Sensory TractNeuroanatomy block-Anatomy-Lecture 3

Editing file

01 Define the meaning of a tract02 Distinguish between the different types of tracts03 Locate the position of each04 Describe the sensory pathway05 Identify the different sensory spinal tracts and their functions 06 Identify the course of each of these tracts07 Know some associated lesions regarding the main tracts

Color guide ● Only in boys slides in Green● Only in girls slides in Purple● important in Red● Notes in Grey

At the end of the lecture, students should be able to:

Objectives

3

White matter tracts

● The grey matter of the spinal cord is completely surrounded by the white matter.● The White matter of the spinal cord consists of Ascending and Descending Nerve Fibers.● It is divided into Dorsal, Lateral & Ventral Columns or Funiculi.

Posterior funiculus

● Is Bundles or fasciculi of fibers that occupy more or less definite positions in the white matter. They have the same Origin, Termination and carry the same Function.

● They are classified (according to the length) into:

Lateral funiculus

Anterior funiculus

White matter of spinal cord

Types

Short tracts(intersegmental or propriospinal)

Long tractsDivided according to the function

Fibers occupy narrow band immediately peripheral to the

grey matter (fasciculus proprius).

1. Ascending (sensory or afferent)

2. Descending (motor or efferent)

Function

They interconnect adjacent ordistant spinal segments & Permit

intersegmentalcoordination

They serve to join the brain to the spinal cord.

Fasciculus proprius

Ascending tracts

4

● Carry impulses from pain, thermal, tactile, muscle and joint receptors to the brain.

● Some of this information eventually reaches a conscious level (at the cerebral cortex), while some is destined for subconscious centers (e.g at the cerebellum)

● Pathways that carry information to a conscious level (which we feel) share certain common characteristics:

● There is a sequence of Three Neurons between the peripheral receptors and the cerebral cortex.

Conscious level Subconscious level

Cerebral hemisphere Cerebellum

5

Ascending tracts cont’● The axons of the first-order neuron or primary afferent

neuron: enters the spinal cord through the dorsal root of a spinal nerve and its cell body lies in the dorsal root ganglion.

01

02

03

● The main fiber remains on the ipsilateral (uncrossed/same) side of the cord and terminates in synaptic contact with the second neuron which lies either in the spinal grey matter or in the medulla oblongata of the brain stem.

● The axon of the second order neuron crosses over (decussates) to the opposite side of the CNS and ascends to the thalamus, where it terminates.

● The third-order neuron (ventral posterior nucleus) has its cell body in the thalamus. Its axon passes to the somatosensory cortex of the parietal lobe of the cerebral hemisphere.

● Contain the axons of primary afferent neurons that have entered cord through dorsal roots of spinal nerves, from ipsilateral side of the body.

● They are concerned with:1. Discriminative touch: Ability to

localise accurately the area of the body touched.

2. Two point discrimination: To be aware that two points are touched simultaneously even they are close together.

3. Proprioception: from muscles and joints for the movement & position of different parts of the body.

6

Sensory pathways

Dorsal (Posterior) column

Anterolateral (Spinothalamic)

Spinocerebellar

Fasciculus gracilis

Fasciculus cuneatus

Dorsal column

Spinothalamic

Spinocerebellar

contains fibers that are received at upper thoracic and cervical

levels

contains fibers that are received at sacral, lumbar and lower thoracic

levels

Fasciculus gracilis (FG)

Fasciculus cuneatus (FC)

7

Fibers ascend without interruption where they terminate upon 2nd order neurons in nucleus gracilis and nucleus cuneatus.

The axons of the 2nd order neurons decussate in the medulla as internal arcuate fibers, and ascend through the brainstem as Medial Lemniscus.

The medial lemniscus terminates in the ventral posterior nucleus of the thalamus (3rd order neurons), which project to the somatosensory cortex (thalamocortical fibers)

Dorsal column

1

2

3

- In the case of dorsal column, the 2nd order neuron is found in the medulla oblongata.- Whether to terminate in nucleus gracilis or cuneatus depends on which tract is ascending, each tract terminate in its corresponding nucleus (fasciculus gracilis > nucleus gracilis, fasciculus cuneatus > nucleus cuneatus).

nucleus gracilis

Tabes dorsalis (venereal disease)

Subacute Combined Degeneration of the spinal cord Multiple sclerosis

1. A late manifestation of syphilitic infection on the CNS

2. Affects the lumbosacral dorsal spinal roots (carried by fasciculus gracilis that’s why the lower limbs are affected & the upper limbs are intact) and dorsal columns of the spinal cord

3. Leads to loss of proprioception which is manifested by a high Steppage & unsteady gait (Sensory Ataxia/loss of sensation with intact muscles)

1. A systemic disease results from B12 deficiency

2. It produces Sensory Ataxia3. Lateral columns are also affected

(combined) causing weak and spastic limbs

4. It is completely recovered by proper treatment with B12

1. An immune disease affects specifically fasciculus cuneatus (there will be upper limb manifestations) of the cervical region.

2. Leads to loss of proprioception in hands and fingers (astereognosis = inability to determine the shape of an object through touch)

3. Its signs include Musculoskeletal: weakness,spasms, ataxiaSensation: pain, hypoesthesia, paraesthesias

Steppage gait8

Diseases associated with dorsal column lesion

Spinothalamic tract

9

1

2

3

4

Located lateral and ventral to the ventral horn.

Contains axons of second-order neurons, the cell bodies of which lie in the contralateral dorsal horn, then decussate and ascend as spinal lemniscus

● Lateral spinothalamic tract: carry impulses with pain and thermal sensation.

● Anterior spinothalamic tract: carry ½ non-discriminative touch and pressure.

*from contralateral side

In the brain stem the two tracts constitute the spinal lemniscus.

5 The information is sent to the primary sensory cortex on the opposite side of the body.

So the first order neurons terminate as soon as they enter to the spinal cord in area called substantia gelatinosa , once it terminate the second order neurons will start and they will cross through the anterior white commissure to the contralateral side and then ascend

At the level of medulla they fuse together forming a single bundle called spinal lemniscus.

They terminate in the ventral posterior nucleus of the thalamus

10

Because along the spinal cord as we

ascend the neurons are added to the tract

so first will be the sacral then comes the lumbar medially and

so on

Spinothalamic tract cont,Lateral spinothalamic tract Anterior spinothalamic tract

FunctionCarries pain and temperature to thalamus

and sensory area of the cerebral cortex.(conscious level)

Carries crude touch (non-discriminative) and pressure to thalamus and sensory

cortex.

Neurons

1- Neuron I : small cells in the dorsal root ganglia.2- Neuron II : cells of Substantia gelatinosa of Rolandi in the (contralateral) posterior horn.(in the spinal cord)After 2nd order neuron the fibers decussate then ascend and called lateral spinothalamic tract.3- Neuron III : cells of ventral posterior nucleus of the thalamus. Then continue till the somatosensory cortex of the cerebral .

1- Neuron I : medium sized cells in the dorsal root ganglia.2- Neuron II : cells of main sensory nucleus or (nucleus proprius; laminae IV,V,VI, and I).Fibers arising from Substantia gelatinosa and Nucleus proprius, decussate in the anterior white commissure , then ascend as anterior spinothalamic tract.3- Neuron III : cells of ventral posterior nucleus of thalamus.

Arrangement of fiber:sacral are more superficial then lumber, thoracic and lastly cervical which are closer to the gray matter

Spinocerebellar tracts● The spinocerebellar system consists of a sequence of only two neurons. (subconscious)

Neuron I : large cells of dorsal ganglia.Neuron II : cells of the nucleus dorsalis; Clark’s nucleus(column).

● Two tracts : dorsal (posterior) and ventral (anterior).● Located near the dorsolateral and ventrolateral surfaces of the cord.● Contain axons of the second order neurons.● Carry information derived from muscle spindles, Golgi tendon organs and tactile

receptors, joints, skin, and subcutaneous tissue to the cerebellum for the control of posture and coordination of movements.

● Cerebellum controls the same side of the body.

11

● The cell bodies of 2nd order neuron lie in base of the dorsal horn of the lumbosacral segments.

● Axons of 2nd order neuron cross to opposite side, ascends as far as the midbrain then make a sharp turn caudally and enter the superior cerebellar peduncle

● the fibers cross the midline for a second time within cerebellum before terminates in the cerebellar cortex.

● So ventral spinocerebellar tract conveys sensory information to the same side of the cerebellum.

● Present only above L3.● The cell bodies of 2nd order neuron lie in

clark’s column.● Axons of 2nd order neuron terminate

ipsilaterally (uncrossed) in the cerebellar cortex by entering through the inferior cerebellar peduncle.

● Posterior spinocerebellar tract convey sensory information to the same side of the cerebellum

Dorsal (Posterior) spinocerebellar tractVentral (Anterior) spinocerebellar tract

Spinothalamic tracts lesion

12

1

2

3

4

It is a selectively damaged in syringomyelia

The central canal becomes enlarged forming a cavity compressing the adjacent nerve fibers (while the fibers decussate through the white commissure, the lateral spinothalamic will be closer to the central canal then the anterior)Fibers serving pain and temperature are damaged as they decussate in the ventral white commissure close to the central canal causing selectively loss of pain and temperature in the upper limbs (dissociation sensory loss)Light touch and proprioceptive sensations are retained. Because it’s carried by the dorsal column

5 Joints of the limbs become disorganized without discomfort (Charcot’s joint)

Spinocerebellar tracts lesion

Friedreich's ataxia:1

2

3

4

5

An inherited degenerated disease

Affecting the spinocerebellar tracts

Leading to incoordination of arms, intense tremor, wide base reeling gait ataxia.

It begins in childhood.

Wheelchair is bound by 20 years of age

13

Spinotectal tract Spinoreticular tract

● Ascends in the anterolateral part, in close association with spinothalamic system.

● Primary afferents reach dorsal horn through dorsal roots and terminate on 2nd order neuron.

● The cell bodies of 2nd order neuron lie in base of the dorsal horn.

● Axons of 2nd order neuron cross to opposite side, and project to the periaqueductal gray matter and superior colliculus in midbrain.

● Involved in reflexive turning of head and eyes toward a point of cutaneous stimulation. (spino-visual reflex)

● Originates in the dorsal horn, and ascends in the ventrolateral region of the cord.

● Contains:1- uncrossed fibers that end in medullary reticular formation.2- crossed & uncrossed fibers that terminates in pontine reticular formation.

● Then to brain stem reticular formation finally to the thalamus , that activates the cerebral cortex.

● Forms part of the ascending reticular activating system.

● Involved in perception of dull aching (slow pain).

Spino-olivary tract

● Indirect spinocerebellar pathway.● Impulses from the spinal cord are relayed to the cerebellum via inferior olivary

nucleus.● Conveys sensory information to the cerebellum.● Fibers arise at all levels of the spinal cord.● Contribute to movement coordination association primarily with balance.

Other spino-tractsSpinotectal tract Spinoreticular tract

Spino-olivary tract

Males’ doctor note: you only need to know the names and the function for these three

Practice Q1: Fibers occupy narrow band immediately peripheral to the grey matter:

A. Fasciculus cuneatus

B. Fasciculus gracilis

C. Fasciculus proprius

D. Spinocerebellar

Q2: The third-order neuron has its cell body in:

A. Thalamus

B. Dorsal root ganglion

C. Spinal grey matter

D. Medulla oblongata

Q3: The dorsal column carry impulses which are concerned of all of the following EXCEPT:A. Proprioception

B. Pain

C. Discriminative touch

D. Crude touch

Q4: A late manifestation of syphilitic infection on the CNS:

A. Multiple sclerosis

B. Subacute combined degeneration of the spinal cord

C. Friedreich's ataxia

D. Tabes dorsalis

Q5: spinotectal tract in close association with:

A. Spinothalamic tract

B. Spinocerebellar tract

C.spino-olivary tract

D. Spinoreticular tract

Q6: lateral spinothalamic tract carry:

A.temperature

B.pain

C.pressure

D.A&B

Q7: spinal lemniscus constitute ………………….. when they enter the brainstem

A.lateral spinothalamic tract + anterior spinothalamic tract

B. lateral spinothalamic tract + posterior spinothalamic tract

C. lateral spinothalamic tract + spinotectal tract

D.non of the above

Q8 : charcot’s joint seen in:

A. Spinothalamic tract lesion

B.spinocerebellar tract lesion

C. Dorsal column lesion

D. Posterior column lesion

Answers: Q1(C) Q2(A) Q3(B) Q4(D) Q5(A) Q6(D) Q7(A) Q8(A) 14

Girls team :

● Ajeed Al Rashoud● Taif Alotaibi● Noura Al Turki● Amirah Al-Zahrani● Alhanouf Al-haluli● Sara Al-Abdulkarem● Renad Al Haqbani● Nouf Al Humaidhi● Jude Al Khalifah● Nouf Al Hussaini● Rahaf Al Shabri● Danah Al Halees● Rema Al Mutawa● Amirah Al Dakhilallah● Maha Al Nahdi ● Razan Al zohaifi ● Ghalia Alnufaei

Boys team:

● Mohammed Al-huqbani● Salman Alagla● Ziyad Al-jofan● Ali Aldawood● Khalid Nagshabandi● Omar Alammari● Sameh nuser● Abdullah Basamh● Alwaleed Alsaleh● Mohaned Makkawi● Abdullah Alghamdi

Team leaders

● Ateen Almutairi● Abdulrahman Shadid

Contact us:

Editing file

Members board

most probably you don't need this