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WSU BIOLOGY 315 - Spinal Cord and Brain
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Lecture 15Outline of Last Lecture I. Overview and Gross Anatomy Systema. Divisionsb. Spinal nervesc. true proportionsd. nerve plexusII. Classifying Input and Output III. Sensory Part of the PNSIV. Motor Part of the PNSOutline of Current LectureI. Inside the spinal corda. Tractsb. 3 functional groups of somatic sensec. The pathways of the 3 functional groupsi. Dorsal column pathwayii. Spinothalmic pathwayiii. Spinocerebellar pathwayII. The Brain: Cerebral CortexCurrent LectureI. Inside the spinal cord, white mattera. Fiber tracts: bundles of axons running up and down the spinal cordb. Tract: a group of axons within the central nervous system c. All the axons in a tract go to similar destinations and carry similar kinds of informationd. Many long tracts  brain i. The brain and spinal cord are the 2 main parts of the CNSe. Descending tracts carry instruction for movementsf. Ascending tracts carry sensory informationi. General somatic sensory information about the skin senses and proprioceptionii. The spinal cord carries this sensory information from the parts of the body belowthe head (neck, trunk, and limbs)** The spinal cord does not carry much sensory information from the head, instead head-sensor information is carried to the brain stem by cranial nerves**iii. Some general sensory information travel up the spinal cord to reach the cerebral cortex of the telencephalon, where the information is processed and comes to consciousness iv. Other GSI run from spinal cord up to cerebellum where processed to help coordinate movementsv. Different classes of GSI are carried in different chains of fiber tracts, called pathways, to the brain = separation of fiber tracts by sensory modalityg. 3 functional groups of general somatic sensei. Conscious senses that are precisely localized on the body BIOL_315 1nd Edition1. Include fine touch, vibration, pressure, joint stretch and some muscle stretch2. Can tell within small radius of where touch occurred 3. The awareness of joint movement during exercise produces a mildly pleasurable experience and may partly explain why joggers like to runii. Conscious senses that are difficult to localize precisely 1. Include pain and temperature 2. seem to radiate from a much larger area of skin than was actually3. Provoke an emotional response? Respond angrily to pain and burnsiii. Senses of which one is not conscious 1. All aspects of tendon stretch are relayed to the cerebellum, not to the cerebrum 2. Inform the cerebellum of our body’s movementsh. The pathways of the 3 types of sensory information  brain i. The pathways are the same for both the right and left sides of the body1. Mirror images that isii. Dorsal column pathway: carries the first class of information to the cerebral cortex, here are the steps:1. The sensory neurons receive the stimulus and their central processes carry it into the spinal cord2. Each central process divides and one of the axonal branches enters the dorsal white areasa. Such branches from many sensory neurons ascend through the spinal cord together as the dorsal column tractb. The axons in the dorsal column tract run all the way up to medullaoblongata of the brain, where they synapse with interneurons in the dorsal column nuclei3. The sensory information has been relayed to a second set of neurons in the ascending pathway. The axons of these second-order neurons run in the medial lemniscus tract, which in the medulla crosses over to the opposite side of the brain.4. These axons ascend to the thalamus of the diencephalon, where they synapse on cell bodies of third-order neurons in the ventral posterior lateral nucleus.5. The axons of these third-order neurons in turn project up to the cerebral cortex, within the cortex, the sensory information is processes and comes to consciousness.iii. Spinothalamic pathway: carries sensory information of the second type1. Sensory neurons of this pathway do not send branches into the dorsal columns, but just synapse with interneurons in the gray matter of the spinal cord, at the same level they enter the cord. 2. The second-order neurons in the pathway, have branched axons, one branch of which crosses over to the opposite side of the spinal cord andthen turns and ascends all the way to the ventral posterior lateral nucleusof the thalamus 3. These ascending axons form the spinothalmic tract, which occupies the lateral and anterior white regions of the spinal cord 4. From thalamus, third-order axons  cerebral cortexiv. Spinocerebellar pathway: the third type of information, unconscious aspects of muscle stretch and tendon stretch1. Sensory neurons synapse in the spinal cord with interneurons, whose axonal branches ascend to the cerebellum2. These long axons form the spinocerebellar tracta. In the lateral funiculus of the white matter of the cord 3. Using proprioceptive information it receives from this pathway, the cerebellum calculates how to maintain balance and muscle tone, and howto coordinate our movementsv. Common features that the ascending pathways share:1. Separation of tracts by sensory modality (different classes of sensory information are carried by different pathways)2. The pathways going to cerebral cortex cross over at some point to the other side of the CNSa. The axon of the second neuron in the three-neuron pathway always does the crossing over3. Sensory information is carried to the brain by chains of neurons, rather than just one neuron = multi-neuron pathways4. There are relay nuclei along the way, containing the cell bodies of the second and third order neurons a. In medulla and thalamus, sensory information can be organized and modified before reaching the cerebral cortex5. Somatotopy: axons carrying information from different parts of the body are kept separate throughout the ascending pathways Make sure to review and understand the 4 main concepts about ascending pathways:1. Separation by sensory modality2. Crossing over3. Multi-neuron pathways4. Somatotopy II. The Brain: Telencephalon: Cerebral Cortexa. Cerebral cortex: the outer layer of gray matter on the cerebral hemispheres i. <0.5 cm thick, it forms 40% of the volume of the entire brainii. The site of consciousness, both sensations and control of movementsiii. Site of cognition and stores memories of events and learned facts1. Cognition : all aspects of thinking and knowing b. Primary somatosensory area of the cerebral cortexi. Region of the cerebral cortex where the information is relayed:


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