Class 3
The Biology of Mind
Chapter 2 (Myers)
“Everything psychological is simultaneously biological.”
1. Neural Communication
a. Neurons
i. Neurons: nerve cells
ii. Sensory neurons: carry messages from the body’s tissues
and sensory organs inward to the brain and spinal cord for
processing.
iii. Motor neurons: how the brain and spinal cord send
instructions out to the body’s tissues
iv. Interneurons: the brain’s internal communication system
between sensory and motor neurons
1. “Our nervous system has a few million sensory
neurons, a few million motor neurons, and billion
and billions of interneurons.”
2. Interneurons consist of:
a. Dendrite: receive information and conduct it
toward the cell body
b. Axon: passes message to other neurons,
muscles, or glands
c. “Axons speak, dendrites listen.”
d. Axons are generally longer than dendrites,
sometimes projecting several feet through
the body.
v. Myelin sheath: fatty tissue that insulates axons of some
neurons and speeds their impulses
vi. Action Potential / Threshold
2. How Neurons Communicate
a. Synapse: the space between an axon tip of the sending neuron and
the dendrite or cell body of the receiving neuron
i. Synaptic gap/ Synaptic cleft
ii. Less than a millionth of a inch wide
b. Santiago Ramon y Cajal: Protoplasmic kisses
c. Neurotransmitters: chemical messengers that cross synaptic gaps
and bind to receptor sites on the receiving neuron, thereby
influencing whether that neuron will generate a neural impulse.
d. Reuptake: a neurotransmitter’s reabsorption by the sending
neuron.
3. How Neurotransmitters Influence Us
a. Acetylcholine (Ach): one of the best understood neurotransmitters
i. Role in learning and memory
ii. At every junction between motor neuron and skeletal
muscle
b. Endorphins: neurotransmitters linked to pain control and pleasure
c. How Drugs and Other Chemicals Alter Neurotransmitters
i. If we flood the brain with artificial chemicals, like drugs,
our brain may stop producing it’s own (chemical addition
and dependency)
ii. Agonist: mimics a neurotransmitter’s functioning
iii. Antagonist: block a neurotransmitter’s functioning
4. The Nervous System
a. Peripheral Nervous System:
i. Somatic: enables voluntary control of our skeletal muscles
ii. Autonomic: controls glans and the muscles of our internal
organs
1. Sympathetic nervous system: arouses and expends
energy (arousing)
2. Parasympathetic nervous system: conserves energy
and calms you (calming)
b. Central Nervous System
i. “Tens of billions of neurons, each communicating with
thousands of other neurons, yield and ever-chaining wiring
diagram that dwarfs a powerful computer. With some 40
billion neurons, each having roughly 10,000 contacts with
other neurons, we wend up with perhaps 400 trillion
synapses…” (57)
ii. Neural networks
1. Think: Why do cities exist? Why don’t people
distribute themselves evenly? It is the same with
neural networks…(Kosslyn and Koenig, 1992)
2. Learning something new builds neural networks
iii. Spinal cord: information highway that connects PNS to
brain
5. The Endocrine System: the body’s slow chemeical communication system;
a set of glands that secrete hormones into the bloodstream.
a. Hormones: chemical messengers that are manufactured by the
endocrine glands, travel through the bloodstream, and affect other
tissues.
i. Some are chemically identical to neurotransmitters
b. Adrenal gland
c. Pituitary gland
6. The Brain
a. Tools of Discovery: Having Our Head Examined
i. Brain damage gives us answers
ii. Recording the Brain’s Electrical Activity
1. Electroencephalogram (EEG): amplified read-out of
electrical waves in the brain
iii. Neuroimaging Techniques
1. Position emission tomography scan (PET): depicts
brain activity by showing each brain areas
consumption of it’s chemical fuel (glucose)
2. Magnetic resonance imaging (MRI): puts the head in
a strong magnetic field, which aligns the spinning
atoms of brain molecules.
3. Functional MRI (fMRI): can show both structure and
functioning
b. Older Brain Structures
i. The Brainstem: oldest and innermost region
1. Medulla: the base of the brainstem; controls
heartbeat and breathing
a. Pons: helps coordinate movements
2. Reticular formation: finger-shaped network of
neurons that extends from the spinal cord right up
to the thalamus.
ii. The Thalamus: acts as the brain’s sensory switchboard
iii. The Cerebellum: the “little brain” at the rear of the
brainstem; functions include processing sensory input and
coordinating movement output and balance.
iv. The older brain functions without any conscious effort: our
brains process most information outside of our awareness.
v. The Limbic System: the border between the brain’s older
parts and the cerebral hemispheres
1. The Amygdala: two bean sized neural clusters that
influence aggression and fear
2. The Hypothalamus: directs several maintenance
activities helps govern the endocrine system via the
pituitary gland, and is linked to emotion and reward
a. Reward centers
b. Animals come equipped with built-in systems
that reward activities essential to survival
c. Addictive behaviors results from a reward
deficiency syndrome
c. The Cerebral Cortex:
i. Structure of the cerebral cortex
1. Cerebrum: the two large hemispheres that
contribute 85% of the brain’s weight
2. Cerebral cortex: the think surface layer of
interconnected neural cells covering the cerebral
hemispheres (right and left); he body’s ultimate
control and information processing center
a. Contains 20-23 billion nerve cells and 300
trillion synaptic connections
3. Glial cells: like worker bees in a hive, they provide
nutrients, guide connections, and clean up ions and
neurotransmitters; may also play a part in learning
and thinking by “chatting” with other cells
4. Lobes of the brain (see picture below for location
and function)
ii. Functions of the Cortex
1. Motor functions: In the motor cortex, controls
movement
2. Sensory functions: in the sensory cortex
3. Association areas: areas of the cerebral cortex that
are not involved in primary motor or sensory
functions; rather are involved in higher mental
functions such a learning, remembering, thinking,
and perceiving
a. Found in all lobes of the brain
4. Phineas Gage
iii. The Brain’s Plasticity
1. Plasticity: the brain’s ability to change, especially
during childhood, by reorganizing after damage or
by building new pathways based on experience
a. Neural pathways that are severed will not
reconnect
b. Neurogenesis: the formation of new neurons
d. Our Divided Brain
i. Hemispheric specialization (lateralization)
ii. Splitting the brain
1. Corpus callosum: the wide band of axon fibers that
connects the two hemispheres (sides) of the brain
and carries messages between them.
2. Split brains: patients who had the corpus callosum
severed
e. Right-Left Differences in the Intact Brain
i. Perceptual task = right hemisphere
ii. Speaks or calculates = left hemisphere
iii. Deaf people use left hemisphere to process sign language
(just as hearing people use right hemisphere to process
speech)
1. To the brain, language is language, whether spoken
or signed.
7. Brain Organization and Handedness
a. 90% of the population is right handed
b. Left handedness is slightly more common in males
c. Right handers process speech in the left hemisphere, left handed
process speech in the left hemisphere 70% of the time, and 30% of
the time a mix
d. Is handedness inherited?
i. Begins in the womb, so probably