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Peripheral Nervous System
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Sensory
Afferent
Dorsal root
Peripheral
nervous
system (PNS)
Motor
Efferent
Dorsal root
ganglia
where cell
body of
sensory
neuron is
located
Somatic Motor
Ventral root
Autonomic Motor
interneuron
Skeletal muscle
smooth
muscles,
cardiac
muscles, and
glands
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Efferent division of PNS is divided:
somatic NS & autonomic NS.
1-Somatic neurons innervate skeletal
muscles,
2-Autonomic neurons innervate smooth &
cardiac muscle, glands, and GIT (Enteric
NS ).
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Somatic Division
1. Innervates skeletal muscles: Conscious of its
activity.
2. Only one motor neuron to effector (no gangalia)
3. NT: only Ach
4. Only stimulatory/excitatory signals
5. Fast-conducting, thick (9-13 um), myelinated
axons (A fibers).
6. Severing neurons causes muscle paralysis
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Autonomic Division
1-Innervates glands, smooth, & cardiac muscles. Usually
unaware of its actions.
2-Two motor neurons control effector (ganglion).
3-NT: Ach, norepinephrine & epinephrine.
4-Stimulatory & inhibitory signals.
5-Slow-conducting: preganglionic thin (3 um) (B fibers); ,
lightly myelinated axons; postganglionic very thin (1 um),
unmyelinated axons (C fibers).
6- Denervation causes muscle hypersensitivity of effector. A
phenomena called (Denervation hypersensitivity)
Neurons & Nervous
Systems
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Neurons & Nervous
Systems
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Neurons & Nervous
Systems
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The autonomic nervous system( ANS( )or Visceral
nervous system)
ANS is the part of the peripheral nervous system that acts as a
control system, maintaining homeostasis in the body. These
activities are generally performed without conscious control
or sensation.
The ANS affects heart rate, digestion, respiration rate,
salivation, perspiration, diameter of the pupils, urination, and
sexual arousal .
ANS main components are parasympathetic nervous system
and sympathetic nervous system
Autonomic system
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The sympathetic and parasympathetic systems are
similar in the following aspects:
a.
Both function automatically and usually in an
involuntary manner.
b. Both innervate all internal organs. Visceral organs
(organs within body cavity).
c. Breathing rate and blood pressure are regulated by
reflex actions to maintain homeostasis.
d. Both utilize two neurons and one ganglion for each
impulse.
1)
The first neuron has a cell body within the CNS: it
is called preganglionic neuron and it sends a
preganglionic fiber.
2) The second neuron has a cell body within the
ganglion it is called postganglionic neuron and it
sends a postganglionic fiber.
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preganglionic
Autonomic neuron
effector
neuron
Preganglionic
Postganglionic
Autonomic
Axon will
neuron has a
Axon will
neuron
in
cell body
synapse
synapse with
Autonomic
within
cell within
Ganglion
is
Autonomic
target tissue
called
Nuclei in
postganglio
the gray
nic neuron
matter
of brain or
spinal cord.
Autonomic Nerve Pathway
Two-neuron chain
Sympathetic Division
1. Sympathetic preganglionic fibers are cholinergic;
postganglionic fibers are adrenergic (NT: norepinephrine )
2. Sympathetic division activates body to fight or flight through
adrenergic effects.
3. Too much stimulation cause aging
4. To defend or flee, muscles need a supply of glucose and
oxygen; the sympathetic system accelerates heartbeat, and
dilates bronchi.
5. To divert energy from less necessary digestive functions, the
sympathetic system inhibits digestion.
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6. Preganglionic neurons of sympathetic division originate in
thoracic & lumbar regions (T1-L2) (thoracolumbar division).
7. Preganglionic fibers are short.
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8. Most terminate in sympathetic ganglia that lies parallel the spinal cord, that is,
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preganglionic fibers synapse with ganglia located in two sympathetic chains close
to the spinal cord (double rows called paravertebral ganglia).
Some ascend/descend within sympathetic trunk to synapse with another paravertebral
ganglion.
Others pass through the ganglion and emerge from the sympathetic chain without
synapsing.
9.Synapses in Paravertebral (sympathetic chain) Ganglion: 19
Postganglionic axons enter the ventral ramus of the joining
spinal nerves via communicating branches called gray rami
communicantes .
The ganglia are distinguished as cervical, thoracic, lumbar, and
sacral
The ganglia are distinguished as cervical, thoracic, 20
lumbar, and sacral
Preganglionic fiber serving head, neck, and thorax emerge from21
spinal cord segments T1-T6 and ascend the sympathetic chain
to synapse with postganglionic neurons within cervical ganglia
(inferior, middle, and superior)
- Superior cervical
ganglion:
 Stimulates dilator
muscles of irises
 Inhibits nasal and
salivary glands
 Stimulates copious
sweating
 Stimulates arrector
pili muscle to
contract
 Causes blood
vessel vasodilation
 Provides branches
to carotid body
(oxygen sensor)
and larynx &
pharynx.
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Middle cervical ganglia - innervates heart and skin
Inferior cervical ganglia innervates heart, aorta, dilates
bronchioles, constrict esophageal sphincter
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10-Synapses in Prevertebral (Collateral) Ganglion:
 Preganglionic fibers of T5-L2 synapse in prevertebral ganglia.
Fibers enter and leave without synapsing and form several
nerves collectively called splanchnic nerves (greater, lesser,
and lumbar).
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Greater splanchnic nerve
Celiac ganglion - innervates
1-stomach (decrease muscle
activity/constricts pyloric
sphincter),
2-adrenal medulla (secretes
epinephrine/norepinephrine),
3-liver (epinephrine stimulates
liver to release glucose),
4-kidney (vasoconstriction,
decrease urine output),
5-intestine (decrease smooth
muscle activity).
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Lesser
splanchnic
nerve
Superior
mesenteric
(via celiac)
ganglion innervates
small
intestine
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•Lumbar
splanchnic nerve
Inferior
mesenteric
ganglion innervates
large intestine
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- Lumbar splanchnic
nerve
 Hypogastric
ganglion innervates
bladder and
urethra (causes
relaxation of
smooth muscle
of bladder wall
and constricts
urethral
sphincter/inhibits
voiding),
genitalia (causes
ejaculation in
males and
vaginal
contractions in
females)
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Adrenal gland: Located above each kiddney
Upon stimulation by Sympathetic system:
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A- Cortex: releases steriod hormones
B- medulla: releases adrenaline (epinephrine) 85% and
norepinephrine 15% they differ slightly from each other
and termed catacholamines
Sympathetic system and Adrenal gland together are
called Sympathoadrenal system
Stimulation of the adrenal medulla releases adrenaline
(epinephrine) into the bloodstream which will act on
adrenoceptors, producing a widespread increase in
sympathetic activity.
Parasympathetic Division
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1. Pre- & postganglionic parasympathetic fibers are cholinergic
(secrete Ach)
2. The neurotransmitter released is acetylcholine.
3. Parasympathetic exerts antagonistic actions via cholinergic effects
(house keeping).
4. It promotes internal responses resulting in a relaxed state.
5.
The parasympathetic system causes the eye pupil to constrict,
promotes digestion, and retards heartbeat.
1. (Craniosacral division): Preganglionic neurons originate in brain
stem (CN III, VII, IX, X)
III oculomotor 3
VII facial, 7
IX, glossopharyngeal; 9
X, vagus;10
and 2-4 sacral region of spinal cord.
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7. Preganglionic fibers are long. They synapse in ganglia that
contains the postganglionic neurons which are found in
 terminal ganglia: are located close to the target organ
 intramural ganglia: located within the wall of the target organ
7.
Postganglionic fibers are short. E.g fibers that innervate the
digestive tube, are located inside its walls.
8. Cutaneous effectors such as arrector pili, sweat glands, and blood
vessels do not get Parasympathetic innervations.
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10. The vagus (X) nerve synapses in terminal ganglia located in
so many regions of the body (heart, lungs, esophagus,
stomach, liver, small intestine, and upper half of the large
intestine).
11. Parasympathetic outflow from the sacral levels of the spinal
cord innervates the lower half of the large intestine, rectum,
urinary, and reproductive systems.
12. The parasympathetic fibers within III oculomotor 3 ,VII
facial, 7 and IX, glossopharyngeal; synapses in ganglia
located in the head.
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pterygopalatine
ganglia
Parasympathetic (Craniosacral Division)
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Cranial Outflow
 Oculomotor nerve (III)
- Preganglionic fibers from oculomotor nuclei in the midbrain
synapses in the ciliary ganglion (in eye), postganglionic
fiber innervates smooth muscle of eye
 Pupil constriction and lens movement to cause focusing
 Facial nerve (VII)
- Preganglionic fibers from lacrimal nuclei in the pons
synapses in the pterygopalatine ganglia, postganglionic
fiber innervates lacrimal glands of eye
 Lubrication of eye and tear formation
- Preganglonic fibers from superior salivatory nuclei in the
pons synapses in the submandibular ganglia,
postganglionic fibers innervate submandibular and
sublingual salivary glands
 Production of saliva and secretion of salivary enzymes
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 Glossopharyngeal nerve (IX)
- Preganglionic fibers from the inferior salivary nuclei in
the medulla synapses in the otic ganglia,
postganglionic fibers innervate the parotid salivary
gland.
 Vagus nerve (X)
- Preganglionic fibers from the dorsal motor nuclei of
the medulla synapses in terminal ganglia located
within the walls of the target organ
 Intramural ganglia ....effects:
1. Heart -decreases heart rate and constricts
coronary veins
2. Lung - constricts bronchioles
3. Gall bladder - expel bile
4. Stomach - stimulates secretion of enzymes
5. Intestines - increase motility (peristalsis) and
relaxes sphincters
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Sacral Outflow
Preganglionic fibers from lateral gray matter of
spinal cord in segments S2-S4 synapse in
ganglia within walls of the target organ
- Intramural ganglia....effects:
1. Distal large intestines - relaxes sphincters
2. Bladder - contraction of smooth muscle of
bladder wall; relaxes urethral sphincter promotes voiding
3. Genitalia - causes penile and clitoral
erection
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Response to Adrenergic Stimulation
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Adrenergic effects (epinephrine from adrenal gland) and
norepinephrine ) of sympathetic nerves include both excitatory and
inhibitory effects. Stimulation of the heart, vasoconstriction in the
viscera and skin, and glycogenolysis in the liver. (is the break down of
glycogen to glucose-1-phosphate and glucose) . The smooth muscles of bronchoils
and some blood vessels are inhibited from contraction resulting in bronchodilation,
vasodilation.
Adrenergic receptor classes are α and β. Some organs have only α or β
receptors; other organs (heart) have both types of receptors.
There are two subtypes of alpha receptors )α 1 and α 2) and two
subtypes of beta receptors )β 1 and β 2).
These subtypes can be selectively stimulated or blocked by therapeutic
drugs.
Examples:
Heart (ß1), muscle of iris (α1), smooth muscle of blood vessels (α1) are
stimulated to contract, smooth muscle of bronchioles (ß2) dilates.
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Adrenergic Receptors
o α1  Excitatory; e.g., arteriolar constriction
o α2  Inhibitory; e.g., GI smooth muscle
o β1  Excitatory; e.g., increased rate and force of
cardiac contraction
o β2  Inhibitory; e.g., arteriolar & bronchiolar
(dilation)
Response to cholinergic stimulation
Acetylcholine is the preganglionic neurotransmitter for
both divisions of the ANS, as well as the
postganglionic neurotransmitter of parasympathetic
neurons .
Nerves that release acetylcholine are said to be
cholinergic .
In the parasympathetic system, ganglionic neurons use
acetylcholine as a neurotransmitter, to stimulate
muscarinic receptors.
Ach binding to muscarinic receptors located in cardiac
muscle  hyperpolarization  Inhibitory signals 
slow heart rate
Ach binding to muscarinic receptors located in smooth
muscle and glands  depolarization  excitatory
signals  contraction
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Autonomic agonists and antagonists
 Agonist
Binds with a neurotransmitter’s receptor and elicits an
effect that mimics that of the neurotransmitter.
 Antagonist
Binds with a neurotransmitter’s receptor and blocks the
neurotransmitter’s response.
Autonomic agonists and antagonists
 Atropine
oBlocks the effect of acetylcholine at muscarinic
receptors but does not affect nicotinic receptors
oSuppresses salivary and bronchial secretions
before surgery, to reduce the risk of a patient
inhaling these secretions into the lungs
Autonomic agonists and antagonists
 Salbutamol
oSelectively activates β 2 adrenergic receptors at
low doses
oDilate the bronchioles in the treatment of asthma
without undesirably stimulating the heart
Other autonomic neurotransmitters
• Certain postganglionic fibers do not produce
their effect through Acetylcholine or
norepinephrine, hence they are termed
nonadrenergic, noncholinergic fibers .
• Proposed NT of these fibers include,
vasoactive intestinal peptide (VIP), and Nitric
oxide (NO).
• NO causes vasodilation of cerebral arteries. It
promotes relaxation of smooth muscles.
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• ORGANS WITH DUAL INNERVATION.
• Most organs receive DUAL INNERVATION
• ORGANS WITHOUT DUAL INNERVATION
• some organs receive only sympathetic innervations.
• Adrenal medulla, arrector pili muscle, sweat glands,
and most blood vessels.
• Regulation in these cases is achieved by increasing or
decreasing the tone (firing rate) of sympathetic fibers.
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Control of autonomic system by higher brain centers
Visceral functions are largely regulated by autonomic
reflexes.
Sensory input is transmitted to brain centers that
integrate this information and respond by modifying
the activity of preganglionic autonomic neuron
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The medulla oblongata is the area that directly controls the
activity of the autonomic system. Medulla is regulated by
higher brain areas, these include the hypothalamus
cerebellum, and cerebrum.
located in medulla are centers for the control of the
cardiovascular, pulmonary, reproductive ,urinary and
digestive systems. Mush of the sensory input of these
centers travels in the afferent fibers of the vagus nerve.
Since medulla oblongata controls the activity of the
autonomic motor fibers a reflex takes place.
The hypothalamus is influenced by input from the limbic
system (group of forebrain nuclei and fiber tracts that form a
ring around brain stem)
The limbic system is involved in basic emotional drive.
These interconnections provide an autonomic component to
some of the visceral responses that accompany emotions.
limbic system
hypothalamus
medulla
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Medulla is also regulated by higher brain areas,
which are the cerebellum, and cerebrum
Nerve impulses from cerebellum to Medulla affect
motion sickness, Nausea, sweating, and CV
changes.
Frontal and temporal lobes of cerebral cortex are
involved in personality.
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‫ غير مطلوب ولكن للعلم فقط‬Brain-computer interface
Amyotrophic lateral sclerosis (ALS, also called Lou Gehrig’s
Disease) is a neurological disease characterized by the
degeneration of the motor neurons that control voluntary
movements. The disease begins with muscle weakening and
lack of coordination and eventually destroys the neurons that
control speech, breathing, and swallowing; in the end, the
disease can lead to paralysis. At that point, patients require
assistance from machines to be able to breathe and to
communicate. Several special technologies have been
developed to allow “locked-in” patients to communicate with
the rest of the world. One technology, for example, allows
patients to type out sentences by twitching their cheek. These
sentences can then be read aloud by a computer.
A relatively new line of research for helping paralyzed patients,
including those with ALS, to communicate and retain a degree
of self-sufficiency is called brain-computer interface (BCI)
technology and is illustrated in Figure 15. This technology
sounds like something out of science fiction: it allows
paralyzed patients to control a computer using only their
thoughts. There are several forms of BCI.
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Figure 15: With brain-computer interface technology,
neural signals from a paralyzed patient are collected,
decoded, and then fed to a tool, such as a computer, a
wheelchair, or a robotic arm.
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Some forms use EEG recordings from electrodes taped onto the
skull. These recordings contain information from large
populations of neurons that can be decoded by a computer.
Other forms of BCI require the implantation of an array of
electrodes smaller than a postage stamp in the arm and hand
area of the motor cortex. This form of BCI, while more invasive,
is very powerful as each electrode can record actual action
potentials from one or more neurons. These signals are then
sent to a computer, which has been trained to decode the signal
and feed it to a tool—such as a cursor on a computer screen.
This means that a patient with ALS can use e-mail, read the
Internet, and communicate with others by thinking of moving his
or her hand or arm (even though the paralyzed patient cannot
make that bodily movement). Recent advances have allowed a
paralyzed locked-in patient who suffered a stroke 15 years ago
to control a robotic arm and even to feed herself coffee using
BCI technology.
Despite the amazing advancements in BCI technology, it also
has limitations. The technology can require many hours of
training and long periods of intense concentration for the
patient; it can also require brain surgery to implant the devices.
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