Corticospinal Tract

Dorn Spinal Therapy

Spine Healing Therapy

Get Instant Access

cu to c

2 ca

The brain stem consists of the midbrain (mesencephalon), pons, and medulla. It contains the nuclei of the cranial nerves and ascending and descending tracts running to and from the brain, cerebellum, and spinal cord. It also contains au-tonomic centers that regulate cardiovascular function, breathing, and eating behavior as well as acoustic and vestibular relay nuclei. The flow of information along afferent and efferent pathways is regulated by reflex systems.

Nerve Pathways

All motor (p. 44) and sensory projection systems (p. 104) pass through the brain stem and communicate with its intrinsic structures at various sites. The central sympathetic pathway (p. 90) originates in the hypothalamus.

Reticular Formation

The reticular formation (RF) is a network of nuclei and interconnecting fibers that is anatomically intertwined with the cranial nerve nuclei and other fiber tracts of the brain stem. Different parts of the reticular formation perform different functions. The reticular activating system (RAS) provides the anatomical and physiological basis for wakeful consciousness (p. 116). The medullary RF contains the vital centers controlling the heartbeat, breathing, and circulation as well as reflex centers for swallowing and vomiting. The pontine RF contains centers for coordination of acoustic, vestibular, respiratory, and cardiovascular processes. The midbrain RF contains centers subserving visuospatial orientation and eating behavior (chewing, sucking, licking).

Reflex Systems (pp. 118ff)

Pupillary light reflex. The Edinger-Westphal nucleus in the midbrain, which is adjacent to the oculomotor nucleus, provides the efferent arm of the reflex loop (p. 90; examination, p. 92.) Vestibulo-ocular reflex (VOR, p. 84). The vestibular nuclei receive their main input from the labyrinthine semicircular canals and collateral input from the cerebellar nuclei; their output is conveyed to the extraocular muscles through the medial longitudinal fasciculus, and to the spinal cord through the vestibulospinal tract. Examination: Suppression of visual fixation: the subject extends his arms and stares at his thumbs while spinning on a swivel chair. Nystagmus does not occur in normal subjects. Oculocephalic reflex (doll's eyes phenomenon): Horizontal or vertical passive rotation of the subject's head causes the eyes to rotate in the opposite direction; normally suppressible by awake persons, this reflex is seen in patients with impaired consciousness but preserved vestibular function. Caloric testing: The examiner first confirms that the patient's eardrums are intact, then instills cold water in the external auditory canal with the head elevated at a 30° angle (which inactivates the ipsilateral horizontal semicircular canal). This normally causes nystagmus in the contralateral direction, i.e., slow ipsilateral conjugate deviation of the eyes, followed by a quick jerk to the other side. Corneal reflex. Afferent arm, CN V/1; efferent arm, CN VII, which innervates the orbicularis oculi muscle. Examination: Touching the cornea from the side while the subject looks forward evokes blinking. The reflex can also be assessed by electromyography (EMG). Pharyngeal (gag) reflex. Afferent arm, mainly CN IX, X, and V/2; efferent arm, CN IX and X. The gag reflex may be absent in normal persons. Examination: Touching the soft palate or back of the pharynx evokes pharyngeal muscle contraction. Cough reflex. Afferent arm, CN IX and X; efferent arm, via the solitary tract to the diaphragm and other participating muscle groups. Examination: Tested in intubated patients with endotracheal suction (tracheal reflex).

Masseter (jaw jerk) reflex. Afferent arm, probably CN V/3; efferent arm, CN V. Examination: Tapping the chin evokes jaw closure. Acoustic reflex (p. 68). Afferent arm, projections of the cochlear nuclei to the RAS. Examination: Sudden, intense acoustic stimuli evoke a fright reaction including lid closure, startle, turning of the head, and increased alertness.

Corticonuclear tract Corticopontine tract Medial longitudinal fasciculus Medial lemniscus Red nucleus

Corticospinal tract

¡- Corticopontine tract

Thalamu:

B -— Cerebral peduncle

Corticonuclear tract Corticopontine tract Medial longitudinal fasciculus Medial lemniscus Red nucleus

Corticospinal tract

¡- Corticopontine tract

Thalamu:

B -— Cerebral peduncle

Choroid plexus (fourth ventricle)

Medial lemniscus

Corticospinal Tract

Vestibular nuclei

Was this article helpful?

+1 -1
Spiritual Weight Loss Mentality

Spiritual Weight Loss Mentality

Awesome Ways To Get Over Your Mentality That Keeps you Overweight! This Book Is One Of The Most Valuable Resources In The World When It Comes To Results In Your Slim-down and Health Efforts! Day in day out we keep ourselves absorbed with those matters that matter the most to us. A lot of times, it might be just to survive and bring in some money. In doing so we at times disregard or forget about the extra matters that are essential to balance our lives. They’re even more essential to supply real meaning to our world. You have to pay attention to your wellness.

Get My Free Ebook


Responses

  • FIORENZA
    Where is medial longitudinal fasciculus?
    8 years ago

Post a comment