Reticular Formation Flashcards
What is known as a network of reticulum of many neurons that comprises the core of the neuroaxis?
Reticular Formation
What is composed of many well defined groups of neurons that receive collaterals from all ascending and descending systems and distribute their axons widely in caudal and rostral directions?
Reticular Formation
Are all levels of the CNS interconnected by way of the reticular formation?
YES
Role of the nuclei in the reticular formation?
regulating muscle tone for postural control during voluntary and reflexive movement; modulating the sense of pain, regulating arousal, sleep, and attention; and coordinating autonomic respiratory and cardiac function
What is the largest division of the RF?
Central Division (Lateral and Medial zone)
What nuclei of the RF involves a thin column of neurons along the midline of the brainstem?
Raphe Nuclei (Midline Zone)
What 4 nuclei are considered miscellaneous nuclei of the RF?
- paramedian ponitine RF
- pedunculopontine nucleus
- locus ceruleus
- ventral tegmental area
The central division is a continuous but diffuse column of neurons that begins as a continuation of what? and ends where?
begins as a continuation of the central gray interneuron network of the spinal cord (Lamina X) and ends in the midbrain
The central division consists of what 2 zones?
- Medial zone (efferent) - larger
- Lateral zone (afferent) - smaller
Lateral zone consists of neurons with large dendrites that receive collateral input from all sensory and motor information carried by what?
- cranial nerves
- spinal sensory pathways
- corticospinal, corticobulbar, and corticopontine pathways
The lateral zone relays this integrated information (sensory and motor) to what?
the medial zone
What other areas, besides the medial zone, does the lateral zone project to?
- cerebrum
- cerebellum
- thalamus (central median nucleus)
- spinal cord
The medial zone gives rise to what?
the major efferent pathways from the RF
Nuclei of the medial zone receive input from what three areas?
- lateral zone
- a variety of peripheral receptors, including the carotid body relayed through the solitary nucleus
- hypothalamus
- prefrontal cortex
Role of the nuclei of the medial zone?
to regulate vital cardiac and respiratory function through output to preganglionic sympathetic neurons in the lateral horn of the thoracic spinal cord and preganglionic parasympathetic neurons associated with the vagus nerve (cardiac), and to spinal cord for somatic control of motor neurons in the spinal cord that regulate inhalation and expiration
Lesions to the brainstem that involve the regulatory centers of the medial zone nuclei result in what?
abnormal respiratory patterns or difficulty regulating blood pressure with hypertension
Additional reticular nuclei regulate what?
swallowing and vomiting
Nuclei in the pons and medulla receive input from where? via what?
the cortex (corticobulbar pathway), cerebellum, vestibular nuclei, and somatosensory area, via the lateral zone
Role of the nuclei in the pons and medulla?
to influence LMNs for the purpose of regulating postural, reflexive, and voluntary muscle control
Fibers of the nuclei of the pons and medulla descend in two separate pathways. Both pathways descend ipsilaterally or contralaterally? This makes the influence bilaterally or unilaterally?
ipsilaterally; bilaterally
What are the two descending pathways from the nuclei of the pons and medulla?
- medial (pontine) reticulospinal tract
- lateral (medulla) reticulospinal tract
Which pathways is part of the medial activation system?
medial (pontine) reticulospinal tract
Pathway of the medial (pontine) reticulospinal tract? (where does it originate, descend, terminate)
cell bodies originate in the pontine RF, descend in ventral funinculus as part of the MLF to end in the medial parts of the ventral horn, primarily at the cervical level
Function of the medial (pontine) reticulospinal tract?
to facilitate axial and proximal limb muscles; tonically excites extensors and inhibits flexors
Medial (pontine) reticulospinal tract arises from neurons located where?
LATERALLY in pons and medulla
Which pathway is spontaneous and which is under more cortical control?
- medial (pontine) is more spontaneous
- lateral (medulla) is under more cortical control
The axons of the medial (pontine) RS tract run ipsilaterally or contralaterally in the ventral funiculus?
ipsilaterally
Lateral (medulla ) RS tract arises from neurons located where?
MEDIALLY in the medulla
Function of the lateral (medulla) RS tract?
inhibition of neurons to extensor muscles and excitation of of neurons to flexor muscles
Lateral (medulla) RS tract descends bilaterally in what?
the lateral funiculus (part of lateral motor system)
Which pathway can be viewed as the antagonistic system of the lateral vestibulospinal pathway and is under a great deal of cortical control?
lateral reticulospinal pathway
Which pathway is tonically active and works alongside the vestibulospinal pathways in that it facilitates extensors, primarily at the proxial joints of upper and lower extremities?
medial reticulospinal pathway
Which pathway is involved in generalized inhibition of all muscles?
lateral (medulla) reticulospinal pathway
Activation of which pathways results in inhibition of extensors and tonic facilitation of flexors?
lateral (medulla) reticulospinal pathway
Where is the raphe nuclei located?
located in the brainstem along the midline just anterior to the periaqueductal gray (central gray)
Many neurons of the Raphe nuclei use what as a neurotransmitter?
serotonin (5-HT)
The raphe nuclei receives input from where?
from a wide variety of brainstem, cortical, cerebellar, and spinal area
Output of the Raphe nuclei consists of ascending pathways, descending pathways, or both?
BOTH
Ascending pathways of the Raphe nuclei are involved in what?
Serotonergic neurons of the raphe play a major role in the reticular activating system that regulates arousal, sleep, and mood
Projection of the ascending pathways of the raphe nuclei is throughout what?
the cerebrum and cerebellum
Descending pathways of the raphe nuclei are involved in what?
Serotonergic neurons modulate pain input at the level of the “gate” in dorsal horn of the spinal gray
Modulation of visceral (CN X) and facial (CN V) pain also occurs at what two nuclei?
solitary nucleus and spinal trigeminal nucleus
What is important in activating the system of descending pathways of the raphe nuclei?
input from the periaqueductal gray area that are receiving input from spinoreticular pathways (part of the anterolateral system)
What pathway is a nonspecific tract that provides diffuse activation of motor neurons in the anterior horn and may be involved in influencing motor output during levels of high motivation and arousal?
Raphespinal pathway
Raphespinal neurons in the lateral horn influence what body system?
cardiovascular system
What miscellaneous RF nuclei is associated with cranial nerves of the extraocular eye muscles?
Paramedian pontine RF (PPRF)
Where is the PPRF located?
located at the level of the facial colliculus
What nucleus does the PPRF surround?
abducens nucleus
Where is the pedunculopontine nucleus located?
in the caudal midbrain
Where does the pedunculopontine nucleus project?
projects to parts of the basal ganglia, vestibular nuclei and reticular spinal nuclei
What is the neurotransmitter of the pedunculopontine nucleus?
acetylcholine
What is the role of the pedunculopontine nucleus?
It is thought to have a role as a brainstem central pattern generator to induce walking without cerebral control. It sends rhythmic impulses to caudate and putamen of the basal ganglia
Where is the locus ceruleus located?
located in the rostral pontine central gray region
What is the neurotransmitter of the locus ceruleus?
norepinephrine
Locus ceruleus receives only what kind of information from where?
restricted input from two brainstem nuclei
Locus ceruleus sends what kind of connections?
widespread ascending and descending connections
What ascending pathways to what structures are involved in the ability to maintain and direct attention?
ascending pathways to the thalamus, hypothalamus, basal forebrain, and neocortex
The descending cerulospinal tract provides nonspecific activation of what? and modulation of what information to where?
of the motor neuron pool in the anterior horn, and modulation of pain information in the dorsal horn
What are the two dopamine projecting systems in the brainstem?
- Ventral tegmental area
- substantia nigra
VTA fibers project to where?
to limbic and frontal cortical areas
VTA fibers play a role in what?
cognition (decision making) and motivation
VTA fibers projecting to the frontal lobe are balanced with what pathways?
the serotonergic pathways
Disturbances in dopamine and serotonergic systems play a role in what?
depression and other disorders of cognition and affect
Cell bodies of lateral corticospinal pathway originate where?
areas 8, 6, 4, 3, 2, 1, 5
Lateral corticospinal pathway fibers terminate where?
terminate in the lateral part of the contralateral ventral horn
Lateral corticospinal pathway fibers projecting from area 3,1, 2, 5 terminate where?
dorsal horn
Function of lateral corticospinal pathway?
voluntary motor activity of proximal and distal limb musculature, fractionated fine motor activity
Lateral corticospinal tract fibers terminating in the dorsal horn are involved in what?
feedback and modulation of incoming sensory signals specific to ongoing motor activity
Cell bodies of the anterior (medial ) corticospinal pathway originate where?
area 4 (primary motor cortex), 6 (premotor and supplementary motor cortical regions)
Anterior (medial) corticospinal tract fibers terminate where?
terminate in medial part of contralateral ventral horn
Function of anterior (medial) corticospinal tract?
voluntary activity of axial musculature
Cell bodies of the Rubrospinal pathway originate where?
Red nucleus
Rubrospinal pathway fibers terminate where?
terminate in lateral part of contralateral ventral horn (primarily cervical region)
Function of rubrospinal pathway?
voluntary (fractionated) activity of distal UE musculature, primarily flexors of the digits
Cell bodies of tectospinal pathway originate where?
superior colliculus
Tectospinal tract fibers terminate where?
terminate in the medial part of the contralateral ventral horn (primarily cervical region)
Function of Tectospinal pathway?
coordination of neck movements with eye movements, reflexive turning toward stimulus
Cell bodies of Lateral Vestibulospinal Pathway originate where?
Lateral Vestibular nucleus
Lateral Vestibulospinal tract fibers terminate where?
terminate in ipsilateral ventral horn of all levels, but heavier in lower thoracic through sacral levels
Function of Lateral Vestibulospinal pathway?
facilitory to extensor lower motor neurons as response to head movement
Cell bodies of Medial Vestibulospinal pathway originate where?
in medial and inferior vestibular nuclei
Medial Vestibulospinal tract fibers terminate where?
terminate bilaterally in ventral horn of cervical and upper thoracic cord
Function of Medial Vestibulospinal pathway?
facilitory to ipsilateral lower motor neurons of neck, inhibitory to contralateral lower motor neurons of neck, facilitory to extensors of upper etremities
Cell bodies of Lateral (medullary) reticulospinal pathway originate where?
medullary reticular formation
Lateral (medullary) reticulospinal tract fibers terminate where?
terminate in lateral part of ventral horn on interneurons effecting bilateral segmental LMNs
Function of Lateral (medullary) reticulospinal pathway?
facilitate flexor LMNs and thus decrease the activity of extensor LMNs
Cell bodies of Medial (pontine) reticulospinal pathway originate where?
pontine reticular formation
Medial (pontine) reticulospinal tract fibers terminate where?
terminate in medial part of ventral horn on interneurons effecting bilateral segmental LMNs, primarily in the cervical region
Function of medial (pontine) reticulospinal pathway?
facilitate extensors of the UE bilaterally
The brainstem pathways function to help in maintaining what?
static and reactive posture through vestibular input, through ascending sensory information that is entering the reticular formation, or through cerebellar influences via the red nucleus, vestibular nuclei, and reticular formation
Voluntary motor activity is dependent on what?
the cortex
What is the main pathway necessary to generate volitional movement?
lateral corticospinal pathway
What pathway runs parallel to the lateral corticospinal pathway?
corticoreticulospinal pathway
Area 6 (premotor and supplementary motor cortical regions) serves what three functions?
- direct corticospinal fibers
- direct input to area 4
- indirect corticoreticulospinal fibers
Anticipatory postural responses (preparatory postural responses prior to voluntary limb movements) are prepared through what projections from where?
corticospinal projections from the supplementary motor cortex
Influence from areas 4 and 6 onto the reticulospinal pathways is important for what?
regulating the excitability of these pathways
What results when brainstem pathways are disconnected form the cortex by a midbrain lesion caudal to the red nucleus?
decerebrate posture
Role of Lateral vestibulospinal tract during decerebrate posture?
maintains tonic activity over extensors of the upper and lower extremities
Role of Reticulospinal tract during decerebrate posture?
devoid of influence from cortex due to lesion (thahis allows the vestibulospinal pathways to maintain their activity without antagonistic activity of the reticulospinal paths)
During decerebrate posture, what happens to the flexor influence from rubrospinal tract?
it gets lost also
What does decerebrate posture look like?
extension of both the upper and lower extremities
What is the result of a lesion above the level of the red nucleus?
decorticate posture (rubrospinal influence on UE flexors causes flexor posture in UE, while extensor tone is still dominant in LE)
What does decorticate posture look like?
flexion at the elbow in UE with extension of the LE
Upper motor neuron pathways (8)
- Lateral corticospinal pathway
- Anterior (medial) corticospinal pathway
- Rubrospinal pathway
- Tectospinal pathway
- Lateral Vestibulospinal pathway
- Medial Vestibulospinal pathway
- Lateral (medullary) reticulospinal pathway
- Medial (pontine) reticulospinal pathway
