CRANIAL NERVES
, OVERVIEW OF CRANIAL NERVES
• There are 12 pairs of cranial nerves, which are numbered I–XII, from
rostral to
caudal
• Their names reflect their general distribution or function.
• Cranial nerves carry one or more of the following five main
functional components •
• 1 . Motor fibers to voluntary (striated) muscle.
• 2 . Motor fibers involved in innervating involuntary (smooth)
muscles or glands.
• 3. Fibers transmitting general sensation (e.g., touch, pressure, heat, cold,
etc.), mainly carried by CN V, but also by CN VII, CN IX, and CN X.
• 4. Fibers conveying sensation from the viscera. These include visceral
sensory (general visceral afferent) fibers
• 5. Fibers transmitting unique sensations.
• These include special sensory fibers conveying taste and smell
(special visceral afferent fibers)
• and those serving the special senses of vision, hearing, and balance
(special
somatic afferent fibers).
•
, OVERVIEW OF CRANIAL NERVES
• Some cranial nerves are purely sensory, others are considered purely
motor, and several are mixed.
• CN III, CN IV, CN VI, CN XI, CN XII, and the motor root of CN V are
considered to be pure motor nerves that appear to have evolved from
primordial anterior roots.
• However, a small number of sensory fibers for proprioception (nonvisual
perception of movement and position) are also present in these nerves,
the cell bodies of which are probably located in the mesencephalic nucleus
of CN V.
• The sensory root of CN V is purely a somatic (general) sensory nerve.
• Four cranial nerves (CN III, CN VII, CN IX, and CN X) contain presynaptic
parasympathetic (visceral motor) axons as they emerge from the
brainstem.
• CN V, CN VII, CN IX, and CN X are mixed nerves with both somatic
(branchial) motor and somatic (general) sensory components, and each
nerve supplies derivatives of a different pharyngeal arch.
• The fibers of cranial nerves connect centrally to cranial nerve nuclei—
groups of
neurons in which sensory or afferent fibers terminate and from which
motor or
• efferent fibers originate.
• Except for CN I and CN II, which involve extensions of the forebrain, the
nuclei of the cranial nerves are located in the
, OVERVIEW OF CRANIAL NERVES
• There are 12 pairs of cranial nerves, which are numbered I–XII, from
rostral to
caudal
• Their names reflect their general distribution or function.
• Cranial nerves carry one or more of the following five main
functional components •
• 1 . Motor fibers to voluntary (striated) muscle.
• 2 . Motor fibers involved in innervating involuntary (smooth)
muscles or glands.
• 3. Fibers transmitting general sensation (e.g., touch, pressure, heat, cold,
etc.), mainly carried by CN V, but also by CN VII, CN IX, and CN X.
• 4. Fibers conveying sensation from the viscera. These include visceral
sensory (general visceral afferent) fibers
• 5. Fibers transmitting unique sensations.
• These include special sensory fibers conveying taste and smell
(special visceral afferent fibers)
• and those serving the special senses of vision, hearing, and balance
(special
somatic afferent fibers).
•
, OVERVIEW OF CRANIAL NERVES
• Some cranial nerves are purely sensory, others are considered purely
motor, and several are mixed.
• CN III, CN IV, CN VI, CN XI, CN XII, and the motor root of CN V are
considered to be pure motor nerves that appear to have evolved from
primordial anterior roots.
• However, a small number of sensory fibers for proprioception (nonvisual
perception of movement and position) are also present in these nerves,
the cell bodies of which are probably located in the mesencephalic nucleus
of CN V.
• The sensory root of CN V is purely a somatic (general) sensory nerve.
• Four cranial nerves (CN III, CN VII, CN IX, and CN X) contain presynaptic
parasympathetic (visceral motor) axons as they emerge from the
brainstem.
• CN V, CN VII, CN IX, and CN X are mixed nerves with both somatic
(branchial) motor and somatic (general) sensory components, and each
nerve supplies derivatives of a different pharyngeal arch.
• The fibers of cranial nerves connect centrally to cranial nerve nuclei—
groups of
neurons in which sensory or afferent fibers terminate and from which
motor or
• efferent fibers originate.
• Except for CN I and CN II, which involve extensions of the forebrain, the
nuclei of the cranial nerves are located in the
