5) Somatosensory Flashcards
What are the different types of Modalities ?
Spinothalamic:
> Pain
> Temperature
> Crude Touch
Dorsal Column Medial Lemniscus System: > Vibration > Proprioception > Fine Touch > 2 Point Discrimination
Describe the different types of Neurones
Primary: > Communicate with Receptor > Cell Bodies in DRG > Central Axon projects Ipsilateral to the cell body > Project onto Secondary
Secondary:
> Cell bodies located in the spinal cord or medulla
> Decussate
> Relay Information up the spinal cord
Tertiary:
> Cell bodies located in the Thalamus
> Project information to the primary sensory cortex
What two adapting states can receptors have ?
Rapidly Adapting Receptors
> Receptors emit a high frequency of APs initially but then the rate slows down
> For example, Mechano Receptors allow you to initially aware of a stimulus but eventually you become less aware e.g. Sitting Down and Clothes
Slowly Adapting Receptors
> Frequency of APs doesn’t change
> For Example Pain
Define Receptive Fields
The region of skin supplied by a single primary sensory neurone
How the does the size of Receptive Fields affect Acuity
A Large Receptive Field means a low Sensory Acuity
> Therefore will have poor 2 point discrimination
> For example the Back
A Small Receptive Field means a high Sensory Acuity
> Good 2 Point Discrimination
> For example Skin of fingertip
Describe the pathway of the Spinothalamic Pathway in Lower Regions / Upper Regiions
First order neurones:
> Enter the spinal cord ipsilateral and synapses in the Dorsal Horn
> Projects on to Secondary neurones
Secondary Neurones
> Decussate at the Ventral White Commisure - Forming the Spinothalamic Tract
> Ascends the spinal cord and synapses at the Thalamus
Tertiary Neurones
> Projected onto the Medial Cortex (Lower Regions)
> Projected onto the Lateral Cortex (Upper Regions)
Higher Fibres are added medially
Describe the pathway for the Dorsal Column Tract for the Lower Regions
Primary Neurones
> T7 - Below
> Enter the spinal cord Ipsilateral
> Ascends the spinal cord via the Gracile Fasciculus (Medially)
> Synapse at Gracile Nucleus in the Medulla
Secondary:
> Ascend to the Thalamus known as the Medial Lemniscus Pathway
> Decussates
> Synapses at the Thalamus
Tertiary:
> Projects Medially
Describe the pathway for the Dorsal Column Tract for the Upper Regions
Primary: > T6 and Above > Enter the spinal cord Ipislateral > Ascends the spinal cord Laterally > Synapses with secondary neurone at the Cuneate Nucleus in the medulla via Cuneate Fasciculus
Secondary:
> Decussates
> Synapses at Thalamus
Tertiary:
> Projects onto Lateral Cortex
Describe the presenting case of someone with Brown Sequard Syndrome.
Complete Cord Hemisection of a single cord segment
1) Anaesthesia of Single Dermatome
2) Ipsilateral loss of DC Modalities from segment and below - Decussation has yet to occur
3) Contralateral loss of Spinothalamic Modalities from segment below - Decussationg occurs at the level
IF a lesion affected Central Grey Matter what can be expected ?
Bilateral Loss of Modalities
IF a lesion affected the Dorsal Roots what can be expected ?
All Modalities Lost as Primary neurones are all found in DRG
Ipsilateral
IF a central bilateral lesion is increasing what can be expected ?
Gradual loss of Lower tracts in the spinothalamic tract
Outline the Control of Pain ?
How can it be Alleviated?
> Part of the Spinothalamc System
Primary Neurones are known as C fibres Involved in the sensation of pain
Rubbing site of pain activated Mechanoreceptors which excite inhibitory Enkephalinergic Interneurones which inhibit pain via A fibres
Apart from the activation of mechanoreceptors, how else can Enkephalinergic interneurones be activated ?
> Descending projections from higher centres such as the Periaqueductal Grey Matter or Nucleus Raphe Magnus
Opiates
