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Chapter 3 Summary (Biology and Behavior)
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Chapter 3 Biology and BehaviorHow does the nervous system operate?
The entire nervous system is divided into two basic units: the central nervous system and the
peripheral nervous system.
Central nervous system (CNS): The brain and the spinal cord
Peripheral nervous system (PNS): all nerve cells in the body that are not part of the central nervous
system. The peripheral nervous system includes the somatic and autonomic nervous systems.
The somatic component is involved in voluntary behavior. The autonomic component is responsible
for the less voluntary actions of your body.
3.1 Neurons are the basic units of the nervous system
Neurons: the basis units of the nervous system: cells thar receive, integrate, and transmit
information. They operate though electrical impulses, communicate with other neurons through
chemical signals, and from neural networks.
Complex networks of neurons sending and receiving signals are the functional basis of all
psychological activity.
- Functions of neurons
Neurons are specialized for communication with each other. Nerve cells are excitable: they are
powered b electrical impulses and communicate with other nerve cells through chemical signals.
During the reception phase, neurons take in chemical signals from neighboring neurons.
During integration, incoming signals are assessed.
During transmission, neurons pass their own signals to yet other receiving neurons.
There are many types of neurons:
Somatosensory nerves → the sensory nerves that provide information from the skin and muscles.
Motor neurons → direct muscles to contract or relax, thereby producing movement.
Interneurons → act as relay stations facilitating communication between sensory and motor neurons
Sensory neurons → detect information from the physical world and pass that information along the
brain.
Sensory and motor neurons work together to control movement.
, - Neuron structure
A typical neuron has four structural regions that participate in communication functions: the
dendrites, the cell body, the axon, and the terminal buttons.
Dendrites: branchlike extensions of the neuron that detect information from other neurons.
Cell body: the site in the neuron where information from thousand of other neurons is collected and
integrated.
Axon: a long, narrow outgrowth of a neuron by which information is conducted from the cell body to
the terminal buttons.
Terminal buttons: at the ends of axons, small nodules that release chemical signals from the neuron
into the synapse
Synapse: the gab between the terminal buttons of a “sending” neuron and the dendrites of a
“receiving” neuron, where chemical communication occurs between the neurons.
The outer surface of a neuron is a membrane. The membrane is selectively permeable.
Located on the membrane are ion channels. These specialized pores allow ions to pass in and out of
the cell when the neuron transmits signals down the axon.
By controlling the movement of ions the membrane plays an important role in communication
between neurons: it regulates the concentration of electrically charged molecules that are the basis
of the neuron’s electrical activity.
Massages are received by the dendrites, processed in the cell body, transmitted along the axon, and
sent to other neurons via chemical substances released from the terminal buttons across the
synapse.
, 3.2 Action potentials produce neural communication
Neural communication depends on a neuron’s ability to respond to incoming stimulation. The neuron
responds by changing electrically and then passing along chemical signals to other neurons. An action
potential is the electrical signal that passes along the axon. This signal causes the terminal buttons to
release chemicals that transmit signals to other neurons.
Action potential: the electrical signal that passes along the axon and subsequently causes the release
of chemicals form the terminal buttons.
- Resting membrane potential
Resting membrane potential: the electrical charge of a neuron when it is not active.
The difference in the electrical charge occurs because the ratio of negative to positive ions is greater
inside the neuron than outside it. When a neuron has more negative ions inside than outside, the
neuron is described as being polarized.
Two types of ions that contribute to a neuron’s resting membrane potential are sodium ions and
potassium ions.
Ions pas through the neuron membrane at the ion channels. Each channel matches a specific type of
ion. The flow of ions through each channel is controlled by a gating mechanism. When a gate is open,
ions flow in and out of the neuron through the cell membrane. Ion flow is also affected by the cell
membrane’s selective permeability.
Another mechanism in the membrane that contributes to polarization is the sodium-potassium
pump. This pump increases potassium and decreases sodium inside the neuron, thus helping
maintain the resting membrane potential.
- Changes in electrical potential lead to an action potential
A neuron receives chemical signals from nearby through its dendrites. These chemical singals impact
the local ion channels, thus influence the polarization of the neuron. By affection polarization, these
chemical signals tell the neuron whether to fire. The signals arrive at the dendrites by thousands and
are of two types: excitatory and inhibitory.
Excitatory signals depolarize the cell membrane (i.e., decrease polarization by decreasing the
negative charge inside the cell relative to outside the cell). Through depolarization, these signals
increase the likelihood that the neuron will fire.
Inhibitory signals hyperpolarize the cell (I.e., increase polarization by increasing the negative charge
inside the cell relative outside the cell). Through hyperpolarization, these signals decrease the
likelihood that the neuron will fire.
Excitatory and inhibitory signals received by the dendrites are combined within the neuron.
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