Week 2 - B -Pharmacology 2b - DCML, Spinothalamci, Trigeminothalamic, Neglect syndrome

Question 1

What are the two main sensory pathways to the brain?

Answer 1

Dorsal column medial lemniscus (DCML) and Spinothalamic tract

Question 2

What sensations do the DCML and the spinothalamic tract mediate? What is the spinothalamic tract also known as?

Answer 2

DCML - fine (discriminative) touch, vibration and proprioception SPinothalamic tract (anterolateral tract) - crude touch, pressure, temperature, pain

Question 3

Describe the DCML tract pathway? For the leg

Answer 3

1st order neruones travel from the leg to the fasciculus gracilis region of the dorsal column (more medial) and travel in the dorsal column to the medulla where they synapse in the gracile nucleus to become second order neurones, They then decussate in the medulla and second order neurons travel in the contralateral medial lemniscus to the thalmaus where they synapse again, Third order neurones now travel to the primary somatosensory cortex - postcentral gyrus of parietal lobe

Question 4

The fasciculus gracilis region of the dorsal column is the region for sensation from the lower limbs What is the region for sensation from the upper limbs?

Answer 4

This is the fasciculus cuneatus

Question 5

In the dorsal column of the spinal cord, sensation from the spinal cord nerves ie cervical, thoracic, lumbar and sacral is in what order when the neurons enter the column?

Answer 5

From lateral to medial is Cervical - thoracic - lumbar - sacral

Question 6

Sensory input from what spinal cord vertebral levels travels in the fasciculus gracilis? Sensory input from what spinal cord vertebral levels travels in the fasciculus cuneatus?

Answer 6

Sensory input to T6 and below (including legs and lower trunk) travels in the fasciculus gracilis (which runs the length of the cord) whereas input above T6 (including the arms and upper trunk) travels in the fasciculus cuneatus

Question 7

The major route by which touch and proprioceptive information ascends to the cerebral cortex (apart from anterior head) is in the dorsal column medial lemnsicus At what point does the information change from being represented ipsilaterally to contralaterally? What is the nucleus in the thalamus where the second order neurons of the dorsal column medial lemniscus tract synapse?

Answer 7

Ipsilateral from spinal cord level to medulla Contralateral after the first order neurons synapse in the medulla and decussate This is the ventral posterolateral nucleus (VPL) of the thalamus

Question 8

What is the ability to recognise an object by feeling it known as? What pathway is capable of this?

Answer 8

This is known as stereognosis The DCLM pathway is capable of this

Question 9

Fine touch – ability to recognise exact location of light touch – two point discrimination Conscious proprioception – awareness of body position and awareness of body movements (kinaesthesia) How is conscious proprioception tested?

Answer 9

The clinician moves a hand, toe, finger, foot up or down when the patients eyes are closed The patient has to report whether it is being moved up or down

Question 10

The dorsal colum medial lemnsicus tract mediates vibration also How is vibration tested for the tract?

Answer 10

A clinican holds a 128Hz tuning fork to the bony prominences and patient says when they can and cannot feel the buzzing

Question 11

What part of the DCML pathway does testing stereognosis evaluate?

Answer 11

It evaluates cortical function of stereognosis

Question 12

Describe the spinothalamic tract

Answer 12

Mediates crude touch, pressure, temperature and pain First order neurones enter dorsal column of the tract and travel in Lissauer’s tract to reach the dorsal horn where they synapse in the substantia gelatinosa - second order neurones then decussate at the level of entry (or a few vertebral levels above) to the anterolateral column - the neurones assend in the spinothalamic tract to reach the thalamus where they synapse in the VPL nucleus. Third order neurones travel to primary somatosensory

Question 13

The anterior and lateral spinothalamic tracts are very closely related hence why they are usually categorised under one name Which tract mediates what sensations?

Answer 13

Lateral spinothalamic tract - pain and temperature Anterior spinothalamic tract - crude touch and pressure

Question 14

Dorsal column medial lemniscus tract shown clearly hear First order neurons synapse in medulla in cuneate or gracile nucleus (upper trunk and upper limb T6 vertebra and above, lower trunk and lower limbs, T6 vertebrae and below)

Answer 14

Spinothalamic tract shown here Reach the dorsal horn via the Lissauer tract (connects dorsal column to dorsal horn) to synapse in substantia gelatinosa and decussate

Question 15

The DCML and the Spinothalamic tract are the two main tracts fro providing sensation to almost all the regions of the body bar the anterior head What pathway provides sensation here?

Answer 15

The trigeminothalamic tract provides sensation here

Question 16

Where are the soma (cell body) of the sensory neurones for the trigeminothalamic pathways?

Answer 16

These cell bodies are located in the trigeminal ganglion

Question 17

What are the three sensory nuclei of the trigeminal nerve where the cell bodies from the trigeminal ganglion will synapse? What sensation do each of the nuclei mediate?

Answer 17

Mesencephalic neucleus - proprioception from chewing muscles and joints Pontine (primary) trigeminal nucleus - fine touch and vibration Spinal nucleus - pain and temperature

Question 18

The neurones decussate at the level of the trigeminal nuclei before projecting in what pathway to what region of the thalamus?

Answer 18

Project in the trigeminal lemnsicus to the ventroposteromedial (VPM) nucleus of the thalamus before travelling to the postcentral gyrus for the primary somatosensory area

Question 19

Firs order neurones are from the anterior head to the trigeminal nucleus (one of three) where they synpase 2nd order neurones are from the nucleus up the trigeminal lemniscus to the thalamus 3rd order neurones travel via what neurones from thalamus to the primary somatosensory area?

Answer 19

They travel via thalamocortical neurones

Question 20

Where is the primary somatosensory cortex located?

Answer 20

It is located in the postcentral gyrus of the parietal lobe which is immediately posterior to the central sulcus

Question 21

The Homunculus This model shows what a man’s body would look like if each part grew in proportion to the volume of the somatosensory cortex concerned with its sensory perception

• The toes are at the top of the post central gyrus with the tongue at the lower end What separates the head from the homonculus from the face?

Answer 21

The hand separates the head of the homunculus from the face

• Toe - head - hand - face - tongue

Question 22

What happens if a finger (say D3) is lost in an accident, or amputated. Does the area of SI (somatosensory cortex) representing the finger: simply go unused? atrophy? be utilized by other sensory inputs?

Answer 22

The area representing the finger is utilized by other sensory inputs

Question 23

The area formerly representing D3, after several months, now responds to stimulation of the adjacent digits (D2 and D4 – their cortical representation expands into the territory formerly representing D3) How is this relevant when talking about the phantom limb? eg if their was a hand amputated and lip was evoked

Answer 23

Due to the somatopic region of the cortex that is for the lip and hand being bordered to one another If the lip was touched after a hand amputee, this could stimulate skin regions in the brain that used to represent the amputated hand

Question 24

Damage to the posterior parietal cortex (e.g. through stroke) can cause bizarre neurological disorders (e.g. agnosia, astereognosia, hemispatial neglect syndrome) with simple sensory skills remaining intact What is agnosia? What is astereognsosia?

Answer 24

Agnosia is the inability to interpret sensations and hence recognize things Asterognosis - inability to identify somthing by touch with hand without visual or other sensory input

Question 25

Damage to the posterior parietal cortex can also result in neglect syndrome What is this syndrome?

Answer 25

Neglect syndrome is usually the result of damage to the right parietal cortex. Patients believe the left side of the world does not exist and may even disclaim the existence of the left side of their body

Question 26

A man awakes in hospital to find an amputated leg next to him in his bed. Disgusted and outraged he hurls it out of bed, but ends up on the floor along with the leg which is, or course, his own This was a book about a man with neglect syndrome Where is the posterior parietal cortex in relation to the postcentral gyrus?

Answer 26

It is located directly behind the postcentral gyrus