Somatic Sensation Flashcards
Which modalities are associated with the Spinothalamic pathway?
Temperature,
Pain,
Pressure/crude touch.
Which modalities are associated with the Dorsal column?
Fine touch,
Proprioception,
2 point discrimination,
Vibration.
Give an example of a rapidly adapting receptors.
Mechanoreceptor in skin,
Baroreceptors in skin.
Give an example of a slowly adapting receptor.
Nociceptors in skin (pain receptors).
Where do second order sensory neurones synapse to their third order counterparts?
Thalamus (3 order are thalamocortical neurones)
What is Somatotopy?
What is its advantage?
Point for point correspondence of an area of the body to a specific point within the central nervous system.
The parallel topographical layout saves resources as it provides a quick route to each part of the body.
What is the relationship between acuity and receptive field?
Acuity is inversely proportional to the size of a receptive field
What is the area where second order neurones in the dorsal column cross called?
Medial leminiscus.
What is the purpose of Lissauers tract?
Enables the first order neurones of the spinothalamic system to ascend 2-3 spinal segments before synapse goes onto their second order neurone, as such avoiding possible hemisections and nerve lesions.
Why might central lesions in the spinothalamic pathway result in bilateral signs?
May compress decussating fibres on both sides as they cross over.
How might a central nerve lesion result in Dissociation (sensory damage in both upper body and lower body modalities)?
Grow to compress the spinothalamic system located centrally and the Dorsal column system dorsally. As these are arranged in opposite directions, different parts of the body are affected in each.
How does rubbing an injury help alleviate pain?
Stimulates ABeta neurones that stimulate inhibitory interneurones to prevent the spread of pain signal to the second order neurone.
How might hypnosis be able to modulate pain?
Which areas of the brain are involved?
Stimulation of cortical neurones that excite the periacqueductal grey area of the brain. This then stimulates the nucleus raphe mag is found in the medulla, which in turn stimulates the inhibitory interneurones.
What would strong receptor activation lead to in terms of action potential?
Hih frequency action potentials.
Name an area of the body with high sensory acuity.
What about low sensory acuity?
Skin of the fingertips.
Skin of the back.
Why do dermatomes have ‘fuzzy’ boundaries?
Overlap of sensory receptive fields that supply them. Particularly noticeable over the trunk of the body.
The gracile fasciculus facilitates ascension of which nerve roots?
T7 and below of the dorsal column system.
In the dorsal column system, T6 and above first order neurones ascend in which structure?
Cuneate fasciculus
Where do the second order neurones of the spinothalamic system decussate?
In the ventral white commisure of the cord (at the level of the entry of first order neurones)
In the spinothalamic tract, where do axons from the lower part of the body run?
Most laterally/superficially. As you ascend, fobres are added medially.
In the dorsal column, where do the axons from the lower body run?
Most medially. As you ascend, axons are added laterally.
Brown-Sequard syndrome (complete hemisection) leads to what sensory distrubances?
Ipsilateral complete segment anaesthesia of the affected dermatome,
Ipsilateral loss of dorsal column modalities below the hemisection,
Contralateral loss of spinothalamic modalities below the hemisection (note 1 or 2 levels may ascend in Lissauers tract and remain intact)
Which descending input centres of the brain can activate encephalinergic neurones that regulate pain?
Periacqueductal grey,
Nucleus raphe magnus.
