How Many Pairs Of Cranial And Spinal Nerves Are Present In The Human Body?

In the human skeleton system, there are 12 pairs of cranial nerves and 31 pairs of spinal nerves.

The human nervous system consists of the brain, nerves, and spinal cord. The entire system enables the communication between the brain and the other body parts. For this, nerves play a vital role. A nerve is formed of a bundle of nerve fibres known as axons covered by a protective sheath (myelin sheath). The messages sent through the nerves are called nerve impulses. The dendrites of the nerve cell have the nucleus. The signals travel away from the dendrites towards the target site. The nervous system has two divisions.

• The central nervous system, constituted by the brain and spinal cord

• The peripheral nervous system has nerves extending from the spinal cord to various body parts.

Nervous system

The human nervous system is divided based on its location into the central and peripheral nervous systems. There are also voluntary and involuntary nervous systems where the nature of reaction differs. In the voluntary system, the person consciously controls the actions like the movement of arms, legs, or other body parts. The involuntary nervous system deals with vital body functions, like a heartbeat, respiration, and metabolism.

Central Nervous System (CNS)

The brain and spinal cord constitute the CNS. The cranial nerves convey the information from the brain to the spinal cord and vice versa. There are 12 pairs of cranial nerves, each with its specific functions.

• The olfactory nerve is a sensory nerve acting between the brain and the nose. It is the shortest of the twelve pairs.

• The optic nerve corresponds to vision and emerges from the diencephalon (a part of the forebrain).

• The oculomotor nerve originating in the midbrain controls pupil size and eye movement.

• The trochlear nerve helps in eyeball movement.

• The trigeminal nerve has mixed functions as a sensitive, motor, and sensory nerve. The sensitive nerves carry out the chewing-related information, and the sensory nerves convey touch, pain, and temperature sensations.

• Abducent nerves help in the movement of the eyes to the opposite side of the nose (motor nerve).

• The facial or intermediate nerve is a mixed nerve that deals with facial expressions and salivary and lacrimal glands. It also collects taste information.

• The Vestibulocochlear is a cranial sensory nerve known as the auditory and vestibular nerve. It corresponds to balance and hearing.

• Glossopharyngeal nerve influences the tongue and pharynx. It collects sensory information from the pharynx and taste information from the taste buds. It controls the salivary glands, monitors blood pressure, and aids swallowing.

• The Vagus nerve starts in the medulla and carries impulses to major organs like the heart, lungs, stomach, and liver.

• Accessory (or spinal) nerve controls head and shoulder movements.

• The hypoglossal nerve is involved in speech, swallowing, and movement of tongue muscles.

Peripheral Nervous System (PNS)

The PNS has the nerves and ganglions (neuron cell bodies) outside the brain and spinal cord. It connects the CNS to the other body parts, and the spinal nerves pass signals between the spinal cord and other nerves in the body. There are somatic and autonomic nervous systems under the PNS.

Somatic Nervous System

The somatic nervous system controls voluntary actions, while the sensory system forms a part of it by transmitting sense signals to the spinal cord and brain. The spinal cord gives rise to the 31 pairs of spinal nerves. Each of the nerves exists in pairs.

• Cervical (8)

• Thoracic (12)

• Lumbar (5)

• Sacral (5)

• Coccygeal (1)

These names correspond to the vertebrae to which they are attached.

Autonomous Nervous System

The autonomous nervous system controls involuntary functions, including heart and respiration rates. The sympathetic and parasympathetic systems form a part of it.

• The sympathetic system gets activated when there is a fight or flight situation. It results in the release of neurotransmitters like epinephrine (adrenaline). The activities of these neurotransmitters include raised heartbeat, perspiration, increased blood supply to the limbs, etc. It decreases blood flow to the non-critical units like the digestive system.

• The parasympathetic system acts opposite to the sympathetic system by putting the body in a state of rest. It uses the neurotransmitter Acetylcholine. Parasympathetic activities like digestion increase and decrease heart rate and other sympathetic responses.

• These systems act one after the other countering the effect of the other.