Anatomy of Sensory and Motor pathway

Question 1

Define these terms: Tract, Nerve, Nucleus, Ganglion

Answer 1

Tract – A collection of axons in the central nervous system
Nerve - A collection of axons in the peripheral nervous system
Nucleus - A collection of neuronal bodies in the central nervous system
Ganglion - A collection of neuronal bodies in the peripheral nervous system

Question 2

Describe the segments of the spinal cord incl. length, upper and lower border, structure of ending

Answer 2

Extent- Base of brain to lower border of L1 Vertebra (adults)

Segments-
C1-8, T1-12, L1-5, S1-5, Co-1

Conus Medullaris – Terminal portion of the spinal cord, tapered like a cone.

Cauda Equina- a collection of nerve roots distal to the conus medullaris, which are horsetail-like in appearance and hence called the cauda equina (Latin for horse’s tail)

Filum terminale- Tapering end of the spinal cord beyond conus medullaris, which contains mostly extensions of piamater.

Question 3

Describe the location of the spinal cord

Answer 3

Inside the vertebral canal
Enclosed in meninges- Dura, arachnoid and Pia mater
Surrounded by Extradural fat which contains lymphatics and veins
Cerebrospinal fluid located in Subarachnoid space

Question 4

Describe or draw a cross section of the spinal cord

Answer 4

White matter on outside, divided into anterior, lateral and posterior funiculi. Grey matter butterfly in the middle with a centre canal. Has dorsal and ventral grey horn, sometimes lateral horn (only found in ANS sections)

Question 5

What is the dorsal column-medial lemniscus pathway and what modalities does it carry?

Answer 5

It consists of two tracts (fasciculus gracilis and fasciculus cuneatus). It is an ascending tract so is sensory. Its modalities include two point discrimination, vibration, proprioception, stereognosis (identifying shapes by touch and feeling), deep pressure

Question 6

What are the modalities of dorsal column tracts and its receptors?

Answer 6

Fine touch, vibration, proprioception, stereognosis, deep pressure. Receptors: meissners, markels, tendon organs, muscle spindle (they are mechano and proprio receptors)

Question 7

Describe the order of neurones in the dorsal column pathway (where its cell body is)

Answer 7

First order neurone = dorsal root ganglion, second order = nucleus gracilis and cuneatus (medulla), third order = thalamus, decussation = medulla

Question 8

What neurones go up the gracile fasciculus and which go up cuneate fasciculus, in term of area of body?

Answer 8

Fibres from the lower half of the body, below T6, ascend in the medial part of the dorsal column: Gracile fasciculus

Fibres from the upper half of the body, above T6 ascend in the lateral part of the dorsal column: Cuneate fasciculus

Medial to lateral – Sacral, Lumbar, Thoracic and then cervical (in terms of organisation of the nerve fibres)

Question 9

Describe the pathway of the dorsal column-medial lemniscus in terms of neurone order, synapse locations, decussation

Answer 9

1st order neurons pass through the dorsal column (gracile fasciculus and cuneate fasiculus), to reach the gracile and cuneate nuclei in Medulla.
Here they synapse with second-order neurons
2nd order neurons (these neurones form the internal arcuate fibres in medulla) -> Cross over to the opposite side.
Ascend through brainstem as Medial lemniscus.

Question 10

Describe pathway of dorsal column in cerebrum

Answer 10

Medial lemniscus terminates on the ventral posterolateral (VPL) nucleus of the thalamus by synapsing to the 3rd order neuron

3rd order neuron -> posterior limb of the internal capsule -> primary somatosensory cortex

Question 11

What is the clinical testing of the dorsal column pathway - how do we test it in clinical settings?

Answer 11

The dorsal column pathway is concerned with fine, precisely-localised (or discriminative) touch, joint position sense, proprioception and vibration sense.

It is tested using a high-amplitude, low-frequency (128Hz) tuning fork applied to bony prominences- Vibration

Question 12

What is the spinothalamic tract and what modalities does it carry?

Answer 12

The tract is sub divided into two tracts - lateral (pain and temp) and anterior (crude touch, pressure).

Question 13

Describe the order of the neurones of the spinothalamic tract and its receptors

Answer 13

Receptors- Free nerve endings.
First order- dorsal root ganglia.
Second order - Substantia gelatinosa (dorsal grey horn)
Third order - Thalamus.
Decussation: For lateral ST tract - At the same spinal segment or one segment above. For anterior: Decussation - Some segments above the spinal level of entry

Question 14

Describe the pathway of the spinothalamic tract in the cerebrum

Answer 14

Once 2nd order neurones pass the pons, they are referred to as the spinal lemniscus.

2nd order neurons terminate in the ventral posterolateral (VPL) nucleus of the thalamus

3rd order neurons project to the primary somatosensory cortex via the posterior limb of the internal capsule

Question 15

How to clinically test lateral spinothalamic tract?

Answer 15

Pain is usually tested using sterile neurological examination pins and temperature by a volatile spray (e.g. ethyl chloride) which produces a cold sensation.

To test lateral spinothalamic function, pain is tested (most commonly, but temp may also be used)

Question 16

Describe the general order of descending pathways

Answer 16

Upper motor neurone then lower motor neurone

Question 17

What is the basic function of the corticospinal tract and what is another name for it?

Answer 17

The corticospinal referred to as the pyramidal tract – Voluntary movements. Corticospinal tract: Controls voluntary movements of the contralateral (opposite) limbs/trunk. There is the lateral CS tract and ventral CS tract

Question 18

What are the extra pyramidal tracts?

Answer 18

Vestibulospinal / Reticulospinal / Rubrospinal / Tectospinal

Question 19

Describe key features of corticospinal tract

Answer 19

Longest continuous white matter pathway in the CNS

Control of precision and speed of skilled movements

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

Question 20

Where do the UMNs originate from in CS tract and what is the pathway in the cerebrum to the brainstem?

Answer 20

Origin of UMN – Cortex (pyramidal cells) in the pre-central gyrus.

corticospinal tract fibres originate from the motor and premotor areas of the frontal lobe.
They pass from cerebral cortex to enter the subcortical white matter - passing first through the fan-like corona radiata (‘radiating crown’) before entering the posterior limb of the internal capsule. then to anterior part of the brainstem in the crus cerebri in midbrain then to basilar pons then pyramids of the medulla (located on either sid eof the midline)

Question 21

Where does decussation happen for CS tract?

Answer 21

The corticospinal tract decussates at the lowermost border of the medulla - known as decussation of pyramids

Question 22

How are the ventral CS tract and lateral CS tract formed in terms of fibres?

Answer 22

Approximately 90% of fibres cross in the caudal medulla at the decussation of the pyramids – Form Lateral corticospinal tract

Remaining 10% fibres- Ventral corticospinal tract – Cross at the target spinal segment

Question 23

Where does the lateral CS tract lie?

Answer 23

In the lateral funiculus

Question 24

Where does the ventral CS tract lie?

Answer 24

In anterior funiculus, it crosses at its target spinal level (decussates)

Question 25

Where are lower motor neurones found?

Answer 25

LMN- Anterior horn cell in the Ventral grey horn of spinal cord at the respective level

Question 26

What happens if there are lesions in the lower motor neurones?

Answer 26

Paralysis/ paresis of specific muscles, loss or reduction of tendon reflex activity and reduced muscle tone, fasciculations and muscle atrophy

Question 27

What happens if there are lesions in the upper motor neurones?

Answer 27

Paralysis/ paresis of movements, increased tendon reflex activity and increased muscle tone, spasticity