Chapter 2Brain and Behavior

Neuron and Its Parts

• Neuron: Individual nerve cell; 100 billion in brain

Neuron’s Parts

– Soma: Cell body; body of the neuron. Receives messages and sends messages down axon

– Axon: Fiber that carries information away from the cell body of a neuron

– Axon terminals: Branches that link the dendrites and somas of other neurons

– Dendrites: Receive messages from other neurons

Fig. 2-1, p. 49

Fig. 2-4, p. 51

Video: Main Parts of the Neuron

The Nerve Impulse

• Resting potential: Electrical charge of an inactive neuron

• Threshold: Trigger point for a neuron’s firing• Action Potential: Nerve impulse

Fig. 2-2, p. 50

More on Nerves

• Ion channels: Tiny openings through the axon membrane

• Negative after-potential: A drop in electrical charge below the resting potential

• Synapse: Microscopic space between two neurons over which messages pass

Saltatory Conduction

• Process by which nerve impulses conducted down the axons of neurons coated with myelin jump from gap to gap in the myelin layer

• Myelin: A fatty layer coating some axons

Fig. 2-5, p. 51

Fig. 2-3, p. 50

Video: Action Potential

Video: Synaptic Transmission

Neurotransmitters

• Chemicals that alter activity in neurons; brain chemicals

• Receptor site: Area on the surface of neurons and other cells that is sensitive to neurotransmitters or hormones

Types of Neurotransmitters

– Acetylcholine: Activates muscles– Dopamine: Muscle control– Serotonin: Mood and appetite control

Neural Regulators

• Neuropeptides: Regulate activity of other neurons– Enkephalins: Relieve pain and stress;

similar to endorphins– Endorphins: Released by pituitary gland;

also help to relieve pain• Placebos raise endorphin levels

Fig. 2-6, p. 52

Neuroplasticity

• Capacity of our brains to change in response to experience

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

Nerves and Neurons (cont)

• Neurilemma: Thin layer of cells wrapped around axons outside brain and spinal cord; forms a tunnel that damaged fibers follow as they repair themselves

Fig. 2-7, p. 53

Two Divisions of the Peripheral Nervous System

• Somatic System: Carries messages to and from skeletal muscles and sense organs; controls voluntary behavior

• Autonomic System: Serves internal organs and glands; controls automatic functions such as heart rate and digestion pressure

Two Divisions of the Autonomic Nervous System

• Sympathetic: Arouses body; emergency system

• Parasympathetic: Quiets body; most active after an emotional event

Fig. 2-8, p. 54

The Spinal Cord

• Spinal Nerves: 31 of them; carry sensory and motor messages to and from the spinal cord

• Cranial Nerves: 12 pairs that leave the brain directly; also work to communicate messages

The Spinal Cord and Behavior

• Reflex Arc: Simplest behavior; occurs when a stimulus provokes an automatic response

• Sensory Neuron: Nerve cell that carries messages from the senses toward the CNS

• Connector Neuron: Nerve cell that links two others

• Motor Neuron: Cell that carries commands from the CNS to muscles and glands

Fig. 2-9, p. 54

Effector Cells

• Cells capable of producing a response

Neurogenesis

• The production of new brain cells

Brain Imaging Techniques

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

• Magnetic Resonance Imaging (MRI): Uses a strong magnetic field, not an X-ray, to produce an image of the body’s interior

Localization of Function

• Research strategy of linking specific structures in the brain with specific psychological or behavioral functions

Researching the Brain

• Ablation: Surgical removal of parts of the brain

• Deep lesioning: A thin wire electrode is lowered into a specific area inside the brain; electrical current is then used to destroy a small amount of brain tissue

• Electrical stimulation of the brain (ESB): When an electrode is used to activate target areas in the brain

Electroencephalograph (EEG)

• A device that detects, amplifies, and records electrical activity in the brain

More Brain Imaging Techniques

• Functional MRI: MRI that makes brain activity visible

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

Fig. 2-12, p. 58

Fig. 2-11, p. 57

Fig. 2-14, p. 59

Fig. 2-10, p. 57

Fig. 2-15, p. 59

Cerebral Cortex

• Definition: Outer layer of the brain; contains 70% of neurons in CNS

• 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

Neurological Soft Signs

• Subtle behavioral signs of brain dysfunction– Clumsiness– Awkward gait– Poor hand-eye coordination– Other perceptual and motor problems

Fig. 2-17, p. 60

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

Fig. 2-20, p. 62

Fig. 2-16, p. 60

Right Brain/Left Brain

• Humans use 95 percent of our left brain for language– Speaking, writing, understanding

The Left Hemisphere

• Left hemisphere better at math, judging time and rhythm, and coordinating order of complex movements– Processes information sequentially

The Right Hemisphere

• Right hemisphere good at perceptual skills, and at expressing and detecting other’s emotions– Good at recognizing patterns, faces, and

melodies– Processes information simultaneously and

holistically

Frontal Lobe

• Movement, sense of smell, higher mental functions– Contains primary motor cortex; controls motor

movement• Mirror neurons: Contained in motor cortex;

become active when motor action is carried out and when another organism is observed carrying out the same action

Video: Frontal Lobe

p. 65

Association Cortex

• All areas of cerebral cortex that are not primarily sensory or motor in function

Aphasia

• Language disturbance resulting from brain damage

Broca’s Area

• Related to grammar and pronunciation– If damaged, person knows what s/he wants

to say but can’t say the words

Prefrontal Cortex

• Front of frontal lobes; involved in sense of self, reasoning, and planning

Parietal Lobe

• Just above occipital; bodily sensations such as touch, pain, and temperature (somatosensory area)

• Primary somatosensory cortex: Receiving area for bodily sensations

Temporal Lobe

• Each side of the brain; auditory center and, for 95 percent of humans, language centers

• Primary auditory area: Auditory information is first registered here

Wernicke’s Area

• Related to language comprehension; in left temporal lobe– If damaged, person has problems with

meanings of words, NOT pronunciation

Fig. 2-24, p. 66

Occipital Lobe

• Back of brain; vision center• Primary visual area: Part of occipital lobe that

first receives input from the eyes

Fig. 2-19, p. 61

Fig. 2-22, p. 63

Fig. 2-23, p. 64

Agnosias

• Visual Agnosia: Inability to identify seen objects

• Facial Agnosia: Inability to perceive familiar faces

Fig. 2-18, p. 61

Subcortex

• All brain structures immediately below cerebral cortex

Hindbrain (Brainstem)

• Consists mainly of medulla and cerebellum• Also includes pons and reticular formation

Video: Hindbrain

Medulla

• Controls vital life functions such as heart rate, swallowing, and breathing

Pons (Bridge)

• Pons (Bridge): Acts as a bridge between medulla and other structures– Influences sleep and arousal

Cerebellum

• Cerebellum: Located at base of brain– Regulates posture, muscle tone, and

muscular coordination

Reticular Formation (RF)

• Inside medulla and brainstem– Associated with alertness, attention, and

some reflexes (breathing, coughing, sneezing, vomiting)

Reticular Activating System (RAS)

• Part of RF that keeps it active and alert– RAS acts like the brain’s alarm clock– Activates and arouses cerebral cortex

Video: Brainstem

Forebrain

• Structures are part of the limbic system, the system within the forebrain closely linked to emotional response and motivating behavior

Video: Limbic System

Thalamus

• Relays sensory information on the way to the cortex; switchboard

Hypothalamus

• Regulates emotional behaviors and motives (e.g., sex, hunger, rage, hormone release)

Amygdala

• Associated with fear responses

Hippocampus

• Associated with storing permanent memories; helps us navigate through space

Endocrine System

• Glands that pour chemicals (hormones) directly into the bloodstream or lymph system

Pituitary Gland

• Regulates growth via growth hormone• Its hormones influence other endocrine glands

Pituitary Problems

• Too little growth hormone means person will be smaller than average– Hypopituitary dwarfism: As adults, perfectly

proportioned but tiny• Treatable by using human or synthetic

growth hormone; will add a few inches

Fig. 2-25, p. 68

Fig. 2-26, p. 69

Pituitary Problems (cont)

• Too much growth hormone leads to gigantism (excessive body growth)

• Acromegaly: Enlargement of arms, hands, feet, and facial bones; due to too much growth hormone secreted late in growth period– Andre the Giant

• Pituitary also governs functioning of other glands, especially thyroid, adrenals, and gonads

The Pineal Gland

• Regulates body rhythms and sleep cycles– Releases the hormone melatonin, which

responds to daily variations in light

The Thyroid Gland

• In neck; regulates metabolism– Hyperthyroidism: Overactive thyroid;

person tends to be thin, tense, excitable, nervous

– Hypothyroidism: Underactive thyroid; person tends to be inactive, sleepy, slow, obese, and depressed

The Adrenal Glands

• Adrenals: Arouse body, regulate salt balance, adjust body to stress, regulate sexual functioning; located on top of kidneys– Releases epinephrine and norepinephrine

(also known as adrenaline and noradrenaline)

Adrenal Hormones

• Epinephrine arouses body; is associated with fear

• Norepinephrine arouses body; is linked with anger

The Adrenal Glands (cont)

• Adrenal medulla: Inner core of adrenals; source of epinephrine and norepinephrine

• Adrenal cortex: Produces hormones known as corticoids– Regulate salt balance, among other

functions

Adrenal Malfunctions

• Oversecretion of adrenal sex hormones can cause virilism: exaggerated male characteristics (bearded woman)– May also cause premature puberty if

oversecretion occurs early in life

Fig. 2-27, p. 70

Fig. 2-29, p. 74

Handedness

• Preference for right or left hand in most activities• Dominant Hemisphere: Term usually applied to

the side of the human brain that produces language

• Lateralization: Specialization in abilities of brain hemispheres