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NERVOUS

SYSTEM

The Nervous System

NERVOUS SYSTEM

Basic functions

Monitor changes

Sensory input

Inside & outside body

Integrate input

Process, analyze,

interpret response

Store information

(memory)

Initiate response

Motor output

Fig. 45-4 3

Organizational Overview

Two primary divisions

Central nervous system (CNS)

Peripheral nervous system (PNS)

4



Afferent (sensory) division

Impulses from body CNS

Somatic afferents

From skin, muscles, joints

Visceral afferents

From visceral organs

5




Efferent (motor) division

Impulses from CNS body

6




Efferent (motor) division

Somatic nervous system

CNS skeletal muscle, joints

Autonomic nervous system

Sympathetic division

Mobilize body in response to stress

Fight or flight (4-E’s)

Parasympathetic division

Maintenance, energy conservation

measures

Rest & digest (3-D’s) 7

The parasympathetic nervous system is a

subdivision of all of these EXCEPT:

A) Central nervous system

B) Peripheral nervous system

C) Efferent nervous system

D) Autonomic nervous system

8

Histology

Neuron

General structure

Receptive, conductive,

secretory components

Cell body

Processes

Dendrites

Axon

Axon terminus

General characteristics

Fig. 45-1 9

Histology

Supportive cells

CNS

Glial cells

Astrocytes

Microglia

Ependymal cells

Oligodendrocytes

PNS

Satellite cells

Schwann cells

10

Functional Classes of Neurons

Motor neurons

Impulses sent away from CNS

Multipolar

Sensory neurons

Impulses sent from receptors toward CNS

Unipolar, bipolar, multipolar

Interneurons (association neurons)

Send impulses between neurons

Largest group of neurons

Multipolar

11

A neuron which receives information from a

neuron and passes information to another

neuron is a(n)…

A) Sensory neuron

B) Motor neuron

C) Interneuron

D) May be any of the above

12

Generation of Nerve Impulses

Membrane potential

Voltage across the surface of a membrane

Diffusion potential is the result of a concentration

gradient across a membrane

Nernst potential

Figs. 5-2,3 13

Generation of Nerve Impulses

Membrane potential

Voltage across the surface of a membrane

Nernst potential

EMF = ±61 · log ( [ion]inside / [ion]outside )

EMF = electromotive force

Figs. 5-2,3 14

What is the EMF when there is a 10:1 ratio of K+

inside:outside the cell?

A) 10 V

B) -10 mV

C) 61 V

D) -61 mV

15

Membrane Potential

Primary ions involved in

establishing charge

differential

Na+

K+

Fig. 5-5 16

Membrane Potential

Ion movement driven by electrochemical

gradients

Diffusion in response to ion concentration

Diffusion in response to charge differential

17

Membrane Potential

18

Membrane Potential

Establishing resting potential

Fig. 5-4

Leak channels

Passive process

Randomly flicker between

open/closed

states

~100x more permeable to K+ than Na+

more K+ leaks out

Resting potential depends more on K+

gradient than Na+ gradient

Na+/K+ ion pump

Active process

Pump more Na+ out (3:2 ratio) 19

Resting membrane potential depends mostly on

the potassium (K+) concentration gradient

because…

A) It is the largest gradient

B) The plasma membrane has the most

permeability to K+ at rest

C) K+ ions are larger than Na+ ions, so they

move faster

D) All of the above

20

Membrane Potential

Controlled depolarization of the resting

membrane creates an electrical signal

Involves voltage-gated ion channels

Open/close in response to changes in voltage

Generates nerve impulses (action potentials)

Allows rapid long-distance communication

Fig. 5-7 21

Generation of an Action Potential

Figs. 5-6,9

22

Action Potentials

Like the “ideal toilet”

Push the handle…

Threshold stimulus

Depolarize membrane

Drain the bowl…

All or nothing

Action potential

Refill the tank…

Refractory period

Return to resting potential

23


Resting potential

Voltage gated Na+ &

K+ channels closed

Leak channels active

24

Fig. 5-10


Stimulus / Depolarization

Na+ gates begin to open Na+ influx

25

Fig. 5-10


Stimulus / Depolarization Reach threshold voltage

Activation of voltage-gated Na+ channels (mass Na+ influx)

Leads to complete depolarization of membrane

Generates action potential: all-or-nothing

26 Fig. 5-10


Repolarization

Na+ gates inactivated

K+ gates open

27

Fig. 5-10


Afterpotential (undershoot)

K+ gates slow to close

Membrane is refractory to new stimuli

28

Fig. 5-10


Return to resting potential

K+ & Na+ voltage gated channels closed

Ion distribution restored by Na+/K+ ion pump

Membrane can respond to another stimulus

29

Fig. 5-10

During an action potential, the voltage of the

membrane changes because…

A) The concentration gradient for K+ changes

B) The concentration gradient for Na+ changes

C) The permeability of the membrane to Na+

changes

D) All of the above

30

Given typical K+ and Na+ concentration

gradients at rest, what is the concentration of

Na+ inside the cell during depolarization?

A) 14 mEq/L

B) 142 mEq/L

C) 140 mEq/L

D) 4 mEq/L

31

Propagation of the Action Potential

Voltage change spreads in all directions

from action potential

Activates nearby gates

and continues impulse

Continues along entire

length of membrane

Depolarization wave

followed by

repolarization wave

So how can this occur

unidirectionally along

an axon? Fig. 5-11

32

Propagation of the Action Potential

Voltage change spreads in all directions

from action potential

Activates nearby gates

and continues impulse

Continues along entire

length of membrane

Depolarization wave

followed by

repolarization wave

So how can this occur

unidirectionally along

an axon?

33

Saltatory Conduction

Involves myelin sheath along axon

Ion gates concentrated at Nodes of Ranvier

Fig. 5-17

34

Saltatory Conduction

Benefits

Increases transmission rate ~50x (~100 m/s)

Depolarization occurs at regular gaps instead of

every point along the membrane

Ion need reduced by 100x

Less energy to repolarize membrane

Na+/K+ ion pump

Repolarization occurs faster

Fewer ions need to be replaced

35

Myelination

Myelin lipoprotein within a plasma

membrane

Schwann cells

Single cells wrap around axon

Schwann cell partially wraps around multiple

axons of adjacent neurons

Fig. 5-16 36

Myelination

Myelin lipoprotein within a plasma

membrane

Schwann cells

Oligodendrocytes

Single cells extend projections to wrap around

axons of multiple neurons

37

Myelination

Multiple sclerosis

Demyelination of neurons

Autoimmune reaction

Decreases nerve transmission rate

Vision problems, muscle control, speech

problems, incontinence

Periods of Remission

Axon not initially damaged

New ion channels develop to restore

transmissibility (temporary)

38

Myelination increases speed of transmission

by…

A) Making current flow faster through the

voltage-gated channels

B) Reducing the number of action potentials

required to propagate a signal down the axon

C) Preventing leakage of ions

39

Transmission of Nerve Impulses

The chemical synapse

Space (gap) between axon terminus and effector cell

Electrical stimulus is converted to chemical message to transfer stimulus

Ca2+ required for neurotransmitter release

Activates proteins at release sites to promote fusion / exocytosis of secretory vesicles

Fig. 45-6 40 synapse

Transmission of Nerve Impulses

The chemical synapse

Fig. 45-5 41

Chemical Synapses

Two categories based on how they affect

membrane potential

Excitatory postsynaptic potentials (EPSP’s)

Open Na+ channels (influx)

Inhibit K+ & Cl- channels

Begin to depolarize membrane

May lead to action potentials

Fig. 45-9 42

Chemical Synapses

Two categories based on how they affect

membrane potential

Excitatory postsynaptic potentials (EPSP’s)

Inhibitory postsynaptic potentials (IPSP’s)

Open K+ (outflow) and Cl- (inflow) channels

Hyperpolarizes membrane

Inhibits ability to generate action potentials

Fig. 45-9 43

Chemical Synapses

Outcome of EPSP / IPSP stimulation results

from the summation of the signals

Single EPSP or IPSP insufficient to induce or inhibit

action potential

Both EPSP/IPSP typically present dominant

signal dictates outcome

“Integrated” at axon hillock

Fig. 45-11 44

Chemical Synapses

Spatial summation

Fig. 45-10 45

Chemical Synapses

Temporal summation

46

EPSPs are typically generated as a result of…

A) Opening potassium channels

B) Opening sodium channels

C) Closing potassium channels

D) Closing sodium channels

47

Neurotransmitters

Group 1: Small molecule, rapidly acting

transmitters

General mode of action

Alter ion channel conductance

OR

Stimulate receptor-activated enzyme systems

Synthesis

Synthesized in cytosol of presynaptic terminal

Stored / exocytosed in secretory vesicles

See Table 45-1 48

Neurotransmitters

Acetylcholine (ACh)

Location

Many CNS neurons

All neuromuscular junctions

Preganglionic neurons of ANS

Postganglionic neurons of Parasympathetic NS;

few Sympathetic NS

49

Neurotransmitters

50

Neurotransmitters

Acetylcholine (ACh)

Action

Typically excitatory

Some inhibitory effects in Parasympathetic NS

Drug interactions

Release blocked by botulinum toxin

Effects prolonged by nerve gas,

organophosphates

Inactivate acetylcholinesterase

Many snake venoms block postsynaptic

receptors

Enhanced by nicotine (binds nACh receptors) 51

Neurotransmitters

Biogenic amines

Dopamine

Location

Secreted by neurons of midbrain (substantia

nigra)

Action

“feel good”

Usually inhibitory

Target of recreational drugs

Release enhanced by amphetamines

Uptake blocked by cocaine

52

Neurotransmitters

Biogenic amines

Norepinephrine

Location

Many CNS neurons (mood, increasing

wakefulness)

Most postganglionic neurons of SNS

Action

Excitatory or inhibitory depending on target

Synaptic removal blocked by cocaine & other

antidepressants

53

Neurotransmitters

Biogenic amines

Serotonin

Location

Secreted by neurons of brain stem

Action

Pain inhibitor, mood enhancer (inhibitory

effects), sleep

Re-uptake blocked by Prozac (SSRI)

Relief of depression / anxiety

54

Neurotransmitters

Amino acids & derivatives

Glutamate

Action

Fast excitatory synapses of brain

Fast-pain fibers in spinal cord

Role in stroke (enhances damage)

Damaged brain cells (O2 deprivation)

release mass amounts of glutamate

Overexcites neighboring cells

Leads to generation of free radicals

(destroy cells)

55

Neurotransmitters

Nitric oxide (NO)

Location

Nerve terminals in brain related to long-term

behavior & memory

Action

Synthesized as needed (not stored)

Readily diffuses through membranes

Doesn’t significantly directly alter membrane

potential

Modifies intracellular metabolic activity of post

synaptic neuron to affect neuronal excitability

56

Which of these NTs acts only in an excitatory

fashion?

A) Acetylcholine (ACh)

B) Norepinephrine (NEpi)

C) Dopamine

D) Glutamate

57

Neurotransmitters

Group 2 : Neuropeptides (slow-acting transmitters or growth factors)

Hormones or releasing/inhibitory factors

Affect neuron receptors / synapses (#’s & sizes)

Characteristics

More potent than fast acting transmitters

Smaller quantities released

Actions more prolonged

Synthesis

Synthesized in neuron cell body, packaged by Golgi and transported down axon to termini

Then stored / exocytosed in secretory vesicles

See Table 45-2 58

Clearance of the Synapse

Enzymatic degradation

E.g., ACh

Split in synapse by cholinesterase (ACh

choline + acetate)

Choline transported back into presynaptic

terminal

More Ach synthesized (acetyl-CoA + choline

ACh)

Re-uptake

E.g., dopamine

Diffusion

59

NPY is a neurotransmitter involved in appetite

regulation. Would you guess that it is fast-

acting (Group 1) or slow-acting (Group 2)?

A) Fast – Group 1

B) Slow – Group 2

60

Characteristics of Synaptic Transmission

Fatigue Protection against excess neuronal activity

Causes

Exhaustion of transmitter stores

Inactivation of postsynaptic membrane receptors

Abnormal ion concentrations

Effect of pH Alkalosis → increases excitability

May lead to seizure

Acidosis → decreases excitability

May lead to coma

61

Characteristics of Synaptic Transmission

Effect of hypoxia

O2 deprivation can lead to cessation of excitability

Effects of anesthetics

Increase membrane threshold

Lipid-based forms may alter threshold by

integrating into membrane

62

The lack of awareness of certain stable stimuli,

such as clothes touching your skin, or a stable

environmental temperature, may be partially

due to…

A) The effect of pH on the NT release

B) The effect of hypoxia on NT receptor action

C) Synaptic fatigue due to reduced NT

receptor activation

D) All of the above

63

Classes of Sensory Receptors

5 classes based on type of stimulus detected

Mechanoreceptors

Deformation of membrane receptors opens ion

channels

Thermoreceptors

Change in temp alters membrane permeability

See Table 46-1 64

Classes of Sensory Receptors

5 classes based on type of stimulus detected

Chemoreceptors

Chemical binding opens ion channels

Electromagnetic receptors

Light alters conformation of membrane proteins

Nociceptors

E.g., pain

65 See Table 46-1

Baroreceptors are a type of…

A) Mechanoreceptor

B) Thermoreceptor

C) Chemoreceptor

D) Electromagnetic receptor

E) Nociceptor

F) None of the above – it’s its own class

66

Sensory Receptor Specialization

Receptive component

Highly specialized to detect specific stimuli

Fig. 46-1 67

Detection & Transmission of Stimuli

How are sensory impulses regulated to

differentiate stimuli of varied intensities?

Stimulate multiple receptors

Varied responses from individual receptors

Development & rate of action potentials are

dependent on the intensity of the stimulus at the

receptor

This allows a single receptor to respond to a

range of stimuli with a range of responses

Weak extreme

Based on receptor potential

68

Receptor Potential

The change in electrical potential of the

receptor

Action potentials result when this rises above

the threshold

69

Fig. 46-3


Increasing receptor potentials increase the

frequency of action potentials

Fig. 46-2 70


Receptor potential (amplitude) relates to

stimulus strength

Allows receptors to transmit a range of

responses

Weak stimulus =

receptor potential =

low frequency of action

potentials

Strong stimulus =

receptor potential =

high frequency of action

potentials Fig. 46-2

71

Signal Transmission in Nerve Tracts

Based on principles of summation

Spatial summation

Fig. 46-7

72

Signal Transmission in Nerve Tracts

Based on principles of summation

Spatial summation

Temporal summation

Fig. 46-8 73

Adaptation

Receptors can adapt to repetitive stimuli

Frequency of action potentials begins to decrease

with continuous stimuli

74 Fig. 46-5

True or false: Stronger stimuli make the

receptor generate bigger action potentials.

A) True

B) False

75

Adaptation

Adaptation may be partial or complete

Rate and degree varies with receptor type

Fast adapting receptors

Send impulses to notify brain of changes in stimulus strength

E.g., Pacinian corpuscle (mechanoreceptor)

Slow adapting receptors

Keep brain constantly apprised of body status

May never completely adapt

Continue to send signals to brain, although not at maximum rate

E.g., nociceptors, chemoreceptors 76

Adaptation Example:

Pacinian Corpuscles

Sensory mechanism

Pressure forces redistribution of fluids within

corpuscle

Mechanical gated ion channels open

Generates initial stimulus

If maintained, fluids equalize throughout corpuscle

Gates close

Stimulus ceases (adaptation to extinction)

If pressure released, fluids redistributed again

Gates open

Stimulus generated

77

Adaptation

Methods for adaptation may involve…

Readjustments to the structure of the receptor

E.g., Pacinian corpuscle fluid redistribution

Accommodation

Inactivation of Na+ channels in nerve fiber

78

True or false: Adaptation of receptors means

that receptors will continue to send a signal as

long as the stimulus is present.

A) True

B) False

79

Signal Processing & Transmission

Neuronal pools

Functional groups of neurons that integrate and

relay information

Fig. 46-9 80

Neuronal Pools

Neuronal pools

Discharge zone (center of field)

Provide primary stimulatory / inhibitory

potentials

Fig. 46-10 81

Neuronal Pools

Neuronal pools

Facilitated zones (periphery of field)

Provide sub-threshold stimuli but may facilitate

input from other neurons

82 Fig. 46-10

Circuit Patterns

Diverging circuits

Presynaptic fiber(s) influence multiple post synaptic

neurons

Amplified divergence (single tract)

Divergence occurs along same tract

E.g., neurons in motor cortex & muscle control

Fig. 46-11 83

Circuit Patterns

Diverging circuits

Presynaptic fiber(s) influence multiple post

synaptic neurons

Amplified divergence (single tract)

Multiple tract divergence

Signal diverges along multiple nerve tracts

E.g., spinal reflex

Fig. 46-11 84

Circuit Patterns

Converging circuits

Presynaptic fiber(s) converge to influence a single

post synaptic neuron

Single source convergence

Fig. 46-12 85

Circuit Patterns

Converging circuits

Presynaptic fiber(s) converge to excite a single

post synaptic neuron

Multiple source convergence

Input may come from several different areas

Results in spatial summation

Fig. 46-12 86

Circuit Patterns

Inhibitory circuits

Involve both EPSP’s and IPSP’s

E.g., antagonistic muscle groups

E.g., spinal reflexes

Fig. 46-13

87

Circuit Patterns

Reverberating (oscillating) circuits

Provide positive feedback to amplify or maintain a

signal (after discharge)

Often involve axon collaterals

Some reverberate continuously

E.g., respiratory centers (medulla, pons)

Intrinsic excitability (unstable membrane

potentials always on)

EPSP’s output

IPSP’s output Fig. 46-14

88

Reverberating Circuits

Fig. 46-14 89

A neuronal circuit which begins with one

neuron, then spreads to many other neurons is

a ________ circuit.

A) Diverging

B) Converging

C) Reverberating

D) Oscillating

90

Circuit Patterns

Control over neuronal circuits

Inhibitory feedback circuits

Stimuli from circuit terminus sent back to inhibit

input or intermediary neurons

Common in sensory pathways

91

Circuit Patterns

Control over neuronal circuits

Synaptic fatigue

Prolonged / intense periods of excitation

weaken synaptic transmission

Short term adjustments – constraints on

neurotransmitter production / release /

uptake

Long term adjustments – downgrade

receptors due to over activity, upgrade

receptors with under activity

92

Fig. 46-14, 15

Signal Output

Synaptic

fatigue

93

Synaptic Fatigue

Fig. 46-18

94

The role of synaptic fatigue in regulation of

neuronal circuits is to…

A) Inhibit signals which have been “on” for

some time already

B) Potentiate (enhance) signals which have

been “on” for some time already

C) Recharge neurons so they can send

additional signals

D) All of the above

95

THE CENTRAL NERVOUS SYSTEM

Structural and functional overview of the brain

96

THE CNS

Structural and functional overview of the

spinal cord

97

Nerve Pathways

Afferent nerve tracts

Dorsal column-medial

lemniscal pathway

Crossover in

medulla

Critical tactile input

Fig. 47-3 98

Nerve Pathways

Afferent nerve tracts

Anteriolateral pathway

Crossover in spinal

cord (immediate)

Pain, temp,

mechanoreceptors

99 Fig. 47-13

Motor & Somatosensory Areas of Cerebral Cortex

See Fig. 47-5,6,7, 55-1,2,3 10

0

Nerve Pathways

Efferent nerve tracts

Direct pathway

Pyramidal tracts

(corticospinal tracts)

Crossover in inferior

medulla or spinal

cord

Fig. 55-4 10

1

Nerve Pathways

Efferent nerve tracts

Indirect pathway

Branching in basal ganglia, cerebellum, etc.

Fig. 56-6

10

2

Somatosensory-Motor Pathways

Fig. 56-8 10

3

Spinal Reflexes

Response to stimuli without cortical

involvement

Typically involve extreme or potentially damaging

stimuli

E.g., flexor-crossed

extensor reflex

Diverging circuit

(multiple tract) with

reciprocal

inhibition

Fig. 54-8 10

4

THE PERIPHERAL NERVOUS

SYSTEM: EFFERENT PATHWAYS

Central nervous system

Peripheral nervous system

Afferent (sensory) nervous system

Efferent (motor) nervous system

Somatic nervous system

Autonomic nervous system (ANS)

Sympathetic nervous system (SNS)

Parasympathetic nervous system

105

Somatic Nervous System

Neuron cell bodies

Myelination

Neurotransmitter

Effect

Target

CNS

Heavy

ACh

Stimulatory

Skeletal muscle

106

Which of these NTs is used in the somatic

nervous system?

A) Acetylcholine (ACh)

B) Norepinephrine (NEpi)

C) Dopamine

D) Glutamate

E) All of the above

107

Autonomic Nervous System


Preganglionic neurons

Cell body

Axon length

Myelination

Neurotransmitter

Effect

Target

CNS

Typically short

Light

ACh

Stimulatory

A) neurons in ganglion,

B) adrenal medulla

A

B

108



Postganglionic neurons

Cell body

Axon length

Myelination

Neurotransmitter

Effect

Target

Ganglia

Long

Nonmyelinated

1° norepinephrine

Target dependent

Smooth muscle, glands,

heart, misc. organs

A

B

109



Adrenal medulla (as “postganglionic neuron”)

Cell body

Axon length

Myelination

Neurotransmitter

Effect

Target

Medulla (modified neurons)

n/a

n/a

Epinephrine & NorEpi

Target dependent (prolonged)


heart, misc. organs

A

B

110

Sympathetic Spinal Nerves

Exit from thoracic

& upper lumbar

regions (T1-L2)

Synapses

Sympathetic chain

ganglia

(paravertebral

ganglia)

Prevertebral

ganglia

Celiac

Hypogastric Fig. 60-1

111

True or false: All postganglionic neurons use

the same neurotransmitter.

A) True

B) False

112

The adrenal medulla is analogous to which of

the following structures?

A) Preganglionic sympathetic neuron

B) Postganglionic sympathetic neuron

C) Preganglionic parasympathetic neuron

D) Postganglionic parasympathetic neuron

113



Preganglionic neurons

Cell body

Axon length

Myelination

Neurotransmitter

Effect

Target

CNS

Typically long

Light

ACh

Stimulatory

Ganglion / effector

114



Postganglionic neurons

Cell body

Axon length

Myelination

Neurotransmitter

Effect

Target

Ganglion / on effector

Shorter

None

ACh

Target dependent


heart, misc. organs

115

Parasympathetic Nerves

Exit from cranial and

sacral regions

Synapse near/on

effector organ

Fig. 60-3 116

Vagus Nerve (X)

Emerges from

medulla oblongata

Only cranial nerve

to extend beyond

head/neck

Mixed nerve

Efferents primarily

parasympathetic

Fig. 60-3 117

The Vagus nerve uses which neurotransmitter?

A) Acetylcholine

B) Epinephrine

C) Norepinephrine

D) Glutamate

118

Neurotransmitter Synthesis:

Acetylcholine

choline + Acetyl-CoA → Acetylcholine

Synthesized in axon terminals by choline acetyltransferase

Stored in secretory vesicles

Degraded in synaptic cleft (acetylcholinesterase)

Acetate + choline

Choline uptake by axon terminals 119


Norepinephrine

Synthesis begins in cytoplasm of axon

terminals but is completed within secretory

vesicles

Tyrosine → DOPA

DOPA → Dopamine (transported into secretory

vesicles)

Dopamine → Norepinephrine

120


Epinephrine

Synthesis begins in cytoplasm of axon terminals but

is completed within secretory vesicles

Occurs in adrenal medulla via methylation

Norepinephrine Epinephrine

121

Neurotransmitters & Receptors of ANS

Cholinergic fibers & receptors

Release & bind ACh (“parasympathetic

transmitter”)

122

Neurotransmitters & Receptors of ANS

Cholinergic fibers & receptors

Release & bind ACh (“parasympathetic transmitter”)

Adrenergic fibers & receptors

Release & bind norepinephrine (“sympathetic

transmitter”)

123

Adrenergic fibers release which of the following

neurotransmitters?

A) Acetylcholine

B) Epinephrine

C) Norepinephrine

D) Glutamate

124

Cholinergic Fibers & Receptors

Cholinergic fibers

All ANS preganglionic fibers

All parasympathetic postganglionic fibers

125


2 categories of cholinergic receptors

Nicotinic receptors (nAChRs)

Direct ion channels

Effects always stimulatory

Found on…

Skeletal muscle

All ANS preganglionic neurons

Hormone-producing cells of the adrenal

medulla

126


2 categories of receptors

Muscarinic receptors (mAChRs)

G-protein coupled receptors

Effects depends on effector

Found on:

All parasympathetic target organs

E.g., heart, lungs, digestive organs

Some sympathetic target organs (where ACh

involved)

E.g., eccrine sweat glands, some blood

vessels of skeletal muscle

127

Adrenergic Fibers & Receptors

Fibers

(Nearly) All sympathetic postganglionic fibers

See Table 60-1 128

Adrenergic Fibers & Receptors

2 primary categories of receptors: (1, 2),

(1, 2, 3)

Organs responding to norepinephrine or

epinephrine contain both types

Norepinephrine binds stronger than

Epinephrine binds both , nearly equally

Effect…

Dependent on type & number of receptors on

effector organ

Receptor classes not necessarily associated

with direct stimulation or inhibition

129 See Table 60-1

Muscarinic receptors work by which of the

following mechanisms?

A) Depolarizing membrane directly via

opening ion channels

B) Depolarizing membrane indirectly via

intracellular signaling mechanisms

C) Hyperpolarizing membrane directly via

closing ion channels

D) All of the above

130

Autonomic Pharmacology

Sympathomimetic drugs

Epinephrine

Phenylephrine – alpha

Isoproterenol – beta

Albuterol – beta2

Drugs that block adrenergic activity

Alpha blockers – phenoxybenzamine

Beta blockers - propanolol

Parasympathomimetic drugs

Pilocarpine, methacholine

Antimuscarinic drugs - ??? 131

If you only had these four drugs to choose from,

which of these drugs would you likely

administer to reduce a rapid heart rate?

A) Alpha receptor blocker - phenoxybenzamine

B) Beta receptor blocker - propranolol

C) Parasympathomimetic - pilocarpine

D) Antimuscarinic - atropine

132

Primary Effects of ANS Stimulation

Organ Symp. Stimulus Parasymp. Stimulus

Eye (iris) dilation of pupil constriction of pupil

Salivary/gastric glands inhibits secretions stimulates secretions

Sweat glands stimulates sweating none / palms

Arrector pili contraction none

Heart increases rate / force decreases rate / force

Blood vessels vasoconstriction little / none

Lungs bronchiole dilation bronchiole constriction

Digestive organs decreased gland activity, increased secretion &

muscle constriction motility, sphincters relax

Liver stimulates glucose release slight glycogen synthesis

Pancreas inhibits secretions stimulates secretions

Adrenal medulla stimulates secretions none

Kidney decreased urine output none

Metabolism increased rate none

Mental function increased alertness none See Table 60-2

133

Patterns of ANS Stimulation

Mass vs. discrete discharge


Displays mass discharge effects

E.g., stress response

Arterial pressure

Blood flow to skeletal muscle / strength

Blood flow to GI / renal organs

Cellular metabolism / glycolysis / blood [glusose]

Mental activity

Blood coagulation

Can show discrete control

E.g., heat regulation in skin


Typically discrete 134

Role of the Adrenal Medulla in the ANS Response

Stimulated simultaneously with sympathetic

mass discharge

Produces sustained effect (5-10x)

Longer time required to clear hormone from blood

than synapse

May compensate for destruction / interference

of sympathetic fibers

Allows stimulation of targets not innervated

by sympathetic fibers

E.g., general cellular metabolism

135

What is the benefit of discrete discharge as

compared to mass discharge?

A) Faster response

B) Longer-lasting response

C) More specific response

D) All of the above

136

Sympathetic & Parasympathetic Tone

Both systems continually active at some

basal level (tone)

Both neural and adrenal

Tone allows both systems to either or

activity of a particular organ

Fine-tuned regulation

E.g., vasodilation / vasoconstriction

Tone provides normal degree of constriction (~1/2

diameter)

sympathetic stim. vasoconstriction

sympathetic stim. vasodilation

137

Sympathetic & Parasympathetic Tone

Effect of denervation on tone

Immediate loss of tone

Intrinsic tone develops over time

Up-regulation of receptors to increase sensitivity

Fig. 60-4 138

Autonomic Control

Brain stem

Arterial pressure

Heart rate

Respiratory rate

Hypothalamus

Control over

most brain stem

function

Fig. 60-5

139

Autonomic Reflexes

Cardiovascular reflexes

Response to change in arterial blood pressure

Gastrointestinal reflexes

Salivation, increased motility in response to smell

Emptying of rectum

Urinary reflexes

Emptying of the urinary bladder

140

Which is these is not a mechanism which can

alter sympathetic tone?

A) Medullary signals

B) Hypothalamic regulation

C) Emotional input to hypothalamus

D) Conscious effort

141

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