Lecture 16 - 3rd Asessment - S.s

Somatosensory central mechanisms: Somatic sensory pathways: 1. Dorsal column system : (Medial lemniscal) Dorsal white column 2. Anterolateral system: (Spinothalamic tract) Anterior & lateral white columns Ventral spinoth. tract: touch Lateral spinoth. tract: pain & temp

Dorsal column system modalities: 1. Light touch 2. Vibration 3. Proprioception *Thalamus : ventral posterior lateral nucleus VPL

Anterolateral system modalities: 1. 2. 3. 4. 5.

Crude touch Pain (fast, slow) Temp (warm, cold) Tickle & itch Sexual sensation

*Thalamus: - VPL nucleus - posterior nuclei - intralaminar nuclei

Dorsal column properties: - Large myelinated fibers A-alpha: muscle spindle, Golgi tendon A-beta: light touch receptors - High velocity - Discrete connections, sp.c., B.stem, th, cx Accurate localization

Anterolateral system properties: - A-delta: fast pain, cold Type C: slow pain, crude touch, warmth - Low velocity - Diffuse connections, sp.c., brain stem, th, cx Poor localization

Lateral inhibition : e.g., in dorsal column S. S. cortical neurons Center is excited Surrounding is inhibited Inhibitory interneurons Sharpness (contrast)

Thalamus : - Modality detection - Crude localization Especially pain, thermal

Primary somatosensory cx : Postcentral gyrus S. S. area I Brodmann areas 1, 2, 3 Modality, intensity, location Modality – specific columns

Somatosensory association cx: Posterior parietal cortex Brodmann areas 5,7 Integrating S. S. modalities Meaning of somatosensory signal

Astereognosis : - Inability to recognize objects by touch - Damage to posterior parietal cx Size, shape, weight

Paresthesia : - Abnormal sensation e.g., numbness due to peripheral N. lesion

Hypoesthesia : Decreased sensation - Dorsal column lesion: Light touch, vibration, proprioception - Anterolateral lesion: Thermal, crude touch

Dermatomes : - Dorsal root injury  Loss of sensation - Dermatomal map is useful to determine the level of D. root injury

End of Lecture

Dorsal column system: * In spinal cord, dorsal column: Fasciculus gracilis: from leg Fasciculus cuneatus: from arm * Spinocerebellar tract: from leg Cuneocerebellar tract: from arm from m. spindle, Golgi, touch

* Amorphosynthesis: inability to recognize objects Agnosia: inab. to recognize vis. aud. tactile stimuli Apraxia: inab. to correctly move * 5, 7 proximal association areas : S. S. meaning * 39, 40 distal areas: integrate S. S., visual, auditory stimuli

Dorsal column system Medulla : dorsal column nuclei Crosses in medulla Medial lemniscus Ventral posterior lateral n. (VPL) (Th) S.S areas I & II Posterior parietal cortex

Anterolateral system : Crosses in sp. cord Reticular formation (Brain Stem) Ventral posterior lateral n. (VPL) (Th) Posterior nuclei (Th) Intralaminar nuclei (Th) S.S areas I & II Posterior parietal cortex