Session 3 - Somatosensory System Flashcards
What are the two divisions of general sensation?
Somatic (conscious)
Visceral (unconscious)
Name the ascending tracts of the spinal cord.
Dorsal column Spinothalamic tract Spinorecticular tract Dorsal spinocerebellar tract Ventral spinocerebellar tract
Name the two fasciculi of the dorsal column.
Fasciculus gracilis
Fasciculus cuneatus
Name all the modalities.
Temperature Pain Pressure/crude touch Vibration Proprioception Fine touch/discriminative touch Two point discrimination
Which modalities are conducted through the spinothalamic system?
Temperature
Pain
Pressure/crude touch
Which modalities are conducted through the dorsal column system?
Vibration
Proprioception
Fine touch/discriminative touch
Two point discrimination
What are rapidly adapting receptors?
Receptors that initially create a high frequency train of action potentials when there is high receptor activation, but which then decrease the action potential firing over time.
What are slowly adapting receptors?
Receptors which don’t reduce their action potential frequency when subjected to high receptor activation, or which do so very slowly.
Give an example of a type of slowly adapting receptor.
Nociceptor (pain receptor)
What is a receptive field?
An area of skin supplied by a sensory neurone.
What is meant by low acuity with regards to sensory innervation of skin?
If the region of skin supplied by a single sensory neurone is very large, it is said to have low acuity.
What creates the poorly defined boundaries of dermatomes?
Overlap of receptive fields
Where is the cell body of a primary sensory neurone found?
In the dorsal root ganglia
Where is the cell body of a secondary sensory neurone found?
In the dorsal horn of the spinal cord or the medulla
Where is the cell body of a tertiary sensory neurone found?
In the thalamus
Where does the axon of a primary sensory neurone run in relation to its cell body?
Axon runs ipsilateral to the cell body
Which type of sensory neurone decussates?
Secondary sensory neurone
Which type of sensory neurone projects into the primary sensory cortex?
Tertiary sensory neurone
In the dorsal column pathway, the lower body maps on to which portion of the tract?
The medial portion of the tract.
In the spinothalamic pathway, the lower body maps on to which portion of the tract?
Lateral/superficial parts of the tract
In the dorsal column pathway, primary sensory neurones coming from the upper body synapse in which nucleus?
Cuneate nucleus
In the dorsal column pathway, primary sensory neurones coming from the lower body synapse in which nucleus?
Gracile nucleus
In the dorsal column pathway, where are the cell bodies of secondary sensory neurones found?
Medulla
In the spinothalamic pathway, where are the cell bodies of secondary sensory neurones found?
Dorsal horn
Isolated lesions of the dorsal column pathway lead to what signs?
Ipsilateral loss of dorsal column modalities below the lesion.
Isolated lesions of the spinothalamic pathway lead to what signs?
Contralateral loss of spinothalamic modalities below the lesion.
Describe the pattern of sensory loss seen in Brown-Sequard syndrome.
Ipsilateral complete segmental anaesthesia of a single dermatome.
Ipsilateral loss of dorsal column modalities below the lesion.
Contralateral loss of spinothalamic modalities below the lesion.
What is the role of A fibres?
Carry impulses from mechanoreceptors in the skin.
What is the role of C fibres?
Carry pain from nociceptors.
How does rubbing a painful area alleviate pain?
Rubbing an area activates mechanoreceptors, which activates A frisbees. The A fibres then excite inhibitory enkephalinergic interneurones in the cord. This inhibits the transmission of pain sensation.
