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11.4C: Pons

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    7621
  • The pons is a relay station between the forebrain and cerebellum that passes sensory information from the periphery to the thalamus.

     

    LEARNING OBJECTIVES

     

    Describe the role and location of the pons region of the brainstem

     

    KEY TAKEAWAYS

    Key Points

     

    • The pons is a structure located on the brainstem, named after the Latin word for “bridge.”
    • This white matter includes tracts that conduct signals from the cerebrum down to the cerebellum and medulla, as well as tracts that carry the sensory signals up into the thalamus.
    • The pons contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.
    • Within the pons is the pneumotaxic center, a nucleus that regulates the change from inspiration to expiration.
    • The pons also contains the sleep paralysis center of the brain and plays a role in generating dreams.
    • The functions of these four nerves include sensory roles in hearing, equilibrium, taste, and in facial sensations such as touch and pain. They also have motor roles in eye movement, facial expressions, chewing, swallowing, urination, and the secretion of saliva and tears.

     

    Key Terms

     

    • pons: Contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that regulate sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.
    • pneumotaxic center: A network of neurons in the rostral dorsal lateral pons that regulates the respiratory rate; also known as the pontine respiratory group (PRG).
    • Basal plate: The region of the neural tube ventral to the sulcus limitans and containing primarily motor neurons.
    • alar plate: Also called the alar lamina, it is a neural structure in the embryonic nervous system; the caudal part later becomes the sensory axon aspect of the spinal cord.

    image

    Pons/Brainstem: Structure of the brainstem showing the location of the pons in relation to the midbrain and medulla.

    The pons is a structure located on the brainstem, named after the Latin word for “bridge.” It is above the medulla, below the midbrain, and anterior to the cerebellum. The white matter of the pons includes tracts that conduct signals from the cerebrum down to the cerebellum and medulla, and tracts that carry the sensory signals up into the thalamus.

    Structure

    The pons measures about 2.5 cm in length in adults. Most of it appears as a broad anterior bulge rostral to the medulla. Posteriorly, it consists mainly of two pairs of thick stalks called cerebellar peduncles. These connect the cerebellum to the pons and midbrain.

    The pons contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that regulate sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture. Within the pons is the pneumotaxic center, a nucleus that regulates the change from inspiration to expiration. The pons also contains the sleep paralysis center of the brain and also plays a role in generating dreams.

    Development

    During embryonic development, the metencephalon develops from the rhombencephalon and gives rise to two structures: the pons and the cerebellum. The alar plate produces sensory neuroblasts, which will give rise to the solitary nucleus and its special visceral afferent column, the cochlear and vestibular nuclei (which form the special somatic afferent fibers of the vestibulocochlear nerve), the spinal and principal trigeminal nerve nuclei (which form the general somatic afferent column of the trigeminal nerve), and the pontine nuclei, which is involved in motor activity. Basal plate neuroblasts give rise to the abducens nucleus (forms the general somatic efferent fibers), the facial and motor trigeminal nuclei (form the special visceral efferent column), and the superior salivatory nucleus, which forms the general visceral efferent fibers of the facial nerve.

    Cranial Nerves of the Pons

    A number of cranial nerve nuclei are present in the pons:

    • The chief or pontine nucleus of the trigeminal nerve sensory nucleus (V)- mid-pons
    • The motor nucleus for the trigeminal nerve (V)-mid-pons
    • Abducens nucleus (VI)-lower pons
    • Facial nerve nucleus (VII)-lower pons
    • Vestibulocochlear nuclei (VIII)-lower pons

    Functional Characteristics

    The functions of the four nerves of the pons include sensory roles in hearing, equilibrium, taste, and facial sensations such as touch and pain. They also have motor roles in eye movement, facial expressions, chewing, swallowing, urination, and the secretion of saliva and tears. Central pontine myelinosis is a demyelination disease that causes difficulty with sense of balance, walking, sense of touch, swallowing, and speaking. If it is not diagnosed and treated, it can lead to death or locked-in syndrome (a condition in which a person is conscious but cannot move or communicate).