Brain Stem Anatomy

Brain Stem

• Consists of three areas: medulla oblongata, pons, and midbrain
• Medulla oblongata: continuous with the superior part of the spinal cord, contains sensory and motor tracts, and regulates vital activities
• Medulla oblongata features:
  • Pyramids containing motor tracts with decussation (crossing of neurons)
  • Nuclei that regulate vital activities, such as cardiovascular and respiratory centers
  • Controls swallowing, coughing, vomiting, sneezing, and hiccupping

Pons (Bridge)

• Lies directly superior to the medulla oblongata
• Contains a respiratory center to help control breathing
• Associated with several cranial nerves

Midbrain

• Extends from the pons to the diencephalon
• Divided into two parts: cerebral peduncles (motor tracts) and the tectum (corpora quadragemina)
• Features:
  • Superior colliculi for vision
  • Inferior colliculi for audition
  • Reticular formation: a netlike arrangement with gray and white matter, involved in maintaining consciousness and detecting light, touch, pain, but not temperature and smell

Cerebellum

• Consists of two hemispheres united by the vermis
• Features:
  • White matter called arbor vitae
  • Gray matter called folia
  • Coordinates skeletal muscle contractions

Diencephalon

• Composed of the thalamus, hypothalamus, and epithalamus
• Hypothalamus:
  • Controls the endocrine system
  • Regulates body temperature, thirst, hunger, and autonomic tone
  • Maintains balance
• Epithalamus:
  • Mostly consists of the pineal gland, which produces melatonin

Cerebrum

• The largest part of the brain, considered the "seat of intelligence"
• Divided into an outer cerebral cortex and internal white and gray matter
• Features:
  • Cerebral cortex: made of gray matter with grooves (sulci) and ridges (gyri)
  • Central sulcus dividing the frontal and parietal lobes
  • Longitudinal fissure separating the right and left hemispheres
  • Transverse fissure separating the cerebrum and cerebellum
  • Divided into lobes: frontal, parietal, occipital, and temporal
• White matter consists of myelinated axons in three tracts: association, commissural, and projection tracts
• Basal nuclei: collections of gray matter deep within the white matter, involved in involuntary skeletal muscle movement
• Limbic system: a collection of structures involved in emotion and memory