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Biological Bases of Behavior

Why study biology in a psychology class?
 “Everything psychological is simultaneously biological.”  Every thought, behavior, emotion, perception, etc. is rooted in our biology, particularly our brain  The brain is a “psychological organ” as well as a biological one

 Biological psychology: studies the link between our biology and our behaviors and mental processes  a.k.a. biopsychology, neuroscience

Starting small: The Neuron
 neuron: a nerve cell; receives signals from other neurons or sensory organs, processes these signals, and sends signals to other neurons, muscles, or bodily organs  the basic unit of the nervous system

The Neuron
3 types of neurons:
1. sensory neurons: respond to input from sensory organs (skin, eyes, etc.) 2. motor neurons: send signals to muscles to control movement 3. interneurons: connect the sensory neurons and motor neurons most of the neurons in the brain = interneurons

average human brain

100 billion neurons

plus 10x as many glial cells glial cell: a cell that fills the gaps between neurons, facilitate communication between neurons, and help in the care and upkeep of neurons

Structure of the Neuron

Structure of the Neuron

 cell body (soma): the central part of the neuron, contains the nucleus  regulates cell functioning

 dendrites: the branching part of the neuron that receives messages from other neurons and relays them to the cell body

Structure of the Neuron

 axon: the long, cable-like extension that delivers messages to other neurons  myelin sheath: layer of fatty tissue that insulates the axon and helps speed up message transmission  multiple sclerosis: deterioration of myelin leads to slowed communication with muscles and impaired sensation in limbs

 terminal button: structure at the end of one of the axon’s branches that releases chemicals into the space between neurons, when the neuron is fired

The Neuron in Action
resting potential: the negative charge maintained within neurons that are at rest due to more sodium ions outside neuron than inside, and more potassium inside neuron than outside

messages from other neurons are either excitatory (like pushing the neuron’s accelerator) or inhibitory (like pushing the neuron’s brakes) threshold: the level of stimulation required to trigger a neural impulse

The Neuron in Action
When the threshold is reached, channels in the cell membrane open and allow transfer of sodium and potassium ions action potential: a neural impulse; the shifting change in charge that moves down the axon to terminal buttons all-or-none law

From Neuron to Neuron
≈100 billion neurons in a human brain, connected to an average of 10,000 others; some up to 100,000 (Shepherd, 1999) synapse: the place where an axon of one neuron meets with the dendrite/cell body of another neuron

From Neuron to Neuron

From Neuron to Neuron
synaptic cleft: the gap between the axon and the dendrite/cell body across which neural transmission occurs neurotransmitters: a chemical that sends signals from one neuron to another over the synaptic cleft

From Neuron to Neuron
 Neurotransmitters are stored in vescicles in the terminal buttons, and bind to receptors on the cell membrane of the next neuron. Each receptor can only bind with one kind of neurotransmitter.  Some of the neurotransmitter remains in the synaptic cleft, needs a special chemical reaction to reuptake (reabsorb) to vescicles

Neurotransmitters at Work: An Example
Low levels of the neurotransmitter serotonin have been associated with clinical depression. depression treated with selective serotonin-reuptake inhibitors (SSRIs) e.g. Prozac, Zoloft, Paxil

(Some) Neurotransmitters
Neurotransmitter Function Examples of malfunctions

Acetylcholine (ACh)

Enables muscle action, learning & memory
Influences movement, learning, attention, & emotion Affects mood, hunger,...
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