Lecture Notes: Muscle Tissue Types

Overview

• Muscles are one of the four basic tissue types, alongside epithelial, connective, and nervous tissues.
• Three types of muscles:
  • Skeletal Muscle
  • Cardiac Muscle
  • Smooth Muscle
• The session involves examining these muscle types under a microscope and studying a skeletal muscle model.

Skeletal Muscle

• Known as skeletal muscle fibers—long, skinny cells.
• Typically attached to bones; responsible for voluntary movement (with exceptions).

Characteristics:

• Striations: Visible stripes due to the arrangement of contractile proteins (actin and myosin).
• Multi-nucleate: Multiple nuclei due to the fusion of embryonic muscle cells (myoblasts).

Observations:

• Striations are a result of actin and myosin overlap.
• High number of nuclei per cell.

Cardiac Muscle

• Found exclusively in the heart walls.
• Involuntary muscle with intrinsic rhythm and strength.

Characteristics:

• Striations: Present but less prominent than in skeletal muscle.
• Uni-nucleate: Usually one nucleus per cell.
• Intercalated Discs: Unique feature, consisting of:
  • Gap Junctions: Electrically connect cells, enabling unified contraction.
  • Desmosomes: Mechanically attach cells strongly.

Observations:

• Occasional double nuclei.
• Visible intercalated discs.

Smooth Muscle

• Found in walls of hollow organs (e.g., blood vessels, digestive tract, respiratory pathways).
• Involuntary muscle.

Characteristics:

• Lack of Striations: Despite having actin and myosin, lacks visible striations.
• Observed in transverse and longitudinal sections.

Observations:

• No striations observed.
• Presence of nuclei.

Skeletal Muscle Fiber Model

• Sarcolemma: Plasma membrane of the muscle cell.
• Endomysium: Connective tissue wrapping around muscle cells.
• Motor End Plate: Part of the sarcolemma interacting with neuron axon terminals.
• Neuromuscular Junction: Synapse between axon terminal and motor end plate.

Observations:

• Axon Terminals: Release acetylcholine, triggering muscle contraction.
• Striations: Observable horizontal stripes due to protein arrangements.
• Myofibrils: Bundles of proteins (actin and myosin) within the muscle fibers.

Final Observations

• Reviewed images highlighting muscle fibers, striations, nuclei, and neuromuscular junctions.
• Telodendria and axon terminals visualized in the microscopic views.

End of Lab 23. The focus for the next session will continue with related muscle tissue studies.