Chapter 57. Touch, Movement, and Pain

Learning Objectives

axon
part of a neuron specialized to send impulses to other neurons
inner ear
innermost part of the ear, containing the cochlea and semicircular canals
kinesthesia
one of the senses; receptors in muscles, tendons, and joints detect position and movement of the parts of the body
mechanoreceptors
receptor cells that generate neural impulses when stimulated by pressure, vibration, or stretching
myelin
fatty, insulating coating on some axons; speeds up the movement of the neural impulse
neural impulse
an electrical signal that carries a message along an axon
nociceptors
receptors that signal potential tissue damage; brain uses these signals to perceive pain
pain
unpleasant perceptual experience that arises when body tissues are damaged
parietal lobe
upper back part of each hemisphere; processes sensory input for touch and body position
perception
organizing and interpreting information from the senses to understand its meaning
semicircular canals
three small tubes in the inner ear that detect head position and rotation
sensory receptors
specialized cells in the sensory systems that can capture energy or information from a stimulus and convert that information into neural impulses
somatosensory cortex
area within the parietal lobes that receives and processes information from the body senses
thalamus
main relay center in the brain for sensory information on the way to processing areas in the cerebral cortex
thermoreceptors
receptors that signal warmth or cold
touch
one of the senses; receptors in the skin and other organs detect pressure, vibration, movement, temperature, and pain
vestibular sense
one of the senses; receptors in the inner ear detect movements of the head
Touch, Movement, and Pain
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Learning Objectives:

Identify the receptor cells for the sensations generated within the skin and internal organs.

Identify the brain area that processes and perceives the information from body senses within the skin and internal organs.

Explain how touch signals can sometimes diminish the experience of pain.

Review

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1. How many senses do humans have? If you say “five,” you are lumping several distinctively different senses under the label touch. It would be better to call the sense of touch something like “body-sense,” to include a group of systems that detect the following: a) external objects pressing or vibrating against our skin, b) temperature, c) pain signals indicating damage to our skin or internal organs, and d) changes to our body position.

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2. The body sensations we call touch originate in specialized sensory receptor cells buried in the skin. Most of these cells are mechanoreceptors, because they generate neural impulses when the skin around them is squeezed or moved. Some receptors respond primarily to light touch or vibration, while others are specialized for heavy, continuous pressure. Other cells called thermoreceptors detect warmth or cold.

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3. Scattered throughout the body, in both the skin and internal organs, are special “harm detectors” called nociceptors. These sensory receptors generate neural impulses when they detect potentially damaging events, such as extreme heat or a cut on the skin. The brain uses these signals to create the perception of pain, which helps us avoid further damage.

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4. In addition to detecting external objects, our “body-sense” detects the position and movement of the body. Mechanoreceptors in the muscles, tendons, and joints generate neural impulses when the arms or legs are moved—a sense called kinesthesia. Highly specialized cells in the semicircular canals of the inner ear are responsible for our vestibular sense, detecting rotation of the head or forward-backward movement of the head (and the whole body).

Review

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5. All the neural impulses from these various “body-sense” receptors travel to the brain’s parietal lobe, where they are processed in the somatosensory cortex, creating perceptions of events happening outside or inside the body.

Practice 1: Exploring the Body Senses

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Practice 1: Exploring the Body Senses

Roll over each label to view that component of somatosensory perception.

Somatosensory component:

Special mechanoreceptors in the semicircular canals within the inner ear detect rotation of the head and straight-line movement of the head.

Nociceptors in the skin and internal organs detect injury or potential damage to body tissues.

Thermoreceptors in the skin and internal organs detect warmth and cold.

Mechanoreceptors embedded in the skin detect light touch, heavy pressure, vibration, and stretching of the skin.

Mechanoreceptors in muscles, tendons, and joints detect position and movement of arms and legs.

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Practice 2: Interaction of Pain and Touch

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Practice 2: Interaction of Pain and Touch

This person has an injured elbow. Select the "Pain pathway" button to view the signals that will be perceived as pain. Then select the "Block pain" button to view one way of reducing the experience of pain.

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Quiz 1

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Quiz 1

Match the terms to their descriptions by dragging each colored circle to the appropriate gray circle. When all the circles have been placed, select the CHECK ANSWER button.

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Perhaps you should go back to review sensory receptors and brain areas involved in touch, movement, and pain.
somatosensory cortex
mechanoreceptor
vestibular sense
kinesthesia
nociceptor
thermoreceptor
generates neural impulses when stimulated by pressure, vibration, or stretching
generates neural impulses that signal potential tissue damage; brain uses these signals to perceive pain
receives and processes information from the skin and internal organs
has receptors in the inner ear that detect movements of the head
has receptors in muscles, tendons, and joints that detect position and movement of the parts of the body
generates neural impulses that signal warmth or cold

Quiz 2

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Try to respond to the statements again.

Quiz 2

Indicate whether each of the statements below is True or False. Then, select the CHECK ANSWER button.

TrueFalse

The sensory receptors that the body uses to detect touch and vibration are different from the receptors that detect tissue damage.

Signals travel from nociceptors to the spinal cord on thick, myelinated axons.

The experience of pain can be influenced by other simultaneous events detected by the somatosensory system.

Conclusion

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