• Cell crawling - caused by actin filaments growing in one direction, moving the cell
• Intermediate Filaments

  • Defined by size instead of composition
  • Many types exist, each consisting of a different protein
  • Provide structural support for the cell and aren’t involved in movement
• Microtubules

  • Provide stability and structural framework for organelles
  • Involved in movement
  • Separate chromosomes during cell division
  • Serve as “railroad tracks” for vesicle transport - motor protein kinesin “walks” along as it hydrolyzes ATP
• Animal Movement

  • Two types of movement: movement of entire animal relative to its environment + movement of one part of the animal relative to the entire body
• Muscle Tissues

  • All vertebrates share same three types of muscle tissue: smooth, cardiac, skeletal
  • All tissues share several properties: contract by sliding-filament model, contract in response to electrical stimulation
  • All vary in different ways:
  • Voluntary muscles can contract in response to conscious thought and are stimulated by neurons in the somatic division
  • Involuntary muscles contract only in response to unconscious electrical activity and are stimulated and inhibited by neurons in the autonomic division
  • Multinucleate vs. Uninucleate
  • Striated vs. Unstriated
• Cardiac Muscle

  • Makes up the walls of the heart and is responsible for pumping blood throughout the body
  • Muscles contain sarcomeres and are striated
  • Have unique branched structure, directly connected end to end by intercalated discs - discs critical to flow of electrical signals from cell to cell, and to coordination of the heartbeat
  • Cardiac muscle is involuntary, contracts following spontaneous depolarizations
• Smooth Muscle

  • Cells are unbranched, tapered at each end, often organized in sheets
  • Cells lack sarcomeres found in skeletal and cardiac muscle
  • Cells are unstriated and appear smooth, and are relatively small and have a single nucleus
• Smooth Muscle (Part 2)

  • Smooth muscles essential to function of the lungs, blood vessels, digestive system, urinary bladder, + reproductive system
  • Innervated by autonomic motor neurons and is involuntary
  • ACh released by parasympathetic neurons stimulates contractions throughout the digestive system
  • Sympathetic neurons release norepinephrine and the adrenal glands release epinephrine, which both inhibit the muscle contraction of the digestive tract