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- are nerve cells that transfer information within the body
- Neurons use two types of signals to communicate: electrical signals (long-distance) and chemical signals (short-distance)
Processing of information takes place in simple clusters of neurons called ganglia or a more complex organization of neurons called a brain
Nervous systems process information in three stages which are?
sensory input, integration, and motor output
Sensors detect external stimuli and internal conditions and transmit information along sensory neurons
Sensory information is sent to the brain or ganglia, where what integrate the information
Motor output leaves the brain or ganglia via what, which trigger muscle or gland activity
central nervous system (CNS)
integration takes place; this includes the brain and a nerve cord
peripheral nervous system (PNS
brings information into and out of the CNS
Most of a neuron’s organelles are in the what?
highly branched extensions that receive signals from other neurons
an axon joins the cell body at the what?
- typically a much longer extension that transmits signals to other cells at synapses
- An axon joins the cell body at the axon hillock
junction between an axon and another cell
of one axon passes information across the synapse in the form of chemical messengers called neurotransmitters
Information is transmitted from a what cell to a what cell?
Information is transmitted from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell)
Most neurons are nourished or insulated by cells called
glia cells (nurse cells)
- Every cell has a voltage (difference in electrical charge) across its plasma membrane called a membrane potential
- Messages are transmitted as changes in membrane potential
The resting potential is the membrane potential of a neuron not sending signals
An action potential occurs if a stimulus causes the membrane voltage to cross a particular
An action potential is a brief all-or-none what of a neuron’s plasma membrane
Action potentials are signals that carry information along what?
In a mammalian neuron at resting potential, the concentration of what+ is greater inside the cell, while the concentration of what+ is greater outside the cell
Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane
These concentration gradients represents what?
the chemical potential energy
The opening of what in the plasma membrane converts chemical potential to electrical potential
A neuron at what potential contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cell
Anions trapped inside the cell contribute to the what charge within the neuron
Neurons contain what that open or close in response to stimuli
gated ion channels
- after an action potential, a second action potential cannot be initiated
- The refractory period is a result of a temporary inactivation of the Na+ channels
- Inactivated Na+ channels behind the zone of depolarization prevent the action potential from traveling backwards
Action potentials travel in only one direction which is?
toward the synaptic terminals
The speed of an action potential increases with the axon’s
- In vertebrates, axons are insulated by a myelin sheath, which causes an action potential’s speed to increase
- made by glia
what are the 2 types of glia cells that make the myelin sheath?
oligodendrocytes in the CNS and Schwann cells in the PNS
nodes of Ranvier
Action potentials are formed only at nodes of Ranvier, gaps in the myelin sheath where voltage-gated Na+ channels are found
Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction
At electrical synapses, the electrical current flows from one neuron to another
- At chemical synapses, a chemical neurotransmitter carries information across the gap junction
- Most synapses are chemical synapses
The presynaptic neuron synthesizes and packages the neurotransmitter in what located in the synaptic terminal
The action potential causes the release of the what
The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell
Excitatory postsynaptic potentials (EPSPs)
depolarizations that bring the membrane potential toward threshold
Inhibitory postsynaptic potentials (IPSPs)
are hyperpolarizations that move the membrane potential farther from threshold
Unlike action potentials, postsynaptic potentials are graded and do not what
Most neurons have many synapses on their what and what?
dendrites and cell body
A single EPSP is usually too small to trigger an action potential in a
If two EPSPs are produced in rapid succession, an effect called temporal summation occurs
The same neurotransmitter can produce different effects in different types of cells
there are 5 classes of neurotransmitters what are they?
- biogenic amines
- amino acids
- a common neurotransmitter in vertebrates and invertebrates
- In vertebrates it is usually an excitatory transmitter
- One proposed cause of Alzheimer's disease is reduced synthesis of Acetlcholine
what 3 drugs affect receptors?
biogenic amines (4)
- They are active in the CNS and PNS
- Dopamine used in reward driven learning–Cocaine and methamphetamine act on dopamine receptors
- Diseases associated with dopamine include schizophrenia and ADHD
Two amino acids are known to function as major neurotransmitters in the CNS:
- gamma-aminobutyric acid (GABA)
- GABA is never incorporated into a protein
- GABA is inhibitory
- Glutamate is excitatory
Several neuropeptides, relatively short chains of amino acids, also function as neurotransmitters
they include what 2?
- Neuropeptides include substance P and endorphins, which both affect our perception of pain
- Opiates bind to the same receptors as endorphins and can be used as painkillers
- Naked mole rats lack sensitivity to substance P and thus insensitive to pain on their skin