Ascending Neural Pathways

Question 1

What modality do the following receptors pick up on:

• Hair follicle receptors,
• Merkel endings,
• Meissner Corpuscles,
• Pacinian corpuscles,
• Ruffini endings,
• Nociceptors,
• Muscle Spindles,
• Golgi Tendon Organ.

Answer 1

• Hair follicle receptors - Touch,
• Merkel endings - Pressure and low freq vibration,
• Meissner Corpuscles - Light tough,
• Pacinian corpuscles - vibration and JPS,
• Ruffini endings - Skin stretch, pressure and JPS,
• Nociceptors - Pain,
• Muscle Spindles - Muscle length and proprioception,
• Golgi Tendon Organ - JPS.

Question 2

Look at the dermatomes for clinical knowledge

Answer 2

Google there… i swear to god if you don’t actually google these …

Question 3

Explain the concept of lateral inhibition.

Answer 3

The neuron which high a high frequency of action potentials due to a strong stimuli sends signals to inhibitory interneurons to allows for a greater accuracy of the localisation of pain.

Question 4

All sensory neurons enter the spinal cord via?

Answer 4

The dorsal root (the 1st order neuron does anyway)

Question 5

What are the divisions of the dorsal column medial lemniscus and what sensations do they carry?

Answer 5

Fasciculus gracilis and fasciculus cuneatus.
Gracilis carries info from lower limbs (G for Ground)
Cuneatus carries information about upper limbs and is more laterally positioned in the spinal cord.
It mainly carries conscious proprioception, discriminative touch, vibration and pressure

Question 6

What are the divisions of the spinocerebellar tract and the modality they carry?

Answer 6

It is divided into dorsal and ventral tracts. They carry proprioceptive information from muscle spindles (runs in dorsal) and GTO (runs in ventral)

Question 7

What are the divisions of the spinothalamic tract and the modality it carries

Answer 7

Anterior and lateral divisions (hence it can be referred to as the anterolateral system) It carries pain and temperature transmission

Question 8

What is the exception to the rule that all sensory info passes through the thalamus?

Answer 8

Olfaction

Question 9

What is the function of the thalamus?

Answer 9

It is a relay station between the periphery and the cortex.

Question 10

How to the neurons running in the dorsal column medial meniscal pathway run?

Answer 10

First order neurons enter, travel up the dorsal column to synapse at the dorsal column nuclei, they then cross over in the brain stem. 2nd order neuron synapses in thalamus and 3rd order synapses in cortex. So they don’t cross over till later

Question 11

So what will occur if there is a lesion in the spinal tract in the DCML?

Answer 11

The mechanical and JPS stimuli will be absent ipsilateral from the spinal segment of the lesion and below (think that the lesion is going to block anything that tried to get past)

Question 12

How is the fine tactile and prorioceptive information that runs in the DCML used?

Answer 12

To determine the shape of an object without site and to determine the texture of an object without site. Therefore a lesion could cause asteriogenosis.

Question 13

What can occur if there is a lesion in one of the somatosensory association cortex?

Answer 13

It can lead to amorphosynthesis. This is where a patient lacks the ability to recognise sensory stimuli on the side of the body opposite to the lesion. Because there is a lesion high up, after the cross over

Question 14

What will cause gait ataxia?

Answer 14

Lesions in the gracile fasciculus.

Question 15

What will cause upper extremity ataxia?

Answer 15

Lesions in the cuneatus fasciculus.

Question 16

Describe how neurons running in spinothalamic pathways travel?

Answer 16

1st order neurons synapse in the dorsal horn of spinal cord and then very quickly cross over (decussate) to the opposite side. They then ascend in either the anterior or lateral spinothalamic tract. They synapse in the thalamus and 3rd order neurons synapse in the cortex.

Question 17

What sensations do A-Delta fibres recognise?

Answer 17

Heat, cold and sharp pain.

Question 18

What sensations do C fibres recognise?

Answer 18

Dull aching pain and itch. Plus thermal and mechanical.

Question 19

What fibres travel in the lateral spinothalamic route and the anterior spinothalamic route?

Answer 19

Lateral/Neospinothalamic - Carries both A-delta and C fibres

Anterior/palaeospinothalamic - Only carries C fibres. So sharp/dull pain and temp in lateral and only course non-discriminating (hard to locate) touch in anterior.

Question 20

What will occur as a result of a lesion in the lateral spinothalamic tract?

Answer 20

Decreased perception of pain and temperature on the contralateral side of the body, one or two dermatomes below the level of the lesion. It can also cause paraesthesia.

Question 21

Describe the travel of neurons in the spinocerebellar pathways

Answer 21

They travel up to the cerebellum to provide information about muscle length and proprioception for the control of posture and coordinated movement. This pathway only contains two neurons (second order neuron cell body located in dorsal horn and terminates in the vermis of cerebellum) and they remain on the ipsilateral side. SO lesion will affect the same side