Muscle Types and Their Functions

Muscle Types

• Circular muscles have fibers arranged in concentric rings like a circle. The orbicularis oculi (muscle around the eye) is an example.
• Fusiform muscles are spindle-shaped with a thick center and tapering ends, like the biceps brachii (upper arm muscle).
• Flat parallel muscles have fibers arranged parallel to each other and are often accompanied by a fibrous sheet called an aponeurosis. The external oblique muscles in the abdomen are an example.
• Bipennate muscles have fibers attaching obliquely to a central tendon. The rectus femoris (thigh muscle) is an example.
• Unipennate muscles have fibers attached obliquely to a tendon on one side only. The extensor digitorum longus (lower leg muscle) is an example.
• Multipennate muscles have fibers attaching to a central tendon from multiple angles. The deltoid (shoulder muscle) is an example.
• Convergent muscles are wide at one end and narrow at the other (the fibers converge at the tendon). An example is the pectoralis major (chest muscle).
• Some muscles have tendinous intersections where tendons cross over or merge within the muscle. The rectus abdominis is an example.
• Thin parallel muscles have muscle fibers arranged in a parallel pattern but are slender and flat. The sartorius (thigh muscle) is an example.
• Digastric muscles have two bellies separated by a tendon. The omohyoid is an example.

Facial Anatomy Layers

• The skin (epidermis and dermis) layer is the most superficial.
• The superficial fat (subcutaneous) layer is the second layer from the surface.
• The SMAS (superficial musculoaponeurotic system) layer is the third layer from the surface.
• The retaining ligaments and spaces are the fourth layer from the surface.
• The deep fat layer is the fifth layer from the surface and is absent on the forehead.
• The periosteum and deep fascia are the sixth layer from the surface.
• The bones are the deepest layer of facial anatomy.

Joint Types and their Characteristics

• Pivot Joints are uniaxial, allowing rotation. The atlanto-axial joint is an example.
• Ball and Socket Joints are multiaxial, allowing movement in multiple directions. The hip joint is an example.
• Plane Joints are usually uniaxial, allowing gliding or sliding movements. The acromioclavicular joint is an example.
• Hinge Joints are uniaxial, permitting flexion and extension movements only. The elbow joint is an example.
• Saddle Joints are biaxial, allowing movement in two different planes. The carpometacarpal joint is an example.
• Condyloid Joints are biaxial, permitting flexion, extension, abduction, adduction, and circumduction. The metacarpophalangeal joint is an example.

Anatomical Position

• The anatomical position is:

  • Body erect
  • Feet slightly apart
  • Palms facing forward
  • Thumbs point away from the body
  • Similar to "standing at attention"

• Other Positions:

  • Supine: Lying down in anatomical position, face up.
  • Prone: Face down.

Classification of Bones by Shape

• Flat bones are flat and thin, like the frontal bone of the skull.
• Sutural bones are small, flat bones found within the sutures (joints) of the skull.
• Short bones are small and cube-shaped, like carpal bones in the wrist.
• Irregular bones are complex-shaped, like vertebrae in the spine.
• Sesamoid bones are small, round bones located within a tendon, like the patella (kneecap).
• Long bones are long and cylindrical, like the femur (thigh bone).

Nervous System - Spinal Cord and Brain Diagram

• The brain is the top section of the nervous system, connected to the spinal cord by the brainstem.
• The spinal cord is a long thin structure running down the back.
• Cervical nerves (C1 to C8) originate from the neck area.
• Thoracic nerves (T1 to T12) originate from the upper back.
• Lumbar nerves (L1 to L5) originate from the lower back.
• Sacral nerves (S1 to S5) originate from the sacral region.
• Coccygeal nerve is the lowest nerve pair emanating from the coccyx.
• Cranial nerves (12 pairs) are directly connected to the brain.
• Spinal ganglion is a cluster of neuron cell bodies along the spinal cord containing sensory neurons.
• The cervical enlargement is a wider section of the spinal cord in the neck area.
• The lumbar enlargement is a wider section of the spinal cord in the lower back area.

Anterosuperior View of Right Leg

• Posterior Compartment:

  • Cutaneous nerve
  • Fibula
  • Deep fascia (outer, circumferential layer)
  • Plantar flexor muscles
  • Superficial vein

• Lateral Compartment:

  • Subcutaneous tissue (superficial fascia)
  • Intermuscular septa
  • Evertor muscles
  • Neurovascular sheath

• Medial Compartment:

  • Long flexor muscles of foot and ankle
  • Interosseous membrane
  • Tibia
  • Deep fascia blended with periosteum of bone
  • Investing fascia of muscle

• Anterior Compartment:

  • Dorsiflexor muscles
  • Skin

Explore the different types of muscles in the human body, including circular, fusiform, flat parallel, bipennate, unipennate, multipennate, and convergent muscles. Each type serves a unique function and has distinct structural characteristics. Test your knowledge on these classifications and their examples!