Cultural Globalization and Societal Change

Human Neuroanatomy

• The central nervous system (CNS) is represented by the neuraxis.
• The CNS is composed of the encephalon and spinal cord.
• In cross-section, the neuraxis consists of grey matter and white matter.
• Grey matter contains neuronal cell bodies, dendrites, and unmyelinated axons.
• White matter contains myelinated nerve fibers.

Spinal Cord

• The spinal cord has a segmental organization resembling its embryonic and phylogenetic origin.
• The spinal cord extends from the brain to the level of vertebrae L1-L2.
• The spinal cord has cervical and lumbosacral enlargements.
• The spinal cord ends in a structure called the conus medullaris.
• The filum terminale is a fibrous extension of the spinal cord.
• The spinal cord does not occupy the full length of the vertebral column, the nerves that extend beyond the cord are called the cauda equina.

Spinal Cord Morphology and General Features

• The spinal cord is characterized by two fusiform enlargements:
  • Cervical enlargement (C3-T2)
  • Lumbosacral enlargement (T9-L1)
• The spinal cord has a tapering end called the conus medullaris
• The filum terminale is a fibrous strand that extends from the conus medullaris
• The spinal cord has curvatures mirroring the vertebral column
• The spinal cord is made up of 31 pairs of spinal nerves which are subdivided into cervical, thoracic, lumbar, sacral and coccygeal nerves
• The spinal nerves are also divided into neuromeres and myomeres

Dermatomes

• A dermatome is the cutaneous territory innervated by the fibers from a single sensory root.
• The specific regions of the body innervated by each spinal nerve root.

Myomeres

• A myomere is the muscular territory innervated by the fibers from a single motor root.
• The specific muscle groups of the body innervated by each spinal nerve root.

Spinal Nerves

• 31-33 pairs of spinal nerves connect to the spinal cord.
• The spinal nerves are categorized into 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 3 coccygeal nerves.

Nerve Roots

• Dorsal/posterior root carries sensory information to the spinal cord
• Ventral/anterior root carries motor information from the spinal cord

Spinal Cord Meninges

• The spinal cord is enveloped by three meninges:
  • Pia mater
  • Arachnoid mater
  • Dura mater

Apparent vs. Real Origin of a Nerve

• Apparent origin is where the nerve emerges from the CNS
• Real origin is location of the nerve cell bodies

The Grey Matter

• Golgi Type I neurons have an axon leaving the grey matter, subdivided into motor and visceral motor neurons
• Golgi Type II neurons are interneurons and their axons remain confined to the grey matter
• The grey matter consists of columns and nuclei

The White Matter

• The white matter consists of the myelinated axon tracts carrying information to and from the CNS
• The white matter consists of funiculi, made up of bundles of fibers

Sensory Nuclei in the Posterior Horn, The Grey Matter

• The posterior horn contains somatosensitive nuclei (receiving stimuli from the skin, muscles, and joints)and viscerosensitive nuclei (receiving stimuli from the viscera).

Spinal Cord Nuclei and Columns, The Grey Matter

• The anterior horn contains motor nuclei (somatic motor and visceral motor) that generate axons that innervate skeletal and involuntary muscles
• The lateral horn also contains visceral motor nuclei (preganglionic neurons) responsible for involuntary muscle control
• The posterior horn also comprises numerous nuclei responsible for sensory functions (e.g. Posterior Nuclear columns, Marginal Zone, Clarke's Column)

Sensory Pathways

• Somatic sensory pathways carry signals for touch, pressure, temperature, pain, proprioception.
• Three main pathways involve:
  • Posterior columns
  • Spinothalamic tracts
  • Spinocerebellar tracts
• Viscerosensitive pathways relay sensory info from internal organs.

Motor Pathways

• The pyramidal system is responsible for conscious/voluntary movement
• Three descending motor tracts carry signals:
  • Corticobulbar tract
  • Lateral corticospinal tract
  • Anterior corticospinal tract
• These motor pathways and origin/termination sites are crucial for functions and pathways

Reflexes

• A reflex is an involuntary motor response to a stimulus
• Reflex arcs are the neural circuits that mediate reflex actions
• There are innated and acquired reflexes, and they can be monosynaptic or polysynaptic, according to the complexity of the circuit.