Skip to main content

Table 2 Functional anatomy of the brainstem

From: Brainstem dysfunction in critically ill patients

Brainstem structures

Functions

Centers

Symptoms

Midbrain (rostral to the pons and caudal to the thalamus and the basal ganglia)

Eye movements

Cranial nerve nuclei:

III oculomotor nerve (mainly motor)

IV trochlear nerve (motor)

Oculomotor signs:

Ptosis (III)

Ophthalmoplegia (III, IV)

Pupillary size: sphincter pupillae and muscles of the ciliary body, pupil light reflex

Cranial nerve nuclei:

III oculomotor nerve

Pupillary anomalies:

Myosis (sympathetic lesion)

Mydriasis (parasympathetic lesion)

Anisocoria

Movement control

Substantia nigra

Parkinsonian syndrome and movement disorders (hemichorea, hemiballism, dystonia, tremor, asterixis, pseudo-athetosis, non-epileptic myoclonus)

Posture tone

Red nucleus

Postural tone impairment

Posture/auditory and visual integration

Accessory optic tractus

Balance disorder

Posture and movement integration

Tectum (dorsal part)

Balance disorder

Posture and inhibitor motor centers

Tegmentum (ventral portion) (basal ganglia and thalamus connections)

Involuntary movements

Sleep/wake cycles, alertness, and arousal

ARAS: composed of almost 100 nuclei, including locus coeruleus-raphe nuclei with neocortex connections

Sleep disturbance

Consciousness disorders

Central thermic regulation

ARAS-hypothalamus connections

Hypo/hyperthermia

Pons (between the medulla and the midbrain)

Facial sensitivity, muscles of mastication

Cranial nerve nuclei:

V trigeminal nerve (sensory and motor)

Facial symptoms:

Facial dysesthesia

Oculomotor signs:

Corneal/ciliary reflex impairment

Facial muscles and taste from the anterior 2/3 of the tongue (VII)

Cranial nerve nuclei:

VII facial nerve (sensory and motor)

Facial symptoms:

Peripheral facial palsy

Eye movement (abduction)

Cranial nerve nuclei:

VI abducens nerve (motor)

Oculomotor signs:

Ophthalmoplegia

Posture, sensation of rotation, gravity, and sound

Cranial nerve nuclei:

VIII vestibulocochlear nerve (mostly sensory)

Cerebellum tract

Altered audition (VIII)

Balance disorders (VIII and cerebellum tract)

Posture

Posture and inhibitor motor center

Spinocerebellar tracts

Tegmentum (thalamus and basal nuclei connections)

Cerebellar ataxia

Involuntary movement

Motor efference integration

Sensory efference integration

Tracts carrying signals to the thalamus

Motor deficit

Sensory deficit

Consciousness, alertness, and sleep regulation

Tracts carrying signals to the thalamus

Sleep disturbance

Consciousness disorders

Sleep/wake cycles, alertness, and arousal

ARAS: composed of almost 100 nuclei, including raphe nuclei and locus coeruleus-raphe nuclei-neocortex connections

Sleep disturbance

Consciousness disorders

Emotion

ARAS: locus coeruleus and amygdala connections

Anxiety and post-traumatic stress disorder (PTSD)

Central thermic regulation

ARAS-hypothalamus connections

Hypo/hyperthermia

Respiratory drive: respiratory rate and tidal volume control

Pedunculopontine tegmentum, locus coeruleus, lateral parabrachial respiratory group, and Kölliker-Fuse nuclei

Respiratory drive dysfunction:

Kölliker-Fuse and parabrachial nuclear: increase tidal volume, decrease respiratory rate

Lower part/ponto-peduncular injury: respiratory asynchronism

Medulla (lower half of the brainstem, connects the higher levels of the brain to the spinal cord)

Taste from the posterior 1/3 of the tongue

Cranial nerve nuclei:

IX glossopharyngeal (sensory and motor)

Tongue sensory impairment

Pharyngo-laryngeal reflex

Cranial nerve nuclei:

IX glossopharyngeal nerve

X vagus nerve (sensory and motor)

XI spinal nerve (motor)

Oro-pharyngo-laryngeal anomalies:

Dysphagia (swallowing impairment)

Dysphonia

Velo-pharyngo-laryngeal impairment

Absence of pharyngeal/gag reflex

Glossal muscles

XII hypoglossal (mainly motor)

Tongue motor impairment (fasciculation, motor deficit)

Cough

IX glossopharyngeal nerve

X vagus nerve

Absence of cough reflex (IX, X)

Posture

Spinocerebellar tracts

Cerebellar ataxia

Regulation of autonomic nervous system:

Sympathetic nuclei

Parasympathetic nuclei: vagus nerve (X) control of the heart, lung, digestive tracts

Autonomic dysfunction

Cardiac regulation

Sympathetic nuclei

Parasympathetic nuclei: vagus nerve (X) control of the heart, lung, digestive tracts

Oculocardiac reflex impairment (X)

Dysautonomia: tachycardia (parasympathetic impairment), bradycardia (sympathetic impairment), sudden death

Vasomotor regulation

Hemodynamic failure:

Dysautonomia with hypertension (parasympathetic impairment), hypotension (sympathetic impairment)

Gastrointestinal motility

Gastrointestinal motility anomalies

Respiratory drive: respiratory rate and tidal volume control

Respiratory centers: dorsal respiratory complex

Respiratory drive dysfunction: respiratory rate irregularities and ataxic breathing, hyperventilation, respiratory-ventilator asynchronism, central apnea

Microbiota gut-brain axis, senses and peripheral inflammation modulation

Vagus nerve (X)

Maladaptive immune response, gut-brain axis impairment

Tracts all along the brainstem

Connection of the oculomotor nerves (see Fig. 1)

Medial longitudinal fasciculus

Internuclear ophthalmoplegia

Motor information from the periphery to supratentorial structures

Corticospinal tract

Pyramidal and extrapyramidal tracts

Motor deficit, locked-in syndrome

Tetrapyramidal and extrapyramidal syndromes with movement disorders (tremor)

Non-epileptic myoclonus

Sensory information from the periphery to supratentorial structures

Posterior column-medial lemniscus pathway and spinothalamic tracts

Sensory deficit

Oculosympathetic control

Centers control of the ciliary nerve, superior tarsal muscle, pupillary sphincter/dilator

Horner’s syndrome (ptosis, myosis, enophtalamos, anhidrosis)