Peter's Physiology 4 - Somatosensory Innervation 2 Flashcards
Which pathway senses discriminatory touch, pressure, vibration and conscious proprioception?
Dorsal column medial leminscal pathway
How many orders of neurones are involved in the dorsal column medial leminscal pathway?
3
Where does the first synapse of the dorsal column medial leminscal pathway occur?
In the dorsal column nuclei (gracile nucleus and cuneate nucleus) of the brainstem (some synapse deep in the dorsal horn upon entering the brainstem)
Where does the decussation of the dorsal column medial leminscal pathway occur?
At the great sensory decussation in the brainstem (after the synapse) -> information as far as the dorsal column nuclei are ipsilateral
Where does the 2nd synapse of the dorsal column medial lemniscal pathway occur?
At the ventral psoteriolateral (VPL) nucleus of the thalamus
What type of primary sensory afferent nerves carry the initial sensory information in the dorsal column medial leminscal pathway?
A alpha or A beta fibres
What pathway senses pain, thermosensation, crude touch, itch and tickle?
Spinothalamic tract
How many orders of nerves are involved in the spinothalamic tract?
3
What type of primary afferent nerves carry the initial sensory information in the spinothalamic tract?
A delta or C fibres
Where is the first synapse in the spinothalamic tract?
In the spinal cord at the level of entry
where does decussation occur in the spinothalamic tract?
In the spinal cord (at all levels of the cord - close to point of entry via Lissaeur’s tract)
Where is the second synapse in the spinothalamic tract?
Thalamus (VP nucleus)
What 2 tracts make up the dorsal columns?
Medial fasiculus gracillis (gracile tract)
Lateral fasciculus cunaetus (cuneate tract)
What anatomical sensory area inputs travel in the fasciculus gracillis?
Sensory input to T6 and below (including legs and lower trunk)
What anatomical sensory area inputs travel in the fasiculus cuneatus?
Input above T6 (including arms and upper trunk)
How do second order neurones of the dorsal column medial lemniscal pathway ascend to the VPL nucleus of the thalamus from their decussation?
In the medial lemniscus
How do 3rd order neurones of the dorsal column medial lemniscal pathway project to the primary somatosensory cortex?
Via the posterior internal capsule
What system conveys equivalent information as the dorsal column medial lemniscal pathway from the anterior head?
Trigeminal system
What is stereognosis?
Ability to recognise an object by feeling it
What is another name for conscious proprioception?
Kinaesthesia
What frequency of tuning fork is used to identify vibration?
128Hz tuning fork
What is the name for the amplification in the differences in activity of adjacent neurones as information is conveyed from one neurone to the next in a sensory pathway?
Contrast enhancement
What is the name for the ability of an excited neurone to reduce the activity of its neighbours?
Lateral inhibition
In contrast enhancement, what causes the increased gain and lateral inhibition?
Interneurones
What pathways carry the general somatic information from the anterior head?
Trigeminothalamic pathways (X2) aka trigeminal system
What are the 3 divisions of the trigeminal nerves?
V1 = ophthalmic V2 = maxillary V3 = mandibular
Where are the soma of sensory neurones of the trigeminal system located?
in the trigeminal sensory ganglion
Where do central terminals of the trigeminal nerve synapse upon second order neurones?
In the chief sensory nucleus (general tactile stimuli) or spinal nucleus (pain, temperature information) of the pons -> decussate after this
Where does the 2nd synapse of the trigeminothalamic pathways occur?
Ventropsoteriomedial (VPM) nucleus of the thalamus
How do 3rd order neurones of the trigeminal system relay information to the cortex?
Via thalamocortical neurones
Where is the somatosensory cortex located?
Post central gyrus of the parietal cortex
What are brodmann areas?
Ways to divide the cerebral cortex into different areas based on their different cellular components and specific neurological functions
What broaden areas does the somatosensory cortex consist of?
BA 1, 2, 3a and 3b
What is the input to brodmann area 3a?
Proprioceptors
What is the input to brodmann area 3b?
Cutaneous (SA e.g. merkel cells and RA receptors e.g. meissner’s corpuscles)
BA 3a
What is the input to brodmann area 1?
Cutaneous (RA mechanoreceptors)
BA 3b
What is the input to brodmann area 2?
Joint afferents Golgi tendon organs Deep tissues BA 3a BA 3b
What modality is Brodmann area 3b sensitive to?
Touch (texture, shape, stimulus size)
What modality is Brodmann area 1 sensitive to?
Texture discrimination
What modality is Brodmann area 2 sensitive to?
Object perception (size, shape of object - steroegnosis)
What is the name for impaired grasping and size and shape discrimination?
Astereognosis
How many cell layers does the somatosensory cortex have?
6
Which cell layer do thalamic inputs to the somatosensory cortex mainly terminate on?
Layer IV (which in turn projects to cells towards the surface of the cortex and also deeper layers)
Multiple somatotopic maps of the somatosensory cortex exist.
What do adjacent strips of the cortex always map?
The same parts of the body in parallel to each other
What happens if to the somatosensory cortex if a finger (for example) is lost in an accident?
The area representing the finger is utilised by another sensory input
What symptom can be described by the fact somatotopic maps are plastic?
Phantom limb sensations in amputees
What does the posterior parietal cortex do?
Receives and integrates information from somatosensory cortex and other cortical areas (visual, auditory) and sub-cortical areas (thalamus) - important for deciphering the deeper meaning of the information in the primary somatosensory cortex)
What area is usually damage in neglect syndrome where someone bellicose the left side of the world does not exist?
Right parietal cortex
