(Lec.3) AP Psych. Biological Bases of Behavior…
Neuroanatomy … refers to the study of the parts and functions of neurons. Neurons are individual nerve
cells, and these cells make up our entire nervous system. Every neuron is made of discrete parts:
Dendrites root-like parts of the cell that stretch out from the cell body. Dendrites grow to make
synaptic connections with other neurons
Cell body contains the nucleus and other parts of the cell needed to sustain its life
Axon wire-like structure ending in the terminal buttons that extends from the cell body
Myelin Sheath a fatty covering around the axon of some neurons that speeds neural impulses
Terminal Buttons the branched end of the axon that contains neurotransmitters
Neurotransmitters chemicals contained in terminal buttons that enable neurons to communicate.
Neurotransmitters fit into receptor sites on the dendrites of neurons (like a key fits into a lock)
Synapse the space between the terminal buttons of one neuron and the dendrites of the next neuron
How a neuron “fires” : In its resting state a neuron has an overall slightly negative charge because
mostly negative ions are within the cell and mostly positive ions are surrounding it. The cell membrane
of the neuron is selectively permeable and prevents these ions from mixing. Visualize a two-neuron
chain, the reaction begins when the terminal buttons of the neuron are stimulated and release
neurotransmitters into the synapse. These neurotransmitters fit into receptor sites on the dendrites of
the second neuron. If enough transmitters are received the cell membrane of the second neuron will
become permeable and positive ions rush into the cell. The change in charge spreads down the length of
the second neuron like a bullet from a gun. This electric message firing is called an action potential
(roughly 120m/s). When the charge reaches the terminal button of the second neuron, the buttons
release neurotransmitters into the synapse. The process may begin again if enough neurotransmitters
are received by that next cell to pass the threshold (note that a neuron either fires completely or it does
not fire; all or nothing principle). If the dendrites of a neuron receive enough neurotransmitters to push
the neuron past its threshold, the neuron will fire completely every time. A neuron cannot fire a little or
a lot; the impulse is the same every time
Neurotransmitters: are the chemicals held in the terminal buttons that travel in the synaptic gap
between neurons. It is important to understand that different types of neurotransmitters exist. Some
neurotransmitters are excitatory, meaning that they excited the next cell into firing. Other
neurotransmitters are inhibitory, meaning they inhibit the next cell from firing. Each synaptic gap may
contain different amounts and types of inhibitory and excitatory neurotransmitters, and this will
determine whether it will pass the threshold and fire.
Acetylcholine (motor movement) – lack of acetylcholine is associated with Alzheimer’s disease Dopamine (motor movement and alertness) – lack of dopamine is associated with Parkinson’s
disease, overabundance is associated with schizophrenia
Endorphins (pain control) – involved in addictions
Serotonin (mood control) – Lack of serotonin is associated with clinical depression
Nervous system: Because neurons only fire in one direction, we need two sets of “wires” in order to take
in information as well as function.
Afferent (Sensory) Neurons: take the external information collected from the body’s senses to the brain
Interneurons: takes the information and send them between other (sensory/motor) neurons
Efferent (Motor) Neurons: take the information from the brain to the rest of the body to perform a
Central Nervous System: consists of our brain and spinal cord- all the nerves housed within bone.
Information about the structure and function of different parts of the brain is available in a later section.
The spinal cord is a bundle of nerves that runs through the center of the spine. It transmits information
from the rest of the body to the brain.
Peripheral Nervous System: consists of all the other nerves in your body- all the nerves not encased in
bone. The peripheral nervous system is divided into two categories: the somatic and the autonomic
- Somatic Nervous System: controls our voluntary muscle movements. The motor cortex of the
brain sends impulses to the somatic nervous system, which controls the muscles that allow us to
- Autonomic Nervous System: controls the automatic functions of our body- our heart, lungs,
internal organs, glands, and so on. These nerves control our responses to stress- the fight or
flight response that prepares our body to respond to a perceived threat. The autonomic nervous
system is divided into two categories: sympathetic and parasympathetic.
1) Sympathetic: mobilizes our body to respond to stress. This part of our nervous system
carries messages to the control systems of the organs, glands, and muscles that direct our
body’s response to stress. It accelerates some functions (heart rate, blood pressure,
respiration, etc.) but conserves resources needed for a quick response by slowing down
other functions. 2) Parasympathetic: responsible for slowing down our body after a stress response. It carries
messages to the stress response system that causes our body to slow down. Think of the
parasympathetic nervous system as the brake pedal that slows down the body’s autonomic
Normal Peripheral Nervous System Transmission: the normal transmission of messages traveling
through the nervous track (spine, brain), then a normal response of required movement or action. An
exception to normal peripheral transmission is reflexes. For instance under the knee people have
reflexes where the leg with reflex without conscious control. This instance, the information isn’t reached
the brain until after the body reacts.
Brain: has the main control of the human thought and behavior. Studying how the brain works is
challenging is difficult because we cannot explicitly see how the brain functions.
Ways to study the brain:
- Accidents patients who undergo accidents that affect their brain function can give
researchers clues about the brain function, and concluded that brain damaged in accidents are
affected by emotional control
- Lesion is the removal or destruction of the brain. This is never done for experimental
purposes, only in surgical procedures [removing of a brain tumor], and even after the surgery is
performed, the doctor monitors the behavior of the patient to see the effects.
- Electroencephalogram (EEG) detects brain waves, and researchers can examine what type of
waves the brain produces during different stages of consciousness and use this information to
generalize about brain function [widely used in stages of sleep and dreaming]
- Computerized Axial Tomography (CAT or CT) a sophisticated X-ray that is used to develop a
three dimensional picture of the brain’s structure, however