Somatosensory System I- Introduction Flashcards
What are the modalities that the sensory system mediates?
- Discriminative Touch
- Proprioception
- Nociception
- Temperature Sense
- Light Touch
Define Discriminative Touch
The ability to recognize the shape, size, and texture of objects and their movement across the skin. Includes vibratory sense and pressure.
What is Conscious Proprioception and what are its categories?
The sense of static position and movement of the limbs and body.
- Limb Position Sense: The sense of the stationary position of the limbs.
- Kinesthesia: The sense of limb movement.
What does unconscious proprioception refer to?
Proprioceptive information that is conveyed from the spinal cord to the cerebellum for the modulation of movements.
Define nociception?
the signaling of tissue damage or chemical irritation, typically perceived as pain or itch.
define Temperature Sense
the sense of warmth or cold
define light touch
the sense of cutaneous touch or light pressure. Absence produces little, if any disturbance in tactile sensibility.
What class of neurons do all modalities share?
Dorsal root ganglion neurons (pseudounipolar)
What are the two regions of dorsal root ganglions?
- Receptors
2. Fibers (Axons)
What does the structure of a receptor determine?
the sensory function of each dorsal root ganglion
Describe the structure of a dorsal root ganglion receptor.
Most of them have specialized CT capsules surrounding the nerve terminal, when they become deformed in particular ways, this excites the dorsal root ganglion neuron
What do Mechanoreceptors in the skin do?
Mediate touch
Receptive fields are smaller in what part of the skin? Why is it important?
Smaller in the superficial part of the skin
-important for tactile discrimination
Receptive fields are larger in what part of the skin? Why is it important?
Larger in the deep layer of the skin
-important for detecting global properties of objects
RA receptors sense what?
The motion of the objects (speed and duration).
-Have lower thresholds, so they detect minute vibrations
SA receptors sense what?
- Signal the pressure and shape of objects
- Higher thresholds, that require more salient bumps or edges to activate. Once stimulated, have a clearer image of contours.
The spatial characteristics of objects are signaled by what?
Populations of mechanoreceptors
What do Mechanoreceptors in muscles and joints do, and what are examples?
Mediate proprioception
-Muscle spindles, golgi tendon organs, joint receptors
What do Nociceptors do?
Mediate Pain
-Serve an important protective function, warning of injury that should be avoided or treated.
What types of pain are there?
- Acute vs. Chronic
2. Nociceptive vs. Neuropathic
Nociceptive pain has what 2 levels?
- Sharp, Localized
2. Second- Dull/Burning, Diffiuse
What are the 3 types of Nociceptors?
- Mechanical
- Thermal
- Polymodal
What effective stimuli does the Mechanical receptors cause?
Intensive pressure applied to the skin. Evokes sensations of sharp or pricking pain.
What effective stimuli do thermal receptors cause?
Extreme temperatures (too hot or too cold).
What effective stimuli do polymodal receptors cause?
High intensity mechanical, thermal (both hot and cold), or chemical stimuli. Evokes sensations of slow, burning pain.
Describe Thermoreceptors
Mediate temperature
-Show a graded response to changes in temperature
What are the types of thermal sensation?
- Cold
- Cool
- Warm
- Hot
What does the code for skin temperature involve?
Comparing the relative activity of the different populations of thermal receptors.
How are fibers classified?
- Based on conduction velocity in mixed peripheral nerves
2. Fiber diameter in cutaneous nerves
Proprioceptors and mechanoreceptors are innervated by what type of fibers?
-Large-diameter myelinated axons with fast conduction velocities
Nociceptors and thermoreceptors are innervated by what type of fibers?
-Small myelinated or unmyelinated axons with slow conduction velocities.
The sensory specialization of dorsal root ganglion neurons are preserved where?
In the central nervous system through distinct ascending pathways for various modalities.
Describe the neural pathways of the somatosensory system.
-Comprised of 3 neurons (periphery to the highest levels of CNS
Where are the cell bodies of 1st order neurons?
Dorsal root or cranial nerve ganglia
Where are the cell bodies of the 2nd order neurons?
Lie in the nuclei in the spinal cord and brainstem
Where are the cell bodies of the 3rd order neurons?
Lie in the thalamus
