The Anatomy of the Pons

The pons is part of a highway-like structure between the brain and the body known as the brainstem. The brainstem is made up of three sections, and carries vital information to the body. The pons relays information about motor function, sensation, eye movement, hearing, taste, and more. 

This article discusses the function and anatomy of the pons, as well as conditions that can affect this part of the brain.

What Is the Function of the Pons?

Like the other parts of the brainstem, the pons plays an important role in the functioning of the autonomic nervous system. This system controls the body's "automatic" functions, or things you do without thinking of, like breathing and digesting. The main functions of the pons deal with sensation and motor function, especially for the head and neck.

Four of the body's 12 cranial nerves are in the pons, as well as the reticular activating system. The reticular activating system operates the body's sleep-wake cycle, alertness, pain responses, and is part of the body's fight-or-flight system.

The cranial nerves that arise from the pons focus on motor responses, and eye and facial movement. These are:

Cranial nerve five: The trigeminal nerve is the largest cranial nerve, controlling both motor and sensory function. This nerve provides sensation to the face and head, controls the muscles used to chew and bite, and conveys information about pain and temperature.

Cranial nerve six: The abducens nerve controls eye movement. It powers the lateral rectus muscle, housed on the outer part of the eye, that allows the eye to move outward and away from the nose.

Cranial nerve seven: The facial nerve controls most of the muscles and sensation in the face. It makes the eyes water and the mouth salivate, and contributes to taste, hearing, and facial sensation and control.

Cranial nerve eight: The vestibulocochlear nerve is responsible for hearing, but also helps to control balance and movement.

Anatomy

The pons is located in the brainstem, which is the area where the brain connects to the spinal cord. The brainstem includes three pieces—the midbrain, pons, and medulla oblongata. Each piece plays a different role, relaying messages from the brain to the rest of the body.

Structure

The pons is divided into two sections—the pontine tegmentum on the interior part and the basilar pons on the outer part.

The basilar pons forms a bulb-like protrusion from the pons that is a notable feature on the brainstem. The basilar pons sits on the occipital bone (which forms the base of the skull) and contains the basilar artery.

The pontine tectum makes up the bottom of the brain’s fourth ventricle and is where fibers called peduncles originate to connect the cerebellum to the midbrain.

Associated Conditions

Injury can occur to the pons from trauma or other injury to the brainstem. An injury to the pons would impair the cranial nerve functions associated with this part of the brain stem. You could experience damage to facial sensation, eye movement, hearing, taste, and more.

One example of an injury to the pons is the pontine stroke. This can be caused by a blood clot or a broken blood vessel that causes bleeding in or around the brain. Either way, these strokes cut off the oxygen supply to the affected area of the brain, causing damage to the areas where the clot or bleeding occurred. Other conditions, such as tumors or demyelinating disease, can also affect the pons.

Damage to specific parts of the pons can result in a number of syndromes including locked-in syndrome. Locked-in syndrome is a rare condition where there is complete paralysis of voluntary muscles in all parts of the body except for the ones that control eye movement.

Tests

Damage to the pons can be detected by assessing symptoms such as problems with eye movements, taste, and balance. A cranial nerve assessment will test the function of the cranial nerves within the pons, as well as other parts of the brain.

Additionally, imaging may help provide more specific information about an injury to the pons and the extent of the damage. The following are a few examples of tests that may be done to determine the level of function in the brainstem.

• Cranial nerve assessment: A physical assessment that allows a medical provider to see what functions may be impaired based on what tasks you are able to perform.
• Computer tomography (CT) scan or magnetic resonance imaging (MRI): These will help a provider visualize areas of damage.
• Brain perfusion scan: This test allows the doctor to see which areas of the brain are receiving blood flow, and is useful in diagnosing brain death.
  

Summary

The pons is one of three parts of the brainstem. Its functions include sensation and motor function, especially in the head and neck. Four of the 12 cranial nerves are present in the pons, as well as the reticular activating system.

Injuries or strokes affecting the pons may lead to problems with facial sensation, motor function, vision, hearing, taste, balance, and more. Damage to the pons can be assessed using functional tests and scans.