Neuro Lecture 10: Reticular Formation

Where is the reticular formation located?

- Brainstem tegmentum

- Ventral to cerebral aqueduct

What is the reticular formation?

A complex network of specific nuclei and neurons

Does the reticular formation have distinct boundaries?

No

What is the function of the neurons and nuclei of the reticular formation?

- Multimodal

- Act as relay/integration centers to important brain centers

- Coordinates consciousness, attention, and arousal for survival

What are the major functions of the reticular formation? (7)

- Arousal

- Consciousness

- Circadian rhythm

- Coordination of motor movements

- Cardiovascular/respiratory control

- Pain modulation

- Habituation

What is the reticular formation rostrally connected to?

- Diencephalic nuclei (thalamus)

- Projections to cortical/subcortical structures

What is the rostral portion responsible for?

- Consciousness, attention, and arousal

- Sleep-wake cycle

What is the reticular formation caudally connected to?

- Intermediate zone of spinal cord (cervical)

What is the caudal portion responsible for?

- Regulates motor function

- Protective reflexes

- Autonomic functions of visceral organs (circulatory/respiratory)

- Muscle tone, posture, coordination

What is the rostral reticular formation also known as?

Pontomesencephalic RF

What structures are involved in the rostral RF?

- RF of mesencephalon

- Upper pons

- Thalamus connected with cortical structures

- Forebrain connections

What structures are involved in the caudal RF?

- Lower pons

- Medulla

- CN nuclei and spinal cord

What is consciousness?

State of awareness of self and the embedded environment

What structures are involved in the consciousness system?

- Frontoparietal association cortex

- Arousal circuits in upper brainstem and diencephalon

What 2 components make up the consciousness system?

- Level of consciousness

- Content of consciousness

What is the level of consciousness component responsible for? (4)

- Arousal

- Alertness (arousal circuits and cortex)

- Attention (arousal circuits, cortex, frontoparietal)

- Awareness (subjective/personal)

What is the content of consciousness component responsible for?

- Sensory

- Motor

- Memory

- Emotional functions

How many stages occur in a sleep cycle?

4

What occurs in stages 1-3?

- Non-rapid eye movement (Non-REM)

- Physical restoration

What occurs in N1 of the sleep cycle?

Falling asleep

What occurs in N2 of the sleep cycle?

- HR and breathing slows

- Muscles relax

- Temperature drops

What occurs in N3 of the sleep cycle?

- Delta waves

- Hard to arouse

- Physical restoration

- Strengthening immune system

What occurs in stage 4 of the sleep cycle?

- REM

- Restores mind

- Vivid dreams

- Active brain processing events of day and saves in LTM

- No muscle activity

What does a midbrain transection lead to?

Coma (hypersomnia)

What does a lower pons transection lead to?

Reduces sleep (insomnia)

What is a coma?

- Unarousable

- Lying with eyes closed

What can cause a coma?

- Damage at pontomesencephalic RF

- Damage to bilateral large areas of cortex

- Bilateral lesions of thalamus

What is the presentation of a coma? (6)

- May show reflexive eye movements (vestibulo-ocular reflex)

- May show respiratory movements

- Posturing

- No purposeful movements

- No response to painful stimuli

- Not permanent (may deteriorate/improve)

Where is the site of a lesion leading to decorticate posturing?

- Forebrain

- Diencephalon rostral to midbrain

- Above red nucleus

What is decorticate posturing also known as?

Flexor posturing

What are signs of decorticate posturing?

- Closed hands

- Legs are internally rotated

- Feet turned inward

- Arms adducted, flexed against chest

Where is the site of a lesion leading to decerebrate posturing?

- Below mid brain

- Vestibular nuclei not modulated

What is decerebrate posturing also known as?

Extensor posturing

What are signs of decerebrate posturing?

- Head and neck arched

- Legs straight

- Toes pointed downwards

- Arms straight, extended

- Hands curled

What is a vegetative state?

An extreme case of alertness without awareness

What is the presentation of a vegetative state?

- Open their eyes

- Responses to stimuli, but not meaningful

- May turn head/eyes toward tactile/auditory stimuli

What sets apart a persistent vegetative state?

- >1 month of no meaningful motor/cognitive function

- Absence of awareness of themselves/environment

What is a persistent vegetative state > 6 months considered (traumatic vs. nontraumatic)?

Nontraumatic

What is a persistent vegetative state > 12 months considered (traumatic vs. nontraumatic)?

Traumatic

What is the prognosis of a persistent vegetative state?

Poor

What is a minimally conscious state?

Do not have reliable interactive verbal/nonverbal communication

What is the presentation of a minimally conscious state?

- Visual tracking

- Minimal level of responsiveness

What is the Glasgow Coma scale used for?

Determine severity

What responses does the Glasgow Coma scale measure?

- Eye opening

- Verbal

- Motor

What is the Rancho Los Amigos Levels of Cognitive Functioning (LOCF) scale used for?

Communicate the cognitive/behavioral state and planning intervention

What causes Locked-in Syndrome?

Lesion in ventral pons affecting the bilateral corticospinal and corticobulbar tracts

What is the presentation of Locked-in Syndrome? (5)

- Absent motor function (no voluntary movement)

- Reticular activating system spared (conscious)

- Intact sensation and cognition

- Vertical eye movements spared

- Eyelid elevation spared

What causes Horner's Syndrome?

Interruption of sympathetic nerve arising from T1, T2

What are the symptoms of Horner's Syndrome?

- Miosis

- Ptosis

- Anhidrosis

- Dilation of blood vessels on face and head

What is miosis?

- Decreased pupil size

- Loss of SNS innervation to pupillary dilator

What is ptosis?

- Drooping of upper eyelid

- Loss of innervation to superior tarsal muscle (Müller's muscle)

What is anhidrosis?

Decreased sweating