Medulla Oblongata - Benifla Flashcards
What are the borders of the medulla oblongada?
Superior: inferior pontine sulcus, stria medullaris
Anterior: Clivus
Where does the pyramidal tract originate and decussate? What is the clinical significance?
Begins in pyrimidal cells of the motor cortex. Continuous with corticospinal tract.
Decussate in spinal tract. Injury below causes ipsilateral hemiplagia and injury above causes contralateral hemiplasia.
What is the path of the proprioceptive pathways?
Peripheral nerves from from the organs and ascend up the spinal cord on the ipsilateral posterior column through the dorsal root entry zone. The synapse for the first time at the gracilis (if from below T6) and cuneate nuclei (if from above T6) at the medulla oblongada. Postsynaptic (second order) fibers decussate as arcuate fibers to the medial lemniscus. The arcuate fibers continue as the medial lemniscus to the thalamus where they synapse again. Post-synaptic fibers ascend to the sensory cortex.
What is the effect of a lesion of the hypoglossal nucleus?
What is the effect of an injury to the cortex impairing the hypoglossal nerve?
Injury to hypoglossal nucleus causes tongue deviation to ipsilateral side.
Injury to cortex causes deviation contralateral to the injured side.
What is the nucleus ambiguous?
Motor nucleus.
Afferent fibers from both motor cortices (Rt and Lt), innervates muscles from (constrictor of) pharynx and (intrinsic) larynx (and stylopharyngeal) through CN IX, X and XI.
Controls swallowing and breathing.
Situated in reticular formation (RF).
What is the dorsal vagal nucleus?
• parasympathetic nucleus.
– Afferent Fibers: Hypothalamus
– Efferent Fibers: Involuntary
muscles of the bronchi, heart,
(lower 2/3 of esophagus), stomach, small
intestine, large intestine as far
as the distal 2/3 of the
transverse colon
What is the nucleus tractus solitarius and what is its classification?
– Afferent Fibers: Taste via
peripheral axons of the inferior
ganglion on the vagus (epiglottis),
glossopharyngeus and facial (anterior 1/3 taste)
nerves
– Efferent: Thalamus,
hypothalamus
What is the function of the glossopharyngeal nerve?
- Sensory innervation of external acoustic meatus – sup.
ganglion- spinal trigeminal nuc.
• Parasympathetic innervation of parotid
gland- inferior salivary nuc. (others go through superior salivary nucleus and facial nerve)
• Taste from posterior third of the tonguenuc. Tractus solitarius.
• Motor to Stylopharyngeus muscl- nucleus ambigous
What is the result of a lesion in the glossopharyngeal nerve?
• Isolated injury-rare
• Loss of gag reflex
• Loss of carotid sinus reflex
• Loss of taste and general sensation in the
posterior third of the tongue
What do the fibers of the vagus nerve consist of?
What is the head and neck innervation of the vagus nerve?
Consists of fibers from ambigus, dorsal vagal and tractus solitarius nuclei. Leaves the anterolateral surface of the medulla by rootlets between the olives and inferior cerebellar peduncle
80% ascending fibers
20% descending fibers
• Sensory innervation of the infratentorial
dura (supratentorial is trigeminal), EAM, tympanic membrane, back of
the ear - sup. ganglion- spinal trigeminal
nuc.
• Taste from the epiglotis- NTS
• Motor: Laryngeal and pharyngeal muscles, striated
muscle of the upper 2/3 esophagus- nucleus
ambigous
• Motor: Viscera of the neck thoracic and abdominal
cavities- dorsal vagal nuc
What is the effect of a lesion to the vagus nerve?
• Ipsilateral paralyisis of the soft
palate, pharynx and larynx leading to
dysphonia (hoarsness), dyspnea, dysarthria (trouble articulating), dysphagia
• Loss of gag reflex
• Anesthesia of the larynx and pharynx
-Patients can die of aspiration pneumonia
Loss of carotid sinus reflex (descending vagus of ascending glossopharyngeal):
• Increased carotid arterial pressure
• Excite carotid sinus baroreceptors
• The impulses conveyed by the IX to NTS (so injury here will also cause problem)
• Second order neuron to dorsal vagal nuc.
• Vagus- reduction in heart rate and heart
muscle contractility, decreased blood pressure and cardiac output.
How is the accessory nerve formed?
What are its afferent and efferent fibers?
What is the effect of a lesion?
Formed by the union of a cranial and spinal root.
• Afferent Fibers: Crossed and uncrossed fibers from precentral gyrus- motor.
• Efferent Fibers: Cranial and spinal root. Cranial root is formed from axon of the inferior part of the nucleus ambiguous. Joins the vagus and supplies some of the soft palate and larynx muscles. The spinal root joins the cranial root as they pass the jugular foramen. Supplies the sternocleidomastoid and the trapezius muscles
Lesion causes weakness of the ipsilateral sternocleidomastoid (difficulty in turning head in opposite direction)
Ipsilateral trapezius weakness causes shoulder drop.
Can have laryngeal paralysis.
What are the signs and symptoms of Wallenberg’s (Lateral Medullary) Syndrome?
• Wallenberg’s Syndrome:
Injury to: dorsal vagal nucleus, nucleus ambiguous, nucleus tractus solitarius, and spinal trigeminal nucleus. Doesn’t involve motor pathways. No hemiparesis or hemiplasia, no proprioception problems.
a) Homolateral palatal paralysis causing dysphagia and dysarthria (involvement of the nucleus ambigus)-injury/ischemia to lateral medullary bulb
b) Ipsilateral Loss of pain and thermal sensation of the face (involvement of the spinal
nucleus of trigeminal nerve and spinal trigeminal tract)
c) Cerebellar signs as disturbance of equilibrium: contralateral sensory pathways cause contralateral loss of sensation
d)Contralateral loss of pain and thermal sensation of trunk
and limbs (spinothalamic tract).
e) Horizontal nystagmus (vestibular nuclei)
f) Homolateral Horner’s Syndrome (involvement of
descending sympathetic fibers)
What are the signs and symptoms of Medial Medullary Syndrome?
Vascular injury to: hypoglossal nucleus, medial lemniscus-contralateral (above arcoid fibers), and corticospinal (before decussation-contralateral hemiplegia)
- Contralateral hemiparesis
- Contralateral loss of proprioception, tactile and vibration
- Ipsilateral flacid paralysis of the tongue
