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Encyclopedia > Brain stem
Brain: Brain stem
Latin truncus encephali
Gray's subject #187
Part of Brain
Components Medulla, Pons, Midbrain
NeuroNames ancil-218
MeSH Brain+Stem
Dorlands/Elsevier b_21/12195821

The brain stem is the lower part of the brain, adjoining and structurally continuous with the spinal cord. Most sources consider the pons, medulla oblongata, and midbrain all to be part of the brainstem.[1] Image File history File links Gray719. ... For other uses, see Latin (disambiguation). ... For other uses, see Brain (disambiguation). ... Medulla in general means the inner part, and derives from the Latin word for marrow. In medicine it is contrasted to the cortex. ... For other uses, see Pons (disambiguation). ... In biological anatomy, the mesencephalon (or midbrain) is the middle of three vesicles that arise from the neural tube that forms the brain of developing animals. ... NeuroNames is a system of nomenclature for the brain and related structures. ... Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ... Elseviers logo. ... For other uses, see Brain (disambiguation). ... The Spinal cord nested in the vertebral column. ... For other uses, see Pons (disambiguation). ... The medulla oblongata is the lower portion of the brainstem. ... In biological anatomy, the mesencephalon (or midbrain) is the middle of three vesicles that arise from the neural tube that forms the brain of developing animals. ...


Differentiation of the brain stem from the cerebrum is complex, with regard to both anatomy and taxonomy. Some taxonomies describe the brain stem as the medulla and mesencephalon, whereas others include diencephalic regions. The telencephalon (te-len-seff-a-lon) is the technical name for a large region within the brain which is attributed many functions, which some groups would class as unique features which make humans stand out from other species. ... The diencephalon is the region of the brain that includes the thalamus, hypothalamus, epithalamus, prethalamus or subthalamus and pretectum. ...

Contents

General anatomy

Ventral view/medulla and

The most medial part of the medulla is the anterior median fissure. Moving laterally on each side are the pyramids. The pyramids contain the fibers of the corticospinal tract, or the upper motor neuronal axons as they head inferiorly to synapse on lower motor neuronal cell bodies within the ventral horn of the spinal cord.
The anterolateral sulcus is lateral to the pyramids. Emerging from the anterolateral sulci are the hypoglossal nerve (CN XII) rootlets. Lateral to these rootlets and the anterolateral sulci are the olives. The olives are swellings in the medulla containing underlying inferior olivary nuclei (containing various nuclei and afferent fibers). Lateral (and dorsal) to the olives are the rootlets for cranial nerves IX and X (glossopharyngeal and vagus, respectively). The pyramids end at the pontomedullary junction, noted most obviously by the large basal pons. Between the basal pons, cranial nerve 6, 7 and 8 emerge (medial to lateral). These cranial nerves are the abducens nerve, facial nerve and the vestibulocochlear nerve, respectively. At the level of the midpons, the large trigeminal nerve, CN V, emerges. At the rostral pons, the occulomotor nerve emerges at the midline. Laterally, the trochlear nerve has emerged after emerging out of the dorsal rostral pons and wrapping around to the anterior. The corticospinal or pyramidal tract is a massive collection of axons that travel between the cerebral cortex of the brain and the spinal cord. ... The anterior horn is the anterior division of the lateral ventricle of the brain. ... The hypoglossal nerve is the twelfth cranial nerve. ... In anatomy, the olivary bodies or simply olives (Latin oliva and olivae, singular and plural, respectively) are a pair of prominent oval structures in the medulla oblongata, the lower portion of the brainstem. ... Grays FIG. 791 - Plan of upper portions of glossopharyngeal, vagus, and accessory nerves. ... The vagus nerve is tenth of twelve paired cranial nerves and is the only nerve that starts in the brainstem (somewhere in the medulla oblongata) and extends all the way down past the head, right down to the abdomen. ... The sixth of twelve cranial nerves, the abducens nerve is a motor nerve that innervates the lateral rectus muscle and therefore controls each eyes ability to abduct (move away from the midline). ... The facial nerve is the seventh (VII) of twelve paired cranial nerves. ... The vestibulocochlear nerve (also known as the auditory or acoustic nerve) is the eighth of twelve cranial nerves, and is responsible for transmitting sound and equilibrium (balance) information from the inner ear to the brain. ... The trigeminal nerve is the fifth (V) cranial nerve, and carries sensory information from most of the face, as well as motor supply to the muscles of mastication (the muscles enabling chewing), tensor tympani (in the middle ear), and other muscles in the floor of the mouth, such as the... The oculomotor nerve () is the third of twelve paired cranial nerves. ... The fourth of twelve cranial nerves, the trochlear nerve controls the function of the superior oblique muscle, which rotates the eye away from the nose and also moves the eye downward. ...


Dorsal view/medulla and pons

The most medial part of the medulla is the posterior median fissure. Moving laterally on each side is the fasciculus gracilis, and lateral to that is the fasciculus cuneatus. Superior to each of these, and directly inferior to the obex, are the gracile tubercles and cuteanus tubercles, respectively. Underlying these are their respective nuclei. The obex marks the end of the 4th ventricle and the beginning of the central canal. The posterior intermediate sulci separates the fasciculi gracilis from the fasciculi cuneatus. Lateral to the fasciculi cuneatus is the lateral funiculus.
Superior to the obex is the floor of the 4th ventricle. In the floor of the 4th ventricle, various nuclei can be visualized by the small bumps that they make in the overlying tissue. In the midline and directly superior to the obex is the vagal trigone and superior to that it the hypoglossal trigone. Underlying each of these are motor nuclei for the respective cranial nerves. Superior to these trigones are fibers running laterally in both directions. These fibers are known collectively as the striae medullares. Continuing in a rostral direction, the large bumps are called the facial colliculi. Each facial colliculus, contrary to their names, do not contain the facial nerve nuclei. Instead, they have facial nerve axons traversing superficial to underlying abducens (CN VI) nuclei. Lateral to all these bumps previously discussed is an indented line, or sulcus that runs rostrally, and is known as the sulcus limitans. This separates the medial motor neurons from the lateral sensory neurons. Lateral to the sulcus limitans is the area collectively known as the vestibular area, which is involved in special sensation. Moving rostrally, the inferior, middle, and superior cerebellar peduncles are found connecting the midbrain to the cerebellum. Directly rostral to the superior cerebellar peduncle, there is the superior medullary velum and then the two trochlear nerves. This marks the end of the pons as the inferior colliculus is directly rostral and marks the caudal midbrain. The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... The fasciculus cuneatus (tract of Burdach) is triangular on transverse section, and lies between the fasciculus gracilis and the posterior column, its base corresponding with the surface of the medulla spinalis. ... IrOBEX (or just OBEX) is a communications protocol that facilitates the exchange of binary objects between devices. ... Cross-section through cervical spinal cord. ... The most lateral of the bundles of the anteior nerve roots is generally taken as a dividing line which separates the antero-lateral region into two parts, viz. ... The cells of the dorsal nucleus are spindle-shaped, like those of the posterior column of the spinal cord, and the nucleus is usually considered as representing the base of the posterior column. ... In the upper part of the medulla oblongata, the hypoglossal nucleus approaches the rhomboid fossa, where it lies close to the middle line, under an eminence named the hypoglossal trigone. ... In zootomy, several terms are used to describe the location of organs and other structures in the body of bilateral animals. ... The facial colliculus is an elevated area located on the dorsal medulla. ... Sulcus (pl. ... In the fourth ventricle, the sulcus limitans forms the lateral boundary of the medial eminence. ... The paired inferior colliculi together with the superior colliculi form the eminences of the corpora quadrigemina. ...


Spinal Cord to Medulla Transitional Landmark: From a ventral view, there can be seen a decussation of fibers between the two pyramids. This decussation marks the transition from medulla to spinal cord. Superior to the decussation is the medulla and inferior to it is the spinal cord. Decussation is used in biological contexts to describe a crossing. ... This is about the polyhedron. ...


Midbrain

The midbrain is divided into three parts. The first is the tectum, which is "roof" in Latin. The tectum includes the superior and inferior colliculi and is the dorsal covering of the cerebral aqueduct. The inferior colliculus, involved in the special sense of hearing sends its inferior brachium to the medial geniculate body of the diencephalon. Superior to the inferior colliculus, the superior colliculus marks the rostral midbrain. It is involved in the special sense of vision and sends its superior brachium to the lateral geniculate body of the diencephalon. The second part is the tegmentum and is ventral to the cerebral aqueduct. Several nuclei, tracts and the reticular formation is contained here. Last, the ventral side is comprised of paired cerebral peduncles. These transmit axons of upper motor neurons. The tectum is the dorsal part of the midbrain, derived in embryonic development from the alar plate of the neural tube. ... For other uses, see Latin (disambiguation). ... The paired inferior colliculi together with the superior colliculi form the eminences of the corpora quadrigemina. ... The medial geniculate nucleus is a nucleus of the thalamus that acts as a relay for auditory information. ... The diencephalon is the region of the brain that includes the epithalamus, thalamus, and hypothalamus. ... The superior colliculus is part of the brain that sits below the thalamus and surrounds the pineal gland in the mesencephalon of vertebrate brains. ... The lateral geniculate nucleus (LGN) of the thalamus is a part of the brain, which is the primary processor of visual information, received from the retina, in the CNS. Schematic diagram of the primate lateral geniculate nucleus. ... The midbrain tegmentum is part of the midbrain extending from the substantia nigra to the cerebral aqueduct. ... The cerebral peduncle, by most classifications, is everything in the mesencephalon except the tectum. ...


Midbrain internal structures

Periaqueductal Gray: The area around the cerebral aqueduct, which contains various neurons involved in the pain desensitization pathway. Neurons synapse here and, when stimulated, cause activation of neurons in the raphe nucleus magnus, which then project down into the dorsal horn of the spinal cord and prevent pain sensation transmission.
Occulomotor nerve nucleus: This is the nucleus of CN III.
Trochlear nerve nucleus: This is the nucleus of CN IV.
Red Nucleus: This is a motor nucleus that sends a descending tract to the lower motor neurons.
Substantia nigra: This is a concentration of neurons in the ventral portion of the midbrain that uses dopamine as its neurotransmitter and is involved in both motor function and emotion. Its dysfunction is implicated in Parkinson's Disease.
Reticular formation: This is a large area in the midbrain that is involved in various important functions of the midbrain. In particular, it contains lowermotor neurons, is involved in the pain desensitization pathway, is involved in the arousal and consciousness systems, and contains the locus ceruleus, which is involved in intensive alertness modulation and in autonomic reflexes.
Central tegmental tract: Directly anterior to the floor of the 4th ventricle, this is a pathway by which many tracts project up to the cortex and down to the spinal cord.
The red nucleus is a structure in the rostral midbrain involved in motor coordination. ... The substantia nigra, (Latin for black substance, Soemering) or locus niger is a heterogeneous portion of the midbrain, separating the pes (foot) from the tegmentum (covering), and a major element of the basal ganglia system. ... The reticular formation is a part of the brain which is involved in stereotypical actions, such as walking, sleeping, and lying down. ... The Locus ceruleus, also spelled locus caeruleus or locus coeruleus (Latin for the blue spot), is a nucleus in the brain stem responsible for physiological responses to stress and panic. ... Anatomy and Physiology of the A.N.S. In contrast to the voluntary nervous system, the involuntary or autonomic nervous system is responsible for homeostasis, maintaining a relatively constant internal environment by controlling such involuntary functions as digestion, respiration, and metabolism, and by modulating energy needed to cope with stressful...


Embryology

The adult human brainstem emerges from two of the three primary vesicles formed of the neural tube. The mesencephalon is the second of the three primary vesicles, and does not further differentiate into a secondary vesicle. This will become the midbrain. The third primary vesicle, the rhombencephalon, will further differentiate into two secondary vesicles, the metencephalon and the myelencephalon. The metencephalon will become the cerebellum and the pons. The myelencephalon will become the medulla. In the developing vertebrate nervous system, the neural tube is the precursor of the central nervous system, which comprises the brain and spinal cord. ... In biological anatomy, the mesencephalon (or midbrain) is the middle of three vesicles that arise from the neural tube that forms the brain of developing animals. ... The rhombencephalon (or hindbrain) is a developmental categorization of portions of the central nervous system in vertebrates. ... The metencephalon is a developmental categorization of portions of the central nervous system. ... The myelencephalon is a developmental categorization of a portion of the central nervous system. ...


Physiology

There are three main functions of the brainstem. The first is its role in conduit functions. That is, all information related from the body to the cerebrum and cerebellum and vice versa, must traverse the brain stem. The ascending pathways coming from the body to the brain are the sensory pathways, and include the spinothalamic tract for pain and temperature sensation and the dorsal column, fasciculus gracilis, and cuneatus for touch, proprioception, and pressure sensation (both of the body). (The facial sensations have similar pathways, and will travel in the spinothalamic tract and the medial lemniscus also). Descending tracts are upper motor neurons destined to synapse on lower motor neurons in the ventral horn and intermediate horn of the spinal cord. In addition, there are upper motor neurons that originate in the brainstem's vestibular, red, tactile, and reticular nuclei, which also descend and synapse in the spinal cord. Second, the cranial nerves 3-12 emerge from the brain stem. Third, the brain stem has integrative functions (it is involved in cardiovascular system control, respiratory control, pain sensitivity control, alertness, and consciousness). Thus, brain stem damage is a very serious and often life-threatening problem. The spinothalamic tract is a sensory pathway originating in the spinal cord that transmits information about pain, temperature, itch and crude touch to the thalamus. ... // Proprioception (PRO-pree-o-SEP-shun (IPA pronunciation: ); from Latin proprius, meaning ones own and perception) is the sense of the relative position of neighbouring parts of the body. ... The medial lemniscus, also known as Reils band or Reils ribbon, is a pathway in the brainstem that carries sensory information from the gracile and cuneate nuclei to the thalamus. ... The anterior horn is the anterior division of the lateral ventricle of the brain. ...


Physical signs of brainstem disease

Diseases of the brainstem can result to abnormalities in the function of cranial nerves, which may lead to visual disturbances, pupil abnormalities, changes in sensation, muscle weakness, hearing problems, vertigo, swallowing and speech difficulty, voice change, and co-ordination problems. Localizing neurological lesions in the brainstem may be very precise, although it relies on a clear understanding on the functions of brainstem anatomical structures and how to test them.[2]


See also

A cranial nerve nucleus is a collection of neurons (gray matter) in the brain stem that is associated with one or more cranial nerves. ... Location of the amygdala in the human brain Located in the brains medial temporal lobe, the almond-shaped amygdala (in Latin, corpus amygdaloideum) is believed to play a key role in the emotions. ...

References

  1. ^ http://wordnet.princeton.edu/perl/webwn?s=brainstem
  2. ^ http://www.asktheneurologist.com/lectures-brainstem.html

  Results from FactBites:
 
Human brain - Wikipedia, the free encyclopedia (2896 words)
Brain stem structures are almost completely enveloped by the cerebellum and telencephalon, with only the medulla oblongata visible as it merges with the spinal cord.
Nerves from the brain stem complex where autonomic functions are modulated join nerves routing messages to and from the cerebrum in a bundle that passes through the spinal column to related parts of a body.
Further, the molecular and cell biological examination of brain pathology is hindered by the scarcity of appropriate samples for study, the (usual) inability to biopsy the brain from a living person suffering from a malady, and an incomplete description of the brain's microanatomy.
Brain stem - Wikipedia, the free encyclopedia (224 words)
The lower part of the brain stem is the medulla oblongata, grossly comprising the medullary pyramids and the olivary bodies or olives.
Differentiation of the brain stem from the cerebrum is complex, both anatomically and taxonomically.
The brain stem is the stalk of the brain below the cerebral hemispheres.
  More results at FactBites »

 
 

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