7 - Chapter 2 - The Biology of Mind

Neural Communication

Note the similarities in the above brain regions, which are all engaged in information processing.

Neurobiologists and other investigators understand that humans and animals operate

similarly when processing information.

Neural Communication

The body’s information system is built from billions of interconnected cells called neurons, a nerve cell which is the basic building block of the

nervous system.

Neuron A nerve cell, or a neuron, consists of many

different parts.

Parts of a Neuron

Cell Body: Life support center of the neuron.

Dendrites: Branching extensions at the cell body. Receive messages from other neurons.

Axon: Long single extension of a neuron, covered with myelin [MY-uh-lin] sheath to insulate and speed up messages through neurons.

Terminal Branches of axon: Branched endings of an axon that transmit messages to other neurons.

Fig. 3-2, p. 75

Action PotentialA neural impulse. A

brief electrical charge that travels down an

axon and is generated by the movement of positively charged atoms in and out of

channels in the axon’s membrane.

Potential = Voltage (Action potential refers to the impulse during action/Resting Potential refers to the impulse during rest)

Threshold Threshold: Each neuron receives excitatory (like

pushing the accelerator) and inhibitory (like

pressing the brake) signals from many neurons. When the excitatory signals

minus the inhibitory signals

exceed a minimum intensity

(threshold) the neuron fires an action potential.

Action Potential Properties

All-or-None Response: A strong stimulus can trigger more neurons to fire, and to fire more often, but it does not affect the

action potentials strength or speed.

Intensity of an action potential remains the same throughout the length of the

axon. It does not slow down as it travels.

What the what?

We have just described how an action potential moves through a single nerve

cell.

Now we will look at how that action potential gets from one nerve cell to

another!

Synapse Synapse: a junction between the axon tip of the sending neuron and the dendrite or

cell body of the receiving neuron. This tiny gap is called the synaptic gap or

cleft.

NeurotransmittersNeurotransmitters

(chemicals) released from the sending

neuron travel across the synapse and bind to receptor sites on

the receiving neuron, thereby influencing it to

generate an action potential.

Reuptake

Neurotransmitters in the synapse are

reabsorbed into the sending neurons

through the process of

reuptake. This process applies the

brakes on neurotransmitter

action.

Fig. 3-4, p. 78

Reuptake Inhibitors

• Serotonin: Regulation of mood, sleep, muscle contraction and some cognitive functions including memory and learning

• Selective Serotonin Reuptake Inhibitors (SSRI): treat depression and anxiety by preventing the reuptake of serotonin.

• Common SSRI’s: Paxil, Zoloft, Prozac

How Neurotransmitters Influence Us

Serotonin pathways are involved with mood regulation.

From Mapping the Mind, Rita Carter, © 1989 University of California Press

Dopamine Pathways

Dopamine pathways are involved with

diseases such as schizophrenia and

Parkinson’s disease.

From Mapping the Mind, Rita Carter, © 1989 University of California Press

Parkinson’s Disease• Different areas of the brain must

communicate in order to produce smooth and coordinated muscle movements.

• Dopamine is a key neurotransmitter involved in this communication.

• Parkinson’s Disease is caused by a deterioration of brain neuron’s that produce dopamine (it is still unknown why this occurs).

• A lack of dopamine results in abnormal nerve functioning, causing a loss in the ability to control body movements.

Schizophrenia• Symptoms consist of

hallucinations, delusions and irrational behavior.

• Although not the sole cause of schizophrenia, dopamine unbalance is consistently seen found in patients with schizophrenia.

• Schizophrenia may result from biopsychosocial factors. Some evidence supports a genetic predisposition.

• Drugs that prevent dopamine from binding to receptors reduce the symptoms of schizophrenia.

A Schizophrenic’s paintings of his cat

Fig. 3-28, p. 103

Neurotransmitters

Lock & Key Mechanism

Neurotransmitters bind to the receptors of the receiving neuron in a key-lock

mechanism.

Agonists

Endorphin Agonists

• Endorphins are chemicals produced by the body during times of physical or psychological stress.

• Relieve pain, relaxation, feeling of well being

• Morphine binds to endorphin receptors causing the same effects.

Antagonists

Curare: ACh Antagonist

• Acetylcholine (Ach) enables muscle activity, learning and memory.

• Historically, indigenous South Americans have used blowgun darts dipped in Curare when hunting.

• Curare blocks ACh from binding to receptors.

• Result: muscles unable to contract, paralysis of respiratory muscles

High blood Pressure• Epinephrine (also called adrenaline because it

is released by the adrenal gland) is release in times of stress (fight or flight, adrenaline rush).– Epinephrine “fits into” β-receptors

• Epinephrine in the blood reaches β-receptors (such as those in the heart) - prepares the body for an emergency.– Increases heart rate, elevates blood sugar, dilates

pupils, etc.– boosts the supply of oxygen and glucose to brain and

muscles– suppresses non-emergency bodily functions (ie:

digestion)

• In people with hypertension this response leads to complications such as blood vessel damage, stroke, heart attack, etc.

Beta-Blockers for High blood Pressure

• High blood pressure medications, called Beta-blockers, block beta receptors.

• In other words they act as epinephrine antagonists.

Nervous System

CentralNervousSystem(CNS)

PeripheralNervousSystem(PNS)

The Nervous System

Nervous System: Consists of all the nerve cells. It is the body’s speedy, electrochemical communication system.

Central Nervous System (CNS): the brain and spinal cord.

Peripheral Nervous System (PNS): the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body.

The Nervous System

The Brain and Neural Networks

Interconnected neurons form networks in the brain. Theses networks are complex and modify with growth and experience.

The NervesNerves consist of neural “cables”

containing many axons. They are part of the peripheral nervous system and connect muscles, glands, and sense

organs to the central nervous system.

Kinds of Neurons by Function

• Sensory Neurons carry incoming information from the sense receptors to the CNS.

• Motor Neurons carry outgoing information from the CNS to muscles and glands.

• Interneurons connect the two neurons.

Sensory Neuron(Bipolar)

Interneuron Neuron (Unipolar)

Motor Neuron(Multipolar)

Peripheral Nervous SystemSomatic Nervous System: The division of the peripheral nervous system that controls the body’s skeletal muscles.

Autonomic Nervous System: Part of the PNS that controls the glands and internal organs.

Autonomic Nervous System (ANS)Sympathetic Nervous System: arouses the body, mobilizing its energy in stressful situations, “fight or flight”

Parasympathetic Nervous System: calms the body, conserving its energy, rest & digestion.

Autonomic Nervous System (ANS)

Sympathetic NS “Arouses”

(fight-or-flight)

Parasympathetic NS “Calms”

(rest and digest)

Fig. 3-8, p. 83

Central Nervous SystemThe Spinal Cord and Reflexes

Simple Reflex

Nervous System vs. Endocrine System

Nervous System• Chemicals of Nervous

System = neurotransmitters

• Nervous system secretes neurotransmitters b/w nerve cells

• Signals sent in fractions of a second

Endocrine System• Chemicals of

Endocrine = hormones

• Endocrine system secretes hormones into blood stream

• Chemicals can take many seconds to begin working, effects can last longer (hours, days)

Both:Regulate conditions in body

Use chemicals for communication

The Endocrine System

The Endocrine System is the body’s “slow”

chemical communication

system. Communication is

carried out by hormones

synthesized by a set of glands.

HormonesHormones:• chemicals synthesized by the endocrine glands• secreted in the bloodstream• affect the brain and many other tissues of the body.

Example: epinephrine (adrenaline) increases heart rate, blood pressure, blood sugar, and feelings of excitement during emergency situations.

Brain

Glands

Hormones

Hormones are Specific• Only certain cells in the body can respond to

hormones and, often, only at limited times. – In order for cells to respond they must have the

hormone receptor molecule Example:• Oxytocin is released by the posterior pituitary,

carried through the bloodstream to all the tissues in the body.

• It acts on only two tissues, the breasts and uterus in the female. • It acts only under certain conditions,

such as:• Oxytocin causes uterine contractions

at the end of pregnancy.• Oxytocin causes breast tissue to eject

milk only if the female has recently given birth and is nursing.

Pituitary Gland

Is called the “master gland.” The anterior pituitary lobe releases hormones that

regulate other glands. The posterior lobe regulates water and salt balance.

Pituitary GlandIs called the “master gland.”

anterior pituitary lobe

releases hormones that

regulate organs and other glands.

posterior lobe regulates water and salt balance.

Thyroid & Parathyroid Glands

Regulate metabolic and calcium rate.

Diet & Bone Health• Normal blood pH ~7.4

– required for effective transport of Oxygen• Excessive protein and not enough fruits and

veggies causes your blood to become acidic

• Soda causes your blood to become acidic

• Your body must restore normal pH

• Parathyroid hormone is released causing calcium to leach from your bones into blood.

• This restores pH

Adrenal GlandsAdrenal glands consist of the adrenal medulla and the cortex. The medulla secretes hormones (epinephrine and norepinephrine) during stressful and

emotional situations, while the adrenal cortex regulates salt and carbohydrate

metabolism.

Adrenal GlandsThe medulla secretes hormones (epinephrine and norepinephrine) during stressful and emotional situations.

The adrenal cortex regulates salt and carbohydrate metabolism.

Gonads

Sex glands are located in different places in men and women. They regulate bodily

development and maintain reproductive organs in adults.

The BrainTechniques to Study the Brain

• A brain lesion experimentally destroys brain tissue to study animal behaviors after such destruction.

• Remember, the hippocampus was removed from rats at various times after learning a maze.

Hubel (1990)

Clinical ObservationClinical observations have shed light on a number of brain disorders. Alterations in brain morphology due to neurological and psychiatric diseases are now being

catalogued.

Tom L

anders/ Boston G

lobe

Studying the Living Human Brain

• Animal studies and clinical observations are useful, but often, such as when we need to diagnose or treat illness, we want to know what is happening inside the brain of a living human.

• For this we have:– EEG: Electroencephalogram

– MRI: Magnetic resonance imaging

– PET Scan: Positron emission tomography

– CT Scan (or CAT Scan): Computerized Tomography

Electroencephalogram (EEG)An amplified recording of the electrical

waves sweeping across the brain’s surface, measured by electrodes placed

on the scalp.

AJ P

hoto/ Photo R

esearchers, Inc.

MRI: Magnetic Resonance Imaging

• MRI uses magnetic fields and radio waves to produce computer-generated images that distinguish among different types of brain tissue.

Both photos from Daniel Weinberger, M.D., CBDB, NIMH

James Salzano/ Salzano Photo Lucy Reading/ Lucy Illustrations

• Top images show ventricular enlargement in a schizophrenic patient.

• Bottom image shows brain regions when a participants lies.

PET Scan: Positron Emission Tomography

• PET Scan is a visual display of brain activity

• Detects gamma rays emitted by a radioactive form of glucose while the brain performs a given task.

Courtesy of N

ational Brookhaven N

ational Laboratories

CT Scan: Computerized Tomography

• X-ray rotates around head.

• May be done with or without contrasting dye.

• Images taken from different angles are assembled into 3-D image

• CT scan produces much more detailed image than x-ray of bone and soft tissue

The Brain The Brain

Brain stem CerebellumCerebrum

Cerebrum

Cerebellum

Brain Stem

The Brain Stem: Older Brain Structures

The Brainstem is the oldest part of the brain, beginning where the spinal cord swells and enters the skull. It is responsible for automatic survival

functions.

Brainstem

Thalamus

The Thalamus [THAL-uh-muss] is the brain’s sensory switchboard, located on top of the brainstem.

It directs messages to the sensory areas in the cortex and transmits replies to the cerebellum and medulla.

To medulla

To cerebellum

1.2.

3.

4.

Pons

The Pons plays a role in muscle coordination.

Pons

Reticular Formation

• Reticular Formation is a nerve network in the brainstem that plays an important role in controlling arousal.

• Damage to this causes a disorder called narcolepsy in which a person falls asleep suddenly during the daytime and cannot resist the sleep.

Medulla

The Medulla [muh-DUL-uh] is the base

of the brainstem that controls heartbeat

and breathing.

• The “little brain” attached to the rear of the brainstem.

• It helps coordinate voluntary movements and balance.

• Implicit (procedural) memory.

Cerebellum

• The Limbic System is a doughnut-shaped system of neural structures at the border of the brainstem and cerebrum

• Associated with emotions such as fear, aggression and drives for food and sex.

The Limbic System

Amygdala

The Amygdala [ah-MIG-dah-la] consists of two lima bean-sized neural clusters linked to the emotions of fear and

anger.

Hypothalamus• Hypothalamus lies below

(hypo) the thalamus. • Directs maintenance activities

like eating, drinking, body temperature, and control of emotions.

• It stimulates or inhibits pituitary gland other endocrine glands

Rats cross an electrified grid for

self-stimulation when electrodes are placed

in the reward (hypothalamus)

center (top picture). When the limbic

system is manipulated, a rat

will navigate fields or climb up a tree

(bottom picture).

Reward CenterS

anjiv Talwar, S

UN

Y D

ownstate

The Cerebral CortexThe intricate fabric of interconnected neural cells

that covers the cerebral hemispheres. It is the body’s ultimate control and information processing

center.

Structure of the CortexEach brain hemisphere is divided into four lobes

Functions of the Cortex• The Motor Cortex is the area at the rear of the

frontal lobes that control voluntary movements. • The Sensory Cortex (parietal cortex) receives

information from skin surface and sense organs.

Visual Function

Visual Function

• Notice the visual cortex is located in the occipital lobe.

• The functional MRI scan shows the visual cortex is active as the subject looks at faces.

Courtesy of V

.P. Clark, K

. Keill, J. M

a. M

aisog, S. Courtney, L

.G.

Ungerleider, and J.V

. Haxby,

National Institute of M

ental Health

Auditory Function• The auditory cortex contains distinct

subregions that are important for decoding complex sound.

• Auditory cortex is in the temporal lobe.

2. information travels through the brainstem and midbrain to the auditory cortex.

3. information from the auditory cortex interacts with many other brain areas, especially the frontal lobe, for memory formation and interpretation.

4. The frontal lobe is involved in emotional evaluation.

5. The motor cortex is involved in sensory–motor feedback, in controlling movements needed to produce music using an instrument.

1. Sound waves enter ear, and are turned into neural impulses by the inner ear

1

2

3

4

5

Auditory Hallucinations

The functional MRI scan shows the auditory cortex is active in patients who hallucinate.

More intelligent animals have increased “uncommitted” or association areas of

the cortex.

Association Areas

LanguageAphasia is an impairment of language,

usually caused by left hemisphere damage either to Broca’s area (impaired speaking)

or to Wernicke’s area (impaired understanding).

Specialization & Integration

Brain activity when hearing, seeing, and speaking words

The brain is sculpted by our genes but also by our experiences.

Plasticity refers to the brain’s ability to modify itself after some types of injury or

illness.

The Brain’s Plasticity

Our Divided Brain

Our brain is divided into two hemispheres.

The left hemisphere processes reading, writing, speaking, mathematics, and

comprehension skills. In the 1960s, it was termed as the dominant brain.

Splitting the BrainA procedure in which the two hemispheres of

the brain are isolated by cutting the connecting fibers (mainly those of the corpus

callosum) between them.Corpus Callosum

Ma

rtin M

. Ro

the

r

Courtesy of Terence W

illiams, U

niversity of Iowa

Split Brain Patients

With the corpus callosum severed, objects (apple) presented in the right visual field can be named. Objects (pencil) in the left

visual field cannot.

Try This!

Try drawing one shape with your left hand and one with your right hand,

simultaneously.B

BC