Flashcards in 3.1+2 Somatosensory Deck (53):
What is the butterfly shaped structure in the spinal cord?
What are the two major pathways involved in somatic sensory perception?
Dorsal columnar-medial lemniscal pathway
What are the two fasciculi in the dorsal column?
What is a sensory modality?
Distinct mode of sensation
e.g. touch vs pain
Is stickiness a modality?
No, it is a mixture of modality
Pressure, stretch, pain etc
Which modalities run through the dorsal column system?
Which modalities run through the spinothalamic tract?
Where is the cell body of a primary sensory neurone located?
Dorsal root ganglion
What is a spinal nerve?
Both sensory and motor fibres
Formed by dorsal and ventral root coming together
What supplies a single myotome and dermatome?
What are the two different types of sensory neurone units?
What is the feature of rapidly adapting sensory neurones?
Good at detecting changes in activation of the receptor
Give an example of a rapidly adapting sensory neurone in action
Detect pressure when you sit
Adapt rapidly and slow down in firing
You soon dont feel chair
What is the feature of slowly adapting sensory neurones and give an example of when they might be useful?
Wont really change in its firing
Pain receptors, dont want them to stop until stimulus is removed
What is meant if a neurone has a 'low acuity'?
Area sensed by the sensory neurone is large
What is the relationship between acuity and the size of a receptive field?
Why are there fuzzy boundaries to dermatomes?
Because receptive fields can overlap
What is the receptive field?
The region of the skin detected by ONE sensory neurone
What do the 'laws' of primary sensory neurones of somatosensory pathways dictate?
Cell body in DRG
Receives information from receptor
Within CNS - neurone remains IPSILATERAL to cell body
What do the 'laws' of secondary sensory neurones of somatosensory pathways dictate?
Second order neurone DECUSSATES to the CONTRALATERAL side
Cell body in dorsal horn of medulla
What do the 'laws' of tertiary sensory neurones of somatosensory pathways dictate?
Projects to primary sensory cortex
Cell body in Thalamus
Where is the primary sensory Cortex located in the brain?
Post central gyrus
From a dermatomal pattern, to what do the sensory fibres reorganise in the cortex?
How does the Dorsal Column pathway map to the tract in the spinal cord?
MEDIAL PORTION of tract
How does the spinothalamic tract map to the tract in the spinal cord?
LATERAL/SUPERFICIAL part of tract
How do sensory neurones add to the DCML pathway?
Add onto the OUTSIDE
How do sensory neurones add to the Spinothalamic tract?
Add to the INSIDE
How is the upper half of the body represented in the DCML pathway?
On the OUTSIDE
How is the upper half of the body represented in the ST?
On the INSIDE
What does the medial lemniscus connect?
Gracile and Cuneate nuclei
In which nucleus do first order somatosensory neurones of the lower body synapse?
In which nucleus do first order somatosensory neurones of the upper body synapse?
Where are the gracile and cuneate nuclei found?
Where do first order DCML neurones synapse?
In the medulla
Where do second order DCML fibres synapse?
In the thalamus
Where is the lower body represented on the homunculus?
Where is the upper body represented on the homunculus?
Is there crossing over of third order DCML fibres?
What is another name for the spinothalamic tract?
Which side do ISOLATED DCML lesions affected?
Below the lesion
Which side do isolated spinothalamic tract lesions affect?
Below the lesion
How do spinothalamic sensory neurones decussate?
Enters dorsal horn of grey matter and synapses
Decussates via the ventral white commissure fibres and ascend in the ST
What are commissure fibres?
Fibres which connect the two halves of the CNS
Which order of somatosensory neurone always performs the decussation?
Where do the second order neurones of the spinothalamic tract synapse?
Where the ascending somatosensory pathways located, white or grey matter?
All pathways in white?
What has been damaged in Brown-Sequard Syndrome?
Complete cord hemisection
Destruction of single cord segment
What are the signs experienced in Brown-Sequard Syndrome?
COMPLETE anaesthesia affecting the corresponding dermatome
Ispsilatereal loss of DCML modalities BELOW lesion
Contralateral loss of ST modalities BELOW lesion
Through which somatosensory system does pain run through?
What is the major primary afferent fibre for pain?
What do A fibres do?
Carry impulses from mechanoreceptors in the skin
How does rubbing a painful area, relieve the pain?
Mechanoreceptors detect rubbing
Activates inhibitory neurones
Inhibits second order neurones