Sensorimotor systems Flashcards
What is the spinal organisation of a reflex arc?
Muscle spindle - type 1a proprioceptor - cell body in DRG - axonal projection to the dorsal horn -
1) - synapse with inhibitory internueron - synpase with antagonist muscles alpha motor neuron in ventral horn - project to muscle - relaxation
2) syanpse directly with agaonist muscle alpha maotor neuron in ventral horn - project to muscle - contraction.
Where do proprioceptors project to?
Includes type Ia, Ib and type 2
Project to different layers of the ventral horn.
Or project up the spinal cord via the dorsal columns or the spinocerebellar tracts
Where do primary sensory neurons project to?
Different layers of the dorsal horn
What do primary mechanoreceptors neurons project to?
Are sensory neurons
Project to the dorsal horn locally as well as up the dorsal columns in the spinal cord.
What are some different mechanoreceptors linked to the function of A-beta fibres?
Pacinian corpuscles - vibration
Meissners corpuscles - fine touch, dscriminative touch
Ruffini endings - twisting
Alpha-beta is responsible for pressure and vibration
What is the role of C-fibres?
Type of sensory neuron
Project to dorsal horn
Responds to nociceptors - chronic, dull, poorly localised pain or delayed pain
What is the role of A-delta fibres?
Type of sensory neuron
Project to the dorsal horn
Responds to nociceptors - fast pain and cold
What is the difference between a funiculus and a fasiculus?
Funiculus = big chunk of white matter
Fasiculus = particular axon tract
For example cuneate fasiculus is in the dorsal white funiculus.
What is the dorsal intermediate sulcus?
Groove separating gracile fasiculus and cuneate fasiculus - appears at T6 level.
What are the two axon tracts for the DCML (touch signalling) pathway in the spinal cord?
The cuneate fasiculus - (the lateral one) appears at T6 above level, for upper limbs
The gracile fasiculus - (the medial one), present throughout the spinal cord, for lower limbs.
Label the following cross section of the spinal cord.
What are the dark green tracts?
The dorsal and ventral spinocerebellar tracts
What is the orange tract?
The spinothalamic and spinoreticular tracts
What are the blue tracts?
The ventral and lateral corticospinal tracts
What is the brown tract?
The vestibulospinal tract
What is the purple tract?
The recticulospinal fibres
What tract is responsible for the mechanosensory circuitry of touch for the body?
The DCML pathway
Describe the mechanosensory circuitry pathway underpinning touch in the body?
The DCML pathway
Mechanosensory receptors active primary sensory neurons from lower/upper body have cell bodies in the DRG
Then travel up the the gracile tract and cuneate tract respectively.
Synapse with a secondary neuron in the gracile and cuneate nucleus respectively in the medulla
Internal arcuate fibres desicate to the contralteral side
Contineu as the medial lemnisuc axons projecting the the ventral posterior lateral nucleus of the thalamus
Synapse with a tertiary neuron which projects to S1.
Describe the mechanosensory circuitry responsible for pain/touch in the head.
Primary somatosensory neurons has cell bodies in the trigeminal ganglion
Axonal projections to the trigeminal sensory nucleus in the pons - synapse with secondary neuron
Thse trigeminal leminscus axons desicate to the contralateral side and project to the ventral posterior Medial nucleus of the thalamus.
Synapse with tertiary neuron
Ventral posterior medial nucleus axons project to S1.
What is the embryological origin (secondary vesicle) from which the thalamus develops from?
The diencephalon.
What nucleus in the thalamus does the limbic system use?
The anterior nuclear group
What nucleus in the thalamus does the sleep pathway use?
Thalamic reticular nucleus
What nucleus in the thalamus does the motor basal ganglia function use?
The ventral anterior
The ventral lateral.
What nucleus in the thalamus does the body somatosensation pathway use?
The ventral posterior lateral
What nucleus in the thalamus does the head somatosensation and taste use?
The ventral posterior medial
What nucleus in the thalamus does the visual system use?
The lateral geniculate nucleus
What nucleus in the thalamus does the auditory system use?
The medial geniculate complex
What nucles in the thalamus is responsible for visual attention?
The pulvinar
What nucleus in the thalamus is responsible for the affective pain/lmibis basal gangli circuits?
The midline thalamic
The medical nuclear group (mediodorsal)
Intralaminar
What are the key players involved in proprioception?
Muscle spindle (collection on intrafusal muscle fibres) - type 1a and type 2 afferents - gamma motor efferent for proprioceptive gain.
Golgi tendon organs - type 1b afferents
Where do the proprioceptors signalling travel up the spinal cord?
Lower body signals - the dorsal and ventral spinocerebellar tracts
Upper body signals - the cuneate fasiculus.
What is the circuitry for unconscious proprioception for the lower body?
Cell body in dorsal route ganglion, pass through dorsal horn, travel up ventral and dorsal spinocerebellar tracts
Project to and synapse in Clarkes nucleus (found in C8-L3)
Sends projection to cerebellum - integrates information with descending motor commands.
What is the circuitry for unconcsious proprioception for the upper body?
Cell body in the DRG, axonal projects pass through the dorsal horn, travels up the spinal cord in the cuneate fasiculus.
Projects to and synpases in the external cuneate nucleus
Projects to the cerebellum which integrates proprioceptive information with descending motor controls.
What is the circuitry for conscious proprioception from the body?
The DCML pathway
Mechanosensory receptors active primary sensory neurons from lower/upper body have cell bodies in the DRG
Then travel up the the gracile tract and cuneate tract respectively.
Synapse with a secondary neuron in the gracile and cuneate nucleus respectively in the medulla
Internal arcuate fibres desicate to the contralteral side
Contineu as the medial lemnisuc axons projecting the the ventral posterior lateral nucleus of the thalamus
Synapse with a tertiary neuron which projects to S1.
**
What is the ciruity of conscious pain from the head?
Primary neuron has cell bodies in the trigeminal ganglion
Axonal projections to the trigeminal sensory nucleus in the pons - synapse with secondary neuron
Thse trigeminal leminscus axons desicate to the contralateral side and project to the ventral posterior Medial nucleus of the thalamus.
Synapse with tertiary neuron
Ventral posterior medial nucleus axons project to S1.
**
What is the myelination patterns of different sensory neurons?
Proprioceptors are the most heavily myelinated - adaptive evolutionary for MSK function
Then mechanoreceptors of the skin
Then pain fibres (A-delta)
C-fbres for temp, pain and itch are unmyelinated.
What are the two waves of spatially localised pain?
An initial first pain - mediated by alpha delta fibres, this is quick, relatively shorter and of greater intensity
Delay then second pain wave mediated by C-fibres - this is not as intense and lasts longer. Is more like an ache.
How does the projection of A-delta and C-fibres vary in the dorsal horn?
Each nueron can project to multiple targets
A-delta - mainly lamina 1(marginal zone), and V
C-fibres - mainly lamina 1 (maringal zone), 2 (substantial gelatinosa) and 5.
Also lots of local projections within this.
What is the nociceptive circuitry in the body?
Spinothalamic tract
A delta/c fibres synapse in dorsal horn, desicate in the anterior white commissure.
Project via anterolateral system through the spinothalamic tracts in the spinal cord
Axons terminate/synapse in the ventral posterior lateral nucleus of the thalamus
Thalamocortical neurons project to S1.
What is the nociceptive circuitry for the head?
Primary neuron has cell bodies in the trigeminal ganglion
Axonal projections to the trigeminal sensory nucleus in the pons - synapse with secondary neuron
Thse trigeminal leminscus axons desicate to the contralateral side and project to the ventral posterior medial nucleus of the thalamus.
Synapse with tertiary neuron
Thalamocortical axons project to S1.
What are the different broadmans areas in S1?
what is the function of each area
1 - nocicpetive
2
3a - proprioceptive signals, nocicpetive
3b -mechanoreceptirve, nociceptive
What broadman areas make up the association cortex for S1?
5 and 7
What are the two different distinct ascending pain tracts?
Discriminative pain - Spinothalamic tract
Affective pain - spinoreticular tracts
What is the circuit pathway for affective pain to the cortex?
A-delta/c-fibres (DRG, ant white commisure desication etc)-
Projects up the spinoreticular tracts in the spinal cord
Synapse in the reticular nuclei in pontine reticular formation- secondary neuron
Synapse in the medial thalamic nuclei (the mediodorsal and intralaminar nuclei) in the thalamus - tertiary neurone
These project widely throughout the cortex particularly within the limbic system
**
What is the reticular formation?
Huge netlike structure of nuclei and tracts in brain stem.
What other circuity besides projections to the cerebral cortex may be involved in the affective pain pathway?
Spinoreticular tracts
Projections to the superior colliculus, periaqueductal grey, reticular formation
Project to parabrachial nucleus to the hypothalamus, amygdala. **
How can we used descending systems to modulate pain?
Conscious (determination)
Unconscious (Distraction)
What is the circuitry underpinning the descending pain modulation systems?
1) projection from secondary somatosensory cortex down tracts in the spinal cord
2) Projectstion from anterior cingulate cortex and insula to the PAG in the midbrain, to multiple nuclei including medullary reticular formation such as raphe nucleus, down the spinal cord in tracts
Both in the dorsal horn of the spinal cord can activate inhibitory internuerons to indirectly stop STT or can inhibit STT directly.
**
What is the method of local modulation of pain in the dorsal horn?
Dorsal coloum mechanoreceptive neurons (A-beta etc) modulate pain sensation in the dorsal horn
Via GABAergic mechanisms - directly or indirectly through inhibitory interneurons
**Also brainstem reticular nuclei (locus coerulus, raphe nuclei) can modulate in the brainstem through local enkaphalinergic interneurons. **
What is the function of the vestibulospinal tract?
Vestibular motor signals - motor reflexes to body in response to head position/balance to maintain body balance
innervates LMNs
What is the function of the tectospinal tract?
Originate in inferior/superior colliculus of the midbrain
Reflexes in head/eye movements with visual and audiostimuli - neck and shoulder LMNs and nuclei of CN3,4,6 9 (extraocular muscles)
(look at bright loud screechy bird)
What is the function of the reticulospinal tracts?
Responsible for sub-conscious motor control such as posture, by coordinating motor signals
What are the pyramidal tracts and what are their functions?
The corticobulbar
Lateral corticospinal
Anterior corticospinal
Voluntary movement
