Anatomy Review: Skeletal Muscle Tissue

Introduction

Skeletal muscle cells have unique characteristics which allow for body movement.

 Goals

To compare and contrast smooth muscle cells, cardiac muscle cells, and skeletal muscle cells.

To review the anatomy of the skeletal muscle.

To examine the connective tissue associated with the skeletal muscle.

To review the intracellular organization of the skeletal muscle cell.

 Comparison of Skeletal, Cardiac and Smooth Muscle Cells

Skeletal Muscle Cell:

Cardiac Muscle:

Smooth Muscle Cell:

Elongated Cells

Branching Cells

Spindle-Shaped Cell

Multiple Peripheral Nuclei

Single Central Nucleus

Single Central Nucleus

Visible Striations

Visible Striations

Lack Visible Striations

Voluntary

Involuntary

Involuntary

 

                                                

Whole Skeletal Muscle

Skeletal muscles attach to bones via tendons.

Internal Structure of a Skeletal Muscle

Skeletal muscles are composed of connective tissue and contractile cells.

The connective tissues surrounding the entire muscle is the epimysium.  Bundles of muscle cells are called fascicles.  The connective tissues surrounding the fascicles is called perimysium.

Label this diagram:

 

Internal Structure of a Fascicle

Important Points About Endomysium:

Made of connective tissue.

Surrounds individual muscle cells.

Functions to electrically insulates muscle cells from one another.

Three connective tissue layers of the muscle (endomysium, perimysium, and epimysium):

Bind the muscle cells together.

Provide strength and support to the entire muscle.

Are continuous with the tendons at the ends of the muscle.

Label this diagram:

Internal Structure of a Skeletal Muscle Cell

Label this diagram:

 Muscle fibers:  Alternative name for skeletal muscle cells.

Nucleus: Contains the genetic material.

Sarcolemma:  Plasma membrane of the muscle cell.

Sarcoplasmic reticulum (SR): Interconnecting tubules of endoplasmic reticulum that surround each myofibril.

Terminal cisternae: Sac-like regions of the sarcoplasmic reticulum that contain calcium ions. 

T tubules:  Invaginations of the sarcolemma that project deep into the cell.

Triad: A group of one T tubule lying between two adjacent terminal cisternae. 

Cytosol:  Intracellular fluid. 

Mitochondria: Sites of ATP synthesis. 

Myofibril: Contains the contractile filaments within the skeletal muscle cell.

 Structure of a Myofibril

Myofibrils: Contractile units within muscle cells.

Made of myofilaments called thin filaments and thick filaments.

Thin and thick filaments are made mainly of the proteins actin and myosin.

Arrangement of Myofilaments

      Label the diagram:

A bands: Dark areas that correspond to the areas where thick filaments are present.  

I bands: Light areas that contains only thin filaments. 

Z line: A protein disk within the I band that anchors the thin filaments and connects adjacent myofibrils.

H zone: Located in the middle of each A band, this lighter stripe appears corresponding to the region between the thin filaments. 

M line: Protein fibers that connect neighboring thick filaments. 

Sarcomere:  The region of the myofibril between two Z lines.

** Keep in mind, this information is crucial for your understanding of the sliding filament theory.

Review: Organizational Levels of Skeletal Muscle

"Bundle-within-a-bundle" organization of skeletal muscle:

myofilaments

myofibril

muscle cell or muscle fiber

fascicles

whole skeletal muscle

 

Pyramid of Subunits

Whole muscle as a pyramid of subunits: 

Fascicles

Muscle cells (Muscle Fibers)

Myofibrils

Myofilaments

  Summary

The three types of muscle cells in the body are skeletal, cardiac, and smooth.

Skeletal muscle has three layers of connective tissue: epimysium, perimysium, and endomysium.

The striations of skeletal muscle cells are due to the organized arrangement of contractile proteins called thick and thin filaments.

A whole muscle demonstrates a bundle-within-a-bundle organization:

myofilaments myofibrils muscle cells (muscle fibers) fascicles whole muscle

Review Questions               Home