Cranial Nerves Flashcards
What are cranial nerves prone to? and what do the symptoms relate to?
compression due to inflammation, tumours and fractures
symptoms relate to the function of the nerves
What may cranial nerves contain?
Somatic motor fibres - supply striated muscle
Autonomic motor fibres - cranial division of the parasympathetic supply innervates smooth muscle & glands
Visceral sensory - afferent inputs from pharynx, larynx, heart, lung, gut etc - not normally conscious
General sensory - afferent inputs (eg touch, temperature, pain) from skin & mucous membranes
Special sensory – taste, smell, vision, hearing & balance
Why do cranial nerves not carry sympethetic fibres?
As sympathetic fibres arise form the thoraco-lumbar region
Name fibre type A?
sensory (afferent) fibres
Name fibre type B?
somatic motor (efferent) fibres
Name fibre type C?
autonomic motor (efferent) fibres
Do nerves carry sensory or motor fibres or both?
Some are purely sensory, some purely motor but lots of them are mixed and have both sensory and motor fibres in them
What fibres does the Olfactory (CNI) carry?
sensory (smell)
What fibres does the Optic (CNII) carry?
sensory (vision)
What fibres does the Oculomotor (CNIII) carry?
motor (eye movement)
What fibres does the Trochlear (CNIV) carry?
motor (eye movement)
What fibres does the Trigeminal (CNV) carry?
mixed (sensation from face & mouth, muscles of mastication)
What fibres does the Abducent (CNVI) carry?
motor (eye movement)
What fibres does the Facial (CNVII) carry?
mixed (muscles of facial expression, parasymp, taste)
What fibres does the Vestibulocochlear (CNVIII) carry?
sensory (hearing & balance)
What fibres does the Glossopharyngeal (CNIX) carry?
mixed (swallowing, sensation from tongue, parasymp)
What fibres does the Vagus (CNX) carry?
mixed (muscles of throat, parasymp, visceral sensory)
What fibres does the Accessory (CNXI) carry?
motor (soft palate, throat & neck)
What fibres does the Hypoglossal (CNXII) carry?
motor (tongue)
What is CNI?
olfactory nerve
What is the pathway of the olfactory nerve?
receptors in olfactory epithelium of nasal cavity, olfactory nerve fibres pass through foraminifera in cribriform plate of ethmoid bone and enter olfactory bulb in the anterior cranial fossa
What is the clinical application of the olfactory nerve?
fractured cribriform plate may tear olfactory nerve fibres causing anosmia (loss of sense of smell)
Whatis CN II?
optic nerve
What is the pathway of the optic nerve?
enters via optic canal, nerves join to form optic chiasm, fibres from medial (nasal) half of each retina cross to form optic tract
What is the clinical application of the optic nerve?
increase in CSF pressure can cause papilloedema (optic disc swelling that is caused by increased intracranial pressure due to any cause)
section of right optic nerve causes blindness through right eye
section of optic chiasm causes loss of peripheral vision (bitemporal hemianopsia)
section of right optic tract causes blindness in left temporal and right nasal fields (left homonymous hemianopsia)
What is CN III?
oculomotor nerve
What is the pathway of the oculomotor nerve?
emerges from midbrain and exits via superior orbital fissure
What are the components of the oculomotor nerve?
somatic motor - extraocular muscles (superior, medial & inferior rectus and inferior oblique) and eyelid (levator palpebrae superioris)
autonomic motor - parasympathetic to pupil causing constriction and to ciliary muscle causing accommodation of the lens