caudal ribbons forming swellings are called fasciculis gracilis and cuneatus respectively: axons of first-order neurons
first-order neurons synapse in nuclei on second-order neurons, which cross midline as internal arcuate fibers becoming Medial Lemniscus
Cerebellar Peduncles
: distinct from Cerebral Peduncles; the way in and out of the cerebellum
Superior cerebellar peduncle
(aka brachium conjunctivum): midbrain and rostral pons
decussation takes place here
Middle cerebellar peduncle
(aka brachium pontis): pons; largest
made up of the secondaryneurons from the pontine nuclei on their way to the cerebellum
Inferior cerebellar peduncle
(aka restiform body): medulla
Inferior and ventral to 4th ventricles
Cerebral Peduncles
(crus cerebri) – midbrain; CN III emerges medially above pons; optic tracts laterally wrap around most rostral portion into the medial ventrally located optic chiasm.
Crus cerebri = descending
fibers = cortico spinal and cortical Pontine. Former go to spine, latter to Pons
Substantia niagra
: regulates motor activity of cerebral nuclei
Tegmentum
: body of the mid brain; contains many fiber tract and nuclei (ie red nucleus, CNIII nuclei) see below
Pontine enlargement
– pons; Transverse fibers to cerebellum are unique to this region
cortico-spinal tracts are broken up by cortical pontine nuclei, which send fibers into the Cerebellum
Pyramids
of medulla contain only cortico-spinal fibers -seen in all levels of brain stem
Olives
are lateral to pyramids
Medial lemniscus
: sits dorsal to pyramids
Tegmentum
collection of sensory and motor nerve groups in the brainstem
loaded with ascending pathways, nuclei to CN’s and reticular formation nuclei
Principles of organization
motor neurons/ nuclei
are closer to the midline
Sensory neurons/nuclei
are further from the midline
Ascending longitudinal sensory nuclei system
Trigeminal system
: nuclei that process somatic sensory information from face; runs length of brainstem
Divisions: Mesencephalic nucleus, Chief sensory nucleus of CN V, Spinalnucleus
Solitary tract: Visceral sensory system that processes info from vagus (carotid body and sinus etc.) and taste - Solitary tract surrounded by nuclei that run mostly the length of the medulla
Cranial nerve motor nuclei (letters correspond to diagram below)
Visceral Motor nuclei (B)
: parasympathetic nuclei to gland and smooth muscle of head
Skeletal muscle (of head) nuclei:
CN III, IV, VI, XII (A)
: innervate skeletal muscle derived from somites, so nuclei are located near the midline
CN V, VII, IX, X (C)
: innervate skeletal muscle derived from neural crest cells in brachial arches
somite derived nuclei are most medial, next are visceral motor, next are brachial derived motor. All motor nuclei are medial to the Sulcus Limitans and all sensory nuclei are lateral to it
Peripheral Targets
A = striated muscle of eye and tongue, somite derived nuclei
B = (parasympathetic preganglionic neurons to) smooth muscle, cardiac muscle and glands innervated by cranial division of cranio-sacral division (=parasympathetic division) of autonomic nervous system i.e., by cranial nerves III, VII, IX and X) – visceral derived motor
C = striated muscle of jaws, face, soft palate, pharynx, larynx + trapezius and sternocleidomastoid (muscles of facial expression, muscles of mastication, muscles of swallowing and phonation +) – branchial derived motor
nA = nucleus ambiguus (branchiomeric nucleus of CN IX and X