Bio Review Notes #49
CENTRAL NERVOUS SYSTEM
Performance Objectives:
Most invertebrates have nervous systems derived from the ladder-like arrangement in flatworms. Vertebrate brains develop in three portions (forebrain, midbrain, hindbrain). In mammals, the cerebral hemispheres enlarge, and their size and complexity become a crude measure of intelligence.

 Invertebrate nervous systems:   Cnidaria have a nerve net of interconnected neurons with no center. Flatworms have two long chains of ganglia in a ladder-like arrangement; the largest ganglia, near the eyes, form the beginnings of a "brain." Most other invertebrates have modifications of this ladder-like pattern; a major nerve cord runs along the ventral midline, splits to form an esophageal ring, and reunites above the mouth to form a cerebral ganglion or brain.

Embryonic vertebrate brains form as three major divisions:
  • Forebrain (prosencephalon), primitively devoted to smell
  • Midbrain (mesencephalon), primitively concerned with vision
  • Hindbrain, dealing with sound and vibrations

Adult vertebrate brains: Organized into five regions:
  • Telencephalon: paired parts of the forebrain, including olfactory bulbs, olfactory lobes, and cerebral hemispheres, which enlarge greatly in mammals and take over many added functions.
  • Diencephalon: unpaired, second portion of the forebrain, including the pineal body (epiphysis); tela choroidea (thin roof); thalamus (controls many emotions); hypothalamus (controls appetite and body temperature); and part of the pituitary gland.
  • Mesencephalon: midbrain, including corpora quadrigemini
  • Metencephalon: includes cerebellum and pons
  • Myelencephalon: medulla, continuing into the spinal cord

Brain ventricles: cavities containing cerebrospinal fluid

Spinal cord:
      White matter: myelinated tracts
      Gray matter: unmyelinated motor and sensory columns

Spinal reflex pathway:
  • Sensory neuron runs from a receptor cell in skin to cell body in dorsal root ganglion, then into somatic sensory column of spinal cord.
  • Association neuron connects somatic sensory column to somatic motor column in spinal cord.
  • Motor neuron runs from somatic motor column out ventral root to a to a voluntary muscle or other effector cell.

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