Biological Basis of Behavior
Activity in the Central nervous system
begins at the cellular level, with both electrical and chemical processes. In psychology, we first study the activity of the central nervous system at the cellular level.
Neurons receive information via the dendrite and pass information down the axon to the synapse.
The Action Potential:
Excitatory impulses and inhibitory impulses alter a cells internal potential or charge.
When a cell's potential reaches a certain level, the cell "depolarizes" or becomes positive, causing an action potential.
Ion Movement within the Action Potential:
The action potential causes a rush of sodium ions (positive) into the neuron and potassium ions (minus) out of the neuron, The cell "repolarizes" as the ions become balanced, often causing a "hyperpolarization".
"Lock and Key":
As a result of the action potential, neurotransmitters are released into the synaptic junction. Specific neurotransmitters bind with specific receptor sites to allow the passage of chemicals into the receptor neuron.
Overview of the Synapse:
The action potential causes a release of neurotransmitters which bind to the receptor site
much like a key in a lock. This triggers a post-synaptic potential, which opens the post-synaptic membrane.
Excess neurotransmitters are cleared from the synapse so future action potentials can occur.
Reuptake of Neurotransmitter:
The terminal button of the axon reabsorbs (takes up) the left-over neurotransmitter in the synapse.
This reduces the chance of the post-synaptic cell from being re-excited by the initial action potential.
Blocking the Receptor:
Antagonists can block the receptor site, as with the orange chemicals in the movie, thereby preventing
neurotransmitters from binding with receptor sites. Drugs such as Curare, can cause lethal paralysis by preventing activity in motor neurons, including those which control the muscles in the lung. You may be more familiar with Novicaine, a centrally-acting blocker. After being injected with Novicaine at the dentist's office, you experience a loss of feeling, as Novicaine occupies or blocks sensory receptors.
Drugs Acting as Transmitters:
Agonists, as pictured in purple, can act as neurotransmitters, thereby causing the post-synaptic membrane to "open" or "fire".
A drug such as Mescaline mimics the neurotransmitters Dopamine and Norepinephrine which are responsible for initiating and maintaing arousal and alertness.
Drugs which Block Reuptake:
Cocaine, commonly known as a stimulant, blocks the reuptake of dopamine, seratonin, and norepinephrine, which play a role in regulation of mood. Initial use can cause elevated mood, as excess amounts are released.
When the reuptake of these transmitters is blockes, the excess dopamine continues to excite the receptor. However, over time the body produces less and less, and the natural stores are depleted, resulting in decreased mood.
- Cells communicate through electrical and chemical interactions.
- Electric communication begins with Action Potential
- Depolarization causes release of neurotransmitters
- Chemical interactions are caused by release of neurotransmitters
- Neurotransmitters cause a change in the post-synaptic cell
- The post-synaptic cell can also be changed through:
- drugs which act as neurotransmitters (agonists)
- increase release of neurotransmitter
- increase production of neurotransmitter
- mimic presence of neurotransmitter
- act directly on receptor
- drugs which block receptors (antagonists)
- drugs which cause neurotransmitters to remain (block re-uptake)
Organization & Structure:
The central nervous system has an inherent organization and structure. With an understanding of cellular activity, we then study this organization.
The Central Nervous System comprises the brain and spinal cord.
The Peripheral Nervous System comprises the nerves external (peripheral) to the spinal cord.
The Autonomic Nervous System is comprised of the Sympathetic and
Parasympathetic Nervous Systems. These systems are responsible for activating and de-activating internal states needed at moments of
"fight vs. flight".
Historical Perspective of Brain Functioning:
- Trephanation: early brain surgery
- Phrenology: function and skull shape
- Mass Action: Size related to behavior
- Localization of function
Luria's Working Brain
Unit I: Regulating and Maintaing Arousal
Unit II: Receiving, Storing, Transmitting
Unit III: Executive Functions
Brains of a rabbit, cat, and monkey, showing both the lateral surface (top) and the medial surface (bottom). The limbic system (dark area) shows less variation in size across mammalian species than does the cerebral cortex.
(From MacLean, 1954)
Division of the Lobes of the Cerebral Cortex
- Planning, coordinating, inhibiting actions
- Supervisory control over cortex
- Motor relay station
- Primary auditory reception and relay (cortical)
- Auditory and musical memory
- Sense of timing
- Primary somatosensory reception and relay
- Arithmetic & Language Organization (angular gyrus)
- Sense of position & direction
Sensory and Motor Areas:
- Primary (cortical) visual reception and relay
- Visual perception
- Cortical sensory perception
- Cortical morot control
Neuropsychology of Speech:
Broca's Area (expressive) and Wernike's Area (receptive) are crucial to communication.
Epileptic Seizures result from random electrical activity. This electrical activity spreads from one
brain area to many, creating an overload of synaptic activity.
In order to control the electrical activity caused by epileptic seizures, researchers separated the hemispheres of the brain.
By cutting the corpus collosum, which connects the two hemispheres, activity was localized to one side of the brain. The video explains the procedure and the resulting cognitive changes.