CHAPTER 3 psych 100

THE NEURAL BASES OF BEHAVIOUR

neurons are the basic building blocks of the nervous system linked together in circuits, not unlike the electrical circuits in a computer -vary greatly in size and shape --neurons have been exquisitely sculpted by nature to perform their function of receiving, processing, and sending messages -3 PARTS: 1.) a cell body- or soma, contains the biochemical structures needed to keep the neuron alive, and its nucleus carries the genetic information that determines how the cell develops and functions.The surface of the cell body also has receptor areas that can be directly stimulated by other neurons 2.) dendrites (tree)- emerge from cell body in branchlike fibres. specialized receiving units are like antennas that collect messages from neighbouring neurons and send them on to the cell body. There the incoming information is combined and processed 3.) axon-extends from one side of the cell body ; conducts electrical impulses away from the cell body to other neurons, muscles, or glands. branches out at its end to form a number of axon terminals; Each axon may connect with dendritic branches from numerous neurons, making it possible for a single neuron to pass messages to as many as 50,000 other neurons
Structural elements of a typical neuron. Stimulation received by the dendrites or soma (cell body) may trigger a nerve impulse, which travels down the axon to stimulate other neurons, muscles, or glands. Some axons have a fatty myelin sheath interrupted at intervals by the nodes of Ranvier. The myelin sheath helps to increase the speed of nerve conduction.

glial cells (glue)- support neurons in their functions. -surround neurons and hold them in place -manufacture nutrient chemicals that neurons need -form the myelin sheath around some axons -absorb toxins and waste materials that might damage neurons -prenatal brain development: glial cells send out long fibres that guide newly divided neurons to their targeted place in the brain -to protect the brain from toxins -walls of the blood vessels within the brain contain smaller gaps than elsewhere in the body, and they are also covered by a specialized type of glial cell blood-brain barrier- specialized barrier; prevents many substances, including a wide range of toxins, from entering the brain
:: the smaller gaps and glial cells keep many foreign substances from gaining access to the brain -2 IMPORTANT FUNCTIONS
1. generate electricity that creates nerve impulses.
2. release chemicals that allow them to communicate with other neurons and with muscles and glands. HOW NERVE ACTIVATION OCCURS (3 STEPS) At rest, the neuron has an electrical resting potential due to the distribution of positively and negatively charged chemicals (ions) inside and outside the neuron.
When stimulated, a flow of ions in and out through the cell membrane reverses the electrical charge of the resting potential, producing an action potential, or nerve impulse.
The original distribution of ions is restored, and the neuron is again at rest.
-neurons are surrounded by body fluids and separated from this liquid environment by a protective membrane.
-this cell membrane is a bit like a selective sieve; allows certain substances to pass through ion channels into the cell while refusing or limiting passage to other substances. ion channels - passageway or channel in the membrane that can open to allow ions to pass through
The chemical environment inside the neuron differs from its external environment in significant ways the process whereby a nerve impulse is created involves the exchange of electrically charged atoms called ions. outside: Na+ (sodium) and Cl- (chloride) inside: A- (anions) K+(Potassium) resting potential- internal difference of around 70 millivolts (thousandths of a volt) is called the neuron's
At rest, the neuron is said to be in a state of polarization.
(a) This resting potential