The Reticular Formation
The reticular formation is a widespread network of tracts and nuclei spread across the brainstem. Single cells can have connections in the spinal cord, thalamus, and hypothalamus at the same time. Some can even synapse directly in the cortex, bypassing the usualy thalamic relay station. This arrangement allows for much convergence of sensory information and divergence of systemic effects.
- regulates consciousness, arousal, sensation
- located centrally in the brainstem; projects to spinal cord and thalamus
- well-organized collection of white and gray matter (like a net), with multiple nuclei
- contains ensembles of local-circuit interneurons
- contains noradrenergic, serotonergic, cholinergic, and histaminergic pathways
- can almost act as a CNS almost unto itself, generating motor patterns and coordinating reflexes
- appear evolutionarily old
Components
medullary and pontine reticular nuclei
The reticulospinal tracts carry information from reticular nuclei to lower motor neurons.
- project to spinal cord and brainstem
- both excitatory and inhibitory
- inhibit flexor muscles during reflexes
- appear involved in coordination and control of locomotion
- visceromotor control- heart rate, blood pressure, respiratory rate
raphe nuclei
- means "ridge" - flattened nuclei extend through brainstem parallel to midline
- use serotonin
- midbrain periaqueductal gray, though the nucleus raphe magnus, signals to dorsal horn of spinal cord, producing the spinal gate
- project to virtually all structures of the CNS, including basal ganglia and spinal cord
- mediates sleep-wake cycles and apparently mood and emotional behaviour
midbrain reticular formation
- involved in arousal and sleep-wake cycles
- spinal cord input about sensory info/activity projects to the thalamus, which has widespread effects on the cortex
locus ceruleus
- invloved in regulation of attention, arousal, sleep-wake cycles, learning, memory, anxiety, pain, mood, and brain metabolism
- small nucleus (~12,000 cells) of deeply pigmented cells located near the floor of the fourth ventricle in the pons and medulla
- uses norepinephrine as an neurotransmitter; likely the primary site of its use in the CNS
- tremendously widespread connections - cortex,
thalamus, hypothalamus, olfactory bulb, cerebellum, midbrian, spinal cord
- each neuron can have 250,000 synapses, and one cell can send axon branches across the whole brain