Detailed Anatomy of the Skeleton, Vertebrae, and Lower Limb Muscles

Human Skeletal System Structure

The skeleton is divided into two main parts: the Axial Skeleton (forming the central axis of the body, including the head and trunk) and the Appendicular Skeleton.

Bones of the Head and Skull

The bones of the head are generally flat and irregular, having no movement except for the mandible (lower jaw).

Cranium and Facial Bones

The Cranium protects brain structures. The Face (Cara) unites with the cranium and includes:

• 2 Nasal bones
• 2 Maxillae
• 2 Palatines
• 2 Zygomatics
• 2 Lacrimals
• 1 Vomer
• 1 Inferior Nasal Concha (Cornete)
• 1 Mandible (Maxilla Inferior)

Middle Ear Bones (Oído)

Located in the middle ear:

• 2 Malleus (Martillos)
• 2 Incus (Yunques)
• 2 Stapes (Estribos)

Vertebral Column (Spine)

The vertebral column is located posteriorly and is formed by 33 bones (vertebrae):

• 7 Cervical vertebrae
• 12 Thoracic (Dorsal) vertebrae
• 5 Lumbar vertebrae
• 5 Sacral vertebrae (fused)
• 4 Coccygeal vertebrae (fused)

Parts of a Vertebra

The primary parts of a vertebra are:

1. Body: Supports the weight.
2. Neural Arch (Axis): Protects the spinal cord (medulla).
3. 3 Apophyses (Processes).

Thorax Structure

The Thorax consists of 12 pairs of ribs (costillas) and 1 Sternum.

Bone Anatomy Terminology

Long bones are typically described using the following terms:

• Epiphyses: Proximal and distal ends. They are broad and provide a large surface area for articulation.
• Diaphysis: The central shaft or body of the bone.
• Metaphysis: The area situated between the diaphysis and the epiphyses.

Joints and Muscle Tissue

Joints (Articulations)

Joints are the connections between the rigid components of the skeleton, whether bone or cartilage. Examples include Synarthrosis (immovable joints).

Muscle Structure and Characteristics

Muscles are characterized principally by their capacity for contraction. Muscle fibers are organized with surrounding connective tissue layers:

• Endomysium
• Perimysium
• Epimysium

Muscles of the Lower Limb

Antagonistic leg muscles include the Biceps Femoris, Semimembranosus, and Semitendinosus (Hamstrings).

Quadriceps Femoris

The Quadriceps is made up of four portions, each originating in a different place:

• Vastus Intermedius: Anterior and exterior of the diaphysis.
• Vastus Lateralis (External): Outer zone of the femur.
• Vastus Medialis (Internal): Inner femur.
• Rectus Femoris: Anterior superior iliac spine (ASIS).

Sartorius Muscle

The Sartorius is the longest muscle in the body, originating at the iliac spine.

• Insertion (I): Anteromedial side of the tibia.
• Innervation (IN): Femoral nerve.
• Action (A): Flexion of the leg on the thigh and internal rotation.

Biceps Femoris (Hamstring)

• Origin (O): Ischium and another portion on the outer side of the femur.
• Insertion (I): Inserts into the fibula (perone) via a common tendon.
• Innervation (IN): Internal Popliteal Nerve.
• Action (A): External rotation of the leg.

Semimembranosus (Hamstring)

• Origin (O): Ischium.
• Insertion (I): Three tendons inserting into the tibia.
• Innervation (IN): Sciatic Nerve (ICC).
• Action (A): Bending (flexion) of the leg and internal rotation.

Semitendinosus (Hamstring)

• Origin (O): Ischium.
• Insertion (I): Inner side of the tibia.
• Innervation (IN): Sciatic Nerve.
• Action (A): Flexion of the leg.

Lower Leg and Foot Muscles

• Soleus and Tibialis Anterior:
  • Origin (O): Tibia and Fibula.
  • Insertion (I): Achilles tendon (for Soleus).
  • Innervation (IN): Sciatic Nerve (ICC) and Posterior Tibial Nerve.
  • Action (A): Plantar flexion of the foot, adduction, and internal rotation.
• Gastrocnemius (Twin):
  • Origin (O): Femoral Condyles.
  • Insertion (I): Achilles tendon.
  • Innervation (IN): Sciatic Nerve (ICC).
  • Action (A): Foot flexion (plantar flexion) and rotation.

Thoracic and Abdominal Musculature

Muscles of the Chest

The chest muscles include three types of Intercostal muscles: External Intercostal, Internal Intercostal, and Innermost Intercostal.

Abdominal Muscles

The abdominal muscles are used for abdominal breathing and core stability. The text describes two specific muscles:

Rectus Abdominis

• Origin (O): Pubic Symphysis.
• Insertion (I): External face of the costal cartilage (ribs).
• Innervation (IN): Intercostal nerves.
• Action (A): Flexion of the vertebral column and aids in defecation.

Pyramidalis Muscle

• Origin (O): Pubis (lateral or cranial side).
• Insertion (I): Average area of the abdomen (Linea Alba).
• Action (A): Tenses the Linea Alba and reinforces the lower abdominal wall.