Ascending and descending pathways

Question 1

What are the two main divisions of spinal cord tracts?

Answer 1

Ascending and Descending pathways.

Question 2

Where are ascending tracts found?

Answer 2

In all funiculi of the spinal cord.

Question 3

Where are descending tracts primarily located?

Answer 3

Primarily in the lateral and anterior funiculi

Question 4

What type of information do ascending pathways conduct?

Answer 4

Sensory information from soma or viscera to higher centers.

Question 5

What happens to sensory information that reaches the thalamus before being relayed to the cerebral cortex?

Answer 5

It is perceived consciously.

Question 6

What is the function of information that reaches the cerebellum, and is it consciously perceived?

Answer 6

It is used in the regulation of motor patterns and is not perceived consciously.

Question 7

Name six major ascending tracts.

Answer 7

Lateral spinothalamic, Ventral spinothalamic, Posterior column/fascicullus, Dorsal spinocerebellar, Ventral spinocerebellar, Spino-olivary.

Question 7

How many neurons typically make up the anatomical organization of ascending pathways?

Answer 7

Usually a chain of three neurons: first-, second-, and third-order neurons.

Question 7

Where is the cell body of first-order (primary) neurons in ascending pathways located?

Answer 7

In the posterior root ganglion

Question 7

Which ascending pathway mediates conscious proprioception?

Answer 7

The Posterior column pathway.

Question 7

What kind of input does the posterior column pathway receive?

Answer 7

Input from Pacinian and Meissner’s corpuscles, joint receptors, and muscle spindles.

Question 7

Where are the first-order neurons for the posterior column pathway located?

Answer 7

In the posterior root ganglion (PRG) at all levels.

Question 7

What are the two fasciculi of the posterior white column?

Answer 7

Fasciculus gracilis and Fasciculus cuneatus.

Question 8

Which fasciculus of the posterior column carries fibers from the upper thoracic and cervical regions?

Answer 8

Fasciculus cuneatus.

Question 8

Where are the second-order neurons of the posterior column located?

Answer 8

In the gracile and cuneate nuclei of the caudal medulla.

Question 8

Which fasciculus of the posterior column is present at all levels and carries fibers from sacral, lumbar, and lower thoracic regions?

Answer 8

Fasciculus gracilis.

Question 8

What do the second-order neurons of the posterior column give rise to after decussating?

Answer 8

Internal arcuate fibers that form the medial lemniscus.

Question 8

Where do the third-order neurons of the posterior column pathway project?

Answer 8

Via the posterior limb of the internal capsule and corona radiata to the postcentral gyrus (somatosensory cortex).

Question 9

Which tract transmits unconscious proprioception (muscle, joint sense, and pressure) and projects to the cerebellum via the inferior cerebellar peduncle?

Answer 9

Posterior spinocerebellar tract.

Question 10

What is the function of the ventral spinocerebellar tract?

Answer 10

Transmits unconscious proprioception to the cerebellum from the trunk, upper, and lower limbs.

Question 11

Which cerebellar peduncle does the ventral spinocerebellar tract enter?

Answer 11

Superior cerebellar peduncle.

Question 12

Which ascending tract mediates pain and temperature sensation?

Answer 12

Lateral spinothalamic tract

Question 13

Where are the first-order neurons for the lateral spinothalamic tract located?

Answer 13

In the dorsal root ganglia (DRG).

Question 14

What tract is formed by the ascending and descending branches of the central processes of first-order neurons in the pain and temperature pathway

Answer 14

Posterolateral tract of Lissauer.

Question 15

Which ascending tract mediates light touch and pressure?

Answer 15

Anterior spinothalamic tract.

Question 16

Where are the second-order neurons of the anterior spinothalamic tract located?

Answer 16

In the posterior grey horn.

Question 17

What is the upper-extremity equivalent of the dorsal spinocerebellar tract?

Answer 17

Cuneocerebellar tract.

Question 18

Where do the second-order neurons of the cuneocerebellar tract project to the cerebellum?

Answer 18

Via the inferior cerebellar peduncle.

Question 19

Where does the spino-olivary tract originate and terminate?

Answer 19

Originates in spinal grey and terminates in the olivary nucleus of the medulla.

Question 20

Which peduncle does the spino-olivary tract use to reach the cerebellum?

Answer 20

Inferior cerebellar peduncle.

Question 21

What are the neurons in the anterior grey horn of the spinal cord that innervate skeletal muscles called?

Answer 21

Lower motor neurons (LMN)

Question 22

What are the nerve fibers descending from the brainstem and cerebral cortex that control LMNs called?

Answer 22

Descending tracts (Upper Motor Neurons).

Question 23

Name four major descending pathways.

Answer 23

Lateral corticospinal tract, Ventral corticospinal tract, Rubrospinal tract, Tectospinal tract, Vestibulospinal tract, Reticulo-spinal tract, Autonomic.

Question 24

What is the function of the corticospinal tract?

Answer 24

Voluntary, discrete, skilled movement.

Question 25

What is the function of the vestibulospinal tract?

Answer 25

Inhibits flexor muscles and facilitates extensor muscles and posture through balance.

Question 26

From where do the corticospinal tracts arise?

Answer 26

From neurons in the motor and sensory cortex.

Question 27

What percentage of corticospinal fibers decussate at the spino-medullary junction?

Answer 27

Most (75-90%).

Question 28

What tract is formed by the crossed corticospinal fibers

Answer 28

Lateral Corticospinal tract.

Question 29

What percentage of corticospinal tracts are uncrossed and travel in the anterior white matter?

Answer 29

% (Ventral corticospinal tract).

Question 30

Where do the fibers of the ventral corticospinal tract cross?

Answer 30

At the spinal cord level.

Question 31

From where does the Rubrospinal tract arise?

Answer 31

From the Red nucleus in the midbrain.

Question 32

What is an ascending pathway?

Answer 32

A series of connected neurons that transmit sensory information (like touch, pain, or temperature) from the body to the brain.

Question 32

From where does the Tectospinal tract arise?

Answer 32

From the superior colliculus of the midbrain

Question 32

What types of reflexes are associated with the Tectospinal tract?

Answer 32

Acoustic, visual, auditory, and tactile neck reflexes.

Question 32

From where does the Vestibulospinal tract arise?

Answer 32

From the Vestibular nuclear complex in the floor of the 4th ventricle

Question 32

Are Vestibulospinal tracts crossed or uncrossed?

Answer 32

Uncrossed.

Question 32

What is a descending pathway?

Answer 32

A series of connected neurons that transmit motor commands from the brain to the muscles, enabling movement.

Question 32

What are Upper Motor Neurons (UMNs)?

Answer 32

Cortical neurons that give rise to corticobulbar or corticospinal tracts, or neurons in brainstem nuclei that influence lower motor neurons.

Question 32

What are some acute-stage lesions symptoms of UMN lesions?

Answer 32

Transient spinal shock, flaccid paralysis, areflexia, and hypotonia.

Question 33

What are some chronic-stage lesions symptoms of UMN lesions?

Answer 33

Spastic paralysis, hypertonia, reduction or loss of superficial abdominal and cremasteric reflexes, extensor toe response (Babinski sign), and clonus.

Question 33

Where are Lower Motor Neurons (LMNs) found?

Answer 33

In the ventral horns of the spinal cord or in the motor nuclei of cranial nerves III, IV to VII, and IX to XII.

Question 33

What are some results of LMN lesions?

Answer 33

Flaccid paralysis, areflexia, muscle atrophy, fasciculations, and fibrillations

Question 34

o tracts in conscious sensory pathways reach the cerebral cortex?

Answer 34

Yes, they do

Question 35

Does an ascending pathway carrying conscious information pass through the thalamus?

Answer 35

Yes, it will pass through the thalamus.

Question 36

In conscious sensory pathways, which order of neurons crosses the midline?

Answer 36

The second-order neurons.

Question 37

What is the key difference in conscious perception for sensory information reaching the thalamus vs. the cerebellum?

Answer 37

nformation reaching the thalamus before being relayed to the cerebral cortex is perceived consciously. Information reaching the cerebellum is used in motor pattern regulation and is not perceived consciously.

Question 38

Outline the typical neuronal chain for ascending pathways and identify the location of the first-order neuron's cell body.

Answer 38

Ascending pathways usually consist of a chain of three neurons: first-, second-, and third-order neurons. The cell body of the first-order (primary) neuron is in the posterior root ganglion

Question 39

Compare and contrast the Lateral Spinothalamic and Posterior Column pathways regarding the type of sensation they mediate and their crossing patterns.

Answer 39

Lateral Spinothalamic: Mediates pain and temperature. It is a conscious/crossed pathway. Posterior Column: Mediates conscious proprioception, two-point tactile discrimination, and vibration sensation. Second-order neurons decussate in the caudal medulla.

Question 40

Describe the general organization of descending pathways originating from the cerebral cortex in terms of neuronal series and their final targets.

Answer 40

Descending pathways from the cerebral cortex are often made up of a series of three neurons. First-order neurons are in the cerebral cortex (and sometimes brainstem). Second (internuncial) neurons are in the anterior grey column, and they synapse on third-order neurons (LMNs) in the ventral horn.

Question 41

A patient presents with spastic paralysis, hypertonia, and a positive Babinski sign. What type of motor neuron lesion is suspected?

Answer 41

Upper Motor Neuron (UMN) lesion.

Question 42

A patient exhibits flaccid paralysis, areflexia, and muscle atrophy. What type of motor neuron lesion is indicated?

Answer 42

Lower Motor Neuron (LMN) lesion.

Question 43

Distinguish between the acute and chronic stages of an Upper Motor Neuron (UMN) lesion based on clinical signs.

Answer 43

Acute-stage: Transient spinal shock, flaccid paralysis, areflexia, hypotonia. Chronic-stage: Spastic paralysis, hypertonia, reduction/loss of superficial reflexes, extensor toe response (Babinski sign), clonus.

Question 44

What are propriospinal fibers and their general location within the spinal cord?

Answer 44

Propriospinal (inter-segmental) fibers mostly surround the grey matter and interconnect various spinal cord levels, responsible for coordinating flexor reflexes.

Question 45

Which specific part of the thalamus do conscious sensory pathways (e.g., posterior column, spinothalamic tracts) terminate in?

Answer 45

Ventral posterolateral (VPL) nucleus of the thalamus.

Question 46

What is the somatotopic organization of the lateral spinothalamic tract regarding sacral and cervical fibers?

Answer 46

Sacral fibers are dorsolateral, while cervical fibers are ventromedial.

Question 47

Which descending tract's myelination is not fully achieved until the end of the second year of life?

Answer 47

Lateral Corticospinal tract (implied as 'E' in the diagram represents Lateral Corticospinal tract, and 'E' is the answer for myelination being achieved by end of 2nd year).

Question 48

Which descending tract plays a role in regulating extensor tone?

Answer 48

estibulospinal tract (implied as 'D' in the diagram represents Vestibulospinal tract, and 'D' is the answer for regulating extensor tone).

Question 49

What are the largest cells of origin for the corticospinal tracts, and where are they located?

Answer 49

Giant pyramidal cells, or Betz cells, located in the primary motor cortex.

Question 50

Which descending tract is poorly defined in humans despite being present in other species?

Answer 50

Rubrospinal tract.