Spinothalamic Tract – Ascending Tracts

Question 1

Ascending Tracts

Answer 1

These tracts are responsible to take information from lower part of CNS to the upper part.

Question 2

Anterior root (ventral root)

Answer 2

is a pure motor root .

Question 3

dorsal root

Answer 3

is a pure sensory root

Question 4

Trunk and rami

Answer 4

have both types of fibers i.e., sensory and motor fibers.

Question 5

dorsal column.

Answer 5

Only ascending tracts pass through This is a modern and highly myelinated system with high velocity. There are following sensations which are carried by this system.

Fine touch.

Proprioception. (sensation coming from locomotor system)

Vibration.

Two points discrimination.

Question 6

Anterolateral Column (Anterolateral Tract/System)

Answer 6

Both ascending and descending tracts are passing through this system. This is a primitive and poorly myelinated system with low velocity. There are following sensations which are carried by this system.

Crude touch.

Temperature.

Pain.

Tickling sensation.

Itching

Sexual sensation.

Question 7

First Order Neurons of Dorsal Column

Answer 7

Those are the neurons having their cell bodies in dorsal root ganglion. In dorsal column, axons from the lower extremity ascend as fasciculus gracilis; and axons from the upper extremity ascend as fasciculus cuneatus. These axons terminate by giving connections in nucleus gracilis and cuneatus respectively in the medulla.

Question 8

If a patient has tumor in the medial part of the spinal cord

Answer 8

he/she will loose the dorsal column sensations in the lower part of the body

Question 9

if a patient has tumor in the lateral part of the spinal cord

Answer 9

he/she will loose the dorsal column sensations in the upper part of the body.

Question 10

fasciculus gracilis.

Answer 10

Sensation fibers from the lower part of the body (from lower limb upto T-6) are located medially in the spinal cord, making a special bundle that goes upward.

Question 11

fasciculus cuneatus.

Answer 11

Sensation fibers from the upper part of the body are located laterally in the spinal cord, also making a special bundle that moves upward.

Question 12

Second order neurons of dorsal column

Answer 12

have their cell bodies in nucleus gracilis and nucleus cnueatus. Axons of those neurons emerge from respective nucleuses, cross to opposite side and move upwards making a very special type of another ascending system.

Question 13

Internal Arcuate Fibers

Answer 13

The axons of second order neurons of dorsal column which decussate to contra lateral sides within the medulla are called internal arcuate fibers.

Question 14

Medial lemniscus

Answer 14

the compact group of fibers which ascend after decussating. Left medial lemniscus contains information from right side of the body and right medial lemniscus contains information from left side of the body. Medial lemniscus terminates in VPL nucleus of thalamus.

Dorsal column system has major decussation in lower part of medulla. Then medial lemniscus system will pass through upper medulla, pons and mid brain.

Question 15

fasciculus

Answer 15

lots of axons makes a circular bundle

Question 16

lemniscus.

Answer 16

lots of axon makes a flattened bundled

Question 17

Thalamus

Answer 17

very large piece of Grey matter. It has special Y shaped white matter which divides into anterior, medial and lateral parts. Lateral part is further divided into ventral part and dorsal part. Ventral part has three nucleuses which are ventroanterior, ventrointermediate and ventroposterior. Ventroposterior nucleus is further divided into ventropostero lateral (VPL) and ventropostero medial (VPM). VPL receive most of the sensation (touch, pain, vibration, position) from the most of the body. VPM receive sensation fibers from head and neck region.

Question 18

Internal Capsule

Answer 18

a lot of pressed white matter between thalamus and caudate nucleus medially and lentiform nucleus laterally. Internal capsule is located in inferomedial part of the each cerebral hemisphere of brain.

Question 19

Third Order Neuron of Dorsal Column

Answer 19

Start from VPL nucleus, pass through posterior limb of internal capsule. Then ascend, form corona radiata and connects with cerebral cortex in post central gyrus (sensory cortex).

Question 20

Pain and Temperature Pathway

Answer 20

In peripheral tissue, there are receptors for thermal stimulus and free nerve endings for pain. Thermal and pain sensations pathway are the same.

Question 21

2 fibers in pain pathway to carry out information from periphery to CNS

Answer 21

a) A-: These are lightly myelinated fibers. They carry fast pain.
b) C- fibers: These are non-myelinated fibers. They are slow fibers.

Question 22

Pain is produced by tissue injury which leads to release of certain chemicals. They stimulate the pain receptors.

Answer 22

5-hydroxytryptamine, histamine, bradykinin, acids and potassium.

Question 23

the substances that reduce the threshold for the pain.

Answer 23

Prostaglandins and substance P

Question 24

First Order Neuron of Pain Pathway

Answer 24

They have their cell bodies in dorsal root ganglion. Their fibers enter into spinal cord and terminate into substantia gelatinosa in dorsal Grey horn.

Question 25

Dorsolateral Tract of Lissauer

Answer 25

As first order neuron enters into spinal cord, they give ascending and descending branches which contribute in the formation of local tract in the spinal cord. These ascending and descending branches connect with second order neuron.

Question 26

Second Order Neuron of Pain or temp Pathway

Answer 26

Cell body of second order neuron is present in substantia gelatinosa of dorsal horn. Their axons decussate in the ventral white commissure and ascend in the lateral white column of opposite side. These ascending fibers terminate in the VPL nucleus of thalamus. This tract which is located in lateral part of spinal cord and goes up to thalamus is called lateral spinothalamic tract.

Question 27

Pathway for Crude Touch

anterior

Answer 27

First order neuron of crude touch pathway has their cell body in dorsal root ganglion. Upon their entry into spinal cord, they also give ascending and descending branches. Their second order neuron decussate, go to anterior white column of contra lateral side and ascends toward thalamus. They form anterior spinothalamic tract.

Question 28

Spinal Lemniscus

Answer 28

Lateral spinothalamic tract, anterior spinothalamic tract and spinotectal tract fuse together at the level of medulla and ascend as a single bundle. This bundle is called spinal lemniscus. Spinotectal tract become the part of spinal lemniscus and terminates in tectum of midbrain.

Fast pain fibers A terminate in VPL nucleus of thalamus. Slow pain fibers C have different faiths. Some of them terminate in VPL nucleus; some fibers terminate in intralaminar nuclei of thalamus. On their pathway, slow pain fibers also stimulate reticular formation.

Question 29

Reticular Formation

Answer 29

mixture of Grey and white matters extend throughout the brain stem. All the day reticular formation work and stimulate cerebral cortex. It plays important role in maintaining consciousness. Reticular formation has connections with intralaminar nuclei of thalamus that stimulates whole cerebral cortex.

it keeps whole cerebral cortex active via intralaminar nuclei. All ascending tracts give collaterals to reticular formation. Slow pain fibers make special connections with them

Question 30

Third Order Neuron of Anterolateral Tract System

Answer 30

These neurons have their cell bodies in VPL and their axons pass through posterior limb of internal capsule, and their final destination is post central gyrus (sensory cortex).

Some fibers of pain pathway will make special connections to cingulate gyrus that deals with associated emotional component of pain and there are some other fibers which make connections to insular cortex that initiate response to associated autonomic component of pain.