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Biological Basis of Behavior
Wadsworth, a division of Thomson Learning
Nervous System
Peripheral Nervous System• Somatic Nervous System-voluntary system• Autonomic Nervous System-involuntary
system• Parasympathetic System-calming
• Sympathetic System-activating
Central Nervous System• Brain• Spinal Cord
Anatomy of the Brain Hindbrain
• Medulla-controls vegetative function• Pons-serves as an area of decussation at the
hindbrain level• Cerebellum-coordination of movement and
postural reflex Midbrain
• Reticular Formation-oversees arousal and attentional processes
Forebrain• Limbic System-composed of the hippocampus,
hypothalamus and amygdala and controls emotions and memory
• Thalamus-primary relay station for the senses• Cortex-composed of the frontal, temporal,
parietal, and occipital lobes
Cerebral Cortex Frontal Lobes
• controls body movement through the motor cortex
• decision making• speech production
Temporal Lobes• critical region for hearing and balance• important in memory
Occipital Lobes• responsible for visual processes
Parietal Lobes• receives contralateral sensory information
Neurons Anatomy
• Cell Membrane• semipermeable, bilipid layer that provides protection for the
cell• Dendrites
• the branching part of the neuron that receives information from other cells
• Cell Body• The part of the cell that contains the DNA and the machinery
for producing energy in the cell• Axon Hillock
• The region of the axon that determines if an action potential should occur
• Axons• The part of the neuron that sends information to other cells and
muscles• Axon Terminals
• Located at the end of the axon, they are the area from which neurotransmitters are released
• Myelin Sheaths• Fatty, insulating substance that covers some axons• Increases the speed of information traveling down the axon
Between Cell Communication Some Definitions
• Synaptic Cleft-the small space that occurs between the axon terminal of one cell and the dendrite of another
• Vesicles-small packages that store neurotransmitter in preparation for release from the presynaptic cell
• Neurotransmitters-chemicals capable of eliciting change in a receiving cell
• Postsynaptic cell-the cell that receives the new message
• Presynaptic cell-the cell that is sending the new message
Between Cell Communication The Process
• When a message needs to be passed on to other cells, vesicles which contain neurotransmitter merge with the cell membrane and release neurotransmitter into the synaptic cleft
• Neurotransmitters pass across the synaptic cleft and binds to receptors on a postsynaptic cell
• The neurotransmitter binds the receptor in a lock and key fashion
• Once neurotransmitter has bound the receptor, it pops off the receptor and must be eliminated so that it does not continue to bind to the postsynaptic cell
Terminating Neurotransmission
Enzymatic Degradation• When an enzyme breaks down the
neurotransmitter in the synaptic cleft
Reuptake• Taking the neurotransmitter back into the
terminal button from where it was released
Select Neurotransmitters Acetylcholine
• Involved in muscle movement and memory Gamma-aminobutyric acid
• The primary inhibitory neurotransmitter in the brain Serotonin
• Involved in mood and sleep Dopamine
• Involved in movement and reward systems Norepinephrine
• Involved in arousal, mood, and sympathetic nervous system activation
Opioids• Involved in pathways that reduce pain
Within Cell Communication Resting Membrane Potential
• -70mV• Due to separation of ions across the membrane• During rest, there are more negatively charged
ions on the inside of the cell than on the outside
Combining Within and Between Cell Communication Excitatory Postsynaptic Potentials-when
neurotransmitter in the synapse binds receptors and positively charged ions enter the cell
Inhibitory Postsynaptic Potentials-when neurotransmitter in the synapse binds receptors and negatively charged ions enter the cell
Within Cell Communication Action Potential
• occurs when a cell becomes depolarized• at the axon hillock the cell suddenly allows
positively charged ions to pass to the inside of the cell
• this change occurs at every segment of the cell from the axon hillock to the terminal buttons
• the action potential is all-or-none, indicating that it does not change in strength as it passes down the axon
• saltatory conduction occurs in myelinated cells
The Steps of the Action Potential Cell begins in resting state (-70mV) Cell reaches threshold and signals an action
potential Cell reaches the peak of the action potential by
allowing positive ions to rush to the inside of the cell (+40mV)
Cell begins to return to resting state by pumping positively charged ions to the outside of the cell
Cell enters absolute refractory period (a period when an EPSP cannot signal a new action potential)
Cell enters relative refractory period (a period when only a very strong EPSP can signal a new action potential)
A return to resting state
Endocrine System Hypothalamus signals to the pituitary Pituitary signals other glands of the
endocrine system to secrete hormones Examples of hormones:
• Estrogen/testosterone• Thyroid• growth hormone• follicle-stimulating hormone