Chapter 3 The Brain and the Nervous System
The Organism as a Machine
Idea that human behaviors, thoughts and feelings are a product of the brain.
Attributed to the philosopher Rene Descrates (1596 - 1650)
Building Blocks of the Nervous System
Neuroscience: a multidisciplanary effort that effort that seeks to understand the nature, function, and
origins of the nervous system.
Uses insights from psychology, but also draws from biology, computer science, medicine, and
Neurons: a specialized cell in the nevous system that accumulates and transmits information.
Nerve Impulse: means through which individual neurons communicate with each other.
Neurons specialize in sending and recieving information
Have 3 main parts
Dendrites: the branched part of a neuron that recieves impulses and conducts them toward the
Cell body: portion of the neuron contaning the metabolic machinery that keeps the cell alive and
Axon: part of neuron that transmits impulses to glands, muscles or other neurons.
Motor Neurons: transmits neural impulses from the brain to the muscles.
Efferent Neurons: nerves that carry messages outward from the central nervous system.
Afferent Neurons: nerves that carry messages inward toward the central nervous system.
Interneurons: neurons that are neither afferent nor effernt, but instead carry information from
one neuron to another.
provides nourishment for the neurons.
controls the amount of nutrient supply.
sensitive to activity level in each neuron and increase the blood flow.
Plays a role in brain development.
to increase the speed of neural communication. o substance that speeds this up the most is Myelin ( a fatty substance that makes up some
types of glial calls; these cells wrap around the axon of some neurons, providing an
insulating "myelin sheath" around these neurons.
o Nodes of Ranvier: gaps between myelin sheaths.
o White Matter: consists of myelinated axons traversing long distances either within the
brain or to and from the body
o Gray Matter: consists of cell bodies, dendrites and the unmyelinated axons.
send signals that help regulate the strenght of connections between adjacent neurons.
Some circumstances they can also release chemicals that increase the reactivity of neurons.
Possible seperate slow signaling system within the brain.
Respond to various electrical, chemical and mechanical stimuli.
form networks that communicate with each other and that may modulate the activity level of
neurons near by.
Communications Among Neurons
we look at the functioning of individual neurons and ask what is it about these cells that allows them to -
to change their functioning to response to stimulation.
how response is transmitted witin the neuron.
how info travels between neurons.
communication within the nueron.
take a closer look at the chemical signals that trigger neurons communication with one another.
Activity and Communication within the Neuron
Action Potential: a breif change in teh electircal charge of a neuronal membrane; the physical basis of
the signal that travels the length of the neuron.
this signal is sent from one end of the neuron to another.
is the nuerons main response to input as wall as the fundamental information carrier of the
Resting Potential: the voltage difference between the inside and outside of a neuronal membrane when
the neuron is not firing.
Excitiation Threshold: the voltage difference a neuron's interior and exterior that, if exceeded, causes
the neuron to fire.
Explaining the Action Potential Refractory Period:time after an action potential during which a neurons cell membrane is unprepared
for the next action potential.
Propagation of The Action Potential
Depolarize: in the nervous system, to lost the charge that normally exists across the neuronal
Propagation: the spread of the action potential down an axon, cause by successive changes in electrical
charge along the length of the axon's membrane.
All or None Law
all of none law: the law that all action potentials have the same strenght and speed regardless of the
synapse: small gap between two adjacent neurons, consisting of the presynaptic and postsynaptic
neurons membranes and the space between them.
The Synaptic Mechanism
Neurotransmitters: chemicals released by one neuron, which triggers a response in another neuron; the
cheif means of communication among neurons.
Synaptic Re-uptake: presynaptic neuron's process of reabsorbing its own neurotransmitters after
signaling so that they can be released again the next time the neuron fires.
Drugs and Neurotransmitters
Agonists: drugs that enhance a neurotransmitters activity.
Antagonists: drugs that impede the activity of a neurotransmitter.
Blood Brain Barrier: specialized membranes that surround the blood vessels within the brain and filter
harmful chemicals out of the brains blood supply.
Communication through the Blood Stream
endocrine system: system of the glands that release secretions directly into the bloodstream and affect
organs elsewhere in the body. hormone: a chemical rele