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9.14 Week 5
Vocab from Schneider Chapters 13-15
| Term | Definition |
|---|---|
| Claustrum | The claustrum receives inputs from visual, auditory and somatosensory cortical areas and is also connected to motor cortex. Functions of the claustrum are not known. |
| Growth Cone | The motile tip of a growing axon. Growth cones of dendrites have also been observed. |
| Selective Adhesion | By means of specific cell adhesion molecules, cells or parts of cells may adhere much more to some surfaces than to others. This kind of selective adhesion is important in the guidance of growing axons. It is also important in cell sorting. |
| Growth Factor | A protein, that when present, increases proliferation of cells or growth of cell processes and/or causes changes in the direction of growth, either up or down a gradient of the factor. |
| Fibroblast | The most common type of cell in connective tissue, fibroblasts move to sites of injury and secrete collagen and extra-cellular matrix molecules. |
| Neurotrophins | A particular family of growth factors important in the development of both PNS and CNS. They are also important in some types of neuronal plasticity in the mature nervous system. They bind to trk receptors in cell membranes, |
| Peripheral Domain (of an Axonal Growth Cone) | Thin filopodial processes filled with actin filaments, and thin sheets of membrane enclosing an actin meshwork constitute the peripheral domain of a growth cone. |
| Central Domain (of an Axonal Growth Cone) | The central domain is closer to the trunk of the axon, and contains microtubules and various cytoskeletal proteins with anchoring functions. |
| Lamellipodia (s. Lamellipodium) | Some growth cones are dominated by lamellipodia and have few filopodia. They are the actin meshwork in the peripheral domain of a growth cone. |
| Guidepost Cells | Non-neuronal cells that guide growing axons. In some cases, they serve as temporary anchoring points along the growth trajectory of axons. |
| Pioneer axon | One of the first axons to grow in the formation of a nerve or axon tract. Pioneer axons can extend independent of the presence of neighboring axons. Axons of the same type which grow afterwards, can use the pioneer axon like a road to the destination. |
| Mauthner Cells | A pair of very large neurons of the middle hindbrain of amphibians or fishes with axons that cross the midline and extend to motor neurons that activate escape movements. |
| Stereotropism | Guidance of the direction of axon growth by surfaces of other cells and the contours of those surfaces. |
| Galvanotropism | Guidance of axon growth by minute electrical currents. It is debated whether such electric currents play important roles except for rare instances in a few species. |
| Differential Adhesion | Strong adhesion will stop growing axons. Weaker adhesion guides axonal growth as filopodia adhere, pull the growth cone, and break contact. The duration of the adhesion varies with strength, and thus differential adhesion guides the growth of the axon. |
| Chemotropism | Chemical effects on direction of growth of cell processes, like axons. |
| Chemorepulsion | Blocking of axon growth by a chemical barrier, or growth of the axon away from a source of a diffusing substance. |
| Chemoattraction | Growth of axons towards a source of the diffusing substance. |
| Contact Attraction | Growth of axons along a particular surface due to molecules in that surface, or adherence to a surface because of molecules in that surface. |
| Contact Repulsion | Movement away from a surface containing certain molecules. |
| Semaphorins | A family of molecules that strongly affect the direction of growth of particular axon populations. |
| Tropic | Affecting the direction of growth of cell processes, like axons. |
| Trophic | Increasing the amount or rate of cell or axonal growth, or preventing cells from dying. Increasing the growth vigor of developing axons. |
| Collapsin | A molecule when encountered by a growth cone, results in the collapse of the growth cone and retraction of the axon for a short distance before the growth cone re-forms. |
| Netrin | A class of proteins involved in axon guidance. Netrins are chemotropic; a growing axon will either move towards or away from a higher concentration of netrin. |
| Arborization | The formation of tree-like branching by a growing axon, or the branching structure formed by such a process. Such structures are where synapses are made by an axon, usually on neuronal dendrites and cell bodies. |
| Initial Focalization | During development of an axon, the losing of rudimentary widespread branches and the augmentation of branches in one small region. |
| Laminar Focalization | Growth of more branches of an axon in one layer with loss of branches in other layers of the tissue. |
| Arbor Maturation | The final period of development of an axon when the end arbors undergo changes in synapse distribution and appearance. |
| Pretectal Area | The region just rostral to the midbrain tectum that is part of the epithalamus . The area is traversed by optic-tract axons, which form synaptic terminals in several pretectal cell groups. |
| Ephrin | The presence of these membrane-bound molecules in neurons allows cell-cell contacts during axonal growth to affect axon guidance. |
| Map Compression | After brain damage that destroys part of a topographic sensory map in the CNS, the entire map can become compressed into the remaining tissue. This only happens after lesions very early in life in mammals, but it happens even in adult fish and amphibians. |
| Map Expansion | After damage to sensory inputs to the CNS, the topographic representation in the CNS can expand until the limited input still enervates the same area. This happens only after very early damage in mammals, but it can happen in adult fish and amphibians. |
| Dorsal Lateral Geniculate Nucleus (LGd) | The dorsal nucleus of the lateral geniculate body (LGB) is the major recipient of retinal projections in the thalamus. |
| Ventral Lateral Geniculate Nucleus (LGv) | The ventral nucleus of the LGB is the recipient of retinal projections in the subthalamus, adjacent to the dorsal nucleus of the LGB. |
| Medial Geniculate Nucleus (MGN) | Also called the medial geniculate body (MGB), it is the major recipient of ascending auditory pathways in the mammalian thalamus. |
| Lateral Posterior Nucleus (LP) | A caudal portion of the lateral group of thalamic nuclei in mammals, the LP is found dorsal and medial to the LGd. It receives dense projections from the superior colliculus, and expands into the large pulvinar nucleus in primates. |
| Ventrobasal Nucleus | The cell group of the ventral thalamus in mammals that receives somatosensory projections. It is also called the ventral posterior nucleus. |
| Axonal Competition | Axons that reach the same regions may show competitive interactions, competing for a limited amount of terminal space or competing for a limited quantity of trophic substance. |
| Axonal Spreading | In response to removal of competing axons, the remaining axons may spread their terminals out over a larger than normal territory. The total number of terminal may be the same after the spreading out. |
| Growth Potency | The tendency for an axon to grow more terminals in a terminal region. Its growth potency tends to decrease after it begins to arborize, as it forms more and more terminals, often dropping to zero or near zero. |
| Pruning Lesion | Damage that destroys part but not all of an axon’s end arbor or arbors. |
| Apoptosis | Cell “suicide” in which the cell dies from factors generated from within the cell. This can be from a shortage or lack of trophic substances. Apoptosis is sometimes called programmed cell death, in contrast to necrosis that occurs due to traumatic injury. |
| Supernumerary Limbs | Additional abnormal limbs that develop because of transplants or because of genetic anomalies. |
| Population Size Matching | When excess cells die, such that the source population of axons matches the synaptic targets of that population. The cells that die, often die from a lack of sufficient trophic factor, caused by too much axonal competition. |
| Error Correction | Loss of connections made by axons that do not form in the proper topographic positions in a mapped representation. This is often due to degeneration of axons or axon collaterals, which may be a result of cell loss in the source structure. |
| PNS Bridge | A segment of peripheral nerve implanted in the CNS so it forms a bridge over a site of damage where axons have been severed. The purpose is to provide a growth-friendly pathway in which CNS axons can regenerate. |
| Self-Assembling Protein | A manufactured protein which will form a solid or gel when it contacts a salt solution like cerebrospinal fluid or some other bodily fluid. |
| Tectospinal Tract | The axonal pathway from the deep layers of the midbrain tectum that crosses the midline of the midbrain and descends as far as the cervical spinal cord. Activation results in turning of head and eyes and associated postural adjustments. |
| Rubrospinal Tract | The axons from the red nucleus cross to the opposite side of the midbrain and descend through the lateral hindbrain reticular formation and through the lateral column of the spinal cord, terminating in the spinal enlargements. |
| Magnocellular Red Nucleus | The caudal, large-celled portion of the red nucleus. Source of the rubrospinal tract. |
| Parvocellular Red Nucleus | The rostral, small-celled portion of the red nucleus. Many of its axons ascend to thalamic ventrolateral and ventral anterior nuclei (VL and VA), which project to motor cortical areas. |
| Motor System Hierarchy | The entire network of neurons of the CNS that control somatic movements, extending from the neocortex to motor neurons of the hindbrain and spinal cord. |
| Central Pattern Generators | Networks of interconnected neurons of the hindbrain and spinal cord that generate largely inherited patterns of somatic movements. |
| Central Pattern Initiators | Brainstem, especially midbrain, neuronal groups where activity can activate central pattern generators of more caudal parts of the CNS. Example: the midbrain locomotor area. |
| Central Pattern Controllers | Neuronal groups above the midbrain that can activate central pattern initiators of the midbrain. Examples: the hypothalamic locomotor area, which are neurons of the hypothalamus that can activate predatory attack behavior. |
| Motor Neuron Pools | Groups of spinal or hindbrain motor neurons that can activate a particular somatic movement. |
| Vestibular Nuclei | The secondary sensory neuron groups in the rostral hindbrain, other than those located in the cerebellum, that are innervated by primary sensory axons from the vestibular organ. |
| Lateral Vestibulospinal Tract | Descending pathway from the large cells of the lateral vestibular nucleus with inputs from the vestibular apparatus and fastigial nucleus. It is an uncrossed pathway which primarily effects antigravity muscles (extensors). |
| Medial Vestibulospinal Tract | Descends from the medial and descending vestibular nuclei. It is a caudal extension of the medial longitudinal fasciculus that controls eye muscles. It descends to cervical levels of the spinal cord where it influences neck muscles. |
| Vestibulocular Reflex | The counter-rotation of the eyes in response to turning of the head. |
| Medial Longditudinal Fasciculus | A bundle of axons on each side of the medial brainstem that extend from the midbrain to the cervical levels of the spinal cord. Many of its fibers originate in the vestibular nuclei. It coordinates eye movements. |
| Flocculus | The egg-shaped lateral protrusion of the vestibular part of the cerebellar cortex, located at the caudolateral margin of the structure. |
| Nodulus | The medial portions of the vestibular part of the cerebellar cortex, located at the caudal margin of the structure, which in large animals becomes overhung by the remainder of the cerebellar cortex. |
| Vermis | The medial parts of the cerebellar cortex, coordinating movements of the axial musculature. It projects to the fastigial nucleus, the most medial of the deep nuclei of the cerebellum. |
| Fastigial Nucleus | The most medial of the 3-4 deep nuclei of the cerebellum. |
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