Fundamentals of the Nervous System and Nervous Tissue

Overview of the Nervous System

The nervous system is the master controlling and communicating system of the body. It uses electrical and chemical signals to coordinate rapid, specific, and almost immediate responses to internal and external stimuli.

• Communication: Achieved via electrical impulses and neurotransmitters.

• Speed: Responses are rapid and specific, ensuring immediate action.

Main Functions of the Nervous System

The nervous system performs three essential, overlapping functions:

• Sensory Input: Information is gathered by sensory receptors about changes inside and outside the body.

• Integration: The nervous system processes and interprets sensory input and decides what should be done at each moment.

• Motor Output: The nervous system activates effector organs (muscles and glands) to cause a response.

Example: Touching a hot object triggers sensory input (pain receptors), integration (processing in the brain/spinal cord), and motor output (muscle contraction to withdraw the hand).

Divisions of the Nervous System

The nervous system is structurally and functionally divided into two main parts:

• Central Nervous System (CNS):

  • Consists of the brain and spinal cord, located in the dorsal body cavity.

  • Acts as the integration and control center, interpreting sensory input and dictating motor output.

• Peripheral Nervous System (PNS):

  • Includes all neural structures outside the CNS: mainly nerves extending from the brain and spinal cord.

  • Spinal nerves: Carry impulses to and from the spinal cord.

  • Cranial nerves: Carry impulses to and from the brain.

  • The enteric nervous system is a specialized network of neurons in the walls of the gastrointestinal tract.

Functional Divisions of the Peripheral Nervous System

The PNS is further divided based on function:

• Sensory (Afferent) Division:

  • Somatic sensory fibers: Transmit impulses from skin, skeletal muscles, and joints to the CNS.

  • Visceral sensory fibers: Transmit impulses from visceral organs to the CNS.

• Motor (Efferent) Division:

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

  • Subdivided into:

    • Somatic Nervous System: Voluntary control of skeletal muscles via somatic motor nerve fibers.

    • Autonomic Nervous System (ANS): Involuntary control of smooth muscle, cardiac muscle, and glands.

Somatic Nervous System

The somatic nervous system is responsible for voluntary movements:

• Somatic motor nerve fibers conduct impulses from the CNS to skeletal muscles.

• Enables conscious control of skeletal muscle contractions.

Autonomic Nervous System (ANS)

The ANS regulates involuntary functions:

• Composed of visceral motor nerve fibers.

• Controls smooth muscle, cardiac muscle, and glands.

• Divided into two opposing subdivisions:

  • Sympathetic Division: Mobilizes body systems during activity ("fight or flight").

  • Parasympathetic Division: Conserves energy and promotes housekeeping functions during rest ("rest and digest").

Summary Table: Organization of the Nervous System