Download Ch 48 49 Notes - Dublin City Schools

Fig. 48-1
Chapter 48/49: Nervous
Systems; Neurons,
Synapses, and Signaling
Conus geographus-The cone snail kills prey with
venom that disables neurons
An Overview of Animal Nervous System
• 49.1 Nervous systems process information in
three stages: sensory input, integration, and
motor output
• Neurons are nerve cells that transfer
information within the body
– use two types of signals to communicate:
electrical signals (long-distance) and
chemical signals (short-distance)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 49-2
A nerve net is a series of interconnected nerve cells
More complex animals have nerves
Eyespot
Brain
Radial
nerve
Nerve
cords
Nerve
ring
Transverse
nerve
Nerve net
Brain
Ventral
nerve
cord
Segmental
ganglia
(a) Hydra (cnidarian)
(b) Sea star (echinoderm)
(c) Planarian (flatworm)
(d) Leech (annelid)
Brain
Brain
Ventral
nerve cord
Anterior
nerve ring
Ganglia
Brain
Longitudinal
nerve cords
Ganglia
(f) Chiton (mollusc)
(g) Squid (mollusc)
Spinal
cord
(dorsal
nerve
cord)
Sensory
ganglia
Segmental
ganglia
(e) Insect (arthropod)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
(h) Salamander (vertebrate)
• Bilaterally symmetrical animals exhibit
cephalization
• Cephalization is the clustering of sensory
organs at the front end of the body
• Relatively simple cephalized animals, such as
flatworms, have a central nervous system
(CNS)
• The CNS consists of a brain and longitudinal
nerve cords
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Organization of the Nervous System
• Many animals have a complex nervous system
which consists of two main divisions:
– A central nervous system (CNS) where
integration takes place
• this includes the brain and a nerve cord
– A peripheral nervous system (PNS),
• Made mostly of nerves which brings information into
and out of the CNS
• A nerve is a communication line made from cable like
bundles of neuron fibers
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 49-4
Central nervous
system (CNS)
Brain
Spinal
cord
Peripheral nervous
system (PNS)
Cranial
nerves
Ganglia
outside
CNS
Spinal
nerves
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Peripheral Nervous System
• The PNS transmits information to and from the
CNS and regulates movement and the internal
environment
• In the PNS, afferent neurons transmit
information to the CNS and efferent neurons
transmit information away from the CNS
• Cranial nerves originate in the brain and
mostly terminate 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 49-7-2
PNS
Afferent
(sensory) neurons
Efferent
neurons
Autonomic
nervous system
Motor
system
Locomotion
Sympathetic
division
Parasympathetic
division
Hormone
Gas exchange Circulation action
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Hearing
Enteric
division
Digestion
• The PNS has two functional components: the
motor system and the autonomic nervous
system
• The motor system carries signals to skeletal
muscles and is voluntary
• The autonomic nervous system regulates the
internal environment in an involuntary manner
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• The sympathetic division correlates with the
“fight-or-flight” response
• The parasympathetic division promotes a
return to “rest and digest”
• The enteric division controls activity of the
digestive tract, pancreas, and gallbladder
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 49-8
Sympathetic division
Parasympathetic division
Action on target organs:
Action on target organs:
Constricts pupil
of eye
Dilates pupil
of eye
Stimulates salivary
gland secretion
Inhibits salivary
gland secretion
Constricts
bronchi in lungs
Cervical
Sympathetic
ganglia
Relaxes bronchi
in lungs
Slows heart
Accelerates heart
Stimulates activity
of stomach and
intestines
Inhibits activity
of stomach and
intestines
Thoracic
Stimulates activity
of pancreas
Inhibits activity
of pancreas
Stimulates
gallbladder
Stimulates glucose
release from liver;
inhibits gallbladder
Lumbar
Stimulates
adrenal medulla
Promotes emptying
of bladder
Promotes erection
of genitals
Inhibits emptying
of bladder
Sacral
Synapse
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Promotes ejaculation and
vaginal contractions
Concept 49.2: The vertebrate brain is regionally
specialized
• All vertebrate brains develop from three
embryonic regions: forebrain, midbrain, and
hindbrain
• By the fifth week of human embryonic
development, five brain regions have formed
from the three embryonic regions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 49-9
Cerebrum (includes cerebral cortex, white matter,
basal nuclei)
Telencephalon
Forebrain
Diencephalon
Midbrain
Diencephalon (thalamus, hypothalamus, epithalamus)
Mesencephalon
Midbrain (part of brainstem)
Metencephalon
Pons (part of brainstem), cerebellum
Myelencephalon
Medulla oblongata (part of brainstem)
Hindbrain
Diencephalon:
Cerebrum
Mesencephalon
Hypothalamus
Metencephalon
Thalamus
Midbrain
Hindbrain
Forebrain
Diencephalon
Pineal gland
(part of epithalamus)
Myelencephalon
Spinal cord
Telencephalon
Brainstem:
Midbrain
Pons
Pituitary
gland
Medulla
oblongata
Spinal cord
Cerebellum
Central canal
(a) Embryo at 1 month
(b) Embryo at 5 weeks
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
(c) Adult
Fig. 49-UN4
•The cerebrum has right and left
cerebral hemispheres
•Each cerebral hemisphere
consists of a cerebral cortex
(gray matter) overlying white
matter and basal nuclei
•In humans, the cerebral cortex
is the largest and most complex
part of the brain
•The basal nuclei are important
centers for planning and
learning movement sequences
Fig. 49-5
Gray matter
White
matter
Ventricles
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• The central canal of the spinal cord and the ventricles
of the brain are hollow and filled with cerebrospinal
fluid
• The cerebrospinal fluid is filtered from blood and
functions to cushion the brain and spinal cord
• The brain and spinal cord contain
– Gray matter, which consists of neuron cell bodies,
dendrites, and unmyelinated axons
– White matter, which consists of bundles of
myelinated axons
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 49-UN1
The brainstem
coordinates and
conducts information
between brain
centers
The brainstem has three
parts: the midbrain, the
pons, and the medulla
oblongata
• The midbrain contains centers for receipt and
integration of sensory information
• The pons regulates breathing centers in the
medulla
• The medulla oblongata contains centers that
control several functions including breathing,
cardiovascular activity, swallowing, vomiting,
and digestion
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 49-UN2
The cerebellum is important for
coordination and error checking during
motor, perceptual, and cognitive
functions
It is also involved in learning and
remembering motor skills
Fig. 49-UN3
The thalamus is the
main input center for
sensory information
to the cerebrum and
the main output
center for motor
information leaving
the cerebrum
The hypothalamus
regulates homeostasis
and basic survival
behaviors such as
feeding, fighting, fleeing,
and reproducing
Fig. 49-13
Left cerebral
hemisphere
Right cerebral
hemisphere
Corpus
callosum
Thalamus
Cerebral
cortex
Basal
nuclei
•A thick band of axons called the corpus callosum provides
communication between the right and left cerebral cortices
•The right half of the cerebral cortex controls the left side of the
body, and vice versa
Fig. 49-15
Frontal lobe
Parietal lobe
Speech
Frontal
association
area
Somatosensory
association
area
Taste
Reading
Speech
Hearing
Smell
Auditory
association
area
Visual
association
area
Vision
Temporal lobe
Occipital lobe
Practice Parts
Fig. 49-UN1
Fig. 49-UN2
Fig. 49-UN4
Fig. 48-2
Nerves
with giant axons
Ganglia
Brain
The squid possesses extremely large
nerve cells and is a good model for
studying neuron function
Arm
Eye
Mantle
Nerve
Ch. 48 Neuron,
Synapses, Signaling
48.1 Three interconnected functions of the nervous
system are carried out by three types of neurons
1. Sensory neurons
• Convey sensory input.
2. Interneurons
• Perform integration, the interpretation of the
sensory signals.
3. Motor neurons
• Carry out motor input
Effector cells: perform the body’s response to motor
output
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-5
Dendrites
Axon
Cell
body
Portion
of axon
Sensory neuron
Interneurons
Cell bodies of
overlapping neurons
80 µm
Motor neuron
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Figure 27.2 part 1
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Figure 27.2 part 2
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Figure 27.2 part 3
Examples…
• The spinal cord conveys information from the
brain to the PNS
• The spinal cord also produces reflexes
independently of the brain
• A reflex is the body’s automatic response to a
stimulus
– For example, a doctor uses a mallet to trigger
a knee-jerk reflex
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 49-3
Quadriceps
muscle
Cell body of
sensory neuron in
dorsal root
ganglion
Gray
matter
White
matter
Hamstring
muscle
Spinal cord
(cross section)
Sensory neuron
Motor neuron
Interneuron
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Neuron Structure and Function
• Functional unit of nervous system
• Vary widely in shape but share common
features
1. Most of a neuron’s organelles are in the cell
body
–
Most neurons have dendrites, highly branched extensions
that receive signals from other neurons
–
The axon is typically a much longer extension that
transmits signals to other cells at synapses
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-4
Dendrites
Stimulus
Nucleus
Cell
body
Axon
hillock
Presynaptic
cell
Axon
Synapse
•A synapse is a junction between an
axon and another cell
•The synaptic terminal of one axon
passes information across the
synapse in the form of chemical
messengers called
neurotransmitters
Information is transmitted from a
presynaptic cell (a neuron) to a
postsynaptic cell (a neuron, muscle,
or gland cell)
Synaptic terminals
Postsynaptic cell
Neurotransmitter
Supporting cells…
• Most neurons are protected, nourished, or
insulated by cells called glia
– Outnumber neurons by as many as 50 to 1
• Glia have numerous functions
– Ependymal cells promote circulation of cerebrospinal
fluid
– Microglia protect the nervous system from
microorganisms
– Oligodendrocytes and Schwann cells form the myelin
sheaths around axons
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 49-6a
CNS
VENTRICLE
PNS
Neuron
Ependymal
cell
Astrocyte
Oligodendrocyte
Schwann cells
Microglial
cell
Capillary
(a) Glia in vertebrates
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
48.2 Sending a Signal through a Neuron
A resting neuron contains potential energy that
resides in an electrical charge difference
across its plasma membrane.
• The voltage (difference in electrical charge)
across its plasma membrane called a
membrane potential
• A neuron that is not sending signals is said to
have a resting potential (usually between -60
and -80 mV)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Formation of the Resting Potential
• In a mammalian neuron at resting potential, the
concentration of K+ is greater inside the cell,
while the concentration of Na+ is greater
outside the cell
• Sodium-potassium pumps use the energy of
ATP to maintain these K+ and Na+ gradients
across the plasma membrane
• These concentration gradients represent
chemical potential energy
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-6b
Key
Na+
K+
OUTSIDE
CELL
INSIDE
CELL
(b)
Sodiumpotassium
pump
Potassium
channel
Sodium
channel
• The opening of ion channels in the plasma
membrane converts chemical potential to
electrical potential
• A neuron at resting potential contains many
open K+ channels and fewer open Na+
channels; K+ diffuses out of the cell
• Anions trapped inside the cell contribute to the
negative charge within the neuron
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• In a resting neuron, the
currents of K+ and Na+
are equal and opposite,
and the resting
potential across the
membrane remains
steady (at equilibrium)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
48.3 Action potentials
• A stimulus is any factor that causes a nerve
signal to be generated
• Action potential is the technical name for a
nerve signal.
–
A strong stimulus results in a massive change in membrane
voltage
–
An action potential occurs if a stimulus causes the
membrane voltage to cross a particular threshold
– Action potentials are signals that carry information
along axons
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Propagation of Action Potential
• An action potential is a localized electrical
event.
• To function as a nerve signal, this event must
be passed along the neuron.
• Action potential propagation is like a “domino
effect” along a neuron.
• They are all-or-none events; that is they are the
same no matter how strong or weak the
stimulus that triggers them.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-10-1
Key
An action potential
can be broken
down into a series
of stages:
Na+
K+
Membrane potential
(mV)
+50
Action
potential
–50
Plasma
membrane
Cytosol
Inactivation loop
1
Resting state
2
–100
Sodium
channel
4
Threshold
1
5
Resting potential
Depolarization
Extracellular fluid
3
0
Time
Potassium
channel
1
• At resting potential
1. Most voltage-gated Na+ and K+ channels are
closed, but some K+ channels (not voltagegated) are open
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-10-2
Key
Na+
K+
Membrane potential
(mV)
+50
Action
potential
–50
2
Plasma
membrane
Cytosol
Inactivation loop
1
Resting state
2
–100
Sodium
channel
4
Threshold
1
5
Resting potential
Depolarization
Extracellular fluid
3
0
Time
Potassium
channel
1
2. A stimulus opens ion channels. Voltage-gated
Na+ channels open first and Na+ flows into
the cell. Additional channels open; in that
region of the neuron, interior become more
positive than outside.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-10-3
Key
Na+
K+
3
Rising phase of the action potential
Membrane potential
(mV)
+50
Action
potential
–50
2
Plasma
membrane
Cytosol
Inactivation loop
1
Resting state
2
–100
Sodium
channel
4
Threshold
1
5
Resting potential
Depolarization
Extracellular fluid
3
0
Time
Potassium
channel
1
3. During the rising phase the membrane potential
increases (more and more positive), the
threshold is crossed, and, thus the action
potential is triggered.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-10-4
Key
Na+
K+
3
4
Rising phase of the action potential
Membrane potential
(mV)
+50
Action
potential
–50
2
Plasma
membrane
Cytosol
Inactivation loop
1
Resting state
2
–100
Sodium
channel
4
Threshold
1
5
Resting potential
Depolarization
Extracellular fluid
3
0
Time
Potassium
channel
1
Falling phase of the action potential
4. During the falling phase, voltage-gated Na+
channels become inactivated; voltage-gated K+
channels open, and K+ flows out of the cell
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-10-5
Key
Na+
K+
3
4
Rising phase of the action potential
Falling phase of the action potential
Membrane potential
(mV)
+50
Action
potential
–50
2
2
4
Threshold
1
1
5
Resting potential
Depolarization
Extracellular fluid
3
0
–100
Sodium
channel
Time
Potassium
channel
Plasma
membrane
Cytosol
Inactivation loop
5
1
Resting state
Undershoot
5. During the undershoot, membrane permeability
to K+ is at first higher than at rest, then voltagegated K+ channels close; resting potential is
restored
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• During the refractory period after an action
potential, a second action potential cannot be
initiated
• The refractory period is a result of a temporary
inactivation of the Na+ channels
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Conduction of Action Potentials
• An action potential can travel long distances by
regenerating itself along the axon
• Inactivated Na+ channels behind the zone of
depolarization prevent the action potential from
traveling backwards
• Action potentials travel in only one
direction: toward the synaptic terminals
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-11-3
Axon
Plasma
membrane
Action
potential
Cytosol
Na+
K+
Action
potential
Na+
K+
K+
Action
potential
Na+
K+
Conduction Speed
• The speed of an action potential increases with
the axon’s diameter
• In vertebrates, axons are insulated by a myelin
sheath, which causes an action potential’s
speed to increase
• Myelin sheaths are made by glia—
oligodendrocytes in the CNS and Schwann
cells in the PNS
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-12
Node of Ranvier
Layers of myelin
Axon
Schwann
cell
Axon
Nodes of
Myelin sheath Ranvier
Schwann
cell
Nucleus of
Schwann cell
0.1 µm
• Action potentials are formed only at nodes of
Ranvier, gaps in the myelin sheath where
voltage-gated Na+ channels are found
• Action potentials in myelinated axons jump
between the nodes of Ranvier in a process
called saltatory conduction
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-13
Schwann cell
Depolarized region
(node of Ranvier)
Cell body
Myelin
sheath
Axon
48.4 Passing a Signal from a Neuron to a Receiving
Cell
• At electrical synapses, the electrical current
flows from one neuron to another
• At chemical synapses, a chemical
neurotransmitter carries information across the
gap junction
• Most synapses are chemical synapses
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Generation of Postsynaptic Potentials
1/2. Action potential depolarizes membrane of synaptic
terminal and opens voltage-gated Ca2+ channels influx
of Ca2+
3. Increased Ca2+ causes synaptic vesicles (with
neurotransmitter) to fuse with presynaptic membrane
4. The neurotransmitter diffuses across the synaptic cleft
and is received by the postsynaptic cell
5. Neurotransmitter initiates a response from postsynaptic
cell
6. Neurotransmitter diffuses out of cleft, taken up by
surrounding cells or is degraded by an enzyme.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-15
5
Synaptic vesicles
containing
neurotransmitter
Voltage-gated
Ca2+ channel
Postsynaptic
membrane
1 Ca2+
4
2
Synaptic
cleft
Presynaptic
membrane
3
Ligand-gated
ion channels
6
K+
Na+
• The same neurotransmitter can produce
different effects in different types of cells
• Postsynaptic potentials fall into two categories:
– Excitatory postsynaptic potentials (EPSPs)
are depolarizations that bring the membrane
potential toward threshold
– Inhibitory postsynaptic potentials (IPSPs)
are hyperpolarizations that move the
membrane potential farther from threshold
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Neurotransmitters
• Common neurotransmitters:
–
Acetylcholine: In vertebrates it is usually an excitatory
transmitter (but can also be inhibitory)
–
Epinephrine and norepinephrine
–
Dopamine and serotonin affect mood, learning, sleep and
attention
–
Endorphins affect our perception of pain (produced during
physical or emotional stress)
• Opiates bind to the same receptors as endorphins and
can be used as painkillers
• Other drugs that act at synapses: caffeine, nicotine, alcohol, Rx
drugs, cocaine, LSD, and marijuana.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Marijuana's Influence at Synapse
• THC (delta-9-tetrahydrocannabinol) acts upon specific sites in
the brain, called cannabinoid receptors, kicking off a series of
cellular reactions that ultimately lead to the “high” that users
experience when they smoke marijuana.
• Some brain areas have many cannabinoid receptors; others
have few or none. The highest density of cannabinoid receptors
are found in parts of the brain that influence pleasure, memory,
thoughts, concentration, sensory and time perception, and
coordinated movement.
• http://learn.genetics.utah.edu/content/addiction/drugs/mouse.ht
ml
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings