Anatomy Unit: Nerve Tissue

Nerve Tissue Composition

• Composed of neurons (nerve cells) and supporting cells.
• High capability to respond to stimuli and transmit impulses.

Neuron Structure

• Main functional unit of the nervous system, consisting of:
  • Cell Body (Perikaryon/Soma): Contains the nucleus and cytoplasm.
  • Dendrites: Numerous processes that receive stimuli.
  • Axon: Single process that conducts nerve impulses to other cells.

Types of Neurons

• Multipolar Neurons: One axon and two or more dendrites; most common type in motor and interneurons.
• Bipolar Neurons: One axon and one dendrite; found in the retina, olfactory mucosa, and inner ear.
• Unipolar Neurons: Single process dividing into two branches; associated with spinal ganglia and cranial ganglia.

Functional Classification of Neurons

• Motor (Efferent) Neurons: Control effector organs, like muscles and glands.
• Sensory (Afferent) Neurons: Receive sensory stimuli from the environment and body.
• Interneurons: Connect motor and sensory neurons, forming a communication network.

Neuron Cell Body and Components

• Contains Nissl bodies (RER and ribosomes), visible as basophilic clumps under a microscope.
• The axon originates from the axon hillock, transitioning into the axon cylinder or nerve fiber.

Nerve Fiber (Axon) Characteristics

• Myelinated axons have a lipid-rich myelin sheath, segmented by nodes of Ranvier.
• Schwann Cells: Surround and form an insulating cover (neurolemma) around the axon.

Nerve Organization

• Endoneurium: Innermost connective tissue layer around a single axon.
• Perineurium: Connective tissue layer surrounding fascicles of axons.
• Epineurium: Outermost layer of dense connective tissue around the entire nerve.

Glial Cells (Neuroglia)

• Non-neuronal cells that maintain homeostasis, support, and protect neurons.
• Occupy space between neurons and separate them from blood vessels.

Functions of Glial Cells

• Support and stabilize neurons in place.
• Supply essential nutrients and oxygen.
• Insulate neurons from each other.
• Eliminate pathogens and dead neurons.
• Line brain ventricles and spinal cord's central canal.

Types of Glial Cells

• Astrocytes: Most abundant, play key roles in maintaining homeostasis and linking to blood vessels.
• Oligodendrocytes: Form myelin in the central nervous system.
• Microglia: Act as immune cells for the nervous system.
• Ependymal Cells: Line ventricles and central canal.