9/12 Brainstem - Rasin

Question 1

3 parts of brainstem 3 fx of brainstem

Answer 1

1. medulla 2. pons 3. midbrain 3 primary fx: - conduit - CN fx - integrative (collect info from periph and act on it)

Question 2

ventricular system association with brainstem

Answer 2

lateral ventricles lie within forebrain 3rd ventricle at level of diencephalon cerebral aqueduct is at level of midbrain 4th ventricle is at level of pons and rostral medulla, beyond which central canal begins (caudal medulla)

Question 3

3 exit points for CSF circ (within brainstem) 4 cisterns what’s special about magna?

Answer 3

medial foramen of Magendie 2 lateral foramina of Luschka csf goes from ventricles into 4 cisterns: 1. interpeduncular 2. prepontine 3. quadrigeminal 4. cisterna magna [secondary site for csf sampling]

Question 4

rostral medulla structures transverse section keys

Answer 4

medial to lateral: -pyramids (CST) - axons -olive -inf cerebellar peduncle in transverse section, - see 4th ventricle with choroid plexus on dorsal side

Question 5

corticospinal tract decussation

Answer 5

approx halfway through medullary pyramid, CST will split up: 90% will decussate to contralateral side 8% will go to ipsilateral anterior CST 2% will go uncrossed to the ipsilateral lateral CST

Question 6

corticonuclearbulbar pathways

Answer 6

descending control AND modulation of sensory/motor nuclei of cranial nerves 1st order: widespread areas of cerebral cortex 2nd order: pontine/medullary reticular formation AND nuclei of CN - mostly bilateral innervation with a few exceptions… *mostly contralateral for nucleus of CN XII, nucleus ambiguus innervation of soft palate/uvula (CN X)I **ONLY ipsilateral for nucleus of CN XI

Question 7

caudal medulla dorsal view structures

Answer 7

medial to lateral: -gracile tubercle (at terminus of fasciculus gracilis) -cuneate tubercle (at terminus of fasciculus cuneatus)

Question 8

recap: DCMLS what does it carry? neurons at each level crossing level WHAT’S IN THE MEDULLA?

Answer 8

posterior/dorsal column medial lemniscal pathway carries: discriminative touch, pressure, proprioception 1st order - large myelinated fibers of DRG 2nd order - dorsal column nuclei (gracilis, cuneatus); fibers decussate as internal arcuate fibers 3rd order - VPL nucleus of thalamus decussation at: LOWER MEDULLA 2nd order neuron in medulla - travels through medial medulla

Question 9

recap: spinothalamic pathway (anterolateral system) what does it carry? neurons at each level crossing level WHAT’S IN THE MEDULLA?

Answer 9

carries: pain and temperature 1st order - small myelinated/unmyelinated fibers of DRG 2nd order - dorsal horn layers I, II, V 3rd order - VPL nucleus of thalamus decussation at: SPINAL SEGMENTAL LEVELS 2nd order neuron in spinal cord - travels through lateral medulla

Question 10

which motor and sensory pathways are associated with the medulla? which ones synapse? which ones travel through?

Answer 10

synapse in medulla: - corticobulbar pathway - DCML pathway travel through medulla: - corticospinal pathway - spinothalamic tract (anterolateral pathways)

Question 11

cranial nerve summary (sensory vs mixed vs motor

Answer 11

12 pairs of CN provide motor/sensory innervation to somatic and visceral structures sensory: I, II, VIII mixed: V, VII, IX, X motor: III, IV, VI, XI, XII

Question 12

CN motor efferent nuclei types

Answer 12

1. somatic (S) : relate to framework of body (skeletal muscles originating from embryonic SOMITES, ex. extraocular and tongue muscles) 2. visceral (V) : activate viscera or organs - GENERAL (G): pregang PSNS for cranial, thoracic, abd smooth muscles (viscera) - SPECIAL (S): striated muscles (NOT from embryonic somites - from embryonic BRANCHIAL ARCHES; aka branchiomotor/branchial efferents) ex. muscles of facial exp, jaw muscles, laryngeal/pharyngeal muscles, SCN, traps

Question 13

CN sensory afferent nuclei types

Answer 13

1. somatic (S) : carry info about changes in environment from body to brain -GENERAL - impulses beginning at or near body surface (pain, temp, touch, pressure) -SPECIAL - specialized sensory systems (vision, hearing) 2. visceral (V) : impulses arising in or around viscera/organs -GENERAL - receptors in/on mucous membranes or organ wall carrying impulses re: physical distention or chemical composition of substances or organ wall -SPECIAL - specialized chemical stimuli (smell, taste)

Question 14

CN sensory/motor/both mnemonic

Answer 14

some say money matters but my brother says big brains matter most

Question 15

2:2:4:4 rule

Answer 15

outside brainstem : midbrain (III, IV) : pons (V-VIII) : medulla (IX-XII)

Question 16

general placement of motor and sensory nuclei within brainstem

Answer 16

motor tend to be MEDIAL sensory tend to be LATERAL

Question 17

CN XII course/exit function

Answer 17

CN XII has cell bodies in hypoglossal nucleus (cell column on dorsal side), nerve exits on ventral side between pyramid and olive general somatic efferent - ipsilateral muscles of tongue (all intrinsic, all but one of extrinsic tongue muscles) - movement of tongue - maintainance of muscle tone RECALL: UMN for CN XII come from contralateral corticobulbar tract!

Question 18

innervation of CN XII

Answer 18

1. corticonuclear/corticobulbar neurons - control of voluntary movements/articulation 2. reticular neurons - automatic/reflex movements (control of stereotypes movements while eating/swallowing)

Question 19

lesions of CN XII UMN lesion? LMN lesion?

Answer 19

UMN lesion: tongue deviation to contralat side + spasticity LMN lesion: tongue deviates to ipsilat side + atrophy

Question 20

bilateral lesion of CN XII issues causes of CN XII lesions

Answer 20

issues speaking, swallowing ALS, demyelinating disease, bleeding, tumors

Question 21

CN XI nerves contained parts and functions

Answer 21

ACCESSORY NERVE moves neck/shoulder contains nerves originating from both: 1. accessory nucleus (in medulla) 2. ventral motor horn (cervical spinal cord) brancial motor part: ipsilateral SCM, trap muscles (neck/shoulder) aka “spinal part” visceral motor part: joins CN X for control of larynx aka “accessory part”

Question 22

lesion of CN XI

Answer 22

-can’t rotate to healthy side against pressure -ipsilat shoulder drop -weakened voice/hoarseness