Download MCB 163: Mammalian Neuroanatomy

MCB 163: Mammalian Neuroanatomy
Name: Key
Fall 2005 Seat #______
LABORATORY EXAMINATION TWO
1. LUMBAR SPINAL CORD: Distinguishing features include the large size of the ventral horns and
the presence only of the gracile fasciculus in the dorsal columns; the corticospinal tract is
reduced relatively since many descending fibers have already terminated; the relative ratio of
gray to white matter favors the gray, suggesting that many tracts are small.
2. GRACILE FASCICULUS: This tract contains ganglion cell axons representing cutaneous Merkel
and Meissner and Pacinian corpuscles and muscle spindles (Ia) and Golgi tendon organ (Ib)
receptors from the hindlimb and inferior trunk that are ascending towards the gracile nucleus in
the medulla to form topographic excitatory connections before becoming and joining lemniscal
axons.
3. LAMINA I-V: The sources of the neo- (Aδ) and paleospinothalamic (C fiber) projections to the
pain and temperature system. In it, first-order primary afferents (glutamatergic for Aδ
substance P-containing for C fibers) synapse and decussate, the second-order cells forming the
spinothalamic lemniscus and projecting to the posterior thalamus or to the central gray and
reticular formation, respectively.
4. LAMINA VIII, IX: These are lower motoneurons immediately presynaptic to muscle, including
α and γ motoneurons and the associated Renshaw and other local cells. These motoneuron pools
represent, respectively, flexors in more dorsal parts of the ventral horn, and extensors in the
ventral part. Proximal or axial or trunk muscles are represented in more medial parts of the
ventral horn (near lamina VIII), and distal muscles are represented more laterally.
5. TRACT OF LISSAUER: This is a small fiber tract that lies dorsal to Rexed’s lamina I. It contains first
order spinothalamic axons and is continuous through the dorsoventral extent of the spinal cord, and it
represents the entry point for pain and temperature fibers to ramify before entering a dorsal horn to
synapses. Such fibers at any given spinal level can synapse within three segments of their specific entry;
this means that the dermatomes for pain have coarser somatotopy than those for touch and pressure.
6. THORACIC SPINAL CORD: The reduced gray matter, the presence of a distinct intermediolateral
cell column, and the tiny ventral horn each signify the representation of the intercostal muscles;
concomitantly, the dorsal horn is small, too, and the dorsal column representation is limited to
the lower leg and trunk.
7. INTERMEDIOLATERAL CELL COLUMN: A specialized pool of preganglionic sympathetic
neuronal cell bodies in the thoracicolumbar spinal cord whose axons project to the sympathetic
chain before terminating in their targets on smooth muscle. These inputs oppose the
complementary craniosacral parasympathetic efferents that usually serve to reduce neural
activity in smooth muscle.
8. VESTIBULOSPINAL AND RETICULOSPINAL TRACTS: These (and other) tracts project
preferentially to the proximal axial muscles of the trunk and limbs; the tracts extend the entire
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length of the spinal cord, are primarily ipsilateral, and have no known topography in their
projection; the vestibulospinal tract is driven primarily by otolith organ input, reticulospinal by
all modalities.
9. LATERAL CORTICOSPINAL TRACT: Upper motoneurons that project the length of the spinal
cord to α motoneurons and which are responsible for rapid and precise muscle contractions and
powerful movements, especially of the distal extremities; often damage by stroke, these neurons
arise from motor and sensory cortex in the contralateral hemisphere and are unique to primates.
10. SPINOCEREBELLAR TRACT: These are second-order undecussated axons en route to the
cerebellum (via the inferior cerebellar peduncle) or to the inferior olive and which carry
subconscious proprioceptive information to Purkinje cells (as mossy fiber endings) or to inferior
olivary cells; the latter terminate in the cerebellar cortex as climbing fibers and are active
phasically during complex motor learning, but otherwise only active tonically. This
spinocerebellar tract parallels the dorsal columns save that the information in it is subconscious.
11. GRACILE NUCLEUS: The axons representing the bottom of the foot, the ankle, the shin, the
knee and the lower half of the body ascending as first-order primary afferents in the dorsal
columns terminate in this nucleus before decussating and terminating in the contralateral
ventrobasal complex. The nucleus as well as the fibers has a somatotopic arrangement.
Check #11: Was not caudal medulla? (you could see the cerebellum)
12. SPINAL TRIGEMINAL NUCLEUS: This nucleus contains first-order spinotrigeminothalamic
neurons whose axons decussate and terminate in the central gray, posterior thalamus, or reticular
formation; these structures propagate nociceptive information to the hypothalamus and to insular
and cingulate cortex. This structure is analogous to layers I-V of the dorsal horn, and includes a
raphetrigeminal component for descending modulation of pain.
13. MEDIAL LONGITUDINAL FASCICULUS: a tract that spans the cervical spinal cord to the rostral
midbrain to interconnect the vestibular (VIII) and oculomotor (III, IV, VI) systems using
ascending and descending axons to provide for conjugate and consensual eye movements that are
linked with the input from the labyrinths and otolith organs.
14. INFERIOR OLIVE: Source of climbing fibers that form a 1:1 relation to postsynaptic Purkinje
cells; this fiber makes complex spikes that are essential for skilled motor learning; well
developed in primates.
15. VESTIBULAR NUCLEI: The site of first order terminations from ganglion cell axons
innervating the three semicircular canals or the saccular and utricular maculae. Consists of four
nuclei, of which the most medial feed forward into the medial longitudinal fasciculus, while the
lateral (Deiters’) nucleus is the primary source of reticulospinal fibers, which are undecussated,
without topography, and project the length of the spinal cord.
16. NUCLEUS AMBIGUUS: A tiny group of cholinergic lower motoneurons innervating the
oropharyngeal area and vocal cords and important in the control of vocal tone and in the
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integration of behaviors such as swallowing, speech, and voice pitch; contains alpha
motoneurons and is a target of significant corticobulbar projections.
17. FACIAL MOTOR NUCLEUS: Lower motor neurons responsible for innervating the muscles of
facial expression; nucleus contains α and γ motoneurons, Renshaw cells, Ia and Ib interneurons
responsible for stretch reflexes; often affected in Bell’s palsy with consequent weakness of facial
muscles.
18. DENTATE NUCLEUS: This cerebellar relay nucleus is enormous in humans and one of the
main sources of the lateral cerebellar system that travels to the parvocellular part of the red
nucleus, and then to the ventroanterior-ventrolateral thalamic nucleus, and from there to the
premotor and motor cortex for long term motor planning prior to the execution of serial
movements.
Did he really point to this?
19. FACIAL NERVE AND GENU: These axons of lower motoneuron represent the final common
pathway of α and γ motoneurons en route to the muscles of facial expression for power and
precision of their contractions. A few axons are also en route to the tensor tympani to support its
withdrawal from the repeated effects of loud sounds, thus attenuating their impact on hearing.
Damage to the VIIth nerve because of its long intracranial course is not uncommon; the motor
nucleus itself receives bilateral, predominantly crossed, corticofugal input.
20. SUPERIOR CEREBELLAR PEDUNCLE: The output pathway from the cerebellar deep nuclei
toward the parvocellular (small-celled) subdivision of the red nucleus. Sends axons from there
to the ventral anterior/ventral lateral thalamic nucleus, which projects to motor cortex. Crucial
for motor planning and for informing motor cortex of subconscious state of muscle, joint, and
cutaneous receptors.
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