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Chapter 10: Muscles of the Human Body

1. Introduction to Muscle Anatomy

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2. Muscle Structure and Types

2.1 Muscle Types
  • Skeletal Muscle
    • Composed of muscle fibers and connective tissues including:
    • Tendon
    • Fascia
    • Aponeurosis
  • Fascia is a sheet of connective tissue separating muscles and enclosing other structures.
  • Muscle organization:
    • Muscle fibers grouped into fascicles.
    • Fascicles grouped into whole muscles.
2.2 Muscle Layers
  • Epimysium: Outer layer surrounding the entire muscle.
  • Perimysium: Surrounds each fascicle.
  • Endomysium: Surrounds each muscle fiber.
  • Cross-section views include:
    • Muscle fiber (c.s. – cross-section)
    • Fascicle (c.s.)
    • Muscle fiber (l.s. – longitudinal section)
    • Fascicle (l.s.)

3. Muscle Architecture

3.1 Types of Muscle Arrangement
  • Fusiform: Spindle-shaped muscles.
  • Parallel: Long fibers running parallel to each other.
  • Triangular: Broad origin converging towards a narrow insertion.
  • Unipennate: Fibers on one side of the tendon.
  • Bipennate: Fibers on both sides of the tendon.
  • Multipennate: Multiple tendons with fibers branching out from that.
  • Circular: Muscles that form circular rings.
3.2 Examples of Muscles by Type
  • Fusiform: Biceps brachii.
  • Parallel: Rectus abdominis.
  • Triangular: Pectoralis major.
  • Unipennate: Palmar interosseous.
  • Bipennate: Rectus femoris.
  • Multipennate: Deltoid.
  • Circular: Orbicularis oculi.

4. Compartmental Organization of Muscles

4.1 Compartment Definitions
  • Anterior Compartment: Muscles located in the front part of a limb, primarily responsible for extension.
  • Lateral Compartment: Muscles on the side, often involved in adduction or abduction.
  • Posterior Compartment: Muscles at the back, responsible for flexion and rotation.
  • Deep Layer: Additional muscle layers beneath superficial muscles.
4.2 Major Muscle Groups: Thigh and Leg
  • Anterior compartment: Extensors (e.g., quadriceps).
  • Lateral compartment: Evertors and abductors (e.g., fibularis longus).
  • Posterior compartment: Flexors (e.g., gastrocnemius, soleus).

5. Muscles of the Upper Body

5.1 Face and Neck Muscles
  • Occipitofrontalis
    • Frontal Belly: Elevates eyebrows.
    • Occipital Belly: Retracts scalp.
  • Orbicularis oculi: Closes eyelids.
  • Zygomaticus Major: Elevates the corner of the mouth.
5.2 Muscles of Expression
  • Muscles are categorized by regions of the face (e.g., orbital, nasal, oral).
  • Innervations for facial muscles are primarily through the facial nerve.
5.3 Muscles of Mastication
  • Masseter: Elevates the mandible.
  • Temporalis: Elevates and retracts mandible.
  • Lateral Pterygoid: Protracts and laterally moves mandible.

6. Muscles of the Trunk

6.1 Abdominal Muscles
  • Rectus Abdominis: Flexes the vertebral column.
  • External Oblique: Provides support and abdominal compression.
  • Internal Oblique: Same action as external but on the opposite side when acting unilaterally.
6.2 Muscles of Respiration
  • Diaphragm: Prime mover of inspiration. Contracts to flatten and increase thoracic volume.
  • External Intercostals: Elevates ribs during inhalation.
  • Internal Intercostals: Aids in forced expiration.

7. The Muscular System of the Lower Body

7.1 Upper Thigh Muscles
  • Quadriceps Femoris: Extends the knee (consists of four heads).
  • Hamstrings: Flex the knee and extend the hip (e.g., biceps femoris, semitendinosus).
7.2 Hip Muscles
  • Iliopsoas: Major hip flexor (comprised of iliacus and psoas major).
  • Gluteus Maximus: Major extensor of the thigh.
  • Adductor Muscles: Bring thighs together (e.g., adductor longus).

8. Muscular Functions

8.1 General Actions of Muscles
  • Flexion/Extension: Decrease/increase angle at a joint.
  • Abduction/Adduction: Movement away from/toward the midline.
  • Medial/Lateral Rotation: Rotate toward/away from the midline.
8.2 Mechanisms of Muscle Action
  • Contraction leads to force generation and movement.
  • Muscles often work in pairs (e.g., flexor and extensor).
8.3 Innervation Patterns
  • Most muscles are innervated by spinal nerves. Specific nerve pathways control distinct muscle actions.

9. Summary

  • Understanding muscle arrangements, types, and functions enriches knowledge in fields like anatomy, physiology, and clinical practices.
  • Key muscle groups, actions, and innervations are critical for application in health sciences and physical therapies.