Download Chapter 48

Chapter 48: Nervous Systems
1. What are the 3 main fcns of the nervous system?
- Sensory input – stimulus – PNS
- Integration– brain & spinal cord – CNS
- Motor output – response –PNS
Figure 48.3 Overview of information processing by nervous systems
Sensory input
Integration
Sensor
Motor output
Effector
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
Protected by bone
Chapter 48: Nervous Systems
1. What are the 3 main fcns of the nervous system?
- Sensory input – stimulus – PNS
- Integration– brain & spinal cord – CNS
- Motor output – response –PNS
2. How does a reflex work?
Figure 48.4 The knee-jerk reflex
2 Sensors detect
a sudden stretch in
the quadriceps.
3 Sensory neurons
convey the information
to the spinal cord.
Cell body of
sensory neuron
in dorsal
root ganglion
4 The sensory neurons communicate with
motor neurons that supply the quadriceps. The
motor neurons convey signals to the quadriceps,
causing it to contract and jerking the lower leg forward.
Gray matter
5 Sensory neurons
from the quadriceps
also communicate
with interneurons
in the spinal cord.
Quadriceps
muscle
White
matter
Hamstring
muscle
Spinal cord
(cross section)
Sensory neuron
Motor neuron
1 The reflex is
initiated by tapping
the tendon connected
to the quadriceps
(extensor) muscle.
Interneuron
6 The interneurons
inhibit motor neurons
that supply the
hamstring (flexor)
muscle. This inhibition
prevents the hamstring
from contracting,
which would resist
the action of
the quadriceps.
No brain involvement = faster response
Chapter 48: Nervous Systems
1. What are the 3 main fcns of the nervous system?
- Sensory input – stimulus – PNS
- Integration– brain & spinal cord – CNS
- Motor output – response –PNS
2. How does a reflex work?
3. What cells make up the nervous system?
- Neurons – functional unit of the nervous system
- Supporting cells (glia)
- Astrocytes, radial glia, oligodendrocytes, & Schwann cells
- provide nutrition & support
Figure 48.5 Structure of a vertebrate neuron
Dendrites
Cell body
Nucleus
Synapse
Signal
Axon direction
Axon hillock
Presynaptic cell
Postsynaptic cell
Myelin sheath
Cell body – has nucleus
Dendrites – bring signal to cell body
Synaptic
terminals
Axon – takes signal away from cell body
Axon hillock – cell body region where impulse is generated & axon begins
Myelin – sheath that insulates axons made of supporting cells
- PNS – Schwann cells secrete myelin
- CNS – oligodendrocytes secrete myelin
Synapse – junction between neurons or neuron & muscle or gland
Chapter 48: Nervous Systems
1. What are the 3 main fcns of the nervous system?
2. How does a reflex work?
3. What cells make up the nervous system?
- Neurons – functional unit of the nervous system
- Supporting cells (glia)
- Astrocytes
- regulate extracellular concentration of ions & neurotransmitters
- Form tight junctions between cells that line capillaries of brain &
and spinal cord
- Blood-brain barrier – restricts passage of substances into CNS
- Can act as multipotent stem cells
- Radial glia
- Forms tracts for neurons to migrate in formation of neural tube
- Can act as multipotent stem cells
- Oligodendrocytes & Schwann cells
Students
-Test Monday means LL due Monday
-Bozeman – 21, 22, 23, 37, 39, 41, 45
-Crash Course – 21, 26, 32, 33
-Phones in bin…muted or off…please & thank you!,
Figure 48.8 Schwann cells and the myelin sheath
Node of Ranvier
Layers of myelin
Axon
Schwann
cell
Axon
Myelin sheath
Nodes of
Ranvier
Schwann
cell
Nucleus of
Schwann cell
Node of Ranvier – space between Schwann cells on axon
0.1 µm
Chapter 48: Nervous Systems
1.
2.
3.
4.
What are the 3 main fcns of the nervous system?
How does a reflex work?
What cells make up the nervous system?
What is the charge of a neuron?
- -70 mV
- WHY???
Microelectrode
–70 mV
Voltage
recorder
Reference
electrode
Figure 48.10 Ionic gradients across the plasma membrane of a
mammalian neuron
EXTRACELLULAR
FLUID
CYTOSOL
[Na+]
15 mM
–
+
[Na+]
150 mM
[K+]
150 mM
–
+
[K+]
5 mM
–
+
[Cl–]
10 mM
–
[Cl–]
+ 120 mM
[A–]
100 mM
–
+
Plasma
membrane
[A-] – DNA, RNA, proteins
What happens when Na+ comes in & K+ leaves?
Figure 48.11 Modeling a mammalian neuron
–92 mV
Outer
chamber
–
150 mM
KCL
+62 mV
+
5 mM
KCL
150 mM
NaCl
Cl–
+
–
Cl–
+
Artificial
membrane
–
(a) Membrane selectively permeable to K+
Outer
chamber
–
15 mM
NaCl
K+
Potassium
channel
Inner
chamber
+
Inner
chamber
+
–
+
–
Na+
Sodium
channel
(b) Membrane selectively permeable to Na+
As K+ leaves, the cell loses (+) charge As Na+ enters, the cell gains (+) charge
It becomes more (-)
It becomes more (+)
Chapter 48: Nervous Systems
1.
2.
3.
4.
5.
What are the 3 main fcns of the nervous system?
How does a reflex work?
What cells make up the nervous system?
What is the charge of a neuron?
How is neuron polarity altered?
Figure 48.12 Graded potentials and an action potential in a neuron
Stimuli
0
Threshold
0
–50
0 1 2 3 4 5
Time (msec)
(a) Graded hyperpolarizations
produced by two stimuli that
increase membrane permeability
to K+. The larger stimulus produces
a larger hyperpolarization.
Hyperpolarization
K+ channels open
Threshold
Action
potential
0
–50
Resting Depolarizations
potential
Resting
potential Hyperpolarizations
–100
+50
Membrane potential (mV)
+50
Membrane potential (mV)
Membrane potential (mV)
+50
–50
Stronger depolarizing stimulus
Stimuli
–100
Threshold
Resting
potential
–100
0 1 2 3 4 5
Time (msec)
(b) Graded depolarizations produced
by two stimuli that increase
membrane permeability to Na+.
The larger stimulus produces a
larger depolarization.
Slight depolarization
Na+ channels open
NEURONS ARE ALL OR NONE!!
0 1 2 3 4 5 6
Time (msec)
(c) Action potential triggered by a
depolarization that reaches the
threshold.
More depolarization
More Na+ enters
Threshold achieved (-55 mV)
LOTS of Na+ channels open
Chapter 48: Nervous Systems
1.
2.
3.
4.
5.
6.
What are the 3 main fcns of the nervous system?
How does a reflex work?
What cells make up the nervous system?
What is the charge of a neuron?
How is neuron polarity altered?
How is an action potential (nerve impulse) created?
Figure 48.13 The role of voltage-gated ion channels in the generation
of an action potential
Membrane potential
(mV)
+50
3
0
2
–50
–100
Extracellular fluid
Na+
Action
potential
5
1
Activation
gates
Potassium
channel
+ + + + + + + +
+ +
+ +
+ +
– –
– –
– –
1
Resting state
1
Resting potential
Time
Plasma membrane
– – – – – – – –
Cytosol
Sodium
channel
4
Threshold
K+
Inactivation
gate
Undershoot
Figure 48.13 The role of voltage-gated ion channels in the generation
of an action potential
Na+
+ +
+ +
+ +
– –
– –
+ +
– –
– –
K+
Membrane potential
(mV)
+50
Na+
3
0
2
–50
–100
2 Depolarization
Extracellular fluid
Na+
Action
potential
5
1
Resting potential
Time
Activation
gates
Potassium
channel
+ + + + + + + +
+ +
+ +
+ +
Plasma membrane
– – – – – – – –
Cytosol
– –
– –
– –
Sodium
channel
1
Resting state
K+
4
Threshold
Inactivation
gate
1
Figure 48.13 The role of voltage-gated ion channels in the generation
of an action potential
Na+
Na+
– –
– –
– –
– –
+ +
+ +
+ +
+ +
K+
3
Rising phase of the action potential
Na+
+ +
+ +
+ +
– –
– –
+ +
– –
– –
K+
Membrane potential
(mV)
+50
Na+
3
0
2
–50
–100
2 Depolarization
Extracellular fluid
Na+
Action
potential
5
1
Resting potential
Time
Activation
gates
Potassium
channel
+ + + + + + + +
+ +
+ +
+ +
Plasma membrane
– – – – – – – –
Cytosol
– –
– –
– –
Sodium
channel
1
Resting state
K+
4
Threshold
Inactivation
gate
1
Figure 48.13 The role of voltage-gated ion channels in the generation
of an action potential
Na+
Na+
– –
– –
– –
– –
+ +
+ +
+ +
+ +
K+
3
Na+
Na+
+ +
+ +
+ +
+ +
– –
– –
– –
– –
K+
Rising phase of the action potential
4 Falling phase of the action potential
Na+
+ +
+ +
+ +
– –
– –
+ +
– –
– –
K+
Membrane potential
(mV)
+50
Na+
3
0
2
–50
–100
2 Depolarization
Extracellular fluid
Na+
Action
potential
5
1
Resting potential
Time
Activation
gates
Potassium
channel
+ + + + + + + +
+ +
+ +
+ +
Plasma membrane
– – – – – – – –
Cytosol
– –
– –
– –
Sodium
channel
1
Resting state
K+
4
Threshold
Inactivation
gate
1
Figure 48.13 The role of voltage-gated ion channels in the generation
of an action potential
Na+
Na+
– –
– –
– –
– –
+ +
+ +
+ +
+ +
K+
3
Na+
Na+
+ +
+ +
+ +
+ +
– –
– –
– –
– –
K+
Rising phase of the action potential
4 Falling phase of the action potential
Na+
+ +
+ +
+ +
– –
– –
+ +
– –
– –
K+
Membrane potential
(mV)
+50
Na+
3
0
2
–50
–100
2 Depolarization
Action
potential
4
Threshold
5
1
1
Resting potential
Time
Na+
Extracellular fluid
Na+
Activation
gates
Potassium
channel
+ + + + + + + +
+ +
+ +
+ +
Plasma membrane
– – – – – – – –
Cytosol
– –
– –
– –
Sodium
channel
1
Resting state
K+
Inactivation
gate
Na+
+ +
+ +
+ +
+ +
– –
– –
– –
– –
K+
5
Undershoot
Figure 7.16 The sodium-potassium pump: a specific case of active
transport
1 Cytoplasmic Na+ binds to
the sodium-potassium
pump.
EXTRACELLULAR
[Na+] high
FLUID
[K+] low
Na+
2 Na+ binding stimulates
phosphorylation by ATP.
Na+
Na+
Na+
Na+
[Na+] low
Na+
+
CYTOPLASM [K ] high
3 K+ is released and Na+
sites are receptive again;
The cycle repeats.
P
ADP
Na+
ATP
4 Phosphorylation causes the
protein to change its conformation,
expelling Na+ to the outside.
Na+
Na+
K+
P
K+
5 Loss of the phosphate
restores the protein’s
original conformation.
6 Extracellular K+ binds to the
protein, triggering release of the
Phosphate group.
K+
K+
K+
K+
P
Maintains charge of -70 mV.
NOT THE SAME AS A Na+ or K+ channel.
Pi
Chapter 48: Nervous Systems
1.
2.
3.
4.
5.
6.
7.
What are the 3 main fcns of the nervous system?
How does a reflex work?
What cells make up the nervous system?
What is the charge of a neuron?
How is neuron polarity altered?
How is an action potential (nerve impulse) created?
Why does an action potential only travel in 1 direction?
Figure 48.14 Conduction of an action potential
Axon
Action
potential
– –
+
+ ++
–
Na
–
+ +
– –
+
K+
+ +
– –
– –
+ +
K+
+
+
–
–
+
+
+
+
+
–
–
+
–
–
+
–
–
+
–
–
+
–
–
+
Action
potential
– –
+ ++
Na
+ +
– –
K+
+
–
–
+
+ +
– –
– –
+ +
K+
+
–
–
+
+
–
–
+
Action
potential
– –
+ ++
Na
+ +
–
–
+
–
–
+
–
+
+
–
1
An action potential is generated
as Na+ flows inward across the
membrane at one location.
2
The depolarization of the action
potential spreads to the neighboring
region of the membrane, re-initiating
the action potential there. To the left
of this region, the membrane is
repolarizing as K+ flows outward.
3
The depolarization-repolarization process is
repeated in the next region of the
membrane. In this way, local currents
of ions across the plasma membrane
cause the action potential to be propagated
along the length of the axon.
+
–
–
+
–
+
+
–
Domino analogy….
Where does this depolarization & repolarization take place?
Figure 48.15 Saltatory conduction
Schwann cell
Depolarized region
(node of Ranvier)
Myelin
sheath
––
–
Cell body
+
++
+
++
–––
––
–
+
+
Axon
+
++
––
–
Depolarization jumps down the axon from node to node.
Na+ & K+ channels are only found at the node of Ranvier.
Action potentials can travel 120 m/sec
Chapter 48: Nervous Systems
1.
2.
3.
4.
5.
6.
7.
8.
What are the 3 main fcns of the nervous system?
How does a reflex work?
What cells make up the nervous system?
What is the charge of a neuron?
How is neuron polarity altered?
How is an action potential (nerve impulse) created?
Why does an action potential only travel in 1 direction?
How does a neuron communicate with another cell?
- Chemical synapse
- Signal changes from electrical  chemical  electrical
Figure 48.17 A chemical synapse
Postsynaptic cell
Presynaptic
cell
Synaptic vesicles
containing
neurotransmitter
5
Presynaptic
membrane
Neurotransmitter
Postsynaptic
membrane
Ligandgated
ion channel
Voltage-gated
Ca2+ channel
1 Ca2+
4
2
Synaptic cleft
Na+
K+
3
Ligand-gated
ion channels
Postsynaptic
membrane
6
Chapter 48: Nervous Systems
1.
2.
3.
4.
5.
6.
7.
8.
9.
What are the 3 main fcns of the nervous system?
How does a reflex work?
What cells make up the nervous system?
What is the charge of a neuron?
How is neuron polarity altered?
How is an action potential (nerve impulse) created?
Why does an action potential only travel in 1 direction?
How does a neuron communicate with another cell?
How does a single neuron interpret multiple inputs?
Figure 48.18 Summation of postsynaptic potentials
Terminal branch of
presynaptic neuron
Postsynaptic
E1
neuron
E1
E2
E1
E1
I
Membrane potential (mV)
Axon
hillock
Threshold of axon of
postsynaptic neuron
0
Action
potential
Action
potential
Resting
potential
–70
E1
E1
(a) Subthreshold, no
summation
E1
E1
(b) Temporal summation
E1 + E2
(c) Spatial summation
Axon hillock determines overall charge.
If threshold is met then action potential is fired.
E1
I
E1 + I
(d) Spatial summation
of EPSP and IPSP
Na+
K+
Chapter 48: Nervous Systems
1. What are the 3 main fcns of the nervous system?
2. How does a reflex work?
3. What cells make up the nervous system?
4. What is the charge of a neuron?
5. How is neuron polarity altered?
6. How is an action potential (nerve impulse) created?
7. Why does an action potential only travel in 1 direction?
8. How does a neuron communicate with another cell?
9. How does a single neuron interpret multiple inputs?
10. Let’s look at some neurotransmitters….
Table 48.1 Major Neurotransmitters
Chapter 48: Nervous Systems
1. What are the 3 main fcns of the nervous system?
2. How does a reflex work?
3. What cells make up the nervous system?
4. What is the charge of a neuron?
5. How is neuron polarity altered?
6. How is an action potential (nerve impulse) created?
7. Why does an action potential only travel in 1 direction?
8. How does a neuron communicate with another cell?
9. How does a single neuron interpret multiple inputs?
10. Let’s look at some neurotransmitters….
11. How is the nervous system organized?
Figure 48.19 The vertebrate nervous system
Central nervous
system (CNS)
Brain
Spinal cord
Peripheral nervous
system (PNS)
Cranial
nerves
Ganglia
outside
CNS
Spinal
nerves
Figure 48.20 Ventricles, gray matter, and white matter
Gray matter
White
matter
Ventricles
Gray matter – dendrites, unmyelinated axons & neuron cell bodies
White matter – myelinated axons
Ventricles – filled with CSF (cerebrospinal fluid)
Figure 48.21 Functional hierarchy of the vertebrate peripheral
nervous system
Peripheral
nervous system
Somatic
nervous
system
Autonomic
nervous
system
Sympathetic
division
Parasympathetic
division
Enteric
division
Figure 48.22 The parasympathetic and sympathetic divisions of
the autonomic nervous system
Parasympathetic division
Sympathetic division
Action on target organs:
Location of
preganglionic neurons:
brainstem and sacral
segments of spinal cord
Neurotransmitter
released by
preganglionic neurons:
acetylcholine
Location of
postganglionic neurons:
in ganglia close to or
within target organs
Action on target organs:
Dilates pupil
of eye
Constricts pupil
of eye
Inhibits salivary
gland secretion
Stimulates salivary
gland secretion
Constricts
bronchi in lungs
Sympathetic
ganglia
Cervical
Accelerates heart
Slows heart
Stimulates activity
of stomach and
intestines
Inhibits activity of
stomach and intestines
Thoracic
Inhibits activity
of pancreas
Stimulates activity
of pancreas
Stimulates
gallbladder
Neurotransmitter
released by
postganglionic neurons:
acetylcholine
Stimulates glucose
release from liver;
inhibits gallbladder
Lumbar
Stimulates
adrenal medulla
Promotes emptying
of bladder
Promotes erection
of genitalia
Rest & digest
Relaxes bronchi
in lungs
Inhibits emptying
of bladder
Synapse
Sacral
Location of
preganglionic neurons:
thoracic and lumbar
segments of spinal cord
Neurotransmitter
released by
preganglionic neurons:
acetylcholine
Location of
postganglionic neurons:
some in ganglia close to
target organs; others in
a chain of ganglia near
spinal cord
Neurotransmitter
released by
postganglionic neurons:
norepinephrine
Promotes ejaculation and
vaginal contractions
Fight or flight