Chapter 9 Somatic Sensory System: Touch & Proprioception Flashcards
Mechanoreceptors: Merkel Cell Afferent
Epidermis. Fine edges. Texture and form. Sustained (slow adaptation). Smallest receptive field.
Mechanoreceptor: Pacinian Corpuscle
Dermis & Subcutaneous. Vibration, tool use. Entire finger or hand receptive field. Rapid adaptation (not sustained) response. Onion layers. Deepest. Very sensitive.
Meissner Afferent
Dermis. Close to skin surface. Rapid adaptation (not sustained). Motion detection, grip control. Make up 40% innervating human hand.
Ruffini corpuscle
Dermis. Skin stretch. Sustained (slow adaptation)
Dermatomes
Territory innervated by each spinal nerve. Segmental arrangement of somatic nerves and targets they innervate (arise from somites - embryonic tissue)
Adequate stimulus
hearing: sound; retina: light;
What disease related to dermatomes? Chicken pox for adults
Herpes Zoster aka shingles
2 Point Discrimination
The minimal receptor distance that two neurons can each distinctly detect a sensory stimuli
Sensitivity vs Resolution
Sensitivity based on how tiny the stimulus is. Resolution is ability to discriminate. The larger the resolution, the lower the sensitivity
Free nerve endings
Pain receptors
The somatosensory afferents travel in bundles in the dorsal columns known as?
Fasciculus gracilus (lower limbs) Fasciculus cuneatus (upper limbs, trunk, and neck)
Cranial Nerve Ganglia vs Dorsal Root Ganglia
Head Neurons vs Body Neurons that provide information from PNS to CNS.
Other name for somatotopic map
Homunculus (small man)
Why is homunculus distorted?
It is systematic but distorted bc it is proportional to the amount of receptors found at different parts of the body. Finger tips have more receptor density than back.
Neurons in dorsal root ganglia are often considered?
Pseudounipolar. Peripheral and central components of afferent fibers are continuous (central axon and peripheral axon are continuous)
What are distinguished features of sensory afferents?
How are they differentiated
- Axon diameter (The wider the faster the conduction speed of AP; e.g. pain/temp small, muscle sensory receptors largest)
- Receptive Field size (Spatial accuracy) - the larger the less sensitive (more branching, smaller receptive field sizes) – dense innervation like fingers have smaller receptive fields (movement)
- Temporal Dynamics. Rapid followed by silence vs slow response and sustained discharge (size and shape)
- Quality of somatic sensory stimulation
(1. Conduction velocity, receptive field size, dynamics, and effective stimulus features vary in parallel pathways)
Receptive field
area that corresponds to a significant change in the rate of AP.
Affect the spatial accuracy
Nocireceptors
pain. free nerve endings.
Meissner Afferent
Dermis. Close to skin. 40%. Rapid response. Sensitive, larger receptive field, lower spatial resolution, low spatial acuity (than Merkel). Skin motion detection, grip
Merkel Afferents
Epidermis. Slow response. Form and texture. Details.
Pacinian corpuscle
Dermis. Deepest. Vibrations, tools. Fastest response. Sensitive, large receptive field, low spatial resolution.
Ruffini Afferent
Dermis. Deep. Slow response. Conformation/motion of finger/hand. Stretch.
Increase sensitivity, what happens to receptive field?
Receptive field increases, spatial resolution decreases.
nearsighted /myopia corrective lens
convex (minus)
