Chapter 14: The body and cutaneous senses Flashcards
What other senses could be derived from touch itself?
- Skin deformation (tactile perception)
- Muscle stretch and joint angle (proprioception)
- Potential tissue damage (pain)
- Temperature (thermoception)
- Object shape (haptics)
- Balance and acceleration of body (vestibular sense)
What are the 2 skin types?
- Hairy
- Glabrous
What are the 2 major skin layers?
- Epidermis (outermost thinner layer)
- Dermis (inner, thicker layer, where most receptors are found)
What are the two major types of mechanoreceptors?
- Slowly adapting (SA) receptors
- Rapidly-adapting (RA) receptors
what are the two types of SA receptors?
- Merkel receptors (SA1) - Have small receptive fields. and are densely packed nearer the skin surface. Specialized for detailed touch perception
- Buffini Cylinders (SA2) - Have larger receptive fields (5x larger than SA1), found deeper in the dermis, more sparse. Involved in skin stretch (hand conformation). Helps us adjust hand for precision grips
What are the two types of RA receptors?
- Meissner Corpuscles (RA1) - Relatively small receptive fields, found nearer skin surface, densely packed. Help us perceive slipping objects, helps maintain grip (involves a feedback system)
- Pacinian Corpuscles (RA2) - Larger receptive fields, deeper in dermis, sparse. Extremely sensitive to very fine vibrations (helps perceive textures, can also perceive texture through tools)
What are C-tactile mechanoreceptors?
- Discovered recently
- Type of free nerve ending only found in hairy skin
- Respond to slow, gentler touch
- Signals to the insular cortex (either pleasant/unpleasant)
What’s the two-point threshold?
- A measure of tactile acuity
- The minimum separation between 2 points on the skin that can be perceived as 2 points 75% of the time.
- Minimum thresholds found in face and fingers
- Generally corresponds to density of Merkel cells (but not always)
What’s grating acuity?
- A measure of tactile acuity
- Press a grooved object into the skin, and ask person to identify the direction of the grooves
- Also try to identify the narrowest spacing while still accurate
- Differs across the body in the same pattern as the two-point threshold
How does the Pacinian Corpuscle (RA2) identify vibrations?
- Due to the structure of the nerve-ending
- The ending is multi-layered, with layers separated by fluid/gel
- Can absorb direct pressure, but vibrations cause the fluid to shift, which makes its way tot he nerve fibre
What does the term kinesthesis refer to?
- The perception of the position and movement of body parts
What info is used to determine proprioception?
- Largely based on info about joint angles and distances
What are the three types of sensory organs involved in proprioception?
- Muscle spindles (most important) - provide info about muscle length. Afferent neurons fire when muscles stretch
- Golgi Tendon organs - Provide info about muscle tension/force. Afferent neurons fire when muscles contract
- Joint receptors - provide info about joint angle, but likely only to signal when it has reached its limits
What are the three types of physical pain (nociception)?
1) Nociceptive pain = Arises from tissue damage due to physical trauma
2) Inflammatory pain = After damage, chemical substances released by damaged areas activate receptors directly or reduce threshold so more sensitive to pain
3) Neuropathic pain = Due to damage to CNS or PNS
What are nociceptors?
- Sensory receptors involved in transducing physical stimuli associated with mechanical, thermal, or chemical damage
- It’s a type of free nerve ending in the dermis and epidermis
- Found in almost every tissue of the body except the brain
- They have a fairly high threshold (only respond to potential damage)
Why does sensitization of nociceptors occur?
- Decrease the threshold of pain to protect damaged tissue
- Also allow time for damaged tissue to heal
How do nociceptors transmit pain signals to the spinal cord?
- Done via two types of nerve fibres:
1) A-delta fibres - Myelinated, more associated with acute, intense pain, respond most to damaging mechanical stimuli and excessive heat
2) C-fibres - Unmyelinated, dull throbbing pain, respond to a wide range of stimuli - Both signals can occur at once (ex. stubbing your toe)
What does the term homunculus refer to?
- Latin for ‘little man’
- The cortex is like a map of the body, adjacent body parts will activate adjacent parts of the brain
- This map is distorted, as in greater areas of sensitivity will take up more space in the cortex, such as the face
What are the 4 main areas of the somatosensory cortex?
1: mechanoreceptors
2: Proprioception
3a: Proprioception and pain
3b: mechanoreceptors and pain
