Anatomy and Physiology: Brain Stem

Here is anatomy and physiology of brain stem. Where we will discuss all three parts of brain stem. Starting from medulla, second is pons and third is mid brain. In this video I am presenting anatomy and physiology of medulla. Anatomy of medulla: Medulla Oblongata or more simply medulla is part of brain stem which forms base of the brain stem. Location of medulla oblongata is superior to spinal cord and inferior to Pons. 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. Functions of medulla or what dose medulla do? So medulla controls blood pressure, diameter of wall of arteries, heart rate, basal respiration rate and also vomiting, swallowing, hiccuping, coughing and sneezing.
In this video, we explain you about anatomy and physiology of Pons. The reference material used to make video is: Principles of Anatomy and Physiology Gerard J. Tortora, Bryan H. Derrickson. Pons is part of brain stem, present superior to medulla, inferior to mid brain and anterior to cerebellum. Pons means a bridge. As the name denotes, it connects other areas of brain. Neurons extending from cerebral cortex to pons makes corticopontine tract. Pons is connected to cerebellum by middle cerebral peduncle. Pons has vestibular nuclei, which is part of equilibrium pathways from inner ear to brain. Pons has also respiratory nuclei. Along with rhythmicity area of medulla, pons controls basal respiratory rhythm. Pons also contains nuclei for cranial nerve number V, VI,VII, and VIII.

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 H iccupping

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.

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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. Oliv e: 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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32. Pons

33. The pons (bridge) lies directly superior to the medulla and anterior to the cerebellum and is about 2.5 cm (1 in.) long. As its name implies, the pons is a bridge that connects different parts of the brain with one another. These connections are provided by bundles of axons .

34. Like the medulla, the pons consists of nuclei, sensory tracts, and motor tracts . Signals for voluntary movements from motor areas of the cerebral cortex are relayed through several pontine nuclei into the cerebellum.

35. Pons also contains vestibular nuclei that are components of the equilibrium pathway from the inner ear to the brain.

36. Other nuclei in the pons are the pneumotaxic area and the apneustic area of the respiratory center. Together with the medullary rhythmicity area, the pneumotaxic and apneustic areas help control breathing.

37. The pons also contains nuclei associated with the following four pairs of cranial nerves: Trigeminal (V) nerves, Abducens (VI) nerves, Facial (VII) nerves, and Auditory (VIII ) nerves

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39. Location : Anterior to Cerebellum Superior to Medulla Inferior to Mid Brain

40. Nuclei Present: Vestibular Nuclei Respiratory Nuclei 1. The pneumotaxic area and 2 . The apneustic area

41. Cranial Nerve: Trigeminal (V) nerves, Abducens (VI) nerves, Facial (VII) nerves, and Auditory (VIII) nerves

42. Mid Brain

43. The midbrain or mesencephalon extends from the pons to the diencephalon and is about 2.5 cm (1 in .)long .

44. The cerebral aqueduct passes through the midbrain, connecting the third ventricle above with the fourth ventricle below .

45. The anterior part of the midbrain contains paired bundles of axons known as the cerebral peduncles . The cerebral peduncles consist of axons of Corticospinal , Corticopontine , and Corticobulbar tracts , which conduct nerve impulses from motor areas in the cerebral cortex to the spinal cord, pons, and medulla, respectively.

46. The posterior part of the midbrain, called the tectum , contains four rounded elevations. Two superior elevations: Superior Colliculi Two inferior elevations: Inferior Colliculi

47. The superior colliculi serves as reflex centers for certain visual activities . Visual activities like, eye movements for tracking moving images (such as a moving car) and scanning stationary images (as you are watching this slide).

48. The superior colliculi are also responsible for reflexes that govern movements of the head, eyes, and trunk in response to visual stimuli .

49. The inferior colliculi are part of the auditory pathway , relaying impulses from the receptors for hearing in the inner ear to the brain. These two nuclei are also reflex centers for the startle reflex , sudden movements of the head, eyes, and trunk that occur when you are surprised by a loud noise such as a gunshot.

50. The midbrain contains several other nuclei, including the left and right substantia nigra . Neurons that release dopamine, extending from the substantia nigra to the basal ganglia, help control subconscious muscle activities . Loss of these neurons is associated with Parkinson disease .

51. Also present are the left and right red nuclei , which look reddish due to their rich blood supply and an iron-containing pigment in their neuronal cell bodies.

52. Axons from the cerebellum and cerebral cortex form synapses in the red nuclei, which help control some voluntary movements of the limbs.

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54. Mid Brain Location: Superior to pons and inferior to diencephalon

55. Anterior part of Mid brain: Cerebral Peduncles which contains Corticospinal , Corticopontine , and Corticobulbar tracts Posterior part of mid brain: Known as Tectum and contains 4 elevations. 2 superior colliculi: serving as reflex center for serval visual activity 2 inferior colliculi: part of auditory pathway.

56. Substantia nigra : Posterior to cerebral peduncles, contains dopaminergic neurons and having role in controling subconscious muscle activity Red Nuclei: Next to substantia nigra there is red nuclei involved in voluntary movements of limbs.

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