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9.14 Week 3
Vocab from Schneider Chapters 7-9
| Term | Definition |
|---|---|
| Lemniscus | The term is used for pathways ascending to the brain carrying sensory information from the spinal cord, usually fairly compact groups of myelinated axons. It is also applied to pathways ascending to the forebrain from the hindbrain. |
| Diaschisis | A loss of function of one region of the brain caused by damage in another part that is connected with it. The loss is usually not permanent. It is caused by deafferentation depression. The word is from Greek, meaning a division or separation. |
| Deafferentation Depression | Depressed neuronal function caused by a major loss of inputs, usually inputs from excitatory axons. |
| Spinal Shock | Loss of function of the spinal cord caudal to the site of a transection. Spinal reflexes are lost for a period of time, with the degree and duration of this loss being proportional to the quantity of descending axons destroyed by the transection. |
| Collateral Sprouting | When there is a partial loss of axons connected to a part of the CNS, the remaining, undamaged, axons often grow new collaterals that form synapses that replace the lost synapses. |
| Denervation Supersensitivity | After diaschisis, neurons that have lost many inputs become more sensitive to remaining inputs of the same type as the lost ones through the increase of postsynaptic receptors, thus recovering function. |
| Reflex Spasticity | Is caused when denervation supersensitivity ovecompensates for loss of input, causing reflexes to become overactive. |
| Procedural Learning | Habit formation by reinforcement learning, often over many repetitions. |
| Implicit Learning | Learning without much awareness of the changes in behavior that are occurring. |
| Entrain | Refers to entrainment of a rhythm so the oscillation matches the rhythm of an external stimulus. In animal behavior, there is normally an entrainment of the innate circadian rhythm so it matches the 24-hr day-night rhythm. |
| Neurohypophysis | The neural portion of the pituitary organ; the posterior pituitary. |
| Pineal Organ | The pineal gland. It forms in the roof of the third ventricle, and functions as an endocrine organ, producing melatonin. (Melatonin secretion is greater during the sleep phase of the daily activity rhythm.) |
| Neolemniscus | Carries somatosensory information from the spinal cord to the thalamus faster than the spinoreticular or spinothalamic tract. Also known as the dorsal column-medial lemniscus in mammals, this pathway exists, abeit smaller, in amphibians and reptiles too. |
| Dorsal Column | The fiber columns located dorsomedially in the spinal cord. The ascending axons of the dorsal columns are axons of primary sensory neurons of dorsal root ganglia. They terminate in the dorsal column nuclei. |
| Dorsal Column Nuclei | Groups of secondary sensory neurons located in the rostral end of the spinal cord’s dorsal columns or caudal hindbrain. They receive inputs from primary sensory axons of the dorsal roots of the spinal cord that ascend in the dorsal columns. |
| Nucleus Gracilis | Slender Nucleus. The medial nucleus of the dorsal columns, it relays information about touch, pressure and proprioception from the lower trunk, legs (rear legs), and anogenital region. It projects axons to contralateral thalamus via medial lemnicus. |
| Nucleus Cuneatus | Wedge-Shaped Nucleus. The more lateral nucleus of the dorsal columns, it relays somatosensory and proprioceptive information from the upper trunk, arms (front limbs), and neck. It projects axons to contralateral thalamus via medial lemnicus. |
| Medial Lemniscus | Ascending axons from the dorsal column nuclei to the ventral-posterior nucleus of the thalamus. On leaving the nuclei, they dessicate and then turn rostrally. Some branches terminate in the mid and hindbrain before reaching the thalamus. |
| Corticospinal Tract | Axons which originate in somatosensory, motor and premotor cortical areas, travel through the hemispheres, internal capsule, cerebral penduncle, pons, and the pyramidal tract before desuccating at the caudal hindbrain and decending down the spinal cord. |
| Pyramidal Tract | In the the hindbrain caudal to the pons, corticospinal tract axons bilaterally form a compact, pyramidal shaped bundle located ventrally next to the midline. |
| Wulst | From the German for bulge, the term usually refers to the hyperpallial region of birds that receives visual information from a nucleus of the thalamus that is directly connected to the retina. |
| Hyperpallium | The dorsalmost surface layers of the avian endbrain, derived from the pallium. Some of it is above a lateral ventricle, as in the case of the neocortex of mammals. |
| Neocortical Function | Looked at broadly, major neocortical functions include high resolution perception and fine motor control, and cognitive abilities that include anticipation of inputs and planning of actions |
| Internal Model | The neuronal activity caused by external stimulation which causes a neocortical representation of the perceived world. The model is constantly being updated by sensory input. It makes possible anticipation of sensory inputs and planning of actions. |
| Neurulation | The earliest appearance of the central nervous system that results from inducing ectodermal cells to thicken, then invaginate by molecules diffusing from the notochord. |
| Morula | The raspberry-like clump of dividing cells after fertilization of the egg. |
| Blastula | When the morula develops a fluid-filled center, it is called a blastula. |
| Gastrula | After the blastula forms an invagination that leads to the development of a channel to the other side (the precursor of the alimentary tract), it becomes a gastrula. The whole process is called gastrulation. |
| Neurula | The gastrula becomes a neurula when it forms the precursors of a nervous system. See “neurulation.” |
| Filopodia | Filamentous processes containing actin that extend from cells during some stages of embryogenesis. The cell membrane at the tip of a filopodium contains cell adhesion molecules. Contraction of filopodia can cause movement of cells or parts of cells. |
| Mesoderm | The middle layer of the early embryo of a bilaterally symmetric animal. In chordates, it forms the notochord, the bones of the skeleton, muscle, connective and a few other tissues. |
| Ectoderm | The surface layer of the early embryo of a bilaterally symmetric animal, which includes chordates. It forms the epidermis, the nervous system, pigment cells, tooth enamel, the lining of the mouth, nostrils and anus, the sweat glands, hair and nails. |
| Endoderm | The innermost layer of the early embryo. It forms the linings of the two main tubes of the body—the alimentary canal (except for the mouth and anus) and the respiratory tract. |
| Alar Plate | The dorsal part of the lateral wall of the neural tube, dorsal to the sulcus limitans in the ventricular surface. Most secondary sensory neurons are formed in the alar plate. |
| Basal Plate | The ventral part of the lateral wall of the neural tube, ventral to the sulcus limitans. Somatic motor neurons form in the basal plate (as well as many interneurons). |
| Roof Plate | The ependymal cells of the most dorsal neural tube that form the connection between the left and right alar plates. |
| Floor Plate | The floor plate cells separate the left and right basal plates. It forms at the place where the notochord contacts the neural plate, and some cells of the embryonic notochord become part of the floor plate of the neural tube. |
| Neural Plate | Differentiation of the primitive ectoderm above the forming notochord is characterized by a thickening of the ectodermal cells called the neural plate. |
| Neural Groove | The neural plate develops an invagination along the back of the chordate embryo, caused by inductive influences from the underlying notochord. The result is the neural groove. |
| Neural Crest Cells | Neural plate cells at the lips of the neural groove do not become incorporated into the neural tube. They will become glial cell, melanocytes, the aorta, and part of the cartilage and bone of the head. |
| Sonic Hedgehog Protein (SHH) | A molecule that diffuses from the embryonic notochord and induces the formation of the neural plate and tube, and then acts as a “ventralizing factor” in the differentiation of the basal plate neurons. |
| Neural Tube | The tube, initially one-cell thick, formed by an invagination of neural plate cells above the notochord. It develops into the central nervous system. |
| Sulcus Limitans | A groove in the lateral walls of the ventricle of the embryonic spinal cord, hindbrain and midbrain. In development, it separates the alar plate from the basal plate of the thickening walls of the neural tube. |
| Paravertebral Ganglion | Outside the vertebrae, they form an interconnected chain of compact peripheral motor neurons of the sympathetic nervous system. They receive input from pre-ganglionic motor neurons in the lateral horns, and innervate smooth muscles and glands. |
| Prevertebral Ganglion | A sympathetic nervous system ganglion with connections like those of the paravertebral ganglia, but located more anteriorly in the body, ventral to the vertebrae. They innervate the digestive tract of the abdominal cavity and pelvic organs. |
| Symmetric Cell Division | Mitosis in the CNS that results in two cells that each remain in the cell cycle. The cell divides along a line approximately at right angles to the ventricular surface. |
| Asymmetric Cell Division | Mitosis in the CNS that results in one post-mitotic cell and one cell that remains in the cell cycle. The post-mitotic cell migrates towards its final location. |
| Ventricular Layer | In the embryonic CNS, the ventricular layer includes many mitotic cells. In regions generating particularly large numbers of neurons, a subventricular layer of dividing cells develops. |
| Intermediate Layer | In the embryonic CNS, the intermediate layer is a layer of migrating cells and of developing axons. |
| Marginal Layer | In the embryonic CNS, the marginal layer is the most superficial, covered by pial cells. It contains few neurons but many cell processes, like radial glia processes attached to the pial surface, dendrites, and axons. |
| Pial Surface | The surface of the CNS is covered by flattened cells called pial cells, generally only one-cell thick. Attached to it on the CNS side are the endfeet of astrocytes. Pial cells also cover blood vessels that penetrate the CNS. |
| Ventricular Surface | The surface formed by cells that separate the ventricular fluid—the cerebrospinal fluid—from other CNS cells (neuronal and glial cells). The cells at the ventricular surface are the ependymal cells. |
| Nuclear Translocation | The movement of the cell nucleus through the elongated cell. When the embryonic neuron is attached to both the pial surface and the ventricular surface, and the cell body moves from a position next to the ventricle towards a position closer to the pia. |
| Radial Glial Cell | A radially elongated astrocyte, usually with a cell body near the ventricle and a process that extends to the pial surface. It serves as a scaffold for migrating neurons in the cerebral cortex and some other regions of the developing brain. |
| Shepherd's Crook Cell | A neuron in the midbrain optic tectum of a chicken. The beginning of the axon bends like the crook on a shepherd’s staff. Studies with the Golgi stain have demonstrated the progressive translocation of the cell body to the position of axon origin. |
| Ependyma | After development, ependymal cells are glial cells that line ventricles. Cerebrospinal fluid is made by modified ependymal cells, especially in regions where they protrude into the ventricular fluid. These ependymal cells are called the choroid plexus. |
| Lateral Horn | In a section of the spinal cord between T1 and L2/3, the gray matter has small lateral horn. These are preganglionic motor neurons of the sympathetic nervous system, projecting to the paravertebral and prevertebral ganglia. |
| Myelin | The glial cells that sheath of axons, speeding the conduction of action potentials by making them jump between nodes. In the PNS, the glial cells that form myelin are Schwann cells, while in the CNS, myelin is formed by oligodendrocytes. |
| Rexed Layers | The cytological organization of the spinal gray matter into 9 layers. The first layer is at the edge of the dorsal horn and the ventral-most layers (8 and 9) contain the somatic motor neurons. |
| Trigeminal Nerve Nuclei | The primary sensory axons of the trigeminal nerve terminate on secondary sensory neurons found in the alar plate of the rostral hindbrain to the cervical spinal cord. |
| Dorsal Spinocerebellar Tract | Axons from Clark’s column in the spinal cord, which receive proprioceptive information from the joints of the lower parts of the body. They axons then ascend in the lateral column on the ipsilateral side to the cerebellar cortex. |
| Clarke's Column | Also known as nucleus dorsalis, it is located in the medial part of Rexed’s layer 6 |
| Rubrospinal Tract | A bundle of CNS axons from cells of the midbrain’s red nucleus—nucleus ruber—to the contralateral spinal cord. The axons decussate in the midbrain near their cells of origin. |
| Reticulospinal Tract | Axons that come from neurons of the brainstem reticular formation—mostly hindbrain—and travel caudally in the ventral columns of the spinal cord to destinations in the spinal cord. They are involved in whole-body movement patterns which are inherited. |
| Vestibulospinal Tract | Fibers that originate in the vestibular nuclei of the hindbrain and project to the spinal cord. The axons terminate at all levels of the cord, mainly in Rexed layers 7 and 8, in the ventral horn, some directly on motor neurons |
| Fastigiospinal Tract | Axons originating a cerebellar deep nuclus—the fastigial nucleus. This nucleus also projects to the vestibular nuclei, but the fastigiospinal tract fibers deseccate to the contralateral side before terminating in the upper cervical spinal cord. |
| Tectospinal Tract | Large neurons in the deep layers of the superior colliculus of mammals project their axons across the midline before descending near the midline to the ventromedial portions of the cervical spinal cord. Activating the pathway elicits of head-turning. |
| Red Nucleus | A cell group of the midbrain tegmentum, it has a pink color in human brain dissections. The caudal part of the nucleus gives rise to the rubrospinal tract. It plays important roles in limb movements, especially in animals without a large neocortex. |
| Cerebrospinal Fluid (CSF) | The fluid that fills the ventricles of the CNS. It also reaches the subarachnoid space that surrounds the entire brain and spinal cord. |
| Choroid Plexus | The choroid plexus is formed by proliferation of modified ependymal cells which secrete CSF and form strands of tissue that protrude into the lateral ventricles, into the top of the third ventricle, and into the fourth ventricle. |
| Aqueduct of Sylvius | The narrowed ventricle that passes through the midbrain. |
| Lateral Apertures | Small openings in the roof plate of the fourth ventricle, one on each side under the lateral edges of the cerebellum. CSF flows through these apertures from the ventricle to the subarachnoid space that surrounds the entire CNS. |
| Median Aperture | A small opening in the roof plate of the fourth ventricle in the region of the obex. CSF flows from the fourth ventricle into the subarachnoid space through this opening as well as through the lateral apertures. |
| Obex | The point at which the roof plate of the hindbrain narrows and the spinal canal appears. In this region major decussations occur: the decussations of the medial lemniscus axons and of corticospinal axons. |
| Intraventricular Foramen | The confluence of the forebrain ventricles. It interconnects the lateral ventricles and the third ventricle. |
| Lateral Ventricles | The CSF-filled ventricles of the cerebral hemispheres. |
| Third Ventricle | The narrow ventricle at the midline of the ‘tweenbrain (diencephalon). |
| Fourth Ventricle | The ventricle in the center of the spinal cord. |
| Arachnoid Space | The CSF-filled space beneath the arachnoid membrane. It contains many spider-web like strands of arachnoid membrane that connect the arachnoid membrane under the dura with the pial membrane. |
| Sympathetic Ganglion | Ganglia in the peripheral nervous system that are innervated by preganglionic motor neurons in T1-L2/3. These ganglia are the paravertebral ganglia on either side of each spinal vertebra; they form an interconnected chain. |
| Dorsal Motor Nuclei | Are major nuclei of the parasympathetic nervous system, locatedon either side of the hindbrain’s medulla oblongata. Their axons form the vagus nerves, which innervate smooth muscles and glands of the thoracic and abdominal cavities. |
| Somatic System of the CNS | The various structures of the CNS that control the movements of the body using striated muscles. |
| Autonomic Nervous System | The visceral nervous system. It controls smooth muscles and glands throughout the body via the sympathetic and parasympathetic systems. |
| Parasympathic Nervous System | Its preganglionic motor neurons are located in small nuceli within the midbrain and hindbrain. This system’s functions are very specific and are most active during periods of reduced activity, like slowing heart rate and secretions from gland cells. |
| Sympathetic Nervous System | Its preganglionic motor neurons are located in a column of cells on either side of the spinal cord. It acts less specifically than the parasympathetic system, as all parts tend to be activated together, especially during periods of “fight or flight.” |
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