Chapter 2Brain and Behavior

By the End of this Lecture, Students will be able to:

Neuron and Its Parts

• Neuron: Individual nerve cell– Dendrites: Receive messages from other neurons– Soma: Cell body; body of the neuron– Axon: Fiber that carries information away from the

cell body– Axon Terminals: Branches that link the dendrites

and somas of other neurons

Figure 2.1

FIGURE 2.1 A neuron, or nerve cell. In the right foreground you can see a nerve cell fiber in cross section. The upper left photo gives a more realistic picture of the shape of neurons. Nerve impulses usually travel from the dendrites and soma to the branching ends of the axon. The nerve cell shown here is a motor neuron. The axons of motor neuron stretch from the brain and spinal cord to muscles or glands of the body.

Synapses

Messages from one neuron to another pass over a microscopic gap called a synapse– Synapse: Microscopic gap between two

neurons over which messages pass

Figure 2.5

FIGURE 2.5 A highly magnified view of a synapse. Neurotransmitters are stored in tiny sacs called synaptic vesicles (VES-ihkels). When a nerve impulse reaches the end of an axon, the vesicles move to the surface and release neurotransmitters. These molecules cross the synaptic gap to affect the next neuron. The size of the gap is exaggerated here; it is actually only about one millionth of an inch. Some transmitter molecules excite the next neuron, and some inhibit its activity.

Neurotransmitters

• Chemicals that alter activity in neurons; brain chemicals that carry messages.– Acetylcholine: Activates muscles– Dopamine: Muscle control– Serotonin: Mood and appetite control

• Receptor Site: Areas on the surface of neurons and other cells that are sensitive to neurotransmitters

Nerves and Neurons

• Nerves: Large bundles of axons and dendrites (Not neurons)

• Myelin: Fatty layer of tissue that coats axons– Multiple Sclerosis (MS) occurs when myelin layer

is destroyed; numbness, weakness, and paralysis occur

• Neurogenesis: Production of new brain cells

Neural Networks

• Central Nervous System (CNS): Brain and spinal cord• Peripheral Nervous System: All parts of the nervous

system outside of the brain and spinal cord– Somatic System: Links spinal cord with body and

sense organs; controls voluntary behavior– Autonomic System: Serves internal organs and

glands; controls automatic functions such as heart rate and blood pressure

Figure 2.6

FIGURE 2.6 (a) Central and peripheral nervous systems. (b) Spinal nerves, cranial nerves, and the autonomic nervous system.

Two Divisions of the Autonomic System

• Sympathetic: Arouses body; emergency system• Parasympathetic: Quiets body; most active after an emotional

event

Figure 2.8

FIGURE 2.8 Sympathetic and parasympathetic branches of the autonomic nervous system. Both branches control involuntary actions. The sympathetic system generally activates the body. The parasympathetic system generally quiets it. The sympathetic branch relays its messages through clusters of nerve cells outside the spinal cord.

Figure 2.7

FIGURE 2.7 Subparts of the nervous system.

Researching the Brain

• Computed Tomographic Scanning (CT): Computer-enhanced X-ray image of the brain or body

• Magnetic Resonance Imaging (MRI): Uses a strong magnetic field, not an X-ray, to produce an image

• Functional MRI (fMRI): MRI that also records brain activity

• Positron Emission Tomography (PET): Computer-generated color image of brain activity, based on glucose consumption in the brain

Cerebral Cortex

• Definition: Outer layer of the cerebrum• Cerebrum: Two large hemispheres that cover upper

part of the brain• Corticalization: Increase in size and wrinkling of the

cortex• Cerebral Hemispheres: Right and left halves of the

cortex• Corpus Callosum: Bundle of fibers connecting

cerebral hemispheres

Split Brains

• Corpus Callosum is cut; done to control severe epilepsy (seizure disorder).

• Result: The person now has two brains in one body.• This operation is rare and is often used as a last

resort.

Figure 2.19

FIGURE 2.19 Basic nerve pathways of vision. Notice that the left portion of each eye connects only to the left half of the brain; likewise, the right portion of each eye connects to the right brain. When the corpus callosum is cut, a “split brain” results. Then visual information can be sent to just one hemisphere by flashing it in the right or left visual field as the person stares straight ahead.

Figure 2.22

Figure 2.18

Spatial neglect resulting from a right hemisphere stroke. Notice the neglect of the left side of the pictures which were being reproduced.

When the Brain Fails to Function Properly

• Broca’s Area: Related to language and speech production– If damaged, person knows what s/he wants to say

but can’t say the words• Wernicke’s Area: Related to language comprehension– If damaged, person has problems with meanings

of words, NOT pronunciation

Figure 2.25

FIGURE 2.25 This simplified drawing shows the main structures of the human brain and describes some of their most important features. (You can use the color code in the foreground to identify which areas are part of the forebrain, midbrain, and hindbrain.)

Limbic system

• First studied By:

– Paul Broca (1824-1880)– James Papez (1883-1958)

Forebrain

• Structures are part of the Limbic System: System within forebrain closely linked to emotional response– Thalamus: Relays sensory information to the

cortex; switchboard– Hypothalamus: Regulates emotional behaviors

and motives (e.g., sex, hunger, rage, hormone release)

– Amygdala: Associated with fear responses– Hippocampus (Seahorse): Associated with storing

memories; helps us navigate through space

Figure 2.26

FIGURE 2.26 Parts of the limbic system. Although only one side is shown here, the hippocampus and the amygdala extend out into the temporal lobes at each side of the brain. The limbic system is a sort of “primitive core” of the brain strongly associated with emotion.

• Limbic System: • The Emotional Brain Structures lying deep

within the cerebral hemispheres.

Coordinates behaviors needed to satisfy motivational and emotional urges arising in the hypothalamus.

Also involved in memory.

Functions

• “Emotional brainEmotional and motivational aspects of

behavior.Provides emotional component to learning process:

Especially the amygdala.• Associated with memory

Especially the hippocampus.• Associated with pain/pleasure, rage

• Limbic System: Structure

Hippocampus: Learning and Memory

• Limbic System: Structure

Hippocampus: Learning and Memory

Amygdala:Emotions and Aggression

Functions of the Amygdala

• Relate environmental stimuli to coordinated behavioral autonomic and endocrine responses seen in species-preservation.

• Plasticity• Responding to stress• Vigilance/attention• Learning about emotional stimuli• Pavlovian learning, or classical conditioning• Affective state

• Responses include:

Feeding and drinking

Agnostic (fighting) behavior

Mating and maternal care

Responses to physical or emotional stresses.

Model of associative learning in the amygdala

• Limbic System: Structure

Hippocampus: Learning and Memory

Amygdala: Emotions and Aggression

Hypothalamus:Hunger, ThirstTemperature Control

• Limbic System: Structure

Hippocampus: Learning and Memory

Amygdala: Emotions and Aggression

Hypothalamus:Hunger, ThirstTemperature Control

Thalamus:Relay Center for SensoryInformation

• Limbic System: Structure

Hippocampus: Learning and Memory

Amygdala: Emotions and Aggression

Hypothalamus:Hunger, ThirstTemperature Control

Thalamus:Relay Center for SensoryInformation

Pathologies (lesions)

• Voracious appetite• Increased (perverse) sexual activity• Docility:

Loss of normal fear/anger response• Memory loss:

Damage to hippocampus portion:Cells undergoing calcium-induced

changes associated with memory

Kluver-Bucy Syndrome:

• Results from bilateral destruction of amygdala.• Characteristics:

Increase in sexual activity.Compulsive tendency to place objects in

mouth.Decreased emotionality.Changes in eating behavior.Visual agnosia.

Stress

1. A state of threatened homeostasis

2. The thing responsible for the imbalance. aka stressor

3. The body’s response to the imbalance. aka stress-response

The Flight or Fight Response

1. Perceive extreme danger or distress2. Neurons send entire body into “high gear”3. Responsively prepare for “fight or flight”“flight or flight” response = generalized set of changes

in cardiovascular, respiratory, blood flow, and metabolic systems, such as increased blood glucose (e.g.Cannon, 1920)

Hans Selye Experiment

• Early research project: Ovarian extract—What does it do?– Inject rats every day ulcers, enlarged adrenal

glands, & shrunken immune tissues– So did control rats!!– So did others subjected to cold, heat, forced

exercise, surgical procedures– Stress!

Selye’s General Adaptation Syndrome (GAS)

• Described as body’s adaptive response to stress– Stage 1: The alarm reaction in which the

body prepares itself for “fight or flight.”– Stage 2: Since the first stage cannot long be

sustained, there is a general resistance to the stress which is established.

– Stage 3: If the stress is continued for a long period of time, then eventual exhaustion results (the body’s response to prolonged “wear and tear”).

Selye’s Third Stage

• Overcome by physiological, psychological, and environmental changes (stressors)

• Failure to accommodate to changes can lead to exhaustion

• Currently extensive investigation into this as potential contributor to many “western” health problems.

The stress response is non-specific

short-term

adaptive

long-term

maladaptive

Two component stress-response

The fastest response to stress is the activation of the Autonomic Nervous System (ANS) • ON: seconds

The slow response to stress is activation of the Hypothalmus-Pituitary-Adrenal axis (HPA) • ON: minute(s)

Psychological Variables

Learning and habituationSocial factorsIndividual differences

Social Factors

Most studies show that dominant animals have lower cortisol than subordinate animalsParticularly with social unrest

Ex: Vervet monkeys in captivity form social hierarchy then dominants constantly harass subordinates.

Subordinate animals died at younger age and had enlargedadrenal glands, atrophied hippocampus and ulcers (sounds like Selye’s rats)

Opposite Outcome: Dominant African wild dogs and mongooses have higher cortisol than subordinate-likely due to constant defense of hierarchy

Individual differences

• Subordinate baboons = sicker? Too simplistic• Dominant males may fight to stay on top.

• If subordinates not harassed not bad– Things are worst during stable hierarchy ie

dominants have no real challenges so they harass subordinates.

• Social support: groom females, play with kids• Status rising or falling• Glass half full/half empty

Social support appears to serve as a “stress buffer”

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Also, time required to return to baseline:

Paired: 45 min

Single: 75 min

***lactating women and female rats also have dampened HPA axis responses*****

Stress and health

• Long-term uncontrollable stress – Inhibits immune system– Depletes energy stores • always tired, muscle weakness

– Disrupts limbic function• Increases depression• (Interferes with memory)

• Antidepressants • hippocampal neurogenesis as they improve mood.