Quiz 124 · Sensory Abnormalities

Answers to Quiz 123 · Sensory Cortex

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

   Answer: 3, 1 and 2

   SI, in the postcentral gyrus, includes area 3 (3a and 3b), area 1 and area 2. Areas 4 and 6 are the motor cortex, and area 5 is the association cortex. Revise somatosensory cortex

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

   Answer: Superior wall of the Sylvian fissure

   SII lies in the upper wall of the Sylvian (lateral) fissure. The supplementary sensory area is on the medial parietal wall, SI on the back wall and floor of the central sulcus, and area 5 in the posterior parietal lobe. Revise somatosensory cortex

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

   Answer: Area 3a

   Every sub-area of SI is linked both ways with the VPL nucleus, but the main projection back to the thalamus comes from area 3a. Revise somatosensory cortex

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

   Answer: Lateral posterior nucleus

   Area 5 takes thalamic input from the lateral posterior nucleus alone, which gets no direct somatosensory input; most of its input comes from SI and SII. SI is linked with VPL, and SII receives from the ventrobasal nucleus. Revise somatosensory cortex

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

   Answer: Area 1

   Area 1 responds to both. Area 3b responds mainly to skin stimuli, while areas 3a and 2 respond mainly to deep input from muscles and joints. Revise somatosensory cortex

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

   Answer: Deep input from slowly adapting receptors

   Neighbouring columns process different modalities: a column in area 3a takes deep input, mainly from slowly adapting mechanoreceptors, while one in area 3b takes skin input from rapidly adapting ones. Revise somatosensory cortex

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

   Answer: Areas 3b and 1

   SI holds two complete body maps, one in area 3b and one in area 1, and this map is the sensory homunculus. Revise somatosensory cortex

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

   Answer: Medial surface of the hemisphere

   The face is mapped laterally, the hand and upper limb dorsolaterally, and the lower limb on the medial surface of the hemisphere. Revise somatosensory cortex

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

   Answer: Lips and fingers

   Cortical area follows use: the lips (speech) and the fingers (skilled work) get the most cortex, while the trunk and back get little. Revise somatosensory cortex

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

    Answer: Pain

    Pain and temperature are the least impaired after a cortical lesion. Proprioception and fine touch are the most affected, and stereognosis is almost abolished. Revise somatosensory cortex

11. Damage confined to area 5 specifically affects:

    Answer: Stereognosis

    An area 5 lesion affects stereognosis while other touch stays intact. Loss of hard–soft discrimination points to area 1, and failure to learn discriminative tasks to area 3. Revise somatosensory cortex

12. Most neurons of somatosensory area II respond to:

    Answer: Light touch of hair or skin

    Most SII neurons answer light mechanical stimulation of hair or skin, through rapidly adapting mechanoreceptors, and respond poorly to deep stimuli. Revise somatosensory cortex

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

    Answer: Constructional apraxia and hemineglect

    The non-dominant association cortex handles spatial relations, so its loss distorts copied figures and makes the patient deny the opposite side of his body. Language belongs to the dominant hemisphere. Revise somatosensory cortex

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

    Answer: Locus ceruleus and raphe nuclei

    Both SI and SII take monoaminergic fibres from brainstem nuclei, chiefly the locus ceruleus and the raphe nuclei. Revise somatosensory cortex

15 questions on chapter 124. 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. A peripheral nerve is damaged by chronic compression. Which sensations go first, while the others are still felt?

Touch and pressurePain and pressurePain and temperatureTemperature and touch

2. Anesthesia of both hands and both feet, with the trunk spared, points to:

A single sensory nerve root lesionHemisection of the spinal cordA one-sided thalamic lesionA distal, symmetrical polyneuropathy

3. Sensory ataxia in a polyneuropathy is explained by damage to:

Thin fibres carrying pain and temperatureThe lateral spinothalamic tractThe corticospinal tractLarge kinesthetic fibres carrying position and vibration

4. A herniated intervertebral disc compresses one sensory nerve root. What is the expected finding?

Total anesthesia of the whole segment suppliedLoss of touch in the hands and feet aloneLoss of pain and temperature on the other sideSegmental anesthesia that is incomplete, because roots overlap

5. In your book's scheme of cord syndromes, the tabetic syndrome is produced by a lesion of:

The zone around the central canalOne posterior columnBoth posterior columnsThe ventral half of the cord

6. Posterior column syndrome closely resembles a cortical sensory lesion. According to your book, which finding tells them apart?

Loss of vibration senseFailure to recognize objects by touchLoss of pain sensationA wider two-point discrimination

7. A stab wound hemisects the cord on the right at the mid-thoracic level. Below the injury you expect:

Right-sided loss of vibration and position sense, left-sided loss of pain and temperatureLeft-sided loss of vibration and position sense, right-sided loss of pain and temperatureLoss of every modality on the right side onlyLoss of pain and temperature on both sides, with touch intact

8. In Brown-Séquard syndrome, the paresis and spasticity of muscles are found:

On the side opposite the hemisectionOn the same side as the hemisectionEqually on both sidesOnly at the level of the lesion, never below

9. After complete transection of the spinal cord, a narrow band of hyperesthesia is usually found:

At the lowest extent of the numb zoneOn the opposite side of the body onlyOver the same side of the faceJust above the numb zone

10. A cavity forms around the central canal of the cervical cord. The resulting sensory picture is:

Every modality lost below the cavityPain and temperature lost, touch and position preservedPosition and vibration lost, pain preservedPain lost on one side, touch on the other

11. A patient develops sudden spastic paralysis with loss of pain and temperature below the lesion, while position sense stays normal. The likely lesion is:

Occlusion of the anterior spinal arteryA single peripheral nerve lesionA bilateral posterior column lesionTabes dorsalis

12. A one-sided lesion in the medulla produces loss of pain and temperature over:

The whole body below the neck, on both sidesOne side of the face and the other side of the bodyBoth sides of the face and neither side of the bodyOne side of the face and the same side of the body

13. Thalamic syndrome, in which a mildly painful stimulus provokes an exaggerated response and touch feels unpleasant, follows a lesion of which thalamic nuclei?

Reticular and intralaminarMedial and anteriorThe geniculate bodiesLateral and ventral

14. Which of these is NOT counted among the cortical sensations?

Vibration senseStereognosisTactile localizationTwo-point discrimination

15. Somatosensory evoked potentials are of greatest value in deciding:

How much muscle power remainsWhich dermatome is anesthetic at the bedsideWhether a conduction defect is peripheral or centralHow high a patient's pain threshold is

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