Somatosensory Pathways and Motor Systems Flashcards
Where is somatic (from the body) sensation carried?
by peripheral nerve to spinal cord
Where is information passed in somatosensory pathways?
information is passed rostrally (towards heart) through cord and brainstem → thalamus → cerebral cortex
What is the simple rule of the somatosensory pathways?
there is chain of three neurons between peripheral sensory receptor and cortex
What is the 1st order neuron?
- has sensory receptor at its peripheral extremity (extremity of neuron)
- cell body is in dorsal root ganglion
- central branch enters CNS where it synapses
What does the 2nd order neuron do?
- crosses to opposite side
- ascends to thalamus – where it synapses with 3rd order neuron
What is the 3rd order neuron?
- thalamocortical
- projects to somatosensory cortex in parietal lobe
What are the ascending tracts of the spinal cord? (5)
- dorsal columns (fasciculus gracilis and fasciculus cuneatus)
- dorsal spinocerebellar
- ventral spinocerebellar
- lateral spinothalamic
- ventral spinothalamic
Fasciculus Gracilis
- function
touch, proprioception
Fasciculus Cuneatus
- function
- crossed or uncrossed
- conscious muscle sense concerned with awareness of body position
- crossed touch, pressure, vibration
Dorsal Spinocerebellar
- function
- crossed or uncrossed
- unconscious muscle sense – important in control of muscle tone and posture
uncrossed
Ventral Spinocerebellar
- function
- crossed or uncrossed
- unconscious muscle sense
- crossed
lateral spinothalamic
- function
- crossed or uncrossed
- pain and temperature
- crossed
ventral spinothalamic
- function
- crossed or uncrossed
- touch
- crossed
What are the descending tracts? (4)
- lateral corticospinal
- rubrospinal
- ventral corticospinal
- vestibulospinal
lateral corticospinal
- function
- crossed or uncrossed
- voluntary control of skeletal muscles
- crossed
rubrospinal
- function
- crossed or uncrossed
- involuntary control of skeletal muscle concerned with muscle tone and posture
- crossed
ventral corticospinal
- function
- crossed or uncrossed
- voluntary control of skeletal muscles
- uncrossed down spinal cord
- crosses at level of termination in spinal cord
vestibulospinal
- function
- crossed or uncrossed
- involuntary control of muscle tone to maintain balance and equilibrium
- uncrossed
Modalities in spinal cord….
- touch and proprioception from same side
- pain and temperature from opposite side
Touch and Proprioception
- carried from periphery in groups I and II (myelinated and fast) fibres
- reach cord, then ascend in white matter:
- on same side
- without synapsing
- via dorsal columns - in caudal medulla, synapse with 2nd order neuron in dorsal column nuclei
- axon of 2nd order neuron…
- crosses immediately
- ascends through medulla medially – called medial lemniscus
Pain and Temperature
- carried in groups III and IV (slow) fibres
- sharp vs. dull pain – in cord, 1st order axons synapse in dorsal horn with 2nd order neurons
- 2nd order axon crosses in cord at same level, and ascends as spinothalamic tract (travels from spinal cord to thalamus)
- ventrolateral white matter on opposite side
Pain and Temperature + Touch and Proprioception
see notes
corticospinal system
- voluntary movement
- one neuron from cerebral cortex to spinal cord
- cell bodies situated in precentral gyrus of frontal lobe (primary motor cortex)
- situated immediately anterior to sensory cortex
- motor homunculus in cortex: finer movement areas = larger cortical representation
Corticospinal Tract
see notes
internal capsule cerebral peduncles pons medulla lateral column of white matter – lateral corticospinal tract leave tract ventral horn of grey matter synapse with motor neurons
corticobulbar system
- controls muscles of face (bulbar refers to brainstem)
- corticobulbar fibres are identical to corticospinal fibres, except it terminates on cranial nerve (motor) nuclei in brainstem
- voluntary control
reticulospinal
- reticular formation forms central core of grey matter and runs whole length of brainstem
- gives rise to reticulospinal fibres – projects bilaterally (to both sides) down spinal cord
- influence 𝛾-motor neurons
- mingled with other systems in ventral columns of spinal cord
vestibulospinal
- from vestibular nuclei
- medial vestibulospinal tract
- lateral vestibulospinal tract
- projections are ipsilateral (same side) and unilateral (they do not branch)
- they mainly excite extensor motor neurons
Where is the medial vestibulospinal tract?
- from medial vestibular nucleus
- terminates on motor neurons supplying neck and trunk muscles
Where is the lateral vestibulospinal tract?
- arises from lateral vestibular nucleus
- supplies motor neurons of limb muscles
What is 𝛼-𝛾 coactivation?
corticospinal system activates both alpha (𝛼) and gamma (𝛾) motor neurons simultaneously
- ensures that sensitivity of spindle is maintained, regardless of length of extrafusal fibres
- corticospinal and reticulospinal tracts receive same excitatory connections from brain to have full range of motion and control
