Starting small: The Neuron
• neuron: a nerve cell;
receives signals from other
neurons or sensory organs,
processes these signals, and
sends signals to other
neurons, muscles, or bodily
organs
– the basic unit of the nervous
system
The Neuron
• 3 types of neurons:
– 1. sensory neurons: respond to input from sensory
organs (skin, eyes, etc.)
– 2. motor neurons: send signals to muscles to control
movement
– 3. interneurons: connect the sensory neurons and
motor neurons
• most of the neurons in the brain = interneurons
• average human brain  100 billion neurons
Structure of the Neuron
Structure of the Neuron
• cell body (soma): the central part of the neuron, contains
the nucleus
– regulates cell functioning
• dendrites: the branching part of the neuron that receives
messages from other neurons and relays them to the cell
body
Structure of the Neuron
• axon: the long, cable-like extension that delivers messages to other
neurons
• myelin sheath: layer of fatty tissue that insulates the axon and helps
speed up message transmission
– multiple sclerosis: deterioration of myelin leads to slowed
communication with muscles and impaired sensation in limbs
• knobs: structure at the end of one of the axon’s branches that
releases chemicals into the space between neurons, when the neuron
is fired
From Neuron to Neuron
• ≈100 billion neurons in a human brain,
connected to an average of 10,000 others;
some up to 100,000
• synapse: the place where an axon of one
neuron meets with the dendrite/cell body of
another neuron
From Neuron to Neuron
From Neuron to Neuron
• neurotransmitters:
a chemical that
sends signals from
one neuron to
another over the
synapse
From Neuron to Neuron
• Neurotransmitters are
stored in vesicles in
the knobs, and bind to
receptors on the cell
membrane of the next
neuron.
– Each receptor can
only bind with one
kind of
neurotransmitter.
(Some) Neurotransmitters
Neurotransmitter
Function
Examples of
malfunctions
Acetylcholine
(ACh)
Enables muscle action,
learning & memory
Alzheimer’s disease 
less ACh production
Dopamine
Influences movement,
learning, attention, &
emotion
Excess 
schizophrenia
Undersupply 
Parkinson’s disease
Serotonin
Affects mood, hunger,
sleep, and arousal
Undersupply 
depression
Norepinephrine
Helps control alertness &
arousal
Undersupply 
depressed mood
Glutamate
Excitatory neurotransmitter
involved in memory
Excess 
overstimulation of
brain, seizures
The Nervous System
• comprised of the central nervous system and
the peripheral nervous system
• central nervous system: brain and spinal cord
– reflex: an automatic response to an event
• e.g. sensory neuron detects pain, send
signal to spinal cord  signal to
interneurons  signal to motor neurons
The Nervous System
• Peripheral Nervous System: links central
nervous system to organs
–comprised of the skeletal nervous
system and the autonomic nervous
system
–skeletal nervous system: controls
voluntary movements of our skeletal
muscles
The Nervous System
• autonomic nervous system: controls many of the
self-regulatory functions of the body (e.g. digestion,
circulation)
– comprised of the sympathetic and parasympathetic
nervous systems
– sympathetic: prepares us for defensive actions against
threats (e.g. faster heartrate, increased breathing rate,
inhibits digestion, dilates pupils to allow greater light
sensitivity)
– parasympathetic: counteracts effects of sympathetic
nervous system, calms us down
Structure of the Brain
• The human brain is
comprised of “older” and
“newer” parts.
– “older”: lower level
structures, responsible for
basic survival mechanisms
– “newer”: higher level
structures, responsible for
more advanced human
faculties
Structure of the Brain
• brainstem: the set of
neural structures at the
base of the brain,
including the medulla,
the reticular formation,
and the pons
– facilitates communication
between the brain and
spinal cord
The Brainstem
• medulla: controls
heartbeat, breathing,
and swallowing
• pons: bridge from
brainstem to
cerebellum; controls a
variety of functions,
including sleep and
control of facial
muscles
The Cerebellum
• “little brain” extending
from rear of brainstem
– coordinates physical
movement
– contributes to
estimating time and
paying attention
• cerebellum + other lower
level brain structures
occur without conscious
effort
– Much of our brain’s
activity occurs outside
of our awareness
The Brainstem
• thalamus: the brain’s
sensory switchboard;
receives signals from the
sensory and motor systems,
and relays them to the
appropriate parts of the
brain
– also receives signals from
higher brain structures,
relays them to medulla
and cerebellum
The Limbic System
• limbic system: doughnutshaped system of neural
structures at the border of
the brainstem and cerebral
hemispheres
– involved in the basics of
emotion and motivation:
fighting, fleeing, feeding, and
sex
– comprised primarily of the
hypothalamus, the
hippocampus, and the
amygdala
The Limbic System
• hypothalamus: brain
structure that sits
under the thalamus
and plays a central
role in controlling
eating and drinking,
and in regulating the
body’s temperature,
blood pressure, and
heart rate
The Limbic System
• hippocampus: brain
structure that plays a key
role in allowing new
information to be stored
in memory
hippocampus does not
contain memories
itself, but does trigger
processes that store
memories elsewhere
in the brain
The Visible Brain
• cerebral cortex: the
convoluted pinkish-gray
surface of the brain, where
most mental processes take
place
• The brain is divided into two
halves (cerebral
hemispheres), separated by
a deep fissure
– hemispheres control
opposite side of body
(e.g. right-handers’
writing is controlled by
the left hemisphere)
Our Divided Brains
• cerebral hemispheres
connected by the corpus
callosum, a large band of
neural fibers that transmits
messages between
hemispheres
– contains more than 200
million nerve fibers, can
transfer more than 1
billion bits of
information per second
Structure of the Cortex
• cerebral cortex divided
into lobes, or regions of
the brain
– Each lobe is
(roughly) responsible
for different higherlevel functions, but
remember that they
do not work merely
in isolation.
Structure of the Cortex
• occipital lobe: brain lobe at
the back of the head
– responsible primarily
for vision; separate
areas specify visual
properties such as
shape, color, and
motion
Structure of the Cortex
• temporal lobe: the brain
lobe under the temples,
in front of the ears
– many functions,
including processing
sounds, committing
information to
memory, and
comprehending
language
Structure of the Cortex
• parietal lobe: brain lobe
at the top and
center/rear of the head
– involved in registering
spatial location,
attention, and motor
control
Structure of the Cortex
• frontal lobe: the brain lobe
located behind the forehead
– the seat of planning,
memory search, motor
control, reasoning,
emotions, and many
other functions
– In many ways, the frontal
lobe is what makes us
uniquely human.