Final answer:
The layer of skin from which we feel pain when penetrated by a needle is the dermis. This layer contains the nerve endings and blood vessels responsible for the sensation of pain and bleeding upon injury.
Step-by-step explanation:
When a needle penetrates the skin, it is the dermis layer that you can feel pain from. The dermis is located underneath the epidermis and is composed of tough connective tissue, containing blood vessels and nerve endings responsible for sensing pain, which is why we bleed and feel pain when cut. In contrast to the Merkel cells that detect low-frequency vibrations in the stratum basale of the epidermis, it is the deeper sensory neurons in the dermis that communicate the sensation of pain when the skin is punctured.
These nerve endings in the dermis are responsible for our ability to sense touch, pressure, heat, and pain, making the skin a complex sense organ. When we experience a cut deep enough to reach the dermis, we not only bleed but also feel pain due to the presence of these sensory neurons. To explore somatosensation, simple tests like pressing with a fingertip cause little lasting effect, but a similar force applied with the sharp end of a needle can easily break the skin and trigger pain perception.