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Sylvia S. Mader
Immagini e
concetti
della biologia
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
C2 - Nervous
system
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
The response to stimuli
The vertebrate nervous
organization is
characterized by
cephalization, bilateral
symmetry, spinal cord and
an increased number of
neurons.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
The response to stimuli
A neural tube in the embryo is the precursor to the
central nervous system (CNS).
During the embryonic development, the neural tube
differentiates into three regions: hindbrain, midbrain and
forebrain.
hindbrain
midbrain
forebrain
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
CNS
PNS
CNS and PNS
Central nervous system
Comprises the brain and
spinal cord.
Peripheral nervous system
Consists of nerves and
ganglia (neurons organized
into clusters) outside the CNS.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Nervous system organization
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Neuroglia (or glial cells)
Microglia destroy pathogens and
remove dead cells.
Astrocytes supply nutrients.
Oligodendrocytes produce myelin
and insulate axons in the CNS.
node of
Ranvier
Schwann
cells
Schwann cells insulate axons in
the PNS with a myelin sheath.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Neurons are the functional units
Sensory neurons (afferent) transport the input from
receptors to the CNS.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Neurons are the functional units
Motor neurons (efferent) carry commands to effectors
(glands or muscles).
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Neurons are the functional units
Interneurons in the CNS, store information and help with
communication in the system and within motor and
sensor neurons.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Inactive neurons have a resting
potential
In resting potential the
axon is not conducting the
impulse.
Inside, the cell is negative
at rest.
The potential depends on
the concentration of ions
(Na+ and K+) in and out the
membrane.
[ Na+]out > [ Na+]in
[ K+]in > [ K+]out
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
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Active neurons have an action
potential
An action potential is a rapid change in the membrane
axon polarity as the impulse occurs.
Voltage causes Na+ and K+ ions to move across cell
membranes.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Active neurons have an action
potential
An action potential allows Na+ ions to flow in, thus inside
the cell becomes more positive (depolarization).
The action potential ends, K+ channels open and the
equilibrium is reestablished (polarization).
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Propagation of action potential
Ions channels are concentrated at the nodes of Ranvier,
so action potential jumps from one node to the other and
travels faster in a saltatory conduction.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Synapses
Neurons communicate with other neurons at synapses,
regions of close proximity between an axon terminal and
a dendrite.
Neurotransmitters are chemicals that transmit signals
across a synapse.
When a neurotransmitter is released into a synaptic
cleft, transmission of a nerve impulse occurs.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Synapses
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Neurotransmitters
Binding of neurotransmitters to a receptor can cause
either stimulation or inhibition.
Neurotransmitter Actions
Notes
Acetylcholine
Is involved in the Alzheimer’s disease.
Neurotransmitter skeletal
muscles and CNS
Norepinephrine in CNS and PNS, generally
stimulates smooth muscles
Involved in the response to stress and
sugar consumption.
Dopamine
Neurotransmitter of the CNS
Involved in emotions and
schizophrenia (Parkinson’s disease).
Serotonin
Neurotransmitter of the CNS
Involved in pain control, sleep/wake
control and mood.
GABA
Inhibitory neurotransmitter of Valium® amplifies the effects of the
the CNS
GABA.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Neurotransmitters
Neurons integrate (sum) signals.
1. Inhibitory Signals: the threshold is not reached and the
neuron is inactive
2. Excitatory signals: the neuron is activated
3. The Integrated signal is below the threshold and the
impulse is not transmitted
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Some substances interfere
with neurotransmitter dynamics
Drugs (depressant or stimulant), alcohol (depressant),
nicotine (stimulant) and marijuana (creates euphoria)
affect the release of neurotransmitters and modify the
transmission of the nerve impulse.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
CNS
The CNS is composed by the brain and the spinal
cord and is organized in neuronal nets.
Brain and spinal cord function in strict connection and
are protected by different structures:
Brain
Skull, meninges,
cerebrospinal fluid
Spinal cord
Vertebral column
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
CNS: the spinal cord
The spinal cord contains tracts that take the messages
from and to the brain.
The inner region of the spinal cord is the gray matter.
The peripheral region is the white matter.
vertebra
spinal cord
white matter
gray matter
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
CNS: the ventricular system
The brain contains a set of structures producing
cerebrospinal fluid for mechanical protection.
The system is composed of four ventricles:
• right and left lateral ventricles (in the cerebrum)
• third ventricle
• fourth ventricle
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
CNS: the cerebrum
The cerebrum has two lateral cerebral hemispheres
controlling the opposite side of the body connected by the
corpus callosum. Each cerebral hemisphere has four lobes:
frontal, parietal, occipital and temporal.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
CNS: the cerebrum
A layer of neural tissue called the cerebral cortex overlays
the cerebrum and is divided into two areas.
The primary motor area sends voluntary motor
commands to skeletal muscles.
The primary somatosensory area receives sensory
information from the skin and the skeletal muscles.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
CNS: other parts of the brain
The diencephalon is composed by the hypothalamus,
which controls homeostasis, and the thalamus which
sends sensory inputs to the cerebrum.
The cerebellum receives signals from eyes, ears and
muscles and coordinates skeletal muscle contractions.
The impulses to the motor and sensory systems pass
through the brain stem, which contains the centers for
regulating breathing, heartbeat and blood pressure.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
CNS: the limbic system
The limbic system is involved in memory, emotions and
learning.
Hippocampus is involved in storing and retrieving
memories, while the amygdala has a role in emotional
reactions.
The limbic system in purple
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
PNS
Is composed by
NERVES
Bundles of
axons
GANGLIA
Containing the
neuron body cell
Cranial nerves: connect with the brain.
Spinal nerves: connect with the spinal cord.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
PNS - the somatic system
1. Brings sensory information from receptors (skin, joints,
skeletal muscles) to the CNS
2. Transports commands from CNS to skeletal muscles
Responsible for voluntary control of body movements,
with the exception of reflexes (automatic and involuntary).
Reflex arch
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
PNS - the autonomic system
Controls the involuntary visceral functions and
movements (glands, cardiac muscle, smooth muscles).
Parasympathetic
responses during relaxation
and digestion ("rest and
digest")
Sympathetic
responses during times of
stress ("fight or flight")
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012