Medulla Oblongata

Overview:

The brain is one of the most remarkable organs of the body, as it is the controller and coordinator of the body’s functions. It is divided into forebrain, hindbrain and midbrain. The hindbrain is divided further into pons, cerebellum and the medulla oblongata.

The medulla oblongata (or simply medulla) is among the three brainstem areas. It is the most inferior part of the three and connects to the pons above it and the spinal cord beneath. The medulla is home to important ascending and descending nerve passages, and also brainstem nuclei.

It is crucial in transmitting messages between the brain and the spinal cord. It is also necessary for the proper functioning of the respiratory system as well as the cardiovascular system. Damage to your medulla oblongata can result in respiratory malfunction, paralysis, or loss of sensory experiences. 

In this article, the location, structure and function of the medulla oblongata are discussed along with some disease conditions that involve this part of the hindbrain.

Summary:

  • The medulla oblongata is a nerve cell that regulates a variety of involuntary functions
  • It is present at the bottom portion of both the brainstem and the hindbrain, and it is where the brain connects to the spinal cord
  • The medulla is split into two categories: the ventral medulla (the frontal part) and the dorsal medulla (the back portion)
  • It is about three centimetres (3 cm) long and two centimetres (2cm) wide
  • The medulla oblongata is essential for signal transmission between the spinal cord and higher areas of the brain
  • It helps in regulating autonomic operations including respiration and heartbeat.
  • Injury problems or disease of the medulla can result in diseases such as lateral medullary syndrome, Dejerine syndrome, Bilateral medial medullary syndrome and Reinhold syndrome.

Location:

The medulla oblongata is a structure that is present in the brain stem that is anterior to, or in simpler terms, in front of the cerebellum.

The Hindbrain and its parts:

One of the brain’s three major regions is the hindbrain. The other two regions are the Forebrain and the midbrain. The hindbrain is located in the lower back area of the brain. It contains the majority of the brainstem as well as the cerebellum, which is a thick and complex looking structure. Because of its important role in connecting the brain to the spinal cord and coordinating several vital functions, including heart rate and breathing, the brainstem is among the most important components of the whole central nervous system. The hindbrain is divided into three sections: the pons, the cerebellum, and the medulla oblongata (Figure 1).

Figure 1. The three parts that make up the hindbrain are the pons, the cerebellum and the medulla oblongata.The midbrain, together with two parts of the hindbrain, forms the brainstem. These two parts are the pons and the medulla oblongata.

The pons: The pons perform the important task of connecting the cerebral cortex to the rest of the brainstem.  It is a protruding structure that resides directly beneath the midbrain and works to provide a coordination centre for messages and communications that circulate between the two different brain hemispheres and the spinal cord.

Cerebellum:

This part of the hindbrain comprises Purkinje cells, which are particularly unique nerve cells that can process multiple signals simultaneously due to their highly complicated dendrite divisions. The cerebellum is responsible for coordinating the sensations of the body with muscle reactions, allowing the body to perform the majority of our voluntary movements.

Medulla oblongata:

The medulla oblongata is a nerve cell mass that is shaped in the form of a cone located in the hindbrain that regulates a variety of involuntary, or in more technical terms, autonomic functions. This portion of the brain aids in the transmission of signals from different parts of the body to the spinal cord and the thalamus, which is located within the brain. The medulla oblongata is the bottom portion of both the brainstem and the hindbrain, and it is where the brain connects to the spinal cord. If measurements are considered, then it should be made clear that the medulla is only about three centimetres (3cm) in length. However, this relatively small dimension is in no way a reflection of its functions, as the medulla oblongata is an essential nerve tract that comprises the control centres for the autonomic crucial functions. Some of these essential functions include:

  • Heart rate
  • Breathing
  • Blood pressure

Besides its involvement in the above-mentioned processes, it also contains the controlling centres of many involuntary reflexes such as sneezing or swallowing.

Structure:

We now know that the medulla oblongata (also known as the medulla) is the lowest area of the brain and the brainstem. The medulla oblongata is linked to the midbrain region by another part of the hindbrain mentioned above, known as the pons. This makes it continuous with the spinal cord on the posterior side with which it combines at the opening at the base level of the skull. This opening is called the foramen magnum. 

Foramen Magnum: The foramen magnum is a central nervous system route through the skull that connects the brain to the spinal cord (Figure 2). The foramen magnum is the largest foramen (opening) present in the skull. It contains:

  • The medulla oblongata: The medulla oblongata is essential for signal transmission between the spinal cord and the brain.
  • The meninges: The spinal cord and brain are protected by these three layers of membranes called the meninges. The pia mater is the delicate inner layer. The arachnoid is the middle layer, which is a web-like framework full of fluid that blankets the brain. The dura mater is the resilient outer layer.
  • Vertebral arteries: The vertebral arteries are the major arteries that run through the neck.
  • Anterior spinal arteries: The anterior spinal artery is responsible for providing the spinal cord’s anterior part with blood.
  • Posterior spinal arteries: These arteries are responsible for supplying the grey and white columns of the spinal cord that is located posteriorly.
  • The spinal root of cranial nerve XI: This nerve supplies the muscles, which perform a variety of functions such as rotating the head away from the side of the contracting muscle. Tilting the head in the direction of the contracting muscle.
  • Alar ligaments: The alar ligaments’ function is to restrict the amount of movement and rotation of the head, and they connect the skull to the axis, the second cervical vertebra, by acting on the dens of the axis. The tectorial membrane: The tectorial membrane (TM) is a connective tissue that protects the structurally fragile and sensitive hair bundles of the inner ear’s sensory receptor cells.
Figure 2. The Foramen Magnum

The lower surface of the brain’s fourth ventricle is formed by the top of the medulla. Ventricles are voids filled with cerebral spinal fluid (CSF) that aid in the supply of nutrients to the brain.  

The medulla is split into two categories:

  • the ventral medulla (the frontal part)
  • the dorsal medulla (the back portion)

The dorsal medulla is also known as the tegmentum (Figure 3). The pyramidal tracts are located within a pair of triangular structures called pyramids in the ventral medulla (the frontal part). The pyramidal tracts are constituted of the corticospinal and the corticothalamic tract. The corticospinal tract runs from the cerebral cortex to the spinal cord, whereas the corticothalamic tract runs from the motor cortex of the frontal lobe to the cranial nerves that are present in the brainstem’s region.

Figure 3. The dorsal medulla, also known as the Tegmentum. The dorsal side of the midbrain is known as the tectum. 

The vast majority, approximately eighty to ninety per cent (80%-90%) of corticospinal tracts cross in the lower part of the medulla, right above the intersection with the spinal cord. This helps in forming the decussation of the pyramids. The ventral medulla is also the place where the olivary bodies are present. The olivary bodies (also referred to as olives) are located laterally on the pyramids (Figure 4). This is the point where the medullary pyramids’ motor fibres pass the midline. The fibres then travel into the spinal cord in the form of the corticospinal tract.

Fourth Ventricle: The lower region of the 4th (fourth) ventricle is established by the upper part of the dorsal medulla. The fourth ventricle is a cavity that is filled by the CSF (cerebrospinal fluid) formed by the expansion of the central canal of the spinal cord when it is entering the brain. It is present in a diamond-like shape.  The fourth ventricle, just like the spinal cord, is enveloped by white matter on the outside region, while the grey matter is present on the inside.

  • White matter: It includes nerve fibres called axons, which are nerve cell (or neurons) projections.  Most of these nerve fibres are encased in a sheath or covering known as myelin. Myelin is responsible for the colour of white matter. This also helps in the protection of nerve fibres from damage. The transmission and speed of electrical nerve impulses along nerve cell extensions (known as axons) are also improved significantly. 
  • Grey matter: Grey matter is tissue found on the brain’s (cortical) surface. It includes the neuronal cell bodies that give grey matter its colour. This type of brain tissue is found in abundance in the cerebellum, cerebrum, and brain stem (which includes the medulla oblongata). It is also responsible for the butterfly-shaped part of the central spinal cord.

The dorsal medulla is also the place of origin for the last 7 cranial nerves. The majority of these cranial nerves exit the medulla ventrally. The medulla is made up of both myelinated (white matter) and unmyelinated (grey matter) nerve fibres, and, like other systems in the brainstem, the white matter of the medulla is intertwined with the grey matter, eventually leading to a portion of the reticular formation. The reticular formation is a network of neuron clusters that are linked together within the brainstem.

The anterior median fissure, which runs the length of the spinal cord, is positioned in the middle line of the medulla. The decussation of the pyramids, however, briefly interrupts it. Two sulci (in the cerebral cortex, a groove or a depression is called a sulcus) are noticeable as one move away from the middle line (Figure 4):

  • The ventrolateral sulcus: The ventrolateral sulcus (also called the anterolateral sulcus) is a sulcus on one of the medulla oblongata’s side. This sulcus is where the root divisions of cranial nerve XII (which is known as the hypoglossal nerve) arise.
  • The posterolateral sulcus: The posterior nerve roots are affixed along a vertical crevice called the posterolateral sulcus on either side of the spinal cord’s posterior median sulcus and at a small distance from it.
Figure 4. Different structures around the Medulla oblongata

Size and dimensions:

The medulla is conical in shape and narrows as it stretches inferiorly. At its widest point, it is about three centimetres (3 cm) long and two centimetres (2 cm) wide. The medulla oblongata accounts for only 0.5 per cent of the total weight of a person’s brain.

Functions:

Despite the relatively small size, the medulla oblongata serves a variety of important functions. The medulla oblongata is essential for signal transmission between the spinal cord and higher areas of the brain, as well as for regulating autonomic operations including respiration and heartbeat.

The reticular formation’s neurons are crucial in the transfer of sensory and motor impulses. The medulla performs complicated integrative operations; for instance, various structural centres have specific functions in controlling autonomic nervous operations, controlling and regulating the process of respiration, digestive processes and heart rate.

Certain activities of nerve cells in the medulla involve movement control, the transmission of somatic sensory input from internal organs and tissues, and control of arousal and sleep.

Complications that involve Medulla oblongata:

Injury problems or disease of the lateral medulla can result in lateral medullary syndrome (otherwise known as the Wallenberg syndrome). In this syndrome, there is a damage of pain and temperature sensory experiences, which results in the affected person completely losing their pain and temperature senses.

If a section of the medulla is harmed, the body may be unable to relay a particular type of information or message between the body and its brain. These spinal tracts carry these kinds of data:

  • pain and sensory perception
  • proprioception (The sense of self-movement and position of the body, also known as kinaesthesia)
  • vibration interpretation
  • the tone of the muscles
  • pressure perception
  • abrasive touch
  • the function of the eyes
  • a sensitive touch
  • conscious muscle control and coordination
  • balance

In the medulla, motor neurons pass from the left side of the brain to the right side of a person’s spine. If somehow a person damages the left side of their medulla (because of an accident or some other injury), they will lose motor function on their right side. Comparably, if the right side of the medulla is compromised, the left side of your body will suffer.

If the medulla is harmed, the spinal cord and brain will be unable to communicate more effectively.

Destruction of the medulla oblongata can result in:

  • breathing difficulties
  • impairment of the tongue
  • throwing up/vomiting
  • Gagging, sneezing, or coughing reflexes are lost.
  • swallowing difficulties
  • muscle control and coordination loss
  • problems with balance
  • hiccups that are difficult to control
  • sensation loss in the body parts, such as  trunk, limbs or face

If the medulla is damaged as a result of a stroke, brain degenerative changes, or an abrupt head trauma/injury, a range of problems can arise. The symptoms that appear are determined by the specific part of the medulla that has been harmed.

Some conditions that involve damage to the medulla oblongata are described below.

1. Wallenberg syndrome: Wallenberg syndrome, also recognized as a lateral medullary syndrome, is a neurological condition. It is frequently caused by a stroke close to the medulla. Wallenberg syndrome is characterized by the following symptoms:

  • hiccups( that are uncontrollable)
  • swallowing problems
  • dizziness
  • numbness on one side of the body 
  • throwing up/vomiting
  • difficulty in balance
  • nausea
  • pain and temperature sensation loss in one half of the face

2. Bilateral medial medullary syndrome: This is an infrequent and uncommon stroke complicated condition. Just a small percentage of people who have strokes in the back of their brain develop this situation. Among the symptoms are:

  • all four limbs are paralysed
  • failure of the respiratory system
  • dysfunction of the tongue

3.  Reinhold syndrome:  This is also known as hemimedullary syndrome and it is extremely uncommon. In the research records, there are only around ten patients who have established this condition. Among the symptoms are:

  • loss of sensation on one side of the face
  • paralysis
  • throwing up/vomiting
  • one side suffers from sensory loss
  • Horner’s syndrome (a pretty unusual disorder characterized by a constriction of the pupil, drooping upper eyelids, and slumping of the eyeball into the bony chamber that helps protect the eye, as well as a lack of facial sweating)
  • muscle control loss on one side
  • nausea
  • speaking challenges/difficulties

4.    Dejerine syndrome: This is also known as a medial medullary syndrome, and is a rare problem that affects less than 1 per cent of people who’ve had strokes in the back of their brain. Among the symptoms are:

  • Arm and leg weakness on the opposite side of the brain damage area
  • Damage to the opposite side of the brain results in a loss of sensory experience
  • Limb paralysis on the opposite side of the brain injury
  • On the same side, tongue weakness

Conclusion:

The medulla oblongata is a very important part of the brain. It helps in regulating involuntary (or autonomic) functions such as respiration and heartbeat. It is present at the bottom portion of both the brainstem and the hindbrain, and it is where the brain connects to the spinal cord. The medulla is split into two categories: the ventral medulla (the frontal part) and the dorsal medulla (the back portion). The dorsal medulla is also known as the tegmentum. The pyramidal tracts are located within a pair of triangular structures called pyramids in the ventral medulla. The pyramidal tracts are constituted of the corticospinal and the corticothalamic tract. If the left side of the medulla is harmed, there will be a loss of motor function on the right side. Comparably, if the right side of the medulla is compromised, the left side of the body will suffer.

Reference list

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