Medulla Oblongata

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Medulla oblongata or more simply medulla is part of brain stem which forms base of the brain stem. It contains pyramid, olive and above pyramidal structure, there is decussation of pyramids which explains why each part of brain controls opposite part of body. Adding to that medulla also has several nuclei which controls activity of cardiovascular system and respiratory system. Medulla also has nuclei for controlling reflexes of vomiting, swallowing, hiccuping, coughing and sneezing. It has also nuclei for test, hearing and balance. Medulla also contains nuclei of cranial nerve number VIII, IX, X, XI and XII.

1. Brain Stem

2. The brain stem is the part of the brain between the spinal cord and the diencephalon . It consists of three structures: Medulla oblongata, Pons, and Midbrain. Extending through the brain stem is the reticular formation , a net like region of interspersed gray and white matter.

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4. Reticular Formation

5. Medulla Oblongata

6. 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.). Fig. 1 Fig. 2

7. 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. Some of the white matter forms bulges (knobs) on the anterior aspect of the medulla. These knobs , 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.

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9. 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.

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

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12. Cluster of Cell Bodies In CNS Nucleus In PNS Ganglion

13. The medulla also contains several nuclei. ( Recall that a nucleus is a collection of neuronal cell bodies within the CNS .) 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. The cardiovascular center regulates the rate and force of the heartbeat and the diameter of blood vessels . The medullary rhythmicity area of the respiratory center adjusts the basic rhythm of breathing .

14. Nuclei for vital functions Cardiovascular center regulates the rate and force of the heartbeat and the diameter of blood vessels . The medullary rhythmicity area of the respiratory center adjusts the basic rhythm of breathing . Fig. 1 Fig. 2

15. Besides regulating vitals, nuclei in the medulla also control reflexes for Vomiting Swallowing Sneezing Coughing and Hiccupping

16. Stimulation of vomiting center of the medulla causes vomiting, the forcible expulsion of the contents of the upper gastrointestinal (GI) tract through the mouth. The deglutition center of the medulla promotes swallowing of a mass of food that has moved from the oral cavity of the mouth into the pharynx (throat ). Sneezing involves spasmodic contraction of breathing muscles that forcefully expel air through the nose and mouth.

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

18. Nuclei associated with sensations of touch , pressure , vibration , and proprioception (conscious awareness of position) are located in the posterior part of the medulla. These nuclei are the right and left gracile nucleus and cuneate nucleus .

19. The medulla also contains nuclei that are components of sensory pathways for gustation (taste), audition (hearing), and equilibrium (balance). The gustatory nucleus 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.

20. 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.

21. Finally, the medulla contains nuclei associated with five pairs of cranial nerves : Vestibulocochlear (VIII) nerves , Glossopharyngeal (IX) nerves , Vagus (X) nerves, Accessory (XI) nerves (cranial portion), and Hypoglossal (XII) nerves.

22. Quick Revision

23. The brain stem is the part of the brain between the spinal cord and the diencephalon . It consists of three structures: Medulla oblongata, Pons, and Midbrain.

24. Location of medulla oblongata: superior to the spinal cord ; inferior to the pons, 3 cm Long.

25. Anterior aspect of the medulla: Known as the pyramids, Formed by the large corticospinal tracts. Function: Control voluntary movements of the limbs and trunk

26. Decussation of pyramids: A cross over of neurons, Superior to the junction of the medulla with the spinal cord . It explains why each side of the brain controls voluntary movements on the opposite side of the body.

27. Olive: Oval-shaped swelling, just lateral to each pyramid. Within the olive is the inferior olivary nucleus, receiving input from the cerebral cortex, red nucleus of the midbrain, and spinal cord. Neurons of the inferior olivary nucleus regulate the activity of cerebellar neurons by providing instructions, that the cerebellum uses to make adjustments to muscle activity as you learn new motor skills .

28. Nuclei for vital functions Cardiovascular center regulates the rate and force of the heartbeat and the diameter of blood vessels . The medullary rhythmicity area of the respiratory center adjusts the basic rhythm of breathing .

29. Gracile and cuneate nucleus: Located in the posterior part of the medulla, associated with sensations of touch, pressure, vibration, and conscious awareness of position.

30. Medulla contains nuclei associated with cranial nerves

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