3 parts of brainstem 3 fx of brainstem
1. medulla 2. pons 3. midbrain 3 primary fx: - conduit - CN fx - integrative (collect info from periph and act on it)
ventricular system association with brainstem
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)
3 exit points for CSF circ (within brainstem) 4 cisterns what's special about magna?
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]
rostral medulla structures transverse section keys
medial to lateral: -pyramids (CST) - axons -olive -inf cerebellar peduncle in transverse section, - see 4th ventricle with choroid plexus on dorsal side
corticospinal tract decussation
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
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
caudal medulla dorsal view structures
medial to lateral: -gracile tubercle (at terminus of fasciculus gracilis) -cuneate tubercle (at terminus of fasciculus cuneatus)
recap: DCMLS what does it carry? neurons at each level crossing level WHAT'S IN THE MEDULLA?
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
recap: spinothalamic pathway (anterolateral system) what does it carry? neurons at each level crossing level WHAT'S IN THE MEDULLA?
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
which motor and sensory pathways are associated with the medulla? which ones synapse? which ones travel through?
synapse in medulla: - corticobulbar pathway - DCML pathway travel through medulla: - corticospinal pathway - spinothalamic tract (anterolateral pathways)
cranial nerve summary (sensory vs mixed vs motor
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
CN motor efferent nuclei types
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
CN sensory afferent nuclei types
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)
CN sensory/motor/both mnemonic
some say money matters but my brother says big brains matter most
outside brainstem : midbrain (III, IV) : pons (V-VIII) : medulla (IX-XII)
general placement of motor and sensory nuclei within brainstem
motor tend to be MEDIAL sensory tend to be LATERAL
CN XII course/exit function
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!
innervation of CN XII
1. corticonuclear/corticobulbar neurons - control of voluntary movements/articulation 2. reticular neurons - automatic/reflex movements (control of stereotypes movements while eating/swallowing)
lesions of CN XII UMN lesion? LMN lesion?
UMN lesion: tongue deviation to contralat side + spasticity LMN lesion: tongue deviates to ipsilat side + atrophy
bilateral lesion of CN XII issues causes of CN XII lesions
issues speaking, swallowing ALS, demyelinating disease, bleeding, tumors
CN XI nerves contained parts and functions
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"
lesion of CN XI
-can't rotate to healthy side against pressure -ipsilat shoulder drop -weakened voice/hoarseness