LEC 18

Cardiac Muscle and Muscular System Overview

I. Cardiac Muscle

• Definition: A specialized type of muscle found in the heart, responsible for pumping blood throughout the body.
• Characteristics:
  • Striated appearance like skeletal muscle.
  • Involuntary control (not consciously controlled).
  • Contains intercalated discs, allowing heart muscle cells to communicate.
• Function: To contract rhythmically and automatically, maintaining blood circulation.

II. Muscular System

• Sections of the Body Muscles Are Associated With:
  • Shoulder:
  • Trapezius
  • Deltoid
  • Head:
  • Temporalis
  • Masseter
  • Facial Muscles
    • Epicranius (frontal belly)
    • Orbicularis oculi
    • Zygomaticus
    • Orbicularis oris
  • Neck:
  • Platysma
  • Sternohyoid
  • Sternocleidomastoid
  • Thorax:
  • Intercostals
  • Pectoralis minor
  • Pectoralis major
  • Serratus anterior
  • Arm:
  • Triceps brachii
  • Biceps brachii
  • Brachialis
  • Forearm:
  • Pronator teres
  • Brachioradialis
  • Flexor carpi radialis
  • Palmaris longus
  • Pelvis/Thigh:
  • Iliopsoas
  • Pectineus
  • Thigh:
  • Rectus femoris
  • Vastus lateralis
  • Tensor fasciae latae
  • Sartorius
  • Adductor longus
  • Gracilis
  • Vastus medialis
  • Leg:
  • Gastrocnemius
  • Soleus
  • Fibularis longus
  • Extensor digitorum longus
  • Tibialis anterior

III. Important Reminders

• Upcoming Exam: Lecture Exam scheduled for November 13, 2025.
  • Class will not meet on Tuesday before the exam.
  • Study old exams, as 20% of questions on Exam 2 are from Exam 1.
  • Muscle Part II homework due on November 7, 2025.
  • Neurons will be covered after Lecture Exam 2.

IV. Muscle Types

• Three Types of Muscles:
  • Skeletal Muscle:
  • Striated, voluntary control, attached to bones.
  • Smooth Muscle:
  • Non-striated, involuntary control, found in hollow organs.
  • Cardiac Muscle:
  • Striated, involuntary control, found in the heart.

V. Cardiac Muscle Contraction

• Four Main Steps of Cardiac Muscle Contraction:
  1. Electrical stimulation leading to depolarization.
  2. Calcium ions are released, initiating interaction with contractile proteins.
  3. Myosin heads bind to actin forming cross-bridges.
  4. Myosin power stroke occurs, causing muscle contraction.

VI. Comparative Muscle Questions (Clicker Questions)

• Comparison of Cardiac vs. Skeletal Muscle:

  • Calcium Release:
  • A. Calcium is released from the sarcoplasmic reticulum in cardiac but not skeletal (False).
  • B. Sodium enters from outside of the cell in cardiac but not skeletal (True).
  • C. Troponin blocks myosin from binding to actin in cardiac but not skeletal (False).
  • D. A loss of a phosphate group causes the “power stroke” in cardiac but not skeletal (False).

• Comparison of Cardiac vs. Smooth Muscle:

  • Calcium Release:
  • A. Calcium is released from the sarcoplasmic reticulum in cardiac but not smooth (False).
  • B. Gap junctions are found in cardiac but not smooth (False).
  • C. Troponin blocks myosin from binding to actin in cardiac but not smooth (True).
  • D. An enzyme hydrolyzes ATP in cardiac but not smooth (True).

VII. Common Muscle Movements

• Types of Movements:
  • Flexion
  • Extension
  • Hyperextension
  • Abduction
  • Adduction

VIII. Muscles and the Buddy System

• Concept of Muscle Interaction:
  • Muscles can only move structures through contraction.
  • Utilization of antagonistic pairs involves a muscle contracting while its counterpart relaxes.
• Example:
  • Biceps (agonist) contract while Triceps (antagonist) relax, and vice versa during arm flexion.

IX. Muscle Anatomy: Origin and Insertion

• Definitions:
  • Origin: The stationary attachment point of the muscle.
  • Insertion: The attachment point that moves upon muscle contraction.

X. Fascicle Arrangements

• Fascicles: Defined as a bundle of muscle fibers.
• Common Patterns of Fascicle Arrangement:
  • Circular: Example - Orbicularis oris.
  • Convergent: Example - Pectoralis major.
  • Fusiform: Example - Biceps brachii.
  • Parallel: Example - Sartorius.
  • Pennate Types:
  • Unipennate: Example - Extensor digitorum longus.
  • Bipennate: Example - Rectus femoris.
  • Multipennate: Example - Deltoid.

XI. Muscle Functionality

• Muscle Shortening & Power Determination:
  • Muscle Shortening: Determined by the length of fibers and their arrangement (parallel vs. perpendicular).
  • Muscle Power: Derived from the number of fibers present in a muscle.

XII. Review Questions

• For Skeletal, Smooth, and Cardiac Muscles:
  1. Classify whether each has striations, branched fibers, voluntary/involuntary contractions, and presence of gap junctions.
  2. Identify a location for each muscle type.
• Gap Junctions:
  • Definition and function in synchronized contractions in smooth and cardiac muscles.
• Cardiac Muscle Contraction Steps:
  • Details of the procedural steps involved.
• Comparison of Muscle Contractions:
  • Overview of similarities and differences across muscle types.

XIII. Important Muscle Definitions

• Agonist: The muscle that contracts to produce a movement.
• Antagonist: The muscle that opposes the movement of the agonist.
• Fascicles: Bundles of muscle fibers that make up a muscle.

XIV. Movement Descriptions

• List and Define Movements:
  • Rotation, flexion, extension, hyperextension, abduction, adduction, gliding, dorsiflexion, plantar flexion, pronation, supination, eversion, and inversion.
• Identify Movements: Given an example, be able to categorize each.

XV. Fascicle Arrangements Insights

• Different fascicle arrangements can result in different functional capabilities of the muscles.
• Key Distinctions:
  • Unipennate, bipennate, and multipennate are classified based on the distribution of fibers relative to the tendon.

XVI. Muscle Fiber Relationships

• Relationship between muscle fibers, muscle power, and muscle shortening. Factors affecting these dynamics include the length of fibers and their alignment.
• Conclusion: Understanding these aspects is vital for comprehending muscle functionality and effects on movement.