Neuroscience and Behavior

Chapter Two

Lecture Slides

By Glenn MeyerTrinity University

Introduction: Neuroscience and Behavior

Scientific disciplines that contribute to neuroscience: biological psychology, biology, physiology genetics, neurology

Biological psychology

scientific study of the biological bases

of behavior and mental processes

Neurosciencescientific study of the

nervous system

The Neuron

Bring input to the brain; light or

sound, smell, taste, skin senses,

information from internal organs

Communicate information to

the muscles and glands of the

body

Communicate information betweenneurons. By far, most of the neurons in the

human nervous system are

interneurons

Neurons have three major parts

Axon: The long, fluid-filled tube that carries a neuron’s messages to other

body areas.

One axon per cell, branches at end connect to other

cells.

Axon terminals are the tips of the

axons’ branches.

Characteristics of the NeuronCell Body: Processes nutrients and provides energy for the neuron; contains cell’s nucleus; also called the soma.

Contains DNA, chromosomes.

Dendrites: Multiple short fibers that extend from the neuron’s cell body

and receive information from other neurons or from sensory receptor

cells.

The Synapse: The junction between axon terminals and dendrites.

Glial Cells: More than Just the Brain’s Packing Material Outnumber neurons 10 to 1

Support cells that assist neurons by:

a. providing structural support and

nutrition

b. removal of cell wastes

c. manufacturing myelin

Myelin sheath: A white, fatty covering wrapped around axons of some neurons that increases their communication speed.

Astrocytes

Click here

• Provide connections between neurons and blood vessels

• Involved in brain development and communication among neurons

Microglia

Click here

• Remove waste products from the nervous system

Oligodendrocytes(brain), Schwann

cells

Click here

• Form the myelin sheath

Types of

Glial Cells

Between Neurons

Click here

• Between axon and dendrites

• Exchange of chemical neurotransmitters across the synapse

• Trigger by spike potential

Within the Neuron

Click here

• From dendrite to axon

• Based on movement of electrically charged ions from outside and inside of the neuron

• Recorded as the all-or-none action potential or spike potential

Overview of Neural Communication

Communication Within the Neuron The All-or-None Action Potential (1)

Resting Potential

1. The neuron is negatively charged inside -- not outside -- of the cell.

2. Due to presence of positive sodium ions outside of the cell (Na+) and negative proteins inside the cell.

3. This leads to a resting potential of –70 millivolts inside the cell.

4. Potassium ions are also found inside the cell. They are positively charged.

Communication Within the NeuronThe All-or-None Action Potential (2)

Spike or Action Potential1. Neurotransmitter release across the synapse from another

neuron activates receptor sites (sodium channels) on the dendrites

2. Na+ ions rush in, making the cell more positive (depolarization)

3. If sufficient sodium enters the cell, threshold level is reached4. This triggers more sodium channels to open, causing the

spike or action potential5. The action potential has a peak of +30 millivolts and a fixed

time of two to three milliseconds 6. Sodium channels close and potassium channels open.

Potassium ions leave the cell, repolarizing it7. Resting potential is re-established8. Thus, it is an all-or-none event

Communication Within the Neuron The All-or-None Action Potential (3)

Spike or Action Potential1. The spike travels down the axon, jumping between

spaces in the myelin sheaths called the nodes of Ranvier2. When the spike reaches the axon terminal,

neurotransmitters are released3. Following the action potential, there is a refractory period

where the neuron is unable to fire for a thousandth of a second (millisecond)

4. After the action potential, the neurotransmitters are recycled in a process called reuptake

Communication Between Neurons

Neural transmitters can have different effects:• Transmitters open various types of ion channels by

fitting into a receptor site of a specific shape on a specific channel. A good analogy is to a lock (receptor) and key (transmitter)

• Excitatory message—increases the likelihood that the postsynaptic neuron will activate • The neuron becomes more positive or depolarizes

because of Na+ entry• Inhibitory message—decreases the likelihood that the

postsynaptic neuron will activate• The neuron becomes more negative, making it

harder to reach threshold

Excitatory and Inhibitory Messages

Neurotransmitters and Their EffectsMore than 100 neurotransmitters have been identified

Some of the most important ones are...

Acetylcholine… Click here

Dopamine… Click here

Serotonin… Click here

Norepinephrine… Click here

GABA… Click here

Endorphins… Click here

How Drugs Affect Synaptic Transmission Drugs can increase production of

a transmitterL-dopa increases dopamine to aid Parkinson’s sufferers

Drugs can prolong transmitter action by blocking reuptake

Selective serotonin reuptake inhibitors used to treat depression (Prozac)

Some drugs are shaped like neurotransmitters

Antagonists: poorly fit the receptor and block the transmitter

Beta blockers, curare

Agonists: fit receptor well and act like the transmitter

Nicotine

The Nervous System and the Endocrine System

Up to 1 trillion neurons

The Central Nervous System

Spinal Reflex

A simple, involuntary behavior that is processed in the spinal cord without brain involvement

The Peripheral Nervous System

Autonomic Nervous System is the subdivision of the peripheral nervous system that regulates involuntary functions.

Two branches of Autonomic Nervous System:

• Sympathetic Nervous System is the body’s emergency system, rapidly activating bodily systems to meet threats or emergencies. Activates fight-or-flight response.

• Parasympathetic Nervous System conserves and maintains your physical resources.

The Endocrine SystemEndocrine glands communicate information from one part of the body to another by secreting messenger chemicals called hormones into the bloodstream.

The Endocrine SystemControlled by hypothalamus through pituitary gland

Pituitary gland—attached to the base of the brain, hormones affect the function of other glands

Adrenal glands—hormones involved in human stress response

Gonads—hormones regulate sexual characteristics and reproductive processes; testes in males, ovaries in females

The Brain

The human brain Weighs roughly 3

pounds Uses 20% of your

oxygen Consists of many

structures acting as an integrated system

The Dynamic Brain: Plasticity and Neurogenesis• No longer thought to be hard-

wired or fixed for life• It is sculpted by experience• Neuroplasiticity is the ability

to change function and structure• Functional plasticity:

brain’s ability to shift functions from damaged to undamaged brain areas

• Structural plasticity: ability to physically change its structure in response to learning, active practice, or environmental stimulation.

• Neurogenesis: the development of new neurons

Brain Damage Risk

Brain protected by

• Skull

• Three layers of meninges

• Suspension in cerebrospinal fluid

• Brain susceptible to sharp blows, explosions

• Traumatic brain injury can result

• Most common form is concussion

Brain twists or bounces

• Cells damaged

• Axons are sheared, myelin damaged

• Brain chemistry disrupted

Behavioral manifestations of

concussion

• Loss of consciousness

• Dizziness

• Blurred or double vision

• Slurred speech and memory loss

Chronic traumatic encephalopathy

• Caused by repeated concussions

• Progressive, degenerative brain disease that can only be diagnosed after death

Symptoms

• Depression and anxiety

• Poor judgment

• Lack of impulse control

• Problems with memory, concentration, and attention

• Dementia

Been diagnosed in athletes,

especially football players

The Overall Organization of the Brain

• Contralateral control: For many functions such as sensory processing and motor control, the major pathways from the left side of body cross over to the right sight of the brain and vice versa.

• Three Major Sections of the Brain:• Forebrain: uppermost and largest brain region

o Cerebral cortex• Divided into two hemispheres and responsible for

sophisticated mental functions• Connected by corpus callosum

• Midbrain: contains structures involved in processing visual and auditory information

• Hindbrain: region at base of brain that connects the brain to the spinal cord

Click here

Hindbrain

Medulla

• Control autonomic functions - breathing, heart rate, and blood

• Controls swallowing, coughing, vomiting, and sneezing

Pons

• Connects medulla to the two sides of the cerebellum

• Helps coordinate and integrate movements, maintain balance

Cerebellum

• Responsible for muscle coordination and maintaining posture and equilibrium

• Coordinates rapid voluntary movement, responsible for motor memory

• Lesions cause jerky movements, loss of balance

Reticular formation (reticular activating system)

• Network of nerve fibers in center of medulla that helps regulate sleep, attention, arousal

Click here

Midbrain

• Involved in the processing of auditory and visual sensory information

• Midbrain pigmented area called the substantia nigra is involved in motor control and contains a large concentration of dopamine-producing neurons

The Forebrain and Cerebral Cortex

• 90% of the human brain• Expanded over our

evolutionary history• Overall organization

• Two hemispheres connected by corpus callosum

• Has a wrinkled appearance to allow larger surface area to fit into a skull

• Humans have one of the most folded or convoluted brains

Four Major Lobes:FrontalParietal

TemporalOccipital

The Cerebral CortexCerebral cortex is only about a quarter of an inch thick and is composed of: • Gray matter - glial cells and neuron cell

bodies and axons, giving it a grayish appearance

• White matter - White myelinated axons extending inward from the cerebral cortex

Cortex means “bark” and the cerebral cortex

is the outer covering of forebrain

Sulci and Gyri: • Numerous folds, grooves, and bulges

characterize the cerebral cortex. • Allow about three square feet of

surface area to be packed into human skull

Four Major Lobes: Frontal Lobe

• Largest lobe – its expansion differentiates us from other animals

• Involved in thinking, planning, and emotional control – as seen in Phineas Gage case

Role in Motor Control –Primary Motor Cortex

• Involved in planning, initiating, and executing voluntary movements

Four Major Lobes: Parietal Lobe

• Processes somatosensory information, including touch, temperature, pressure, and information from receptors in the muscles and joints

• Somatosensorycortex receives information from touch receptors in different parts of the body

• Body’s representation on the somatosensorycortex is not proportional but based on the sensitivity of that body area

Four Major Lobes: Temporal Lobe

• Contains the primary auditory cortex

• Receives auditory information

Four Major Lobes: Occipital Lobe

Includes the primary visual cortex, where visual information is received

Forebrain Structures

ThalamusClick here

HypothalamusClick here

AmygdalaClick here

HippocampusClick here

• Peanut-sized forebrain structure

• Exerts considerable control over the secretion of endocrine hormones by influencing pituitary gland.

• Suprachiasmatic nucleus (SCN): plays a key role in regulating daily sleep–wake cycles and other rhythms of the body

A curved forebrain structure

Regulates levels of awareness, attention, motivation, and emotional aspects of sensations

An almond-shaped clump of

neuron cell bodies at the base

of the temporal lobe

Amygdala damage

makes it difficult to

identity facial

expressions.

Specialization in the Cerebral Hemispheres

Cortical localization: Different functions are located or localized in different areas of the brain

1700s - established that injury to one side of the brain could produce muscle paralysis or loss of sensation on the opposite side of the body

1800s - animal experiments had shown that specific functions would be lost if particular brain areas were destroyed

Called localization of function

Two hemispheres are not symmetrical and differ in some major functions

Language and the Left Hemisphere

For most people, language functions are located or lateralized in the left hemisphere of the cerebral cortex.

Damage in these regions causes aphasia: a partial or complete inability to articulate ideas or understand spoken or written language because of brain injury or damage

Broca’s Area and Broca’s AphasiaProblems in Speech Production

• 1860s—discovered by French surgeon and neuroanatomistnamed Pierre Paul Broca

• Broca treated a series of patients who had difficulty speaking but could comprehend written or spoken language

• Due to brain damage to an area on the lower left frontal lobe

• Area on the left hemisphere now is referred to as Broca’s area

• Plays a crucial role in speech production

Wernicke’s Area and Aphasia Problems in Speech Perception

• German neurologist Karl Wernicke discovered area in the left hemisphere that, when damaged, produced great difficulty understanding spoken or written communications

• Patients could speak quickly and easily

• However, their speech sometimes made no sense

Example:

In response to the question “How are you feeling?”

The answer might be “Don’t glow glover. Yes, bick, bochipickers the dallydoe mick more work mittle.”

• Differences in hemispherical function were demonstrated after split-brain operation.

• Operation is used to stop or reduce recurring epileptic seizures

• Using specialized apparatus that presented images to the left or right visual fields, Sperry and his colleagues tested the abilities of split-brain patients.

Cutting the Corpus CallosumThe Split Brain

Researchers have concluded that in most people:

• Left hemisphere is superior in language abilities, speech, reading, and writing

• Right hemisphere is more involved in nonverbal emotional expression and visual-spatial tasks

Cutting the Corpus CallosumThe Split Brain

Gender and the Brain• Men’s brains tend to be larger than

women’s brains.

• Women have a higher proportion of gray matter to white matter

• Male brain is more asymmetrical and functions are more lateralized than in the female brain

• Male brains appear to be optimized for network connections within each hemisphere. Female brains have better connections between hemispheres.

• Females have greater ability to integrate the left hemisphere’s verbal-analytical processing with right hemisphere’s spatial and holistic mode of information processing.

Many sex differences

amount to minor variations in a particular brain

region.

Basic brain structures are still the same in men

and women.

Independent of gender, no two

brains are identical.

Brain Myths• Is it true that we only use

10% of our brain?

• Most right-handed people are strongly right-handed. Is the same true of lefties?

• Is it true that some people are “right-brained” and other people “left-brained”?

• Is the right brain responsible for creativity and intuition? Can you train your right brain?

• Is it true that left-handed people process speech and language in their right cerebral hemisphere? Are they right-hemisphere dominant?