CNS Pathways & Limbic System PDF

Structure of CNS pathways & Limbic System  The White Matter Ascending Tracts Descending Tracts Sensory Pathways Motor Pathways In the sensory pathways, sensations are carried from receptors to cerebral cortex by 3 neurons: ...

Structure of CNS pathways & Limbic System  The White Matter Ascending Tracts Descending Tracts Sensory Pathways Motor Pathways In the sensory pathways, sensations are carried from receptors to cerebral cortex by 3 neurons:  Cell of the Dorsal Root Ganglion. First – Order Neuron Carries sensation by its peripheral process. Its central processes to the spinal cord.  Cell in spinal cord or medulla oblongata Axon always decussates to the opposite side Second-Order Neuron Ascends in the brainstem as Lemniscus. To end in the thalamus. thalamus Second Neuron  Cells in the Thalamus (VPLN). Axon ascends upward. Third-order Neuron Pass through internal capsule Through corona radiata Reach sensory area of cerebral cortex. The 4 Long Ascending Tracts  The Spinothalamic Tracts Lateral Spinothalamic Tract Anterior Spinothalamic Tract Pain & Temperature Crude touch & Pressure  The Dorsal Column Tracts Gracile Tract Cuneate Tract Conscious Proprioception & Fine touch  Gracile and Cuneate Tracts Function: Carries Proprioception (deep sensations) and Fine Touch The tract represent the 1st Order Neuron in the pathway. Carries sensation from the same side of the body = Ipsilateral.  Cuneate tract: From the upper part of body. (Above T6). Gracile tract: From the lower part of body. (Below T6).  The 4 Long Ascending Tracts Spinothalamic Tracts Gracile and Cuneate Tracts (Antero-Lateral pathway) = Dorsal Column Pain & Temp (Lateral S.T.) Fine touch Crude touch (Anterior S.T.) Conscious proprioceptive All these ascending sensations from one side of the body ascend to → The Opposite Side of Cerebral Hemisphere (Contralateral ) Dorsal column and Spinothlamic pathways  Descending Tracts Pyramidal (Corticospinal) Tract Origin : neurons of motor and premotor area Axons converge in corona radiata Pass in anterior 2/3 of posterior limb of internal capsule Descends in middle 3/5 of crus of mid brain Descend as scattered bundles in pons Fibers collect to form pyramid of medulla 80% of fibers cross in lower most part of medulla& descend as lateral corticospinal tract in lateral white column 20% are uncrossed and descend as anterior corticospinal( usually they cross at lower level)  Cortico bulbar Some pyramidal fibers end on motor nuclei of cranial nerves present in brain stem All cranial nerve nuclei receive bilateral corticobulbar except Facial nucleus that supplies muscle of lower part of face Hypoglossal nucleus that supplies genioglossus Both receive contra lateral supply only Rubrospinal : Origin : red nucleus Decussate in ventral decussation Lies in lateral white column of cervical segment Lateral group of cervical anterior horn cells Facilitate flexors of upper limb The Limbic System The limbic system is a group of C-shaped cortical and subcortical structures at the medial side of hemisphere + their connections 21  MEMORY CLOSELY RELATED TO OLFACTION EMOTIONS (visceral brain) INSTINCTIVE BEHAVIOR 22  Parts of limbic system: Cortex: 1. Limbic lobe 2. Hippocampal formation (hippocampus & other structures) 3. Prefrontal cortex Nuclei 1. Hypothalamus 2. Anterior nucleus of thalamus 3. Amygdaloid nucleus 4. The septal areas Extended Modular Program 23  Stria terminalis 5 Extended Modular Program 24 Thank you 25