Ascending and Descending Tracts

Question 1

What part of the cortex receives somatic sensory information for the entire body? What part of the this receives most of the impulses first?

Answer 1

The somatosensory cortex

The primary somatosensory cortex

Question 2

Where is the primary somatosensory cortex located?

Answer 2

In the post central gyrus

Question 3

What are ascending tracts?

Answer 3

neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex

Question 4

What type of sensory modalities does the dorsal column medial lemniscal system carry?

Answer 4

fine touch (tactile sensation), vibration and proprioception

Question 5

What do first order neurons of the dorsal column medial lemnsical system do?

Answer 5

carry sensory information regarding touch, proprioception or vibration from the peripheral nerves to the medulla oblongata

Question 6

Describe the two different pathways first order neurons in the dorsal column medial lemniscal system can take?

Answer 6

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.

Question 7

First order neurons from what limb travel in the fasciculus gracilis in the dorsal column medial lemniscal system?

Answer 7

From the lower limb (below T6)

Question 8

First order neurons from what limb travel in the fasciculus cuneatus in the dorsal column medial lemniscal system?

Answer 8

From the upper limb (T6 and above)

Question 9

Describe the route of second order neurons in the dorsal column medial lemniscal system?

Answer 9

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

Question 10

Describe the route of the third order neurons in the dorsal column medial lemniscal system?

Answer 10

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.

Question 11

What type of sensory modalities does the spinothalmic tract carry?

Answer 11

Pain, temperature, deep pressure

Question 12

Describe the route of first order neurons in the spinothalamic tract?

Answer 12

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.

Question 13

Describe the route of second order neurons in the spinothalamic tract?

Answer 13

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.

Question 14

Describe the route of the third order neurones in the spinothalamic tract?

Answer 14

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.

Question 15

Where does the spinothalamic tract cross over vs the DCML system?

Answer 15

spinothalamic crosses over at the level of the spinal cord whereas the DCML crosses over at the medulla

Question 16

Give a brief overview of the spinothalamic tract?

Answer 16

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

Question 17

What area is the primary motor cortex found in?

Answer 17

The pre central gyrus

Question 18

What are the two major groups motor tracts can be divided into?

Answer 18

Pyramidal tracts and extrapyramidal tracts

Question 19

What is the corticospinal tract also called and why?

Answer 19

Pyramidal tract
tract forms visible ridges referred to as the ‘pyramids’ on the anterior surface of the medulla, so also called the pyramidal tract.

Question 20

What motor is the corticospinal tract involved in?

Answer 20

Fine, precise movement, particularly of distal limb muscles (e.g. digits

Question 21

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_______.

Answer 21

1) descending pathways
2) lower motor neurone
3) upper motor neurones

Question 22

The corticospinal tracts begin in the cerebral cortex, from which they receive a range of inputs ________

Answer 22

Primary motor cortex
Premotor cortex
Supplementary motor area

Question 23

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___________

Answer 23

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.

Question 24

Define decussate

Answer 24

cross over to other side of CNS

Question 25

Difference between functions of anterior and lateral corticospinal tract?

Answer 25

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

Question 26

Brief overview of corticospinal tract?

Answer 26

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

Question 27

Name 3 important extra pyramidal descending tracts?

Answer 27

vestibulospinal, reticulospinal, tectospinal

Question 28

What descending tract is thought to initiate movement due to visual stimuli?

Answer 28

tectospinal

Question 29

What extrapyramidal descending tract is involved in influencing voluntary movement?

Answer 29

The reticulospinal tract

Question 30

What extrapyramidal descending tract is in involved in antigravity ie correcting yourself when falling?

Answer 30

vestibulospinal

Question 31

Where does the vestibulospinal tract originate?

Answer 31

Fibres originate in the vestibular nuclei of pons and medulla (these in turn receive input from vestibular apparatus and cerebellum).

Question 32

Where does the reticulospinal tract originate?

Answer 32

Fibres originate in areas of the reticular formation in pons and medulla.

Question 33

Where does the tectospinal tract originate?

Answer 33

In the tectum of the brain (roof)

Question 34

Where do the pyramidal tracts originate?

Answer 34

In the cortex

Question 35

Where do the extra pyramidal tracts originate?

Answer 35

In the brain stem