Peripheral Nerve Regeneration The Nervous System...1/18/2016 1 PNS continued The Nervous System...

1/18/2016

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PNS continued

The Nervous System

Peripheral Nerve Regeneration

• Possible if cell body has not been damaged

• Axon underlying myelin sheath can regenerate

Figure 13.4 (1 of 4)

Endoneurium

Droplets

of myelin

Fragmented

axon

Schwann cells

Site of nerve damage

The axon

becomes

fragmented at

the injury site.

1


Schwann cell MacrophageMacrophages

clean out the

dead axon distal

to the injury.

2


Fine axon sprouts

or filaments

Aligning Schwann cells

form regeneration tube

3 Axon sprouts,

or filaments,

grow through a

regeneration tube

formed by

Schwann cells.


Schwann cell Site of new

myelin sheath

formation

4 The axon

regenerates and

a new myelin

sheath forms.

Single enlarging

axon filament

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Neuritis

• Inflammation of a nerve

– Sciatica

– Bell’s Palsy

Shingles

• Varicella Zoster virus

• Dorsal root ganglia

• Consistent with dermatome

• Vaccine

Multiple Sclerosis

• Loss of myelin in CNS � scleroses

– Visual disturbances

– Muscle weakness

• Autoimmune disorder

• Remissions

• Progressive

Central nervous system (CNS) Peripheral nervous system (PNS)

Motor (efferent) divisionSensory (afferent)division

Somatic nervoussystem

Autonomic nervoussystem (ANS)

Sympatheticdivision

Parasympatheticdivision

Figure 14.1

Autonomic Nervous System (ANS)

• Involuntary

• Sensory (afferent) pathways

• Motor (efferent) pathways

• Visceral reflex system

Structure of the ANS

�Sensory (afferent) pathway

� Visceral interoceptors (visceroceptors)

� Osmolarity

� Pressure

� Temperature

� Blood gases

� Chemical composition of plasma and body fluids

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Structure of the ANS

• Sensory (afferent) pathway

– Single sensory neuron from organ to CNS

• Cell body in dorsal root ganglion

• Synapse with association neurons in spinal cord

Figure 12.32

Somaticsensoryneuron

Dorsal root (sensory)

Dorsal root ganglion

Visceralsensory neuron

Somaticmotor neuron

Spinal nerve

Ventral root(motor)

Ventral horn(motor neurons)

Dorsal horn (interneurons)

Visceralmotorneuron

Interneurons receiving input from somatic sensory neurons

Interneurons receiving input from visceral sensory neurons

Visceral motor (autonomic) neurons

Somatic motor neurons


• ANS Motor (efferent) neurons

– Innervate smooth muscle, cardiac muscle and

glands

– Operate via subconscious control

• Efferent (motor) pathway

– Two motor neurons between CNS and effector

• Preganglionic neuron

– Cell body in CNS

• Postganglionic neuron

– Cell body in autonomic ganglion (outside CNS)


Skeletal muscle

Cell bodies in centralnervous system Peripheral nervous system Effect

+

+

Effectororgans

ACh

AChSmooth muscle

(e.g., in gut),

glands, cardiac

muscle

Ganglion

Adrenal medulla Blood vessel

ACh

ACh

ACh

NE

Epinephrine andnorepinephrine

Acetylcholine (ACh) Norepinephrine (NE)

Ganglion

Heavily myelinated axon

Lightly myelinated

preganglionic axon

Lightly myelinatedpreganglionic axons

Neuro-transmitterat effector

Unmyelinated

postganglionic

axon

Unmyelinated

postganglionic axon

Stimulatory

Stimulatory

or inhibitory,

depending

on neuro-

transmitter

and

receptors

on effector

organs

Single neuron from CNS to effector organs

Two-neuron chain from CNS to effector organs

SO

MA

TIC

NE

RV

OU

SS

YS

TE

M

AU

TO

NO

MIC

NE

RV

OU

S S

YS

TE

M

PA

RA

SY

MP

AT

HE

TIC

SY

MP

AT

HE

TIC

Figure 14.2

Motor PathwaysAutonomic Nervous System (ANS)

• Visceral reflex system

– E.g., coughing, sneezing, swallowing, vomitting

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Figure 14.7

Spinal cord

Dorsal root ganglion

Autonomic ganglion

Stimulus

Response

Visceral sensory

neuron

Integration center� Spinal cord grey matter� Within gastrointestinal

tract wall

Sensory receptor

in viscera

2

3

1

5 Visceral effector

Efferent pathway(two-neuron chain)• Preganglionic neuron• Ganglionic neuron

4

A simple visceral reflex arc





Sympatheticdivision


Figure 14.1

Divisions at a Glance

• Sympathetic

– “Fight or Flight”

– NE and acetylcholine

– Thoracolumbar

• Parasympathetic

– “Rest and Digest”

– Acetylcholine

– Craniosacral

Dual Innervation

Salivaryglands

Eye

Skin*

Heart

Lungs

Liverand gall-bladder

Genitals

Pancreas

Eye

Lungs

Bladder

Liver andgall-bladder

Pancreas

Stomach

Cervical

Sympatheticganglia

Cranial

Lumbar

Thoracic

Genitals

Heart

Salivaryglands

Stomach

Bladder

Adrenalgland

Parasympathetic Sympathetic

Sacral

Brainstem

L1

T1

Figure 14.3

Dual Innervation

Cranial Outflow

Nerve Ganglia (Terminal Ganglia)

Effector Organ(s)

Oculomotor (III) Ciliary Eye

Facial (VII) Pterygopalatine Submandibular

Salivary, nasal, and lacrimal glands

Glossopharyngeal (IX)

Otic Parotid salivary glands

Vagus (X) Within the walls of target organs

Heart, lungs, and most visceral organs

Sacral

Outflow

S2-S4

Within the walls of target organs

Large intestine, urinary bladder, ureters, and reproductive organs

Parasympathetic Division Outflow

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Pterygopalatine

ganglion

Eye

Lacrimal

gland

Nasal

mucosa

Ciliary

ganglion

Pterygopalatine

ganglion

Submandibular

ganglion Submandibular

and sublingual

glands

CN III

CN VII

CN IXCN X

Otic ganglion

Parotid gland

Heart

Lung

Liver and

gallbladder

Stomach

Pancreas

Urinary

bladder

and ureters

Small

intestine

Large

intestine

S2

Pelvic

splanchnic

nerves

Genitalia

(penis,

clitoris, and vagina)

Rectum

Celiac

plexus

Inferior

hypogastric

plexus

Cardiac and

pulmonary

plexuses

S4

Preganglionic

Postganglionic

Cranial nerve

Figure 14.4

Parasympathetic

Division

= Craniosacral





Sympatheticdivision


Figure 14.1

Figure 14.6

Superior

cervical

ganglion

Middle

cervical

ganglion

Inferior

cervical

ganglion

Sympathetic trunk

(chain) ganglia

Pons

L2

T1

White rami

communicantes

Liver and

gallbladder

Stomach

Spleen

Kidney

Adrenal medulla

Small

intestine

Large

intestine

Genitalia (uterus, vagina, and

penis) and urinary bladder

Celiac ganglion

Inferior

mesenteric

ganglion

Lesser splanchnic nerve

Greater splanchnic nerve

Superior

mesenteric

ganglion

Lumbar

splanchnic

nerves

Eye

Lacrimal gland

Nasal mucosa

Blood vessels;

skin (arrector pili

muscles and

sweat glands)

Salivary glands

Heart

Lung

Rectum

Cardiac and

pulmonary

plexuses

Preganglionic

Postganglionic

Sacral

splanchnic

nerves

Sympathetic Division = Thoracolumbar

The Sympathetic Division

• Preganglionic neurons originate in the spinal

cord from T1 – L2

– Thoracolumbar division

• FYI: Lateral horns

Preganglionic

(Sympathetic)

Cell Bodies


1) Preganglionic fibers leave through ventral root of spinal cord

2) Fibers join spinal nerve

3) Spinal nerve divides at ventral rami

4) Rami branch immediately into white rami communicans

5) Join sympathetic (paravertebral) ganglia

Figure 14.5a

Spinal cord

Dorsal root

1) Ventral root

5) Sympathetic trunk ganglion

Sympathetic

trunk

Rib

3) Ventral ramus

Gray ramus

communicans

4) White ramus communicans

Thoracicsplanchnic nerves

(a) Location of the sympathetic trunk

2) Spinal nerve

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Sympathetic Trunk Ganglia

• Form longitudinal pathways adjacent to vertebral column

• Each spinal nerve has an associated ganglion (except in cervical

region, where several ganglia fuse)

Figure 14.6

Superior

cervical

ganglion

Middle

cervical

ganglion

Inferior

cervical

ganglion

Sympathetic trunk

(chain) ganglia

Pons

L2

T1

White rami

communicantes

Liver and

gallbladder

Stomach

Spleen

Kidney

Adrenal medulla

Small

intestine

Large

intestine

Genitalia (uterus, vagina, and

penis) and urinary bladder

Celiac ganglion

Inferior

mesenteric

ganglion

Lesser splanchnic nerve

Greater splanchnic nerve

Superior

mesenteric

ganglion

Lumbar

splanchnic

nerves

Eye

Lacrimal gland

Nasal mucosa

Blood vessels;

skin (arrector pili

muscles and

sweat glands)

Salivary glands

Heart

Lung

Rectum

Cardiac and

pulmonary

plexuses

Preganglionic

Postganglionic

Sacral

splanchnic

nerves

Sympathetic Division = Thoracolumbar


• Sympathetic trunks and pathways

–Upon entering a sympathetic trunk ganglion a

preganglionic fiber may do one of the following:

1. Synapse with a ganglionic neuron within the same ganglion

Figure 14.5b (1 of 3)

To effector

Blood vessels

Skin (arrector

pili muscles

and sweat

glands)

Dorsal root ganglionDorsal ramus of

spinal nerve

Dorsal root

Sympathetic

trunk ganglion

Lateral horn (visceral

motor zone)

Ventral root

Sympathetic trunk

Gray ramus

communicansWhite ramus

communicans

Ventral ramus of

spinal nerve

Synapse at the same level

(b) Three pathways of sympathetic innervation

1

Sympathetic Trunks and Pathways




2. Ascend or descend the sympathetic trunk to

synapse in another trunk ganglion


To effector

Blood vessels

Skin (arrector

pili muscles

and sweat

glands)

Synapse at a higher or lower level


2

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3. Pass through the trunk ganglion and emerge

without synapsing


Splanchnic nerve

Collateral ganglion

(such as the celiac)

Target organ

in abdomen

(e.g., intestine)

Synapse in a distant collateral ganglion

anterior to the vertebral column


3





3. Pass through the trunk ganglion and emerge

without synapsing» Eventually synapse with post-ganglionic neurons in collateral

ganglia, enter an autonomic plexus, and innervate abdominal

viscera

» Form splanchnic nerves

Figure 14.5a

Spinal cord

Dorsal root

Ventral root

Sympathetic

trunk ganglion

Sympathetic

trunk

Rib

Ventral ramus

of spinal nerve

Gray ramus

communicans

White ramus

communicans

Thoracicsplanchnic nerves

(a) Location of the sympathetic trunk

Division Origin of

Fibers Length of

Fibers Location

of Ganglia

Sympathetic Thoracolumbar region of the spinal cord

Short preganglionic and long postganglionic

Close to spinal cord

Parasympathetic Brain and sacral spinal cord (craniosacral)

Long preganglionic and short postganglionic

In visceral effector organs

Differences Between the Divisions Neurotransmitters in the ANS

• Cholinergic fibers release the neurotransmitter ACh

– All ANS preganglionic axons

– All parasympathetic postganglionic axons

• Adrenergic fibers release the neurotransmitter NE

– Most sympathetic postganglionic axons

– Exceptions: sympathetic postganglionic fibers

secrete ACh at sweat glands and some blood vessels

in skeletal muscles

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Figure 14.2

+

AChSmooth muscle

(e.g., in gut),

glands, cardiac

muscle

Ganglion

Adrenal medulla Blood vessel

ACh

ACh

ACh

NE

Epinephrine andnorepinephrine

Acetylcholine (ACh) Norepinephrine (NE)

Ganglion

Lightly myelinated

preganglionic axon

Lightly myelinated

preganglionic axons

Unmyelinated

postganglionic

axon

Unmyelinatedpostganglionic axon

Stimulatory

or inhibitory,

depending

on neuro-

transmitter

and

receptors

on effector

organs

Two-neuron chain from CNS to effector organs

AU

TO

NO

MIC

NE

RV

OU

S S

YS

TE

M

PA

RA

SY

MP

AT

HE

TIC

SY

MP

AT

HE

TIC

Adrenal Medulla

“Sympathomimetic”

Receptors for Neurotransmitters

• Cholinergic receptors for ACh

• Adrenergic receptors for NE

Cholinergic Receptors

• Two types of receptors bind ACh

1. Nicotinic

2. Muscarinic

• Named after drugs that bind to them and mimic

ACh effects


• Nicotinic receptors– Blocked with curare

• Poison arrows and blow darts

• Used as a muscle relaxant for surgery (safer alternatives now available)

– Effect of ACh at nicotinic receptors

• Always stimulatory


�Muscarinic

�Blocked by atropine

�Effect of ACh at muscarinic receptors

�Can be either inhibitory or excitatory

�Depends on the receptor type of the target organ

Clarification, PNS 8: 2d.

acetylcholine is not always stimulatory. It IS always stimulatory at nicotinic and somatic receptors. It may be

inhibitory or excitatory at muscarinic receptors.

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Adrenergic Receptors

• Two types

– Alpha (α) (subtypes α1, α2)

– Beta (β) (subtypes β1, β2, β3)

• Effects of NE depend on which subclass of

receptor predominates on the target organ

Table 14.2

Ignore

Ignore

Cardiovascular Pharmacology

• Heart

– β1 - Excitatory in heart

• increases heart rate, conduction velocity, and contraction

strength

• Major blood vessels

– β2 – Inhibitory

• Vasodilation

– α1 – Excitatory

• Vasoconstriction

Cardiovascular Pharmacology

• Adrenergic blockers

– Used to treat hypertensive disease

– α1 blockers - produce vasodilation

– β1 blockers - decrease heart rate and blood

pressure

Interactions of the Autonomic

Divisions

• Most visceral organs have dual innervation

• Dynamic and precise control of visceral activity

– Sympathetic division increases heart and respiratory

rates, and inhibits digestion and elimination

– Parasympathetic division decreases heart and

respiratory rates, and allows for digestion and the

discarding of wastes

Salivaryglands

Eye

Skin*

Heart

Lungs

Liverand gall-bladder

Genitals

Pancreas

Eye

Lungs

Bladder

Liver andgall-bladder

Pancreas

Stomach

Cervical

Sympatheticganglia

Cranial

Lumbar

Thoracic

Genitals

Heart

Salivaryglands

Stomach

Bladder

Adrenalgland

Parasympathetic Sympathetic

Sacral

Brainstem

L1

T1

Figure 14.3

Peripheral Nerve Regeneration The Nervous System...1/18/2016 1 PNS continued The Nervous System...

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