HUF 2-50 Skin senses: touch and temperature Flashcards
Sensory modalities
different types of sensory inputs
Sensory receptors
- Specialised cells that can detect and convert different kinds of physical / chemical energy into electrical signals of nervous system
- Detection of environment (ext. + int.)
- Vary in morphology and function
1° receptors: specialised endings of aff. n. (e.g. olfactory receptors; pain receptors)
2° receptors: separate cells innervated by aff. n. (e.g. hair cells)
Sensory modalities - receptor cell types:
Vision Hearing Balance Touch Proprioception Temperature Pain Itch Taste Smell
Vision - Rods, cones
Hearing - Hair cells (cochlea)
Balance - Hair cells (vestibular labyrinth)
Touch - Cutaneous mechanoreceptors
Proprioception - Muscle and joint receptors
Temperature - Cold and warm receptors
Pain - Polymodal, thermal and mechanical nociceptors
Itch - Chemical nociceptors
Taste - Taste buds
Smell - Olfactory sensory neurons
Muscle spindle
- Stretch receptor in skl. ms.
- Activated when ms. is being stretched (aff. n.)
=> receptor potential
=> AP in CNS
Generation of receptor potentials (RP)
- Graded depolarising potential when appropriate stimulus is applied
- ↑ stimulus strength
=> ↑ RP - Opening or closing of ion channels in membrane
- Big enough RP => AP
Coding of sensory information
- Modality
- “Type” of sensory sensation
- Diff. parts of brain => generate diff. modalities - Location
- Topographical representation of body in brain (e.g. somatosensory cortex) - Intensity
- Freq. of AP generated (∝ signal strength) - Duration
- “Adaption”
- Continuous presence of sensory stimulus
=> ↓ or absence of signal to CNS
Somatic sensory receptors - modalities
Free nerve endings: pain, heat, cold
Merkel discs: light touch
Krause end bulbs: touch
Root hair plexus: touch
Meissner corpuscles: touch
Pacinian corpuscles: vibration
Ruffini endings: pressure
- 1° aff. to CNS (cell bodies in dorsal root ganglia)
Ascending pathways of somatic sensations
Dorsal column (Nu. cuneatus, gracilis)
- Mechanosensation
- Decussate at brainstem (medial leminiscus)
=> 2° order neurons
=> VP nu. of thalamus (3° order neurons)
=> Primary somatosensory cortex, other cortical areas
Spinothalamic tract - Pain, temperature - Decussate at spinal cord => 2° order neurons => VP nu. of thalamus (3° order neurons) => Primary somatosensory cortex, other cortical areas
Topographical map in somatosensory cortex
- Postcentral gyrus
- Receives info from contralateral side of body
Touch receptors and their distributions
- Touch, pressure, vibration
- Meissner’s corpuscle; Merkel disc; Ruffini ending; Pacinian corpuscle; hair receptor
- Diff. distributed in hairy and non-hairy (glabrous) skin
Coding of touch sensation
- Activation of touch receptors
=> Signals reach “touch area” of somatosensory cortex
=> Modality and location of “touch” - Diff. touch receptors => diff. sub-modalities
- AP: intensity and duration
Receptive fields and adaption of touch receptors
- Area of the skin innervated by aff. neuron
- Diff. receptor types => diff. receptive field size
- Info from diff. types of mechanoreceptors integrated in 1°
somatosensory cortex
=> sensation of touch at specific locations
Fast adaption, small receptive field: Meissner’s corpuscle
Fast adaption, large receptive field: Pacinian corpuscle
Slow adaption, small receptive field: Merkel’s disc
Slow adaption, large receptive field: Ruffini’s ending
Cutaneous thermoreceptors
- Free n. endings with temp. sensitive ion channels
- Warm receptors: narrow temp. range; from 30°C
- Cold receptors: broader temp. range; 20-30°C
- Central thermoreceptors in hypothalamus
=> Control of body temp.
=> Conscious sensation of temp. - More extreme temp.
=> Thermosensitive pain (nociceptive) receptors
=> Pain (Transient Receptor Potential channels)
