III Neuroanatomy and Neurophysiology

• Cranial nerves:

  • 12 pairs pass through various foramina of the skull
  • First two pairs attach to the forebrain; rest originate from the brain stem
  • All except vagus nerve serve only head & neck structures
  • Most cranial nerves are mixed nerves, except those for special sense organs
  • Mnemonic: "On occasion, our trusty truck acts funny - very good vehicle anyhow"
• Olfactory Nerves:

  • From nasal mucosa to olfactory bulbs
  • Fibers extend as olfactory tract to primary olfactory cortex
  • Afferent sensory fibers for smell
• Optic Nerves:

  • Fibers from retina form optic nerve passing through optic foramen of orbit
  • Optic nerves converge to form optic chiasma, then as optic tracts to thalamus, finally as optical radiation to occipital cortex
  • Afferent sensory fibers for vision
• Oculomotor Nerves:

  • Supplies 4/6 extrinsic muscles of eyeball
  • Mixed motor nerves to extrinsic eye muscles, also parasympathetic fibers to iris, lens
• Trochlear Nerves:

  • Innervates one pair of extrinsic eye muscles
  • Motor fibers from dorsal midbrain to superior oblique eye muscle
• Trigeminal Nerves:

  • Largest of cranial nerves with 3 divisions: Opthalmic, Maxillary, Mandibular
  • Sensory fibers from face & motor fibers for chewing (mandibular division)
• Abducens Nerves:

  • Controls extrinsic eye muscle that abducts eyeball
  • Primarily motor to lateral rectus muscle
• Facial Nerves:

  • Large nerve with 5 major branches for facial expression
  • Mixed nerve, primarily motor, also parasympathetic to lacrimal glands and salivary glands
• Glossopharyngeal Nerves:

  • Mixed nerves to & from medulla for tongue & pharynx
  • Sensory from taste, touch, pressure, pain from pharynx, posterior tongue
• Vagus Nerve:

  • Extends beyond head-neck region
  • Mixed nerves to & from medulla, parasympathetic motor to heart, lungs, abdominal viscera
• Accessory Nerves:

  • Accessory part of vagus nerve, mostly motor to pharynx, larynx, soft palate
• Hypoglossal Nerves:

  • Primarily motor to tongue for mixing of food, swallowing, and speech
• Spinal Nerves:

  • 31 pairs, all mixed nerves
  • Named according to point of issue: C1-C8, T1-T12, L1-L5, S1-S5, C0
  • Branch into dorsal and ventral rami carrying sensory and motor fibers
• Sensory Receptors:

  • Allow awareness of surroundings
  • Classified by types of stimuli, location, and structural complexity
• Sensory Receptors according to Stimulus Detected:

  • Mechanoreceptors: touch, pressure, vibration, stretch
  • Thermoreceptors: temperature
  • Photoreceptors: light energy
  • Chemoreceptors: chemicals in solution
  • Nociceptors: damaging stimuli causing pain
• Sensory Receptors according to Location:

  • Exteroceptors: stimuli from outside the body
  • Interoceptors: stimuli from within the body
  • Proprioceptors: monitor stretch in skeletal muscles, tendons, joints
• Sensory Receptors according to Structural Complexity:

  • Nonencapsulated Nerve Endings: pain, temperature, pressure receptors
  • Encapsulated Nerve Endings: mechanoreceptors enclosed in CT capsules
• Encapsulated Nerve Endings:

  • Tactile corpuscles, Lamellar corpuscles, Bulbous corpuscles
  • Muscle spindles, Tendon organs, Joint kinesthetic receptors