4.4 Flashcards
Reticular formation
Cells of the reticular formation are not collected into typical nuclei.
Extends throughout the brainstem
RF send signals to the entire cerebrum
Reticular formation: core of the brainstem
Cranially merges with nuclei of the thalamus.
Caudally extends through the brainstem.
Spinal cord analogue is the intermediate grey matter.
Reticular formation functions through
- skeletal muscle
- ANS
- endocrine system
- biological rhythm
Function of reticular formation
Control of consciousness
Somatic and visceral sensation
Regulation of the respiratory and cardiovascular system
control of muscle tone
Posture maintenance
Movement
Afferents of reticular formation
Sensory
Moto
ANS
Hypthalamus/limbic
Efferents of reticular formation
Every level of CNS
How does the reticular formation control motor function
Corticoreticular fibers synapse with motor interneurons
- function in locomotion and postural control
Control muscle tone and reflex activity
- reflex inhibition
Maintains horizontal gaze steady when the head moves.
How does the reticular formation control pain sensation
Pain pathway from the body = ALS (indirect and direct)
Pain pathway from the head = trigeminothalamic pathway
- collateral branches extend to reticular formation
- RF sends signals to the:
* hypothalamus and limbic systems -> emotional response
* reticulobulbar and reticulospinal tracts -> serotonergic inhibition of pain
How does the reticular formation control the ANS
RF receives afferents from
- cerebral cortex
- hypothalamus
- limbic system
- ascending sensory pathways
The reticulobulbar tract and reticulospinal tracts carry signals to the ANS center of the brainstem.
Arousal and consiousness
Sensory stimuli -> behavioral arousal
- attention is focused
- general alertness increases
Action of the RF = arousal
Consciousness requires the cerebral cortex and RF
Ascending reticular activating system
Ascending pathways (including ALS)
1. send collateral branches to the RF
2. RF to the thalamus and hypothalamus
3. thalamus to the cerebral cortex
- this maintains the sleep-wake cycle
Consciousness
Loss of consciousness can result from multiple injuries
- metabolic derangement (diabetes, hypoxia)
- drugs
- encephalopathies
- trauma
- vascular accidents
Confusion
Impairments speed and clarity, associated with inattentiveness and disorientation
Drowsiness
inability to remain awake without external stimulation
Stupor
only vigorous external stimulation van arouse the patient; once aroused, responses remain markedly impaired
Coma
deep sleep-like state; patient cannot be aroused even with vigorous or repeated external stimulation
Purpose of glasgow coma scale
Communicate severity of brain damage in the moment
Assess likelihood of recovery
Increased intracranial pressure
Trauma –> swelling –> increased ICP
The only outlet for the cranium is the foramen magnum –> pressure on the brainstem
* medulla –> damage to respiratory centers –> apnea
* midbrain –> RF damage and hypersomnia –> coma
SCI T6 or above
Descending reticulospinal tracts innervate sympathetic signals to the ANS organs of the thorax
Early –> reduced SNS activity
Late –> reflex SNS hyperactivity
Decorticate
Injury at the level of the cerebral cortex or below
- flex arms
Decerebrate
Injury at the level of the midbrain of below
- extension
Minimally conscious state
Patient is capable of some rudimentary behavior such as following a simple command
Always in an inconsistent way
Locked in syndrome
Only an inability of the patient to respond adequately with motor activity and speech
Akinetic mutism
Patient is motionless and mute
Catatonia
Individual appears unresponsive
Most often seen with psychosis
