MCB 163: Mammalian Neuroanatomy Fall 2001

Name ____Key_____________________ Third Lab Examination

1. superior cerebellar peduncle a tract that contains cerebellofugal axons arising from the

deep nuclei and ascending towards the red nucleus and reticular formation and vestibular nuclei; the excitatory output from the deep nuclei is modified by corticopontocerebellar influences and by spinocerebellar afferents

2. middle cerebellar peduncle the axons from pontine nuclei that pass as mossy fibers to the cerebellar cortex; their primary role is to convey cortical input to the cerebellar cortex to provide a feedback signal about predicted limb and trunk position that is compared with the spinocerebellar input; if these ‘match’ then movement continues

3. superior colliculus the target of W-ganglion cell and Y-cell input from the retina, it contains three main layers: the upper part has a visuotopic map dominated by rod input, the middle layers are polymodal, and the deep layers from the tectospinal tract and terminate on cervical motoneurons in the upper spinal cord; critical for following moving visual stimuli

4. trigeminal nerve the main afferent trunk for cutaneous and deep tissue sensibility for touch, pain, and temperature for the face; the ganglion cells lie in the trigeminal ganglion and consist of ophthalamic, maxillary, and mandibular peripheral branches whose axons end in the main sensory nucleus (touch) or the spinal trigeminal nucleus (pain and temperature

5. red nucleus a precerebellar relay nucleus that carries cerebellar outflow to the VA/VL thalamic motor nuclei, whose projections to premotor and supplementary motor cortex are critical in initiating movement; also, it is the origin of the rubrospinal tract, which targets distal flexors; this allows subconscious influences to reach muscles for fine motor control

6. medial geniculate body the target of lemniscal input from the inferior colliculus, it is the thalamic nucleus for hearing; it projects both to auditory cortex and to the amygdala, the latter projection allowing for rapid autonomic responses/learning to sound stimuli; projects to primary and nonprimary auditory cortex and essential for normal hearing

7. anterior pretectum a multisensory nucleus located between the medial geniculate body and the reticular formation, it receives brainstem afferents from several modalities; it also receives retinal afferents and sends impulses rostrally to the Edinger-Westphal subdivision of the III nucleus, which then projects to the ciliary ganglion for parasympathetic control of pupillary muscle tone

8. cerebral peduncle a large mass of axons, only slightly smaller than the corpus callosum and internal capsule, that contains corticofugal axons projecting to the midbrain, pons, medulla, and spinal cord; the corticospinal tract is a significant component; small in species with little cerebral cortex, and especially large in humans; probably provides cortical control

9. lateral geniculate body six layered in humans and with hidden lamination in the rat, it has four layers that receive X/P/ß and two that receive Y/M/a input; the X input is cone-dominated, chromatic, and highly topographic, the Y pathway smaller, from rod-driven cells, and less precise topographically; segregates ascending input possibly for cortical control of transmission; essential for normal vision

10. ventrobasal complex consists of the ventroposterolateral (representing trunk and hindlimbs) and the ventroposterolateral nuclei (forelimbs and head) that form the thalamic representation for conscious touch and for muscle sensibility for length (Ia) and tension (Ib) systems; the target of dorsal column input, its neurons have center-surround RFs; complete map of body

11. posterior hypothalamus continuous with the central gray, it has a crucial role in processing noxious/painful stimuli and in thermoregulation; neurons have wide dynamic range and large RFs, and responds to increases in core or peripheral temperature by inducing sweating, vasodilatation, and decreased urinary retention through activation of the sympathetic system

12. thalamic reticular nucleus a thin band of exclusively GABAergic neurons on the lateral perimeter of the thalamus, and with specific auditory, visual, etc. cortical-recipient sectors; hypothesized to allow for selective gating of attention by the GABAergic suppression of irrelevant behavioral stimuli by cortical control; this is Crick’s searchlight hypothesis

13. caudoputamen the main cortical targets in the basal ganglia, these nuclei receive input from most of the neocortex and contain a variety of cell types, including cholinergic interneurons, which project to the internal and external segments of the pallidum, which serve as basal ganglia output nuclei; critical for the initiation and arrest of movement

14. optic chiasm the region at which retinal ganglion cell axons from the nasal retina and representing the temporal visual field decussate en route to the contralateral lateral geniculate body; the degree of decussation is species-specific, e.g., 100% in rats, 70% in humans; not a lemniscus since the decussation is incomplete

15. suprachiasmatic nucleus receives retinal input and has projections to the hypothalamus, this tiny nucleus has a key role in the programming and changes in biological rhythms related to sleeping, waking, steroid hormone secretion, in the modulation of seasonal changes in coat color or skin pigmentation through its actions on the paraventricular and other hypothalamic nuclei

16. corpus callosum the largest single fiber tract in the brain, it contains the axons of pyramidal cells in cortical layers III and V that pass between the hemispheres; the only zones that are not so interconnected reciprocally in adulthood are the hands, face and feet in SI, the central representation of the fovea in VI, and some parts of AI related to binaural hearing; important for interhemispheric coordination of speech and language

17. somatic sensory cortex six layered neocortex (SI, containing areas 3a, 3b, 1, and 2) essential for normal cutaneous sensibility for input from superficial and deep skin receptors, and from muscles, joints, and tendons, and ligaments; feeds forward to SII where higher-order perceptual processing (e.g., texture analysis) occurs

18. anterior commissure consists of interhemispheric axons from the olfactory and inferior temporal and orbitofrontal cortex and other parts of the limbic forebrain that coordinate activity bilaterally in this system, so that an odor in one bulb has access to both hemispheres; large in species with well developed limbic systems, and relatively small in humans

19. inferior colliculus the auditory midbrain, it is presynaptic to the medial geniculate body and has topographic/tonotopic inputs to it; plays an important role in auditory orienting and in acoustic vigilance and spatial localization of sound; especially large in predators; forms two small protrusions in the caudal midbrain

20. fimbria the fringe formed by hippocampal pyramidal cell axons as they leave the dorsal surface of the hippocampus, before they form the compact bundle, or fornix, along which they project into the mammillary bodies to carry hippocampofugal information to the anterior thalamus and to the brain stem via mammillothalamic and mammillotegmental pathways