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Chapter 34
Neural Control- A Summary
AP Biology
Spring 2011
Nervous System
Nervous System
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Sensory Neurons: detect information about stimuli,
such as light
Interneurons: accept the senosory input, process it, and
signal other neurons
Motor Neurons: relay new signals to effectors- muscles
and glands- that carry out
responses
Neuroglia: structurally
and metabolically support
the neurons
Stimulus
Receptors
(sensory neurons)
Integrators
(interneurons)
Motor Neurons
Effectors
(muscles, glands)
Response
Invertebrate Nervous System
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Cnidarians: jellyfish, radial body plan
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Two epithelial tissues: an epidermis and gastrodermis
Nerve net: asymmetrical mesh of neurons, controls simple
movement of both
Motor neurons activate epithelial cells that have long
contractile extensions, by making them contract the nerve net
changes diameter of mouth or body or bends tentacles
Invertebrate Nervous System
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Bilateral animals
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Ex. Flatworm
Bilateral nervous system: have nerves, branching
nerves join two nerve cords in a ladder-like array
Invertebrate Nervous System
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Ganglion: cluster of nerve cell bodies that function as a
local integrating center
Cephalization: formation of a head evolved with
bilateral nervous systems
Ganglion
Ganglion
Vertebrate Nervous System
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Two functional divisions:
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Central Nervous System (CNS): brain and spinal cord
Peripheral Nervous System (PNS): nerves extending
through the rest of the body
Invertebrate Nervous System
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Afferent: deliver signals into the central system
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PNS
Efferent: carry signals out of it
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Motor fibers
Outline of Peripheral Nervous System
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Somatic System: controls the voluntary muscles
Autonomic System: controls involuntary muscles
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Sympathetic: fight or flight response, increase heart and
breathing rate, liver converts glycogen to glucose, bronchi of
lungs dilate and increase gas exchange, adrenaline raises blood
glucose levels
Parasympathetic: opposes sympathetic system, calms body,
decreases heart/breathing rate, enhances digestion
Neurons
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Sensory Neuron: detects a stimulus at one or more
receptor endings and relays information about it to other
neurons
Motor Neuron: delivers excitatory or inhibitory
commands from other neurons to muscles or glands
Interneurons: information
from most sensory neurons
flows through these before
it gets to motor neurons
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Receive, process, and store
sensory information
The Neuron
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Basic functional unit of the nervous system
Cell body: contains nucleus and other organelles
Dendrites: sensory; receive incoming messages from
other cells and carry electrical signals to the cell body
Axons: transmit an impulse from the cell body outward
to another cell
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Has only one axon, most
wrapped in myelin sheet
that protects it and
speeds the impulse
Membrane Gradients and Potentials
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Membrane potential: difference in electrical charge
between the cytoplasm (negative charge) and
extracellular fluid (positive)
Membrane Gradients and Potentials
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Resting Membrane Potential: the steady voltage
difference across the neuron’s plasma membrane
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Is about -70 millivolts
Negative sign indicates that the inside of the cell is negative
relative to the outside of the cell
Membrane Gradients and Potentials
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Action Potential: an
impulse generated in the
axon of a neuron
When stimulated to
overcome threshold
permeability of a region
of the membrane
changes
Sodium-Potassium Pump
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When neuron at rest
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About 15 sodium ions in the fluid inside of plasma membrane
for every 150 outside
About 150 potassium ions inside for every 5 outside
Creates ion gradients
Sodium-Potassium Pump
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Threshold overcome by axon stimulation
Sodium channels open and sodium floods into the cell,
down concentration gradient
Potassium channels open and potassium floods out of the
cell
Wave of depolarization: rapid movement of ions,
reverses polarity of membrane (action potential)
Sodium-Potassium Pump
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Pump restores membrane to original state by pumping
sodium and potassium ions back to original positions
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Repolarization
Refractory period: neuron cannot respond to another
stimuli (ensures impulse moves along axon in only one
direction)
Sodium-Potassium Pump
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Action potential is like dominos
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First action potential generates a second which generates a
third
Impulse moves along axon, without losing strength, if axon
myelinated can travel faster
Sodium-Potassium Pump
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Action potential is all-or-non event
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Either stimulus is strong enough or isn’t
Strong stimulus sets up more action potential than a weak one
does
The Synapse
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Thin cleft separates output zone of one neuron from a
neighboring neuron, gland cell, or muscle cell
At this zone, electrochemical energy of action potential is
transduced to the form of chemical signal that can diffuse
across the cleft and activate or inhibit target cell
Chemical synapse: functional bridge between a neuron
and some other cell
Synapse means to fasten together
The Synapse
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Neurotransmitter: type of signaling molecule that is
synthesized in neurons only
Plasma membrane has many gated channels for calcium
ions
In between action potentials, more calcium ions outside
than inside (gate are shut)
The Synapse
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Action potential makes gates open- calcium ions flow in,
synaptic vesicles move through cytoplasm in the axon
ending and fuse with the membrane
Release neurotransmitter by exocytosis into the synapse,
which sets up another potential on adjacent cell
Shortly after neurotransmitter released, is destroyed by
an enzyme which stops the impulse at that point
The Synapse
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Most common neurotransmitters:
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Acetylcholine: can be inhibitory or excitatory
Serotonin
Epinephrine
Norepinephrine
Dopamine
GABA
Synaptic Integration
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Excitatory Postsynaptic Potential (EPSP): is the
electrical charge caused by the binding of the
neurotransmitter to its receptor on the postsynaptic
membrane
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Has depolarization effect, drive membrane closer to threshold
Inhibitory Postsynaptic Potential (IPSP): is the
voltage charge associated with chemical signaling at an
inhibitory synapse
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Hyperpolarizing effect, can help drive membrane farther from
threshold or help maintain it at resting level
Synaptic Integration
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Synaptic Integration: postsynaptic neuron sums all
signals that are arriving at its input zone on more than
one communication line
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Two or more incoming signals may be dampened, suppressed,
reinforced, or sent on to other cells
Types of Neurotransmitters
Neurotransmitter Functions
Acetylcholine
In skeletal muscles can stimulate contraction; in heart muscles it
slows contraction.
Norepinephrine,
epinephrine
(adrenaline),
dopamine
Made from tyrosine (A.A), prime body to respond to stress.
Dopamine affects fine motor control and pleasure seeking
behaviors (destruction of them causes Parkinson’s).
Serotonin
Derived from tryptophan (A.A), affects mood and memory, low
levels associated with depression.
GABA (gamma
amino butyric acid)
Derived from glutamate (A.A), in the brain it is the major
inhibitor of neurotransmitter release by other neurons.
Neuropeptides
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Neuropeptides: larger than neurotransmitters
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Act as neuromodulators: magnify or reduce the effects of
neurotransmitter on neurons that are either close to the
secreting cell or some distance away
Examples:
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Substance P: enhances pain perception
Enkephalins and endorphins: natural painkillers and
resemble morphine in their structure, inhibit substance P,
secreted in response to strenuous activity or injuries, can
elevate mood and enhance function of immune cells
Endorphins released when people laugh, acupuncture,
massage
The Reflex Arc
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Simplest nerve response
Inborn, automatic, and protective
Ex. Knee jerk reflex
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Consists of only a sensory and a motor neuron
Impulse moves from sensory
neuron in your knee to the
motor neuron that directs
the thigh muscle to contract
Spinal cord not involved
The Reflex Arc
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More complex reflex arc: 3 neurons- a
sensory, a motor, and an
interneuron or association neuron
Sensory neuron transmits an impulse to
the interneuron in the spinal cord which
sends one impulse to the brain for
processing and also one to the motor
neuron to effect change immediately (at
the muscle)
This is the response that quickly jerks
your hand away from a hot iron before
your brain has figured out what has
occurred
The Vertebrate Brain
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Brain is divided into
Forebrain
specialized regions:
forebrain, midbrain,
hindbrain
Midbrain
Brain stem: most
ancient nervous tissue,
persists in all three
regions and is continuous
Hindbrain
with spinal cord
The Vertebrate Brain
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Hindbrain:
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Medulla oblongata: houses reflex centers for respiration,
circulation, and other essential tasks , governs some reflexes
(coughing), affects sleep
Cerebellum: uses inputs from eyes, ears, muscle spindles, and
forebrain regions to help control motor skills and posture
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Axons from its two halves reach the pons (bridge), control signal flow
between the cerebellum and integrating centers in forebrain
The Vertebrate Brain
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Midbrain:
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Has centers for visual input
Forebrain has took over task integrating most visual stimuli
The Vertebrate Brain
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Forebrain:
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Cerebrum: two cerebral hemispheres
Thalamus: sorting out sensory input and relaying it to the
cerebrum
Hypothalamus: main center for homeostatic control of the
internal environment; assesses and regulates all behaviors
related to internal organ activities, such as thirst, sex, and
hunger; governs related emotions, such as sweating with
passion and vomiting with fear
The Vertebrate Brain
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Cerebrospinal fluid: forms inside brain ventricles, seeps
out and bathes tissues of brain and spinal cord; cushions
them against potentially jarring movements
Blood-brain barrier: protects spinal cord and brain
from harmful substances
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Exerts some control over which solutes enter cerebrospinal
fluid
The Human Cerebrum
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Each half of cerebrum (cerebral hemisphere) is divided
into 4 lobes
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Frontal, temporal, occipital, parietal
The Human Cerebrum
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Grey Matter: areas of neuron cell
bodies, dendrites, and unmyelinated
axons, plus neoroglia, in brain and
spinal cord
White Matter: consists mostly of
myelinated axons
Cerebral Cortex: grey matter at
surface of each lobe, distinct areas
receive and process different signals, still interact
Two hemispheres overlap in function
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Left more concerned with analytical skills, math, speech
Right interprets music, judges spatial relations, assesses visual
inputs
The Human Cerebrum
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Motor Areas:
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Body is spatially mapped out in primary motor cortex of each
frontal lobe- controls and coordinates the movements of
skeletal muscles on opposite side of the body
Premotor cortex of each frontal lobe governs leaned patterns
of motor skills
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Ex. Dribble a basketball
Broca’s area helps
translate thoughts into
speech
The Human Cerebrum
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Sensory Areas:
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Primary somatosensory cortex is located at front of parietal
lobe
Organized as a map corresponding to body’s parts
Receiving center for sensory input from skin and joints
Taste perception
At back of occipital lobe,
primary visual cortex
receives signals from eyes
Temporal lobe: perceptions
of sound and odor
The Human Cerebrum
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Association Areas:
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Scattered through cortex, not in primary motor and sensory
areas
Ex.Visual association area around primary visual cortex
compares what we see with visual memories
Prefrontal cortex: foundation of our personality and intellect,
of abstract thought, judgment, planning, and concern for others
Limbic System
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Limbic System: encircles upper brain stem
Governs emotions, assists in memory, correlates organ
activities with self-gratifying behavior
Includes hypothalamus, part of thalamus, and cingulate
gyrus, hippocampus, and amygdala
Reticular Formation
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Reticular Formation: low level path to motor centers
in medulla oblongata and spinal cord
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Network of interneurons, extends from upper spinal cord,
through brain stem, and into cerebral cortex
Promotes chemical changes that affect states of consciousness,
such as sleeping or waking