The underlying molecular mechanisms of this motile behaviour, and its functional significance, are unknown.Ĭonsiderable progress has been made in identifying the molecules that control spine growth and maturation. The shape change involves a remodelling of the cytoskeleton in the spine, and actin-based protrusive activity from the spine head. Moreover, spine morphology is markedly influenced by the activity of glutamate receptors.ĭendritic spines exhibit rapid motility. In general terms, spines seem to be maintained by an 'optimal' level of synaptic activity: spine density increases when there is insufficient activity, and decreases when stimulation is excessive.
Indeed, changes in spine density have been observed in response to changes in the efficacy of neurotransmission. Regulated changes in spine number might reflect mechanisms for converting transient changes in synaptic activity into long-lasting alterations. So, the filopodium–spine transition is unlikely to be a predestined process, but instead one that is reversible and regulated by factors such as synaptic activity. However, a simple developmental relationship between filopodia and spines does not seem to exist. What is the significance of dendritic spines? There is no definitive answer to this question, but the prevailing view is that their primary function is to provide a microcompartment for segregating postsynaptic chemical responses, such as elevated calcium.ĭendritic filopodia are widely believed to be the precursors of dendritic spines. In addition, most spines exhibit a single, continuous postsynaptic density (PSD), but some PSDs are discontinuous or perforated. However, spine morphology is not static spines change size and shape over variable timescales. Spines have been classified by shape as thin, stubby, mushroom- and cup-shaped. So, spines represent the main unitary postsynaptic compartment for excitatory input. Most excitatory synapses in the mature mammalian brain occur on spines. Current research is uncovering important new roles for glia in brain function.Dendritic spines are morphological specializations that protrude from the main shaft of dendrites. Researchers have known for a while that glia transport nutrients to neurons, clean up brain debris, digest parts of dead neurons, and help hold neurons in place. The brain contains at least ten times more glia than neurons. In the brain, the glia that make the sheath are called oligodendrocytes, and in the peripheral nervous system, they are known as Schwann cells. This sheath is made by specialized cells called glia. Many axons are covered with a layered myelin sheath, which accelerates the transmission of electrical signals along the axon. When neurons receive or send messages, they transmit electrical impulses along their axons, which can range in length from a tiny fraction of an inch (or centimeter) to three feet (about one meter) or more. The dendrites are covered with synapses formed by the ends of axons from other neurons. Synapses are the contact points where one neuron communicates with another. The axon extends from the cell body and often gives rise to many smaller branches before ending at nerve terminals.ĭendrites extend from the neuron cell body and receive messages from other neurons. The cell body contains the nucleus and cytoplasm. Each mammalian neuron consists of a cell body, dendrites, and an axon. The mammalian brain contains between 100 million and 100 billion neurons, depending on the species. The brain is what it is because of the structural and functional properties of interconnected neurons. Dendrites extend from the neuron cell body and receive messages from other neurons. The axon extends from the cell body and often gives rise to many smaller branches before ending at nerve terminals. Most neurons have a cell body, an axon, and dendrites. Neurons are cells within the nervous system that transmit information to other nerve cells, muscle, or gland cells. Kibiuk, Baltimore, MD Devon Stuart, Harrisburg, PA
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