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Neuroscience and Behavior

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Neuroscience and Behavior

Neuroscience and Behavior 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 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 Midbrain

    ; 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 emotionsfacially 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

    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 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 systemParasympathetic 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 leve lTransition--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 theor yReticular 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 systemthe 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 Speed

    ;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 schizophreniawhen 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.

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