Somatic Sensory Pathways

Question 1

Somatic sensory pathways

Answer 1

Relay information from somatic receptors to primary somatosensory area in the cerebral cortex, and to the cerebellum

Question 2

Somatic sensory pathway consists of

Answer 2

First order neuron
Second order neuron
Third order neuron

Question 3

First order neuron

Answer 3

Somatic receptors in PNS to CNS

Cranial or spinal nerves

Question 4

Second order neuron

Answer 4

Brain stem or spinal cord to thalamus

This is where crossing over happens

Question 5

Third order neurons

Answer 5

Thalamus to primary somatosensory area (postcentral gyrus of parietal lobe)

Question 6

Relay Station

Answer 6

Region in CNS where neurons synapse with other neurons that are part of a particular pathway

Ex. the thalamus

Question 7

Two main ascending pathways

Answer 7

1. Posterior Column (Medial Lemniscus)

2. Anterolateral (Spinothalamic) pathway

Question 8

Posterior Column-Medial Lemniscus Pathway: impulses

Answer 8

Fine touch, stereognosis, weight discrimination, pressure, vibration, conscious proprioception

From limbs, trunk, neck, and posterior head

Question 9

Posterior Column: two parts

Answer 9

Gracile Fasciculus (lower body; medial)
Cuneate Fasciculus (upper body; joins around T3/T6)

Question 10

Anterolateral Pathway

Answer 10

AKA Spinothalamic Pathway

First order: Receptors of limb,trunk, neck –>
posterior grey horn (same level or pretty darn close). Soma in Dorsal Root Ganglion

Second order: Posterior grey horn –[decussate]–> VPN (thalamus) [called Spinothalamic now]

Third order: to primary somatosensory area

Question 11

Anterolateral Pathway: impulses

Answer 11

Lateral: Pain and temperature
Anterior: tickle and itch, crude touch and pressure.

Question 12

Vibration: Pathway

Answer 12

Posterior column and anterolateral pathway

Question 13

Trigeminothalamic Pathway

Answer 13

Most somatic sensations (tactile, thermal, pain) from the face, nasal cavity, oral cavity and teeth.

First order (trigeminal nerve): sensory receptor –> pons or medulla. Cell body in trigeminal ganglion

Second order: Trigeminal nuclei –[decussation]–> VPN

Third order: VPN –> primary somatosensory area

Question 14

Spinocerebellar Tracts

Answer 14

Two: posterior and anterior

Unconscious proprioception from trunk and lower limbs

Two neuron system
Ipsilateral
Do not decussate

Question 15

Syphillis

Answer 15

Treponema pallidum

Tertiary stage: progressive degeneration of the posterior columns –> loss of sensation; uncoordinated and jerky gait due to loss of proprioception

Question 16

Ascending Pathways: Cell Bodies

Answer 16

Posterior Column: dorsal root ganglia/cuneate or gracile nuclei/ Ventral posterior nuclei

Anterolateral: DRG/posterior grey horn/VPN

Trigeminothalamic: Trigeminal ganglion/trigeminal nuclei (pons or medulla)/VPN

Spinocerebellar: DRG/medial grey horn (maybe?)

Question 17

Syphillis (tertiary)

Answer 17

Causes progressive degeneration of the posterior portions of the spinal cord

Loss of somatic sensations
Proprioceptors impulses don’t reach cerebellum.

Uncoordinated, jerky