Reticular formation - NEUR532 Flashcards
What is reticular formation?
Neurons and neuronal fibres make a netlike (reticular) appearance
What does the retiticular formation exclude?
- The cranial nerve nuclei
- Brain stem long tracts
- Visible grey matter masses
- the medial lemniscus and the nucleus ambiguous
What do ascending reticular formation fibres contributes to?
- Sort sensory stimulation
- Determines where to focus attention
- Circadian rhythm
- Direct and indirect connections with all levels of the CNS
What do descending pathways do?
- Movement of head & body (voluntary and involuntary)
- Facilitate and inhibit movements
- Respiration, blood pressure, heart rate
- Analgesic pathways
- ANS
Reticular formation key elements:
- Neuronal core of brainstem
- Connection point between spinal cord and diencephalon
- Complex
- Disorganised
- Primitive
Where does the reticular formation network extend from the spinal cord?
- Spinal cord to the thalamus
- Connections to the medulla oblongata, midbrain (mesencephalon), pons, diencephalon
Where are these neurons/axons/dendrites interspesed within the CNS?
- Between cranial nerve nuclei and brainstem racts
Where are the reticular formation nuclei found ?
- DEEP WITHIN THE BRAINSTEM
HOW MANY GROUPS OF NUCLEI CAN THE RETICULAR FORMATION BE DIVIDED INTO?
3
What are the 3 groups of reticular formation nuclei?
- Lateral
- Medial
- Median (raphe)
How many groups are found throughout the lateral group of reticular nuclei?
3
How many of cell groups within the lateral reticular neuclei are catecholamine based?
2 (noradrenergic cells A1 - A7)
- Exlucsed A3 in primates
- Adrenergic cels C1 & C2
- Cholingeric cells Ch5 and Ch6
Aggregations of neurons are thereby recognized and are
called nuclei. These include:
the precerebellar nuclei
2. the raphe nuclei
3. the central group of nuclei
4. the cholinergic and catecholamine cell groups,
5. the lateral parvocellular reticular area,
6. the parabrachial area, and
7. the superficial medullary neurons.
PRECEREBELLAR RETICULAR NUCLEI are made up of?
- The lateral reticular nucleus
- The paramedian reticular nucleus, and
- The pontine reticulotegmental nucleus
What’s the function of precerebellar nuclei?
Cooordination and muscle contraction
Describe 4 key elements of the raphe nuclei
- In or adjacent to the midline (raphe) of the brainstem
- Interspersed among bundles of decussating axons
- Many rache neurons synthesize and secrete serotonin
- Serotonin (5-hydroxytryptamine) is principal synapetic transmitter
Describe 4 key elements of the raphe nuclei
- In or adjacent to the midline (raphe) of the brainstem
- Interspersed among bundles of decussating axons
- Many rache neurons synthesize and secrete serotonin
- Serotonin (5-hydroxytryptamine) is principal synapetic transmitter
Describe 4 things about serotonergic raphe neurons
- Thin
- Unmyelinated
- Greatly branched
- Extensively distributed to the grey matter of the CNS
The connections of the medullary raphe nuclei with
the periaqueductal grey matter and the spinal
dorsal horn (and trigeminal sensory nuclei) are
important because….?
- The activity of this pathway can suppress the conscious awareness of pain
The more rostrally located raphe nuclei play a significant role in what?
Sleep
Central group of reticular nuclei includes what 2 nuclei?
- Paramedian pontine reticular formation (PPRF)
- Gigantocellular reticular nuclei
What is the paramedian pontine reticular formation (PPRF) involved in?
- Lateral movements of the eyes
Where does the central nuclei receive afferents from?
all the general and special sensory systems
* from the reticular formation of the midbrain
* the cholinergic reticular nuclei,
* the hypothalamus, and
* the premotor area of the cerebral cortex.
What do the log descending axons from the central groups constitute?
Reticulospinal tracts
What are reticulospinal tracts important for?
Motor pathways
Ascending axons from the central group of reticular nuclei travel in the…?
Central tegmental tract
What involvement of the ascending projections contribute?
- Maintaining consciousness
The reticulothalamic projection also provides an interaction with the corpus striatum, providing what function?
Motor and other functions
Which direction is rostral and caudal?
- Rostral towards the front of the head
- Caudal towards the occipital lobe
What neutoransmitter does cholinergic neurons use?
Acetylcholine
How many groups of cholinergic neurons are there?
2
What are the 2 cholinergic nuclei?
- Pedunculopontine nucleus (larger)
- Lateral dorsal tegmental nucleus
Where is the pedunculopontine nucleus located?
- Rostral pons and caudal misbrain
Where do cholinergic neuclei receive afferents from?
–nearby noradrenergic (locus coeruleus)
- –serotonergic (raphe) nuclei,
- –from histaminergic neurons in the hypothalamus
- –inhibitory (gamma-aminobutyrate [GABA]) descending fibres from the pallidum, and
- –from the preoptic area.
What are catecholamines of the nuclei?
- Noradrenaline
- Adrenaline
- Dopamine
What effect does noradrenline have?
- Excitatory effects on spinal reflexes and alertness
Where is the parvocellullar reticular area located?
- In the medulla and pons
The neurons in the parvocellular reticular area send their axons to the motor nuclei
of the…?
- Hypoglossal CN
- Facial CN
- Trigeminal CN
What happens if you stimulate the parvocellular reticular area?
acceleration of the heart and increased arterial
blood pressure.
Where are superficial medullary reticular neurons found?
In the ventral superficial reticular area in the medullar
What are superficial medullary reticular neurons predominantly associated with?
Cardiovascular and respiratory regulation
Where are the afferents from for the superficial medullary reticular neurons?
Spinal cord and solitary nucleus
What are the receptors the superficial medullary reticular neurons activated by?
- Baroreceptors of the carotid and aortic sinuses
- Oxygen-sensitive chemoreceptors fo the carotid and aortic bodies
Do medullary reticular neurons respond directly to changes in the pH or carbon diaxide concentration?
Yes
What are the efferent projections from the medullary reticular superficial neurons?
- Hypothalamus
- Preganglionic autonomic neurons in spinal cord & medulla
- respiratory motor neurons
what are the Miscellaneous reticular formation groups neurons?
- The area postrema
- The perihypoglossal nuclei
- The accessory oculomotor nuclei
- The interpeduncular nucleus
What chemoreceptors have been found within the area postrema?
- chemoreceptors for emetic drugs such as apomorphine
and digoxin.
What is the area postrema associated with?
The physiology of vomiting
What is the perihypoglossal nuclei associated with?
- Sending efferent fibers to CN III, CN IV and VI
- Complex circuitry of eye movements
- Keeping eyes fixated on a target
Where is the accessory oculomotor nuclei found?
The junction of the midbrain and the diencephalon
What are the 4 key nuclei that the accessory oculomotor nuclei comprise?
- the interstitial nucleus of Cajal,
- the nucleus of Dark-schewitsch,
- the nucleus of the posterior commissure, and
- the rostral interstitial nucleus of the medial
longitudinal fasciculus.
What are the accessory oculomotor nuclei associated with?
- Vertical plane eye movements
Electrical stimulation of the periaqueductal grey
matter cause?
Analgesia
What is the interpeduncular nucleus associated with?
- Pain
- ANS
- Emotions
What does the descending central group of reticular nuclei pathway inhibit?
- Action potentials that report pain
What are the 3 major reticular formation descending pathways involved in the control of movements?
- REticulospinal tracts
- Corticospinal tracts
- Vestibulospinal tracts
The raphespinal tract is a reticulospinal
pathway best known for the involvement of its
serotonergic neurons for the…?
- Modulation of pain sensation
- modulate the activities of motor neurons
Some regions of the reticular formation regulate visceral
functions and breathing through connections with…?
- Amydala
- Hypothalamus
- Spinal cord
- Phrenic nucleus
The gigantocellular nucleus(in the medulla) coordinates…what?
the responses of maximal INSPIRATION
The parvocellular reticular area(in the medulla) coordinates… what?
the responses of maximal EXPIRATION
What is the respiratory rhythm controlled by?
- Pneumotaxic centre
Stimulation in the medial part of the reticular
formation of the medulla… does what?
has a depressor effect
on the circulatory system (i.e., slowing of the
heart rate and lowering of blood pressure).
What do muscular relaxation neurons in the reticular formation use as an inhibitory transmitter?
Glycine
Is the cerebral cortex awake during sleep?
Yes
During REM sleep, there is an inhibition of transmission
from the thalamus to the cerebral cortex in all the specific
sensory pathways (e.g., somatic, auditory), hence, a
resistance to arousal occurs in REM sleep.
Varying levels of consciousness are paralleled and revealed by changes in the
electroencephalogram (EEG), which is a crude indicator of the activity of the
cerebral cortex.
Irreversible coma follows bilateral destruction of the medial parts of the brain stem
at or above the upper pontine levels.
What tract and reticular formation is essential for maintaining a conscious state?
- Rostral pontine reticular formation
- Central tegmental tract
Are cholinergic neurons of the pedunculopontine nucleus active or inactive during non-REM sleep?
Inactive
The tuberomammillary nucleus in the posterior part of the hypothalamus is
composed of… what?
histamine-secreting neurons
What 5 neurons in the brain stem and hypothalamus actively promote sleep.
These neurons include:
The serotonergic raphe neurons
2. The lateral hypothalamus
3. The suprachiasmatic nucleus of the hypothalamus
4. The cholinergic neurons of the pedunculopontine and lateral dorsal tegmental
nuclei
5. GABA-ergic neurons
What neurons are active in deep sleep?
Raphe neurons
What ype of neurons are less active in REM slee?
Serotonergic neurons
Deficiency of orexin in humans is associated with what condition?
Narcolepsy
What is the key hypothalamic nucleus that regulates the circadian rhythm?
The suprachiasmatic nucleus
What nucleus in known as an internal clock for the brain
The suprachiasmatic nucleus
Axons from the suprachiasmatic nucleus contact the
orexin neurons of the lateral hypothalamus and the
dorsomedial hypothalamic nucleus, which projects
caudally to the locus coeruleus.
What injibitory nerons are active in deep (non-REM) sleeo?
GABA-ergic neurons
What are the neurons most present in the preoptic area (immediately anterior to the hypothalamus)?
GABA-ergic neurons
What neurons contain a peptide galanin?
GABA-ergic neurons
Destructive lesions in the preoptic area cause what?
Insomnia
this region is
essential for the occurrence of sleep.
