Reticular formation
The reticular formation (RF) is a phylogenetically old network of interconnected neurons. It permeates the brainstem, continues into the thalamus and hypothalamus, and connects caudally to the propriospinal spinal network.[1]
It begins as a band of grey matter in the cervical part of the spinal cord. A large portion are interneurons.
Functions:
-sensory, motor and autonomic function, complex reflexes
- control centre for respiration, cardiovascular system, vasomotor, sleep, wakefulness
- ARAS - ascending reticular activating system - maintenance of wakefulness, circadian cycle (24 hour)
- reticulospinal system - motor functions
3 main zones of nuclei: a) nuclei raphes b) medial region c) lateral region
Nuclei:
- At the midline of the pontus (nuclei raphe),
- lateral magnocellular RF (mostly efferent),
- at the border of the pontus and oblongata, gigantocellular RF + central reticular nucleus + parvocellular RF (mostly afferent) extending into the mesencephalon,
- in the oblongate nuclei paramedian (connecting the cerebellum) + lateral (connecting the cerebellum and spinal cord),
- function: gigantocellular nucleus - standing + walking, nucleus in lat. pontus - bladder control, central nuclei of the oblongata - circulation + respiration
Nuclei raphes
- along the midline of the brainstem, different species - heterogeneous, produce neurotransmitters such as serotonin, GABA, glycine, neuropeptides, substance P, cholecystokinin
Medial region of nuclei
- source of efferent pathways - effector part
Lateral region of nuclei
- afferent fibres, sensory part
- of the spinal cord, rhombencephalon, cranial nerve nuclei, mesencephalon, cortex, basal nuclei
RF neurons produce:
- serotonin - with a maximum in the ncl. raphe in the oblongata, pontus and mesencephalon,
- dopamine - in the tegmentum of the mesencephalon,
- noradrenaline - in the pontus - locus coeruleus + laterobasally in the wall of the IVth ventricle,
- adrenaline in the oblongata,
- aminergic neurons controlling sleep and wakefulness, attention and mood, with a close relationship to sensation,
- serotonin + noradrenaline in depression, dopamine in schizophrenia[1].
Ascending reticular formation ARAS[edit | edit source]
- receives all stimuli from all afferent sensory + sensory pathways (exteroreceptors, proprioceptors, receptors from internal organs),
- connected to the cerebral cortex,
- its constant activity ensures wakefulness (ARAS - the part of the RF that influences consciousness and wakefulness by its action on the cerebral cortex)
- when disturbed, impaired consciousness (up to coma)[1].
Descending RF[edit | edit source]
- Facilitatory RF - has constant activity, in the rostral region of the trunk,
- inhibitory RF - no spontaneous activity, controlled by cortex + basal ganglia,
Both of these parts are related to momentum, especially γ-motoneuron excitability[1].
