Longevity: Neurons exist for a lifetime; most do not divide and are considered amitotic.
Limited neurogenesis in some brain regions.
Metabolic Rate: High demand for energy; uses significant oxygen and glucose.
Brain disproportionally uses energy compared to its weight.
Neuron Structure
Cell Body (Soma)
Contains nucleus and organelles (rough ER, Nissl bodies).
Functions as the biosynthetic center of the neuron.
Part of the receptive region for receiving signals.
Processes: Include dendrites and axons.
Dendrites: Short, branched processes; receive signals and conduct graded potentials.
Highly specialized for information collection.
Contain dendritic spines for communication with other neurons.
Axons: Long slender projections; conduct electrical impulses.
Start at the axon hillock; may have collateral branches.
End at axon terminals, which release neurotransmitters.
Neuron Cell Locations
Central Nervous System (CNS): Cell bodies cluster as nuclei.
Peripheral Nervous System (PNS): Cell bodies cluster as ganglia.
Axon and Myelination
Myelin Sheath
Insulates axons to increase impulse speed.
Formed by Schwann cells in PNS and oligodendrocytes in CNS.
Myelinated fibers conduct impulses faster than non-myelinated.
Types of Myelin Formation
Schwann cells wrap around axons in PNS.
Oligodendrocytes wrap around multiple axons in CNS.
Nodes of Ranvier: Gaps between myelin sheaths essential for impulse propagation.
Classification of Neurons
Structural Classification
Multipolar: Multiple processes; common in CNS.
Bipolar: One axon and one dendrite; found in sensory organs.
Unipolar: One process; found mostly in PNS.
Functional Classification
Sensory Neurons: Transmit impulses to CNS, mostly unipolar.
Motor Neurons: Carry impulses from CNS to effectors, mostly multipolar.
Interneurons: Connect neurons within CNS, involved in processing.
Brain and Spinal Cord Tissue
White Matter: Myelinated axons; appear white.
Gray Matter: Neuron cell bodies and non-myelinated fibers; appear gray.
Summary
Neurons are specialized cells essential for nervous system function, with distinct structural features that support their roles in processing and transmitting information.
Myelination significantly impacts the speed of neural communication.
Neurons are classified by structure and function, with specific roles in sensory, motor, and integrative processing.