The Phrenic Nerves

Examples of The Phrenic Nerves in the following topics:

• Injuries to the Phrenic Nerves

  • The phrenic nerve provides motor innervation and receives sensory information from the diaphragm.
  • The phrenic nerve is a nerve that originates in the neck and passes down between the lung and the heart to reach the diaphragm.
  • The phrenic nerves contain motor, sensory, and sympathetic nerve fibers.
  • In the thorax, each phrenic nerve supplies the mediastinal pleura and pericardium.
  • The phrenic nerve and its relations with the vagus nerve.

• Neural Mechanisms (Cortex)

  • The phrenic nerves: The nerves that stimulate the activity of the diaphragm.
  • They are composed of two nerves, the right and left phrenic nerve, which pass through the right and left side of the heart respectively.
  • The posterior thoracic nerves: These nerves stimulate the intercostal muscles located around the pleura.
  • Damage to any of these three respiratory nerves can cause severe problems, such as diaphragm paralysis if the phrenic nerves are damaged.
  • Less severe damage can cause irritation to the phrenic or vagus nerves, which can result in hiccups.

• Cervical Plexus

  • The cervical plexus is the plexus of the ventral rami of the first four cervical spinal nerves.
  • There is anastomosis with the accessory nerve, hypoglossal nerve, and sympathetic trunk.
  • The lesser occipital nerve, or small occipital nerve, is a cutaneous spinal nerve that arises between the second and third cervical vertebrae, along with the greater occipital nerve.
  • The supraclavicular nerves (descending branches) arise from the third and fourth cervical nerves.
  • The phrenic nerve (C3–C5, but primarily C4) is a nerve that originates in the neck and passes down between the lung and heart to reach the diaphragm.

• Neural Mechanisms (Respiratory Center)

  • The medulla and the pons are involved in the regulation of the ventilatory pattern of respiration.
  • Involuntary respiration is controlled by the respiratory centers of the upper brainstem (sometimes termed the lower brain, along with the cerebellum).
  • The medulla oblongata is the primary respiratory control center.
  • The pons is the other respiratory center and is located underneath the medulla.
  • Its signals limit the activity of the phrenic nerve and inhibits the signals of the apneustic center.

• Function and Physiology of the Spinal Nerves

  • The peripheral nervous system includes 12 cranial nerves and 31 pairs of spinal nerves that provide communication from the CNS to the rest of the body by nerve impulses to regulate the functions of the human body.
  • The spinal nerve C1 (suboccipital nerve) provides motor innervation to muscles at the base of the skull.
  • These include the greater occipital nerve that provides sensation to the back of the head, the lesser occipital nerve that provides sensation to the area behind the ears, the greater auricular nerve, and the lesser auricular nerve.
  • The phrenic nerve arises from nerve roots C3, C4, and C5.
  • PNS nerves are involved in the erection of genital tissues via the pelvic splanchnic nerves 2–4.

• Trochlear (IV) Nerve

  • The trochlear nerve (cranial nerve IV) is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye.
  • The trochlear nerve (cranial nerve IV) is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye.
  • The trochlear nerve is unique among the cranial nerves in several respects.
  • Other than the optic nerve (cranial nerve II), it is the only cranial nerve that decussates (crosses to the other side) before innervating its target.
  • It is the only cranial nerve that exits from the dorsal aspect of the brainstem.

• Accessory (XI) Nerve

  • The accessory nerve (cranial nerve XI) controls the muscles of the shoulder and neck.
  • The accessory nerve (cranial nerve XI) controls the sternocleidomastoid and trapezius muscles of the shoulder and neck.
  • Unlike the other 11 cranial nerves, the accessory nerve begins outside the skull.
  • Due to its unusual course, the accessory nerve is the only nerve that enters and exits the skull.
  • However, more modern characterizations of the nerve regard the cranial component as separate and part of the vagus nerve.

• Brief Overview of Cranial Nerves

  • Cranial nerves are the nerves that emerge directly from the brain (including the brainstem).
  • Spinal nerves emerge sequentially from the spinal cord with the spinal nerve closest to the head (C1) emerging in the space above the first cervical vertebra.
  • The terminal nerves, olfactory nerves (I) and optic nerves (II) emerge from the cerebrum or forebrain, and the remaining ten pairs arise from the brainstem, which is the lower part of the brain.
  • The optic nerve (II): This nerve carries visual information from the retina of the eye to the brain.
  • The glossopharyngeal nerve (IX): This nerve receives sensory information from the tonsils, the pharynx, the middle ear, and the rest of the tongue.

• Olfactory (I) Nerve

  • The olfactory nerve, or cranial nerve I, is the first of 12 cranial nerves and is responsible for the sense of smell.
  • The olfactory nerve, or cranial nerve I, is the first of the 12 cranial nerves.
  • The olfactory nerve is the shortest of the 12 cranial nerves and only one of two cranial nerves (the other being the optic nerve) that do not join with the brainstem.
  • The specialized olfactory receptor neurons of the olfactory nerve are located in the olfactory mucosa of the upper parts of the nasal cavity.
  • The olfactory nerves consist of a collection of many sensory nerve fibers that extend from the olfactory epithelium to the olfactory bulb, passing through the many openings of the cribriform plate of the ethmoid bone.

• Oculomotor (III) Nerve

  • The oculomoter nerve (cranial nerve III) controls eye movement, such as constriction of the pupil and open eyelids.
  • The oculomotor nerve is the third paired cranial nerve.
  • The occulomotor nerve is derived from the basal plate of the embryonic midbrain.
  • Here the nerve is placed below the trochlear nerve and the frontal and lacrimal branches of the ophthalmic nerve, while the nasociliary nerve is placed between its two rami (the superior and inferior branch of oculomotor nerve).
  • Image of cranial nerves showing the position of the oculomotor nerve.