Cranial Nerves & Spinal Nerves

• Peripheral Nervous System (PNS)


  Includes cranial nerves and spinal nerves
• Cranial Nerves


  • Attach to the brain and pass through foramina of the skull
  • Numbered from I–XII
  • Cranial nerves I and II attach to the forebrain
  • All others attach to the brain stem
  • Primarily serve head and neck structures
  • The vagus nerve (X) extends into the abdomen
• The 12 Pairs of Cranial Nerves

  • Olfactory Nerves
  • Optic Nerve
  • Oculomotor Nerve
  • Trochlear Nerve
  • Trigeminal Nerve
  • Abducens Nerve
  • Facial Nerve
  • Vestibulocochlear Nerve
  • Glossopharyngeal Nerve
  • Vagus Nerve
  • Accessory Nerve
  • Hypoglossal Nerve
• Olfactory Nerves


  Sensory nerves of smell
• Optic Nerve


  Sensory nerve of vision
• Oculomotor Nerve


  Innervates four of the extrinsic eye muscles
• Trochlear Nerve


  Innervates the superior oblique muscle (an extrinsic eye muscle)
• Trigeminal Nerve


  • Provides sensory innervation to the face
  • Motor innervation to chewing muscles
• Abducens Nerve


  Abducts the eyeball – innervates lateral rectus muscle
• Facial Nerve


  Innervates muscles of facial expression
• Vestibulocochlear Nerve


  Sensory nerve of hearing and balance
• Glossopharyngeal Nerve


  Innervates structures of the tongue and pharynx
• Vagus Nerve


  • A mixed sensory and motor nerve
  • Wanders into thorax and abdomen
  • Parasympathetic innervation of organs
• Accessory Nerve


  • An accessory part of the vagus nerve
  • Innervates trapezius muscle
• Hypoglossal Nerve


  • Runs inferior to the tongue
  • Innervates the tongue muscles
• Spinal Nerves


  • 31 pairs – contain thousands of nerve fibers
  • Connect to the spinal cord
  • Named for point of issue from the spinal cord
  • 8 pairs of cervical nerves (C1–C8)
  • 12 pairs of thoracic nerves (T1–T12)
  • 5 pairs of lumbar nerves (L1–L5)
  • 5 pairs of sacral nerves (S1–S5)
  • 1 pair of coccygeal nerves (Co1)
• Dorsal root


  • Contains sensory fibers
  • Cell bodies located in the dorsal root ganglion
• Ventral root


  Contains motor fibers arising from anterior gray column
• Dorsal ramus


  • Innervates back muscles
  • Follows a neat, segmented pattern
  • Innervates a horizontal strip of muscle and skin
  • In line with emergence point from the vertebral column
• Ventral ramus


  • Thoracic region arranged in simple, segmented pattern
  • Intercostal nerves – supply intercostal muscles, skin, and abdominal wall
  • Each gives off lateral and anterior cutaneous branches
• Nerve plexus


  • A network of nerves
  • Ventral rami (except T2 – T12) branch and join with one another to form nerve plexuses
  • In cervical, brachial, lumbar, and sacral regions
  • Primarily serve the limbs
  • Fibers from ventral rami crisscross
• Cervical Plexus


  • Buried deep in the neck
  • Under the sternocleidomastoid muscle
  • Formed by ventral rami of first four cervical nerves (cn 1 – 4)
  • Most are cutaneous nerves
  • Some innervate muscles of the anterior neck
  • Phrenic nerve – the most important nerve of the cervical plexus
• Brachial Plexus


  • Lies in the neck and axilla
  • Formed by ventral rami of C5 – C8
  • Cords give rise to main nerves of the upper limb
• Musculocutaneous Nerve


  • Main branch of the lateral cord
  • Innervates the biceps brachii and brachialis
• Median Nerve


  • Originates from both lateral and medial cords
  • Innervates anterior forearm muscles and lateral palm
• Ulnar Nerve


  • Branches from the medial cord
  • Innervates intrinsic hand muscles and skin of the medial hand
• Radial Nerve


  • Continuation of the posterior cord
  • Largest branch of the brachial plexus
  • Innervates muscles of the posterior upper limb
• Axillary Nerve


  Innervates the deltoid and teres minor
• Lumbar Plexus


  • Arises from L1– L4
  • Smaller branches innervate the posterior abdominal wall and psoas muscle
  • Main branches innervate the anterior thigh
  • Femoral nerve – innervates anterior thigh muscles
  • Obturator nerve – innervates adductor muscles
• Sacral Plexus


  • Arises from spinal nerves L4–S4
  • Caudal to the lumbar plexus
  • Often considered with the lumbar plexus
  • Lumbosacral plexus
• Sciatic Nerve


  • The largest nerve of the sacral plexus
  • Actually two nerves in one sheath
  • Tibial nerve – innervates most of the posterior lower limb
  • Common fibular (peroneal) nerve – innervates muscles of the anterolateral leg
• Superior and Inferior Gluteal Nerves


  Innervate the gluteal muscles
• Pudendal Nerve


  Innervates muscles of the perineum
• Dermatome


  An area of skin innervated by cutaneous branches of a single spinal nerve
• Upper limb skin is supplied by nerves of the brachial plexus
• Lower limb anterior surface skin is supplied by lumbar nerves, posterior surface by sacral nerves
• Migraine headache relates to sensory innervation of cerebral arteries, arteries dilate and compress and irritate sensory nerve endings
• Myasthenia gravis is a progressive weakening of the skeletal muscles, an autoimmune disorder where antibodies destroy acetylcholine receptors
• Spinal nerves form late in week 4, each of the 31 pairs sends motor fibers to an individual myotome and sensory fibers to the overlying band of skin
• During week 5 nerves reach the organs they innervate