Nervous Peripheral System
Outline
Autonomic NS
Sympathetic
Parasympathetic
Neurotransmitters
Somatic NS
Cranial Nerves
Spinal Nerves
Motor Control
Peripheral Nervous System (PNS)
Includes: sensory receptors, peripheral nerves,
associated ganglia, and motor endings
Can be divided into:
Autonomic Nervous System
Somatic Nervous System
Provides links to and from the external environment
Autonomic Nervous System
Efferent innervation of all tissues other than skeletal
muscle
Parallel chains of two neurons connect the CNS and
effector cells
Preganglionic Neuron
Preganglionic Fibers
Autonomic ganglia
Postganglionic Neuron
Postganglionic Fibers
Autonomic Nervous System
Two Divisions
Dual Innervation (sympathetic and parasympathetic)
Two divisions usually activated reciprocally
Autonomic responses usually occur without conscious control
Distinguished by
Their unique origin sites
Relative fiber lengths
Location of their ganglia
Degree of fiber branching
Functional role
Neurotransmitters
Anatomy of ANS
Figure 6.44
Anatomy of ANS
Anatomy of ANS
Division
Origin of Fibers
Length of Fibers
Location of
Ganglia
Sympathetic
Thoracolumbar region of
the spinal cord
Brain and sacral spinal
cord
Short preganglionic and long
postganglionic
Long preganglionic and short
postganglionic
Close to the spinal
cord
In the visceral effector
organs
Parasympathetic
Sympathetic Nervous System
Extensive branching of the preganglionic fibers
Innervates visceral organs in the internal body cavities
and in the superficial part of the body
Anatomy ties the entire system together so that it can act
as a single unit
Role of the Sympathetic Division
The sympathetic division is the fight-or-flight system
Involves E activities exercise, excitement, emergency,
and embarrassment
Promotes adjustments during exercise blood flow to
organs is reduced, flow to muscles is increased
Its activity is illustrated by a person who is threatened
Unique Roles of the Sympathetic
Division
Regulates many functions not subject to
parasympathetic influence
These include the activity of 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
Metabolic effects
Thermoregulatory Responses to Heat
Reflex dilation (local reaction)
Widespread dilation (systemic reaction)
Brings blood vessels to surface
Activates sweat glands (evaporative cooling)
Metabolic Effects
The sympathetic division promotes
metabolic effects that are not reversed by
the parasympathetic division
Increases the metabolic rate of body cells
Raises blood glucose levels
Mobilizes fat as a food source
Stimulates the reticular activating system (RAS)
of the brain, increasing mental alertness
Effects of Sympathetic Activation
Sympathetic activation is long-lasting
because of NE (nor-epi)
Inactivated more slowly than Ach
Indirectly acts (uses second-messenger
system)
Nor-epi and epi are released into blood and
remain until broken down by liver
Parasympathetic Division Outflow
Cranial Output
Run in the oculomotor, facial, glossopharyngeal and
vagus nerves
Oculomotor Nerve III (preganglionic fibers)
Innervate smooth muscles in the eyes that cause the pupils
to constrict and lens to bulge (so that you can focus on
objects close up)
Facial Nerve VII (preganglionic fibers)
Stimulate many large glands in the head
Nasal glands and lacriminal glands
Submandibular and sublingual salivary glands
Parasympathetic Division Outflow
Cranial Output
Glossopharyngeal Nerve IX (preganglionic fibers)
Activate the parotid salivary glands anterior to the ear
Distal ends of the preganglionic fibers from nerve III,
VII and IX jump over to branches of the trigeminal
nerve to synapse with postganglionic fibers in the
trigeminal nerve (V), they travel down the trigeminal
nerve tract to reach the face
Parasympathetic Division Outflow
Cranial Output
Vagus Nerve (X)
Account for about 90% of all preganglionic
parasympathetic fibers
Serve virtually every organ in the thoracic and
abdominal cavities
Have branches that go to the cardiac plexus that
slow heart rate
Have branches that go to the pulmonary plexus
and esophageal plexus
Have branches from the aortic plexus that go to
the abdominal viscera
Parasympathetic Division Outflow
Figure 14.4
Parasympathetic Division Outflow
Sacral Output
Branch of the spinal cord to form the pelvic nerves
that pass through the inferior hypogastric plexus
Have synapses in the distal half of the large intestine,
urinary bladder, ureters and reproduction organs
Made up of relatively independent components
Responses can be quite variable and are tailored to
the demands of the situation
Neurotransmitters and Receptors
Acetylcholine (ACh) and norepinephrine (NE) are the two
major neurotransmitters of the ANS
Cholinergic fibers ACh-releasing fibers
Adrenergic fibers sympathetic postganglionic axons that
release NE
Parasympathetic: ACh at effector
Sympathetic: NE at effector
ACh receptor: Nicotinic
Nicotinic receptors are found on:
Motor end plates (somatic targets)
All ganglionic neurons of both sympathetic and
parasympathetic divisions
The hormone-producing cells of the adrenal medulla
The effect of ACh binding to nicotinic receptors is
always stimulatory
ACh receptor: Muscarinic
Muscarinic receptors occur on all
effector cells stimulated by
postganglionic cholinergic The fibers
effect of ACh binding:
Can be either inhibitory or excitatory
Depends on the receptor type of the target
organ
Adrenergic Receptors
- b1
Location
Heart and Coronary Blood Vessels, kidney, liver and
adipose tissue
Effect
Adrenergic Receptors
- b2
Location
Lungs and most other sympathetic target organs
Abundant on blood vessels serving the heart
Effect
Adrenergic Receptors
- b3
Location
Adipose Tissue
Effect
Stimulates lipolysis by fat cells
- a1
Location
Blood vessels serving the skin
Mucosae, abdominal viscera, kidneys and salivary glands
All sympathetic target organs except the heart
Effect
Constricts blood vessels and visceral organ sphincters
Dilates pupils of the eye
Adrenergic Receptors
- a2
Location
Membrane of adrenergic axon terminals
Blood platelets
Effect
Mediates inhibition of NE release from adrenergic terminal
Promotes blood clotting
Effects of Drugs
Atropine
Neostigmine
Tricyclic antidepressants
Over-the-counter drugs for colds, allergies, and nasal
congestion
Beta-blockers
Homeostatic Imbalances
Hypertension
Can be caused by an overactive sympathetic
vasoconstrictor response promoted by
continuous high levels of stress
Increases the work load on the heart, which
may precipitate heart disease, and increases
wear and tear on the arteries
Homeostatic Imbalances
Raynauds Disease
Characterized by intermittent attacks that cause the skin
of the fingers and toes to become pale then cyanotic
and painful
Caused by exposure to cold or emotional stress
Exaggerated vasoconstriction response
Homeostatic Imbalances
Hirschsprungs Disease
The parasympathetic innervations of the distal
portion of the large intestine fails to develop
The colon is immobile and feces accumulate
prior to the inactive bowel segment
Somatic Nervous System
Cranial Nerves
Twelve pairs of cranial nerves arise from the brain
Two arise from the forebrain and the rest originate from
the brainstem
With the exception of the vagus nerve all serve regions
in the head or neck
Oh Once One Takes The Anatomy Final A Good
Vacation Seems Heavenly
They have sensory, motor, or both sensory and
motor functions.
Cranial Nerves
Figure 13.4a
Cranial Nerve I: Olfactory
Table 13.2(I)
Cranial Nerve II: Optic
Table 13.2(II)
Cranial Nerve III: Oculomotor
Table 13.2(III)
Cranial Nerve IV: Trochlear
Table 13.2(IV)
Cranial Nerve V: Trigeminal
Table 13.2(V)
Cranial Nerve VI: Abducens
Table 13.2(VI)
Cranial Nerve VII: Facial
Table 13.2(VII)
Cranial Nerve VIII: Vestibulocochlear
Table 13.2(VIII)
Cranial Nerve IX: Glossopharyngeal
Table 13.2(IX)
Cranial Nerve X: Vagus
Table 13.2(X)
Cranial Nerve XI: Accessory
Table 13.2(XI)
Cranial Nerve XII: Hypoglossal
Table 13.2(XII)
Spinal Nerves
Thirty-one pairs of mixed
nerves
They are named according
to their point of issue
8 cervical (C1-C8)
12 thoracic (T1-T12)
5 Lumbar (L1-L5)
5 Sacral (S1-S5)
1 Coccygeal (C0)
Figure 13.5
Spinal Nerves
Each spinal nerve connects to the spinal cord by a
dorsal root and ventral root
Spinal nerves are short because after emerging it
divides in three parts
Dorsal ramus
Ventral ramus
Meningeal branch reenters the spinal cord to innervate the
meninges and the blood vessels in the CNS
Innervation of Specific Body Regions
The spinal nerve rami and their main branches
supply the entire somatic region of the body
from the neck down
Dorsal Rami
Supply the posterior body trunk
Ventral Rami
Supply the rest of the trunk and limbs
Innervation of the Back
Innervation follows a neat segmented plan
Each dorsal ramus innervates a narrow
strip of muscle and skin in line with its
emergence point from the spinal column
Innervation of the Anterolateral Thorax and Abdominal Wall
Ventral rami are arranged in a simple
segmental pattern
Form the intercostals nerves and have
cutaneous branches to the skin
Spinal Nerve Innervation: Back, Anterolateral Thorax, and
Abdominal Wall
Figure 13.6b
Cervical Plexus
Formed by the ventral rami of
the first four cervical nerves
Most branches are cutaneous
nerves
Figure 13.7
Cervical Plexus
Branches also innervate the
muscles of the anterior neck
Phrenic nerve
Figure 13.7
Brachial Plexus
Gives rise to almost all the nerves that
innervate the upper limb
Plexus formed from intermixing of ventral rami
from C5-C8 and most of the T1 ramus
Injuries are common when the upper limb is
pulled hard or receives a blow to the top of the
shoulder
Brachial Plexus
Five important nerves
Axillary nerve
Musculotaneous nerve
Median nerve
Ulnar nerve
Radial nerve
Brachial Plexus: Distribution of Nerves
Figure 13.8c
Brachial Plexus: Distribution of Nerves
Figure 13.8c
Lumbar Plexus
Arises from L1-L4 and innervates the thigh, abdominal
wall, and psoas muscle
The major nerves are the femoral and the obturator
Femoral nerve
Obturator Nerve
Figure 13.9
Lumbar Plexus
Figure 13.9
Sacral Plexus
Arises from spinal nerves L4-S4
Has nerves that serve the buttock and lower
limb
Sciatic nerve
Sciatica
Sacral Plexus
Figure 13.10
Skin Innervation - Dermatomes
Dermatomes
Every spinal nerve except C1 innervates
dermatomes
Some overlap between innervation regions
Dermatomes
Figure 13.11
Innervation of Joints
Hiltons law: any nerve serving a muscle that
produces movement at a joint also innervates
the joint itself and the skin over the joint
Summary
PNS
ANS
Sympathetic
Parasympathetic
Neurotransmitters
Somatic
Cranial Nerves
Spinal Nerves