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