Discuss on the different portions of the brain stem? What cranial nerve originates or passes through medulla oblongata?

Brain stem is area at the base of brain. It lies deep between the two hemispheres and cervical spinal cord. It is small yet the most important portion of the brain as it provides nerves connection and communication between main part of the brain and peripheral nervous system. Brain stem has important functions like:

Regulation of respiratory functions

Regulation of cardiac functions

Regulation of central nervous system (CNS)

Regulation of sleep cycle

Maintenance of consciousness

Breathing and eating

Different portions of brain

In human brain, the brain stem includes midbrain, pons, and medulla oblongata of hind brain.

MEDULLA OBLONGATA of the brain stem

Medulla oblongata is also known as myelencephalon is lower half region of brain stem in continuation with the spinal cord. Upper region is connected with pons. In terms of neurobiology it is often termed as simply medulla. Medulla is further divided into two regions.

Upper or superior part

Lower of inferior part

Upper or Superior part of the brain stem

This part forms the dorsal surface of medulla and is formed by the fourth ventricle.

Lower or Inferior part of the brain stem

It is the closed part of the brain where caudal part of fourth ventricle i.e. metacoel is present.

Structure of the brain stem

Structure of medulla includes following parts:

Pyramid of medulla oblongata

Decussation of pyramids

External arcuate fibers

Inferior olivary nucleus

Fasciculus gracilis

Gracile and cuneate tubercles

Inferior cerebral peduncle

Tuberculum cinereum

Commissural fibers.

PONS of the brain stem

Pons is the region present between cerebellum and forebrain and its duty is to transfer sensory information periphery to thalamus. The word pons is picked from Latin word which means, “Bridge”. It is located above the medulla oblongata, below the midbrain and anterior to cerebellum. There is white matter in pons which is responsible for conducting signals cerebrum to cerebellum and medulla and brings the signals back to thalamus.

Structure of the brain stem

Structure of pons looks like a broad bulge but originally it is made up of two thick stalks which are known as cerebral peduncles. Cerebral peduncles connect pons to midbrain. A pneumotaxic center is present within pons which controls and regulates inspiration and expiration. And also generate the capability in an individual to dream.

MID BRAIN of the brain stem

Mid brain is also known as mesencephalon. It is taken from a Latin word which means “roof”.  It is located above the hind brain and beneath the cerebral cortex. Anatomically midbrain consists of corpora quadrigemina, iter, tegmentum, cerebral peduncles and fasciculi. Posteriorly mid brain joins pons with thalamus and hypothalamus. Dopamine plays an important role in habituation and motivation which is produced in substantia nigra, a region in mid brain.

Structure of the brain stem

Structure of mesencephalon consists of:

Superior colliculi

Inferior colliculi

Ventricular mesocoeli

CRANIAL NERVES THAT ORIGINATE OR PASS THRUGH MEDULLA OBLONGATA

Cranial nerves are the nerves which originate directly from brain. There are 12 pairs of cranial nerves that arise from brain, specifically brainstem or cerebrum. There are 4 cranial nerves which arise from medulla oblongata.

Glossopharyngeal nerve (CN IX)

Vagus nerve (CN X)

Accessory nerve (CN XI)

Hypoglossol nerve (CN XII)

Glossopharyngeal Nerve (CN XI) of the brain stem

Glossopharyngeal nerve is the ninth cranial nerve out of 12 pairs. It has motor, sensory and autonomic components. It leaves the brainstem from the sides of medulla. This nerve contributes to pharyngeal plexus and supplies fibers.

Vagus Nerve (CN X) of the brain stem

It is the tenth cranial nerve out of twelve pairs of cranial nerves. It provides a lot function support to heart and GIT system. It is a complex motor, sensory and parasympathetic nerve.

Spinal Accessory nerve (CN XI) of the brain stem

It is simply known as accessory nerve. It is the eleventh nerve from twelve pairs of cranial nerves system. It comprises of two parts, Cranial and spinal part. The cranial part of this nerve is the smallest part arising from the cells and come out as 4 or 5 sensitive rootlets of from side of medulla oblongata.

Hypoglossol nerve (CN XII) of the brain stem

Hypoglossol cranial nerve is the twelfth nerve arising from medulla laterally. Its major role is to provide motor skills to the tongue. Before reaching the tongue, the nerve distributes itself into hitch hiking C1 nerve root fibers.

What are the different functions of medulla oblongata?

It transfers messages from brain to body i.e. thalamus and spinal cord.

It regulates respiration.

It regulates heartbeat.

It is responsible for reflex actions like sneezing, coughing, blinking and swallowing.

Motor and sensory neurons from brain travel through medulla oblongata