II Neuroanatomy and Neurophysiology

• The Brain Stem consists of the midbrain, pons, and medulla oblongata
• Rigidly programmed, automatic behaviours necessary for survival are associated with the brain stem
• The brain stem serves as a pathway between higher and lower neural centres
• The brain stem is associated with 10 pairs of cranial nerves
• Midbrain:
• Contains 2 cerebral peduncles with large pyramidal motor tracts
• The hollow cerebral aqueduct runs through the midbrain
• The periaqueductal gray matter in the midbrain is involved in pain suppression
• Corpora quadrigemina:

  • Superior colliculi are visual reflex centres
  • Inferior colliculi are part of the auditory relay and the startle reflex
• Substantia nigra is a band-like nucleus with high melanin content linked to Parkinson's disease

  • Red nucleus is rich in vascular supply and iron pigment, relaying nuclei for descending pathways influencing limb flexion
• Pons:
• Located at the level of the 4th ventricle
• Primarily consists of conduction tracts

  • Some tracts run longitudinally between higher brain centres and the spinal cord
  • Others are oriented transversely to communicate with the cerebellum
• Cranial nerves V (trigeminal), VI (abducens), and VII (facial) are associated with the pons

  • Pons nuclei are part of the reticular formation and are involved in respiration
• Medulla oblongata:
• Extends from the pons to the spinal cord
• Contains pyramids (large motor tracts) and decussation of pyramids

  • Inferior olivary nuclei relay sensory information regarding muscles and joints to the cerebellum
• Crucial role as an autonomic reflex centre for homeostasis

  • Includes cardiovascular centres, respiratory centres, and other centres for functions like vomiting, hiccupping, swallowing, coughing, and sneezing
• Cerebellum:
• Processes inputs from the cerebral motor cortex, brainstem nuclei, and sensory receptors
• Influences the timing and patterns of skeletal muscle contraction for smooth, daily movements
• Bilaterally symmetrical, connected by vermis, and divided into 3 lobes: anterior, posterior, and flocculonodular
• Anterior and posterior lobes have overlapping sensory and motor maps of the body

  • Multiple maps allow coordination of multiple muscle groups and proprioceptive information
• Cerebellar peduncles connect the cerebellum to the brain stem

  • Superior peduncles connect the cerebellum and midbrain
  • Middle peduncles connect the pons and cerebellum
  • Inferior peduncles connect the cerebellum and medulla
• Cerebellum processes to fine-tune motor activity by receiving proprioceptive information and visual and equilibrium pathways

  • It dispatches blueprints for coordination to the cerebral motor cortex and brain stem nuclei
• Functional Brain Systems:
• Limbic system is the emotional-visceral brain encircling the upper part of the brain stem

  • Components include the amygdala, hippocampus, and anterior cingulate gyrus
• Reticular formation is the central core of the medulla oblongata, pons, and midbrain

  • Neurons project to the hypothalamus
• Reticular formation is the central core of the medulla oblongata, pons, and midbrain
• Neurons from the reticular formation project to the hypothalamus, thalamus, cortex, cerebellum, and spinal cord
• The reticular activating system (RAS) maintains brain arousal by regulating the amount of sensory stimuli that enter the brain
• The spinal cord extends from the foramen magnum to the 1st/2nd lumbar vertebra
• The spinal cord is a 2-way conduction system, a major reflex center, and initiates complex patterns of motor activity
• There are 31 pairs of spinal nerves
• The spinal cord is held in place by denticulate ligaments and the filum terminale
• Gray matter in the spinal cord is organized into paired anterior (ventral) and posterior (dorsal) horns connected by the gray commissure
• Anterior horns contain nerve cell bodies of somatic motor neurons, while lateral horns contain autonomic motor neurons
• Dorsal root ganglia house cell bodies of sensory neurons and afferent fibers from peripheral sensory receptors form dorsal roots
• White matter in the spinal cord consists of myelinated and unmyelinated fibers that communicate between different parts of the cord and the brain
• The blood-brain barrier is composed of three layers: capillary wall epithelium, basal lamina, and astrocytes with pericytes