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CHAPTER 11

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  1. CHAPTER 11 The Body Senses and Movement The Body Senses Movement

  2. The Body Senses Information about our body is processed by somatosensory system vestibular system. Somatosenses include proprioception Skin senses tell us about conditions at the surface of our body, interoceptive system: concerned with sensations in our internal organs. Vestibular system informs the brain about body position Body movement.

  3. Proprioception: sense that informs us about position of limbs and body movement of our limbs and body. Skin senses include: Touch warmth, cold pain. The skin Senses

  4. Two general types of receptors. Free nerve endings: simply processes at the ends of neurons. They detect warmth, cold, and pain. Encapsulated receptors: form all other receptors more complex structures enclosed in a membrane. Their role is to detect touch. The skin receptors

  5. Superficial layers of skin: Meissner’s corpuscles: respond to brief burst of impulses Merkel’s discs: respond to sustained response detect textgure, fine detail of objects also detect movement use both when examining texture, shape of object e.g., when using Braille Deeper layers of skin: Pacinian corpuscles Ruffini endings contribute to perception of shape of grasped object The skin receptors

  6. Sensitivity varies greatly with concentration of receptors most in fingertips, tongue fewer in upper arms, calves of legs, back Different firing rates for different cells: Warmth, cold pain cold receptors near skin’s surface: warmth receptors are deeper pain receptors separate from warmth receptors The skin receptors

  7. Vestibular sense: helps maintain balance provides information about head position and movement. Vestibular organs in the inner ear semicircular canals, the utricle the saccule The vestibular system sends projections to the cerebellum and the brain stem. Parieto-insular-vestibular cortex: Pathway to a cortical area The vestibular Senses

  8. Vestibular sense: helps maintain balance provides information about head position and movement. Vestibular organs in the inner ear semicircular canals, the utricle the saccule The vestibular system sends projections to the cerebellum and the brain stem. Parieto-insular-vestibular cortex: Pathway to a cortical area The vestibular Senses

  9. Somatosensory Pathway First neuron: Free nerve endings or encapsulated receptors To Cell body on dorsal root ganglion of the spinal nerve or cranial nerves Second neuron: Cell body of spinal cord or brainstem. Second neuron's ascending axons cross (decussate) to the opposite side either in the spinal cord or in the brainstem. Axons of these neurons terminate in Thalamus reticular system cerebellum. For Touch/Some types of pain: Third neuron has cell body in the VPN of the thalamus Ends in the postcentralgyrus of the parietal lobe

  10. Pathway into brain From thalamus, body sense neurons go to their projection area:somatosensory cortex located in the parietal lobes just behind the primary motor cortex and the central sulcus. Most of the neurons cross from one side of the body to the other side of the brain Contralateral (crossing) vs ipsilateral (not crossing) touch of an object held in the right hand registered mostly in left hemisphere.

  11. The Body Senses • Dermatomes: • Body is divided into segments • each segment served by a spinal nerve. • Divided into several subdivisions: • Cervical: head, upper neck • Thoracic: lower neck to chest • Lumbar: middle • Sacral or coccygeal: tail

  12. The Body Senses • The labels identify the nerve. • Letters = part of the spinal cord where the nerve located • Numbers = nerve’s position within that section. • For example: Areas I, II,and III on the face innervated by branches of the trigeminal (fifth) cranial nerve.

  13. Somatosensory cortices Primary somatosensory cortex each contains a map of the body Each plays a role in processing sensory information for the body. Secondary somatosensory cortex receives input from the left and the right primary somatosensory cortices, combines information from both sides of the body. Neurons in this area particularly responsive to stimuli that have acquired meaning (e.g., association with reward). Connects to the part of the temporal lobe that includes the hippocampus Hippocampus critical for learning, may determine whether a stimulus is committed to memory.

  14. Posterior parietal cortex • The primary somatosensory cortex also projects to the posterior parietal cortex • Posterior parietal cortex: • association area • brings together the body senses, vision, and audition. • determines • body’s orientation in space, • the location of the limbs, • the location in space of objects detected by touch, sight, and sound. • it integrates the body with the world.

  15. Pain • Pain processing: • begins when free nerve endings stimulated by • intense pressure • temperature • damage to tissue. • There are three types of pain receptors. • Thermal pain receptors: respond to extreme heat/cold. • Mechanical pain receptors: respond to intense stimulation like pinching/cutting. • Polymodal pain receptors: activated by • both thermal and mechanical stimuli • chemicals released when tissue is injured.

  16. Spinal cord response to pain • In the spinal cord: Pain neurons release: • glutamate • substance P: neuropeptide involved in pain signaling. • Substance P released only during intense pain stimulation. • Gate control theory: • Ronald Melzack and Patrick Wall • hypothesized that pressure signals arriving in the brain trigger an inhibitory message • This inhibitory message travels back down spinal cord • Result: closes a neural “gate” in the pain pathway.

  17. endorphins • Endorphins function both as: • neurotransmitters • Hormones • act at opiate receptors in many parts of the nervous system. • Pain = one of stimuli that release endorphins • Only releases under certain conditions. • physical stress • acupuncture • vaginal stimulation in rats and women.

  18. Brain response to pain • Periaqueductal gray area: PAG • Brain stem structure • Contains large number of endorphin synapses. • Stimuli like pain and stress cause the release of endorphins in PAG • Endorphin release inhibits the release of substance P, closing the pain “gate” in the spinal cord. • Activation of the endorphin circuit has multiple neural origins: • cingulate cortex during placebo analgesia • amygdala in the case of fear-induced analgesia.

  19. Cannabinoid receptors • Cannabinoid receptors respond to the active ingredient in marijuana • In rats: blocking cannabinoid receptors in the periaqueductal gray reduces analgesia produced by brief foot shock. • This suggests that cannabinoids also • internal pain relievers • share the neural gating system used by endorphins • May explain ‘pleasure’ sensation

  20. Phantom pain • Phantom pain: • pain that is experienced as located in the missing (amputated) limb. • 70% of amputees experience • Phantom pain real sensation: brain not know that limb is missing • Significant problem in post-amputation pain management.

  21. Phantom pain • The phantom originates in the brain. • Awareness of details of limb's shape/perceived ability to move it tend to fade with time. • Most amputees report continuing to feel some phantom sensations throughout the remainder of their lives. • The neural mechanisms which permit perception of phantom limbs well recognized: • Major muscles in residual limb tense up several seconds before cramping phantom limb pain begins • muscles remain tense for much of duration of episode. • Other studies demonstrated that burning phantom limb pain is closely associated with reduced blood flow in residual limb • Brain acting like limb still there.

  22. Phantom pain • What is brain doing? • Researchers noted that stimulating face often produces sensations in a phantom arm • Team of researchers in Germany used brain imaging to map face and hand somatosensory areas in upper-limb amputees. • In phantom limb pain patients: • neurons from the face area appear to invade the area that normally receives input from the missing hand. • Thus, as face moves, brain processes this as movement of limb, and pain reaction to movement

  23. Phantom pain: Treatment Temperature biofeedback may be helpful The specific aim of the treatment: teach amputees with burning/tingling phantom pain to habitually and unconsciously keep their residual limbs as warm as the intact limb. For amputees with cramping pain: teach to prevent onset of the types of increases in muscle tension in the residual limb which lead to pain.

  24. Phantom pain: Treatment • Several stages: • Subjects are shown the relationship between the residual limb's temperature or muscular activity and the onset and intensity of phantom pain • Given muscle tension and temperature awareness training • begin increasing their awareness of changes in limb temperature and tension patterns • begin to learn to control these parameters. • After several weeks, patients begin doing the exercise at home and in their normal work environment. • Generalize awareness of changes in the parameters to their normal environment.

  25. TaSTE • The simplest form of dietary selection involves: • distinguishing between foods that are safe and nutritious and those that are either useless or dangerous. • Choosing appropriate food for setting • Most likely use taste to do this. • In humans, all taste experience is a result of just five taste sensations: • sour, • sweet, • bitter, • salty, • and the more recently discovered umami. • Umami is often described as “meaty” or “savory.”

  26. Taste Buds • About 10K Taste receptors • Most Taste buds found on surface of tongue • Contained in papillae • Also found in palate, pharynx, larynx • Papillae are small bumps on the tongue and elsewhere in the mouth. • Taste buds = grups of 20-50 receptor cells • Cilia at end of each cell • Form syanapses with dendrites of bipolar neurons of axons of 7th, 9th and 10th cranial nerves • Taste buds only live about 10 days, the replaced!

  27. Pathway for Taste • Taste = chemical transmission at synapses • Tased molecule binds with receptor, produces changes in membrane permeability that produces receptor potentials • Different substances bind with different types of receptors and in different combinations • Taste neurons travel from the • Nucleus of the solitary tract (NST) in the medulla • through the ventral posteromedial thalamic nuclei • Then on to the theinsula, the primary gustatory (taste) area in the frontal lobes. • Then project to secondeary gustatory cortex in caudolateralorbitofrontal cortex • Taste is IPSILATERALLY represented, unlike most other senses! • Also projects to hypothalamus, amygdala and basal forebrain • hypothalamic projections play a role in rewarding aspects of taste

  28. Olfaction • Olfaction = second chemical sense • Olfaction in humans is most enigmatic of all sensory modalities- has peculiar ability to evoke vague memories from distant past • Our nose is up too high to be of much use! • Odorants = scents • Low molecular weight • Most are lipid soluble and organic

  29. Olfaction • Olfactory epithelium • Olfactory receptors reside in olfactory epithelium within 2 patches of mucous membranes • Top center of nasal cavity • Bipolar neurons whose cell bodies lie within olfactory mucosa that lines cribiform plate at rostral base of brain • Supporting cells contain enzymes that destroy odorants, and preserve olfactory receptor cells • Olfactory recpetorcels send process toward surface of mucoas: • Divides into 10-20 cilia that penetrate mucus layer • Odorous molecules dissolve mucus to stimulate receptor molecules on olfctory cilia • Optic nerve = about 35 bundles of axons, sheathed by glial cells, which enter skull via cribiform plate • Also contain free nerve endings of trigeminal nerve axons • Mediate feelings of pain for strong scents

  30. Olfaction • Olfactory Bulb • Base of brain at end of stalk-like olfactory tracts • Each olfactory receptor cells sends single axon into bulb • Axons synapse with dendrites of mitral cells of olfactory glomeruli • About 10K of olfactory glomeruli, which each receive about 2K axons • Then travel to brain via olfactory tracts • Some terminate in ipsilateral forebrain • Some cross and terminate in contralateral olfactory bulb • Olfactory tract axons project directly to • amygdalahypothalaums • limbic cortex’s Piriform cortex  hippocampus • Entorhinal cortex hypothalamus and orbitofrontal cortex (where mixes with taste) • Most mammals also have vomeronasal organ: responds to pheramones

  31. Transduction of Olfaction • Olfactory receptor genes code for families of olfactory receptor proteins (Buck and Axel, 1991, won Nobel for it!) • Humans have 339 different olfactory receptor genes • Mice have 913! • Molecules of odorant bind with olfactory receptors • Metabatropic: g-proteins coupled to receptors open Na+ channels, depolarizing the receptor potentials • How recognize speficic odors? • Humans can recognize 10K+ odors; Other animals recognize many more • Cilia of each olfactory enuron contain only 1 type of receptor • As many types of glomeruli as types of receptor molecules (1 receptor to each) • Location of particular types of glomeruli is same in each olfactory bulb of a specific animal, and highly similar within a species • Odorants bind to MORE than 1 receptor • Is pattern of binding that gives specific odor