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
Organizational Overview
Peripheral nervous system (PNS)
Afferent (sensory) division
Impulses from body CNS
Somatic afferents
From skin, muscles, joints
Visceral afferents
From visceral organs
5
Organizational Overview
Peripheral nervous system (PNS)
Afferent (sensory) division
Efferent (motor) division
Impulses from CNS body
6
Organizational Overview
Peripheral nervous system (PNS)
Afferent (sensory) division
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
Generation of an Action Potential
Resting potential
Voltage gated Na+ &
K+ channels closed
Leak channels active
24
Fig. 5-10
Generation of an Action Potential
Stimulus / Depolarization
Na+ gates begin to open Na+ influx
25
Fig. 5-10
Generation of an Action Potential
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
Generation of an Action Potential
Repolarization
Na+ gates inactivated
K+ gates open
27
Fig. 5-10
Generation of an Action Potential
Afterpotential (undershoot)
K+ gates slow to close
Membrane is refractory to new stimuli
28
Fig. 5-10
Generation of an Action Potential
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
Detection & Transmission of Stimuli
Increasing receptor potentials increase the
frequency of action potentials
Fig. 46-2 70
Detection & Transmission of Stimuli
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
Sympathetic division
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
Autonomic Nervous System
Sympathetic division
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
Autonomic Nervous System
Sympathetic division
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)
Smooth muscle, glands,
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
Autonomic Nervous System
Parasympathetic division
Preganglionic neurons
Cell body
Axon length
Myelination
Neurotransmitter
Effect
Target
CNS
Typically long
Light
ACh
Stimulatory
Ganglion / effector
114
Autonomic Nervous System
Parasympathetic division
Postganglionic neurons
Cell body
Axon length
Myelination
Neurotransmitter
Effect
Target
Ganglion / on effector
Shorter
None
ACh
Target dependent
Smooth muscle, glands,
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
Neurotransmitter Synthesis:
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
Neurotransmitter Synthesis:
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
Cholinergic Fibers & Receptors
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
Cholinergic Fibers & Receptors
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
Sympathetic division
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
Parasympathetic division
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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