[RAP0 21LAB] PRELIM: Lesson 3 (Muscle Cells; Skeletal Muscle Cells; Cardiac Muscle Cells)

Skeletal; Cardiac; Smooth Muscle Cells

3 Main Types of Muscle Cells

Skeletal Muscle Cells

• Striated Muscle

• It is a type of striated muscle tissue that is under voluntary control, meaning it is consciously controlled by the nervous system.

• It is responsible for movement, posture, and stability in the body.

• They are attached to bones via tendons and work by contracting and relaxing to generate force.

5 Level Organization of Skeletal Muscle

• Muscle Fiber (Cell)

• Myofibrils

• Sarcomere

• Fascicles

• Epimysium, Perimysium, and Endomysium

Muscle Fiber (Cell)

• Level Organization of Skeletal Muscle

• The basic unit of skeletal muscle, also called a muscle cell or myocyte.

Myofibrils

• Level Organization of Skeletal Muscle

• Long, rod-like structures inside muscle fibers that contain the contractile proteins.

Sarcomere

• Level Organization of Skeletal Muscle

• The functional unit of contraction within myofibrils, composed of actin (thin filaments) and myosin (thick filaments).

Fascicles

• Level Organization of Skeletal Muscle

• Bundles of muscle fibers grouped together.

Epimysium, Perimysium, and Endomysium

• Level Organization of Skeletal Muscle

• Layers of connective tissue that surround the entire muscle, fascicles, and individual muscle fibers, respectively.

4 Functions of Skeletal Muscle

• Movement

• Posture and Stability

• Heat Production

• Metabolism

Movement

• Functions of Skeletal Muscle

• Skeletal muscles contract to move bones at joints.

Posture and Stability

• Functions of Skeletal Muscle

• They help maintain body posture.

Heat Production

• Functions of Skeletal Muscle

• Muscle contractions generate heat, aiding in temperature regulation.

Metabolism

• Functions of Skeletal Muscle

• Muscles store glycogen and serve as a key site for glucose metabolism.

Cardiac Muscle Cell

• Cardiomyocyte

• It is the fundamental unit of ___ tissue.

• These cells are highly specialized for continuous contraction, allowing the heart to pump blood efficiently throughout the body.

6 Structure of a Cardiac Muscle Cell

• Branched Shape

• Striations

• Single or Dual Nuclei

• Intercalated Discs

• Numerous Mitochondria

• Sarcoplasmic Reticulum (SR) & T-Tubules

Branched Shape

• Structure of a Cardiac Muscle Cell

• Unlike skeletal muscle cells, cardiomyocytes are branched, forming a network that allows coordinated contraction.

Striations

• Structure of a Cardiac Muscle Cell

• Like skeletal muscle, cardiac muscle cells have alternating light and dark bands due to the arrangement of actin and myosin in sarcomeres.

Single or Dual Nuclei

• Structure of a Cardiac Muscle Cell

• Most cardiomyocytes contain a single, centrally located nucleus, though some may have two.

Intercalated Discs

• Structure of a Cardiac Muscle Cell

• Specialized junctions between cardiomyocytes containing

  • Gap Junctions

  • Desmosomes

Gap Junctions and Desmosomes

2 Intercalated Discs

Gap Junctions

• Intercalated Discs

• Allow electrical impulses to spread rapidly between cells for synchronized contraction.

Desmosomes

• Intercalated Discs

• Provide mechanical strength to keep cells connected during forceful contractions.

Numerous Mitochondria

• Structure of a Cardiac Muscle Cell

• Cardiomyocytes have a high mitochondrial density to support continuous energy production for contraction.

Sarcoplasmic Reticulum (SR) & T-Tubules

• Structure of a Cardiac Muscle Cell

• These structures help regulate calcium levels, which are essential for muscle contraction.

4 Functions of Cardiac Muscle Cells

• Generate Force for Heart Contraction

• Autorhythmicity (Self-Excitation)

• Rapid Electrical Signal Transmission

• Resist Fatigue

Generate Force for Heart Contraction

• Functions of Cardiac Muscle Cells

• Enables blood circulation throughout the body.

Autorhythmicity (Self-Excitation)

• Functions of Cardiac Muscle Cells

• Certain cardiomyocytes (e.g., those in the sinoatrial (SA) node) act as pacemakers, generating electrical impulses without nervous system input.

Rapid Electrical Signal Transmission

• Functions of Cardiac Muscle Cells

• Ensures coordinated contraction of the atria and ventricles.

Resist Fatigue

• Functions of Cardiac Muscle Cells

• Due to their high mitochondrial content, cardiomyocytes continuously produce ATP for sustained activity.