brainstem and cranial nerves

Question 1

define brainstem

Answer 1

part of CNS, exclusive of cerebellum, that lies between cerebrum and spinal cord

Question 2

3 major divisions of brainstem (moving superiorly)

Answer 2

medulla oblongata, pons, midbrain

Question 3

where does brainstem sit

Answer 3

posterior cranial fossa

Question 4

posterior: midbrain contents

Answer 4

pineal gland, superior and inferior colliculi, trochlear nerve

Question 5

posterior: what lies inferior to the 4th ventricle (in front of cerebellum)

Answer 5

dorsal columns (medial from leg, lateral from arms); damage causes sensory deficits

Question 6

posterior: what lies superior to 4th ventricle

Answer 6

trochlear nerve (cranial nerve IV) -> supplies superior oblique muscle for eye movement

Question 7

posterior: what lies superior to trochlear nerve a) medially and b) laterally; what are their functions

Answer 7

a) pineal gland on midline (not bilateral) - melatonin for circadian rhythm, b) superior colliculus (coordinated neck and eye movements) and inferior colliculus (basic survival functions based on auditory functions - look towards stimulus) on either side (bilateral)

Question 8

anteroinferior view of brainstem: cranial nerves

Answer 8

I: olfactory nerves; II: optic nerve (half of fibres cross over to occipital lobe at optic chiasm); below optic chiasm is pituitary stalk (infundibulum); below is mammiliary body (base of hypothalamus); below is III: oculomotor nerve (all muscles supplying eye except superior oblique); laterally are cerebral peduncle (cortiospinal tract); from lateral pons V: trigeminal nerve - sensory nerve of head and neck with 3 main divisions from large root, and small root with some motor function used in chewing (mastication) - cross midline connecting cerebral hemispheres; postmedullary junctions below from medial to lateral: VI: abducens nerve moves lateral rectus muscle in eye, VII: facial nerve for facial expression muscles; VIII: vestibulococular nerve: balance and earache to inner ear; below into medulla: IX: glossopharyngeal nerve - toungue and pharynx for swallowing and breaking up food; X - vagus nerve for PSNS innovtion; XI: accessory nerve to shoulder and neck (turns head); XII: hypoglossal nerve to muscles under tongue; below central peduncle reemerges in pyramids - problems to spinotholamic tract (sensory); base of medulla is basis of contralateral motor control (crossing over)

Question 9

4 general (all over body) functional classifications of cranial nerves

Answer 9

general somatic afferent (sensation from skin and mucous membranes), general visceral afferent (sensation from GIT heart, vessels and lungs), general somatic efferent (muscles for eye and tongue movements), general visceral efferent (preganglionic parasympathetic: main is vagus nerve)

Question 10

3 special functional classifications of cranial nerves

Answer 10

special somatic afferent (vision, hearing and eqm), special visceral afferent (smell and taste), special visceral efferent (muscles involved in chewing, facial expression, swallowing, vocal sounds and turning head)

Question 11

embryonic spinal cord development

Answer 11

sulcus limitans (differentiates between dorsal and ventral) in middle of alar (dorsal root) and basal (ventral root) plates; general somatic afferent lateral posterior, general visceral afferent medial posterior, general visceral efferent medial anterior, general somatic efferent lateral anterior

Question 12

embryonic rhombencephalon (hindbrain): cranial nerve nuclei in brainstem

Answer 12

motor nuclei are more medial in brainstem; sensory nuclei are more laterally

Question 13

general shape of midbrain

Answer 13

mickey mouse (inverted structure)

Question 14

midbrain structure: inverted mickey mouse

Answer 14

ears: cerebral peduncle lateral, substantia nigra (black substance - neuromelanin; key pathology for motor symptoms of Parkinson’s disease shown if pale) medial; nose: cerebral aqueduct only present in midbrain; posterior roof of midbrain: inferior colliculus

Question 15

pons structure: posterior view

Answer 15

superior medial: 4th ventricle; lateral: middle cerebellar peduncle (connections to cerebellum); posterior: transverse fibres unique to pons

Question 16

medulla structure

Answer 16

superior medial: 4th ventricle; posterior lateral: inferior olivary nucleus (distinctive wavey shape); posterior medial: bilateral pyramids

Question 17

lower medulla structure

Answer 17

begins to look like spinal cord: central: central canal; posterior: dorsal columns; anterior: pyramidal decussation (fibres crossing over - descending corticospinal tract)

Question 18

2 causes of lateral medullary syndrome

Answer 18

thrombosis of vertebral artery or thrombosis of PICA (posterior inferior cerebellar artery) causing lesion of one small part of brainstem (lateral medulla)

Question 19

symptoms of lateral medullary syndrome

Answer 19

vertigo, ipsilateral cerebellar ataxia (unsteady on feet as one side impaired), ipsilateral loss of pain/thermal sense (face) not touch, Horner’s syndrome (loss of PSNS to face so pinpoint pupils and drooping and lack of sweating around eye), hoarseness (dysphagia), contralateral loss of pain/thermal sense (trunk and limbs)

Question 20

what does lateral medullary syndrome anatomically affect

Answer 20

vestibular nuclei (hence vertigo as loss of balance perception), inferior cerebellar peduncle (sensory balance impaired - ataxia), spinal nerve (trigeminal), ambiguus nerve (hoarseness), spinothalamic tract (contralateral loss of pain/thermal sense), sympathetic tract (Horner’s syndrome)