Post on 25-Jan-2016
description
Chapter 48: Nervous Systems
1. What are the 3 main functions 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
Sensor
Effector
Motor output
Integration
Sensory input
Peripheral nervoussystem (PNS)
Central nervoussystem (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
Sensory neurons from the quadriceps also communicatewith interneurons in the spinal cord.
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.
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.
4
5
6
The reflex is initiated by tapping
the tendon connected to the quadriceps (extensor) muscle.
1
Sensors detecta sudden stretch in the quadriceps.
2 Sensory neuronsconvey the information to the spinal cord.
3
Quadricepsmuscle
Hamstringmuscle
Spinal cord(cross section)
Gray matter
White matter
Cell body of sensory neuronin dorsal root ganglion
Sensory neuron
Motor neuron
Interneuron
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 neuronDendrites
Cell body
Nucleus
Axon hillock
AxonSignal direction
Synapse
Myelin sheath
Synapticterminals
Presynaptic cell Postsynaptic cell
Cell body – has nucleusDendrites – bring signal to cell bodyAxon – takes signal away from cell bodyAxon hillock – cell body region where impulse is generated & axon beginsMyelin – 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
- Oligodendrocytes & Schwann cells
Figure 48.8 Schwann cells and the myelin sheath
Myelin sheathNodes of Ranvier
Schwanncell Schwann
cellNucleus of Schwann cell
Axon
Layers of myelin
Node of Ranvier
0.1 µm
Axon
Node of Ranvier – space between Schwann cells on axon
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?
- -70 mV - WHY???
Microelectrode
Referenceelectrode
Voltage recorder
–70 mV
Figure 48.10 Ionic gradients across the plasma membrane of a mammalian neuron
CYTOSOL EXTRACELLULARFLUID
[Na+]15 mM
[K+]150 mM
[Cl–]10 mM
[A–]100 mM
[Na+]150 mM
[K+]5 mM
[Cl–]120 mM
–
–
–
–
–
+
+
+
+
+
Plasmamembrane
[A-] – DNA, RNA, proteinsWhat happens when Na+ comes in & K+ leaves?
Figure 48.11 Modeling a mammalian neuronInner chamber
Outer chamber Inner
chamberOuter chamber
–92 mV +62 mV
Artificialmembrane
Potassiumchannel
K+
Cl–
150 mMKCL
150 mMNaCl
15 mMNaCl
5 mMKCL
Cl–
Na+
Sodium channel
+ –
+ –
+ –
+ –
+ –
+ –
(a) Membrane selectively permeable to K+ (b) Membrane selectively permeable to Na+
As K+ leaves, the cell loses (+) chargeIt becomes more (-)
As Na+ enters, the cell gains (+) chargeIt becomes more (+)
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?
Figure 48.12 Graded potentials and an action potential in a neuron
+50
0
–50
–100
+50
0
–50
–100
+50
0
–50
–100
Time (msec) Time (msec) Time (msec)0 1 2 3 4 5 0 1 2 3 4 5 0 1 2 3 4 5 6
Threshold Threshold Threshold
Restingpotential
Restingpotential
RestingpotentialHyperpolarizations
Depolarizations
Me
mb
ran
e p
ote
ntia
l (m
V)
Me
mb
ran
e p
ote
ntia
l (m
V)
Me
mb
ran
e p
ote
ntia
l (m
V)
Stimuli Stimuli Stronger depolarizing stimulus
Actionpotential
(a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K+. The larger stimulus producesa larger hyperpolarization.
(b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na+.The larger stimulus produces alarger depolarization.
(c) Action potential triggered by a depolarization that reaches the threshold.
HyperpolarizationK+ channels open
Slight depolarizationNa+ channels open
More depolarizationMore Na+ entersThreshold achieved (-55 mV)LOTS of Na+ channels openNEURONS ARE ALL OR NONE!!
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?
Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential
Plasma membrane
Extracellular fluid Activationgates
Potassiumchannel
Inactivationgate
Threshold
– – – – – – – –
+ + + + + + + + + + + ++ +
– – – – – –
Na+
K+
1 Resting state
Undershoot
1
2
3
4
5 1
Sodiumchannel
Actionpotential
Resting potential
Time
Me
mb
ran
e p
ote
ntia
l (m
V)
+50
0
–50
–100
Threshold
Cytosol
Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential
Plasma membrane
Extracellular fluid Activationgates
Potassiumchannel
Inactivationgate
Threshold
– – – – – – – –
+ + + + + + + + + + + ++ +
– – – – – –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
Na+
K+
K+
Na+ Na+
2 Depolarization
1
2
3
4
5 1
Sodiumchannel
Actionpotential
Resting potential
Time
Me
mb
ran
e p
ote
ntia
l (m
V)
+50
0
–50
–100
Threshold
Cytosol
1 Resting state
Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential
Plasma membrane
Extracellular fluid Activationgates
Potassiumchannel
Inactivationgate
Threshold
– – – – – – – –
+ + + + + + + + + + + ++ +
– – – – – –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
– –
+ +
– –
+ +
– –
+ +
– –
+ +
Na+ Na+
K+
Na+
K+
K+
Na+ Na+
1 Resting state
2 Depolarization
3 Rising phase of the action potential
1
2
3
4
5 1
Sodiumchannel
Actionpotential
Resting potential
Time
Me
mb
ran
e p
ote
ntia
l (m
V)
+50
0
–50
–100
Threshold
Cytosol
Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential
Plasma membrane
Extracellular fluid Activationgates
Potassiumchannel
Inactivationgate
Threshold
– – – – – – – –
+ + + + + + + + + + + ++ +
– – – – – –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
– –
+ +
– –
+ +
– –
+ +
– –
+ +
Na+ Na+
K+
Na+ Na+
K+
Na+
K+
K+
Na+ Na+
1 Resting state
2 Depolarization
3 Rising phase of the action potential
4 Falling phase of the action potential
1
2
3
4
5 1
Sodiumchannel
Actionpotential
Resting potential
Time
Me
mb
ran
e p
ote
ntia
l (m
V)
+50
0
–50
–100
Threshold
Cytosol
Figure 48.13 The role of voltage-gated ion channels in the generation of an action potential
Plasma membrane
Extracellular fluid Activationgates
Potassiumchannel
Inactivationgate
Threshold
– – – – – – – –
+ + + + + + + + + + + ++ +
– – – – – –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
+ +
– –
– –
+ +
– –
+ +
– –
+ +
– –
+ +
Na+ Na+
K+
Na+ Na+
K+
Na+ Na+
K+
Na+
K+
K+
Na+ Na+
5
1 Resting state
2 Depolarization
3 Rising phase of the action potential
4 Falling phase of the action potential
Undershoot
1
2
3
4
5 1
Sodiumchannel
Actionpotential
Resting potential
Time
Me
mb
ran
e p
ote
ntia
l (m
V)
+50
0
–50
–100
Threshold
Cytosol
Figure 7.16 The sodium-potassium pump: a specific case of active transport
Cytoplasmic Na+ binds to the sodium-potassium pump.
1 Na+ binding stimulates phosphorylation by ATP.2
K+ is released and Na+
sites are receptive again; The cycle repeats.
3 Phosphorylation causes the protein to change its conformation, expelling Na+ to the outside.
4
Extracellular K+ binds to the protein, triggering release of the Phosphate group.
6 Loss of the phosphate restores the protein’s original conformation.
5
EXTRACELLULARFLUID [Na+] high
[K+] low
CYTOPLASM
[Na+] low[K+] high
Na+
Na+
Na+
Na+
Na+
Na+
P ATP
Na+
Na+
Na+
P
ADP
PP i
K+
K+
K+
K+ K+
K+
Maintains charge of -70 mV.NOT THE SAME AS A Na+ or K+ channel.
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?
Figure 48.14 Conduction of an action potential
– +– + + + + +
– +– + + + + +
+ –+ – + + + +
+ –+ – + + + +
+ –+ – – – – –+ –+ – – – – –
– – – –– – – –
– –– –
+ +
+ +
+ ++ + – – – –
+ ++ + – – – –
– –– – + + + +– –– – + + + +
Na+
Na+
Na+
Actionpotential
Actionpotential
ActionpotentialK+
K+
K+
Axon
An action potential is generated as Na+ flows inward across the membrane at one location.
1
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 isrepeated 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.
K+
Domino analogy…
Figure 48.15 Saltatory conduction
Cell body
Schwann cell
Myelin sheath
Axon
Depolarized region(node of Ranvier)
++ +
++ +
++ +
++
– –
– –
– –
–––
–
–
–
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. 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?
- Chemical synapse- Signal changes from electrical chemical electrical
Figure 48.17 A chemical synapsePresynapticcell
Postsynaptic cell
Synaptic vesiclescontainingneurotransmitter
Presynapticmembrane
Postsynaptic membrane
Voltage-gatedCa2+ channel
Synaptic cleft
Ligand-gatedion channels
Na+
K+
Ligand-gatedion channel
Postsynaptic membrane
Neuro-transmitter
1 Ca2+
2
3
4
5
6
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?
Figure 48.18 Summation of postsynaptic potentials
E1 E1 E1 E1E1E1 + E2 E1 + II
ActionpotentialAction
potentialRestingpotential
Threshold of axon ofpostsynaptic neuron
(a) Subthreshold, nosummation
(b) Temporal summation (c) Spatial summation (d) Spatial summationof EPSP and IPSP
Terminal branch of presynaptic neuron
Postsynaptic neuron E1
E1E1
E2
E1
IAxonhillock
0
–70
Mem
bra
ne p
oten
tial (
mV
)
Axon hillock determines overall charge.If threshold is met then action potential is fired.
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 nervoussystem (CNS)
Peripheral nervoussystem (PNS)
Brain
Spinal cord
Cranialnerves
GangliaoutsideCNS
Spinalnerves
Figure 48.20 Ventricles, gray matter, and white matter
Gray matter
Whitematter
Ventricles
Gray matter – dendrites, unmyelinated axons & neuron cell bodiesWhite matter – myelinated axons (myelin = white)Ventricles – filled with CSF (cerebrospinal fluid)
Figure 48.21 Functional hierarchy of the vertebrate peripheral nervous system
Peripheralnervous system
Somaticnervoussystem
Autonomicnervoussystem
Sympatheticdivision
Parasympatheticdivision
Entericdivision
Figure 48.22 The parasympathetic and sympathetic divisions of the autonomic nervous system
Parasympathetic division Sympathetic division
Action on target organs: Action on target organs:
Location ofpreganglionic neurons:brainstem and sacralsegments of spinal cord
Neurotransmitterreleased bypreganglionic neurons:acetylcholine
Location ofpostganglionic neurons:in ganglia close to orwithin target organs
Neurotransmitterreleased bypostganglionic neurons:acetylcholine
Constricts pupilof eye
Stimulates salivarygland secretion
Constrictsbronchi in lungs
Slows heart
Stimulates activityof stomach and
intestines
Stimulates activityof pancreas
Stimulatesgallbladder
Promotes emptyingof bladder
Promotes erectionof genitalia
Cervical
Thoracic
Lumbar
Synapse
Sympatheticganglia
Dilates pupilof eye
Inhibits salivary gland secretion
Relaxes bronchiin lungs
Accelerates heart
Inhibits activity of stomach and intestines
Inhibits activityof pancreas
Stimulates glucoserelease from liver;inhibits gallbladder
Stimulatesadrenal medulla
Inhibits emptyingof bladder
Promotes ejaculation and vaginal contractionsSacral
Location ofpreganglionic neurons:thoracic and lumbarsegments of spinal cord
Neurotransmitterreleased bypreganglionic neurons:acetylcholine
Location ofpostganglionic neurons:some in ganglia close totarget organs; others ina chain of ganglia near spinal cord
Neurotransmitterreleased bypostganglionic neurons:norepinephrine
Rest & digest Fight or flight