Question

In man, brachial plexus is formed by
(a) First spinal nerve
(b) Second spinal nerve
(c) Third spinal nerve
(d) Last four cervical and first thoracic spinal nerve

Answer 1

Hint: The brachial plexus is a network of nerves that supplies to the skin and muscles of the upper limbs in the human nervous system. They are found deep in the neck and in the region above the shoulders.

Complete step by step answer:
In man, brachial plexus is formed by the Last four cervical and first thoracic spinal nerves. Axons from anterior rami of the spinal nerves, excluding the thoracic nerves, do not go directly to the parts of bodies they are supposed to supply the nerve impulse. Instead, they form a network on both sides of the body in association with various adjacent axons. There are various kinds of plexus as follows
Cervical plexus: Formed by the first four cervical nerves; present in the neck opposite to the first four cervical vertebrae.
Brachial plexus: Formed by C5- C8 (last four cervical nerves) and first thoracic nerve; present deeply in the neck and above the shoulders and supplies to skin and muscles of upper limbs.
Lumbar plexus: Formed by the first four lumbar nerves; present exactly in front of the lumbar vertebrae.
Sacral plexus: Formed by the first three nerves of sacral nerves; present in the posterior wall of the pelvic cavity.
Coccygeal plexus: Formed by the last two nerves of sacral nerves and the coccygeal nerve; it supplies to skin and muscle around the coccyx.

So, the correct answer is ‘(d) Last four cervical nerves and first thoracic spinal nerve.’

Additional information: Spinal nerves are an integral part of the peripheral nervous system in the human nervous system. The spinal nerves are structures through which the central nervous system receives sensory information from the periphery and transmit the motor commands from the central nervous system to the periphery. The spinal nerves also help in the activity of the trunk and the limbs. There are a total of 31 pairs of spinal nerves emerging from the spinal cord and to exit the vertebral canal, composed of both motor and sensory fibers:
- Cervical - 8
- Thoracic - 12
- Lumbar - 5
- Sacral - 5
- Coccygeal - 1

Note: Although there are only seven cervical vertebrae, there are eight cervical nerves as the first nerve exits the vertebral canal between the occipital bone and the atlas which is in the first cervical vertebrae. Brachial plexus is the network of nerves that supplies the skin and muscles of the upper limbs. It begins in the root of the neck, passes through the axilla, and runs through the entire upper extremity.