MCB 163: Mammalian Neuroanatomy
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Fall 2005 Seat #______
LAB EXAMINATION ONE
1. INTERNEURON Usually a small cell with a locally projecting axon and which uses GABA or
glycine as a neurotransmitter; it has many axonal branches and can supply recurrent or reciprocal
or feedforward inhibition to postsynaptic cells, as do Renshaw cells to the motoneuron that
excites them (autogenetic) and to the Ia inhibitory interneuron (disinhibition). Also known as:
Golgi type II cell, local circuit neuron, intrinsic neuron, etc.
2. AXON The effector, usually presynaptic part of the neuron, it is distinct from dendrites in often
having myelin, in releasing transmitter onto postsynaptic cells, in sending signals faithfully over
long distances, and in carrying information coded by interspike interval. A unique process on
the cell, it is smooth and devoid of spines.
3. OLIGODENDROGLIA A subtype of glial cell responsible for myelination in the central gray
matter, in contrast to Schwann cells which are responsible for peripheral myelination. Each
oligodendrogliocytes myelinates several segments along a single axon.
4. ASTROCYTE A type of glial cell devoted to forming the blood-brain barrier, one process of
which extends to a blood vessel while other processes contact neurons via gap junctions. Permits
gas exchange between neurons and blood and ensures the metabolic readiness of neurons to meet
the demands for synaptic transmission as well as the rapid removal of waste products.
5. CUNEATE NUCLEUS This wedge-shaped nucleus is the recipient of first order ipsilateral input
from representing cutaneous Merkel discs and Meissner and Pacinian corpuscles and muscle
spindles (Ia) and Golgi tendon organ (Ib) receptors for the forelimb; its cells project in
somatotopic fashion to the contralateral ventrobasal complex via the medial lemniscus.
6. SI Six-layered neocortex which has multiple representations of the body map including
separate subregions for cutaneous and deep muscle receptors (areas 3a, 3b) and which is
essential for epicritic discrimination of fine touch from the contralateral body (via dorsal
columns) and head (via trigeminal) inputs.
7. TRACT OF LISSAUER the entry zone for primary afferent nociceptive fibers from the A
(pinprick pain and crude touch) and C-fiber (burning grinding pain) within which they ascend
and descend 2-3 spinal segments before terminating on the second order, decussated neurons of
the spinothalamic lemniscus en route to midbrain, reticular formation, posterior thalamus.
8. CENTRAL GRAY One of the targets of the ascending pain pathway, and the origin of
descending input to the raphe nuclei, which project to enkephalinergic interneurons in the dorsal
horn that use presynaptic inhibition to block the release of transmitter from substance P primary
axons.
9. UPPER MOTOR NEURONS All descending influences, including reafferents, that are
presynaptic to  and and autonomic motoneurons, including motoneurons in the cranial nerve
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motor nuclei. Damage to the upper motoneurons, which are not immediately presynaptic to
muscle, only denervate partially the lower motoneurons which are immediately presynaptic to
muscle and damage to which leaves all muscle paralyzed flaccidly.
10. FLACCID PARALYSIS Destruction of lower motoneurons (e.g., in polio) leads to complete
paralysis of the muscle postsynaptic to  and  and autonomic motoneurons since all upper
motoneuron input converges onto the latter cells, which represent the final common pathway to
skeletal and to smooth muscle.
11. CEREBROCEREBELLUM The lateral lobes of the cerebellar hemispheres are dominated by
corticopontocerebellar mossy fiber projections, especially in mammals with a well developed
neocortex. This allows disynaptic neocortical influence to reach Purkinje cells, especially those
which synapse ultimately into the dentate nucleus and feed forward, through the red nucleus,
onto the ventral anterior/ventral lateral thalamic nuclei, which project to premotor and motor
cortex for planning movement and movement execution, respectively.
12. PURKINJE CELL The sole output cell of the cerebellar cortex, this giant GABAergic neuron projects
to the deep cerebellar nuclei via the superior cerebellar peduncle, and is responsible for providing tonic
input to the vestibulospinal and reticulospinal tracts, which in turn influence  motoneurons for the
maintenance of resting and background muscle tone.
13. RECIPROCAL INHIBITION The condition whereby  flexor and  extensor motoneurons
whose axons innervate the opposing flexor and extensor muscles on a limb mutually inhibit one
another when either muscle is contracted; ensures unanimity of discharge by providing direct
inhibition through an inhibitory interneuron.
14. GRADED POTENTIAL Receptor or generator potentials are linearly related to stimulus
intensity in most modalities and thus send an analog signal to ganglion cells; in contrast to the
all-or-none, constant amplitude of spikes generated by central neurons, except, of course, for the
complex spikes of spinoolivocerebellar climbing fibers onto Purkinje cells in cerebellar cortex.
15. RECEPTIVE FIELD The portion of sensory space in the cutaneous, nociceptive, visual,
auditory, etc. systems that a receptor represents, as limited by its capacity to intercept specific
stimuli. The peripheral RFs feed onto first-order ganglion cells, which in turn project to brain
divergently to create successively larger RFs. Critical for accurate spatial localization of stimuli.
In the brain, RFs often have excitatory subregions flanked by inhibitory surrounds that enhance
their overall resolution.
16. PRESYNAPTIC INHIBITION A special type of inhibition in which one axon synapses onto
another, often just behind the synapse of the postsynaptic cell, e.g., the enkephalinergic
interneuron of the spinal dorsal horn which is presynaptic to the substance P-containing primary
afferent nociceptive ganglion cell, and whose activation via the raphespinal system checks or
blocks transmitter release from the primary afferent ending.
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17. SPINOOLIVOCEREBELLAR A part of the spinocerebellar system, this pathway is parallel to
the spinocerebellar tracts and conveys climbing fiber input to each cerebellar Purkinje cell. This
input elicits complex spikes in the latter which are thought to be crucial for acquisition of fine
motor skills; once learned, the complex, graded spikes elicited by spinoolivocerebellar input
once again become simple all-or-none spikes.
18. LEMNISCUS A decussated second-order sensory axon, this process is responsible for
conveying information from the ipsi- to the contralateral hemisphere in touch, pain and
temperature, and hearing. Does not occur in the spinocerebellar system or in the visual system.
A bundle of second-order fibers representing the ipsilateral receptor array and which decussates.
19 CORPUSCLE OF VATER-PACINI (Pacinian corpuscle) An encapsulated rapidly adapting
mechanoreceptor whose A ganglion cell projects to the dorsal column/trigeminal nuclei.
Responsible for the appreciation of deep somatic pressure that is important in grasping objects
using the correct and appropriate amount of force.
20. OFFICE HOURS Monday and Friday, 3:00-5:00 p.m., and by appointment.
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