Quiz 123 · Sensory Cortex

Answers to Quiz 122 · Thalamus

1. The anterior group of thalamic nuclei lies:

   Answer: In the fork of the internal medullary lamina

   The Y-shaped internal medullary lamina splits the thalamus into anterior, medial and lateral groups, and its fork encloses the anterior group. The reticular nucleus lies outside the external lamina; the intralaminar nuclei sit within the internal one. Revise thalamus: nuclei, functions and thalamic syndrome

2. Which of these is a specific relay nucleus of the thalamus?

   Answer: Ventral posterolateral nucleus

   VPL passes medial lemniscus and spinothalamic input to one cortical area, the somatosensory cortex (areas 3, 1 and 2). The centromedian, reticular and midline nuclei are nonspecific. Revise thalamus: nuclei, functions and thalamic syndrome

3. Which thalamic nucleus forms part of the Papez circuit?

   Answer: Anterior nucleus

   The anterior nucleus receives the mammillothalamic tract from the mammillary body and projects to the cingulate gyrus, so it serves recent memory and emotion. Revise thalamus: nuclei, functions and thalamic syndrome

4. Which pairing of a thalamic nucleus with its cortical target is correct?

   Answer: MGB → auditory cortex

   The MGB relays hearing to the auditory cortex; the LGB relays the optic tract to the visual cortex. The cingulate gyrus is fed by the anterior nucleus, and VA projects to the premotor cortex. Revise thalamus: nuclei, functions and thalamic syndrome

5. Within the VPL nucleus, cutaneous input ends mainly in the:

   Answer: Central core

   VPL is a core of cutaneous input inside a shell of deep input. Its dorsal part takes deep input and its anterior surface takes muscle input. Revise thalamus: nuclei, functions and thalamic syndrome

6. Which thalamic nuclei carry nociceptive input yet have no somatotopic map?

   Answer: Posterior nuclei (PO)

   PO mainly passes on pain: a large PO lesion causes analgesia and stimulating it causes pain. VPL, by contrast, maps face, arm and leg from medial to lateral. Revise thalamus: nuclei, functions and thalamic syndrome

7. The thalamic reticular nucleus differs from the other nonspecific nuclei because it:

   Answer: Sends no fibres to the cortex

   RET is linked both ways with the other thalamic nuclei but does not project to the cortex, so its role is to modulate thalamic activity. Its cells do respond to many somatosensory modalities. Revise thalamus: nuclei, functions and thalamic syndrome

8. Low-frequency stimulation of the intralaminar nuclei of the thalamus produces:

   Answer: EEG synchronization over the same side

   Synchronization of the EEG over the cortex of the same side is the recruiting response. High-frequency stimulation does the reverse: arousal and desynchronization. Revise thalamus: nuclei, functions and thalamic syndrome

9. Which of these is NOT a function of the thalamus?

   Answer: Relaying smell to the cortex

   The thalamus relays every special sense except olfaction. It also perceives pain, temperature and crude touch to some degree, and supplies the sensory feedback that refines movement. Revise thalamus: nuclei, functions and thalamic syndrome

10. After a posterior cerebral artery branch is blocked, a man loses discriminative touch and pressure over the left half of his body. Pain and temperature are only mildly affected, and his face feels normal. The lesion is most likely in the:

    Answer: Right VPL nucleus

    Thrombosis of the posterolateral branch of the posterior cerebral artery damages VPL, and the loss is on the opposite side, so left-sided signs mean a right VPL lesion. The medial VPM is usually spared, which is why the face is normal. Revise thalamus: nuclei, functions and thalamic syndrome

11. Besides the sensory loss, which motor features occur in thalamic syndrome?

    Answer: Low tone, marked weakness and ataxia

    The book lists decreased tone, profound weakness and ataxia, from loss of the cerebellar relay to motor areas 4 and 6. Flinging movements (hemiballismus) come from the subthalamic nucleus instead. Revise thalamus: nuclei, functions and thalamic syndrome

12. An electrical lesion of the intralaminar nuclei of the thalamus:

    Answer: Relieves chronic pain, sparing acute pain

    Destroying the intralaminar nuclei relieves chronic, suffering-type pain, yet acute pain is still perceived. Revise thalamus: nuclei, functions and thalamic syndrome

13. A lesion of the body of Luys produces:

    Answer: Hemiballismus

    The body of Luys is the subthalamic nucleus, which is linked both ways with the globus pallidus. Damage to it causes hemiballismus. Revise thalamus: nuclei, functions and thalamic syndrome

14. Which of these belongs to the epithalamus?

    Answer: Pineal gland

    The epithalamus forms the roof of the third ventricle: the pineal gland, the habenular nuclei and the striae medullaris. The subthalamic nucleus lies in the subthalamus; the pulvinar and MGB are thalamic nuclei. Revise thalamus: nuclei, functions and thalamic syndrome

15. The ventral lateral (VL) nucleus relays cerebellar input to:

    Answer: Motor areas 4 and 6

    VL takes the dentato-rubro-thalamic tract and projects to motor areas 4 and 6. Areas 3, 1 and 2 are fed by the ventrobasal complex, the cingulate gyrus by the anterior nucleus, and the inferior parietal lobe by the pulvinar. Revise thalamus: nuclei, functions and thalamic syndrome

14 questions on chapter 123. Pick one answer for each, then save. Your answers stay in this browser, and the right ones are shown at the top of the next quiz.

1. Somatosensory area I (SI) is made up of Brodmann's areas:

3, 1 and 21, 2 and 54 and 65 and 7b

2. Somatosensory area II (SII) is located in the:

Posterior parietal lobeFloor of the central sulcusMedial wall of the parietal lobeSuperior wall of the Sylvian fissure

3. Which part of SI sends the main projection to the thalamus?

Area 2Area 1Area 3aArea 3b

4. The only thalamic input to area 5 comes from the:

Medial geniculate bodyVentral posterolateral nucleusVentrobasal nucleusLateral posterior nucleus

5. Which area of SI responds to both cutaneous and deep stimulation?

Area 3bArea 2Area 1Area 3a

6. In the columnar organization of SI, a column in area 3a responds mainly to:

Skin input from slowly adapting receptorsSkin input from rapidly adapting receptorsDeep input from rapidly adapting receptorsDeep input from slowly adapting receptors

7. The whole body is mapped twice in SI, once in each of:

Areas 1 and 2Areas 3a and 2Areas 3b and 1Areas 3a and 3b

8. In the sensory homunculus, the lower limb is represented on the:

Superior bank of the lateral sulcusMedial surface of the hemisphereLateral part of the postcentral gyrusDorsolateral part of the postcentral gyrus

9. Which body parts have the largest representation in the sensory homunculus?

Lips and fingersThigh and hipTrunk and backNeck and shoulder

10. Which sensation is least affected by a lesion of the somatosensory cortex?

StereognosisProprioceptionPainFine touch

11. Damage confined to area 5 specifically affects:

StereognosisLearning of discriminative tasksPain and temperatureHard–soft discrimination

12. Most neurons of somatosensory area II respond to:

Light touch of hair or skinMovement of muscles and jointsVisual stimuli from the other sidePainful heating of the skin

13. A lesion of the parietal association cortex of the non-dominant hemisphere typically produces:

Loss of smooth–rough discriminationConstructional apraxia and hemineglectLoss of pain and temperatureA disorder of language

14. SI and SII receive monoaminergic input mainly from the:

Locus ceruleus and raphe nucleiInferior olive and nucleus ambiguusMammillary body and habenulaSubstantia nigra and red nucleus

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