BSC 2086 1st Edition Lecture 2 Outline of Last Lecture I. Afferent DivisionII. Efferent DivisionIII. Somatic Nervous SystemIV. General Senses V. Special SensesVI. Interpreting Sensory InformationVII. Receptors for General Senses Outline of Current Lecture I. Major Sensory PathwaysII. Somatic Motor PathwaysIII. OlfactionIV. Gustation Current LectureI. Major Sensory Pathways a. Somatic Sensory Pathwaysi. Spinothalamic pathway: goes from spinal cord to thalamus 1. Lateral path2. Conscious sensation of crude touch, pressure, temperature and pain3. Very hard to locate visceral pain can feel pain in an uninjured body part when then pain is actually coming from another location4. Why?a. Stimulated interneurons at arriving segment of spinal cord can stimulate primary sensory cortex which leads to pain ina specific body part b. Referred pain: heart attack pain felt in left arm ii. Spinocerebellar pathway: goes from spinal cord to cerebellum1. Lateral path2. Proprioceptive information sent to cerebellumiii. Posterior column pathway: Dorsal side of spinal cord1. Sensation of fine touch pressure, vibration and proprioception II. Somatic Motor Pathways a. Somatic Nervous System (SNS) i. Also known as somatic motor systemii. Contractions of skeletal musclesiii. Processing and control:1. All pathways include series of synapses which affect one another 2. Upper motor neuron damage = spastic paralysis a. Muscles not in relaxed state 3. Lower motor neuron damage = flaccid paralysis a. Wheelchair bound, can’t move limbs at all 4. Homeostasis is kept short term through spinal and cranial reflexes a. Prevents excessive damage to the body 5. Integrative centers in brain perform elaborate processing6. Primary motor cortex is in charge of most complex motor activitiesa. Neurons of PMC innervate motor neurons responsible for skeletal muscle stimulation7. Higher centers in the brain either suppress or facilitate reflexes which can affect voluntary movements iv. Amytrophic Lateral Sclerosis (ALS): A progressive degenerative disorder that affects motor neurons found in the brains stem, spinal cord and cerebral hemisphere. 1. Once these neurons die, skeletal muscles stop being used which causes atrophy 2. Deterioration of skeletal muscles occursb. Autonomic Motor System (ANS)i. Also known as visceral motor system ii. Controls smooth and cardiac muscles as well as glands III. Olfactiona. Olfactory organs found in nasal cavity i. Olfactory epithelium1. Olfactory receptor cellsa. Detect dissolved chemicals as they interact with odorant binding proteins on its cell membrane b. Amount of receptors declines with age 2. Supporting cells3. Basal cells: stem cells that make new receptor cells ii. Lamina propria 1. Olfactory glandsa. Form mucus which coat organs b. Olfactory Pathwaysi. Axons leave olfactory epithelium penetrate cribriform plate olfactory bulbs in cerebrum 1st synapse ii. Axons leave olfactory bulb travel olfactory tract arrive at olfactory cortex, hypothalamus and some parts of limbic system 1. Information arrives at information centers without synapsing in the thalamus first c. Olfactory Discrimination i. Able to distinguish thousands of chemical stimuli ii. Smells interpreted by CNS based on the pattern of receptor activity IV. Gustation a. Taste Receptorsi. Found on tongue, pharynx and larynxii. Taste buds: clusters of taste receptors 1. Epithelial projections known as lingual papillae are found on superior surface of the tonguea. 3 types:i. Filiform Papillae: used for friction, no taste budsii. Fungiform Papillae: 5 taste buds eachiii. Circumvallate Papillae: 100 taste buds each 2. Contain:a. Basal cellsb. Gustatory cells i. Taste hairs extended through taste pore b. Gustatory pathwaysi. Cranial nerves monitorii. Synapse with medulla oblongataiii. Then sent to thalamus and primary sensory cortexc. Gustatory Discriminationi. Four primary sensations: sweet, salty, sour, bitterii. Umami: savory tastes1. Sensitive to amino acids, peptides, nucleotides2. Ex. Beef broth and parmesan cheeseiii. Water is detected by specialized water receptors iv. Chemicals will contact taste hairs and bind to receptor proteins1. Salty and sour receptors are chemically gateda. Depolarization of membrane causes release of neurotransmitters2. Sweet, bitter and umami stimuli will activate G protein by binding to receptor protein a. Activation of G proteins will cause release of neurotransmittersd. Taste Sensitivity i. 1000x more sensitive to sour tastesii. 100x more sensitive to bitter tastesiii. Why?1. Toxic things may be bitter and spoiled foods can be sour defense mechanism iv. Taste buds decline rapidly by age
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