Human Anatomy: Spinal Cord

The Spinal Cord

• The spinal cord is divided into 31 pairs of nerves, which are segmented into cervical, thoracic, lumbar, and sacral regions.
• The cord widens at two points: the cervical enlargement and the lumbar enlargement, where it gives rise to nerves of the upper and lower limbs.
• The lumbar enlargement and medullary cone give off a bundle of nerve roots called the cauda equina, which innervates the pelvic organs and lower limbs.

Cross-Sectional Anatomy of the Spinal Cord

• The spinal cord consists of two kinds of nervous tissue: gray matter and white matter.
• Gray matter has a dull color and contains neurons, while white matter contains an abundance of myelinated axons and appears bright and pearly white.
• In cross-section, the gray matter looks H-shaped, with two posterior (dorsal) horns and two wider anterior (ventral) horns.

The Brain

• The brain is part of the central nervous system and lies inside the cranial cavity.
• It consists of the cerebrum, cerebellum, midbrain, pons, and medulla oblongata.
• The brainstem is composed of the midbrain, pons, and medulla oblongata.

Major Parts of the Brain

• Forebrain: includes the cerebrum and diencephalon
• Midbrain: part of the brainstem
• Hindbrain: includes the medulla oblongata and cerebellum

Cerebrum

• The largest brain structure, divided into left and right hemispheres by the longitudinal cerebral fissure.
• Each hemisphere has an outer layer called the cerebral cortex, made of gray matter (nerve cell bodies).
• The layers below the cerebral cortex are white matter (nerve fibers).
• The cerebral cortex is divided into four lobes: frontal, parietal, temporal, and occipital.

Nervous System

• The nervous system is a major communicating and control system within the body.
• It works with the endocrine system to control many body functions and maintain homeostasis.
• The nervous system can be divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
• The CNS consists of the brain and spinal cord, while the PNS consists of peripheral nerves and ganglia.

Peripheral Nervous System

• The PNS can be divided into the afferent (sensory) and efferent (motor) divisions.
• The autonomic nervous system consists of the sympathetic and parasympathetic nervous systems.
• Neurons (nerve cells) cannot regenerate if damaged.

Brain and Spinal Cord

• The brain is continuous with the spinal cord through the foramen magnum.
• The spinal cord is divided into 31 pairs of nerves, which are attached to the spinal cord within the human body.

Spinal Nerves

• There are 31 pairs of spinal nerves, named and numbered according to the region and level of the vertebral column from which they emerge.
• The pairs are divided into:
  • 8 cervical nerves
  • 12 thoracic nerves
  • 5 lumbar nerves
  • 5 sacral nerves
  • 1 coccygeal nerve