Medulla Oblongata

The Brain Stem

This is a great picture of what was formerly called the brainstemThe lower part of the brain that connects to the spinal cord and controls vital functions.. It’s now called the diencephalonA brain region that includes the thalamus, hypothalamus, and epithalamus. metencephalon. You can use whatever cephalon word that you like. Whatever you collectively call these units does not diminish from the factA statement based on direct observation that is repeatedly confirmed. that they act separately. From superiorAbove or toward the upper part of the body. to inferiorBelow or toward the lower part of the body. we have the midbrainThe upper portion of the brainstem involved in visual and auditory processing. the ponds and the medulla oblongataThe lowest part of the brainstem controlling vital functions like breathing and heart rate.. You can see that the medulla oblongata transitions into the spinal cordThe central nervous system structure that relays signals between the brain and body. at its inferior most border. The blue areas in this diagram are the 4th ventricle and the cerebral aqueduct. This open area contains cerebrospinal fluid(CSF) – A fluid that cushions and nourishes the brain and spinal cord.. It is continuous with the central canalA hollow canal in an osteon containing blood vessels and nerves. known from spinal cord cross sections.

Medulla Oblongata Anatomy

The transverse section A cut or slice of the body or an organ for study. here on the left is a very superior cut of the medulla oblongata. The one on the right is more inferior. It is almost at the point where it changes over into the spinal cord.  This transverse section on the left is so superior, this open area is the 4^th ventricle.  This inferior transverse section has what will become the central canal.  This butt crack is the anterior median fissureA deep groove along the front of the spinal cord that divides it into two halves. and thus the ventralRelating to the front or belly side of the body. side and this is the dorsalRelating to the back side of the body. side.  There are two main anatomical structures of the medulla oblongata that are noteworthy.  The pyramids consist of motor neuronsNeurons that carry outgoing information from the CNS to effector organs.. They descend into the white matterThe outer portion of the spinal cord made of myelinated nerve fibers that transmit signals. motor pathways of the spinal cord. This is similar to the cerebrospinal tract.  These pyramids are directly lateralAway from the midline of the body. to the anteriorThe front of the body or toward the front when standing in the anatomical position. median fissureA deep groove in the brain’s surface..  The other noteworthy anatomical structure is the olives.  They are these squiggly lines here.  I don’t know what they do.  I’m kidding… These form a connection to the Purkinje cellsThe basic structural and functional units of life. of the cerebellumThe brain region responsible for balance, coordination, and fine motor control..  These olives are capable of sending sensory information to the cerebellum.

Medulla Oblongata White Matter

The white matter of the medulla oblongata consists of myelinated axons of spinal tractsBundles of nerve fibers in the CNS that carry signals between brain regions.. It also includes myelinated axons of cranial nervesNerves that arise from the brain and control head and neck functions., as with many of the other structures of the brain stem.  The white matter tracts that run through the medulla oblongata include the lateral spinothalamic tract, which carries conscious information. The corticospinal tractA descending motor pathway controlling voluntary movements. carries both conscious and subconscious information to skeletal muscles. 

The nucleiClusters of neurons in the CNS responsible for processing information. of cranial nerves, VIII, IX, X, and XII are housed in the medulla oblongata.  Go ahead and try….can  you recall what those cranial nerves are called?  VIII…IX…X…XII

Vestibulocochlear, glossopharyngeal, vagus, hypoglossal.

Medulla Oblongata Gray Matter

OK, back to gray matterThe inner portion of the spinal cord composed mostly of neuron cell bodies and synapses..  Sorry, I had to do the pyramids and olives before the white matter. I needed to finish the white matter before discussing this function of the gray matter of the medulla oblongata.  Check out this picture on the right.  This hand is receiving a sensation.  An action potentialA rapid, temporary electrical charge that travels along neurons, allowing signal transmission. travels up the red neuron. It is the 1^st order neuron in this sequence. Here, it enters into an ascending spinal tract.  The red neuron ends in the medulla oblongata. It synapses with another neuron, the neuron of the 2^nd order. This neuron then brings the action potential to, say, the thalamusThe brain’s relay center, sending sensory information to the cerebral cortex..  In the thalamus, the 2^nd order neuron synapses with a 3^rd order neuron. This 3^rd order neuron takes the action potential to the correct place in the brain. The brain then assigns some perception to the sensation.  This neuron of the second order is important.  First, it is an interneuron because it is completely contained in the CNSComposed of the brain and spinal cord; integrates and processes information. .  Secondly, it form a projection fiber, which is a myelinated axon projecting from these brain stem structures into the cerebrumThe largest part of the brain, responsible for thought, memory, and voluntary movements..  You might be examining this diagram. You might say, “But, Amy, that blue neuron of the second order does that too!”  Yes, it does and it is a projection fiber too, but it takes a different pathway to get there.  This sequence of blue neuronsThe functional cells of the nervous system that transmit signals. is moving up the spinothalamic tract.  This is just an example, I don’t know that for sure.