NERVOUS SYSTEM
I.
Nervous systems receive sensory input, interpret it, and send out
appropriate commands
a. NERVOUS SYSTEMS  most intricately organized data
processing system on Earth
b. NEURON  functional unit; specialized nerve cell for carrying
signals from one location in the body to another
c. Nervous system has 3 interconnected functions
i. SENSORY INPUT  conduction of signals from
sensory receptors to integration centers
ii. INTERGRATION  interpretation of the sensory
signals and the formulation of responses
iii. MOTOR OUTPUT  the conduction of signals from the
integration centers to effectors
1. EFFECTORS  muscles or glands that perform
body functions
d. Nervous systems have two main divisions
i. CENTRAL NERVOUS SYSTEM (CNS)  where most
integration occurs; consists of the brain and spinal cord
(in vertebrates)
ii. PERIPHERAL NERVOUS SYSTEM (PNS)  made up
of communication lines called nerves that carry signals in
and out of the CNS
1. NERVE  a cable-like bundle of neuron
extensions tightly wrapped in connective tissue
2. GANGLIA  clusters of neuron cell bodies in the
nerves
e. Three functional types of neurons
i. SENSORY NEURONS  convey signals, or
information, from sensory receptors into the CNS
ii. INTERNEURONS  located entirely within CNS;
integrate data and relay appropriate signals to other
interneurons or to motor neurons
iii. MOTOR NEURONS  function in motor output,
conveying signals from the CNS to effectors
II.
Neurons are the functional units of nervous systems
a. Structure of neuron
i. CELL BODY  houses the nucleus and other organelles
ii. Two types of fibers project from cell body
1. DENDRITES  short, many branches; receive
incoming messages and direct them toward cell
body
2. AXON  usually a single fiber; conducts signal
towards another neuron or effector
iii. SUPPORTING CELLS  protect, insulate, and reinforce
the neurons
1. SCHWANN CELLS
a. MYELIN SHEATH  insulating material
surrounding the axon
b. NODES OF RANVIER  spaces between
Schwann cells
i. Increase speed at which signal travels
ii. Multiple Sclerosis (MS)  disorder
where immune system destroys the
myelin sheath
iv. SYNAPTIC KNOB  ends the neuron; relays signals to
another neuron or effector
III.
A neuron maintains a membrane potential across its membrane
a. RESISTING POTENTIAL  the voltage across the plasma of
a resting neuron
b. SODIUM-POTASSIUM (Na+ - K+) PUMPS  actively
transport Na+ out of the cell and K+ in
IV.
A nerve signal begins as a change in the membrane potential
a. STIMULUS  any factor that causes a nerve signal to be
generated
b. ACTION POTENTIAL  the technical name for the nerve
signal
c. THRESHOLD POTENTIAL  the minimum change that must
occur to generate an action potential
d. CYCLIC PROCESS
V.
The action potential propagates itself along the neuron
a. All-or-none events
b. Different intensities result from frequency of potentials
VI.
Neurons communicate at synapses
a. SYNAPSE  the junction, or relay point, between two neurons
or between a neuron and an effector cell
b. Synapses can be either electrical or chemical
i. Electrical synapses transfer signals faster
ii. Chemical synapses have a narrow gap called a
SYNAPTIC CLEFT
1. SYNAPTIC CLEFT  separates synaptic knobs
from receiving neuron
2. NEUROTRANSMITTER  chemical signal
VII. Chemical synapses make complex information processing possible
a. Multiple signals can be sent to the same receiving neuron
VIII. A variety of small molecules function as neurotransmitters
a. ACETYLCHOLINE  important in the brain; may be
excitatory or inhibitory
b. BIOGENIC AMINES  nitrogen containing neurotransmitters
derived from amino acids
i. Ex. Epinephrine, norepinephrine, serotonin, dopamine
c. Endorphins are peptides that decrease pain perception
d. Dissolved gases like NO (nitrous oxide) act as
neurotransmitters; this is how VIAGRA works; promoting NO
action on smooth muscle
IX.
Many drugs act as chemical synapses
a. Effect us by acting at synapses or changing the neurotransmitter
X.
Nervous system organization usually correlates with body
symmetry
a. NERVE NET  web-like system of neurons extending
throughout the body
b. CEPHALIZATION  concentration of nervous system at the
head end
c. CENTRALIZATION  the presence of a CNS distinct from a
PNS
XI.
Vertebrate nervous systems are highly centralized and cephalized
a. CNS is made up of the spinal cord and brain
i. SPINAL CORD  lies inside the vertebral column, or
spine, receives sensory information from the skin and
muscles and integrates simple responses to certain kinds
of stimuli
ii. BRAIN  master control center; includes homeostatic
centers that keep the body functioning smoothly; sensory
centers that integrate data from the sense organs; in
humans, centers of emotion and intelligence; also sends
out motor commands to muscles
iii. BLOOD-BRAIN BARRIER  maintains a stable
chemical environment in the brain; only essential
nutrients and oxygen pass freely into the brain
iv. VENTRICLES and CENTRAL CANAL  fluid-filled
spaces in brain and spinal cord, respectively
1. CEREBROSPINAL FLUID  fluid that cushions
the CNS and helps supply it with nutrients,
hormones, and white blood cells
2. MENINGES  layers of connective tissue, also
supply cushion
b. CNS has 2 distinct areas
i. WHITE MATTER  mainly axons (with whitish myelin
sheath)
ii. GRAY MATTER  mainly nerve bodies and dendrites;
in mammals it is the area of higher brain function
c. PNS has
i. CRANIAL NERVES  carry signals to or from the
brain
ii. SPINAL NERVES  carry signals to or from the spinal
cord
XII. The peripheral nervous system of vertebrates is a functional
hierarchy
XIII. Opposing actions of sympathetic and parasympathetic neurons
regulate the internal environment
a. Autonomic nervous system has 2 divisions
i. PARASYMPATHETIC DIVISION  primes the body
for digesting food and resting
ii. SYMPATHETIC DIVISION  prepares the body for
intense, energy-consuming activities, such as fighting,
fleeing, or competing in a strenuous game
XIV. The vertebrate brain develops from three anterior bulges of the
neural tube
a. 3 ancestral regions
i. Forebrain  leads to CEREBRUM (dominant part of
forebrain)
ii. Midbrain
iii. Hindbrain
XV. The structure of a living supercomputer: The human brain
XVI. The cerebral cortex is a mosaic of specialized, interactive regions
a. CEREBRAL CORTEX  accounts for 80 % of brains total
mass; involved in reasoning and mathematical abilities,
language skills, imagination, artistic talent, and personality
traits
b. LATERALIZATION  areas in the two hemispheres become
specialized for different functions
XVII. Injuries and brain operations have provided insight into brain
function
a. “Broken brains” have given insight into normal brain function
b. Lack of nerves on the brain allow neurosurgeons to operate and
discern specific aspects of brain function
XVIII. Several parts of the brain regulate sleep and arousal
a. RETICULAR FORMATION  system of neurons that extends
through the core of the brainstem; receives data from sensory
receptors, filters and sends useful data to cerebral cortex
b. Electroencephalogram (EEG)  measures brain wave activity
i. REM SLEEP  “Rapid Eye Movement”; unique brainwave pattern during deep sleep; time when dreams occur
XIX. The limbic system is involved in emotions, memory, and learning
a. LIMBIC SYSTEM  includes parts of thalamus,
hypothalamus, portions of cerebral cortex; amygdala and
hippocampus play key roles in memory, learning, and emotion
i. AMYGDALA  central in recognizing the emotional
content of facial expressions and laying down emotional
memories
ii. HIPPOCAMPUS  involved in formation of memories
and their recall
iii. SHORT-TERM MEMORY vs. LONG-TERM
MEMORY
XX. The cellular changes underlying memory and learning probably
occur at synapses
a. LONG-TERM DEPRESSION (LTD)  decreased
responsiveness to an action potential by a receiving neuron
b. LONG-TERM POTENTIATION (LTP)  an enhanced
responsiveness to an action potential by a receiving neuron