Chapter 12

• Integration is a general term that refers to processes that produce coherency and result in harmonious function.
• Neuron is a cell that is specially adapted to generate an electrical signal, most often in a brief action potential, that travels from place to place in the cell.
• A neuron has four parts that include dendrites, cell body, axon, and presynaptic terminals.
• The four functions of a neuron are input, integration, conduction, and output.
• The cell body is commonly the part of a neuron where signal integration and impulse generation occur.
• A single neuron may receive thousands of synaptic contacts from other neurons.
• The neurotransmitters released across some synapses excite the neuron, those released across other synapses inhibit it.
• The cell membrane of the cell body combined the inhibitory and excitatory synaptic inputs, and if excitatory inputs surpass inhibitory inputs, the neuron may respond by generating one or more action potentials.
• Axon is the conduction component of a neuron, serving to propagate action potentials along its length.
• The axon typically arises from the soma via a conical axon hillock, which leads to the axon initial segment, a specialized area that is commonly the site of action potential initiation,
• The ends of axons are divided into several presynaptic terminals, which constitute the places where neuronal output occurs.
• Neurons that relay sensory signals to integrative centers of the CNS are called afferent neurons.
• Efferent neurons relay control signals from the CNS to gather cells that are under nervous control, such as muscle cells or secretory cells.
• Neurons that are entirely within the CNS are called interneurons.
• Control by a nervous system involves neurons that send axons to discrete postsynaptic cells.
• Neurons generate rapidly conducting action potentials to control the specific targets on which they end.
• Neurons exert fast, specific control by releasing neurotransmitters at synapses.
• Motor neurons have outgoing axons that exit the CNS and innervate muscle.
• Dendrite is considered to be a receptive element of a neuron that conveys information toward the soma.
• Axon is the output element of a neuron, carrying information away from the cell body to other cells.
• the larger vertebrate axons are surrounded by myelin sheaths.
• Myelin sheaths are multiple wrappings of insulating glial cell membranes that increase the speed of impulse transmission.
• The axon is the portion of the neuron that supports action potentials.
• Action potentials propagate or conduct along the axon without decrement, carrying information away from the cell body to the axon terminals.
• Glial cells surround the neurons.
• Glial cells function to bind the neurons together and maintain the form and structural organization of the nervous system.
• The ratio of glial cells to neurons increases with increasing evolutionary complexity.
• The two types of ensheathing glial cells in the vertebrate nervous system are Schwann cells and oligodendrocytes.
• Ensheathing glial cells envelop the axons of neurons.
• Astrocytes line the outside surfaces of capillaries in the vertebrate CNS and act as metabolic intermediates between the capillaries and neurons.
• The net movement if charges constitute an electric current.
• The separation of positive and negative electrical charges constitute a voltage or electrical potential difference.
• Depolarization is a decrease in the absolute value of the membrane potential toward zero.
• Hyperpolarization is an increase in the absolute value of the membrane potential away from zero.
• Cell membranes have properties of electrical resistance and capacitance, which allow them to maintain a voltage and regulate current flow across the membrane.
• Cells have inside-negative resting membrane potentials.
• The passive electrical properties of membranes determine how membrane potentials change with time and with distance.
• Membrane potentials depend on selective permeability to ions.
• Any ion species to which the membrane is permeable will tend to drive the membrane potential toward the equilibrium potential for that ion.
• The Nernst equation calculates the equilibrium potential of a single ion species in terms of its concentrations on both sides of the membrane.