Ascending Neural Pathways Flashcards
Where in the brain does sensory information go ?
Through talamus, to primary (somatic) sensory cortex
How many somatosensory areas are there? What is their main differences ?
2
- Area I much more extensive
- Area 1 does not need area II but area II needs area I to function
- Area I: Is a high degree of localisation of different body parts (Thigh, Thorax, Neck, Shoulder, Hand, Fingers, Tongue, Intra-abdominal)
- Area II: poor localisation of different body parts (face, leg, arm)
Does each lateral side gets sensory info from the same, opp side of body, or both ?
Each lateral side gets sensory info almost exclusively from opp side of body.
Identify organs/body parts whose representation in somatosensory area I of the cortex is large.
Identify organs/body parts whose representation in somatosensory area I of the cortex is small.
Lips, face, thumb get large amounts of space
Trunk and lower limbs assigned small amount of space
How do almost all sensory info from somatic segments of body enters the spinal cord ?
Through the dorsal roots of the spinal nerves.
What are the names of the possible pathways for sensory information once they have entered the spinal cord, to arrive to the brain ? Do these systems meet at any point ?
- Dorsal column–medial lemniscal system
- Anterolateral system (=Spinothalamic tracts)
Two systems come back together partially at the level of the thalamus.
- Spinocerebellar system
What are the different ascending tracts of the spinal cord ?
FASCICULUS GRACILIS and FASCICULUS CUNEATUS (make up Dorsal column–medial lemniscal system)
DORSAL AND VENTRAL SPINOCEREBELLAR
SPINOTHALAMIC TRACTS (anterolateral system)
Where does fasciculus gracilis tract carry sensory information from ?
-From lower body extremities
Where does fasciculus cuneatus tract carry sensory information from ?
-From upper body extremities
Where does dorsal spinocerebellar tract carry sensory information from ?
-From muscle spindles
Where does ventral spinocerebellar tract carry sensory information from ? Does it carry a specific kind of information ?
- From Golgi Organs, touch receptors
- Yes, prioreceptive information
Where do spinothalamic tracts carry sensory information from ? Does it carry a specific kind of information ?
-Yes, pain
Where in the spinal cord does the Fasciculus gracilis enter ?
Up to T6
Where in the spinal cord does the Fasciculus Cuneatus enter ?
Above T6
What are the main differences between the path of sensory information in the Dorsal column-Medial Lemniscal System, and in the Anterolateral system ?
DORSAL COLUMN-MEDIAL LEMNISCAL SYSTEM
Nerve fibres entering dorsal columns pass
uninterrupted up to the dorsal medulla –> Synapse in dorsal column nuclei (the cuneate and gracile nuclei) –> Second-order neurons cross immediately to opposite side of brain stem and continue up through medial lemnisci to the thalamus –> In the thalamus, the medial lemniscal fibres terminate in the thalamic sensory relay area, called the ventrobasal complex –> From the ventrobasal complex, third-order nerve fibres project mainly to the post-central gyrus of the cerebral cortex ie somatic sensory area I.
ANTEROLATERAL SYSTEM
Enter spinal cord via dorsal spinal root nerves –> Synapse in dorsal horns of spinal grey matter –> Cross immediately in the anterior commissure of the cord to the opposite anterior and lateral white columns. –> Then turn up towards brain via the anterior spinothalamic and lateral spinothalamic tracts –> Upper Terminus:
(1) throughout the reticular nuclei of the brain stem and
(2) in two different nuclear complexes of the thalamus, the ventrobasal complex and the intralaminar nuclei.
What are the main differences in myelination and signal velocity between the DORSAL COLUMN-MEDIAL LEMNISCAL SYSTEM, and ANTEROLATERAL SYSTEM.
DORSAL COLUMN-MEDIAL LEMNISCAL SYSTEM
• Large myelinated fibres.
• Signal velocity to brain ~30-110m/s.
ANTEROLATERAL SYSTEM
• Smaller myelinated fibres.
• Signal velocity to brain ~8-40m/s.
What are the main differences in modalities transmitted between the DORSAL COLUMN-MEDIAL LEMNISCAL SYSTEM, and ANTEROLATERAL SYSTEM.
DORSAL COLUMN-MEDIAL LEMNISCAL SYSTEM
- Touch sensations requiring a high degree of localisation of the stimulus
- Touch sensations requiring transmission of fine gradations of intensity
- Phasic sensations, such as vibratory sensations
- Sensations that signal movement against the skin
- Position sensations from the joints
- Pressure sensations related to fine degrees of judgment of pressure intensity
ANTEROLATERAL SYSTEM
- Pain
- Thermal sensations: both warmth and cold sensations
- Crude touch and pressure sensations capable only of crude localising ability on the surface of the body
- Tickle and itch sensations
- Sexual sensations
Which kind of nerve fibers make up the dorsal column-medial lemniscal pathway ?
large diameter, fast Aβ fibres
What are some pathologies associated with the Dorsal column-medial lemniscal pathway ?
- Gait ataxia (brain is deprived of information about the position of the feet)
- Upper extremity ataxia
-Paraesthesias in the distal parts of the extremities (due to ectopic discharge in damaged dorsal column axons and may be present before any abnormalities are detectable on neurologic examination)
How can patients affected by sensory ataxia minimise this ?
Compensate with vision
How may Dorsal column function be tested ?
By testing the ability to feel changes in the position of toes and fingers or feel a tuning fork vibration without lookin (Finger/toe proprioception is not lost until about 75% of posterior column axons have ceased to function)
Do signals in the anterolateral system require:
- Highly discrete localisation
- Discrimination of fine gradations of intensity
- No
2. No
What are the main upper terminuses of the two spinothalamic tracts ? Where are tactile signals mainly transmitted ? Where are pain signals mainly transmitted ?
(1) throughout the reticular nuclei of the brain stem and
(2) in two different nuclear complexes of the thalamus, the ventrobasal complex and the intralaminar nuclei.
In general, the tactile signals are transmitted mainly into the ventrobasal complex, terminating in some of the same thalamic nuclei
where the dorsal column tactile signals terminate. From here, the signals are transmitted to the somatosensory cortex along with the signals from the dorsal columns.
Conversely, only a small fraction of the pain signals project directly to the ventrobasal complex of the thalamus.
Instead, most pain signals terminate in the reticular nuclei of the brain stem and from there are relayed to the intralaminar nuclei of the thalamus where the pain signals are further processed.
What kinds of fibres do the lateral Spinothalamic route contain ? Which modality does that transmit ?
Lateral Spinothalamic route
– Mixture of Aδ and C fibres carrying information about pain and temperature via Aδ heat or cold activated fibres and C fibres (dull pain and itch).
What kinds of fibres do the anterior Spinothalamic route contain ? Which modality does that transmit ?
Anterior Spinothalamic route
– C fibres carrying information about coarse, non discriminating touch via mechanosensitive fibres
What are some pathologies associated with the Spinothalamic pathway ?
- Decreased perception of pain and temperature on the contralateral side of the body, always one or two dermatomes below the level of the lesion.
- Paraesthesia
- Patients become aware of their pain and temperature deficit when they experience painless cuts or burns
What kinds of receptors detect pain ? How ?
Nociceptors, using nerve free endings
What are the 3 which stimuli excite pain receptors ?
Mechanical, thermal, chemical.
Which of the 3 stimuli which excites pain receptors elicits fast pain ? slow pain ?
Fast pain: mechanical and thermal stimuli
Slow pain: elicited by all 3 types
Do nociceptors show adaptation ?
Show little adaptation, sometimes not at all.
Give an example where excitation of nociceptors can become progressively greater.
Hyperalgesia
How fast is fast-sharp pain transmitted ? Via which types of nerve fibers ?
Transmitted via small Aδ fibres at ~6-30m/s
How fast is slow-chronic pain transmitted ? Via which types of nerve fibers ?
Transmitted via C fibres at ~0.5-2m/s.
What is meant by double pain sensation ?
Sharp pain transmitted by Aδ fibres followed second or so later by slow pain transmitted by C fibres.
What is the point of both pains in double pain sensation ?
Fast pain allows for immediate (re)action, slow pain
tends to gets greater over time and stimulates person to keep trying to relieve cause of pain.
What is the function of Capsaicin wrt Nociception ?
-Mimics chemicals produced by the body at sites of tissue damage
How does Capsaicin mimic chemicals produced by the body at sites of tissue damage ?
- Capsaicin activates the Trp1 channel in nociceptor neurons which opens to allow Ca2+ and Na+ into the cell
- This causes depolarisation and the production of an action potential.
What is the result of over stimulation of Trp1 receptors with capsaicin ? How is this applied clinically ?
Causes desensitisation. Capsaicin used (with varying success) in the treatment of chronic pain conditions such as arthritis.
What is referred pain ?
Pain in a location remote from tissue causing pain.
What is the likely mechanism for referred pain ?
- Branches of visceral pain fibres synapse in spinal cord on same 2nd- order neurons that receive signals from skin.
- When visceral pain receptors are stimulated, pain signals from viscera are conducted through some of the same neurons conducting pain signals from skin, so person feels sensations originate in skin.
What is the main objective of the spinocerebellar pathways ?
Takes information about the body’s position and movements to the cerebellum for integration.
What are the two principal routes for information in the spinocerebellar pathway ?
– anterior (ventral) route
– posterior (dorsal) route
How many neurons does each of ventral spinocerebellar pathway and dorsal spinocerebellar pathway have ?
Each pathway (ventral tract or dorsal tract) contains only two neurons along its length (1st and 2nd order).
Describe the path of the nerve fibers in the spinocerebellar pathway.
Cell bodies of the second order neurons are located in the dorsal horn of the spinal cord, and terminate in the vermis of the cerebellum –> Dorsal tract neurons ascend ipsilaterally and enter the cerebellum via the inferior peduncle –> Ventral tract neurons ascend contralaterally and enter the cerebellum via the Superior peduncle
What are some pathologies associated with the spinocerebellar pathway ?
- FRIEDREICH’S ATAXIA
- Inherited disease where spinocerebellar tract becomes increasingly ineffective.
What is the cause of Friedreich’s Ataxia ?
Caused by multiple repeats of a gene for the protein Frataxin which is responsible for iron metabolism in mitochondria.
What are the symptoms of Friedreich’s Ataxia ?
- Progressively uncoordinated arm and leg movements
- Wide based ‘reeling’ gait
- Intention tremor
- Similar to other spinocerebellar dysfunctions
