Cranial/Spinal Nerves

• Cranial Nerve I
• Origin:  olfactory epithelium
• Purely sensory
• Function:  sense of smell
• Clinical Symptoms:  partial/total loss of smell
• Testing:  Asked to sniff different aromas

• Cranial Nerve II
• Origin:  Retina
• Purely sensory
• Function:  vision
• Clinical Symptoms:  partial/total blindness
• Testing:  eye chart, first see object, ophthalmoscope

• Cranial Nerve III
• Origin:  Brainstem
• Mixed function
• Somatic/parasympathetic motor to iris & ciliary muscle for focus.
• Function:  move the eye and eyelid, pupil constriction, lens shape
• Clinical Symptoms:  eye cannot move, at rest rotates laterally, eyelid droop, double vision
• Testing:  Size, shape, equality, reflex of pupil

• Cranial Nerve IV
• Origin:  Brainstem
• Mixed function
• Function:  Moves eye muscle (superior oblique)
• Clinical symptoms:  Double vision, problems rotating eye inferolaterally
• Testing:  Size, shape, equality, reflex of pupil

• Cranial Nerve V
• Origin:  Brainstem
• Mixed function
• Ophthalmic Function:  Sensory from skin of upper face
• Ophthalmic Testing:  Corneal reflex
• Maxillary Function:  Sensory from skin of lower face
• Maxillary Testing:  Safety pin, hot and cold objects
• Mandibular Function:  motor fibers for chewing, sensory from face
• Mandibular Testing:  clench teeth, move jaw
• Clinical Symptoms All:  Stabbing pain to face

• Cranial Nerve VI
• Origin:  Brainstem
• Mixed Function
• Function:  Motor fibers to eye muscle (lateral rectus), proprioceptors from same muscle to brain
• Clinical Symptoms:  Eye cannot move laterally, at rest moves medially
• Testing:  Pupil testing

• Cranial Nerve VII
• Origin:  Brainstem
• Mixed Function
• Somatic/Parasympathetic Motor:  Lacrimal and salivary glands
• Function:  Facial expression, proprioceptor to pons, taste buds anterior 2/3 of the tongue
• Clinical Symptoms:  Bell's palsy, paralysis of facial muscles on affected side
• Testing:  taste buds tested, symmetry of face checked

• Cranial Nerve VIII
• Origin:  Inner ear
• Mostly Sensory
• Function:  Equilibrium, hearing
• Clinical Symptoms:  Deafness, dizziness, REM, loss of balance
• Testing:  Hearing is checked

• Cranial Nerve IX
• Origin:  Brainstem
• Mixed Function
• Somatic/Parasympathetic Motor:  Salivary
• Function:  Tongue & pharynx, taste and touch from posterior 1/3 tongue,
• Clinical Symptoms:  Impairment of swallow/taste
• Testing:  Gag/swallow reflex, speak/cough

• Cranial Nerve X
• Origin:  Brainstem
• Mixed function
• Somatic/Parasympathetic Motor:  Vagus, ventral body cavity
• Function:  Motor to pharynx/larynx (swallowing); parasympathetics to ventral body cavity
• Clinical Symptoms:  Loss of voice, difficulty swallowing, impaired digestive system
• Testing:  Gag/swallow reflex, speak/cough

• Cranial Nerve XI
• Origin: Brainstem
• Mixed Function
• Function:  Joins with Vagus, spinal root moves head/neck, conveys proprioceptors
• Clinical Symptoms:  Head turned toward injury side, difficulty shrugging shoulder
• Testing:  Head rotation and shoulder shrug

• Cranial Nerve XII
• Origin:  Brainstem
• Mixed function
• Function:  Muscles of tongue,
• Clinical Symptoms:  Difficulties in speech and swallowing
• Testing:  Protrude and retract tongue

31 pairs

• 8 cervical
• 12 thoracic
• 5 lumbar
• 5 sacral
• 1 coccygeal

All are mixed

• All dorsal rami
• Ventral rami from T₂ to T₁₂

All cervical, lumbar, sacral, coccygeal and T₁ of thoracic

Innervates the posterior trunk in a narrow strip in line with the exit site, segmental fashion.

Innervates the ventral region of the trunk (segmental fashion to the intercostals: ribs & branches to the skin) and the limbs (plexi)

• Cervical (C₁-C₅)
• Brachial (C₅-T₁)
• Lumbar (L₁-L₄)
• Sacral (L₄-S₄)

• Cervical plexus
• Motor/sensory of the diaphragm
• C₃, C₄, C₅

• Brachial plexus
• Shoulder joint and deltoid

• Brachial plexus
• biceps brachii, brachialis, sensory lateral forearm

• Brachial plexus
• forearm flexors, palm
• Carpal tunnel syndrome

• Brachial plexus
• Medial forearm and hand
• Funny bone

• Brachial plexus
• Posterior arm to hand: extensors

• Lumbar plexus
• Anterior thigh muscles
• Mostly anteromedial skin of leg
• Gait problem if herniated disc in region

• Sacral plexus
• Posterior thigh, leg and foot
• Thickest/longest in the body

• Nerves can regenerate if cell body is unharmed
• Further away from the cell body the more successful the regeneration
• Difference from CNS:  Schwann cells promote regeneration, CNS glial cells inhibit
• 1.  Fragmentation of the axon at the injury site.
• 2.  Macrophages destroy the axon distal to the injury.
• 3.  Axon filaments grow within a regeneration tube formed by Schwann cells.
• 4.  Regenerated axon and the formation of a new myelin sheath

• The area of skin innervated by the cutaneous branches of a single spinal nerve
• Mapping of skin area or sensory field carried/represented in a single dorsal root

• Rapid movement that occurs automatically, with no conscious effort
• Inborn/intrinsic
• Learned/conditioned

• Visceral - at the level of the organs
• Does not require cerebrum
• Usually protective
• Spinal/brainstem reflexes
• Rapid/predictable response
• Somatic

• Requires cerebrum
• Becomes a reflex with practice
• i.e. foot on the brake

• Receptor
• Sensory neuron
• Integration center
• Motor neuron
• Effector

• Start at receptors
• Integration center (CNS)
• Dorsal root first to spinal cord
• Exit to receptor

• Outflow
• Where they start
• Number of neurons in the pathway

• Pain from viscera perceived as somatic in origin
• Visceral pain afferents travel with somatic nerves
• Confuses CNS in the spinal cord

• 1 synapse in the CNS
• Ipsilateral
• Direct to motor neuron
• Patellar reflex

• More than 1 synapse
• Involves interneurons inhibiting on antagonistic
• Component of stretch reflex is reciprocal inhibition
• Stepping - need the other foot down to lift the first foot
• Opposite sides of the spinal cord

• Cranial nerves I and II and VIII is mostly sensory
• Olfactory, optic and vestibulocochlear

• Cranial nerve I, olfactory from olfactory epithelium
• Cranial nerve II, optic from retina
• Cranial nerve VIII, vestibulocochlear from inner ear

• Cranial nerve III, oculomotor, ciliary muscle and iris of the eye
• Cranial nerve VII, facial, salivary and lacrimal glands
• Cranial nerve IX, glossopharyngeal, salivary
• Cranial nerve X, vagus, ventral body cavity