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