Download Chapter 9

The Nervous System
Chapter 9
Objectives
•  To identify the basic structure of a neuron.
•  To explain the main components of the nervous
system.
•  To compare and contrast the central nervous
system and the peripheral nervous system.
•  To differentiate between the somatic and
autonomic nervous systems.
Functions of the Nervous System
•  Sensory input (gathering information): to monitor
changes occurring inside and outside the body
o  Changes = stimuli
•  Integration: to process and interpret sensory input
and decide if action is needed
•  Motor output: a response to integrated stimuli
o  The response activates muscles or glands
Functions of the Nervous System Structure of a Neuron
•  Neuron= Nerve Cell
•  Reacts to physical/chemical
changes in surroundings
•  Transmit information through
nerve impulses to other
neurons and other cells.
Anatomy of a neuron video
•  https://www.youtube.com/watch?v=ob5U8zPbAX4
Nervous Tissue
•  Neuroglia
o  Definition: all support cells in the CNS (Central nervous
system)
o  Function: to support, insulate, and protect neurons
•  Neurons
o  Function: transmit messages
o  Major regions of neurons
•  Cell body – nucleus and metabolic center of the cell
•  Processes – fibers that extend from the cell body
o Dendrites – conduct impulses toward the cell
body
o Axons – conduct impulses away from the cell
body
CNS vs. PNS
•  CNS (Central Nervous System):
o  Brain
o  Spinal Cord
•  PNS (Peripheral Nervous System):
o  Cranial nerves
o  Spinal Nerves
PNS
•  Contains a sensory division and a motor division.
•  Sensory Division:
o  Contains sensory receptors that convert info into a nerve impulse
and transmit it back to the CNS to make sense of it.
o  Monitors environmental changes such as light and sound
o  Detects changes in homeostasis ( ex: temperature, oxygen level)
Motor Division
•  Utilize peripheral neurons to carry impulses from the
CNS to an effector which will cause a response
o  Ex: muscle contraction, gland secretion, etc.
Motor Division
•  Somatic Nervous System:
o  Controls skeletal muscle
and voluntary
movement.
•  Autonomic Nervous System:
o  Controls effectors that
are involuntary
•  Ex: heart, smooth
muscle, certain glands
Objectives
•  To identify and explain the 3 different structures of
neurons.
•  To compare and contrast sensory, motor, and
interneurons and explain a general pathway.
•  To determine the functions of the 5 types of
neuroglia.
Types of Neurons
Multipolar:
o  Many processes
stemming from cell
body.
o  *most neurons in
brain and spinal
cord are
multipolar
Types of Neurons
Bipolar:
o  Only two
processes (one at
each end.
o  *found in eyes,
nose, ears..
Types of Neurons
Unipolar:
o  One single process
extending from cell
body.
o  one side of axon is the
peripheral process
associated with body
part, other side is the
central process that
enters brain or spinal
cord.
o  Cell bodies create a
tissue mass called
ganglia.
Types of Neurons
Neuron Classification
•  Sensory Neurons (afferent):
o  Carry impulses from PNS
to CNS
o  Contain “receptor ends”
at the tips of dendrites
o  Changes outside the
body stimulate receptor
ends triggering an
impulse
o  *Most are unipolar
Neuron Classification
•  Interneurons (association):
o  Completely in brain or
spinal cord.
o  Link neurons together.
o  *multipolar
Neuron Classification
•  Motor Neurons (efferent):
o  carry impulses out of
brain or spinal cord to
the effector and
stimulate response.
General Pathway
Neuroglial Cells
*More numerous than neurons, support neurons in
different ways.
•  Microglial Cells:
o  Phagocytize bacterial cells and cellular debris
•  Oligodendrocytes:
o  Provide insulating layers of myelin
•  Astrocytes:
o 
o 
o 
o 
Provide structural support
join parts (ex: neuronàcapillary)
help regulate concentrations of nutrients and ions
Form scar tissue in the CNS
•  Ependymal Cells:
o  Forms membrane that covers specialized brain parts and forms inner linings
within the brain and spinal canal
•  Schwann cells:
o  Forms myelin sheath around axons.
Nervous Tissue: Support Cells Nervous Tissue: Support Cells Nervous Tissue: Support Cells Nervous Tissue: Support Cells Nervous Tissue: Support Cells Neuroglial Cells
Myelin
•  A lipid that sometimes coats axons
o White matter = myelinated axons in CNS
o Gray matter = cell bodies & unmyelinated
axons in CNS
•  Produced by some neuroglial cells
•  Insulates neurons & increases efficiency of
nerve impulses
Objectives
•  To explain how a nerve impulse occurs.
•  To determine what types of stimuli elicit an action
potential.
•  To explain different things that inhibit an action
potential.
•  To understand components of a neuron that
contribute to impulse velocity.
Cell Membrane Potential
•  The membrane is electrically charged, “polarized”
due to Na+ and K+ ions
o  Greater concentration of sodium ions outside
and potassium ions inside.
o  Potassium ions pass through more easily
o  Active transport (sodium/potassium pump)
maintains balance
•  This is essential in the propagation of a nerve
impulse.
Resting Potential
•  When a nerve cell membrane is undisturbed, the
membrane remains polarized staying more
negative on the inside and positive on the outside.
Threshold Potential
•  If the nerve cell detects a change in light/temp/
pressure it effects the resting potential and the
membrane begins depolarizing.
o  Sodium channels open and + ions flow in, making the
inside less negative.
•  Change in potential is proportional to the intensity
of the stimulation.
•  Stimulation + more stimulation before initial
stimulation subsides is called summation.
•  Once the threshold is reached, an action potential
occurs.
Action Potential •  Definition: change in
neuron membrane
polarization and return
to resting state
•  Nerve Impulse: chain of
action potentials from
neuron to neuron
Action Potential •  Depolarization: a decrease in membrane potential
•  Repolarization: increase in membrane potential,
causes membrane to become negatively charged
again
Action Potential
1.  Stimuli (temperature, light, pressure, other neurons)
decreases membrane potential
2.  When threshold potential (~55 mV) is reached,
stimulus is big enough to cause neuron to send a
signal.
Action Potential Continued
3. Reaching threshold potential triggers Na+ and K+
channels (located in nodes of Ranvier) to open and
equalize charges
3a. Na+ channels open faster, causing rapid
depolarization.
3b. As K+ channels open slowly, membrane
becomes more polarized, Na+ rushes out.
4. Further parts of axon are triggered and action
potentials propagate down length of axon causing
nerve impulse.
5. Results in neurotransmitters being released into
synapse
Action Potential
Action potential video •  https://www.youtube.com/watch?v=ZAmUjvgoO0A
•  https://www.youtube.com/watch?v=HnKMB11ih2o
Impulse Conduction
•  Unmyelinated nerve = impulse conducted over the
entire surface.
•  Myelin insulates and prevents ion flow, would
prevent conduction if it were continuous and
didn’t have the nodes of ranvier.
•  Myelinated nerve= impulse jumps from node to
node and creates a saltatory response and is much
faster than unmyelinated.
All-­‐‑or-­‐‑None •  Nerve impulses create an “all or none response”.
•  Once the stimulus reaches threshold, it generates
an action potential.
Objectives
•  Identify the different components of a reflex
arc.
•  Explain different autonomic reflexes found
throughout the body.
Reflexes
•  Ordinarily, a receptor sends a signal to the brain
where the brain coordinates a response.
•  What happens when you touch something hot?
Reflex Arcs •  Reflex: a rapid, predictable, and involuntary
response to a stimulus
•  Reflex Arc: Direct route from sensory neurons, to an
interneuron, to an effector.
o  Interneuron: neuron between the primary sensory
neuron and the final motor neuron.
•  A reflex is a rapid action that happens without
thought and does not involve the brain.
Reflex Arc
1)  Receptor- sense organ in skin, muscle, or other
organ
2)  Sensory Neuron- carries impulse towards CNS from
receptor
3)  Interneuron- carries impulse within CNS
4)  Motor Neuron- carries impulse away from CNS to
effector
5)  Effector- structure by which animal responds
(muscle, gland, etc).
Steps in a Reflex Arc
1.  Stimulus: A receptor receives a stimulus
2.  Afferent Pathway: Receptor sends message to
integrating center (CNS) via a sensory neuron
3.  Integration: CNS makes correct connection
between sensory neuron and motor neuron; usually
involves an interneuron
4.  Efferent Pathway: Motor neuron carries message
from CNS to effector
5.  Response: Effector carries out appropriate
response
Reflex Arc
Reflex arc video •  https://www.youtube.com/watch?v=wLrhYzdbbpE
Types of Reflexes
•  Somatic reflexes: Activation of skeletal muscle
o  Example: when you move your hand away from
a hot stove
•  Autonomic reflexes: Regulation of smooth muscle;
regulation of cardiac muscle, regulation of glands
o  Example: Heart rate and blood pressure
regulation; digestive system regulation;
regulation of fluid balance
NeurotransmiLers •  Definition: chemicals that transmit signals from
neurons to a target cell across a synapse
•  NTs can be either excitatory (excite) or inhibitory
(inhibit)
•  Each neuron generally synthesizes and releases a
single type of neurotransmitter
Neurotransmitter
Role in the Body
Acetylcholine
Excitatory. Used by spinal cord neurons to control muscles; used
by neurons in the brain to regulate memory. In most instances,
acetylcholine is excitatory.
Dopamine
Inhibitory. Produces feelings of pleasure when released by the
brain reward system.
GABA
(gamma-aminobutyric
acid)
The major inhibitory neurotransmitter in the brain.
Glutamate
The most common excitatory neurotransmitter in the brain.
Glycine
Inhibitory. Used mainly by neurons in the spinal cord.
Norepinephrine
Mostly excitatory, can be inhibitory in a few brain areas. Acts as
both neurotransmitter and hormone. In PNS, part of fight or
flight response. it is part of the flight-or-flight response. In
brain, regulates normal brain processes.
Serotonin
Inhibitory. Involved in many functions including mood, appetite,
and sensory perception.
Drugs Interfere with Neurotransmission
•  Drugs can affect synapses at a variety of sites and
in a variety of ways, including:
o  Increasing number of impulses (firing of nerves)
o  Release NT from vesicles with or without impulses
o  Block reuptake of neurotransmitters or block
receptors
o  Produce more or less NT
o  Prevent vesicles from releasing NT
Three Drugs (of many) which affect Neurotransmission Methamphetamine
Nicotine
Alcohol
Methamphetamine
•  Meth alters Dopamine transmission in two ways:
o  Enters dopamine vesicles in axon terminal
causing release of NT
o  Blocks dopamine transporters taking dopamine
back into the transmitting neuron
•  Result: More dopamine in the synaptic cleft
o  This causes neurons to fire more often than
normal resulting in a euphoric feeling.
Methamphetamine •  Problems…
o  After the drug wears off, dopamine levels drop,
and the user “crashes”. The euphoric feeling will
not return until the user takes more
methamphetamine.
o  Long-term use of meth causes dopamine axons
to wither and die.
o  Note that cocaine also blocks dopamine
transporters, thus it works in a similar manner.
Nicotine
•  Similar to methamphetamine and cocaine, nicotine
increases dopamine release in a synapse.
•  However, the mechanism is slightly different
•  Nicotine binds to receptors on the presynaptic
neuron
Nicotine •  Nicotine binds to the presynaptic receptors exciting
the neuron to fire more action potentials causing an
increase in dopamine release.
•  Nicotine also affects neurons by increasing the
number of synaptic vesicles released.
Alcohol •  Alcohol has multiple effects on neurons. It alters
neuron membranes, ion channels, enzymes, and
receptors.
•  It binds directly to receptors for acetylcholine,
serotonin, and gamma aminobutyric acid (GABA),
and gluatmate.
GABA and the GABA receptor •  GABA is a neurotransmitter that has an inhibitory
effect on neurons.
•  When GABA attaches to its receptor on the
postsynaptic membrane, it allows Cl ions to pass
into the neuron.
•  This hyperpolarizes the postsynaptic neuron to inhibit
transmission of an impulse.
Alcohol and the GABA Receptor •  When alcohol enters the brain, it binds to GABA
receptors and amplifies the hyperpolarization effect
of GABA.
•  The neuron activity is further diminished.
•  This accounts for some of the sedative affects of
alcohol.
The Adolescent Brain and Alcohol
•  The brain goes through dynamic change during
adolescence, and alcohol can can seriously
damage long and short-term growth processes.
•  Frontal lobe development and the refinement of
pathways and connections continue until age 16,
and a high rate of energy is used as the brain
matures until age 20.
•  Damage from alcohol at this time can be long-term
and irreversible.
The Adolescent Brain and Alcohol
•  In addition, short-term or moderate drinking impairs
learning and memory for more in youth than adults.
•  Adolescents need only drink half as much as adults
to suffer the same negative effects.
Drugs that Influence NeurotransmiLers Change in Neurotransmission
Effect on Neurotransmitter release or
availability
Drug that acts this way
increase the number of impulses
increased neurotransmitter release
nicotine, alcohol, opiates
release neurotransmitter from
vesicles with or without impulses
increased neurotransmitter release
amphetamines
methamphetamines
release more neurotransmitter in
response to an impulse
increased neurotransmitter release
nicotine
block reuptake
more neurotransmitter present in
synaptic cleft
cocaine
amphetamine
produce less neurotransmitter
less neurotransmitter in synaptic
cleft
probably does not work this way
prevent vesicles from releasing
neurotransmitter
less neurotransmitter released
No drug example
block receptor with another
molecule
no change in the amount of
neurotransmitter released, or
neurotransmitter cannot bind to its
receptor on postsynaptic neuron
LSD
caffeine
CNS (Brain Structure)
Regions of the Brain
Cerebral Hemispheres (Cerebrum)
•  Structure of cerebrum: Paired (left and right)
superior parts of the brain
•  Function of cerebrum: Higher brain function
(thought and action)
Regions of the Brain: Cerebrum
Four (Main) Lobes of the Cerebrum
•  Frontal lobe: problem solving, judgment, motor
function (Primary Motor Area), speech (Broca’s
Area)
•  Parietal lobe: sensation, handwriting, body position
(Primary Somatic Sensory Area)
•  Occipital lobe: visual processing system
•  Temporal lobe: memory and hearing
Regions of the Brain: Cerebrum
Regions of the Brain: Diencephalon Regions of the Brain: Diencephalon Diencephalon
•  Structure: sits on top of brain stem; enclosed by
cerebral hemispheres
Diencephalon
Three parts
•  Thalamus: relay station for sensory
impulses
•  Hypothalamus: autonomic nervous system center;
involved in emotion
o  Helps regulate body temperature
o  Controls water balance
o  Regulates metabolism
•  Epithalamus: houses the pineal gland (involved in
sleep); forms CSF (Cerebrospinal fluid)
Regions of the Brain: Diencephalon Brain Stem
Structure: Attached to the spinal cord
•  Midbrain
o  Mostly composes of tracts of nerve fibers
o  Function: reflex center for vision and hearing
•  Pons
o  Structure: bulging center part of the brain stem
o  Function: control of breathing
•  Medulla Oblongata
o  Structure: most inferior part of the brain stem; merges into
spinal cord
o  Functions: heart rate control, blood pressure regulation,
breathing, swallowing, vomiting
Regions of the Brain: Brain Stem Cerebellum •  Structure: looks like a “little cerebrum”, sits inferior to
cerebrum, posterior to brain stem
•  Function: provides involuntary coordination of body
movements
Regions of the Brain: Cerebellum Ventricles •  Structure: four chambers within the brain filled with
cerebrospinal fluid
o  Lateral Ventricles: within Cerebrum
o  Third Ventricle: in Diencephalon
o  Fourth Ventricle: between pons and cerebellum
Ventricles •  Functions
1.  Transport of waste and nutrients
2.  Protects cerebrum from trauma
3.  Contain signaling molecules that direct
development and function
Spinal Cord Anatomy and PNS
Spinal Cord – General Info
•  Structure: extends from foramen magnum of skull to
the first two lumbar vertebra
Spinal Cord Anatomy Spinal Cord Anatomy •  Internal gray matter – mostly cell bodies; surrounds
central canal
o  Central canal is filled with cerebrospinal fluid
•  Exterior white matter - axons
Spinal Cord Anatomy Peripheral Nervous System (PNS)
•  Definition: nerves and ganglia outside the central
nervous system
•  Ganglia: mass of nerve cell bodies
•  Nerve: bundle of neuron fibers
PNS: Classification of Nerves •  Mixed nerves: both sensory and motor fibers
•  Sensory (afferent) nerves: carry impulses toward the
CNS
•  Motor (efferent) nerves: carry impulses away from
the CNS
PNS: Cranial Nerves •  Definition: 12 pairs of nerves that serve the head
and neck
PNS: Cranial Nerves I Olfactory nerve – sensory for smell
II Optic nerve – sensory for vision
III Oculomotor nerve – motor fibers to eye muscles
IV Trochlear – motor fiber to eye muscles
V Trigeminal nerve – sensory for the face; motor
fibers to chewing muscles
•  VI Abducens nerve – motor fibers to eye muscles
•  VII Facial nerve – sensory for taste; motor fibers to
the face
•  VIII Vestibulococlear nerve – sensory for balance
and hearing
• 
• 
• 
• 
• 
PNS: Cranial Nerves •  IX Glossopharyngeal nerve – sensory for taste; motor
fibers to the pharynx
•  X Vagus nerves – sensory and motor fibers for
pharynx, larynx, and viscera
•  XI Accessory nerve – motor fibers to neck and upper
back
•  XII Hypoglossal nerve – motor fibers to tongue
Spinal Nerves •  Structure: formed by the combination of the ventral
and dorsal roots of the spinal cord
o  31 pairs of spinal nerves arise from the spinal cord
•  Cauda equina: collection of spinal nerves at the
inferior end
Autonomic Nervous System
•  Definition: involuntary nervous system
•  Function: regulates activities of cardiac and smooth
muscles and glands
•  Two subdivisions
o  Sympathetic divisions
o  Parasympathetic division
Sympathetic Division (E)
•  Sympathetic Function – “fight or flight”
o  Response to unusual stimulus
o  Takes over to increase activities
o  Remember the “E” division: Exercise, excitement,
emergency, and embarrassment
•  Neurotransmitters
o  Norepinephrine
o  Epinephrine
Parasympathetic Division (D)
•  Parasympathetic function – “housekeeping”
activities
o  Conserves energy
o  Maintains daily necessary body functions
o  Remember as the “D” division: digestion,
defecation, and diuresis
•  Neurotransmitter
o  Acetylcholine
Difference between Somatic and Autonomic Nervous System •  Nerves
o  Somatic: one motor neuron
o  Autonomic: preganglionic and postganglionic nerves
•  Effector organs
o  Somatic: skeletal muscle
o  Autonomic: smooth muscle, cardiac muscle, and glands
•  Neurotransmitters
o  Somatic: acetylcholine
o  Autonomic: acetylcholine, epinephrine, or norepinephrine
Review video (show on review day!!)
•  https://www.youtube.com/watch?v=UabDiuTtU0M