Nerve and Skeletal System Anatomy Essentials

Nerve Structure

• Nerve: Formed by neurons.
• A typical neuron has a body with a nucleus and extensions:

- Axon: The longest extension that carries the nerve impulse from the cell body to dendrites or the body of another neuron.

- Dendrite: Shorter and more numerous extensions that receive nerve impulses from other neurons and lead them to the cell body.

Each neuron can contact different cells simultaneously to send and receive information throughout the body.

Helper Cells

These cells provide protection and support:

• Schwann cells: Produce myelin, which covers axons in the central and peripheral nervous systems, providing insulation and accelerating nerve impulses.
• Astrocytes: Provide nutritional support and connect neurons to blood vessels.
• Microglia: Responsible for cleaning and defense.
• Ependymal cells: Cover the internal cavities of the brain and spinal cord and produce cerebrospinal fluid.

Skeletal System

• During embryonic development in vertebrates, the notochord develops as a precursor to the adult skeleton. In some vertebrates, it persists throughout adult life (lampreys), while in others, it is replaced by the spine.
• The skeleton is composed of jointed parts, with the front widened to form the skull.
• The skeleton consists of cartilage (in sharks and rays) or bone (in other vertebrates), which is harder and more resistant.
• The human skeleton is composed of cartilage during early embryonic development and is gradually replaced by bone. Ossification begins in the sixth week of gestation and continues until adulthood.
• The human skeleton is divided into two main sections:
• Axial Skeleton: Covers the head and trunk.

Skull and Face

- Cranium: Formed by bones that protect the brain: frontal, parietal, temporal, occipital, ethmoid, and sphenoid bones. It also includes facial bones that define face shape.

Upper Jaw: Includes the cheek, zygomatic, nasal, vomer, palatine, and maxillary bones.

Lower Jaw: Mandible.

Trunk

- Spine: Protects the spinal cord and serves as an anchor for other bones. It is formed by 33 or 34 vertebrae (7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused), and 4 or 5 coccygeal (fused)) and 12 pairs of ribs (10 attached to the sternum and 2 floating).