Somatic sensation and ascending pathways Flashcards
What is a sensory modality? Give general somatic sensory examples
How a stimulus is perceived temperature pain pressure/crude touch vibration fine touch proprioception 2 point discrimination
What determines the sensory modality
The type of receptor
What modality is wetness?
It is a combination of modalities (e.g. temp and fine touch)
Briefly describe the route of a primary sensory neurone
Cell body is found in the dorsal route ganglion
Crosses from PNS to CNS
Briefly describe the route of a secondary sensory neurone
Cell body is found in the spinal cord (sometimes brainstem) Crosses midline (decussates)
Briefly describe the route of a tertiary sensory neurone
Cell body is found in the thalamus
Projects to the primary sensory cortex
Briefly describe the types of primary neurones
Rapidly adapting- signal degenerates over time
e.g. mechanoreceptors in the skin
Slow adapting- signal frequency doesn’t decay
e.g. nociceptors (pain transmission)
What is a receptive field
The area of skin that a sensory neurone collects information from
What is the relationship between acuity and the receptive field?
Inversely proportional
Smaller receptive field= greater acuity
What is the clinical significance of receptive fields overlapping?
Determine dermatomal sensation in the middle of the dermatome, where it is less likely there will be any overlap
Briefly describe two benefits of the orderly and parallel way in which the corresponding CNS is organised
Requires minimum amount of ‘building material’ e.g. axons, myelin, neurones
Converts information from dermatomes into the homunculus
What system is the modality of pain relayed to the cortex by?
Spinothalamic (anterolateral) system
What system is the modality of crude touch relayed to the cortex by?
Spinothalamic (anterolateral) system
What system is the modality of temperature relayed to the cortex by?
Spinothalamic (anterolateral) system
What system is the modality of fine touch relayed to the cortex by?
Dorsal column system
What system is the modality of 2 point discrimination relayed to the cortex by?
Dorsal column system
What system is the modality of vibration relayed to the cortex by?
Dorsal column system
Briefly describe the medial lemniscus
Connects the gracile and cuneate nucleus with the thalamus
What is the cervical nucleus in the dorsal column called?
Cuneate nucleus
What is the lumbar nucleus in the dorsal column called?
Gracile nucleus
How are neurones added on as they travel up the dorsal column? How is this drawn topographically?
Neurones are added laterally
Lumbar is most medial, and cervical is most lateral
(Check cross sectional diagram with notes)
How are neurones added on as they travel up the spinothalamic tract? How is this drawn topographically?
Neurones are added medially
Lumbar is the most lateral, and cervical is the most medial
(Check cross sectional diagram with notes)
Briefly describe where the primary and secondary sensory neurones synapse in the spinothalamic system
In the spinal cord, near the same level the primary neurone entered the spinal cord
What is the spinothalamic tract?
The tract connecting the spinal cord to the thalamus
Briefly describe why you rub an area of pain
Stimulates mechanoreceptors
Stimulates A-Beta fibres
Stimulates inter neurone
Inhibits secondary sensory neurones
Briefly describe what happens during hypnosis to reduce pain
Stimulates excitatory cortical neurone
Acts on periaqueductal grey in midbrain
This then synapses at the nucleus raphe magnus
This then stimulates inhibitory interneurones
Briefly describe how proprioception works
Muscle spindles report muscle length
There are also receptors in joints
Briefly describe lissauer’s tract
It allows first order sensory neurones of the spinothalamic tract to ascend or descend before decussating
