The Biology of

Mind

Chapter 2

Parts of a Neuron Dendrites: Branching extensions at the cell body. Receive messages from other neurons.

Cell Body: Life support center of the neuron.

Axon Terminals: Branched endings of an axon that transmit messages to other neurons.

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

Dendrites

Cell Body

Axon Terminals

Parts of a Neuron – Summary

Action Potential – Summary

Figure 2.3

Refractory Period & Pumps Refractory

Period: After a neuron fires an action potential, it pauses for a short period to

recharge itself to fire again. It

pumps positively charged sodium

ions back outside the neuron.

Action Potential Properties Threshold: Each neuron

receives excitatory and inhibitory signals from many

neurons. When the excitatory signals minus the inhibitory signals exceed a minimum intensity (threshold) the neuron fires

an action potential.

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.

How Neurons CommunicateSynapse [SIN-aps] 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.Neurotransmitters are chemical messengers that

traverse the synaptic gaps between neurons.When released by the sending neuron, neurotransmitters

travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether it will

generate a neural impulse.

Neurotransmitters – Summarized

ReuptakeNeurotransmitters in

the synapse are reabsorbed into the

sending neurons through the process of reuptake. This

process applies the brakes on

neurotransmitter action.

NeurotransmittersTable 2.1

Lock & Key MechanismNeurotransmitters bind to the receptors of the receiving

neuron in a key-lock mechanism.

The Nervous SystemFigure 2.7

Kinds of Neurons – A ReviewSensory 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)

Central Nervous SystemThe Spinal Cord and Reflexes

Figure 2.10 A Simple Reflex

The spinal cord is an information highway connecting the peripheral nervous system to the brain.

The neural pathways governing our reflexes, our automatic responses to stimuli, illustrate the spinal

cord’s work.

The Endocrine SystemThe

Endocrine System is the body’s “slow”

chemical communicatio

n system. Communicatio

n is carried out by

hormones synthesized by a set of

glands.

Pituitary GlandThe 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.

Other Endocrine Glands

The thyroid and parathyroid regulate metabolic and calcium rate.

The 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.

Other Endocrine 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.

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

BrainA brain lesion experimentally destroys brain tissue to study animal behaviors after

such destruction.

An electroencephalogram (EEG) is an amplified recording of the electrical waves

sweeping across the brain’s surface, measured by electrodes placed on the scalp.

Computerized Axial Tomography (CAT Scan) is a series of X-Ray photographs

taken from different angles and combined by computer into a composite

representation of a slice through the body. Also called a Computed Tomograph (CT)

Scan.

The BrainTechniques to Study the Brain

A Positron Emission Tomography (PET) Scan is a visual display of brain activity that detects a

radioactive form of glucose while the brain performs a given task.

Magnetic Resonance Imaging (MRI) uses magnetic fields and radio waves to produce computer-generated images that distinguish among different types of brain tissue. Top images show ventricular enlargement in a

schizophrenic patient. Bottom image shows brain regions when a participants lies.

Courtesy of N

ational Brookhaven N

ational Laboratories

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

the brainstem that controls heartbeat and

breathing.

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

arousal.

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.

Medulla

Reticular Formatio

n

Thalamus

Thalamus

The cerebellum, or “little brain,” is attached to the rear of the

brainstem.

It helps us judge time, modulate our emotions, discriminate sounds and textures as well as coordinate voluntary movements and balance.

Cerebellum

Amygdala and HypothalamusThe Amygdala [ah-

MIG-dah-la] consists of two lima bean-

sized neural clusters linked to the

emotions of fear and anger.

The Hypothalamus lies below (hypo) the thalamus. It directs several maintenance activities like eating,

drinking, body temperature, and

control of emotions. The hypothalamus helps govern the

endocrine system via the pituitary gland. The hippocampus processes memory.

Without it, we cannot process new

memories of facts and episodes.

Amygdala

Hypothalamus

Pituitary Gland

Thalamus

Hippocampus

The Cerebral CortexThe cerebral cortex is the intricate fabric of interconnected neural cells that covers the cerebral hemispheres like the bark of a tree. It

is the body’s ultimate control and information processing center.

Structure of the CortexNeurons are like

queen bees…they cannot feed

or sheathe (protect)

themselves.

Glial cells are worker bees…they provide nutrients and

insulating myelin, guide

neural connections, and mop up ions and neurotransmitte

rs.

Glial Cells

Structure of the CortexThe frontal lobe is involved in speaking

and muscle movements (motor cortex) and in

making plans and judgments

The parietal lobe integrates sensory information from

various parts of the body and includes the

sensory cortex.The occipital lobe includes the visual

areas which receive visual information from

the opposite visual field.

The temporal lobe is concerned with

hearing, memory, emotion, and speaking.

Frontal Lobe Parietal Lobe

Occipital Lobe

Temporal Lobe

Functions of the CortexThe 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.

The sensory and motor cortexes take up about one quarter of the

cerebral cortex.

Neurons in the other three quarters are called association

areas. Association areas are found in all four lobes of the

brain and are largest in humans.

Electrically probing these areas does not trigger any observable

response, so mapping these areas cannot be neatly done. This has led to the erroneous claim that we only use 10% of

our brain (but that would mean a bullet would have a 90%

chance of hitting an unused area).

Association Areas

Our Divided BrainOur brain is divided into two hemispheres.

For more than a century, clinical evidence has shown that the brain’s two sides serve differing functions.

Lateralization (hemispheric specialization) is apparent after brain damage.

The left hemisphere processes reading, writing, speaking, mathematics, and comprehension skills. In the 1960s, it was termed as the dominant brain.

Splitting the BrainA commissurotomy is a procedure in which the two hemispheres of

the brain are isolated by cutting the connecting fibers (mainly those of the corpus callosum) between them.

This surgery was done as a treatment for epileptic seizures.

Corpus Callosum

Ma

rtin M

. Ro

the

r

Courtesy of T

erence William

s, University of Iow

a

Split Brain PatientsWith the corpus callosum severed, objects (apple)

presented in the right visual field can be named. Objects

(pencil) in the left visual field cannot.

Divided Consciousness

“What did you see?” “With your left hand, select the object you saw from those behind the screen.”