{"id":4409,"date":"2019-07-28T23:57:57","date_gmt":"2019-07-28T23:57:57","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-dutchess-anatomy-physiology\/?post_type=chapter&p=4409"},"modified":"2019-08-11T20:36:43","modified_gmt":"2019-08-11T20:36:43","slug":"medulla-oblongata","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-dutchess-anatomy-physiology\/chapter\/medulla-oblongata\/","title":{"raw":"Brainstem: Medulla Oblongata, Pons, and Midbrain","rendered":"Brainstem: Medulla Oblongata, Pons, and Midbrain"},"content":{"raw":"

Brain Stem<\/h2>\r\n[caption id=\"\" align=\"alignright\" width=\"450\"]\"This Figure\u00a01.\u00a0The Brain Stem.<\/strong> The brain stem comprises three regions: the midbrain, the pons, and the medulla.[\/caption]\r\n\r\nThe midbrain and hindbrain (composed of the pons and the medulla) are collectively referred to as the brain stem (Figure\u00a01). The structure emerges from the ventral surface of the forebrain as a tapering cone that connects the brain to the spinal cord. Attached to the brain stem, but considered a separate region of the adult brain, is the cerebellum. The midbrain coordinates sensory representations of the visual, auditory, and somatosensory perceptual spaces. The pons is the main connection with the cerebellum. The pons and the medulla regulate several crucial functions, including the cardiovascular and respiratory systems and rates.\r\n\r\nThe cranial nerves connect through the brain stem and provide the brain with the sensory input and motor output associated with the head and neck, including most of the special senses. The major ascending and descending pathways between the spinal cord and brain, specifically the cerebrum, pass through the brain stem.\r\n

Medulla Oblongata<\/h3>\r\nThe medulla oblongata (or just medulla) is the region known as the myelencephalon in the embryonic brain. The initial portion of the name, \u201cmyel,\u201d refers to the significant white matter found in this region\u2014especially on its exterior, which is continuous with the white matter of the spinal cord.\u00a0 The medulla itself is directly attached to the spinal cord, and represents the most inferior area of the brain.\r\n\r\n[caption id=\"attachment_4415\" align=\"alignleft\" width=\"300\"]\"Cross<\/a> Figure 2.<\/strong> Cross section through medulla.[\/caption]\r\n\r\nOn the anterior side of the medulla are a pair of large tracts of white matter call the pyramids (Figures 2).\u00a0 The pyramids contain axons of somatic motor neurons from the cerebrum that are transmitting signals through the medulla and towards the spinal cord.\u00a0 At the pyramids, 75-90% of the motor axons decussate, or switch sides so that those that originated on the right cerebral hemisphere move to the left and vice versa.\u00a0 Also visible from the ventral view are a pair of areas of grey matter called the olives (Figures 2).\u00a0 The olives are responsible for relaying sensory information to the cerebellum.\u00a0 Other important areas of grey matter in the medulla include the nucleus cuneatus and nucleus gracilis, both of which are used for relaying sensations to the thalamus to be perceived in the cerebral cortex.\r\n\r\n[caption id=\"attachment_4417\" align=\"alignright\" width=\"500\"]\"\"<\/a> Figure 3.<\/strong> Cross section through the inferior area of the medulla.[\/caption]\r\n\r\nA diffuse region of gray matter known as the\u00a0reticular formation\u00a0<\/strong>extends from the medulla into the pons and midbrain.\u00a0 It\u00a0is related to sleep and wakefulness, general brain activity and attention.\u00a0 In brain injuries that damage the reticular formation, individuals fall into a coma as they are unable to generate a state of wakefulness.\u00a0 Within the reticular formation of the medulla are other areas of grey matter that include a cardiovascular center which regulates heart rate and blood pressure, a respiratory center that works in conjunction with the pons to involuntarily regulate breathing rate.\u00a0 Additionally, other centers act to generate involuntary actions in the body such as vomiting, sneezing, hiccuping, and coughing.\r\n\r\nCranial nerves whose nuclei can be found in the medulla include the vestibulocochlear (VIII), glossopharyngeal (CN IX), vagus (CN X), and hypoglossal (XII).\u00a0(Figure 7)\r\n

Pons<\/h3>\r\nThe word pons comes from the Latin word for bridge. It is visible on the anterior surface of the brain stem as the thick bundle of white matter. The pons is the main connection between the cerebrum, cerebellum and the brain stem. Large tracts within the pons include the cerebellar peduncles, which carry axons for motor and sensory signals to the the cerebellum.\u00a0 Pyramidal motor tracts in the pons carry somatic motor signals from the cerebrum along a descending path towards the medulla.\r\n\r\n[caption id=\"attachment_4424\" align=\"alignright\" width=\"600\"]\"Sagittal<\/a> Figure 4.<\/strong> Sagittal view of the brainstem showing corticopontine fibers relaying motor signals to the pontine nuclei, which then communicate with the cerebellum via the middle cerebellar peduncle.[\/caption]\r\n\r\nThe bridge-like white matter is only on the anterior surface of the pons; the gray matter beneath that is a continuation of the tegmentum from the midbrain. Gray matter in the tegmentum region of the pons contains neurons receiving descending input from the cerebral cortex from corticopontine fibers to an area called the pontine nuclei.\u00a0 The pontine nuclei relay motor signals from the cerebrum to the cerebellum via axons in the middle cerebellar peduncle (Figure 4).\u00a0 This allows the cerebellum to modify and correct voluntary muscle movements initiated in the cerebrum.\u00a0 In addition, the reticular formation extends into the pons and forms a respiratory center that works together with that found in the medulla.\r\n\r\nCranial nerves whose nuclei are found in the pons include the trigeminal (CN V), abducens (CN VI), and facial (CN VII).\u00a0(Figure 7)\r\n

Midbrain<\/h3>\r\nOne of the original regions of the embryonic brain, the midbrain is a small region between the thalamus and pons. It is separated into the\u00a0tectum<\/strong>\u00a0and\u00a0tegmentum<\/strong>, from the Latin words for roof and floor, respectively. The cerebral aqueduct passes through the center of the midbrain, such that these regions are the roof and floor of that canal.\r\n\r\nThe tectum is composed of four bumps known as the corpora quadrigemina.\u00a0 Each pair of bumps are called colliculi (singular = colliculus), which means \u201clittle hill\u201d in Latin. The\u00a0inferior colliculi<\/strong>\u00a0are the inferior pair of these enlargements and is part of the auditory brain stem pathway (Figure 5). Neurons of the inferior colliculi project to the thalamus, which then sends auditory information to the cerebrum for the conscious perception of sound.\u00a0 The inferior colliculi also process sudden sounds to produce a reflex reaction by which the head and eyes involuntarily turn towards the sound.\u00a0 If you were sitting quietly taking a test and heard the person next to you drop their pencil, the sudden sound would cause your inferior colliculi to turn your head and eyes towards the pencil where it sat on the floor.\u00a0 The\u00a0superior colliculi<\/strong>\u00a0are the superior pair and combine sensory information about visual space (Figure 5). Activity in the superior colliculi is related to orienting the eyes to track a moving object, to scan an area when looking for something, or to track words on a page while reading.\u00a0 If you were searching a crowded room to locate your friend, the pattern with which your eyes scanned the room would be controlled by the superior colliculi.\r\n\r\n[caption id=\"attachment_4433\" align=\"alignleft\" width=\"500\"]\"Posterior<\/a> Figure 5.<\/strong> Posterior view of brainstem and inferior diencephalon.[\/caption]\r\n\r\nThe tegmentum is continuous with the gray matter of the rest of the brain stem. Throughout the midbrain, pons, and medulla, the tegmentum contains the nuclei that receive and send information through the cranial nerves, as well as regions that regulate important functions such as those of the cardiovascular and respiratory systems.\r\n\r\nImportant areas of grey matter on the interior of the midbrain include the red nucleus and the substantia nigra (Figure 6).\u00a0 The red nucleus is a region that possesses a reddish color due to the abundance of blood vessels that flow through this area.\u00a0 Functionally, the red nucleus plays a role in producing involuntary skeletal muscle contractions.\u00a0 The substantia nigra is also visually distinctive in that it possesses neurons with melanin, giving this group of neurons a darker appearance.\u00a0 The neurons of the substantia nigra produce dopamine, which is transported via their axons to the basal nuclei of the cerebrum where the dopamine is used to regulate motor signals.\r\n\r\n[caption id=\"attachment_4430\" align=\"alignleft\" width=\"600\"]\"Cross<\/a> Figure 6.<\/strong> Cross section through the midbrain showing the superior colliculus, red nucleus, substantia nigra, and cerebral aquaduct.[\/caption]\r\n\r\nAreas of white matter include the cerebral peduncles, which can be seen on the anterior view of the midbrain, and the cerebellar peduncles.\u00a0 The cerebral peduncles transmit motor signals along axons from the cerebrum to the midbrain.\u00a0 The cerebellar peduncles allow for communication of sensory and motor signals from the cerebellum to the midbrain and other parts of the brainstem. (Figure 7)\r\n\r\nCranial nerve nuclei found in the midbrain include those for the oculomotor nerve (CN III) and the trochlear nerve (CN IV). (Figure 7)\r\n\r\n \r\n\r\n[caption id=\"attachment_4432\" align=\"aligncenter\" width=\"700\"]\"Anterior<\/a> Figure 7.<\/strong> Anterior view of the brainstem and inferior portion of diencephalon.[\/caption]","rendered":"

Brain Stem<\/h2>\n
\"This<\/p>\n

Figure\u00a01.\u00a0The Brain Stem.<\/strong> The brain stem comprises three regions: the midbrain, the pons, and the medulla.<\/p>\n<\/div>\n

The midbrain and hindbrain (composed of the pons and the medulla) are collectively referred to as the brain stem (Figure\u00a01). The structure emerges from the ventral surface of the forebrain as a tapering cone that connects the brain to the spinal cord. Attached to the brain stem, but considered a separate region of the adult brain, is the cerebellum. The midbrain coordinates sensory representations of the visual, auditory, and somatosensory perceptual spaces. The pons is the main connection with the cerebellum. The pons and the medulla regulate several crucial functions, including the cardiovascular and respiratory systems and rates.<\/p>\n

The cranial nerves connect through the brain stem and provide the brain with the sensory input and motor output associated with the head and neck, including most of the special senses. The major ascending and descending pathways between the spinal cord and brain, specifically the cerebrum, pass through the brain stem.<\/p>\n

Medulla Oblongata<\/h3>\n

The medulla oblongata (or just medulla) is the region known as the myelencephalon in the embryonic brain. The initial portion of the name, \u201cmyel,\u201d refers to the significant white matter found in this region\u2014especially on its exterior, which is continuous with the white matter of the spinal cord.\u00a0 The medulla itself is directly attached to the spinal cord, and represents the most inferior area of the brain.<\/p>\n

\"Cross<\/a><\/p>\n

Figure 2.<\/strong> Cross section through medulla.<\/p>\n<\/div>\n

On the anterior side of the medulla are a pair of large tracts of white matter call the pyramids (Figures 2).\u00a0 The pyramids contain axons of somatic motor neurons from the cerebrum that are transmitting signals through the medulla and towards the spinal cord.\u00a0 At the pyramids, 75-90% of the motor axons decussate, or switch sides so that those that originated on the right cerebral hemisphere move to the left and vice versa.\u00a0 Also visible from the ventral view are a pair of areas of grey matter called the olives (Figures 2).\u00a0 The olives are responsible for relaying sensory information to the cerebellum.\u00a0 Other important areas of grey matter in the medulla include the nucleus cuneatus and nucleus gracilis, both of which are used for relaying sensations to the thalamus to be perceived in the cerebral cortex.<\/p>\n

\"\"<\/a><\/p>\n

Figure 3.<\/strong> Cross section through the inferior area of the medulla.<\/p>\n<\/div>\n

A diffuse region of gray matter known as the\u00a0reticular formation\u00a0<\/strong>extends from the medulla into the pons and midbrain.\u00a0 It\u00a0is related to sleep and wakefulness, general brain activity and attention.\u00a0 In brain injuries that damage the reticular formation, individuals fall into a coma as they are unable to generate a state of wakefulness.\u00a0 Within the reticular formation of the medulla are other areas of grey matter that include a cardiovascular center which regulates heart rate and blood pressure, a respiratory center that works in conjunction with the pons to involuntarily regulate breathing rate.\u00a0 Additionally, other centers act to generate involuntary actions in the body such as vomiting, sneezing, hiccuping, and coughing.<\/p>\n

Cranial nerves whose nuclei can be found in the medulla include the vestibulocochlear (VIII), glossopharyngeal (CN IX), vagus (CN X), and hypoglossal (XII).\u00a0(Figure 7)<\/p>\n

Pons<\/h3>\n

The word pons comes from the Latin word for bridge. It is visible on the anterior surface of the brain stem as the thick bundle of white matter. The pons is the main connection between the cerebrum, cerebellum and the brain stem. Large tracts within the pons include the cerebellar peduncles, which carry axons for motor and sensory signals to the the cerebellum.\u00a0 Pyramidal motor tracts in the pons carry somatic motor signals from the cerebrum along a descending path towards the medulla.<\/p>\n

\"Sagittal<\/a><\/p>\n

Figure 4.<\/strong> Sagittal view of the brainstem showing corticopontine fibers relaying motor signals to the pontine nuclei, which then communicate with the cerebellum via the middle cerebellar peduncle.<\/p>\n<\/div>\n

The bridge-like white matter is only on the anterior surface of the pons; the gray matter beneath that is a continuation of the tegmentum from the midbrain. Gray matter in the tegmentum region of the pons contains neurons receiving descending input from the cerebral cortex from corticopontine fibers to an area called the pontine nuclei.\u00a0 The pontine nuclei relay motor signals from the cerebrum to the cerebellum via axons in the middle cerebellar peduncle (Figure 4).\u00a0 This allows the cerebellum to modify and correct voluntary muscle movements initiated in the cerebrum.\u00a0 In addition, the reticular formation extends into the pons and forms a respiratory center that works together with that found in the medulla.<\/p>\n

Cranial nerves whose nuclei are found in the pons include the trigeminal (CN V), abducens (CN VI), and facial (CN VII).\u00a0(Figure 7)<\/p>\n

Midbrain<\/h3>\n

One of the original regions of the embryonic brain, the midbrain is a small region between the thalamus and pons. It is separated into the\u00a0tectum<\/strong>\u00a0and\u00a0tegmentum<\/strong>, from the Latin words for roof and floor, respectively. The cerebral aqueduct passes through the center of the midbrain, such that these regions are the roof and floor of that canal.<\/p>\n

The tectum is composed of four bumps known as the corpora quadrigemina.\u00a0 Each pair of bumps are called colliculi (singular = colliculus), which means \u201clittle hill\u201d in Latin. The\u00a0inferior colliculi<\/strong>\u00a0are the inferior pair of these enlargements and is part of the auditory brain stem pathway (Figure 5). Neurons of the inferior colliculi project to the thalamus, which then sends auditory information to the cerebrum for the conscious perception of sound.\u00a0 The inferior colliculi also process sudden sounds to produce a reflex reaction by which the head and eyes involuntarily turn towards the sound.\u00a0 If you were sitting quietly taking a test and heard the person next to you drop their pencil, the sudden sound would cause your inferior colliculi to turn your head and eyes towards the pencil where it sat on the floor.\u00a0 The\u00a0superior colliculi<\/strong>\u00a0are the superior pair and combine sensory information about visual space (Figure 5). Activity in the superior colliculi is related to orienting the eyes to track a moving object, to scan an area when looking for something, or to track words on a page while reading.\u00a0 If you were searching a crowded room to locate your friend, the pattern with which your eyes scanned the room would be controlled by the superior colliculi.<\/p>\n

\"Posterior<\/a><\/p>\n

Figure 5.<\/strong> Posterior view of brainstem and inferior diencephalon.<\/p>\n<\/div>\n

The tegmentum is continuous with the gray matter of the rest of the brain stem. Throughout the midbrain, pons, and medulla, the tegmentum contains the nuclei that receive and send information through the cranial nerves, as well as regions that regulate important functions such as those of the cardiovascular and respiratory systems.<\/p>\n

Important areas of grey matter on the interior of the midbrain include the red nucleus and the substantia nigra (Figure 6).\u00a0 The red nucleus is a region that possesses a reddish color due to the abundance of blood vessels that flow through this area.\u00a0 Functionally, the red nucleus plays a role in producing involuntary skeletal muscle contractions.\u00a0 The substantia nigra is also visually distinctive in that it possesses neurons with melanin, giving this group of neurons a darker appearance.\u00a0 The neurons of the substantia nigra produce dopamine, which is transported via their axons to the basal nuclei of the cerebrum where the dopamine is used to regulate motor signals.<\/p>\n

\"Cross<\/a><\/p>\n

Figure 6.<\/strong> Cross section through the midbrain showing the superior colliculus, red nucleus, substantia nigra, and cerebral aquaduct.<\/p>\n<\/div>\n

Areas of white matter include the cerebral peduncles, which can be seen on the anterior view of the midbrain, and the cerebellar peduncles.\u00a0 The cerebral peduncles transmit motor signals along axons from the cerebrum to the midbrain.\u00a0 The cerebellar peduncles allow for communication of sensory and motor signals from the cerebellum to the midbrain and other parts of the brainstem. (Figure 7)<\/p>\n

Cranial nerve nuclei found in the midbrain include those for the oculomotor nerve (CN III) and the trochlear nerve (CN IV). (Figure 7)<\/p>\n

 <\/p>\n

\"Anterior<\/a><\/p>\n

Figure 7.<\/strong> Anterior view of the brainstem and inferior portion of diencephalon.<\/p>\n<\/div>\n\n\t\t\t

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Candela Citations<\/h3>\n\t\t\t\t\t
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