Medulla Oblongata

Question 1

What is the brain stem?

Answer 1

The brain stem is the part of the brain between the spinal cord and the diencephalon. It consists of three structures: (1) medulla oblongata, (2) pons, and (3) midbrain. Extending through the brain stem is the reticular formation, a netlike region of interspersed gray and white matter.

Question 2

What is the medulla oblangata?

Answer 2

The medulla oblongata, or more simply the medulla, is continuous with the superior part of the spinal cord; it forms the inferior part of the brain stem. The medulla begins at the foramen magnum and extends to the inferior border of the pons, a distance of about 3 cm (1.2 in.).

Question 3

What doesn the white matter of the medulla contain?

Answer 3

The medulla’s white matter contains all sensory (ascending) tracts and motor (descending) tracts that extend between the spinal cord and other parts of the brain.

Question 4

In terms of the medulla, what are pyramids?

Answer 4

Some of the white matter forms bulges on the anterior aspect of the medulla. These protrusions, called the pyramids, are formed by the large corticospinal tracts that pass from the cerebrum to the spinal cord.

The corticospinal tracts control voluntary movements of the limbs and trunk.

Question 5

What is the decussation of pyramids?

Answer 5

Just superior to the junction of the medulla with the spinal cord, 90% of the axons in the left pyramid cross to the right side, and 90% of the axons in the right pyramid cross to the left side. This crossing is called the decussation of pyramids and explains why each side of the brain controls voluntary movements on the opposite side of the body.

Question 6

What is a nucleus with regards to the CNS?

Answer 6

A nucleus is a collection of neuronal cell bodies within the CNS.

Question 7

Give a couple of examples of nuclei within the medulla?

Answer 7

The medulla contains several nuclei. Some of these nuclei control vital body functions. Examples of nuclei in the medulla that regulate vital activities include the cardiovascular center and the medullary rhythmicity area.

Question 8

What does the cardiovascular centre of the medulla regulate?

Answer 8

The cardiovascular center regulates the rate and force of the heartbeat and the diameter of blood vessels.

Question 9

What does the medullary rhythmicity area of the medulla do?

Answer 9

The medullary rhythmicity area of the respiratory center adjusts the basic rhythm of breathing.

Question 10

Other than cardiovascular and repiratory rate control, give some other examples of what nuclei in the medulla control?

Answer 10

Nuclei in the medulla also control reflexes for vomiting, swallowing, sneezing, coughing, and hiccupping.

Question 11

What is vomiting?

Answer 11

The forcible expulsion of the contents of the upper gastrointestinal (GI) tract through the mouth.

Question 12

What does the deglutition centre of the medulla promote?

Answer 12

The deglutition center of the medulla promotes deglutition (swallowing) of a mass of food that has moved from the oral cavity of the mouth into the pharynx (throat).

Question 13

What does sneezing involve?

Answer 13

Sneezing involves spasmodic contraction of breathing muscles that forcefully expel air through the nose and mouth.

Question 14

What does coughing involve?

Answer 14

Coughing involves a long-drawn and deep inhalation and then a strong exhalation that suddenly sends a blast of air through the upper respiratory passages.

Question 15

What causes a hiccup?

Answer 15

Hiccupping is caused by spasmodic contractions of the diaphragm (a muscle of breathing) that ultimately result in the production of a sharp sound on inhalation.

Question 16

Where in the medulla would you find an olive?

Answer 16

Just lateral to each pyramid is an oval-shaped swelling called an olive.

Question 17

What is found inside an olive of the medulla?

What is it and what does it do?

Answer 17

Within the olive is the inferior olivary nucleus, which receives input from the cerebral cortex, red nucleus of the midbrain, and spinal cord. Neurons of the inferior olivary nucleus extend their axons into the cerebellum, where they regulate the activity of cerebellar neurons. By influencing cerebellar neuron activity, the inferior olivary nucleus provides instructions that the cerebellum uses to make adjustments to muscle activity as you learn new motor skills.

Question 18

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Answer 18

Question 19

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Answer 19

Question 20

What nuclei are found in the posterior part of the medulla and what are they associated with?

Answer 20

Nuclei associated with sensations of touch, pressure, vibration, and conscious proprioception are located in the posterior part of the medulla. These nuclei are the right and left gracile nucleus (GRAS-il slender) and cuneate nucleus (KU ̄-ne ̄-a ̄t wedge).

Question 21

How do the gracile and cuneate nuclei work?

Answer 21

Ascending sensory axons of the gracile fasciculus (fa-SIK-u ̄-lus) and the cuneate fasciculus, which are two tracts in the posterior columns of the spinal cord, form synapses in these nuclei. Postsynaptic neurons then relay the sensory information to the thalamus on the opposite side of the brain. The axons ascend to the thalamus in a band of white matter called the medial lemniscus (lem-NIS-kus ribbon), which extends through the medulla, pons, and midbrain. The tracts of the posterior columns and the axons of the medial lemniscus are collectively known as the posterior column-medial lemniscus pathway.

Question 22

What three sensory nuclei and pathways does the medulla contain?

Answer 22

The medulla also contains nuclei that are components of sensory pathways for gustation (taste), audition (hearing), and equilibrium (balance). The gustatory nucleus (GUS-ta-to ̄ -re ̄) of the medulla is part of the gustatory pathway from the tongue to the brain; it receives gustatory input from the taste buds of the tongue. The cochlear nuclei of the medulla are part of the auditory pathway from the inner ear to the brain; they receive auditory input from the cochlea of the inner ear. The vestibular nuclei of the medulla and pons are components of the equilibrium pathway from the inner ear to the brain; they receive sensory information associated with equilibrium from proprioceptors in the vestibular apparatus of the inner ear.

Question 23

List the 5 cranial nerves that the medullas nuclei are associated with?

Answer 23

Vestibulocochlear (VIII) nerves

Glossopharyngeal (IX) nerves

Vagus (X) nerves

Accessory (XI) nerves (cranial portion).

Hypoglossal (XII) nerves.

Question 24

What do the vestibulocochlear nerves do in relation to the medullary nuclei?

Answer 24

Vestibulocochlear (VIII) nerves. Several nuclei in the medulla receive sensory input from and provide motor output to the cochlea of the internal ear via the vestibulocochlear nerves. These nerves convey impulses related to hearing.

Question 25

What do the glossopharyngeal nerves do in relation to the medullary nuclei?

Answer 25

Glossopharyngeal (IX) nerves. Nuclei in the medulla relay sensory and motor impulses related to taste, swallowing, and salivation via the glossopharyngeal nerves.

Question 26

What do the vagus nerves do in relation to the medullary nuclei?

Answer 26

Vagus (X) nerves. Nuclei in the medulla receive sensory impulses from and provide motor impulses to the pharynx and larynx and many thoracic and abdominal viscera via the vagus nerves.

Question 27

What do the accessory nerves do in relation to the medullary nuclei?

Answer 27

Accessory (XI) nerves (cranial portion). These fibers are actually part of the vagus (X) nerves. Nuclei in the medulla are the origin for nerve impulses that control swallowing via the vagus nerves (cranial portion of the accessory nerves).

Question 28

What do the hypoglossal nerves do in relation to the medullary nuclei?

Answer 28

Hypoglossal (XII) nerves. Nuclei in the medulla are the origin for nerve impulses that control tongue movements during speech and swallowing via the hypoglossal nerves.

Question 29

Explain injury to the medulla?

Answer 29

Given the vital activities controlled by the medulla, it is not surprising that injury to the medulla from a hard blow to the back of the head or upper neck such as falling back on ice can be fatal. Damage to the medullary rhythmicity area is particularly serious and can rapidly lead to death. Symptoms of nonfatal injury to the medulla may include cranial nerve malfunctions on the same side of the body as the injury, paralysis and loss of sensation on the opposite side of the body, and irregularities in breathing or heart rhythm. Alcohol overdose also suppresses the medullary rhythmicity area and may result in death