CHAPTER 11

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

2. The Body Senses Information about our body is processed by somatosensory system vestibular system. Somatosenses include Proprioception: spatial location of body via touch 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: positionof limbs and body movementof our limbs and body. Skin senses include: Touch warmth, cold pain. The skin Senses

4. Four types of skin receptors Meissner’s corpuscles Merkel’s discs Pacinian corpuscles Ruffini endings Two general types of skin receptors. Free nerve endings: simply processes input 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. Meissner’s corpuscles: respond to brief burst of impulses distributed on various areas of the skin, concentrated in areas especially sensitive to light touch, (e.g., fingers and lips) Merkel’s discs: respond to sustained response to mechanical deflection of the tissue, particularly low vibrations wide distribution in superficial skin layers clustered beneath the ridges of the fingertips that make up fingerprints and in specialized "touch domes" or "hair disks“ of hairy skin responsible for the ability to feel fine detailed surface patterns (e.g. for reading Braille). Both meissner’s and merkel’s detect texture, fine detail of objects detect movement use both when examining texture, shape of object Superficial layers skin:

6. 2 kinds Pacinian corpuscles Ruffini endings Both contribute to perception of shape of grasped object Pacinian corpuscles Larger, fewer in number than both Merken cells or Meissner's corpuscles detect gross pressure changes/vibrations rapidly adapting (phasic) receptors. large receptive field Deeper skin receptors

7. Ruffini endings sensitive to skin stretch Important for kinesthetic sense of and control of finger position and movement register mechanical deformation within joints (more specifically angle change up to 2 degrees) Also detect continuous pressure states Deeper skin receptors

8. 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: Particularly warmth, cold pain cold receptors near skin’s surface: warmth receptors are deeper pain receptors separate from warmth receptors The skin receptors

10. 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

11. 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

13. Somatosensory Pathway First neuron: Free nerve endings or encapsulated receptors Connect to cell body on dorsal root ganglion of the spinal nerve or cranial nerves Thus form the first link in the chain 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 Third neuron has cell body in the ventral posterior nucleus or VPN of the thalamus Ends in the postcentralgyrus of the parietal lobe

14. Pathway into brain From thalamus, body sense neurons go to their projection area: somatosensory cortex located in the parietal lobes (remember?) 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 Ipsilateral= not crossing; stays on same side touch of an object held in the right hand registered mostly in left hemisphere.

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

16. Identifying nerve position • 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.

17. The cranial nerves • I-Olfactory nerve • II-Optic nerve • III-Oculomotor nerve • IV-Trochlear nerve • V-Trigeminal nerve • VI-Abducens nerve • VII-Facial nerve • VIII-Vestibulocochlear nerve/Auditory nerve • IX-Glossopharyngeal nerve • X-Vagus nerve • XI-Accessory nerve/Spinal accessory nerve and • XII-Hypoglossal nerve. • On Old Olympus' Towering Top AFinn And German Viewed Some Hops

19. 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 temporal lobe and hippocampus Hippocampus critical for learning, may determine whether a stimulus is committed to memory.

20. 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.

21. 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.

22. 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 to brain trigger an inhibitory message • This inhibitory message travels back down spinal cord • Result: closes a neural “gate” in the pain pathway.

23. endorphins • Endorphins function both as: • neurotransmitters and as • 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.

24. 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.

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

27. 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.

28. Phantom pain • originates in the brain. • With loss of limb: awareness of the 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.

29. Phantom pain • Good news: Neural mechanisms which permit perception of phantom limbs well understood. • Major muscles in residual limb tense up several seconds before cramping • This coincides with phantom limb pain begins • Muscles remain tense for much of duration of episode. • Burning phantom limb pain also closely associated with reduced blood flow in residual limb • Brain acting like limb still there because other muscles “cue” brain to act

30. What is brain doing? • Researchers noted that stimulating face often produces sensations in a phantom arm (huh?) • used brain imaging to map face and hand somatosensory areas in upper-limb amputees to determine this relationship. • Found that neurons interpreting facial areas moving into and forming pathways in other areas….missing limb areas.

31. In Phantom Limp patients neurons from the face area appear to invade 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 Facial movement produces sensation of missing limb “hurting”

32. Phantom pain: Treatment Temperature biofeedback may be helpful teach amputees with burning/tingling phantom pain to habitually and unconsciously keep their residual limbs as warm as the intact limb. For cramping pain: teach relaxation in related muscles to prevent onset of the muscle tension “cues” in residual limb which lead to pain.

33. Phantom pain: Treatment • How do this? Several stages: • Subjects shown the relationship between 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 exercise at home and in their normal work environment. • Generalize awareness of changes to their normal environment.