NERVES
Neurons & Supporting Cells
 Neurons- nerve cells
o There are 100 billion in the human brain
 Nerves- bundles of fiber-like extensions of neurons
 Greater complexity of nervous systems evolved with cephalization (the
clustering of neurons in a brain near the anterior (front) end in animals
with elongated, bilaterally symmetrical bodies)
 Central nervous system- small brain and longitudinal nerve cords
o Consists of brain and spinal cord
o Located along the dorsal (back) side of the body
 Peripheral nervous system- nerves that connect the CNS with rest of body
o Nerves and ganglia comprise the PNS
 Ganglia- ventral nerve cords containing segmentally
arranged clusters of neurons
 Information processing: 3 stages produce reflexes
o Sensory input- transmit information from sensors that detect
external stimuli (light, sound, touch, heat, etc.) and internal
conditions (blood pressure, blood CO2 level, etc.)
o Integration- interneurons analyze and interpret the sensory input
o Motor output- motor neurons leave the CNS who communicate
with effector cells (muscle cells and endocrine cells)
 Neuron structure: depends on the ability of neurons to receive and
transmit info
o Most organelles are located in cell body
o 2 types of extensions from cell body
 Dendrites: highly branched extensions that that RECEIVE
signals from other neurons
 Axon: much longer extensions that TRANSMIT signals to
other cells
o Axon hillock: conical region where axon joins cells body
o Myelin sheath: lipid membranes that surround the axon to provide
electrical insulation
o Synaptic terminal: ending of several branches of axon
o Synapse: the site of communication between a synaptic terminal
and another cell
 Presynaptic cell: transmitting neuron in synapse
 Postsynaptic cell: receiving cell in synapse
 Neurotransmitters: chemical messengers
o Glia: supporting cells that are essential for structural integrity
 Several types of glia:
 Astrocytes: provide structural support for neutron
and regulate the extracellular concentrations of
ions and neurotransmitters; stimulate blood
vessel dilation; induce formation of tight junctions
(aka blood-brain barrier (restricts the passage of
most substances into the CNS))
 Radial glia: forms tracks along which newly
formed neurons migrate from the neural tube (the
structure that gives rise to the CNS)
 Oligodendrocytes (located in the CNS) &
Schwann cells (located in the PNS): glia that
form the myelin sheaths around the axons of
many vertebrate neurons
Vertebrate Nervous System
 CNS (filled with cerebrospinal fluid (which is formed in the brain by
filtration of the blood) & serves as a cushion)
o Brain- provides the integrative power that underlies the complex
behavior of vertebrates
 White matter: well-defined bundles of axons whose
myelin sheath give them a whitish appearance
 Gray matter: which consists mainly of dendrites,
unmyelinated axons, and neuron cell bodies
 Divided into 4 ventricles
o Brainstem- composed of 3 parts that function in homeostasis,
coordination of movement, and conduction of information
 Medulla oblongata: contains centers that control
homeostatic functions, including breathing, heart, and
blood vessel activity, swallowing, vomiting, and digestion
 Pons: participates in some of these activities; it regulates
the breathing centers in the medulla
 The medulla and the pons together help
coordinate large-scale body movements; both
contain centers that cause sleep when stimulated
 Midbrain: contains centers for the receipt and integration
of several types of sensory information; it also sends
coded sensory information along neurons to specific
regions of the forebrain
 Has an area that causes arousal
 The brainstem and the cerebrum control sleep and
arousal
 Reticular formation: diffuse network of neurons
are present in core of brainstem; regulate sleep
and arousal; selects with information reaches the
cerebral cortex
 In the case that these brain functions do not act
as needed, melatonin has been promoted as a
dietary supplement
o Cerebellum- important for coordination and error checking during
motor, perceptual, and cognitive functions
 Likely involved in learning and remembering motor skills,
such as those involved in riding a bicycle
 Receives input concerning motor commands issued by
the cerebrum
 Is involved in hand-eye coordination
o Diencephalon- composed to 3 adult brain regions
 Epithalamus: includes the pineal gland and coroid plexus,
one of several clusters of capillaries that produce
cerebrospinal fluid from blood
 Thalamus: main input center for sensory information
going to the cerebrum and the main output center for
motor information leaving the cerebrum
 Receives input from the cerebrum and other
parts of the brain that regulate emotion and
arousal
 Hypothalamus: source of two sets of hormones, posterior
pituitary hormones and releasing hormones that act on
the anterior pituitary
 Also contains the body’s thermostat, as well as
centers for regulating hunger, thirst, sexual and
mating behaviors
 Controls circadian (daily) rhythms
o Biological clock: pair of hypothalamic
structures called the suprachiasmatic
nuclei; involved in maintaining circadian
rhythms; require external cues to remain
synchronized with environment
o Cerebrum- divided into right and left cerebral hemispheres
 Left hemisphere: control language, math, logical
operations, and serial processing of sequences
 Right hemisphere: stronger at pattern recognition, face
recognition, spatial relations, nonverbal thinking,
emotional processes, and simultaneous processing of
info
 Each hemisphere consists of an outer covering of gray
matter, the cerebral cortex, internal white matter, and
basal nuclei (important centers for planning and learning
movement sequences)
 Cerebral cortex: largest, most complex part of the brain;
sensory information is analyzed, motor commands are
issued and language is generated; composed of 4 lobes
 Frontal: associated with reward, attention, shortterm memory, planning, and motivation
 Temporal: auditory info processed here
 Occipital: visual information processed here
 Parietal: somatosensory information about touch,
pain, pressure, tempterature, and the position of
muscles and limbs
**Cortical surface area devoted to each body part is related to
the number of sensory neurons that innervate that part or to
the amount of skill needed to control the muscles of that**
 Neocortex: forms the outermost part of the mammalian
cerebrum, consisting of 6 parallel layers of neurons
arranged tangential to the brain surface
o Highly convoluted and accounts for 80%
of total brain mass
 Corpus Callosum: thick band of axons that enables
communication between the right and left cerebral
cortices
o Spinal cord- integrates simple responses to certain kinds of
stimuli and conveys information to and from the brain
 Central canal- narrow nerve cord

PNS
Transmits information to and from the CNS & plays a
large role in regulating the vertebrate’s movement and
internal environment
 Consists of left-right pairs of cranial and spinal nerves
and their associated ganglia
 Cranial nerves- originate in the brain and terminate
mostly in organs of the head and upper body
 Spinal nerves- originate in the spinal cord and extend to
parts of the body below the head
o Divided into 2 functional components:
 Somatic nervous system: carried and signals to and from
skeletal muscles, mainly in response to EXTERNAL
stimuli
 Is considered voluntary because it is subject to
conscious control
 Autonomic nervous system: regulates the internal
environment by controlling smooth and cardiac muscles
and the organs of the digestive, cardiovascular, excretory
and endocrine systems
 Is considered involuntary because it is internal
 3 subdivisions of ANS:
o Sympathetic: corresponds to arousal and
energy generation (e.g.: heart beats
faster, liver converts glycogen to
glucose, bronchi of lungs dilate, etc.)
o Parasympathetic: corresponds to
calming and a return to self-maintenance
functions (e.g.: decrease in heart rate,
increase glycogen production, and
enhances digestion, etc.)
o Enteric: consists of networks of neurons
in the digestive tract, pancreas, and
gallbladder; control secretions
Resting and Action Potential
 Membrane potential: all cells have an electrical potential difference
(voltage) across their plasma membrane; typically between -60 & -80 mV



when the cell is not transmitting signals (negative sign indicates that inside
of the cell is negative relative to the outside)
Resting Potential: membrane potential of a neuron that is not transmitting
signals
o Depends on the ionic gradients that exist across the plasma
membrane
o Na+ & K+ gradients are maintained by the sodium-potassium
pump
 If the pump is disabled by the addition of a specific
poison, the gradients gradually disappear & so does the
resting potential
 Membrane contains many ion channels that allow only K+
to diffuse across membrane
 K+ tends to diffuse down its concentration gradient, from
an area of higher concentration to an area of lower
concentration
 At equilibrium, there is no net diffusions of K+ across the
membrane
 Equilibrium potential (Eion): magnitude of membrane
voltage at equilibrium
 Given by Nerst equation (which applied to any
membrane that is permeable to a single type of
ion)
 Equilibrium potential for K+ (Ek): -92 mV (@ 37
°C)
 Equilibrium potential of Na+ (ENa): +62 mV (@ 37
°C)
 NEITHER K+ & Na+ IS AT EQUILIBRIUM SO THERE IS
ALWAYS A NET FLOW OF EACH ION ACROSS THE
MEMBRANE AT REST
 THIS IS THE BASIS OF ELECTRICAL SIGNALS IN
THE NERVOUS SYSTEM:
Gated Ion Channels: channels that open or close in response to one of
three kinds of stimuli; responsible for generating signals to the nervous
system

o Stretch-gated ion channels: found in cells that sense stretch and
open when the membrane is mechanically deformed
o Ligand-gated ion channels: found at synapses and open or close
when a specific chemical, such as a neurotransmitter, binds to the
channel
o Voltage-gated ion channels: found in axons and open or close
when the membrane potential changes
Action Potential: a stimulus strong enough to produce a depolarization
that reaches the threshold triggers a different type of response; once
triggered, it has a magnitude that is independent of the strength of the
triggering stimulus; the signals that carry information along axons; very
brief (1-2 msec)
o Composed of hyperpolarization and depolarization
 Hyperpolarization: an increase in the magnitude of the
membrane potential (the inside of the membrane
becomes more negative)
 Depolarization: a reduction in the magnitude of the
membrane potential (the inside of the membrane
becomes less negative)
 Graded only up to a certain membrane voltage
(threshold)
*****These changes in membrane potential are called
gradient potentials because the magnitude of the
hyperpolarization or depolarization varies with the
strength of the stimulus*****
o Production
1. Resting state: the activation gates on the Na+ and k+
channels are closed, and the membrane’s resting
potential is maintained
2. Depolarization: a stimulus opens the activation gates on
some Na+ channels; Na+ influx through those channels
depolarizes the membrane; if the depolarization reaches
the threshold, it triggers an action potential
3. Rising phase of the action potential: depolarization opens
the activation gates on most Na+ channels, while the K+
channels’ activation gates remain closed; Na+ influx
makes the inside of the membrane positive with respect
to the outside

4. Falling phase of the action potential: the inactivation
gates on most Na+ channels close, blocking Na+ influx;
the activation gates on most K+ channels open,
permitting K+ efflux makes the side of the cell negative
5. Undershoot: both gates of the Na+ channels are closed,
but the activation gates on some K+ channels are still
open; as these gates close on most K+ channels, and the
inactivation gates open on Na+ channels, the membrane
returns to its resting state
6. Refractory period: the downtime following an action
potential when a second action potential cannot be
initiated; sets a limit on the maximum frequency at which
action potentials can be generated
o Conduction
o Action potential must function over a long distance w/o
diminishing from the cell body to the synaptic terminals
1. An action potential is generated as Na+ flows inward
across the membrane at one location
2. The depolarization of the action potential spreads to the
neighboring region of the membrane, re-initiating the
action potential there; the membrane behind the reinitiated action potential is repolarizing as K+ flows
outward
3. The depolarization-repolarization process is repeated in
the next region of the membrane; in this way, local
currents of ions across the plasma membrane cause the
action potential to be propagated along the length of the
axon
Synapses
o Contain gap junctions which allow electrical current to flow directly
from cell to cell
o Chemical synthesis: involve the release of a chemical
neurotransmitter by the presynaptic neuron
o Presynaptic neuron: synthesizes the
neurotransmitter and packages it in
synaptic vesicles, which are stored in the
neuron’s synaptic terminals
1. Action potential depolarizes the plasma
membrane of the synaptic terminal
2. It opens voltage-gated Ca2+ in the membrane,
triggering an influx of Ca2+
3. Elevated Ca2+ concentration in the terminal
causes synaptic vesicles to fuse with the
presynaptic membrane
4. Vesicles release neurotransmitter into the
synaptic cleft
5. The neurotransmitter binds to the receptor
portion of ligand-gated ion channels to the
postsynaptic membrane, opening the channels
6. The neurotransmitter releases from the
receptions and the channels close
o Direct Synaptic Transmission
 Ligand-gated ion channels capable of binding to the
neurotransmitter are clustered in the membrane of the
postsynaptic cell, directly opposite the synaptic terminal
 The receptor opens the channel and allows specific ions
to diffuse across the postsynaptic membrane
 Results in a postsynaptic potential (a change in the
membrane potential of the postsynaptic cell)
 2 types of postsynaptic membrane
o Excitatory postsynaptic potentials:
depolarizations that bring the membrane
potential toward the threshold
o Inhibitory postsynaptic potentials:
postsynaptic membrane hyperpolarizes
o Indirect synaptic transmission
 A neurotransmitter binds to a receptor that is not part of
an ion channel
 Effects have a slower onset but last longer
o Neurotransmitters
 Each neurotransmitter binds to its own group of receptors
 Acetylcholine: one of the most common neurotransmitters
 In cardiac muscle, it activates a signal
transduction pathway that reduce the strength
and rate of contraction of cardiac muscle cells
 Biogenic amines: neurotransmitters derived from amino
acids

Includes epinephrine, norepinenphrine,
dopamine, and serotonin
 Most often involved in indirect synaptic
transmission
 Amino acids and peptides
 4 amino acids know to function as
neurotransmitters in CNS
o Gamma aminobutyric acid (GABA),
glycine, glutamate, and aspartate
 Neuropeptides: short chains of amino acids that
serve as neurotransmitters
o Include substance P and endorphins
CNS Functions and Disease
 Functions
o Language and Speech
 Broca’s area: located in front part of primary cortex that
control muscles of face; controls mouth movement for
speech
 Wernicke’s area: posterior portion of temporal lobe; if
damaged, it can abolish the ability to comprehend speech
but the person him/herself can still speak
 Frontal and temporal areas become active when meaning
must be attached to words, such as when a person
generate verbs to go with nouns or groups related words
o Emotions
 Limbic system: ring of structures around the brainstem;
includes 3 parts (amygdala, hippocampus, and olfactory
bulb)
 Interact with neocortex to mediate primary
emotions that manifest themselves in behaviors
such as laughing, crying, anger, fear, distress
 Phineas Gage: was working on a railroad
construction site when a dynamite explosions
drove a meter-long iron rod through his head; the
rod entered his skull just below his left eye and
exited through the top of his head; he recovered,
but his personality had changed drastically; after
his death, neuroscientists his skill and

determined that the rod had destroyed portions of
his frontal lob known to mediate emotions
o Memory and Learning
 Short-term memory: located in frontal lob
 Long-term memory: activated in process that requires the
hippocampus
 Motor skills like walking is learned by repetition
 Once a memory is learned, it is difficult to unlearn
 Cellular mechanisms of learning
 Long-term potentiation: involves an increase in
the strength of synaptic transmission that occurs
when presynaptic neurons produce a brief, highfrequency series of action potentials
o Because LTP can last for days or weeks,
it may be a fundamental process by
which memories are stored or learning
takes place
o Consciousness
 Consciousness is really studied in psychology, but brainimaging technique reveal and increasingly detailed
picture of how neural activity correlates with conscious
experiences
 Nothing much is really known…
Diseases
o Schizophrenia: a severe mental disturbance characterized by
psychotic episodes in which patients lose the ability to distinguish
reality
 Have hallucinations, delusions, blunted emotions, etc.
 Cause is unknown, but it does have a strong genetic
component
 Treatments for schizophrenia have focused mostly on
brain pathways that use dopamine as a neurotransmitter
o Depression: 2 broad categories
 Bipolar disorder: swings of mood from high to low;
composed of manic and depressive phases
 Affect 1% of people in world
 Manic phase: Characterized by high self esteem,
increased energy, etc.

Depressive phase: lowered ability to feel
pleasure, loss of interest, sleep disturbances, etc.
 Major depression: have a low mood most of the time
 Affect 5% of people in world
 Have genetic component, but indications of stress may
be an important factor
 Several treatments, but they have many other side effects
o Alzheimer’s disease: mental deterioration, or dementia,
characterized by confusion, memory loss, and variety of other
symptoms
 Incidence in age related (as medicine is allowing humans
to live longer, it is increasing the proportion of AD patients
in the population)
 Has a characteristic pathology to it: neurons die in huge
areas
 Enormous effort devoted to developing treatment for AD
o Parkinson’s disease: motor disorder characterize by difficulty in
initiating movements, slowness of movement, and rigidity
 Often have masked facial expression, muscle tremors,
poor balance, flexed posture, and shuffling gait
 Affects 1 million people in the US
 Progressive brain illness whose risk increases with
advancing age
 Symptoms: result from the death of neurons in midbrain
nucleus
 No known cause and there is no cure