Somatosensation (touch)
In this lesson, we’ll begin exploring sensory systems by focusing on somatosensation: sensory information that comes from the body, such as touch and pain.
1) Start with this video to learn about the receptors we use to detect touch sensations:
2) Next, watch these videos to learn about the pathways that carry somatosensory information to the brain, as well as the location in the brain where that information is initially processed (the somatosensory cortex).
3) Read this article about the primary somatosensory cortex: Know Your Brain - Primary Somatosensory Cortex
4) Finally, answer these questions to test your understanding:
1. The somatosensory cortex is arranged in a somatotopic manner. What does this mean?
- A. sensory information is randomly distributed across the cortex
- B. specific regions of the cortex correspond to specific parts of the body
- C. sensory signals are processed according to their intensity, not their location
- D. each sensory modality is processed in separate layers of the cortex
Show Answer
Correct answer: B
Each of the four areas of the primary somatosensory cortex is arranged such that a particular location in that area receives information from a particular part of the body. This arrangement is referred to as somatotopic, and the full body is represented in this way in each of the four regions of the somatosensory cortex.
2. The primary somatosensory cortex is located in which of the following regions?
- A. precentral gyrus
- B. postcentral gyrus
- C. superior temporal gyrus
- D. occipital lobe
Show Answer
Correct answer: B
The primary somatosensory cortex lies in the postcentral gyrus, just posterior to the central sulcus.
3. You run your fingers across the top of your desk and perceive that it is solid but has a smooth surface. Which pathway below was most responsible for carrying this particular sensory information to your brain?
- A. corticospinal tract
- B. dorsal columns-medial lemniscus
- C. spinothalamic tract
- D. spinocerebellar tract
Show Answer
Correct answer: B
The dorsal columns-medial lemniscus pathway is the main pathway that carries tactile sensations---including sensations of touch, pressure, and vibration---to the brain. It also carries information about proprioception. Neurons in the dorsal columns travel up the spinal cord and synapse in the brainstem on neurons that form the second part of the pathway: the medial lemniscus. This travels up to the somatosensory cortex, which is the main cortical area for processing touch sensations.
4. Which of the following are touch receptors?
- A. bipolar cells
- B. hair cells
- C. olfactory receptors
- D. Merkel's discs
Show Answer
Correct answer: D
Merkel’s discs are slowly-adapting touch receptors that have very small receptive fields and high spatial resolution. They are especially dense in the fingertips, and are best-suited for processing information about shape and texture.
5. Which of the following touch receptors have the largest receptive fields, making them well-suited to detect vibrations objects cause when they are contacted or grasped by the hand?
- A. Ruffini's endings
- B. Meissner's corpuscles
- C. Pacinian corpuscles
- D. hair follicle receptors
Show Answer
Correct answer: C
Pacinian corpuscles are rapidly-adapting receptors with very large receptive fields. They are thought to be most effective at transmitting information about vibrations objects cause when they are contacted or grasped by the hand. This information may be important for the use of tools.
