The Body Senses and Movement

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CHAPTER 11

• The Body Senses and Movement
• The Body Senses

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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.

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The skin Senses

• Proprioception sense that informs us about
• position of limbs and body
• movement of our limbs and body.
• Skin senses include
• Touch
• warmth, cold
• pain.

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The skin receptors

• Four types of skin receptors
• Meissners corpuscles
• Merkels 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.

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Superficial layers skin

• Meissners 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)
• Merkels 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 meissners and merkels detect
• texture, fine detail of objects
• detect movement
• use both when examining texture, shape of object

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Deeper skin receptors

• 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

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Deeper skin receptors

• 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

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The skin receptors

• 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 skins surface
• warmth receptors are deeper
• pain receptors separate from warmth receptors

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The vestibular Senses

• 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

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The vestibular Senses

• 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

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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 postcentral gyrus of the parietal
  lobe

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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.

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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

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Identifying nerve position

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

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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 A Finn And German
  Viewed Some Hops

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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.

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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
• bodys 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.

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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.

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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.

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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.

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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.

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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

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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.

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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.

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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

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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.

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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

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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.

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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.