Ascending (sensory) pathways

Question 1

ascending pathways: start in periphery

Answer 1

• The Anterolateral pathway
•The Dorsal column - medial lemniscus pathway
•The spinocerebellar tracts:
- Posterior spinocerebellar & Cuneocerebellar
- Anterior spinocerebellar & Rostral spinocerebellar

Question 2

GENERAL SOMATOSENSORY MODALITIES:

Answer 2

1. Nociception
2. Temperature
3. Crude touch
4. Discriminative touch (localised + 2 point discrimination) 5. Pressure
5. Vibratory sense
6. Conscious proprioception
7. Subconscious proprioception

Question 3

lesion on the side can result in

Answer 3

• loss of tactile discrimination, vibratory and proprioceptive sensations - spatial paralysation on same side
• loss of pain and temp sensationed, impared tactile sense on other side

Question 4

2 neurons

Answer 4

pathway to brainstem or cerebellum:

1. Receptors
2. Afferent neurons
3. Spinal cord
4. Brainstem + / - Cerebellum

Question 5

3 neurons

Answer 5

pathway to the cerebral cortex
1. Receptors
2. Afferent neurons 
3. Spinal cord
4. Brainstem
5. Thalamus
6. Internal capsule 
7. Corona radiata 
8. Cerebral cortex
2nd neuron always decussates

Question 6

Different neurons in different pathways

Answer 6

Conduction velocity depends on axon diameter and myelination
1a and 1b are larger neurons so diameter is bigger = fast conduction velocty
c fibres = unmylinated, small and slow

Question 7

fibre type: 1a

Answer 7

receptor/modality: From muscle spindle (proprioception)

Question 8

fibre type: 1b

Answer 8

receptor/modality: From golgi tendon organs (proprioception) & Ruffini endings (pressure)

Question 9

fibre type: 11

Answer 9

receptor/modality: From skin receptors

Question 10

fibre type: 3/ A delta

Answer 10

receptor/modality: From free nerve endings for fast ‘pain’ & temperature

Question 11

fibre type: 4 / C fibres

Answer 11

receptor/modality: From free nerve endings for slow ‘pain’ & temperature

Question 12

3 main ascending somatosensory pathways from the BODY:

Answer 12

Reach consciousness: have 3 neurons

1. Anterolateral (spinothalamic)
2. Dorsal column – medial lemniscus pathway

Subconscious level (2 neurons)
3. Spinocerebellar pathways -

Question 13

Anterolateral pathway functions:

Answer 13

nociception, temperature & crude touch (not localised)
Receptors = nociceptors, thermoreceptors, mechanoreceptors = free nerve endings of A delta & C fibres
1st order neuron = A delta & C fibres / neurons
Cell body in dorsal root ganglion relatively slow

Question 14

Lissauer’s tract:

Answer 14

Some 1st order neurons enter the dorsal horn & synapse.
Others divide into ascending & descending branches which travel in the dorsolateral tract before entering the dorsal horn & synapsing. Is white matter between the surface of the spinal cord and tip of dorsal horn

Question 15

Anterolateral pathway synapses

Answer 15

1st order neurons synapse primarily in laminae I & II with either a 2nd order neuron or interneurons

Question 16

Anterolateral pathway

Answer 16

2nd order neuron
decussates via the ventral white commissure within 1-2 spinal segments & ascends contralaterally in the anterior 1⁄2 of the lateral column

Question 17

Somatotopic organisation of the anterolateral system

Answer 17

new fibres join the anterolateral tract at its anteromedial edge
- fibres from sacral region are lateral, fibres from the cervical area are located medially
Tract gets smaller as it ascends as some fibres terminate in the brainstem

Question 18

Anterolateral pathway: spinothalamic

Answer 18

conscious awareness of pain

Question 19

Anterolateral pathway: spinoreticular

Answer 19

arousal / attention

Question 20

Anterolateral pathway: spinomesencephalic

Answer 20

intrinsic pain control mechanisms

Question 21

Anterolateral pathway: spinohypothalamic

Answer 21

autonomic responses to nociception

Question 22

Dorsal column – medial lemniscus pathway functions:

Answer 22

discriminative touch, pressure, vibration & proprioception

Receptors = skin receptors & mechanoreceptors
Proprioception uses information from mechanoreceptors & skin receptors
muscle spindles; Golgi tendon organs; Nerve endings in joint capsule; mechanoreceptors in joint connective tissue
1st order neurons: 1a & 1b
cell body in the dorsal root ganglion
fast, myelinated afferents

Question 23

anterolateral exact pathway

Answer 23

1st order neuron synapse at gelatino substantia > 2nd order neuron decussate at lvl of spinal cord d +/- 1 (crosses ventral commissure to anterolateral area) > ascends to medulla > tegmentum > ventral posterolateral nucleus > posterior internal capsule > post central gyrus

Question 24

Dorsal column – medial lemniscus pathway:

Answer 24

1st order neuron enters the dorsal funiculus & ascends ipsilaterally to medulla, at successive rostral levels new fibres are added to the lateral edge of the existing tract
ascend through brainstem as the medial lemniscus rostral pons > 2nd order neuron decussates in medulla
1st order neuron synapses with the 2nd order neuron in Nucleus gracilis/Nucleus cuneatus > 1st order neuron ascends in dorsal column

• Sacral fibres are located medially, cervical fibres laterally in the dorsal columns

Question 25

Ventral posterolateral nucleus (VPL)

Answer 25

= somatosensory information from body

Question 26

Somatotopic organisation of the internal capsule

Answer 26

1. Anterior limb
2. Genu
3. Posterior limb: somatosensory
4. Retrolenticular part
5. Sublenticular part