Sensory: touch and proprioception Flashcards
Mechanically activated ion channels can be gated by forces from the membrane (stretching,
shrinking, bending) or from filaments tethered to extracellular or intracellular parts of the channels.
Give examples for each of these mechanisms.
Forces from filament: receptors involved in hearing (tip-link)
Forces from lipid: Piezo receptors
What is proprioception? Which structures and channels are involved?
Sensing where your body parts are in space. Piezo receptors, muscle spindels, golgi tendon organs, joint receptors
What structures are responsible for sensing touch?
Merkel’s disc, Meissner’s corpuscle (both located right beneath the epidermis, in the upper dermis) and hair follicle receptors (located around the hairs)
What kind of sensing are the pacinian (or lamellated) corpuscle responsible for?
Vibration and pressure
What kind of sensing are the Ruffini’s endings responsible for?
Stretch
Are the merkel cell receptors and meisner corpuscle receptors low treshold or high treshold receptors?
Low treshold
Describe the general route in the PNS for afferent noci-, mechano and proprioceptors
The primary afferent neuron go through the dorsal root ganglion (cell body) –> dorsal horn (Lissauer’s tract) innervating secondary afferent CNS neurons –> CNS neurons go through the spino-thalamic tract –> spine –> thalamus
The proprioceptors also have an alternative root, describe this.
Afferent cells through dorsal horn, connected to efferent motorneurons by interneurons in the dorsal horn –> efferent motorneurons through ventral horn –> periphery. This allows for a quicker response
What are the four types of mechanoceptors?
Pacinin corpuscles, Ruffini corpuscles, Meissner corpuscles and Merkel cell
Describe the configuration of the pacini corpuscles.
Onion configuration, ion channels in the central part of the onion structure
Describe receptive field.
How big of an area are sensing the stimuli
Describe the receptive fields and adaption of the four kinds of mechanoceptors.
Ruffini: large and slow
Merkel: small and slow
Meissner: small and rapid
Pacinian: large and rapid
How can mechanosensitive ion channels be gated?
- Membrane stretch
- Force on extracellular structures
- Deformations of cytoskeletal structures
What are lanciform nerve endings sensing?
Detecting very small bends of hair (e.g., stroking)
Describe the structure of piezo receptors.
Propella-like structure
Where are propioceptors found?
Muscle spindles, golgi tendon organs and in joint receptors (extreme joint angle)
Describe muscle spindles.
- stretch detectors (signal muscle length), and the normal function of stretch reflexes
- modified muscle cells
- group 1: afferents wrapped around the muscle fibers
Describe the monosynaptic stretch reflex.
Muscle spindle detect stretch –> dorsal root ganglion –> dorsal root –> synapse in the ventral horn –> ventral root –> muscle
Describe group 1 and 2 fibers dynamic and static responses.
Group 1: fire max during stretch, provides max input during rapid changes
Group 2: provide static signals at steady state
Describe golgi-tendon organs.
- have a single (1b) sensory axon (polysynaptic)
- runs between collagen bundles
- stretch straightens collagen fibres and compress sensory nerve
- important for fine motor control
Describe the negative feedback via 1b inhibitory interneurons in the golgi-tendon organ pathway.
- negative feedback via 1b inhibitory interneurons –> inhibits homonymous muscle + excite antagonist
Describe the central projections of touch and proprioception from periphery.
Transmitted in the dorsal column-medial lemniscus pathway –> VPLN of thalamus –> primary somatosensory cortex
Describe the central projections of touch and proprioception from the face.
Trigeminal ganglion –> principle nucleus of trigminal complex –> medial lemniscus –> VPMN of thalamus –> primary somatosensory cortex
How are sensory input modulated in relay stations?
By lateral inhibition –> provides contrast
Where in the somatosensory cortex are touch and proprioception perceived?
3a and -b
Where are the signal send to from 3a and -b?
–> secondary somatosensory cortex –> amygdala and hippocampus
How does the use of sense of touch impact the sensory system (plasticity of the sensory system)?
Changes the size of the receptive field, and the extent of the cortical representation
What are the symptoms of lesions in area 5/7?
Sensory neglect
