Notes

Mesencephalon: Overview A structure that can be found above the brain stem. Colliculus Superior and Colliculus Inferior are a pair of nuclei that together form the reflexes associated with vision.

Mesencephalon: Functional Units

1. Tectum (roof)
   • Superior Colliculus: visual and oculomotor reflexes.
   • Inferior Colliculus: relay auditory tract.
2. Tegmentum (floor)
3. Reticular formation: automatic processing of incoming sensation and outgoing motor commands, helps to maintain consciousness, can initiate motor response to stimuli (see also medulla oblongata! Reflex center, some sensory information is directly processed in this area and sends motor commands even before consciousness).
4. Red Nucleus: involuntary control of background muscle tone and limb posture.
5. Substantia Nigra: regulates activity in the basal nuclei, degeneration of dopaminergic cells causes Parkinson's disease.
6. Cerebral Peduncles: connect primary motor cortex with motor neurons in brain and spinal cord, carry ascending sensory information to thalamus.
7. Ventral Tegmental Area (VTA): part of the limbic system, projects e.g. to Nucleus Accumbens and Amygdala, emotional reinforcement and reward function.

Pons: Overview

It is a collection of nuclei and fibers that form a bridge for information coming from one part of the brain and is relayed on the other side.

• Pontine Nuclei receive fibers from all cortical areas and relay to the contralateral cerebellum.
• Locus Coeruleus ("blue spot") contains noradrenergic cells innervating large portions of the brain, mediating physiological response to panic and stress. (secretion of neuroadrenaline).

Medulla Oblongata: Overview

It is part of the brain stem, containing fiber tracks (group of axons).

• Pyramid: contains descending cortico-spinal fibers.
• Olive: relay nucleus for afferent connection from motor cortex and red nucleus, efferent to contralateral cerebellum.
• Reticular Formation: (entire brain stem!) containing the raphe nuclei and magno/parvocellular nuclei, which regulate respiration, circulation, vomiting, swallowing, and pain control. (Without necessarily reaching the conscious level).
• Reflex Centers: for heart and circulation (vasomotor/cardiac) and respiratory rhythmicity. (Without necessarily reaching the conscious level).

Cerebellum: Overview It is important for voluntary movement, posture, equilibrium and motor control.

Spinal Cord: Segmental organization

From each segment 2 spinal nerves are originated. The Radix Posterior (afferent) dorsal root brings input from the periphery to the spinal cord. The Radix Anterior (efferent) ventral root brings motor information from the spinal cord to the periphery.

Spinal Cord: Grey Matter

The grey matter of the spinal cord consists of cell bodies of interneurons, motor neurons and synaptic connections. Fibers of the motor neurons in the ventral horn leave the spinal cord efferent/motor commands to muscles. Afferent/sensory axons enter through the dorsal horn and either synapse on sensory interneurons in the dorsal horn, or join the ascending tracts in the white matter.

Spinal Cord: White Matter

The white matter of the spinal cord mostly consists of myelinated axons of motor and sensory neurons organized in columns (containing several fiber tracts) carrying information to (afferent/ascending) and from (efferent/descending) the brain.