Primary Functions of the Nervous System

The nervous system operates as a specialized unit that controls, regulates, and coordinates all bodily activities by carrying out three fundamental functions:

• Sensory function: detecting and receiving stimuli from the environment and the body, converting these stimuli into neural signals, and transmitting them to the integration centers.
• Integrative function: processing and interpreting the incoming sensory information to decide on the appropriate response.
• Motor function: generating and delivering a suitable response to the effector organs to execute actions

General Organization of the Nervous System

Based on anatomical and physiological considerations, the nervous system can be subdivided into:

• Central Nervous System (CNS): the integrative part
  Also called the neuraxis, it consists of the spinal cord, housed within the vertebral canal, and the brain, located within the cranial cavity. The brain includes the brainstem, cerebellum, and cerebrum.
  The CNS serves as the primary center for regulation and integration of the nervous system. It manages interactions with the external environment, analyzes and interprets sensory information received, sorts and compares it, and formulates an appropriate motor response.

Peripheral Nervous System (PNS): the sensory and motor components

The Peripheral Nervous System (PNS) comprises all the neural structures located outside the brain and spinal cord. It serves as the crucial communication network that links the central nervous system (CNS) to the limbs, organs, and tissues of the body. Functioning as the body's information highway, the PNS enables the relay of sensory data to the CNS and transmits motor commands from the CNS to the periphery.

Structurally, the PNS consists of:

• Cranial nerves: Twelve pairs of nerves that arise directly from the brainstem and innervate structures primarily in the head and neck, though some (like the vagus nerve) extend to thoracic and abdominal organs.
• Spinal nerves: Thirty-one pairs of nerves emerging from the spinal cord, each associated with a specific body segment (dermatome and myotome), responsible for both sensory and motor innervation of the trunk and limbs.
• Ganglia: Collections of neuronal cell bodies located outside the CNS that act as relay stations for nerve signals.

Functional Subdivisions of the PNS

The PNS is functionally divided into two main components based on the type of control and target structures:

1️⃣ The Somatic Nervous System (SNS)

• Voluntary control: The SNS governs conscious and intentional movements.
• Target: It innervates skeletal striated muscles, enabling precise control of body movements, posture, and reflexes.
• Pathways: Somatic motor neurons transmit signals from the CNS to skeletal muscles, while somatic sensory neurons carry information from skin, muscles, joints, and special sensory organs (like the eyes and ears) back to the CNS.

2️⃣ The Autonomic Nervous System (ANS)

• Involuntary control: The ANS regulates automatic or subconscious activities essential for survival and homeostasis.
• Target: It controls the smooth muscle of internal organs, cardiac muscle, blood vessels, and glands.
• Subdivisions:
  • Sympathetic division (fight or flight): Prepares the body for stressful or emergency situations by increasing heart rate, dilating airways, and mobilizing energy stores.
  • Parasympathetic division (rest and digest): Promotes relaxation, digestion, and energy conservation.
  • Enteric nervous system (sometimes considered part of the ANS): A specialized network embedded in the gastrointestinal tract wall that governs digestive functions independently, though it interacts with both sympathetic and parasympathetic divisions.