Chapter 12c - temperature Flashcards
What is the basic mechanisms of temperature sensation?
Nonpainful temperature sensation originates from the receptors in the skin (and elsewhere) and depend on the neocortex for their conscious appreciation.
What are thermoreceptors?
Neurons that are exquisitely sensitive to temperature because of specific membrane mechanisms.
Changes in our average skin temperature of as little as 0.01ºC can be perceived.
What do temperature-sensitive neurons do? Where are they?
How do they relate to thermoreceptors?
They are clustered in the hypothalamus and the spinal cord and are important in the PHYSIOLOGICAL RESPONSES that maintain stable body temperature.
THERMORECEPTORS in the skin are the ones that apparently contribute to the perception of temperature.
How many thermoreceptor (TRP) channels are there? How do they relate to thermoreceptive neurons?
There are 6 TRP channels.
Each thermoreceptive neuron appears to express only a single type of channel. Thus, different regions of the skin can show distinctly different sensitivities to temperature.
What is TRPV1 and how is it special?
It’s a “hot” receptor protein, that senses heat. It is exceptional in the sense that some cold receptors also express TRPV1 and are therefore also sensitive to increases in temperature above 43ºC.
If heat is restricted to small regions of skin innervated by a cold receptor, heat can produce a paradoxical feeling of cold.
How do the responses of thermoreceptors adapt during long-duration stimuli?
The differences between the response rates of warm and cold receptors are greatest during, and shortly after, temperature changes.
This usually matches our perceptions of temperature.
What is the temperature pathway?
Virtually identical to that of the pain pathway. Cold receptors are coupled to Aδ and C fibers, while warm receptors are coupled only to C fibers.
The axons synapse within the substantia gelatinosa of the dorsal horn.
The axons of second-order neurons immediately decussate and ascend in the contralateral spinothalamic tract.
Imagine rubbing your finger across a pane of smooth glass and then across a brick. What kinds of skin receptors help you distinguish the two surfaces? As far as your somatic sensory system is concerned, what is different about the two surfaces
To be detected, the stimulus that glass creates would have to excite slowly adapting mechanoreceptors because its surface does not change. A brick might produce a stimulus with vibrations and changes in pressure related to the raised parts of its surface. To detect the successive peaks and valleys on the surface of the brick, a rapidly adapting receptor might best detect the stimulus.
what purpose is served by the encapsulations around some sensory nerve endings in the skin
Encapsulations around Pacinian corpuscles provide a mechanism that makes the Pacinian corpuscles rapidly adapting, which is a property that makes them sensitive to vibrating high-frequency stimuli. if the encapsulations are stripped away, the naked nerve terminals become less sensitive to vibrating stimuli and more sensitve to steady pressure
If someone tossed you a hot potato and you caught it, which information would reach your CNS first — news that the potato was hot or that it was relatively smooth? Why?
news about the smooth surface would reach your CNS faster than news about the temperature of the potato. In the CNS, C fibers mediate the pain and temperature sensations. They are the slowest axons, conducting at about 0.5-2 m/sec. C fibers are slow because they are the smallest axons, with diameters of less than 1 μm, and they do not contain myelin. On the other hand, cutaneous mechanoreceptors mediate touch sensations. The relatively large Aβ axons, which can conduct at up to 75 m/sec, convey these sensations.
At what levels of the nervous system are all types of somatic sensory information represented on the contralateral side: the spinal cord, the medulla, the pons, the midbrain, the thalamus, the cortex?
Information from the dorsal columns crosses at the level of the medulla after synapsing in the dorsal column nuclei, so dorsal column information is contralateral as it courses through the medial lemniscus to synapse in the thalamus and then in the cortex. As a result, all types of somatic sensory information are represented on the contralateral side at the level of the thalamus.
What lobe of the cortex contains the main somatic sensory areas? Where are these areas relative to the main visual and auditory areas?
Most of the cortex concerned with the somatic sensory system is located in the parietal lobe. In contrast, the main visual areas are in the occipital lobe at the back of the brain, and the main visual areas are in the superior temporal gyrus of the temporal lobe on the lateral surface of the brain
Where can pain be modulated in the body, and what causes its modulation
It can be modulated at the level of pain receptors by simultaneous activity in low-threshold mechanoreceptors, Strong emotions via activity in the periventricular and periaqueductal gray (PAG) matter of the midbrain also modulate pain. In addition, the nervous system produces endogenous opiates or endorphins
Where in the CNS do information about touch, shape, temperature, and pain converge
The posterior parietal cortex is the area where segregated streams of somatosensory information converge to generate complex neural representations. The posterior parietal cortex is essential for the perception and interpretation of spatial relationships, accurate body image, and the learning of tasks involving coordination of the body in space, all of which involve input from the visual system.
Imagine this experiment. Fill two buckets with water, one relatively cold and one hot. Fill a third bucket with water of an intermediate, lukewarm temperature. Put your left hand into the hot water, your right hand into the cold, and wait one minute. Now quickly plunge both hands into the lukewarm water. Predict what sensation of temperature you will feel in each hand. Will they be the same
No, they will not feel the same. The hand previously placed in hot water will feel much cooler in lukewarm water than the hand previously placed in cold water. The lukewarm water will feel relatively warm to the hand previously placed in cold water. These differences, however, will be transient
