EFFERENT NERVOUS SYSTEM (ANS & MOTOR) (1) (1).pdf

anatomy

1. Dr. F. O. Alkizim
Deptof Medical Physiology
JKUAT
EFFERENT NERVOUS SYSTEM

2. 7/20/20192
Divisions of the nervous system
Motor Sensory

3. Introduction
The body has 2 efferent nervous systems:
Somatic nervous system; which is voluntary under conscious
control with a single neuron from the CNS to the effector
organ (muscle fiber).
Autonomic nervous system; which involuntary controlled by
the CNS to regulate primarily visceral functions.
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4. SOMATICN. S. AUTONOMIC N. S.
Control Voluntary Involuntary
Neurons Singleneuron for each effector
organ
Two neurons (Pre and post
ganglionic neurons)
Effectororgans Skeletal muscles Smooth muscle, cardiac muscle
& glands.
Neurotransmitters and
receptors
Acetylcholine
Nicotinic receptors
Ach, NE, Epinephrine, ….
Adrenergic and cholinergic
Neuroeffector junctions
Single neuron, discrete with
well organized specific
receptors at effectororgan
(motor end plates)
Neurons overlap, diffuse
branchingnetworks with
varicosities with widely
distributed receptors on the
target tissue.
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5. Somatic orautonomic nervous system?
A
B
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6. Divisions of the ANS
The two main divisions of the ANS are:
Sympathetic N. S.: which prepares your body for activity in
stressful situations (in fright, fight or flight).
Parasympathetic N. S.: whose overall function is to conserve
energy and regulate vegetative activities like eating and sleeping.
The third division is the enteric nervous system located
in the gastrointestinal tract plexus.
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7. PARASYMPATHETIC N. S.
A division of the ANS that
regulates restorative, energy
conserving, vegetative functions.
The pre-ganglionic neurons have
a craniosacral origin from the
nuclei of the 3
rd
, 7
th
, 9
th
and 10
th
cranial nerves for he cranial part
and
The sacral part originates from
S2,3,4 roots of the pelvic plexus.
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8. Autonomic ganglia of PNS
They are located in or very close to the effector organs.
This makes the pre-ganglionic neuron very long and the post
ganglionic neuron short.
They include ciliary, pterygopalatine, submandibular and otic
ganglia among others.
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9. Neurotransmitters of PNS
The pre-ganglionic neurons release Acetylcholine.
The post-ganglionic neurons’ varicosities release both:
Classic neurotransmitters:
Acetylcholine from small clear vesicles. Ach binds to muscarinic
receptors and effect the physiological function.
NE
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10. Receptors of PNS
The post-ganglionic neurons have nicotinic receptors.
The effector organs of the PNS all have muscarinic receptors.
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11. SYMPATHETIC N. S.
A division of the ANS that mobilizes the
body for activity and managing stressful
situations.
Commonly referred to as the fight/flight
response.
The pre-ganglionic neurons originate from
Thoracolumbar segment of the spinal cord
leaving through the ventral motor roots and
white rami. (From T1 through to L3).
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12. Autonomic ganglia of SNS
The pre-ganglionic neurons synapse with the paravertebral
ganglia (the sympathetic chain) and some synapse on the
adjacent prevertebral ganglia.
The prevertebral ganglia include cervical, celiac, superior
mesenteric and inferior mesenteric ganglia.
These ganglia are very close to the spinal cord making the
pre-ganglionic neurons very short and the post-ganglionic
neurons long. (unlike in PNS).
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13. Neurotransmitters of SNS
The pre-ganglionic neurons release Acetylcholine.
The post-ganglionic neurons’ varicosities release both:
Nor epinephrine: from small clear vesicles.
Ach in sweat glands
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14. Receptors of SNS
The post-ganglionic neurons have nicotinic receptors.
The effector organs of the SNS have adrenoceptors (α& β) .
There are muscarinic receptors specifically for sweat glands.
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15. Adrenal medulla
SNS pre-ganglionic neurons from T5-9 travel through the
greater splanchnic nerve to innervate the chromaffin cells of
the adrenal medulla via Ach on nicotinic receptors.
The chromaffin cells then release Epinephrine (80%) and NE
(20%).
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16. Sympathetic innervation of the adrenal medulla
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17. Areas innervated by the ANS
Eyes
Lachrymal glands
Bronchioles
Heart
GIT
Liver
Kidney
Adipose tissue
Vascular smooth muscles
Bladder
etc
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18. Organ systems innervation
The two arms of the autonomic nervous system work together in
a reciprocal or synergistic fashion in the control of daily
physiological activitiese.g
Sino atrial node in the control of heart rate.
Maintaining the pupil size optimum for vision.
Bronchi
GIT
Bladder etc
There are instances in which the SNS acts alone like in sweat
glands, vascular smooth muscles….
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20. AUTONOMIC RECEPTORS
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The main receptors in the ANS are:
Adrenoceptors for the sympathetic nervous system
αand βreceptors
Cholinoceptors for parasympathetic nervous systems.
Nicotinic and muscarinic receptors

21. Big picture
7/20/201921
1.PNS effector organs have muscarinic receptors
2.SNS effector organs have multiple receptors; α1, α2, β1, β2
and afewmuscarinic receptors (which one?)
3.Among SNS the adrenoceptors are related to the function:
The α1: for contraction of smooth muscles in blood vessels, GI &
bladder sphincters, Radial muscles of the iris, etc
The α2: GI sphincters, pancreas etc
The β1: metabolic functions such as gluconeogenesis, lipolysis,
renin secretion, heart etc
The β2: relaxation of smooth muscles in bronchioles, GIT and
urinary bladder walls.

22. Adrenoceptors
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The α1 receptors
Are coupled to Gq proteins which they activate
leading to release of 2
nd
messengers DAG, IP3 and
calcium which enable the physiological effect to occur
as shown.

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The α2 receptors:
Are coupled to Gi proteins which inhibit adenylyl cyclase
leading to ↓cAMP thereby producing the final effect of
relaxation in the GIT wall.
The β1 receptors:
Are coupled to Gs proteins which activates adenylyl cyclase
leading to ↑cAMP ---protein kinases activation and finally
tissue specific physiological effects.

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Receptor Agentsthat augment
activity (agonists)
Agents thatdepress activity
(antagonist)
α1 Methoxamine
Phenylephrine
Prazosin
α2 Clonidine (Catapress) Yohimbine
Bothα1 andα2 Phentolamine
Phenoxybenzamine
β1 Atenelol
β2 Butoxamine
Both β1 and β2 Isoproterenol Propanolol
Examples of drugs acting on the adrenoceptors

27. CHOLINOCEPTORS
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These are receptors activated by the ligand acetylcholine and
they are:
Nicotinic receptors: Located on NMJ (motor end plates), all
autonomic ganglia and on the chromaffin cells of the adrenal
medulla.
Muscarinic receptors: Located on all the effector organs of the
PNS (heart, GIT, bronchioles, bladder, male sex organ) and on
the SNS effector organ the sweat glands.

28. Nicotinic receptors
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The nicotinic receptors on the NMJ and those on autonomic
ganglia are similar in that they are activated by the same agents
(Ach, Nicotine and Carbachol) BUT
They are not identical in that some agents can block the activity at
the ganglia but not at the NMJ and others block activity at NMJ
but not at the ganglia.
Hence the concept of ganglion blocking agents vs. neuromuscular
blocking agents utilized in anesthesia and treatment of
hypertension.

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What is their mechanism of action?
The receptors are integral proteins of the cell membrane
forming ion channels for Na+ and K+ ions.
The receptor has 5 subunits (2α, β, δand γ)
Ach binds on the 2 subunits causing a conformational change
that opens up the ion channels allowing the Na+ and K+ to
move freely along their electrochemical gradient which leads to
depolarization and the intended physiologic response occurs.

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31. Ionotropic Channels
NT

32. Ionotropic Channels

33. Muscarinic receptors
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Where are they located?
Several types have been described; M1 (brain), M2 (heart),
M4 ( pancreatic islets and acini) and M3 &4 on smooth
muscles.
MOA:
Some act like α1adrenoceptors through G proteins and 2
nd
messengers.
Others act directly on the G protein without 2
nd
messengers
e.g. the muscarinic receptors of the SAN.

34. SAN
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Ach binds on the muscarinic (M2) receptors which lead to Gi
protein activation.
The αisubunit of the Gi protein binds directly to the K+
channels of SAN
The K+ channels open leading to a slower rate of
depolarization thence reduced heart rate.

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Receptor Agentsthat augment
activity (agonists)
Agents thatdepress activity
(antagonist)
Nicotinicreceptors Nicotine
Carbachol
Hexamethonium
Muscarinicreceptors Atropine
Scopolamine (hyoscin)
Ipratropium
Examples of drugs acting on the cholinoceptors

36. Clinical: Explain her symptoms.
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A woman planning a 10-day cruise asks her physician for
medication to prevent motion sickness. The physician
prescribes scopolamine, a drug related to atropine, and
recommends that she take it for the entire duration of the
cruise. While taking the drug, the woman experiences no
nausea or vomiting, as hoped. However, she does experience
dry mouth, dilation of the pupils (mydriasis), increased heart
rate (tachycardia), and difficulty voiding urine.

37. Revision Questions
Compare and contrast the anatomic organization of the two
arms of the autonomic nervous system (10 mks).
Demonstrate how the two arms of ANS work together in the
urinary bladder for Micturition to occur smoothly. (7 mks)
What is pheochromocytoma? (2 mks)
Explain the genesis of the symptoms based on your
knowledge on autonomic nervous system (5 mks).
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38. Revision Questions
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State the general distribution of the autonomic receptors
(5marks).
With the aid of a simple diagram, discuss the structure and
mechanism of action of the nicotinic receptors. (7 marks)
Discuss the effect on autonomic nervous system functioning
and the resulting symptoms that would occur if you gave a
ganglion blocking agent like hexamethonium to your patient.

39. MOTOR SYSTEM
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40. Introduction
Visible movement
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41. All parts of the CNS
participate
Voluntary actions by higher brain
Involuntary actions by spinal
cord (reflexes)
Monosynaptic
Polysynaptic
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42. Spinal cord
Segmental organization:
Circuits confined to single or several neighboring segments e.g.
basic spinal reflexes.
Descending motor tracts:
Interact with spinal circuits to control voluntary movement &
unconscious motor aspects such as muscle tone.
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43. Muscle fibers:
Extrafusal: larger, contract to generate force
Intrafusalfibers: muscle spindles
For proper control of muscle function, both required as latter
gives info on muscle length, and change in length.
Golgi tendon organs required for tension
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Each spindle is 3-10mm long.
It is built around 3-12 very small intrafusalmuscle
fibresthat surrounded by large extrafusialfibres.
Nuclear bag & chain
At centreof intrafusalfibresis an area of no actin or
myosin hence not contractile. Senosory.
Contractile ends inervatedby gamma motor nerve
fibres(efferent)-keeps fibrestensed.
Sensory inervatedby type Ia(nuclear bag) and II
(nublearchain)

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47. Muscle spindle
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51. Golgi tendon reflex
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Encapsulated receptor in which 10-15 tendon
fibrespass
Detects fibretension.
Innervated by type Ibfibres.
Stimulates an inhibitory interneuron and then
anterior horn leading to lengthening reaction to
prevent tearing of tendon and avulsions

52. Golgi tendon
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54. Flexor-withdrawal reflex
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56. Cortical
Conscious control
PMC(Bma-4) –Specific
Premotor (BMa-6) -excites
pattern
Supplementary -Postural
Descending motor pathways
Pyramidal
Extra pyramidal tracts
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58. Pyramidal tracts:
Passthroughthemedullary
pyramidsastheydescendontothe
LMNinthespinalcord
Corticospinaltract-BraintoSC.
Anterior
Lateral
Corticobulbar-conductsimpulses
tocranialnervesforfacial&neck
muscles
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59. Corticospinal
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Fibresoriginate at pyramidal cells of cortex where cell
bodies located Posterior limb of internal capsule 
Brain stem Anterior medulla forming prominent
pyramids Decussate (80%) to form lateral or proceed as
anterior Upper motor neuronSynapse with LMN

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61. Extrapyramidal tracts: modulation and regulation of
anterior horn
Rubrospinaltracts:
Red nucleus to LMN in lateral spinal cord (up to cervical)
Rudimentary in humans –alternative pathway
+ flexor muscles; -extensors
Reticulospinaltracts: Reticular formation to LMN of postural
muscles
Pontine: Pons nuclei to LMN in ventromedial spinal cord
Exitatoryto antigravity muscles
Medullary reticulospinaltracts: Medullary reticular formation
to LMN in spinal cord
Inhibitory
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62. Vestibulospinaltracts:
Vestibular nucleus –SC.
Posture
Tectospinal(colliculospinal)tracts:
Superior –Visual reflex
Inferior –Auditory reflex
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64. Effects of transections:
UMNL
LMNL
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65. ASSIGNMENT
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