Pons Varolii - Structure and Function

What is Brainstem?

Brainstem is the part of the brain that is formed by the midbrain, medulla oblongata and pons. The largest segment of the brainstem is the pons. It connects the descending and ascending tracts between the spinal cord and brain. It also contains many centers for the regulation of vital functions in the body.

Pons Varolii

Pons or pons varolii is a component of the brainstem. It forms a bridge between the midbrain and medulla oblongata. It is located anterior to the cerebellar region. Thus it acts as a major pathway that passes information from the brain to the cerebellum through the brainstem.

Also Read: Human Brain

Pons – Structure

Pons is around 2.5 cm in length and is the largest portion of the brainstem. The pons has two surfaces – ventral and dorsal, and two borders – superior and inferior.

Ventral Surface

The ventral surface of pons is convex in both directions (from backward and from side to side). It forms a large vertical groove called the basilar groove along the median plane. Furthermore, the trigeminal nerve is attached to this surface.

Dorsal Surface

The dorsal surface of the pons is covered by the cerebellum, and separated from it by the cavity of the 4th ventricle. The dorsal surface of the pons is triangular and forms the upper part of the floor of the 4th ventricle.

Additionally, the internal section of pons shows a large ventral or basilar part called the basis pontis, and a small dorsal or tegmental part called the pontine tegmentum. The tegmental part contains the nuclei of trigeminal (5th), abducens (6th), facial (7th), and vestibulocochlear (8th) nerves. The basilar pontis contains the corticospinal tract, pontine nuclei, and transverse pontine fibres.

Pons - Human Brain

Significance and Functions of Pons

  • Pons forms the pathway that connects cerebellum with cerebrum.
  • Pyramidal tracts pass through the pons. Pyramidal tracts include a group of efferent nerve fibres like the corticospinal tract. They play a major role in controlling motor functions.
  • Also, the nuclei of 5th, 6th, 7th and 8th cranial nerves are located in pons.
  • Pons contain apneustic and pneumotaxic (respiratory) centres for the regulation of respiration.
  • Vestibular nuclei are found in both medulla oblongata and pons. Especially, pons has the superior vestibular nucleus. The vestibular nuclei play a vital role in maintaining the head posture and also in the neural control of the body.

Clinical Importance

  • Dysarthria or Clumsy hand syndrome – Lunar stroke is an ischemic stroke due to the blockage of small arteries in the brain. This blockage in the basal pons can lead to dysarthria which is seen as clumsiness or involuntary movements in hands and legs.
  • Millard-Gubler Syndrome – It results from a lesion in the lower part of the pons, which is so placed that it includes the pyramidal tract and the emerging fibres of the abducens and facial nerves.
  • Central pontine myelinolysis – Any damage to the myelin sheath in the pons can cause this disease which leads to difficulty with walking, swallowing, speaking, sense of balance and sense of touch.

Frequently Asked Questions

What are the other structures that make the brainstem?

The other two structures that make up the brainstem are the midbrain and medulla oblongata. The midbrain is the shortest segment of the brainstem. It connects the pons to the diencephalon and cerebrum. The medulla forms the lowest part of the brainstem and is responsible for various involuntary functions.

What are cerebral peduncles?

They are stalks arising from the pons and have the descending and ascending nerve tracts that run between the pons and cerebrum. These cerebral peduncles are actually present on either side of the frontal midbrain. They connect the cerebrum to the brainstem.

What are the four main cranial nerve nuclei present in the pons?

The four main cranial nerve nuclei in the pons are – Cranial nerve nuclei 5 (trigeminal nerve), 6 (abducens nerve), 7(facial nerve) and 8 (vestibulocochlear nerve). These nuclei are responsible for respiration, bladder control, hearing, sleep, swallowing, taste, equilibrium, posture, eye movement, facial sensation and expressions.

Also Check: Central Nervous System

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