Dendrites are branched extensions projecting from a neuron’s cell body, often resembling the branches of a tree. As the primary receivers of information for the nervous system, they act as antennas for neurons, or nerve cells. Dendrites collect signals from other nerve cells, allowing for the complex processing that underlies all brain functions. A single neuron can have thousands of dendritic branches, enabling it to receive messages from a vast number of other neurons at once.
The Structure of a Dendrite
The complete network of a neuron’s dendrites is called a dendritic tree. This extensive branching increases the surface area available for connecting with other neurons. Some large neurons can receive signals from tens of thousands of other cells through this network.
Scattered along these branches are smaller protrusions called dendritic spines. These tiny structures are the primary points of contact where signals are received from other neurons. A single dendrite can be covered in thousands of these spines, which are dynamic and can change in shape and size, affecting the strength of the connection.
The interior of a dendrite contains components like mitochondria for energy and ribosomes for protein synthesis. It also has a cytoskeleton made of proteins like actin. This internal scaffolding is not rigid, allowing dendritic spines to be dynamic and change their shape in response to stimulation, a process important for learning.
How Dendrites Receive Information
Information transfer between neurons occurs at a junction called a synapse. This is where an axon, the signal-sending part of one neuron, meets a dendrite of another, with most connections happening on a dendritic spine. A microscopic gap known as the synaptic cleft separates the two cells.
To send a message, the axon releases chemical messengers called neurotransmitters. These molecules cross the synaptic cleft and attach to specific receptor proteins on the dendritic spine’s membrane. Each neurotransmitter fits only into its corresponding receptor type.
When a neurotransmitter binds to its receptor, it generates a tiny electrical signal called a postsynaptic potential. A single signal is not enough to cause the neuron to fire. The dendrite’s job is to collect and sum up the thousands of incoming signals it receives from all its synapses.
These signals are integrated across the dendrite. If their combined strength reaches a certain threshold, the neuron generates its own electrical impulse, called an action potential. This action potential sends the message onward to other cells.
The Role of Dendrites in Learning and Memory
The brain’s ability to learn and form memories is based on neuroplasticity, its capacity to change its own structure. Dendrites and their spines are central to this process. When we learn something new, the neural pathways involved are repeatedly activated, which strengthens the synaptic connections between the neurons in that circuit.
This strengthening can happen in several ways. Existing dendritic spines can grow larger, creating a more reliable connection with the transmitting axon. Entirely new dendritic spines can also form, creating new synapses and expanding the neuron’s network. Connections used frequently become more robust, while those that fall into disuse may weaken or be eliminated.
Through learning and practice, specific dendritic connections are reinforced. This makes signal transmission along that memory pathway faster and more efficient. These physical changes at the level of the dendrite are the cellular basis for how long-term memories are stored.
Dendrites and Brain Health
The structure and number of dendrites are not static and are linked to brain health. During early development, an overproduction of dendritic connections occurs. This is followed by synaptic pruning, where unused connections are eliminated. This refinement is a normal part of creating a more efficient adult brain.
Disruptions in dendritic structure are associated with various neurological and developmental conditions. For example, studies have linked atypical spine shapes and densities to conditions like autism spectrum disorder and Fragile X syndrome. In these cases, altered spine formation and pruning can lead to differences in brain connectivity.
The loss of dendrites and dendritic spines is a hallmark of several neurodegenerative diseases. In Alzheimer’s disease, the accumulation of toxic proteins contributes to widespread synaptic loss long before the neurons die. This loss of connections disrupts communication between brain cells, contributing to cognitive decline. Maintaining the health of these dendritic structures is therefore important for cognitive function.