PNS

Structure of NervesStructure of Nerves Cranial NervesCranial Nerves Spinal Nerves Spinal Nerves Sensory receptorsSensory receptors Motor controlMotor control

Structure & Classification of Structure & Classification of NervesNerves

Classification:Classification:Sensory, Motor, Mixed, Cranial & Spinal nerves; Ganglia

Cranial NervesCranial Nerves

• 12 pair of nerves

– arise from brain

– exit through foramina leading to muscles, glands and sense organs in head & neck

• Input & output ipsilateral except CN II and IV

I: Olfactory Nerve

II: Optic Nerve

III: Oculomotor Nerve & IV: Trochlear Nerve

V: Trigeminal Nerve

VI: Abducens Nerve

VII: Facial Nerve

VIII: Vestibulocochlear Nerve

IX: Glossopharyngeal Nerve

X: Vagus Nerve

XI: Accessory Nerve

XII: Hypoglossal Nerve

Cranial Nerve Disorders

• Trigeminal neuralgia (tic douloureux)Trigeminal neuralgia (tic douloureux)– recurring episodes of intense stabbing pain in trigeminal nerve

area

– pain triggered by touch, drinking, washing face

– treatment may require cutting nerve

• Bell’s palsyBell’s palsy– disorder of facial nerve causes paralysis of facial muscles on

one side

– may appear abruptly w/ full recovery w/in 3-5 weeks

Spinal Spinal NervesNerves

- 31 pairs of mixed nerves

- connect to cord via dorsal & ventral roots and rootlets

- away from cord branch into dorsal & ventral rami

- nerve plexuses

- nerve damage

Dermatomes:Dermatomes: skin segment skin segment innervated by cutaneous innervated by cutaneous sensory spinal nervesensory spinal nerve

Sensory ReceptorsSensory Receptors

• Stimulus typeStimulus type:– mechanoreceptor, thermoreceptors, nociceptors,

chemoreceptors & photoreceptors

• SourceSource:– exteroceptors, interoceptors & proprioceptors

• Structural complexityStructural complexity:– simple vs. complex

Organization of Organization of Somatosensory Somatosensory SystemSystem

1. Receptor levelReceptor level: sensory receptors

2. Circuit levelCircuit level: ascending fiber tracts

3. Perceptual levelPerceptual level: cerebral cortex

Hierarchy of Motor ControlHierarchy of Motor Control