Fundamentals of the Nervous System and Nervous Tissue

Overview of the Nervous System

The nervous system is the body's rapid communication and control system, responsible for coordinating actions and transmitting signals between different parts of the body. It is essential for maintaining homeostasis and responding to internal and external stimuli.

• Two main anatomical divisions:

  • Central Nervous System (CNS): Consists of the brain and spinal cord.

  • Peripheral Nervous System (PNS): Composed of cranial and spinal nerves that connect the CNS to the rest of the body.

• The CNS and PNS work together as a single, coordinated whole.

Main Functions of the Nervous System

The nervous system performs three fundamental, interconnected functions:

• Sensory Input:

  • Receives information from millions of specialized receptors throughout the body.

  • Detects changes in the internal and external environment.

• Integration:

  • Processes and interprets sensory input.

  • Determines the appropriate response.

• Motor Output:

  • Initiates a response by activating effector organs (muscles and glands).

  • Causes actions such as muscle contraction or glandular secretion.

Central Nervous System (CNS)

Structure and Function

The CNS consists of the brain and spinal cord. It is the main control center for processing and integrating information, storing memories, and determining emotions.

• Processes and integrates information: Receives sensory input, analyzes it, and makes decisions.

• Initiates commands: Sends out instructions for muscle contraction, glandular secretion, and hormone release to regulate and maintain homeostasis.

• Connected to the rest of the body: The CNS communicates with all other body parts via the PNS.

Peripheral Nervous System (PNS)

Structure and Functional Subdivisions

The PNS consists of cranial and spinal nerves that branch out from the CNS to the rest of the body. It is divided into functional subdivisions based on the direction of signal transmission.

• Sensory (Afferent) Division:

  • Composed of nerve fibers (axons) that convey impulses from sensory receptors to the CNS.

  • Somatic afferents: Carry information from skin, skeletal muscles, tendons, and joints.

  • Special sensory afferents: Transmit signals from specialized sensory organs (e.g., eyes, ears).

  • Visceral afferents: Carry information from internal organs (viscera).

• Motor (Efferent) Division:

  • Transmits impulses from the CNS to effector organs (muscles and glands).

  • Consists of motor (efferent) neurons.

  • Controls voluntary and involuntary responses.

Example:

When you touch a hot object, sensory receptors in your skin send a signal via the sensory (afferent) division to the CNS. The CNS processes this information and sends a command through the motor (efferent) division to your muscles to withdraw your hand.

Additional info: The PNS is further subdivided into the somatic nervous system (controlling voluntary movements) and the autonomic nervous system (regulating involuntary functions such as heart rate and digestion).