Ascending and Descending Tracts Flashcards
What part of the cortex receives somatic sensory information for the entire body? What part of the this receives most of the impulses first?
The somatosensory cortex
The primary somatosensory cortex
Where is the primary somatosensory cortex located?
In the post central gyrus
What are ascending tracts?
neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex
What type of sensory modalities does the dorsal column medial lemniscal system carry?
fine touch (tactile sensation), vibration and proprioception
What do first order neurons of the dorsal column medial lemnsical system do?
carry sensory information regarding touch, proprioception or vibration from the peripheral nerves to the medulla oblongata
Describe the two different pathways first order neurons in the dorsal column medial lemniscal system can take?
Signals from the upper limb (T6 and above) – travel in the fasciculus cuneatus (the lateral part of the dorsal column). They then synapse in the nucleus cuneatus of the medulla oblongata.
Signals from the lower limb (below T6) – travel in the fasciculus gracilis (the medial part of the dorsal column). They then synapse in the nucleus gracilis of the medulla oblongata.
First order neurons from what limb travel in the fasciculus gracilis in the dorsal column medial lemniscal system?
From the lower limb (below T6)
First order neurons from what limb travel in the fasciculus cuneatus in the dorsal column medial lemniscal system?
From the upper limb (T6 and above)
Describe the route of second order neurons in the dorsal column medial lemniscal system?
The second order neurones begin in the cuneate nucleus or gracilis. The fibres receive the information from the preceding neurones, and delivers it to the third order neurones in the thalamus.
Within the medulla oblongata, these fibres decussate (cross to the other side of the CNS). They then travel in the contralateral medial lemniscus to reach the thalamus
Describe the route of the third order neurons in the dorsal column medial lemniscal system?
Lastly, the third order neurones transmit the sensory signals from the thalamus to the ipsilateral primary sensory cortex of the brain. They ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule and terminate at the sensory cortex.
What type of sensory modalities does the spinothalmic tract carry?
Pain, temperature, deep pressure
Describe the route of first order neurons in the spinothalamic tract?
The first order neurones arise from the sensory receptors in the periphery. They enter the spinal cord, ascend 1-2 vertebral levels, and synapse at the tip of the dorsal horn – an area known as the substantia gelatinosa.
Describe the route of second order neurons in the spinothalamic tract?
The second order neurones carry the sensory information from the substantia gelatinosa to the thalamus. After synapsing with the first order neurones, these fibres decussate within the spinal cord, and then form two distinct tracts the anterior and the lateral spinothalamic tract.
Although they are functionally distinct, these tracts run alongside each other, and they can be considered as a single pathway. They travel superiorly within the spinal cord, synapsing in the thalamus.
Describe the route of the third order neurones in the spinothalamic tract?
The third order neurones carry the sensory signals from the thalamus to the ipsilateral primary sensory cortex of the brain. They ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule and terminate at the sensory cortex.
Where does the spinothalamic tract cross over vs the DCML system?
spinothalamic crosses over at the level of the spinal cord whereas the DCML crosses over at the medulla
Give a brief overview of the spinothalamic tract?
First order neurones synapses at substantia gelatinosa , there is a crossing over of sides at the level of the spinal cord, second order neuron synapses in the thalamus, third order neuron synapses in the sensory cortex
What area is the primary motor cortex found in?
The pre central gyrus
What are the two major groups motor tracts can be divided into?
Pyramidal tracts and extrapyramidal tracts
What is the corticospinal tract also called and why?
Pyramidal tract
tract forms visible ridges referred to as the ‘pyramids’ on the anterior surface of the medulla, so also called the pyramidal tract.
What motor is the corticospinal tract involved in?
Fine, precise movement, particularly of distal limb muscles (e.g. digits
There are no synapses within the ______1_____. At the termination of the descending tracts, the neurones synapse with a ______2_____. Thus, all the neurones within the descending motor system are classed as _____3_______.
1) descending pathways
2) lower motor neurone
3) upper motor neurones
The corticospinal tracts begin in the cerebral cortex, from which they receive a range of inputs ________
Primary motor cortex
Premotor cortex
Supplementary motor area
After neurons for the corticospinal tract originate from the cortex the neurones converge, and descend through the ____1____ Next, the neurones pass through ___2________ In the most inferior (caudal) part of the medulla, the tract divides into two.
The fibres of the lateral corticospinal tract __________3____________
The fibres of the anterior corticospinal tract
__________4___________
1) internal capsule
2) the crus cerebri of the midbrain, the pons and into the medulla.
3) The fibres within the lateral corticospinal tract decussate (cross over to the other side of the CNS). They then descend into the spinal cord, terminating in the ventral horn (at all segmental levels). From the ventral horn, the lower motor neurones go on to supply the muscles of the body.
4) The anterior corticospinal tract remains ipsilateral, descending into the spinal cord. They then decussate and terminate in the ventral horn of the cervical and upper thoracic segmental levels.
Define decussate
cross over to other side of CNS
Difference between functions of anterior and lateral corticospinal tract?
The lateral corticospinal tract primarily controls the movement of muscles in the limbs, while the anterior corticospinal tract is involved with movement of the muscles of the trunk, neck, and shoulders
Brief overview of corticospinal tract?
neurons originate from cortex, descend through internal capsule, get to medulla, lateral tract crosses over CNS and then descends terming in ventral horn at all levels, anterior doesn’t cross until later when it terminate in ventral horns
Name 3 important extra pyramidal descending tracts?
vestibulospinal, reticulospinal, tectospinal
What descending tract is thought to initiate movement due to visual stimuli?
tectospinal
What extrapyramidal descending tract is involved in influencing voluntary movement?
The reticulospinal tract
What extrapyramidal descending tract is in involved in antigravity ie correcting yourself when falling?
vestibulospinal
Where does the vestibulospinal tract originate?
Fibres originate in the vestibular nuclei of pons and medulla (these in turn receive input from vestibular apparatus and cerebellum).
Where does the reticulospinal tract originate?
Fibres originate in areas of the reticular formation in pons and medulla.
Where does the tectospinal tract originate?
In the tectum of the brain (roof)
Where do the pyramidal tracts originate?
In the cortex
Where do the extra pyramidal tracts originate?
In the brain stem
