RETICULAR FORMATION

RETICULAR FORMATION

RETICULAR FORMATION

• consist of a deeply placed continuous network of nerve cells and fibers which extends from SC —>

  • medulla

  • pons

  • midbrain

  • subthalamus

  • hypothalamus

  • thalamus

Reticular formation: receive input from —

• from most of the sensory systems

• (+) efferent fibers that descend and influence nerve cells at all lvl of CNS

  • (+) sensory neuron —> motor neuron

LOCATION OF RETICULAR AND VESTIBULAR NUCLEI

• Median (column) = Intermediate (size)

• Medial = large

• Lateral = small

Reticular: Afferent projections —

1. SC

2. Cranial nerve nuclei

3. Cerebellum

4. Other afferent tracts

RF afferent fibers: funx

1. Visual impulses (eye coord)

2. Emotional response of the face (via Corpus callosum)

   1. emotional facial expression and mvt of mm in response to emotion

Afferent: SC tracts

1. Spinoreticular

2. Spinothalamic

3. Medial Lemniscus (DCLS)

Cranial nerve nuclei: Afferent

1. Vestibular

2. Acoustic

3. Visual Pathways

Afferent: Cerebellum

1. Cerebelloreticular pathway

Other afferent tracts

1. from Corpus striatum & limbic lobe —>

   1. Subthalamic

   2. Hypothalamic

   3. Thalamic nuclei

2. Primary motor cortex of the frontal lobe

3. Somesthetic cortex of the parietal lobe

Efferent Projections —>

1. Brainstem and Spinal cord

Efferent: Brainstem and SC

Tracts : Reticulobulbar (to brainstem) and Reticulospinal (to SC) & Vestibulospinal tract*

• both tracts resp for MAINTENANCE OF BALANCE AND POSTURAL ADJUSTMENT during perturbation

Efferent: Brainstem and SC: funx

1. Symphathetic outflow and craniosacral parasympathetic outflow of the ANS

RF: General funx (6)

1. Control of Skeletal Muscle

2. Control of SOMATIC AND VISCERAL SENSATIONS

3. Control of ANS

4. Control of Endocrine NS

5. Influence of the Biological Clock

6. RAS (reticular activating system)

Control of Skeletal Muscle: via Tracts

via Tracts: RETICULOSPINAL AND RETICULOBULBAR

• influence the activity of alpha and gamma motor neurons

• modulate mm tone and reflex activity

Control of Skeletal mm: via tract

via Tract: VESTIBULOSPINAL TRACT

• for maintaning of the antigravity(ext) mm during anti-gravity positions like standing

• for BALANCE, EQUILIBRIUM, AND STABILITY

Control of skeletal mm: CENTER

• via CENTER = Respiratory Centers of the brain

  • control of respiratory mm

Reciprocal inhibition

• coined by Margaret Rood

  • In order for somatic mm to move —> mm cxn and relaxation of the ago- and antagonistic mm.

Co-contraction

• for stability

• Both ago- and antagonistic mm contracted at the same time

• Modulated by RF

Control of Somatic and Visceral sensation: via tracts

via Tracts: All ascending pathways that pass thru SUPRASPINAL LVLS

• funx either facilitate or inhibitory

• KEY ROLE in gating mechanism/gate control theory

  • for control of pain percep (amt)

CONTROL OF THE ANS: via tracts

via TRACTS: Reticulobulbar and Reticulospinal Tract

• HIGHER CONTROL OF THE ANS (connection c hypothalamus)

• Descend fibers for sympathetic outflow and parasympathetic craniosacral outflow

Control of the ENDOCRINE NS

• via hypothalamic nuclei (direct or indirect)

  • Influence the synthesis or release of releasing/ release-inhibiting factors

    • to control the activity of hypophysis cerebri (pituitary gland)

• RF helps hypothalamic nuclei

INFLUENCE ON THE BIOLOGICAL CLOCK

• via MULTIPLE AFFERENT AND EFFERENT PATHWAYS —>

  • hypothalamus (suprachiasmatic nucleus)

• (+) RAS (reticular activating system) = SLEEP, arousal, consciousness

Problem @ biological clock: CAUSES

1. TBI (prob in the neuronal fibers from and to hypo and RFF)

2. Changing of duty/work time

prob @ biological clock leads to:

1. Somnambulism

2. Nocturnal enuresis

3. Hyperinsomnia

4. Apnea

5. Narcolepsy

RAS (reticular activating system)

via MULTIPLE ASCENDING PATHWAYS CARRYING SENSORY INFORMATION

• for arousal(response to noxious stimuli) and lvl of consciousness

LV OF CONSCIOUSNESS (5)

1. Alert

2. Stupor

3. Semi-coma

4. Coma

5. Persistent vegetative state

State of consciousness depends on —

dependent on the CONTINUOUS projection of sensory information to the cortex