Ascending Tracts Flashcards
Conscious ascending tracts
Dorsal column-medial lemniscal
Anterolateral system
Unconscious ascending tracts
Spinocerebellar tracts
Function of dorsal column-medial lemniscal pathway
Carries fine touch, vibration and proprioception
2 different pathways of dorsal column-medial lemniscal pathway first order neurons
Signals from upper limb (T6 and above)
Signals from lower limb (below T6)
dorsal column-medial lemniscal pathway signals from upper limb
Travel in fasciculus cuneatus (lateral part of dorsal column)
Synapse in nucleus cuneatus of medulla
dorsal column-medial lemniscal pathway signals from lower limb
Travel in fasciculus gracilis (medial part of dorsal column)
Synapse in nucleus gracilis of medulla
Where do the dorsal column-medial lemniscal pathway first order neurons synapse
Medulla
Where is the Fasciculus gracilis
Medial part of dorsal column
Where is the Fasciculus cuneatus
Lateral part of dorsal column
Where do the second order neurones of the dorsal column-medial lemniscal pathway decussate
Medulla
dorsal column-medial lemniscal pathway second order neurones
Begin in cuneate or gracilis nucleus
Decussate and travel in the contralateral medial lemniscus
Synapse at thalamus
Where do the 2nd order neurons meet the 3rd order neurons of the dorsal column-medial lemniscal pathway
Thalamsu
What do the 2nd order neurons of the dorsal column-medial lemniscal pathway travel to the thalamus in
Contralateral medial lemniscus
dorsal column-medial lemniscal pathway third order neurons
transmit the sensory signals from the thalamus to the ipsilateral primary sensory cortex of the brain
ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule and terminate at the sensory cortex.
Where do the third order neurons of the dorsal column-medial lemniscal pathway terminate
Sensory cortex
Where does the third order neurons of the dorsal column-medial lemniscal pathway travel through
Ventral posterolateral nucleus of thalamus
Internal capsule
To sensory cortex
2 parts of the Anterolateral system
Anterior Spinothalamic tract
Lateral Spinothalamic tract
Function of anterior Spinothalamic tract
Crude touch and pressure
Function of lateral Spinothalamic tract
Pain and temperature
Anterolateral system first order neurons
arise from the sensory receptors in the periphery.
They enter the spinal cord, ascend 1-2 vertebral levels, and synapse at the tip of the dorsal horn – an area known as the substantia gelatinosa.
Where do the Anterolateral pathway first order neurons synapse
Substantia gelatinosa (tip of dorsal horn)
Where do the second order neurons of the Anterolateral tract decussate
Within spinal cord to form 2 tracts
Where do the second order neurons of the Anterolateral system synapse
Thalamus
Anterolateral system third order neurons
Thalamus to ipsilateral primary sensory cortex
Ascend from ventral posterolateral nucleus of thalamus, through internal capsule
Function of posterior Spinocerebellar tract
Carries proprioceptive information form the lower limbs to ipsilateral cerebellum
4 individual pathways of Spinocerebellar tract
Posterior Spinocerebellar tract
Cuneocerebellar tract
Anterior Spinocerebellar tract
Rostral Spinocerebellar tract
Function of Cuneocerebellar tract
Proprioceptive information from upper limbs to ipsilateral cerebellum
Function of anterior Spinocerebellar tract
Proprioceptive information from lower limbs
Decussate twice so terminate in ipsilateral cerebellum
Function of rostral Spinocerebellar tract
proprioceptive information from the upper limbs to the ipsilateral cerebellum.
Which 2 tracts carry proprioceptive information from upper limbs by the Spinocerebellar tracts
Cuneocerebellar tracts
Rostral Spinocerebellar tracts
Which 2 tracts carry proprioceptive information from lower limbs by Spinocerebellar tracts
Posterior Spinocerebellar tracts
Anterior Spinocerebellar tracts
Lesions of Spinocerebellar tracts
ipsilateral loss of muscle co-ordination.
However, the spinocerebellar pathways are unlikely to be damaged in isolation – there is likely to be additional injury to the descending motor tracts. This will cause muscle weakness or paralysis, and usually masks the loss of muscle co-ordination.
Lesion of DCML
loss of proprioception and fine touch. However, a small number of tactile fibres travel within the anterolateral system, and so the patient is still able to perform tasks requiring tactile information processing.
If the lesion occurs in the spinal cord (which is most common), the sensory loss will be ipsilateral – decussation occurs in the medulla oblongata.
DCML lesions can be seen in vitamin B12 deficiency and tabes dorsalis (a complication of syphilis).
Lesions of Anterolateral system
impairment of pain and temperature sensation. In contrast to DCML lesions, this sensory loss will be contralateral (the spinothalamic tracts decussate within the spinal cord).
Brown-Séquard syndrome refers to a hemisection (one sided lesion) of the spinal cord. This is most often due to traumatic injury, and involves both the anterolateral system and the DCML pathway:
DCML pathway – ipsilateral loss of touch, vibration and proprioception.
Anterolateral system – contralateral loss of pain and temperature sensation.
It will also involve the descending motor tracts, causing an ipsilateral hemiparesis.
Brown - Séquard syndrome
hemisection (one sided lesion) of the spinal cord. This is most often due to traumatic injury, and involves both the anterolateral system and the DCML pathway:
DCML pathway – ipsilateral loss of touch, vibration and proprioception.
Anterolateral system – contralateral loss of pain and temperature sensation.
It will also involve the descending motor tracts, causing an ipsilateral hemiparesis.
Sensory modalities
Nociceptors
Mechanoreceptors
Thermoreceptors
Nociceptors
receptors which respond to noxious stimuli (stimuli would result in tissue injury if it were to persist)
• activation results in sensation of pain
• Receptors are free nerve endings on ends of type A-delta fibres and C fibres
• Can be categorised into mechanical, thermal, chemical or Polymodal
Mechanoreceptors
respond to deformation by means of pressure, touch, vibration or stretch
• located in joint capsules, ligaments, tendons, muscle and skin
Types of Mechanoreceptors
Merkel’s disc
Meissner’s corpuscles
Pacinian corpuscles
Ruffini corpuscles
Muscle spindles and Golgi tendon organs
Merkel’s disc
tonic receptors in skin that respond to pressure. Key role in differentiating textures
Meissner’s corpuscles
phasic receptors in skin, namely in palms of hands, soles of feet, lips and tongue. Detect initial contact or slipping of contact
Pacinian corpuscles
phasic receptors in dermis, hypodermis, ligaments and external genitalia. Respond to high-frequency vibrations
Ruffini corpuscles
tonic receptors in dermis, ligaments and tendons. Respond to stretch and signal position and movement of fingers
Muscle spindles and Golgi tendon organs
found in skeletal muscle and detect stretch as well as involved in proprioception. Transmitted by dorsal column-medial lemniscus pathway
Thermoreceptors
respond to changes in temperature
• found in skin, liver, skeletal muscle and hypothalamus
• Warm temperatures = C fibres
• Cold temperatures = C and A-delta fibres
• Transmitted via lateral Spinothalamic tract
Type of fibres that transmit warm temperatures
C fibres
Type of fibres that transmit cold temperatures
C fibres and A-delta fibres
Spinothalamic tract conveys Nociceptive information to….thalamus
Contralateral
Where in the spinal cord is the spinothalamic tract found
Anterolateral white matter
A 78-year-old lady presents to her GP surgery with an intensely itchy vesicular rash in two separate horizontal lines at the level of the nipple and umbilicus respectively.
Which dermatomal distribution is this affecting?
T4 and T10
