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

2. The Body Senses
Information about our body is processed by 2 main systems:
somatosensory system
vestibular system.
Somatosenses include
Proprioception: Concerned with movement and spatial orientation
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. The skin Senses Proprioception Skin senses include:
Sense that informs us about the position and movement of our limbs and body.
Often in the context of movement and spatial relations (where your butt is in relation to the seat of the chair)
Skin senses include:
Touch: light touch to heavy pressure
Warmth to cold
Pain.

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

5. skin receptors for detecting touch and pressure
Cutaneous mechanoreceptors
Respond to mechanical pressure or distortion caused by physical interaction, including pressure and vibration
Cutaneous = in the skin
There are several kinds of these receptors embedded in our skin:
Ruffini's end organ: detect sustained pressure
Meissner's corpuscle: detect changes in texture, slow vibrations
Pacinian corpuscle: deep pressure, fast vibrations
Merkel's disc: detect sustained touch and pressure

6. Figure 11.1

7. 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
Parieto-insular-vestibular cortex:
Vestibular system sends projections from the cerebellum and the brain stem to the insular cortex of the temporal lobe
Provides information regarding position of body in space and movement

8. Figure 11.2 The vestibular organs
(a) The inner ear, showing the cochlea and the vestibular organs. (b) Enlarged view of a cupula in a semicircular canal. (c) Receptors of the utricle and saccule.

9. Somatosensory Pathway
First neuron junction:
Cell body on dorsal root ganglion of the spinal nerve or cranial nerves
Forms initial connection between body and spinal cord
Second neuron junction:
Cell body either in the spinal cord or in the brainstem.
Second neuron's ascending axons will cross (decussate) to the opposite side either in the spinal cord or in the brainstem.
The axons of these neurons terminate in the thalamus or reticular system or cerebellum.
Third Neuron junction:
Exists for touch and some types of pain:
Cell body in the VPN of the thalamus
Ends in the postcentral gyrus of the parietal lobe 9

10. Pathway into brain Somatosensory cortex
From thalamus, body sense neurons go to their projection area:
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.
Why do you think this is? 10

11. The Body Senses Dermatomes: Divided into several subdivisions:
Body is divided into segments
Each segment served by a spinal nerve.
We process information from each dermatome
Damage to a particular spinal nerve results in damage to the corresponding dermatome
Divided into several subdivisions:
Cervical: head, upper neck
Thoracic: lower neck to chest
Lumbar: middle
Sacral or coccygeal: tail 11

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.
Amount of brain devoted to each area depends on how much we use/sense from that body area
Remember the homunculus 12

13. Figure 11.4

14. Somatosensory cortices
Primary somatosensory cortex
Consists of four areas
Each contains a map of the body
Each plays a role in processing sensory information for the body.

15. Somatosensory cortices
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.

16. Posterior parietal cortex
The primary somatosensory cortex also projects to the posterior parietal cortex
Posterior parietal cortex:
Association area
Brings together the body senses: somatosensory, 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.

17. too much integration of sensory areas
Synesthesia:
too much integration of sensory areas
Synesthesia:
The experience of some kind of cross-activation from one sense to another
The condition of being prone to such experiences.
Several causes:
Brain damage
Psychodelic drug activation
Developmental synesthesia
Why?
Activation of one cortical area by an inducing stimulus (say, letters) causes co-activation of another cortical area (say, the color area),
This produces additional color perceptions or associations.
Letters thus come in specific colors

19. 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.

20. 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
Endorphins released under certain conditions.
Physical stress
Pain
Long term exertion

21. Gate Theory Ronald Melzack and Patrick Wall
In the spinal cord: Pain neurons release:
Glutamate
Substance P:
Neuropeptide involved in pain signaling.
Released only during intense pain stimulation.

22. Gate Theory
Gate theory states that there are two kinds of pain fibers:
Some specific nerve fibers transmit pain to the spinal cord
Input of other nerve fibers inhibits the transmission of pain.
Both groups of pain fibers meet at a sort of ‘mediator' in the spinal cord called the substancia gelatinosa.

23. Gate Theory
Gate theory: Proposes a balance between stimulation of the pain fibers and inhibition of that stimulus,
Pain is perceived only if the pain input overrides the inhibition of pain
Is the sum of the signals transmitting pain + signals transmitting inhibiting of pain
Thus pain is “gated” : If more pain sensation than not pain sensation from free receptors, then perceive sensation as pain

24. Periaqueductal gray area: PAG
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 the PAG
Endorphin release inhibits the release of Substance P, closing the pain “gate” in the spinal cord.

25. Brain response to pain
Activation of the endorphin circuit has multiple neural origins, for example:
Cingulate cortex during placebo analgesia
Amygdala in the case of fear-induced analgesia.
PAG response to pain signals
Multiple areas response to chronic stress signals

26. Figure 11.8

27. 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
Are internal pain relievers
Share the neural gating system used by endorphins
May explain ‘pleasure’ sensation
Cannabinoid substances may be useful as analgesics

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

29. Phantom pain
The phantom “pain” originates in the brain.
Neural circuits for movement involve many movement areas
After amputation: missing limb still has neural contribution to a movement
When move your body, those circuits are stimulated
Brain is interpreting the state of the “missing” limb via the stimulation of those old remaining circuits 29

30. Phantom pain
Awareness of the details of limb's shape/perceived ability to move it tend to fade with time.
Over time, old neural connections fade (no longer stimulated because the limb associated with them is gone)
New circuits form that do not include the neural stimulation caused by the missing limb
Most amputees report continuing to feel some phantom sensations throughout the remainder of their lives. 30

31. Phantom pain
Neural mechanisms which permit perception of phantom limbs are well recognized:
Major muscles in residual limb tense up several seconds before cramping phantom limb pain begins
Remember: those muscles associated with movement in missing limb
Brain interprets this as if the missing limb itself was cramping 31

32. Phantom pain
Muscles remain tense for much of duration of episode.
Muscle fatigue sets in
Reduced blood supply
Eventually, pain sensation in remaining muscles
But, because circuits are tied to missing limb, feel as if missing limb is painful! 32

33. Phantom pain
Burning phantom limb pain closely associated with reduced blood flow in residual limb- is a sensation of a lack of circulation
Brain acting like limb still there
Interprets residual limb activity as if it was activity in the missing limb
Assumes that if residual muscle is “hurting”, the missing limb must be too! 33

34. Phantom pain: Treatment
Main treatment is NOT pain meds, but fixing the miscommunication in the brain through BIOFEEDBACK
Why is biofeedback helpful?
Teach the amputee’s brain to recognize that limb is missing
The specific aim of the treatment:
Teach amputees with phantom pain to habitually and unconsciously keep their residual limbs as warm and as relaxed as the intact limb.
Teach them to increase muscle temperature
Teach them to reduce cramping and muscle tension in surrounding area
Disconnect neural patterns involving the missing limb! 34

35. Phantom pain: Treatment
Have to explicitly TEACH the relationship between sensation and the missing limb:
Feel the muscle tension/temp changes in the tissue surrounding the missing limb
Relate those sensations to the pain sensations “in the missing limb”
Muscle tension and temperature awareness training
Often use mirrors or biosensors:
Show muscle tension in surrounding muscle areas
Have amputee identify pain sensation that goes with the tensing of surrounding muscles: SEE the tension and FEEL the pain
Have them learn to relax surrounding muscles and feel lessening of pain
SEE the relaxation and FEEL the lessening of pain
Begin to learn to control these parameters…..lots and lots of trials and practice 35