If the axon is a neuron's output channel, dendrites are its antennae. These elaborately branching structures receive input from thousands of other neurons, converting chemical signals at synapses into electrical potentials that spread toward the cell body. The dendritic tree's geometry — its branching pattern, total surface area, and the distribution of receptor types along its branches — determines what information the neuron receives and how it integrates that information. Dendrites are not passive receivers; they perform sophisticated local computations that are increasingly recognized as fundamental to brain function.
Key Structures
- Neurons (throughout nervous system) — The electrically excitable cells that process and transmit information through electrical and chemical signaling.
- Axon — The long, slender projection of a neuron that conducts electrical impulses (action potentials) away from the cell body toward other neurons, muscles, or glands.
- Long-Term Potentiation — A persistent strengthening of synapses based on recent patterns of activity — widely considered the cellular mechanism underlying learning and memory.
- Cerebellum — The 'little brain' at the posterior base of the skull, traditionally associated with motor coordination but increasingly recognized for contributions to cognition and language.
- Synapse — The specialized junction between two neurons where information is transmitted from one cell to another through chemical neurotransmitters or electrical coupling.
Key Functions
Receive and integrate excitatory and inhibitory postsynaptic potentials from thousands of upstream neurons.
Structure and Synaptic Reception
Dendrites extend from the cell body in a pattern characteristic of each neuron type. Pyramidal neurons in the cortex have a prominent apical dendrite reaching toward the cortical surface and multiple basal dendrites spreading laterally. Purkinje cells of the cerebellum have spectacularly flat, fan-like dendritic arbors that each receive input from approximately 200,000 parallel fibers. Studding the dendrites of many neurons are dendritic spines — small protrusions (0.5–2 micrometers) that serve as the postsynaptic sites for most excitatory synapses in the brain. A single pyramidal neuron may have 10,000 or more spines, each housing its own complement of receptors, signaling molecules, and even ribosomes for local protein synthesis.
Dendritic Integration
Each synapse produces a small graded potential — excitatory (EPSP) or inhibitory (IPSP) — that decreases in amplitude as it spreads passively toward the soma. The cell body and axon hillock integrate these thousands of inputs through both spatial summation (combining inputs arriving at different locations simultaneously) and temporal summation (combining inputs arriving at the same location in rapid succession). When the integrated signal at the axon hillock exceeds threshold, the neuron fires an action potential.
Dendritic spines are remarkably dynamic structures. During learning, new spines form, existing spines enlarge, and unused spines retract. Long-term potentiation (LTP) — the cellular mechanism thought to underlie memory formation — involves enlargement of the stimulated spine, insertion of additional AMPA receptors, and structural stabilization through actin cytoskeletal remodeling. This structural plasticity means that the physical shape of dendritic arbors is continuously modified by experience, providing a tangible anatomical substrate for learning and memory.
Active Dendritic Computation
Contrary to the classical view of dendrites as passive cables, research has revealed that dendrites contain voltage-gated channels that can generate local dendritic spikes, calcium plateaus, and NMDA spikes. These active properties allow individual dendritic branches to function as semi-independent computational units, dramatically increasing the information-processing capacity of single neurons. Modeling studies suggest that active dendrites may enable neurons to perform computations — such as coincidence detection and nonlinear input integration — that would otherwise require entire networks of simplified neurons.
Disorders
- Dendritic pruning disruption in schizophrenia
- Reduced dendritic branching in depression
- Alzheimer's disease (dendritic loss) — A progressive neurodegenerative disease characterized by memory loss, cognitive decline, and personality changes — the most common cause of dementia in older adults.