Nervous Tissue

Introduction

Nervous tissue is a specialized tissue found in the nervous system, responsible for transmitting electrical and chemical signals throughout the body. It is essential for sensation, movement, and higher cognitive functions.

Anatomic Divisions of the Nervous System

Central Nervous System (CNS)

• Definition: The CNS consists of the brain and spinal cord.

• Function: It processes information, integrates sensory input, and coordinates motor output.

Peripheral Nervous System (PNS)

• Definition: The PNS includes all nervous tissue outside the CNS, such as cranial and spinal nerves.

• Function: It connects the CNS to limbs and organs, serving as a communication relay.

• Components: Cranial nerves, spinal nerves, and peripheral nerves.

Functional Divisions of the PNS

Afferent Division

• Function: Transmits sensory information from receptors to the CNS.

• Receptors: Special sensory receptors (vision, smell, hearing), visceral sensory receptors (internal organs), and somatic sensory receptors (muscles, joints, skin).

Efferent Division

• Function: Carries motor commands from the CNS to effectors (muscles and glands).

• Subdivisions:

  • Somatic Nervous System (SNS): Controls voluntary movements by innervating skeletal muscle.

  • Autonomic Nervous System (ANS): Regulates involuntary functions by innervating smooth muscle, cardiac muscle, and glands. Includes sympathetic and parasympathetic divisions.

Structure of Neurons

Overview

Neurons are the basic functional units of the nervous system, specialized for communication.

• Soma (Cell Body): Contains the nucleus, nucleolus, cytoplasm, and organelles. The neurolemma surrounds the soma.

• Dendrites: Short, highly branched extensions that receive information from other neurons.

• Axon: A single, long, slender process that conducts impulses away from the soma. The axon terminus branches into synaptic terminals.

Diagram of a Typical Neuron

• Dendrites: Receive incoming signals.

• Cell Body (Perikaryon): Contains the nucleus and organelles.

• Axon: Transmits electrical impulses.

• Telodendria: Fine branches at the end of the axon, leading to synaptic terminals.

Additional info:

• Neurons communicate via synapses, where neurotransmitters are released to transmit signals to other neurons or effector cells.

• Neuroglia (glial cells) support and protect neurons, maintain homeostasis, and form myelin.