Neurons, Synapses, and Signaling (Action potentials are the signals…
Neurons, Synapses, and Signaling
Neurons communicate with other cells at synapses
Neuropeptides, short amino acid chains, serve as neurotransmitters that operate via metabotropic receptors.
The amino acid gamma-aminobutyric acid (GABA) is the neurotransmitter at most inhibitory synapses in the brain
Two EPSPs produced in rapid succession at the same synapse can be added in an effect called temporal summation
When the channel opens, the postsynaptic membrane hyperpolarizes to produce an inhibitory postsynaptic potential (IPSP) that moves the membrane potential farther from threshold.
Because this depolarization brings the membrane potential toward threshold, it is called an excitatory postsynaptic potential (EPSP).
At many chemical synapses, ligand-gated ion channels (also called ionotropic receptors) capable of binding to neurotransmitters are clustered in the membrane of the postsynaptic cell, directly opposite the synaptic terminal.
Action potentials are the signals conducted by axons
Myelin sheaths are produced by two types of glia: oligodendrocytes in the CNS and Schwann cells in the PNS.
The adaptation that enables fast conduction in the absence of large diameter is a myelin sheath, a layer of electrical insulation that surrounds vertebrate axons
Action potentials occur whenever a depolarization increases the membrane voltage to a particular value, called the threshold.
Action potentials arise because some ion channels in neurons are voltage-gated ion channels, opening or closing when the membrane potential passes a particular level.
If a depolarization shifts the membrane potential sufficiently, the result is a massive change in membrane voltage called an action potential.
These changes in membrane potential are called graded potentials because the magnitude of the change—either hyperpolarization or depolarization—varies with the strength of the stimulus.
This reduction in the magnitude of the membrane potential is called a depolarization
This increase in the magnitude of the membrane potential, called hyperpolarization, makes the inside of the membrane more negative.
Changes in membrane potential occur because neurons have gated ion channels, which open or close in response to stimuli.
Ion pumps and ion channels establish the resting potential of a neuron
The magnitude of the membrane voltage at equilibrium for a particular ion is called that ion’s
equilibrium potential (Eion)
Ion channels, pores formed by clusters of specialized proteins that span the membrane, allow ions to diffuse back and forth across the membrane
The membrane potential of a neuron that is not transmitting signals is called the resting potential and is typically between −60 and −80 mV.
Because the attraction of opposite charges across the plasma membrane is a source of potential energy, this charge difference, or voltage, is called the membrane potential.
Neuron structure and organization reflect function in information transfer
For example, motor neurons transmit signals to muscle cells, causing them to contract.
The vast majority of neurons in the brain are interneurons, which form local connecting neurons in the brain
Sensory neurons transmit information from sensors that detect external stimuli (light, sound, heat, touch, smell, and taste) and internal conditions (blood pressure, blood CO2 level, and muscle tension).
At most synapses, information is passed from the transmitting neuron (the presynaptic cell) to the receiving cell (the postsynaptic cell) by means of chemical messengers called neurotransmitters.
Glia are supporting cells that nourish neurons, insulate the axons of neurons, and regulate the extracellular fluid surrounding neurons
Neurons that bring information into and out of the CNS make up the peripheral nervous system (PNS).
In many animals, the neurons that carry out integration are organized in a central nervous system (CNS), which includes a brain and longitudinal nerve cord.