Ascending tracts and sensation Flashcards
What does Meissner corpuscle detect?
Discriminative touch (rapidly adapting)
What does Pacinian corpuscle detect?
Deep pressure & vibration; Mechanoreceptors (distortion). (Rapidly adapting)
What do Ruffini endings detect?
Touch; Sheer stress/forces (slowly adapting)
What do Merkel discs detect?
Light, sustained touch (slowly adapting)
What do free nerve endings detect?
Pain (slowly adapting) & temperature (rapidly adapting)
What do muscle spindles detect?
Muscle stretch receptor
What does the primary somatosensory cortex do?
Receives contralateral sensory input from the body (including taste)
What does the superior parietal lobe do?
Integration of sensory inputs, sensory memory, perception of contralateral self/world
What do association fibres do?
Allow one area of cortex to communicate with another area of cortex on the same side of hemisphere
What do commissural fibres do?
Allow communication between different hemispheres eg. corpus callosum
What do projection fibres do?
Allow communication between brainstem and spinal cord
In Dorsal column, where do 1st order neurons travel to?
Nuclei in the lower medulla
In dorsal column, where do 2nd order neurons travel from and to?
From nuclei in lower medulla to thalamus
What tract do 2nd order neurons ascend via?
A lemniscus
Where do 3rd order neurons travel from and to?
From thalamus to primary sensory cortex
What tract do 3rd order neurons ascend via?
Internal capsule
Where does decussation occur?
In second order neurons
What input does ventral posterior medial nucleus (VPM) receive?
Sensory input from face CN V
What input does ventral posterior lateral nucleus (VPL) receive?
Sensory input from body
What type of sensation does dorsal column pathway carry?
Discriminative touch & vibration; conscious proprioception
What type of sensation does spinothalamic tract carry?
Pain & temperature; simple touch
What type of sensation does spinocerebellar tract carry?
Unconscious proprioception
What are the two fasciculi found in dorsal column pathway?
Fasciculus gracilis and fasciculus cuneatus
What sensation and from where does fasciculus gracilis carry?
Discriminative touch & vibration; conscious proprioception from legs (below T6)
What sensation and from where does fasciculus cuneatus carry?
Discriminative touch & vibration; conscious proprioception from arms (above T6)
What are second order neurons of the dorsal column pathway from the body collectively called?
Medial lemniscus
What does the fasciculus gracilis synapse onto?
Nucleus gracilis in the lower medulla
What does the fasciculus cuneatus synapse onto?
Nucleus cuneatus in the lower medulla
What are second order neurons of the dorsal column pathway from the face collectively called?
Trigeminal lemniscus
What are the first order neurons in the dorsal column face pathway and where do they synapse?
Trigeminal sensory nerves enter pons and synapse in CN V nucleus
Where do second order neurons of the dorsal column face pathway ascend to?
Ventral posterior medial nucleus (VPM) of the thalamus
If the dorsal column in spinal cord is damaged? What will be lost and will it be ipsilateral or contralateral?
Loss of discriminative touch, vibration and conscious proprioception BELOW the level of the lesion. Ipsilateral.
How is the decussation of 2nd order neurons different between the dorsal column pathway and the spinothalamic tract?
In dorsal column pathway, 2nd order neurons decussate in the medulla. In STT, 2nd order neurons decussate across the anterior white commissure, 1-2 levels above it’s 1st order neuron entry into the spinal cord.
Along which tract do 1st order neurons travel along in the spinothalamic tract?
Tract of Lissauer
What does the trigeminal lemniscus do?
Carries pain, temperature & simple touch (in STT) and discriminative touch, vibration & conscious proprioception (in dorsal column pathway) to the VPM nucleus of the thalamus
In the brainstem, the Anterior (ASTT) and Lateral (LSTT) spinothalamic tracts merge & are collectively knowns as?
Spinal lemniscus
What is syringomyelia and what does it damage?
Cavitation/expansion of central canal in cervical region. Damages only decussating neurons of the STT but not the spinothalamic tract itself
Pain, temp and simple touch lost in shaded areas
What tracts can the spinocerebellar tract be divided into?
Dorsal (Muscle spindles) and Ventral (Golgi tendon reflexes) Tracts
What sensation is carried in dorsal spinocerebellar tract (DSCT)?
Muscle spindles - monitors muscle length, speed of contraction and tension
Where does decussation happen in dorsal spinocerebellar tract (DSCT)?
No decussation. Uncrossed, ipsilateral 2-neuron pathway
What do the 1st order neurons of lower limb synapse onto in the Dorsal Spinocerebellar Tract (DSCT)?
Clarke’s Dorsal Nucleus
What vertebral levels have Clarke’s Dorsal Nucleus?
C8 - L3
What is affected in Freidrich’s ataxia?
Clarke’s Dorsal Nucleus. Difficulty walking, loss of sensation in arms and legs and impaired speech that worsens over time
Where do the 1st order neurons of the upper limb synapse onto in the Dorsal Spinocerebellar Tract (DSCT)?
In the pons
Where does the Dorsal Spinocerebellar Tract (DSCT) travel to?
Cerebellum
What tract do the 2nd order neurons of the Dorsal Spinocerebellar Tract (DSCT) travel along?
Cuneocerebellar tract
Will a cerebellar lesion result in ipsilateral or contralateral symptoms?
Ipsilateral
What tract carries upper limb sensation in the Ventral Spinocerebellar Tract (VSCT)?
Rostral Spinocerebellar tract
Where does decussation occur in upper limb tract of VSCT?
No decussation
Where does decussation occur in lower limb of VSCT?
2nd order neuron crosses in the spinal cord and then recrosses in the cerebellum
What happens when there is damage to the spinocerebellar tract?
Damage to the spinocerebellar tract is rarely seen in isolation. Symptoms normally masked by other motor weakness/paralysis
Pure lesions could cause:
- Ataxia / malcoordination of motor action
- Wide-based gait
What can cause dorsal column damage?
B12 deficiency Infarction Infection Compression of cord Tertiary Syphilis
What are the signs/symptoms of dorsal column damage?
Pseudoathetosis – writhing of digits, hands and feet
Sensory ataxia – leads to positive Romberg sign & stamping gait
How can a ventral grey matter tumour affect the STT neurons?
Knock out the contralateral, pain/temp but can be SACRAL sparing - due to its somatotopic organisation
