Download Motor pathways - autonomic Nervous system

Motor (efferent) system
 Divided into:
 Somatic motor division that controls skeletal
muscle
 Visceral/autonomic – controls smooth and cardiac
muscles and the glands (exocrine and endocrine)
 These 2 system differ not only in the effector but also
in their descending pathway and the response
Copyright © 2010 Pearson Education, Inc.
ANS Versus Somatic Nervous System (SNS)
 The ANS differs from the SNS in the following three areas
 1. Effectors
 The effectors of the SNS are skeletal muscles
 The effectors of the ANS are cardiac muscle, smooth
muscle, and glands
Copyright © 2010 Pearson Education, Inc.
ANS Versus Somatic Nervous System (SNS)
 2. Efferent pathways
 In the SNS heavily myelinated axons of the somatic motor
neurons extend from the CNS to the effector (one neuron)
 Efferent pathways in the ANS are a two-neuron chain
 The preganglionic (first) neuron has a lightly myelinated
axon
 The post-ganglionic (second) neuron extends to an effector
organ
Pre-ganglionic
Post-ganglionic
Ganglion
Copyright © 2010 Pearson Education, Inc.
ANS Versus Somatic Nervous System (SNS)
 3. Target organ responses
 All somatic motor neurons release Acetylcholine
(ACh), which has an excitatory effect
 In the ANS:
 Preganglionic fibers release ACh
 Postganglionic fibers release norepinephrine or
ACh and the effect is either stimulatory or
inhibitory
 ANS effect on the target organ is dependent
upon the neurotransmitter released and the
receptor type of the effector
Copyright © 2010 Pearson Education, Inc.
Characteristic
Somatic Nervous System
Autonomic Nervous System
Voluntary (skeletal) muscle
Smooth muscle, Cardiac
Muscle, Glands
Adjustment to external
environment.
Adjustment within the
internal environment
(homeostasis)
Number of
neurons from CNS
to effectors
1
2
Ganglia outside
the CNS
0
Chain ganglia, collateral
ganglia or terminal ganglia
Acetylcholine
Acetylcholine, adrenaline,
noradrenalin
Effectors
General function
Neurotransmitter
On NMJ - nicotinic receptors – ACh always excitatory
Copyright © 2010 Pearson Education, Inc.
Receptors for neurotransmitters in the motor division

Receptors are divided into 2 groups:

Cholinergic – receive and respond to acetylcholine (ACh):

Two subgroups that are names of chemicals that mimic some of the
actions of Ach:

Muscarinic (chemical found in the mushroom Amanita
muscarina)

Nicotinic (chemical found in the tobacco plant – nicotina
tabacum)

Adrenergic – receive and respond to norepinephrin (NE) /
epinephrine (E)

Divided into alpha and beta
Copyright © 2010 Pearson Education, Inc.
Cholinergic Nicotinic Receptors location
 Motor end plates of skeletal muscle cells (will be
discussed later)
 All
ganglionic
neurons
(sympathetic
and
parasympathetic)
 Hormone-producing cells of the adrenal medulla
 Effect of ACh at nicotinic receptors is always direct
and stimulatory
Copyright © 2010 Pearson Education, Inc.
Cholinergic Muscarinic Receptors location
 All effector cells stimulated by postganglionic
cholinergic fibers
 The effect of ACh at muscarinic receptors
 Can be either inhibitory or excitatory
 Depends on the receptor type of the target organ
Copyright © 2010 Pearson Education, Inc.
ACh (cholinergic) receptors
Nicotinic receptors (nACh)
Pre-ganglionic
Direct mechanism – open
Na+ channels
(depolarization)
Fast excitatory effect
Muscarinic receptors (mACh)
Post-ganglionic
Indirect mechanism – use of G-protein
and 2nd messenger system
Increase
intracellular
Ca2+ release
Slow excitatory
M1, M3, M5
Copyright © 2010 Pearson Education, Inc.
Inhibition of
adenylate
cyclase
Slow inhibitory
M2, M4
Adrenergic Receptors
 Two types
 Alpha () (subtypes 1, 2) – excited
 Beta () (subtypes 1, 2 , 3)
 Effects of NT depend on which subclass of receptor
predominates on the target organ
 Norepinephrine excites mainly Alpha () receptors
 Epinephrine excites both alpha and beta equally
Copyright © 2010 Pearson Education, Inc.
NE (adrenergic) receptors - all indirect through G-protein
1
2
Increase
intracellular
Ca2+ release
Inhibition of
adenylate
cyclase
Slow excitation
Slow inhibition
Copyright © 2010 Pearson Education, Inc.
1
3
2
2nd messenger – cAMP
Inhibition or activation of
adenylate cyclase
slow
excitation
Slow
inhibition
Lypolysis
(excitation)
Divisions of the ANS
Enteric nervous system
Copyright © 2010 Pearson Education, Inc.
http://www.sirinet.net/~jgjohnso/nervous.html
Autonomic Nervous System (ANS) function
 The ANS major function is to maintain homeostasis
 The ANS :
 functions via visceral (subconscious) reflexes
 The autonomic system is coordinated primarily
by the hypothalamus and the medulla (higher
centers)
 The brain stem and the spinal cord seem to have
direct influence over autonomic functions
Copyright © 2010 Pearson Education, Inc.
Autonomic reflexes
 Autonomic reflexes are mediated by neural circuits in the
spinal cord and brain stem
 The afferent pathways include both visceral and somatic
fibers
 The reflex includes interneurons that receive convergent
input from visceral and somatic fibers
 Efferent
pathway
parasympathetic
can
be
sympathetic
or
 Main difference: visceral reflex arc has two neurons in the
motor pathway
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
The 2 divisions of the ANS exit the spinal cord
in different regions
 There are 2 anatomical differences between the 2
branches:
 The point of origin in the CNS
 Location of autonomic ganglia
Copyright © 2010 Pearson Education, Inc.
Anatomy of ANS
Division
Origin of Fibers
Length of Fibers
Location of
Ganglia
Sympathetic
Thoraco -lumbar
region of the spinal
cord
Short pre - ganglionic
and long post ganglionic
Close to the spinal
cord
Parasympathetic
Brain and sacral
spinal cord
Long preganglionic and
short postganglionic
In the visceral
effector organs
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
The functions of the parasympathetic division
 It is also called the anabolic division
 The functions center on
 Relaxation
 Food processing
 Energy absorption
Copyright © 2010 Pearson Education, Inc.
The major effects of the parasympathetic division
 Constriction of pupils
 Increase secretion of salivary, gastric, duodenal and
intestinal glands, pancreas (both exocrine and endocrine)
and liver
 Increase of digestive system movement (smooth muscle)
 Stimulation of defecation
 Contraction of urinary bladder
 Constriction of respiratory passageways
 Reduction of heart rate and force of contraction
Copyright © 2010 Pearson Education, Inc.
Para sympathetic functions
Copyright © 2010 Pearson Education, Inc.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/PNS.html
Parasympathetic Division Outflow
Cranial
Outflow
Sacral
Outflow
Cranial Nerve
Ganglion
Effector
Organ(s)
Effect on
effector
Occulomotor (III)
Ciliary
Eye (iris)
Constrict pupil
Facial (VII)
Pterygopalatin
Submandibular
Salivary, nasal, Increase
secretion
and lacrimal
glands
Glossopharyngeal
(IX)
Otic
Parotid salivary Increase
secretion
glands
Vagus (X)
Located within the
walls of target organs
Heart, lungs,
and most
visceral organs
Decrease HR,
constrict
bronchioles
S2-S4
Located within the
walls of the target
organs
Large intestine,
urinary bladder,
ureters, and
reproductive
organs
Increase motility
and secretion of
the GI tract,
release of urine,
erection
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Cranial Outflow
Sacral Outflow
Copyright © 2010 Pearson Education, Inc.
Figure 14.4
Parasympathetic pre and post-ganglionic receptors
(nACh)
(mACh)
(nACh) (mACh)
Copyright © The McGraw-Hill Companies, Inc
Copyright © 2010 Pearson Education, Inc.
Break down of ACh


The effect of ACh is short-lived

Inactivated in the synapse by the enzyme
acetylcholinesterase (AChE)

Inactivated
in
cholinesterase
the
surrounding
tissues
The effect of the parasympathetic division is localized
and lasts about 20 msec.
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Parasympathetic drugs
 Modes of action:
 direct agonistic action on the receptor (pilocarpine
and methacholine)
 Indirect agonists work by inactivation of
acetylcholinesterase (enzyme that breaks down
acetylcholine), resulting in accumulation of
acetylcholine in synaptic cleft
 antagonist drugs (for example atropine) block the
muscarinic receptors and thus block the action of
Ach
Copyright © 2010 Pearson Education, Inc.
Drugs affecting the parasympathetic nervous system
 Nicotinic receptors:
 Agonists at muscles will cause contraction
 Antagonists at muscles will cause paralysis.
 Muscarinic receptors:
 Agonists will cause increased bowel and bladder
function, decreased HR, bronchoconstriction, and
miosis.
 Antagonists will cause constipation, urinary
retention, increased heart rate, bronchodilation, and
dilated pupils
Copyright © 2010 Pearson Education, Inc.
Sympathetic division functions
 Involves E activities – exercise,
emergency, and embarrassment
excitement,
 Increases mental alertness
 Increases metabolic rate
 Activates energy reserves
 Increase respiratory rates and dilate respiratory
passageways
 Increase heart rate and blood pressure
 Activate sweat glands
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/PNS.html
Sympathetic division anatomy
 The preganglionic cell bodies are located in the lateral horn
of segments T1 and L2 (thoracolumbar outflow).
 Ganglionic neurons cell bodies are in 3 locations:
 Paired Chain ganglia on both sides of the spinal cord
 All preganglionic fibers go through the chain ganglia.
 Unpaired Collateral/prevertebral ganglia found anterior
to the vertebral column
 Adrenal medulla – modified sympathetic ganglion that
release NT into the blood
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Organization of the sympathetic division
 After passing through the intervertebral foramen the
ventral ramus gives rise to a myelinated white ramus
 The white ramus carries the preganglionic axons to a
sympathetic chain ganglion
 The preganglionic fibers diverge extensively and can
synapse on several ganglionic neurons
Sympathetic Trunks and Pathways
A preganglionic fiber follows one
of three pathways upon entering the
paravertebral ganglia
1. Synapse with the ganglionic
neuron within the same ganglion
2. Ascend or descend the
sympathetic chain to synapse in
another chain ganglion
3. Pass through the chain ganglion
and emerge without synapsing
Copyright © 2010 Pearson Education, Inc.
Figure 14.6
Chain ganglia
 2 possible pathways
 in both the synapse can be either on the same segment or in
a different one (pathways 1 or 2)
 postganglionic unmyelinated fibers return via gray ramus to
the spinal nerve (about 8% of each spinal nerve fibers are
sympathetic postganglionic)
 postganglionic fibers innervate structures in the body wall,
head, neck and limbs (sweat glands, superficial blood
vessels, arrector pilli muscle, skin)
 postganglionic unmyelinated fibers do not return but create
sympathetic nerves
 Those innervate structures in the thoracic cavity
Copyright © 2010 Pearson Education, Inc.
2
1
Collateral ganglia
 Postganglionic fibers that follow the third pathway
synapse in the collteral/prevertebral ganglia
 Those ganglia are not paired and they are found only
in the abdominal and pelvic regions
 They are close to the spinal cord
 As a result the postganglionic fibers are longer than
the preganglionic one
Copyright © 2010 Pearson Education, Inc.
1&2
3
Copyright © 2010 Pearson Education, Inc.
Figure 14.5
Pathways with Synapses in the Adrenal Medulla
 Some preganglionic fibers pass directly to the adrenal
medulla without synapsing
 Upon
stimulation,
medullary
cells
secrete
norepinephrine and epinephrine into the blood
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Sympathetic pre and post-ganglionic receptors
(nACh)




(nACh)
Copyright © The McGraw-Hill Companies, Inc
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Recept Found in
or
Sensitivity Effect
1
Most sympathetic NE>E
target tissue
Smooth muscle contraction
2
Digestive system
and pancreas
NE>E
Smooth muscle contraction
1
Heart muscle,
kidney
NE=E
Heart muscle contraction
2
Smooth muscle of E>NE
some organs
Smooth muscle relaxation
3
Adipose tissue
lipolysis
Copyright © 2010 Pearson Education, Inc.
NE>E
Unique Roles of the Sympathetic Division
 only sympathetic fibers are found on:
 The adrenal medulla, sweat glands, arrector pili muscles,
kidneys, and most blood vessels
 The sympathetic division controls
 Thermoregulatory responses to heat
 Release of renin from the kidneys and increased blood
pressure
 Metabolic effects
 Increases metabolic rates of cells
 Raises blood glucose levels
 Mobilizes fats for use as fuels
Copyright © 2010 Pearson Education, Inc.
Drugs that act on the sympathetic division
 Agonists can work in 2 ways:
 Direct -mimic E, NE function on receptors
 Indirect – cause release of NE from storage vesicles
 Antagonists can:
 Prevent synthesis and storage of NE
 Block release of NE
 Block receptors
Copyright © 2010 Pearson Education, Inc.
Example of Drugs affecting the sympathetic nervous system
• Alpha 1 receptors –
• agonists will raise BP,
• antagonists will lower BP
• Beta 1 receptors –
• agonists will increase heart rate and strength of
contraction,
• antagonists will decrease heart rate and BP
• Beta 2 receptors –
• agonists will increase respiratory airflow, will increase
blood flow to skeletal muscles (via blood vessels dilation)
• antagonists will constrict respiratory flow
Copyright © 2010 Pearson Education, Inc.
Interactions of the Autonomic Divisions
 Most visceral organs have dual innervation
 Dynamic antagonism allows for precise control of visceral
activity
 Sympathetic tone (vasomotor tone)
 Keeps the blood vessels in a continual state of partial
constriction
 Parasympathetic division normally dominates the heart and
smooth muscle of digestive and urinary tract organs
 Slows the heart
 Dictates normal activity levels of the digestive and urinary
tracts
 The sympathetic division can override these effects during times
of stress
Copyright © 2010 Pearson Education, Inc.
More ANS neurotransmitters
Transmitter
Functions
nitric oxide (NO)
parasympathetic - important in erection and in gastric emptying. Activates
guanylate cyclase.
vasoactive intestinal polypeptide
(VIP)
parasympathetic - co-release with ACh affects salivation; also in sympathetic
cholinergic fibres. May be important throughout the gastrointestinal tract.
adenosine triphosphate (ATP)
sympathetic - blood vessels and vas deferens. Co-released with catecholamines.
neuropeptide Y (NPY)
sympathetic - facilitates effect of noradrenaline (co-released). Causes prolonged
vasoconstriction.
serotonin (5HT)
important in enteric neurones (peristalsis)
gamma-amino butyric acid (GABA)
enteric.
dopamine
May mediate vasodilatation in the kidney
gonadotropin releasing hormone
(GnRH)
co-transmitter with ACh in sympathetic ganglia.
Substance P
sympathetic ganglia, enteric neurones
calcitonin gene related peptide
(CGRP)
contributes to neurogenic inflammation
Copyright © 2010 Pearson Education, Inc.
NT-receptor interaction - heart
2
Sympathetic presynaptic
nerve terminal
M2
NE
+
1
2
+ +
ACh
-
parasympathetic nerve
terminal
Copyright © 2010 Pearson Education, Inc.
M2
1
+
2
-