6.1 Touch & Proprioception Flashcards
What is the kind of receptor used for touch (light touch, pressure, vibration) ?
mechanoreceptor
What kind of receptor is used for proprioception (joint position, muscle length, muscle tension)?
mechanoreceptor
What kind of receptor is used for temperature?
thermoreceptor
What kind of receptor is used for pain?
nociceptor
What are the characteristics of a slow adapting receptor?
Starts firing immediately at onset of stimulus → continuous firing as long as stimulus remains (frequency may decrease but still continuous)
What are the characteristics of a fast adapting receptor?
Does not fire continuously throughout (may only fire at the onset or the end of the stimulus or both at the beginning and the end)
What are the characteristics of a plexus?
Simple structures (plexus of axons with free nerve endings)
What are the characteristics of a peritrichial ending?
Nerve terminal wound around hair shaft → movement of hair causes appreciable amount of leverage → increases receptor sensitivity
Pacinian corpuscle: Nerve terminal surrounded by ______________ → allows good response to vibration (on top of pressure)
concentric circles of epithelial cells
Primary sensory neurones have cell bodies in the PNS in the __________ (along spinal cord if from the body) or _____________ (along brainstem if from the head):
• All the sensory neurones transmitting touch and proprioception are ____________ → with variable receptive fields but same coding of stimulus intensity
• Stimulus intensity is coded by the firing frequency in all the neurones → higher stimulus intensity is coded as higher firing frequency
dorsal root ganglion;
trigeminal ganglion;
fast-conducting;
What types of structures have Ia kind of fibres?
Muscle spindle primary afferent
What types of structures have Ib kind of fibres?
Golgi tendon organs
What types of structures have ‘a’ kind of fibres?
Efferents to extrafusal muscle
What types of structures have II/ Aβ kind of fibres?
other encapsulated endings and endings with accessory structures: Meisners corpulscles, Merkle endings, muscle spindle secondary endings
What types of structures have γ kind of fibres?
efferents to intrafusal muscles
What types of structures have III Aδ kind of fibres?
some nociceptors (sharp pain), cold receptors, most hair receptors
What types of structures have B kind of fibres?
preganglionic autonomic efferents
What types of structures have C kind of fibres?
most nociceptors (dull, aching pain), warm receptors, postganglionic autonomic efferents
Face, fingertips
- size: _______
- density: ___________
- localisation: ______________
small;
high;
higher resolution
[dorsal column/ medial leminiscus pathway: primary neurones]
- lumbar & sacral: Impulses from axon of primary sensory neurone (cell body in dorsal root ganglion) → dorsal horn → immediately enters dorsal columns (area of white matter) → move towards _____________ → form ________________
- cervical & thoracic: Impulses from axon of primary sensory neurone (cell body in dorsal root ganglion) → dorsal horn → enters dorsal columns (stay __________ placed) → form ______________
- face: Impulses from axon of trigeminal nerve (cell body in trigeminal ganglion) → _________ → _____________ (synapse with secondary neurone)
midline (more medially);
gracile fasciculus;
laterally;
cuneate fasciculus;
pons (mid-pons)
trigeminal nucleus
[dorsal column/ medial leminiscus pathway: secondary neurones]
- Medulla: Gracile fasciculus and cuneate fasciculus pass up to the level of the medulla → synapse with secondary sensory neurones (gracile and cuneate nuclei) → decussates → turn upwards to form ________ → ___________
- Pons: Secondary neurones (from face) decussate → axons join onto the ____________ end of the medial lemniscus → pass upwards to ____________
medial lemniscus;
thalamus;
medial;
thalamus
[dorsal column/ medial leminiscus pathway: tertiary neurones]
- Brain (from body): Secondary neurones synapse in the thalamic _________________ nucleus (relays somatosensory information from the body) → __________ (white matter) → appropriate part of cortex depending on part of body (according to homunculus)
- Brain (from face): Secondary neurones synapse in the thalamic ____________ nucleus (relays somatosensory information from the face) → somatosensory cortex (more lateral area for the face)
ventroposterolateral (VPL) ;
internal capsule;
ventroposteromedial (VPM)
Where does the sensory information from the body in the dorsal column decussate at?
decussates in the medulla
Where does the sensory information from the face in the dorsal column decussate at?
decussates in the pons
how is the information in the dorsal columns organised (from median to lateral)?
axons from sacral, lumbar, thoracic, cervical
how is the information in the medial lemniscus organised (from median to lateral)?
face, upper limb, lower limb
Intensity of information carried varies depending on the stimulus intensity (firing frequency of various axons):
• As axons synapse with the relay nuclei (gracile and cuneate nuclei), axons with _______________ tend to inhibit axons around them via collateral inhibitory synapses
• Intensifies the process of distinction between the intensity of various inputs → improves resolution of localisation
highest firing frequency
What is the function of the Primary Somatosensory cortex (S1)?
Receives information from dorsal column/medial lemniscus pathway:
• Cells respond according to stimulus properties (e.g. type – touch/vibration, intensity, abstract properties – shape/movement)
• Projects to S2 and posterior parietal cortex
What is the function of the secondary somatosensory cortex (S2)?
Amalgamation of information coming into both hemispheres (strong connections in corpus callosum in S2 areas between hemispheres)
What is the function of the Posterior parietal cortex?
Construction of internal map of body and the body within its extrapersonal space (receives input from S1 area and other modalities like visual inputs)
