Lecture 11- Somatic Sensory System Flashcards
Give a general overview of the sensory pathway from receptor endings (dermatome)
stimuli–> dorsal root ganglion –> pain and temp decussates at level of entry/ mechanosensory fibres travel up through spinal cord to cuneate (upper body)/ gracile (lower body) nuclei then decussate at medial lemniscus in medulla –> up through medulla –> midbrain –> thalamus –> somatosensory cortex of cerebrum
what is sensory transduction?
where the energy of a stimulus is converted to an electrical signal
what are the 2 types of receptors?
rapidly adapting
slowly adapting
what’s the difference between rapidly adapting and slowly adapting receptors?
rapidly adapting are transient, firing maximally in immediate response to stimulus briefly
slowly adapting are tonic and fire as long as stimulus is present
what are the 5 receptors found in the skin for tactile stimulation?
- meissner corpuscle
- pacinian corpuscle
- ruffini’s corpuscle
- merkel’s disc
- free nerve endings
describe Meissner corpuscles
- rapidly adapting
- most common in smooth/hairless skin
- 40% hand innervation
- detects texture moving across skin- useful in detecting object slippage/grip
describe Pacinian corpuscles
- rapidly adapting
- more sensitive that Meissner- fine textures
- 15% hand innervation
- tickle/vibration sensation
- skilled tool use
Describe Ruffini’s Corpuscles
- slowly adapting
- 20% receptors in hand
-unknown function but linked to proprioception
Describe Merkel’s Discs
- slowly adapting
- 25% receptors in hand
- dense in fingertips
- stimulation produces light pressure sensation
- detection of shape/edges/rough texture- braille reading
Describe free nerve endings
pain and temp sensation
Why is it useful to understand these receptors?
developing artificial systems and bioimplants
name 3 areas of the body which have the greatest 2-point discrimination threshold
hands, face, feet
name 3 areas of the body that have the lowest 2-point discrimination threshold
legs, arms, back
what determines 2-point discrimination threshold?
the density of receptors and the size of their receptive field
what are the 2 main types of proprioceptors?
muscle spindles
golgi tendon organs
what do muscle spindles do?
signal muscle length
what do golgi tendon organs do?
signal changes in muscle tension
what does the number of muscle spindles reflect?
how fine the control of each muscle is
where in the body has the highest density of muscle spindles?
oculomotor muscles
what are the 2 types of muscle spindles and what do they indicate?
group 1- info about dynamic movement
group 2- info about static positions of limbs
do golgi tendon organs respond to passive stretch?
no, only active contraction
what are the 3 key somatic sensory pathways?
- dorsal column medial lemniscus
- trigeminal system
- spinothalamic
generally what does the dorsal column medial lemniscus pathway detect?
upper and lower body sensation
generally what does the trigeminal system pathway detect?
face sensation
