**Question:** Appreciation of shape and size of an object placed in hand is lost in the lesion of

A. Corticospinal tract
B. Cervical roots
C. Sensory cortex
D. Spinal cord

**Correct Answer:** D. Spinal cord

**Core Concept:** The appreciation of shape and size of an object placed in hand is a sensory function that is processed in the somatosensory system, which is responsible for detecting the tactile information from the skin surface. This information is conveyed through the sensory nerves to the spinal cord and then to the cerebral cortex, specifically to the primary somatosensory cortex (SI) and the secondary somatosensory cortex (SII).

**Why the Correct Answer is Right:** The lesion in the spinal cord (option D) can impair the transmission of tactile information from the skin surface to the brain. The spinal cord is a crucial component in the somatosensory pathway, receiving sensory inputs from the peripheral nerves and relaying the information to the brain. The specific segment(s) of the spinal cord affected would determine the type and extent of sensory deficit.

**Why Each Wrong Option is Incorrect:**

A. Corticospinal tract (option A) is responsible for motor function, not sensory perception. The corticospinal tract transmits motor commands from the cerebral cortex to the spinal cord and allows voluntary movement control.

B. Cervical roots (option B) are part of the peripheral nervous system and transmit sensory and motor information away from the spinal cord to the brain. They are not responsible for the perception of object shape and size.

C. Sensory cortex (option C) is involved in processing tactile information, but the correct answer (spinal cord) is responsible for transmitting the sensory information to the sensory cortex. A lesion in the spinal cord would result in sensory deficits, while a lesion in the sensory cortex would affect the perception of the object itself rather than its shape and size.

**Clinical Pearl:** Lesions in specific spinal cord segments can lead to various sensory deficits, such as hypoesthesia, paresthesia, or anesthesia, depending on the affected segment. For example, a lesion in the cervical segments would result in loss of sensation in the corresponding dermatomes and not affect the perception of object shape and size.

**Clinical Pearl:** The spinal cord is a crucial component of the somatosensory pathway responsible for processing tactile information from the skin. The lesion in the spinal cord would disrupt the transmission of tactile information, leading to deficits in sensation and perception of object shape and size.