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).
