Intro To Somatosensory System

Question 1

Major modalities of somatosensory information

Answer 1

. Discriminative touch
. Proprioception
. Temp. Sense
. Nociception
. Each is mediated by distinct system of receptors and pathways to the brain

Question 2

Discriminative touch

Answer 2

. Recognize size, shape, and texture of objects and their movement across skin
. Tactile sensitivity is greater on hairless skin of fingers, palm of hand, and sole of foot and lips

Question 3

Proprioception

Answer 3

. Sense of static position and movement of limbs and body

Question 4

Nociception

Answer 4

. Perceived as pain or itch
. Signals tissues damage or chemical irritation
. Pain not the over stimulation of generalized cutaneous receptors but results from electrical activity transmitted by specific receptors and pathways

Question 5

Epicritic sensations

Answer 5

. Involve fine aspects of touch
. Highly localizable and discriminative
. Mediated by encapsulated receptors
. Detect gentle contact of skin and localize position that is touch
. Discern vibration and determine freq. and amplitude
. Resolve by touch spatial detail (texture of surfaces, spacing of 2 points touched simultaneously)
. Recognize the shape of objects grasped in hand (stereognosia)

Question 6

Protopathic sensations

Answer 6

. Involve pain and temp. Sense as well as tickle and itch
. Cruder senses, more intense stimuli (poorly localizable, non-discriminative) are needed to activate
. Mediated by receptors w/ bare n. Endings

Question 7

Exteroceptors

Answer 7

. Conscious appreciation of sensations from external stimuli to our body

Question 8

Proprioceptors

Answer 8

. Info on relative position of body in space
. Movement sense (kinesthesia)
. Conscious proprioception info is relayed to cerebral cortex
. Unconscious proprioception info is relayed to the cerebellum

Question 9

Interoceptors

Answer 9

. Processing of visceral info

Question 10

Mechanoreceptors

Answer 10

. Respond to some sort of a mechanical deformation 
. Tactile receptors: cutaneous and deep receptors reponding tot ouch and pain perception 
. Muscle spindles and joint receptors for proprioception 
. Class A-beta or class II

Question 11

Nociceptors

Answer 11

. Pain perception
. 1st/fast pain (pinprick) and 2nd/slow pain (dull, aching)
. May be due to mechanical, thermal, or chemical timelines
. Class A-gamma (III) or C (IV)

Question 12

Encapsulated receptors

Answer 12

. N. Endings surrounded by CT wrappings
. Meissner’s corpuscles (discriminative touch), rapid adaptation
. Pacinian corpuscles (vibration), rapid adaptation
. Ruffini endings (pressure/stretch and proprioception), thin capsule, slow adaptation

Question 13

Uncapsulated receptors

Answer 13

. No CT wrappings
. Merkel endings: touch sensation (rapid adaptation)
. Free n. Endings: crude touch, pain, and temperature sensation (adaptation varies)
. Endings around hairs: touch sensation (rapid adaptation)

Question 14

Receptive fields

Answer 14

. Area of skin when stimulated activates a particular sensory neuron
. Some small and relay info from discrete skin areas (Meissner’s)
. Some large and relay info from large areas of skin (peripheral axon receptors, pacinian corpuscles)
. Fine touch: many neurons that have small receptive fields
. Crude touch has fewer neurons that have larger receptive fields

Question 15

2-point discrimination

Answer 15

. Minimum distance where 2 stimuli can be separated and still perceived as 2 stimuli
. Most precise where there is high density of sensory receptors w/ small receptive fields (fingertips)

Question 16

Dermatomes

Answer 16

. Area of body that a particular spinal cord segment innervates through its spinal nn.
. Has overlap
. Each dermatome overlaps w/ 2 adjacent dermatomes so that a particular spinal cord segment innervates a portion of 3 successive dermatomal areas
. Lesion in single spinal n. Produces little to no sensory loss due to overlap
. At least 3 successive dorsal roots need to be compromised in order to observe obvious sensory loss

Question 17

Peripheral n. Processes

Answer 17

. Size principle: the larger the diameter of the axon, the faster the conduction velocity
. Myelination: larger axons tend to be more heavily myelinated causing faster APs than smaller axons

Question 18

Thermal receptors class

Answer 18

. A-gamma (III) or C (IV)

Question 19

Muscle spindles class

Answer 19

Ia or II

Question 20

Golgi tendon organs class

Answer 20

. Ib

. In charge of sensing muscle tension

Question 21

Lateral dorsal root entry zone

Answer 21

. Smaller diameter axons that are lightly myelinated or unmyelinated
. Assoc. w/ pain. Temp., crude touch, and visceral afferents
. Assoc. w/ Lissauer’s tract where axons accumulate upon entering spinal cord
. Axons may ascend up or descend down a few spinal segments in this tract

Question 22

Medial dorsal root entry zone

Answer 22

. Larger diameter axons that are heavily myelinated

. Assoc. w/ transmission of highly discriminative forms of touch and proprioception

Question 23

Which sensory pathway is the only one to not stop in the thalamus?

Answer 23

Olfaction pathway

Question 24

Thalamus radiations

Answer 24

. Fibers leaving thalamus radiate toward the cerebral cortex passing through internal capsule forming this

Question 25

Dorsal column-medial lemniscal system

Answer 25

. Serves epicritic sensations

Question 26

Anterolateral system

Answer 26

. Made of set of 3 different anatomical pathways 
. Spinothalamic tract
. Spinoreticulothalamic tract
. Spinotectal tract 
. Carries protopathic sensory abilities