Chapter 18-6. Somatosensory System
Recommended reading: 【Biology】 Chapter 18. Sensory System
1. Overview
3. Type 1. Mechanoreceptors)
4. Type 2. Nociceptors (pain receptors)
1. Overview
⑴ Skin
① An outer covering that wraps the body surface
② The largest organ in our body
③ Component 1. Epidermal layer: Rich in keratin. Impermeable
④ Component 2. Dermal layer: Rich in collagen fibers, water, electrolytes, proteins, and glycosaminoglycans
⑵ The five cutaneous senses: pain, pressure, touch, cold, warmth
Figure 1. Cutaneous receptors for the five skin senses]
① Pain: The sense of feeling pain
○ Involves nerve endings in the dermis (free endings)
○ Has the greatest number of receptors
② Pressure: The sense of pressure
○ Involves Merkel’s disks in the epidermis
○ Involves Pacinian corpuscles (Pacinian corpuscle) in the dermis
○ Pacinian corpuscles contain abundant collagen, showing characteristics of phasic receptors
○ If connective tissue is removed from Pacinian corpuscles, they show characteristics of tonic receptors
③ Touch: The sense felt when something makes contact
○ Involves Meissner’s corpuscles in the epidermis to dermis
○ Many at the lips and fingertips; fewer at the thigh and buttocks
○ More sensitive to hair than to skin
④ Cold: The sense of coldness
○ Involves the endbulb of Krause in the dermis
⑤ Warmth: The sense of warmth
○ Involves Ruffini corpuscles in the dermis
○ Has the fewest receptors among the five senses
⑥ Comparison of receptor numbers: pain＞pressure＞touch＞cold＞warmth
2. Ascending pathways
⑴ Most spinal ascending pathways decussate in the medulla
⑵ Sensory information from the skin, joints, and muscles
① 1st. Ascends ipsilaterally in the spinal cord, then decussates in the medulla
② 2nd. Transmitted along the dorsal column medial lemniscus pathway
③ 3rd. Projects to the primary sensory cortex via the ventrobasal complex, a specific sensory nucleus of the thalamus
⑶ Pain, temperature, crude or light touch
① 1st. Transmitted along the anterolateral system
○ 1st - 1st. Pain is transmitted via the lateral spinothalamic tract within the anterolateral system
○ 1st - 2nd. Temperature is transmitted via the anterior spinothalamic tract within the anterolateral system
② 2nd. Decussates in the spinal cord
Figure 2. Pathways of cutaneous sensation]
3. Type 1. Mechanoreceptors
Figure 3. Major structures along the sensory pathway
⑴ VPL (ventral posterolateral nucleus): Delivers sensory information to Brodmann areas 1, 2, and 3
⑵ Somatosensory cortex: Parietal lobe; Brodmann areas 1, 2, 3, and 5
① Postcentral gyrus: Primary somatosensory cortex
② Superior parietal lobule: Secondary somatosensory cortex
⑶ Somatosensory perception
① Proprioceptive sense (self-receptive sense), deep touch: Involves the primary somatosensory cortex
② Light touch and pain involve the lateral spinothalamic tract (lateral spinothalamic tract, lateral pathway)
4. Type 2. Nociceptors (pain receptors)
Input: 2019.03.02 23:15
Revised: 2022.04.24 12:11