Lecture 5- Ascending pathways Flashcards
The dorsal column-medial lemniscus system
System the CNS uses to carry info to the brain concerned with
- Fine touch
- 2 point discrimination
- Vibration
(not as important for survival as the spinothalamic system)
outline the detecting of vibration in a lumbar dermatome using the dorsal column (medial leminiscus system)
e.g. detecting vibration in a lumbar dermatome
- Receptor in lumbar dermatome communicates with first order sensory neurone (cell body in dorsal root ganglion) and projects into the spinal cord
- First order neurone ascends up the SC via the dorsal column to the medulla of the spinal cord, where it synapses onto a second order neurone
- Second order neurone decussates (cross the midline) and ascends all the way up to the thalamus and synapses onto third order neurone
- Medial lemniscus- pathway connecting the gracile and cuneate nuclei with the thalamus
- Third order neurone projects to the sensory cortex
- Lumbar region of the somatosensory cortex found medially
nuclei of the dorsal column where the first order nuclei synapse
- Nucleus in the medulla where first order neurones from the lower half of the body synapse is called the gracile nucleus
- Nucleus in the medulla where the first order neurone from the upper half of the body synapse is called the cuneate nucleus
In the dorsal column system the higher up the first order neurone (e.g. cervical region) the more …………. the axons will be found
- Clinical relevance- if there is a spinal cord lesion, as it grows it will affect the lumbar region first and then later the cervical region
In the dorsal column system the higher up the first order neurone (e.g. cervical region) the more laterally the axons will be found
- Clinical relevance- if there is a spinal cord lesion, as it grows it will affect the lumbar region first and then later the cervical region
the spinothalamic (anterolateral) system
Ancient system- crucial for the survival of the organism
- temperature
- pain
- pressure/crude touch
outline how pain is detected in the lumbar region
e.g. detecting pain in the lumbar region
- Receptor in lumbar dermatome connects to first order neurone
- Synapses with second order neurone at approx. the level it enters (dorsal horn)
- Second order neurone decussates (crosses midline) and ascends up the cord (spinothalamic tract) into the brainstem and into the thalamus
- In the thalamus the second order neurone synapses with third order neurone which projects to the medial part of the primary sensory cortex (lower body)
outline how pain is detected in the cervical region
e.g. detecting pain in the cervical region
- Receptor in cervical dermatome connects to first order neurone
- Synapses with second order neurone at approx. the level it enters (DH)
- Second order neurone decussates (crosses midline) and ascends up the cord (spinothalamic tract) into the brainstem and into the thalamus
- In the thalamus the second order neurone synapses with third order neurone which projects to the lateral part of the primary sensory cortex (upper body)
Spinothalamic tract projecting info from the upper and lower body (opposite to dorsal columns)
- The second order neurones from the lower half of the body are found in the lateral region of the spinothalamic tract
- The second order neurones from the upper half of the body are found in the medial region of the spinothalamic tract
- Clinical relevance: expanding lesion in spinal cord will first destroy decussating fibres of the second order neurones (would be bilateral), then the lumbar part of dorsal columns will be affected- lower body and then the cervical regions of the spinothalamic tract- upper body
dorsal colum- medial leminscal pathway vs spinothalamic tract system
pain transmission through the
spinothalamic tract
outline pain transmission
- Nociceptive (Sensory C-fibres- slow adapting) first order neurone projects into spinal cord and synapses upon second order neurone in the dorsal horn of the grey matter
- Second order neurone decussates (crosses) at around the level the first order neurone enters the CNS
- Ascends up the spinothalamic tract and synapses with third order neurone in the thalamus
- Third order neurone synapses into somatosensory cortex
which fibres are nociceptive
C fibres- slow adapting (meaning you keep feeling the pain as long as the stimuli is present)
Regulation of pain transmission- need to thin about 2 phenomenon
- Why does rubbing a painful area of a body relieve some of the pain
- How can people deal with extreme pain? e.g. hypnosis and extreme trauma can reduce pain experienced
Why does rubbing a painful area of a body relieve some of the pain e.g.
- You stub your toe
- Pain is detected by C-fibres (nociceptive first order neurones) and carried up via the spinothalamic tract up to the somatosensory cortex of the brain- PAINNNNNNNN
- You start rubbing the sore toe
- Mechanoreceptors detect rubbing movement – ABeta (AB) neurones project into the dorsal horn and synapse mainly with interneuron instead of secondary neurones
- When an interneuron is stimulated it can start inhibiting second order neurones which are sending pain signals up to the somatosensory cortex
which fibres are responsible for transduction of mechanoreceptros
How can people deal with extreme pain? e.g. hypnosis and extreme trauma can reduce pain experienced
Due to descending modulation which inhibits pain pathway
- Hypnosis activates cortical neurones which project down to the midbrain
- These excitatory neurones stimulate neurones in the periaqueductal grey (PAG)
- These activated PAG neurones can project down into the medulla where they are able to stimulate neurones in the nucleus raphe magnus (large nucleus near the midline- part of reticular formation)
- NRM neurones descend down the cord where they have an inhibitory effect on the second order sensory neurone by stimulation the inhibitory interneurons
label
Browns-sequard syndrome
