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Medulla oblongata

Medulla oblongata

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The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla. The medulla contains the cardiac, respiratory
Respiratory center
The respiratory center is located in the medulla oblongata, which is the lowermost part of the brain stem. The RC receives controlling signals of neural, chemical and hormonal nature and controls the rate and depth of respiratory movements of the diaphragm and other respiratory muscles...

, vomiting
Area postrema
The area postrema is a medullary structure in the brain that controls vomiting. Its privileged location in the brain also allows the area postrema to play a vital role in the control of autonomic functions by the central nervous system.-Anatomy:...

 and vasomotor
Vasomotor
Vasomotor refers to actions upon a blood vessel which alter its diameter. More specifically, it can refer to vasodilator action and vasoconstrictor action....

 centers and deals with autonomic
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

, involuntary functions, such as breathing, heart rate and blood pressure.

Two parts: open and closed



The medulla is often thought of as being in two parts:
  • an open part or superior part where the dorsal surface of the medulla is formed by the fourth ventricle
    Fourth ventricle
    The fourth ventricle is one of the four connected fluid-filled cavities within the human brain. These cavities, known collectively as the ventricular system, consist of the left and right lateral ventricles, the third ventricle, and the fourth ventricle...

    .
  • a closed part or inferior part where the metacoel lies within the medulla oblongata.

Between the anterior median sulcus and the anterolateral sulcus


The region between the anterior median sulcus and the anterolateral sulcus is occupied by an elevation on either side known as the pyramid of medulla oblongata
Pyramid of medulla oblongata
The anterior or ventral portion of the medulla oblongata is named the pyramid and lies between the anterior median fissure and the antero-lateral sulcus....

. This elevation is caused by the corticospinal tract
Corticospinal tract
The corticospinal or pyramidal tract is a collection of axons that travel between the cerebral cortex of the brain and the spinal cord....

.

In the lower part of the medulla some of these fibers cross each other thus obliterating the anterior median fissure. This is known as the decussation of the pyramids
Decussation of the pyramids
The two pyramids contain the motor fibers that pass from the brain to the medulla oblongata and medulla spinalis, corticobulbar and corticospinal fibers....

.

Some other fibers that originate from the anterior median fissure above the decussation of the pyramids and run laterally across the surface of the pons are known as the external arcuate fibers.

Between the anterolateral and posterolateral sulci


The region between the anterolateral and posterolateral sulcus in the upper part of the medulla is marked by a swelling known as the Olivary body
Olivary body
In anatomy, the olivary bodies or simply olives are a pair of prominent oval structures in the medulla oblongata, the lower portion of the brainstem...

.

It is caused by a large mass of gray matter known as the inferior olivary nucleus
Inferior olivary nucleus
The inferior olivary nucleus is the largest nucleus situated in the olivary body, part of the medulla oblongata.-Function:It is closely associated with the cerebellum, meaning that it is involved in control and coordination of movements, sensory processing and cognitive tasks likely by encoding the...

.

Between the posterior median sulcus and the posterolateral sulcus


The posterior part of the medulla between the posterior median sulcus and the posterolateral sulcus contains tracts that enter it from the posterior funiculus of the spinal cord. These are the fasciculus gracilis
Fasciculus gracilis
The fasciculus gracilis is a bundle of axon fibres in the posterior column of the spinal cord and carries information from the middle thoracic and lower limbs of the body...

, lying medially next to the midline, and the fasciculus cuneatus
Fasciculus cuneatus
The fasciculus cuneatus is a tract of nerves in the spinal cord which primarily transmits information from the arms...

, lying laterally.

These fasciculi end in rounded elevations known as the gracile and the cuneate tubercles. They are caused by masses of gray matter known as the nucleus gracilis and the nucleus cuneatus.

Just above the tubercles, the posterior aspect of the medulla is occupied by a triangular fossa, which forms the lower part of the floor of the fourth ventricle
Fourth ventricle
The fourth ventricle is one of the four connected fluid-filled cavities within the human brain. These cavities, known collectively as the ventricular system, consist of the left and right lateral ventricles, the third ventricle, and the fourth ventricle...

. The fossa is bounded on either side by the inferior cerebellar peduncle
Inferior cerebellar peduncle
The upper part of the posterior district of the medulla oblongata is occupied by the inferior cerebellar peduncle , a thick rope-like strand situated between the lower part of the fourth ventricle and the roots of the glossopharyngeal and vagus nerves.Each cerebellar inferior peduncle connects the...

, which connects the medulla to the cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...

.

Lower part


The lower part of the medulla, immediately lateral to the fasciculus cuneatus, is marked by another longitudinal elevation known as the tuberculum cinereum
Tuberculum cinereum
It is a raised area between the rootlets of the accessory nerve and posterolateral sulcus. It overlies the spinal tract of trigeminal nerve....

.

It is caused by an underlying collection of gray matter known as the spinal nucleus of the trigeminal nerve.

The gray matter of this nucleus is covered by a layer of nerve fibers that form the spinal tract of the trigeminal nerve
Trigeminal nerve
The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...

.

Base


The base of the medulla is defined , the commissural fibers
Commissural fibers
The commissural fibers or transverse fibers connect the two hemispheres of the brain. They include:* the transverse fibers of the corpus callosum* the anterior commissure* the posterior commissure* the lyra or hippocampal commissure....

, crossing over from the ipsilateral side in the spinal cord to the contralateral side in the brain stem; below this is the spinal cord.

Functions


The medulla oblongata controls autonomic
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

 functions, and relays nerve signals between the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

 and spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...

. It is also responsible for controlling several major points and autonomic
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

 functions of the body:
  • respiration
    Respiration (physiology)
    'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...

     – chemoreceptors
  • cardiac center – sympathetic, parasympathetic system
  • vasomotor center – baroreceptors
  • reflex centers of vomiting, coughing, sneezing, and swallowing

Blood supply


Blood to the medulla is supplied by a number of arteries.
  • Anterior spinal artery
    Anterior spinal artery
    In human anatomy, the anterior spinal artery is the blood vessel that supplies the anterior portion of the spinal cord. It arises from branches of the vertebral arteries and is supplied by the anterior segmental medullary arteries, including the artery of Adamkiewicz, and courses along the anterior...

    : The anterior spinal artery supplies the whole medial part of the medulla oblongata. A blockage (such as in a stroke) will injure the pyramidal tract, medial lemniscus
    Medial lemniscus
    The medial lemniscus, also known as Reil's band or Reil's ribbon, is a pathway in the brainstem that carries sensory information from the gracile and cuneate nuclei to the thalamus.-Path:...

    , and the hypoglossal nucleus
    Hypoglossal nucleus
    The hypoglossal nucleus is a cranial nerve nucleus, and it extends the length of the medulla, and being a motor nucleus, is close to the midline...

    . This causes a syndrome called medial medullary syndrome
    Medial medullary syndrome
    Medial medullary syndrome, also known as inferior alternating syndrome, hypoglossal alternating hemiplegia, lower alternating hemiplegia, or Dejerine syndrome, is a type of alternating hemiplegia characterized by a set of clinical features resulting from occlusion of the anterior spinal artery...

    .
  • Posterior inferior cerebellar artery
    Posterior inferior cerebellar artery
    The posterior inferior cerebellar artery , the largest branch of the vertebral artery, is one of the three main arterial blood supplies for the cerebellum, part of the brain...

     (PICA): The posterior inferior cerebellar artery, a major branch of the vertebral artery, supplies the posterolateral part of the medulla, where the main sensory tracts run and synapse
    Synapse
    In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...

    . (As the name implies, it also supplies some of the cerebellum
    Cerebellum
    The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...

    .)
  • Direct branches of the vertebral artery
    Vertebral artery
    The vertebral arteries are major arteries of the neck. They branch from the subclavian arteries and merge to form the single midline basilar artery in a complex called the vertebrobasilar system, which supplies blood to the posterior part of the circle of Willis and thus significant portions of the...

    : The vertebral artery supplies an area between the other two main arteries, including the nucleus solitarius and other sensory nuclei and fibers. Lateral medullary syndrome
    Lateral medullary syndrome
    Lateral medullary syndrome is a disease in which the patient has a constellation of neurologic symptoms due to injury to the lateral part of the medulla in the brain, resulting in tissue ischemia and necrosis.-Signs and symptoms:This syndrome is characterized by sensory deficits affecting...

     can be caused by occlusion of either the PICA or the vertebral arteries.

Embryology


The medulla oblongata forms from the lower (caudal) half of the embryonic rhombencephalon
Rhombencephalon
The rhombencephalon is a developmental categorization of portions of the central nervous system in vertebrates.The rhombencephalon can be subdivided in a variable number of transversal swellings called rhombomeres...

. Neuroblast
Neuroblast
A neuroblast is a dividing cell that will develop into neurons or glia. The characterisation of neuroblasts and their development in Drosophila melanogaster was widely achieved by Chris Doe, Corey Goodman and Mike Bate. In humans, neuroblasts produced by stem cells in the adult subventricular zone...

s from the alar plate of the neural tube
Neural tube
In the developing vertebrate, the neural tube is the embryo's precursor to the central nervous system, which comprises the brain and spinal cord...

 at this level will produce the sensory nuclei of the medulla. The basal plate neuroblasts will give rise to the motor nuclei.
  • Alar plate
    Alar plate
    The alar plate is a neural structure in the embryonic nervous system, part of the dorsal side of neural tube, that involves the communication of general somatic and general visceral sensory impulses. The caudal part later becomes sensory axon part of the spinal cord.-External links:* *...

     neuroblasts give rise to:
    • The solitary nucleus
      Solitary nucleus
      The solitary tract and nucleus are structures in the brainstem that carry and receive visceral sensation and taste from the facial , glossopharyngeal and vagus cranial nerves.-Anatomy:...

      , which contains the general visceral afferent fibers
      General visceral afferent fibers
      The general visceral afferent fibers conduct sensory impulses from the viscera, glands, and blood vessels to the central nervous system. They are considered to be part of the autonomic nervous system...

       (GVA) for taste
      Taste
      Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....

      , as well as the special visceral afferent
      Special visceral afferent
      ' refers to afferent nerves that develop in association with the gastrointestinal tract. They carry the special senses of smell and taste . The cranial nerves containing SVA fibers are the olfactory nerve , the facial nerve , the glossopharyngeal nerve and the vagus nerve...

       (SVA) column.
    • The spinal trigeminal nerve nuclei
      Trigeminal nerve nuclei
      The sensory trigeminal nerve nuclei are the largest of the cranial nerve nuclei, and extend through the whole of the midbrain, pons and medulla.The nucleus is divided into three parts, from rostral to caudal :...

       which contains the general somatic afferent column
      General somatic afferent fibers
      The general somatic afferent fibers , afferent fibers, arise from cells in the spinal ganglia and are found in all the spinal nerves, except occasionally the first cervical, and conduct impulses of pain, touch and temperature from the surface of the body through the posterior roots to the spinal...

       (GSA).
    • The cochlear
      Cochlear nuclei
      The cochlear nuclei are two heterogeneous collections of neurons in the mammalian brainstem that receive input from the cochlear nerve, which carry sound information from the cochleae...

       and vestibular nuclei
      Vestibular nuclei
      The vestibular nuclei are the cranial nuclei for the vestibular nerve.In Terminologia Anatomica they are grouped in both the pons and medulla.-Subnuclei:There are 4 subnuclei; they are situated at the floor of the fourth ventricle....

      , which contain the special somatic afferent
      Special somatic afferent
      Special somatic afferent refers to afferent nerves that carry information from the special senses of vision, hearing and balance. The cranial nerves containing SSA fibers are the optic nerve and the vestibulocochlear nerve...

       (SSA) column.
    • The inferior olivary nucleus
      Inferior olivary nucleus
      The inferior olivary nucleus is the largest nucleus situated in the olivary body, part of the medulla oblongata.-Function:It is closely associated with the cerebellum, meaning that it is involved in control and coordination of movements, sensory processing and cognitive tasks likely by encoding the...

      , which relays to the cerebellum
      Cerebellum
      The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...

      .
    • The dorsal column nuclei
      Dorsal column nuclei
      In neuroanatomy, the dorsal column nuclei are a pair of nuclei in the brainstem. The name refers collectively to the cuneate nucleus and gracile nucleus, which are present at the junction between the spinal cord and the medulla oblongata...

      , which contain the gracile
      Gracile nucleus
      Located in the medulla oblongata, the gracile nucleus is one of the dorsal column nuclei that participate in the sensation of fine touch and proprioception of the lower body...

       and cuneate nuclei.
  • Basal plate
    Basal plate
    Basal plate may refer to:* Basal plate , the region of the neural tube ventral to the sulcus limitans* Basal plate , between this plate and the uterine muscular fibres are the stratum spongiosum and the boundary layer...

     neuroblasts give rise to:
    • The hypoglossal nucleus
      Hypoglossal nucleus
      The hypoglossal nucleus is a cranial nerve nucleus, and it extends the length of the medulla, and being a motor nucleus, is close to the midline...

      , which contains general somatic efferent fibers
      General somatic efferent fibers
      The *spinal* somatic efferent neurons , arise from motor neuron cell bodies in the ventral horns of the gray matter within the spinal cord...

       (GSE).
    • The nucleus ambiguus
      Nucleus ambiguus
      The nucleus ambiguus is a region of histologically disparate cells located just dorsal to the inferior olivary nucleus in the lateral portion of the upper medulla...

      , which form the special visceral efferent
      Special visceral efferent
      Special visceral efferent refers to efferent nerves which supply muscles which derived from the branchial arches.Some sources prefer the term "branchiomotor", or "branchial efferent"....

       (SVE).
    • The dorsal nucleus of vagus nerve and the inferior salivatory nucleus
      Inferior salivatory nucleus
      In the brain, the inferior salivatory nucleus is a cluster of neurons controlling the parasympathetic input to the parotid gland. It is one of the components of the glossopharyngeal nerve .-Location:...

      , both of which form the general visceral efferent fibers
      General visceral efferent fibers
      The general visceral efferent fibers , probably arise from cells in the lateral column or the base of the anterior column and emerge through the anterior roots and white rami communicantes....

      .

Evolution Theory


Both lampreys and hagfish possess a fully developed medulla oblongata. Since these are both very similar to early agnathans, it has been suggested that the medulla evolved in these early fish, approximately 505 million years ago.

External links