Overview of Central Sensory and Motor Pathways Flashcards
Which area of the central nervous system represents the
highest centre for processing of
sensory information and for
commanding of motor commands?
The cerebral cortex.
Where in the cerebral cortex is sensory information represented?
In the primary sensory cortex.
Where in the cerebral cortex are motor commands represented?
In the primary motor cortex.
What separates the primary motor cortex from the primary sensory cortex?
The central sulcus of the cerebral cortex.
What is an ascending tract?
Any fibre tract of the sensory system by which sensory information is conveyed to the brain.
What are the 3 categories of ascending tracts?
- Dorsal spinocerebellar tract
- Ventral spinocerebellar tract
- Spinothalamic tract
What is conscious sensation?
Sensation is said to be conscious sensation if we are directly
aware of the information.
What is the significance of categorising sensation into conscious and unconscious sensation?
Sensations giving rise to conscious sensation are conveyed
differently from those not giving rise to conscious sensation.
How do primary sensory neurones divide upon reaching the spinal cord?
- Into 3 branches:
- 1 axonal process terminates in the dorsal
horn of its respective spinal segment and synapses with its respective secondary sensory neurone. - Another axonal process is sent to the
dorsal horn of the spinal segment above. - Another axonal process is sent to the
dorsal horn of the spinal segment below.
In which anatomical entity are axonal segments travelling to the spinal segments above and below the level of origin carried in?
The posterolateral tract of Lissauer.
Where in the dorsal horn do sensory fibres conveying pain terminate and synapse with the secondary sensory neurone? What is this area known as?
In laminae 3 and 4.
Known as nucleus proprius.
What is the path taken by a secondary sensory neurone conveying pain and temperature information?
- First travels towards the midline and towards the central canal of the spinal cord.
- Then dives under the central canal.
- Then crosses the midline to emerge on the opposite side.
- Then into the white matter of the opposite side.
- Then into the lateral funiculus, joining the fibres of the lateral spino-thalamic tract.
- Then to the ventral posterolateral nucleus of the thalamus that is opposite to that on which the sensory signal arose.
What is spinal decussation?
The crossing of secondary sensory neurones conveying pain and temperature information over the midline.
What are fibres that comprise spinal decussation known as?
Anterior commissures or spinal arcuate fibres.
What structures in the brain do secondary sensory neurones of the spinothalamic tract ascend?
The medulla, pons, midbrain and end in the ventral posterolateral nucleus of the thalamus.
Where do secondary sensory neurones synapse with tertiary sensory neurones?
In the ventral posterolateral nucleus of the thalamus.
Where do axons of tertiary sensory neurones terminate?
In the post-central gyrus of the cerebral cortex.
What do axons of tertiary sensory neurones travel through?
The internal capsule.
Why is the spinothalamic tract said to be somatotopically organised throughout its full extent?
Because the spatial mapping of the body’s surface is preserved within the tract.
Fibres arising from which part of the body ascend dorsolaterally within the spinothalamic tract?
Fibres arising from the lowest part of the body.
Fibres arising from which part of the body ascend ventromedially within the spinothalamic tract?
Fibres arising from the cervical cord.
What is syringomyelia?
A disorder in which a cyst forms in the spinal cord.
How is the way in which proprioceptive and tactile information is carried different from the way in which pain and temperature information is carried?
- Proprioceptive & Tactile
information is carried on the
same side of the spinal cord as
its origin.
- Pain and Temperature information crosses the midline at the same neural level as its respective dermatome.
Does proprioceptive and tactile information remain ipsilateral throughout its extent of transmission?
No. Only ipsilateral until the medulla, where it decussates.
Where is the motor strip located?
In the precentral gyrus.
What does the motor strip control?
Somatic / skeletal muscles of the body.
How are neurones of the motor strip grouped?
According to the skeletal muscles they command.
Are the brains motor commands of muscles decussated?
Yes.
Where are the cell bodies of the neurones whose axons comprise descending tracts found?
In motor areas of the cerebral cortex such as the motor strip in the pre-central gyrus / frontal cortex.
- Form cortical descending tracts.
or
In sub-cortical areas of the brain such as the midbrain, brainstem, pons and medulla.
-Form non-cortical descending tracts.
What are the two classes of descending tracts?
Cortical and non-cortical descending tracts.
Where are the cell bodies of upper motoneurones found?
In the brain.
Where are the cell bodies of lower motoneurones found?
In the spinal cord.
What are the two classes of upper motoneurones?
Cortical efferents or pyramidal upper motoneurones.
and
Brainstem efferents or extra-pyramidal upper motoneurones
Where can cell bodies of lower motoneurones be found outside of the ventral horn of the spinal cord?
In the motor nuclei of the cranial nerves in the brainstem.
