The Nervous System

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Nervous System

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A control system in animals that controls muscle movement, monitors organs, constructs and stops input from senses, and generates actions

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Nerve Net

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Arrangement of interconnected neurons lacking a brain; simple nervous system found in phyla cnidaria

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Central Nervous System

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The section of a nervous system that contains a brain and longitudinal nerve chords

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Peripheral Nervous System

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The section of the nervous system that connect the central nervous system to the rest of the body

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Neuron

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A class of cells in the nervous system; have excitable membranes that allow them to generate electrical signals

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Sensory Neuron

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A neuron that transmits information from sensors that detect external stimuli

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Interneuron

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A neuron that communicates only with other neurons; interprets signals from other neurons and distributes them accordingly

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Motor Neuron

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A neuron that communicates with effector cells

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Effector Cell

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Muscle or endocrine cells that generate output as a result of signals sent from the nervous system

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Ganglia

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Clusters of neurons in a peripheral nervous system

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Soma/Perikaryon

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The cell body; a bulbous end of a neuron that contains the cell nucleus

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Dendrites

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Branched extensions of a neuron that receive signals from other neurons

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Axon

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A nerve fiber; slender projection from a neuron that conducts electrical impulses away from the soma

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Nerve

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An enclosed, cable-like bundle of axons

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Axon Hillock

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A conical region where an axon joins with a soma

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Myelin Sheath

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An electrically insulating phospholipid layer that surrounds an axon

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Synaptic Terminal

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The tip of a branched end of an axon

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Synapse

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The site of communication between a synaptic terminal and another cell

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Presynaptic Cell

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The neuron that transimits information

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Postsynaptic Cell

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The neuron that receives invormation

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Neurotransmitters

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Chemical messengers sent along an axon

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Glia

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Non-neuronal cells that provide support and nutrition for neurons

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Astrocytes

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Glia in the central nervous system; provide structural support for neurons and regulate extracellular concentrations of ions and neurotransmitters

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Blood-Brain Barrier

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Barrier formed by astrocytes during development via tight-junction inductions between cells lining capillaries and brain in spinal chord; restricts pasage of most substances in CNS, allows for tight control of extracellular fluid composition

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Radial Glia

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Glia that form tracks for newly formed neurons to travel on when migrating from the neural tube

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Oligodendrocytes

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Glia that form myelin sheaths around axons in the central nervous system

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Schwann Cells

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Glia that form myelin sheaths around axons in the peripheral nervous system

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Why is there unidirectional flow across a chemical synapse?

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Anatomy of the nervous system only allows signals to move in one direction; synaptic terminals are only on one end of an axon, thus even if a signal is stimulated in the middle of an axon and extends both ways, it will not continue in the reverse direction as the presynaptic cell has no way of interpreting the signal

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Membrane Potential

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The electrical potential difference across a plasma membrane

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Resting Potential

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The membrane potential of a neuron that is not transmitting signals; dependent upon ionic gradients that exist across the plasma membrane