Brainstem & Cranial Nerves PDF

The Brainstem and Cranial Nerves Images from Human Anatomy 6th ed., © 2009, by Martini, Timmins and Talitsch, denoted by “Ma”. Images from Human Anatomy, 2nd ed., © 2008 by McKinley & O’Loughlin, denoted by “Mc”. 1 BRAINSTEM CERVICAL CORD SENSORY NUCLEI MOTOR NUCLEI The Brainstem vs. the Spin...

The Brainstem and Cranial Nerves Images from Human Anatomy 6th ed., © 2009, by Martini, Timmins and Talitsch, denoted by “Ma”. Images from Human Anatomy, 2nd ed., © 2008 by McKinley & O’Loughlin, denoted by “Mc”. 1 BRAINSTEM CERVICAL CORD SENSORY NUCLEI MOTOR NUCLEI The Brainstem vs. the Spinal Cord • in both, the grey matter is deep and the white matter is superficial • in both, the white matter consists of axons carrying sensory information rostrally, and motor information caudally • while grey matter in the spinal cord is a continuous column, grey matter in the brainstem is broken up into a discontinuous series of functionally specialized nuclei • both subserve somatic and autonomic functions • unlike the spinal cord, the brainstem: LUMBAR CORD – subserves “special senses”: hearing and balance – contains a “reticular formation” responsible for the maintenance of vital functions and one’s level of arousal 2 Brainstem: White Matter Tracts Descending fibre tracts • UMNs carrying voluntary output from the cerebral cortex to the spinal cord, controlling the body; “corticospinal tract” • UMNs carrying voluntary output from the cerebral cortex to the brainstem, controlling the face; “corticobulbar tract” • involuntary descending fibre tracts that modulate & coordinate: – posture, muscle tone, balance (e.g. vestibulospinal tract) – autonomic functions (e.g. from the hypothalamus) Ascending fibre tracts • from the spinal cord to the thalamus – e.g. SS input destined for conscious appreciation in the cerebral cortex • from the spinal cord to the cerebellum – e.g. subconscious proprioceptive input from muscles and joints Peduncles: white matter bundles • paired cerebral peduncles join the midbrain & cerebral hemispheres • 3 paired cerebellar peduncles join the brainstem & cerebellar hemispheres 3 The Brainstem in Context Diencephalon Midbrain Pons Brainstem Medulla Ma15.1 4 The Brainstem: Ventral View A B D C E F H I J K M N O G P L Q Ma15.20 A. diencephalon (thalami and hypothalami) B. optic nerves C. Midbrain D. cerebral peduncles E. occulomotor nerves (CN III) F. trochlear nerves (CN IV) G. Pons H. I. J. K. trigeminal nerves (CN V) abducens nerves (CN VI) facial nerves (CN VII) vestibulocochlear nerves (CN VIII) L. Medulla M. N. O. P. Q. R. glossopharyngeal nerves (CN IX) vagus nerves (CN X) accessory nerves (CN XI) pyramids hypoglossal nerves (CN XII) olives 5 The Cerebellum must be Removed to view the Dorsal Brainstem FOURTH VENTRICLE A C. The inferior cerebellar peduncles connect the medulla and cerebellum B C The cerebellum overlies the fourth ventricle. MEDULLA CEREBELLUM MIDSAGITTAL SECTION thru the CBLM, cutting left cblr peduncles, brainstem intact Ma15.19 A. The superior cerebellar peduncles connect the midbrain and cerebellum B. The middle cerebellar peduncles connect the pons and cerebellum MIDBRAIN PONS Three paired masses of white matter connect the cerebellum and brainstem: Once the peduncles are cut, one sees the floor of the fourth ventricle on the dorsal aspect of the brainstem. 6 The Brainstem: A. thalami Dorsal View B. pineal gland A B C. Midbrain D. superior colliculus (vision) E. inferior colliculus (hearing) D E C F. trochlear nerve (CN IV) F H. Pons G H I I. middle cerebellar peduncle L J. floor of IVth ventricle J O K K. Medulla L. inferior cerebellar peduncles M. posterior median sulcus N M Ma15.16 G. superior cerebellar peduncle N. gracile tubercle O. cuneate tubercle 7 The Cerebellum D • connected to the brainstem by the (A, B, C) superior, middle & inferior cerebellar peduncles E MIDBRAIN D. cortical grey matter PONS B • two bilaterally paired cerebellar hemispheres E. subcortical white matter A C F. cerebellar nuclei Functions of the Cerebellum MEDULLA F Sagittal section Ma15.19 • control of posture, balance • coordination of motor function 8 Inputs to the Cerebellum Frontal lobe Include: • spinocerebellar proprioceptive info. re. ipsilateral body position, muscle tone Thalamus Cerebellum • vestibulo-cerebellar input re. position and acceleration of the head in space Midbrain Pons Medulla CN VIII Cervical cord Vestibular apparatus • contralateral corticopontocerebellar afferents re. movement planning 9 Outputs from the Cerebellum Frontal lobe • motor, premotor ctx via VA, VL thalamus • motor cortex controls mvt of contralateral body…. Thalamus Cerebellum • what an elegant system for control of body movement! Midbrain Pons Medulla CN VIII Cervical cord Vestibular apparatus 10 BRAINSTEM CERVICAL CORD SENSORY NUCLEI MOTOR NUCLEI The Cranial Nerves & their Nuclei • like the body, the head has both: • sensory & motor components • voluntary & involuntary (autonomic) components SOMATIC (VOLUNTARY) MOTOR VISCERAL (AUTONOMIC) MOTOR SOMATIC SENSORY VISCERAL SENSORY • unlike the spinal cord, functional columns disperse into a series of longitudinally arranged, distinct nuclei • unlike spinal nerves, CNs may carry a single modality • unlike the spinal cord, the brainstem and cranial nerves subserve the “special” visceral sensation, taste and the “special senses” of hearing and balance LUMBAR CORD VISCERAL SENSORY INCLUDING TASTE HEARING AND BALANCE Note: for clarity, motor columns are shown on one side and sensory columns are shown on the other. 11 Both, however, are bilateral. Functional Approach to Learning Cranial Nerves 1. Cranial nerves that convey special senses – – – I (the olfactory N.) II (the optic N.) VIII (the vestibulocochlear N.) 2. Cranial nerves that control skeletal muscle – – – – – III (the oculomotor N.)* IV (the trochlear N.) VI (the abducens N.) XI (the accessory N.) XII (the hypoglossal N.) 3. Mixed cranial nerves – – – – V (the trigeminal N.) VII (the facial N.) IX (the glossopharyngeal N.) X (the vagus N.) 12 Cranial Nerves that Convey Special Senses I the olfactory nerve (covered with the nose / respiratory system) • conveys smell from the olfactory epithelium in the roof of the nasal cavity • nerves enter cranium by passing through the cribriform plate of the ethmoid II the optic nerve (covered with the eye) • conveys visual input from the retina • nerve enters cranium through optic foramen VIII the vestibulocochlear nerve (covered with the ear) • conveys auditory sensations from the cochlea via its cochlear division • conveys balance information from the vestibular apparatus via its vestibular division • nerve enters cranium through the internal auditory (acoustic) foramen 13 Cranial Nerves that Control Skeletal Muscle I III the oculomotor nerve* IV the trochlear nerve • exit cranium through superior orbital fissure to enter orbit • control extraocular eye muscles that position the eye in the orbit • nerve damage causes VI the abducens nerve • strabismus (misaligned eye) and • diplopia (double vision) * also controls the levator palpebrae superioris muscle – paralysis causes ptosis (a droopy eyelid) * also conveys parasympathetic preganglionic fibres destined for the eye – nerve damage causes mydriasis (enlarged pupil) 14 Cranial Ns that Control Skeletal Muscle II Jugular foramen Foramen magnum Cervical spinal cord Accessory N. (CN XI) SCM XI the accessory nerve • emerges as a series of rootlets from the lateral aspect of upper cervical segments • coalesce to form the accessory N. which enters the cranium through the foramen magnum • exits via jugular foramen with CN IX & X • controls the sternocleidomastoid (SCM) and trapezius muscles • SCM turns the head to the opposite side • trapezius elevates the shoulder • nerve damage causes……. XII the hypoglossal nerve • exits the cranium via hypoglossal canal Trapezius • controls the shape and position of tongue via its intrinsic and extrinsic muscles McT15.8 • nerve damage causes….. 15 A C Mixed Cranial Nerves 1: The Trigeminal Nerve B D A. the trigeminal nerve • conveys somatic sensation from the face E • consists of three divisions: B. ophthalmic division via superior orbital fissure (with which other three CNs?) C. maxillary division via foramen rotundum B C McT15.7 D D. mandibular division via foramen ovale E. the trigeminal ganglion contains the cell bodies of these pseudounipolar 1° somatic sensory neurons (like a DRG) • mandibular division also voluntary motor to the four muscles of mastication 16 Mixed Cranial Nerves 2: The Facial N (CN VII) pterygopalatine G. greater petrosal N. geniculate G. • exits cranium via internal auditory (acoustic) foramen 1. voluntary motor fibres exit skull via stylomastoid foramen to innervate muscles of facial expression 2. special visceral sensory (taste) from anterior 2/3 of tongue – 1° sensory axons in chorda tympani, cell bodies in geniculate ganglion 3. parasympathetic preganglionic via: stylomastoid foramen chorda tympani submandibular G. – the chorda tympani to submandibular ganglion: postganglionic fibres distributed to the submandibular and sublingual glands, oral mucosa below oral fissure – the greater petrosal nerve to the pterygopalatine ganglion: postganglionic fibres distributed to the lacrimal gland, nasal mucosa, oral mucosa above oral fissure – Nerve damage causes Bell Palsy 17 Mixed Cranial Nerves 3: The Glossopharnygeal N Pons (CN IX) Otic ganglion Pharyngeal branches CN IX Lingual branch Medulla Parotid gland • exits the cranium via the jugular foramen (other nerves?) 1. somatic sensory from post 1/3 of tongue, oropharynx 2. special visceral sensory (taste) from post 1/3 of tongue 3. visceral sensory from carotid body (chemoreceptors) and carotid sinus (baroreceptors) 4. parasympathetic preganglionic fibres to otic ganglion; postganglionic fibres innervate the parotid gland Carotid body Ma15.28 Common carotid A. Carotid sinus 5. voluntary motor to a single pharyngeal muscle 18 Pharyngeal branch Mixed Cranial Nerves 4: The Vagus N (CN X) CN X Laryngeal nerves Cardiac branches Cardiac plexus Right lung Left lung Liver Celiac Stomach plexus Pancreas Spleen Colon Small intestine Ma15.29 • exits the cranium via the jugular foramen 1. voluntary motor to the pharynx and larynx 2. general sensory from laryngopharynx, larynx 3. visceral sensory from chemoreceptors in the aortic body, baroreceptors in the aortic arch, thoracic and abdominal viscera 4. parasympathetic preganglionic fibres to intramural ganglia of thoracic and abdominal viscera 19