Ascending Pathways Flashcards
Sensory information from somatic segments enters the spinal cord to the brain via?
- Dorsal column-medial lemniscal system
2. Anterolateral System
Describe some of the differences between dorsal column-medial lemniscal and anterolateral columns
Dorsal column-medial lemniscal - Large myelinated fibres that conduct quickly (30-110m/s)
Anterolateral - Smaller fibres that conduct up to 40m/s
What type of sensory information is found in the dorsal column-medial lemniscal
Main ones, which we can clinically test are Fine touch, vibration and proprioception
What types of sensory information travels in the anterolateral system?
The main ones which can be clinically tested are pain, temperature and course touch. Others include; tickle, itch and sexual sensations
Describe how neurons travel in the Dorsal column-medial lemniscal
They carry signals up to the medulla in the dorsal columns of the spinal cord, then synapse and then cross to the opposite side in the medulla. Finally travel through the brainstem to thalamus via medial lemniscus
Describe how neurons travel in the anterolateral system
Enter spinal cord and synapse in dorsal horns of grey matter. Then cross to the opposite side of the cord and ascend through anterior and lateral white columns of cord. Finally terminate at all levels of the lower brain stem and in thalamus
What are the gracile and cuneate nuclei?
They are two different sections of the dorsal column-medial lemniscal. The Gracile nuclei are where neurons enter from the lower limb this is the more medial part of the column. The Cuneate nuclei are where neurons of the upper limb enter, this is the more lateral part of the column. The point in which these change is T6 (below T6 sensory neurons enter the gracile and above T6 they enter the cuneate)
How is somatotopic representation shown and why is it important
In the brain and spinal cord you have certain areas which are representative of upper and lower limb, this is important so you can know what parts of the body that will be affected in injury
Where does all this sensory information travel too?
Through the thalamus to the primary (somatic) sensory cortex which is located posterior to the post central sulcus of brain
Explain why some areas of the body have a disproportionately large area of representation on the somatic sensory cortex
Areas with higher discrimination such has face and hands take up a larger proportion of space in brain.
Describe the difference between somatosensory areas 1 and 2
Area 1 - has a high degree of localisation of different body parts
Area 2 - Poor localisation (face, arm, leg) area two is often not referred to.
Because neurons cross over, what does this mean?
Left side of the brain receives information from the right side of the body and vice versa.
What are the differences between the transmission of the anterolateral pathway from the dorsal column-medial lemniscal
- Velocity up to 1/2 of in dorsal column-medial lemniscal (8-40m/s)
- Degree of spatial localisation of signals is poor
- Gradations of intensities are poor
- Ability to transmit rapidly changing/rapidly repetitive signals is poor.
What are the two types of pain?
Fast pain and Slow pain
What are some of the features of fast pain
- Felt within 0.1s after pain stimuli.
- This is sharp pain, pricking pain, acute pain or electrical pain.
- A delta fibres
What are some of the features of slow pain
- Felt within 1s after pain stimuli and then increases over seconds/mins
- This is slow burning pain, aching, throbbing, nauseous or chronic pain.
- Usually associated with tissue destruction
- C fibres
Describe some of the features of pain receptors (nociceptors) (type of nerve fibres, location, excited by and their adaptation)
- Free nerve endings found in superficial layers of the skin or some in internal tissues.
- Excided by mechanical (fast pain), thermal (fast pain) and chemical pain. Slow pain is elicited by all three.
- Little to no adaptation but can increase in sensitivity
What is double pain sensation?
Sharp pain is transmitted by A delta fibres followed by slow pain which is transmitted through C fibres. (fast pain for immediate reaction, slow for reminder)
Where do the fast pain and slow pain pathways run through?
Fast pain - Neospinothalamic Tract
Slow pain - Paleospinothalamic pathway
Describe some of the features of the neospinothalamic tract?
- Fast type A delta fibres
- Terminate mainly in lamina 1 where they excite 2nd order neurons which give rise to long fibres that cross immediately opposite side of cord and then travel to brain in anterolateral columns.
Describe some of the features of the paleospinothalamic pathway?
- Mainly transmits slow-chronic type C pain fibres
- Fibres terminate in laminae 2 and 3, then most signals pass through an additional neuron in laminae 5. Finally give rise to long axons that mostly joining fibres from fast pathway, first crossing to other side of cord. Then travel to brain in anterolateral pathway
What is referred pain and how does it work?
Pain in location remote from tissue causing pain.
Mechanism - When visceral pain receptors stimulated, they are conducted through some of the same neurons conducting pain signals from skin. Person feels sensations originate in skin
What tracts do unconscious proprioception travel in and where do they get their inputs from?
The anterior (lower body) and posterior (upper body) spinocerebellar tracts They get their inputs from muscle spindles, Golgi tendons and touch receptors
For unconscious proprioception travelling in spinocerebellar pathways, what do the neurons do?
1st order synapse in dorsal horn and then 2nd order synapse in ipsilateral cerebellum. Therefore they double cross
Describe how you can get an Anterior Spinal Cord Syndrom and what is results in
Cause - Hyperextension Injury or infarction of anterior spinal artery
Results in - Loss of bilateral pain, temp and course touch but doesn’t effect the dorsal column-medial lemniscal. It also effects motor function below level of injury
What are the causes of Posterior Spinal Cord Syndrome and what can it result in?
Causes - Penetration injury, posterior spinal artery occlusion and multiple sclerosis.
Results in ipsilateral loss of fine touch, vibration and proprioception but maintains contralateral fine touch, vibration and proprioception and bilateral pain, temp and course touch. No effect to motor
Describe the causes of Central Spinal Cord Syndrome and what it results in
Causes - hyperextension and cord compression
Results in - Loss of pain and temp at same level and effects upper limbs more than lower limbs. Leads to sacral sparing and bladder dysfunction.
Describe what causes Brown- Sequard Syndrome and what it results in
Causes - Penetrating trauma
Results in - Same level ipsilateral loss of sensation. 1 level below will have ipsilateral loss of fine touch, vibration and proprioception. 1-2 levels below will result in contralateral loss of pain, temp and course touch.
