Neuroscience and Behavior
Chapter 2
Steven Isonio, PhD
Golden West College
Biological Basis of Behavior
In this unit, we will learn about biological aspects of behavior. Our focus will be on the brain and the
nervous system. This is a journey into an area of psychology that is undergoing explosive growth and
rapid change!
What is the function of the nervous system?
Functions of the nervous system
Information Processing
gather, analyze, encode, store, retrieve, synthesize, interpret, transmit, decide, use, communicate
Maintain consciousness
Create and maintain a working model of the world
Promote survival
General Orientation of Biological Psychology
Biological factors represent a major category of causes of behavior.
They are critical to a full understanding and explanation of behavior and mental processes.
This importance is emphasized by an enormous amount of recent research in most areas of
psychology.
Nervous system and behavior
--structure (parts/areas) of brain and function (behavior/mental processes)--how are they related?
Two basic positions have been taken on this question:
1: Localization of function is the notion that particular functions, such as aggression, vision,
emotions, are localized (controlled by) a specific part of the brain
2: Mass Action is the view that various parts of the brain actually work together ( en mass) to
produce most functions.
Localization of function taken to an extreme: Lessons of Phrenology
Phrenology is the belief that specific mental faculties (functions/traits) are controlled by very specific
parts of the brain which can be measured assessing bumps on the head. For example, a bump over the
self-esteem area indicates high self-esteem.
Research indicates that as a system, phrenology is . . .
UNFOUNDED, AND PERHAPS EVEN DANGEROUS . . .
Localization of function vs. mass action, today
As is often the case, truth lies somewhere between the extremes.
There clearly is an association between certain parts of the brain and functions, but the relationships
are far from perfect.
Localization of function--modern view (continued)
The norm is for multilevel contributions to complex functions.
As the brain develops, it does become less plastic (flexible), but its ability to adapt remains strong
throughout life
Let’s Consider . . .
the Structure of the Nervous System
Overall Structure of the Human Nervous System
Central N.S.
Brain
• Forebrain
• Midbrain
• Hindbrain
Spinal Cord
Peripheral N.S.
Somatic N.S.
• Sensory pathways
• Motor pathways
Autonomic N.S.
• sympathetic n.s.
• parasympathetic n.s.
The Brain
The 3-pound universe. Everything pales in comparison to the brain. The brain is unique all creation.
The Tools of Discovery
Clinical Observation
Manipulating the Brain – stimulate/lesion
Electrical Recording -- EEG
Neuroimaging
PET – activity (more, next slide)
MRI – structure
fMRI – activity of detailed structure
Structure of the Nervous System--
Brain
There are three major brain regions that differ in terms of general function, structure, and age:
• FOREBRAIN
• MIDBRAIN
• HINDBRAIN
Forebrain
Newest part of brain (cf. “the crown of creation”)-- Phylogenetically (species history, in view of
evolutionists), and ontogentically (individual development).
Controls most higher mental functions (e.g., problem solving, decision-making, planning,
contemplating)
Is the most anterior (top) and largest portion of human brain. Its size, relative to the rest of the
brain, is massive, particularly compared with the forebrains of other species.
Outer portion (covering) is the cerebral cortex
It is useful to differentiate subcortical structures (below the cortex) from cortex itself (surface).
Forebrain
Subcortical structures
Hypothalamus plays an important role in several motivated behaviors (sex, aggression, eating,
drinking, etc.) and regulates the pituitary gland.
Pituitary gland the ―master gland‖, it orchestrates the endocrine system, the body’s system of
hormones.
Thalamus is the primary relay center for information directed toward the sensory areas of the cortex.
Hippocampus is critical to the consolidation of new memories.
Forebrain -- cortical regions,
general areas (lobes)
Forebrain -- lobes
(―SURFACE GEOGRAPHY‖)
Frontal Lobe contains motor areas, personality integration and metacognition (prefrontal areas).
Temporal Lobe is essential for understanding of spoken language and some complex aspects of vision.
Parietal Lobe is a somatosensory (information about touch and body location) region.
Occipital Lobe processes visual information in a series of stages that extract and code increasingly
complex aspects of the image.
How we came to know much about the functions of the forebrain
Phinneas Gage had a hole in his head . . . as a result of an explosion that caused this railroad spike to enter
his forehead and exit from the top of his head.
A living experiment on the effects of frontal lobe dissociation:
More dramatic than his physical injury, though, were the changes in character and personality--the
formerly, respected, trusted and liked Phinneas became a drifter, lazy and irresponsible. Indeed,
he became a different person.
Video Segments:
Phinnea Gage: (approx. 12 mins.)
Midbrain
Located in the middle of the brain.
Phylogenetically older than the forebrain.
It’s size is dwarfed by the huge forebrain.
Roof of midbrain is the tectum, which contains the superior colliculus and the inferior colliculus
(sensory relay structures; visual/auditory)
Contains parts of the reticular formation (sets of structures for activation/arousal) and the substantia
nigra (important for initiating motor movements).
Key Midbrain Structures
Superior and inferior colliculi accomplish intermediate level processing of visual and auditory
information, respectively.
Parts of reticular formation which generally activates the brain in response to any stimulus.
Substantia nigra is critical for the initiation of voluntary motor activity.
Hindbrain
Posterior (bottom) part of the brain.
―Old brain‖
Contains the medulla (most posterior structure, becomes top of spinal cord; controls many vital
reflexes), pons (above medulla; contains nuclei for several cranial nerves; initiates REM periods), and
the cerebellum (large highly convoluted structure; helps in organizing sensory information that guides
movement, such as balance and coordination).
Locked-in Syndrome
Cerebral cortex is intact
Impact on emotions—facially expressed are enhanced; general bodily are diminished
Damage to Brainstem
Patient cannot communicate/move
Making connections
The brain has two, largely symmetrical,
halves (hemispheres) that differ in the way they orient to the world. One Brain, two hemispheres
The two halves are connected by bands of nerve tissue called commissures.
The corpus callosum is the largest such connector. It allows the two hemispheres to communicate
with each other.
Specialization of the Hemispheres--Wagner Preference Inventory
Hemispheric Specialization:
Some generalizations
Roger Sperry
S p l i t -B r a i n patients
We have learned a lot about the special qualities of each separate hemisphere through the
research of Roger Sperry, Michael Gazzaniga, and others, on patients whose corpus callosum
has been cut.
About connections . . .
Both control (outgoing commands) and inputs (incoming sensory information) are generally arranged
in a contra-lateral fashion.
That is, the connections are primarily (but not exclusively) left-to-right and right-to-left.
Think about:
Given contralateral control and inputs, and the language (left), visual-spatial (right) difference, how
would split-brain patients do when:
asked to name orally the object they have selected with their left hand; to draw the object with
their left hand . . .
With which hand would a patient do best at solving a visual-spatial puzzle?
Cerebrospinal Fluid (CSF): another ―shock absorber‖
1. CSF functions to protect the brain from damage by serving as a cushion to lessen the impact of the
trauma.
2. The flow from the CSF to the blood takes harmful substances away from the brain.
3. The CSF also provides a transport means for hormones to various areas of the brain. Hormones
released into the CSF can be carried to distant sites of the brain in order to exert some endocrine
influence.
4. It also provides buoyancy. Since the brain is immersed in this fluid, the net weight of the brain is
reduced from about 1,300 gm to about 50 gm. Pressure at the base of the brain is therefore
reduced.
Spinal Column
Spinal column consists of the vertebral column and the spinal cord.
The spinal cord connects the brain to the body below the neck and out to the periphery.
31 pairs of spinal nerves enter/leave the spinal cord, connecting it to the rest of the body (more later)
The spinal column itself consists of both ascending and descending tracts
Spinal cord damage
The nature and extent of spinal cord damage depends entirely on the location and degree of damage.
Damage in the sacral region (near ―tail bone‖) might produce paralysis limited to the lower part of the
body, whereas damage in the cervical region (near neck) would result in quadriplegia. It is also
possible for there to be more damage to sensory than to motor pathways, as well.
Now, beyond the Central Nervous System
Peripheral Nervous System--two aspects
Somatic Nervous System -- communication/ interaction with ―outside world‖. Classic senses
(incoming information); voluntary actions.
Autonomic Nervous System -- interaction with ―inside‖ world. Involuntary/visceral responses.
Somatic Nervous System
Spinal Nerves -- 31 pairs of sensory / motor nerves that synapse on the spinal cord and extend
throughout body.
Sensory = information traveling toward the CNS
Motor = information (commands) traveling away from the CNS
Bell-Magendie Law: sensory pathways enter dorsal side; motor pathways leave ventral side.
Technical Clarification . . .
The spinal cord itself is part of the CNS (Central Nervous System), whereas
The spinal nerves, although they connect to the spinal cord, are part of the PNS (Peripheral Nervous
System)--they ―reach out to the periphery‖.
The autonomic nervous system (ANS)
The ANS parallels the somatic nervous system in comprising the peripheral nervous system.
The ANS acts in an automatic way, generally beyond our direct control.
The ANS has two divisions--sympathetic and parasympathetic
Autonomic Nervous System
SYMPATHETIC BRANCH OF THE AUTONOMIC NERVOUS SYSTEM
Activates, arouses, energizes
Prepares us for emergency
―fight or flight‖ response
is catabolic--expends energy
e.g., increase heart rate and blood pressure, perspiration, respiration
Sympathetic nervous system
Well-integrated; in central regions of spinal cord.
Works in a highly coordinated fashion.
Autonomic Nervous System
PARASYMPATHETIC BRANCH OF THE AUTONOMIC NERVOUS SYSTEM
Deactivates, calms, quiets
Is anabolic (conserves energy)
e.g., lowers heart rate, blood pressure, respiration, etc.
Parasympathetic nervous system
Functions are generally opposite those of the sympathetic nervous system.
Is not arranged in a compact chain near the spinal cord, therefore it worked in a less coordinated
manner.
Transition--to cellular level
Let’s shift level of analysis from the overall structure of the nervous system to the cellular
level.
There are two main types of cells in the nervous system--nerve cells and glia cells.
We’ll start with nerve cells (called neurons when they are located in the brain).
Reticular theory; neuronal theory
Early in the history of psychology, communication networks in the nervous system were believed to be
continuous, similar to electrical circuits (reticular theory)
Santiago Ramon y Cajal using newly refined tools demonstrated that the neuronal theory (separate
units-- cells) is correct and that the reticular theory was wrong.
Neurons and glia cells--
the building blocks of the nervous system
(information-processing units in the nervous system)
The notion of a neural network:
There are more than 100 billion neurons in a typical adult human brain. Each communicates with
between 100 and 500,000 other neurons.
That is, potentially 100,000,000,000 times 500,000 connections
A supercomputer, indeed.
Incredible Variety
There are at least 200 geometrically distinct shapes of neurons.
There is no ―typical neuron‖
However, motor neurons are usually used for discussion purposes because they contain the major
features of neurons, and the features are distinct in motor neurons
A ―typical‖ motor neuron
Major structural features of a motor neuron
Dendrites are the branches that receive information from adjacent neurons
Soma (cell body) contains genetic material for cell, produces energy, makes some neurotransmitters
Major structural features of a motor neuron (continued)
Axon hillock is the ―calculator‖ that summates the incoming messages, some of which are excitatory
and others inhibitory to ―decide‖ if a nerve impulse will occur.
Axon is the elongated part of a neuron down which the impulse travels.
Major structural features of a motor neuron (continued)
Myelin sheath insulates most axons allowing for the rapid transmission of the nerve impulse.
Presynaptic terminal is the ―end-point‖ of the nerve impulse. Here, neurotransmitters are released
into the synapse.
Myelin Sheath and Nodes of Ranvier
Extensive Branching of Dendrites
Dendrites function as antennae, gathering signals from thousands of adjacent neurons.
They are typically widely branched.
Small spines on the branches change shape and number in response to experience.
Neural Communication
A barrage of inputs arrive at a “receiving” nerve cell each moment.
Some are excitatory (increase likelihood of an impulse) and others are inhibitory (decrease likelihood of an
impulse)
If the excitatory inputs sufficiently outweigh the inhibitory ones and the threshold is reached, then an
impulse occurs.
Inputs are summated (added together) if they occur close together in time or location:
All-or-none principle
If the threshold (required level of stimulation to trigger a nerve impulse)is reached, the nerve cell will
respond completely. If the threshold is not reached, there is no response at all.
Myers: ―like guns, neurons either fire or they don’t‖
Speed of the Nerve Impulse
Nerve impulse (action potential) = intra-neuronal communication.
Although the occurrence of an action potential is either “all-or-none”, their speed varies.
The impulse can be as fast as 200+ miles per hour in some myelinated axons or as slow as about 2 mph.
Nerve Impulse vs. Synaptic transmission
Nerve impulse (action potential) = flow of information (in form of electro-chemical event) from point
of entry to point of departure within a single neuron
Synaptic transmission = communication between adjacent neurons; message sent from one to
another via neurotransmitters
Inter-neuronal Communication
Communication between adjacent neurons, across the synapse=
Synaptic Transmission
NEUROTRANSMITTERS are the chemicals of communication in the nervous system.
They accomplish the transmission of information across the synapse.
Synaptic Transmission
NT is released from ―sending‖ neuron
NT crosses synapse and binds to receptor site of ―receiving‖ neuron
Message to receiving neuron is either excitation or inhibition
Barrage of inputs is summated; if the threshold is reached, an action potential (nerve impulse) occurs
Synaptic Transmission
NTs are released into synapse and bind to postsynaptic receptors.
Cajal: ―protoplasmic kisses‖
Then, they are either taken back by the presynaptic cell, destroyed, or diffused.
Neurotransmitters (NTs)
There are dozens of neurotransmitters, all are made from nutrients used by the cell.
Neurotransmitters
NTs ―specialize‖ in certain types of information transmission in different parts of the nervous system.
For example, serotonin is made in relatively few cells in the hindbrain that extensively branch to many
other reasons of the brain; it plays a key role in activation/arousal and mood.
Dopamine plays the key role in motor movement (e.g., Parkinson’s Disease involves extremely low
dopamine levels). It also is the neurotransmitter involved in schizophrenia—when dopamine levels are
excessive.
Neurotransmitters
Nts bind to the receptor site on the receiving neuron where they initiate various processes.
Serotonin and psilocin, chemical similarities
Two other important NTs:
GABA – inhibitory neurotransmitter. Anti-anxiety medications promote the activity of GABA
Ach -- active at neuromuscular junctions; critical for learning and memory
Within the story of synaptic transmission are answers to questions about mood and madness, motives and movement -
-the very nature of the mind.
glial cell
The Rodney Dangerfield of the Nervous System Functions of Glia Cells
Remove waste, particularly dead neurons.
Form the myelin sheath around axons of neurons.
Aid regeneration of damaged axons.
Guide migration of neurons during development.
Provide support structure
Unlike neurons, they do not transmit information.