4 Somatic Sensation and Ascending Pathways Flashcards
What types of general sensation are there?
There are 7 different modalities of the somatic sensory system. Identify all of them and identify which are part of the spinothalamic (anterolateral) system and which are part of the dorsal column system.
(Modality= ‘unit of sensation’ relying on distinct receptor types)
Give an example of a rapidly adapting receptor.
Cutaneous mechanoreceptor
(eg when sitting down, wearing clothes, placing hand in cold then room temperature water and it will feel warmer)
How do rapidly adapting receptors work compared to slowly adapting receptors?
Rapidly adapting receptors: Reduce frequency of action potentials over time even though stimulus still there
Slowly adapting receptors: frequency stays the same with stimulus over time
What is a receptive field?
A receptive field is a portion of sensory space that can elicit neuronal responses when stimulated
How does acuity relate to the size of the receptor fields and the number of sensory neurones?
Where is the autonomous region of a dermatome? Why do we aim for this when testing dermatomes?
Autonomous region= in centre of dermatome
Boundaries between dermatomes can be blurry due to overlap of receptive fields
For the majority of sensory systems, there are 3 neurones (1°, 2° and 3°) between the receptor and the sensory cortex (usually). Where can the cell body for the 1° receptor be found and where does it project on the 2° neurone?
For the majority of sensory systems, there are 3 neurones (1°, 2° and 3°) between the receptor and the sensory cortex (usually). Where can the cell body for the 2° receptor be found, where does the neurone decussate and where does it project on the 3° neurone?
2° neurone always decussates
For the majority of sensory systems, there are 3 neurones (1°, 2° and 3°) between the receptor and the sensory cortex (usually). Where can the cell body for the 3° receptor be found and where does it project on the primary sensory cortex?
At what levels does the cuneate faciculus run and at what levels does the gracile faciculus run? (dorsal column)
Cuneate= above T6
Gracile= below T6
Fill in the missing labels showing the path taken by neurones in the dorsal tract:
Fill in the missing labels:
Where do neurones from higher spinal levels (eg C5 over L3) run relative to lower spinal levels within the dorsal column?
C5 will run lateral to L3 in the dorsal column
Will isolated lesions of the dorsal column pathway in the cord lead to ipsilateral signs below the lesion or contralateral signs below the lesion?
Will isolated lesions of the spinothalamic tract in the cord lead to ipsilateral signs below the lesion or contralateral signs below the lesion?
- Spinothalamic tract- will be contralateral signs
- Dorsal column tract- will be ipsilateral signs
(2° neurone in spinothalamic tract decussates at level of entry, 2**° neurone in dorsal column decussates in medulla)
Where does the 2° neurone decussate in the spinothalamic pathway? Through what structure does it decussate?
At level of entry (into spinal cord)
Decussates in ventral white commisure (white matter)
What are the special senses (special sensation)? (5)
- Taste
- Vision
- Hearing
- Balance
- Smell
Brown-Sequard syndrome can be caused by a complete cord hemisection on one lateral half of a cord segment from trauma or ischaemia. What signs will be seen (in terms of sensory features)?
Eg is patient has lost all sensory modalities in left T3 dermatome and loss of pain and temperature sensation from T4 down on right and loss of vibration and light touch from T4 down then lesion is in left T3 cord segment.
What does nociceptive mean?
=relating to the perception or sensation of pain.
“as the extremity warms, heat sensitive nociceptive afferents are stimulated”
Why is it that rubbing a sore area can relieve pain?
What types of fibres are contained within the cerebral peduncle?
Motor fibres only
Equilibrium (balance) relies on having at least 2 out of 3 inputs to the brain. What are these 3 inputs?
- Vision
- Proprioception
- Input from vestibular system
