Cranial Nerves / Spinal Cord
Cranial Nerves / Spinal Cord

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Cranial Nerves, Spinal Cord and Periphe ral Nervous System - understanding of cranial nerve anatomy is facilitated by correlations with head and neck embryology - overview of head muscle groups - somatic and branchiomeric muscles are skeletal muscles of head/neck with identical histology and physiology, but different embryonic origins - histologically and functionally, there is no difference; however, knowing embryology makes sense of their anatomy, including the location of their cranial nerve nuclei - though not considered ‘mixed’ nerves, motor nerves all have an afferent component, proprioception (position sense) from muscle spindle groups sensing muscle stretch and tension and Golgi tendon organs sensi ng joint position - unlike other afferent sensory fibers, cranial nerve afferent proprioceptor nerve fibers do not have pseudounipolar neuron cell bodies in ganglia outside nerve’s entry into CNS - conscious propri oception is cerebral and unconscious is cerebellar - somatic muscles and somatic motor nerves - somatic muscles of the embryo’s head and body somites - head somites, innervated by cranial nerve nuclei in ventral periaqueductal gray matter of brainstem - extra - ocular muscles - derived from pre - otic somites - motor innervation: oculomotor nerve (CN III ), trochlear nerve (CN IV ), and abducens nerve (CN VI ) - intrinsic muscles of the tongue - derived from occipital somites - motor innervation: hypoglossal nerve (CN XII ) - neck and body somites - all skeletal muscles of body and extremities are derived from body somites, originating along sides of vertebral column, with motor innervation via spinal nerves ©