Peripheral Nervous System. Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright...

Peripheral Nervous System

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Place of the PNS in the structural organization of the nervous system

CNS

Sensory division Motor division

Autonomic nervous system

Sympathetic division

Parasympathetic division

PNS

Somatic nervous system



Structure of a nerve

(a)

(b)

Fascicle

Perineurium Blood vessels

Endoneurium Nerve fibers

Axon

Endoneurium

Perineurium

Epineurium

Myelin sheath

Bloodvessels

Fascicle

Spinal Nerves and Nerve Plexuses

• Characteristics:– Somatic sensation (conscious) and somatic motor control (voluntary

control) of skeletal muscles.– Includes cranial nerves: I, II, IV-VI, VIII, XI and XII.– Spinal nerves: 31

• Cervical: 8 (above C1, and below C1-C7)• Thoracic: 12 (below T1-T12)• Lumbar: 5 (below T1-T5)• Sacral: 5 ( below S1-S5)• Coccygeal: 1 exit coccyx

– Mixed nerves• Sensory • Motor

– Dorsal and ventral rami (nerve branches) plexuses (network of nerves)



Distribution of spinal nerves

CervicalnervesC1– C8

ThoracicnervesT1– T12

LumbarnervesL1– L5

SacralnervesS1– S5

Coccygealnerve

C0

Cervical plexus

Intercostalnerves

Cervicalenlargement

Lumbarenlargement

Cauda equina

Brachial plexus

Lumbar plexus

Sacral plexus

Formation of spinal nerves and rami distribution

(b)

Dorsal ramus

Ventral ramus

Intercostal nerve

Lateral cutaneous

Anterior cutaneous

Spinal nerve

Rami communicantes

Dorsal root ganglion

Sympathetic trunk(chain) ganglion

Dorsal root

Ventral root

Sternum

Thoracic cavity

Branches ofintercostalnerve

The cervical plexus

Hypoglossalnerve (XII)

C1

C2

C3

C4

C5

Segmentalbranches

Lesser occipitalnerve

Greater auricularnerve

Ansa cervicalis

Phrenic nerve

Supraclavicularnerves

Accessory nerve (XI)

Transverse cutaneousnerve

Key:

= Ventral rami

Ventralrami:

The brachial plexus

(a)

= Roots

Key:

= Anterior division= Posterior division

= Trunks

Nerve tosubclavius

Suprascapular

Dorsal scapular

Posteriordivisions

Lateral

Cords

Axillary

Musculo-cutaneous

Radial

Median

Ulnar

Upper

Middle Trunks

Lower

C4

Roots:

C5

C6

C7

C8

T1

Upper subscapular

Lower subscapular

Thoracodorsal

Medial cutaneousnerves of the armand forearm

Long thoracic

Medial pectoral

Lateral pectoral

Posterior

Medial



The brachial plexus

(c)

Mediannerve

Musculo-cutaneousnerve

Radialnerve

Humerus

Ulna

Ulnar nerveMediannerve

Radius

Radial nerve(superficialbranch)

Superficial branchof ulnar nerve

Dorsal branchof ulnar nerve

Digital branchof ulnar nerve

MuscularbranchDigitalbranch

Trunks



The lumbar plexus

(b)

(a)

Iliohypogastric

L1

L2

L3

L4

L5

Ilioinguinal

Genitofemoral

Lateral femoralcutaneous

Obturator

Femoral

Lumbosacraltrunk

Lateralfemoralcutaneous

AnteriorfemoralcutaneousSaphenous

Obturator

IliohypogastricIlioinguinal

Femoral

= Ventral rami

Key:

Ventral rami:



The sacral plexus

(a)

(b)

Superiorgluteal

Lumbosacraltrunk

Inferiorgluteal

CommonfibularTibial

Posteriorfemoralcutaneous

Pudendal

Sciatic

Key:

Commonfibular

DeepfibularSuperficialfibular

Plantarbranches

TibialSural

Posteriorfemoralcutaneous

Pudendal

Sciatic

L4

L5

S1

S2

S3

S4

S5

C0

= Ventral rami

Ventralrami:

SuperiorglutealInferiorgluteal

• Activity 2– Identify spinal chord tracts

• Activity 3– Identify Major nerve plexuses and Peripheral

nerves

The Autonomic Nervous System(ANS)



Place of the ANS in the structural organization of the nervous system

CNS

Sensory division Motor division

PNS

Autonomic nervous system

Sympathetic division

Parasympatheticdivision

Somatic nervous system

Characteristics of the ANS

• Regulates body function unconsciously.– Cardiac muscle, smooth muscle, glands.

• Consists of chains of 2 motor neurons.– Preganglion neuron: located in the CNS. – Ganglion neuron: synapses with pregalnglion, outside

the CNS and its axon synapses with the effector organ.

• Sympathetic (fight or flight) functions are antagonistic to the Parasympathetic (resting and digesting) functions.



Comparison of somatic and autonomic nervous systems

Somatic nervous system Skeletal muscle

Centralnervous system Peripheral nervous system Effector organs

Acetylcholine

Smoothmuscle(e.g., in gut)

Acetylcholine

Ganglion

Adrenal medulla

GlandsBloodvessel

Cardiacmuscle

Sympatheticdivision

Autonomicnervoussystem

Acetylcholine

Acetylcholine

Norepinephrine

Epinephrine andnorepinephrine

Ganglion

Para-sympathetic

division

= Preganglionic axons (sympathetic)

= Postganglionic axons (sympathetic)

= Myelination = Preganglionic axons (parasympathetic)

= Postganglionic axons (parasympathetic)

Key:



Overview of the subdivisions of the ANS

Salivaryglands

Eye

Skin*

Heart

Lungs

Liverand gall-bladder

Pancreas

Eye

Lungs

Bladder

Liver and gall-bladder

Pancreas

Stomach

Cervical

Sympatheticganglia

Cranial

Lumbar

Thoracic

Genitals

Heart

Salivaryglands

Stomach

Bladder

Adrenalgland

Parasympathetic Sympathetic

Sacral

Brain stem

L1

T1

Genitals



Parasympathetic (craniosacral) division of the ANS

EyeLacrimalgland

Nasalmucosa

Ciliary ganglion

Pterygopalatineganglion

Submandibularganglion

Submandibularand sublingualglands

CN III

CN VIICN IXCN X

Otic ganglion

Parotid gland

Heart

Lung

Liver andgallbladder

Stomach

Pancreas

Urinary bladder and ureters

Smallintestine

Large intestine

S2

Pelvicsplanchnicnerves

Genitalia (penis, clitoris, and vagina)

Rectum

Celiacplexus

Inferiorhypogastric plexus

Cardiac and pulmonary plexuses

S4

III: Oculomotor

VII: Facial

IX: GlossopharyngealX: Vagus

Characteristics of the Parasympathetic Division

• Preganglion axons are located in the cranial nerves in the immediate area to be stimulated.

• Terminal or intramural ganglion, which emits a short axon to the organ, synapse with the preganglion ganglion.

• Sacral region ganglions synapse to pelvic splanchnic nerves that travel to the pelvic cavity.



Sympathetic (thoracolumbar) division of the ANS

Midbrain Superiorcervicalganglion

Middlecervicalganglion

Inferiorcervicalganglion

Sympathetic trunk(chain) ganglia

Pons

Medulla

L2

T1

White ramicommunicantes

Liverand gall-bladder

Stomach

Spleen

KidneyAdrenal gland

Smallintestine

Largeintestine

Genitalia (uterus, vagina, andpenis) and urinary bladder

Celiac ganglion

Aorticplexuson aorta

Inferiormesenteric ganglion

Lesser splanchnic nerve

Greater splanchnic nerve

Superiormesentericganglion

Inferiorhypogastricplexus

Lumbarsplanchnic nerves

Eye Lacrimalgland

Nasalmucosa

Blood vessels; skin (arrector pilimuscles and sweat glands)

Salivary glands

Heart

Lung

Rectum

Cardiac and pulmonaryplexuses

Sympatheticdivision(thoracolumbar)

Characteristics of the Sympathetic Division

• Preganglion are located in the lateral ramus of the spinal chord T1 – L2. Axon leaves the chord via ventral root the spinal nerve the ventral ramus white ramus communicans paravertrebral ganglion in the sympathetic chain.

• Preganglion axon may:– Synapse with a same level sympathetic ganglion chain neuron.– Travel up or downward through the sympathetic chain in the paravertebral

region to another ganglion.• (Postganglionic reenter spinal nerve through gray ramus communicans to

travel in dorsal or ventral ramus to innervate organs).– Skip the ganglion and form part of the splanchnic nerves, which travele to

the organ to synapse with prevertebral or collateral ganglion. • Celiac, superior mesenteric, inferior mesenteric, hypogastric ganglia.



Sympathetic trunks and pathways

(a)

(b)

To effector

Blood vessels

Skin (arrectorpili musclesand sweatglands)

Dorsal whitecolumn

Spinal cord

Sympathetictrunk ganglion

Body of avertebra

Thoracicsplanchnicnerves

Dorsal root

Dorsal root ganglion

Ventral rootSympathetic trunk(chain) ganglionLateral horn(visceral motor zone)

Sympathetic trunk

Ventral ramusof spinal nerveGray ramuscommunicans

White ramuscommunicans

Intercostal nerve

Dorsal ramusof spinal nerve

Intercostal muscleof thorax

Splanchnicnerve

Collateral(prevertebral) ganglionsuch as the celiac

Target organ(in abdomen)

Ventral root

Rib

11

23

3

2

1.Synapse in paravertebal region at the same level

2. Synapse in chain ganglion at different level

3. Synapse in prevertebral region anterior to vertebral column

• Activity 4– Locate the ANS chains in the models.

Human Reflex Physiology

• Definition:– Rapid, predictable and involuntary motor

response to stimuli through pathways called reflex arcs.

• Two systems– Autonomic reflexes (unconscious): digestion,

sweating etc.

– Somatic reflexes: activate skeletal muscles.



Hierarchy of motor control

FeedbackInternal

feedback

Cerebellum and basal nuclei

Highest (precommand)

Structures involved

Reflex activity

Segmental motorcontrols (CPG)

Interactions Control level

Middle

Motor cortex (pyramidal system)and brain stem nuclei (vestibular,red, reticular formation, etc.)

Lowest

Spinal cord

Motoroutput

Programs and instructions(modified by feedback)

Projection areas

Sensoryinput CNG: central pattern

generator



The basic components of all human reflex arcs

Stimulus

Receptor

Skin

Sensory neuron

Spinal cord (in cross section)

Integration center

InterneuronMotor neuron

Effector

1

5

4

2 3

The reflex arc

• Characteristics: Structurally (number of neurons involved)– Monosynaptic arc: one synapse– Polysynaptic arc: one or more association neurons.

• Somatic Reflexes (skeletal muscle effectors)– Stretch reflexes: Postural and locomotion reflexes.

• Muscle spindle stimuli/Golgi organ in tendons (stretching) initiates reflex.

– Reciprocal inhibition: antagonistic efferent muscles are relaxed (damped).

– Patellar reflex (activity 1).



The stretch reflex

(a)

(b)

Initialstimulus:musclestretch

Afferent impulsesfrom stretchreceptor tospinal cord

Efferentimpulses toalpha () motorneurons causecontractionof the stretchedmuscle thatresists/reversesthe stretch

Efferent impulsesto antagonistmuscles are damped(reciprocalinhibition)

Spinal cord(L2–L4)

Patella

Cell body ofsensory neuron

Key:+ Excitatory synapse– Inhibitory synapse

Motor neuronserving quadriceps

Motor neuronserving antagonistmuscle group(hamstrings)

Musclespindle

Quadriceps(extensors)

Hamstrings(flexors)

Musclespindle

Patellarligament

Interneuron

–

1

2

3



The Golgi tendon reflex

++

+–

Quadriceps(extensor)

Golgitendonorgan

Hamstrings(flexor)

Afferent fiberfrom Golgitendon organ

Efferent fiberto muscleassociatedwith stretchedtendonEfferent fiberto antagonisticmuscle

Spinal cord

Interneurons




Operation of the muscle spindle

(a) (b) (d)(c)

Musclespindle

Intrafusalmuscle fiber

Primarysensory (la)nerve fiber

Extrafusalmuscle fiber

Time Time Time

Unstretched muscle;AP frequency constant

Stretched muscle;AP frequency increased

Neuron coactivation;AP frequency constant

Motor neuronstimulation only; noAPs, unable to signallength changes

Time

AP: Action Potential



Anatomy of the muscle spindle and Golgi tendon organ

Primarysensoryendings(type Ia fiber)

Muscle spindle

Connectivetissue capsule

Efferentmotor fiberto extrafusalmusclefibers

Extrafusalmusclefiber

Intrafusalmusclefibers

Tendon

Efferent motor fiber to spindle

Secondarysensoryendings(type II fiber)

Golgi tendonorgan

CapsuleSensoryfiber

Somatic ReflexesSomatic Reflexes

• Crossed extensor reflex: Withdrawal reflex, followed by extension of the opposite limb.• Activity 2?



The crossed-extensor reflex

Afferentfiber

Efferentfibers

Extensorinhibited

Flexorstimulated

Right arm(site of stimulus)

Left arm (site ofreciprocal activation)

Arm movements

Interneurons


Efferentfibers

FlexorinhibitedExtensorstimulated

+

–+

–

+

+

Flexes

Extends


• Autonomic Reflexes– Pupillary reflexes

– Salivary reflex

• Reaction time of a reflex– Relative to the myelination of an axon andits

length relative to the interneuron or association center.

– Visual stimulus 150-300 ms.


• Superficial cord reflex: Abdominal, cremaster and plantar reflexes.• Plantar reflex. Normal pyramidal activity, toes

flex and move close together. Activity 3.

– Cranial nerve reflex: optical (motor) nerves.• Corneal reflex (V). Activity 4

Autonomic reflexes

• Pupillary reflexes.– Cranial nerve II, III.

• Actvity 6: Contralateral response, ipsilateral response.

– Ciliospinal reflex. Pupilary.

– Salivary reflex. Smooth/skeletal muscles.



Visceral reflexes

Dorsalrootganglion

Sensoryreceptor inviscera

Centralnervoussystem

Visceral(sensory)fiber

Visceral reflex arc(Autonomic reflex)

Stimulus

Postganglionicaxon

Visceraleffector Integration center

(may be preganglionicneuron)

Preganglionic axonAutonomicganglion

Ganglionicneuron

Response



Referred pain

Heart

Lungs anddiaphragm

Liver

Gallbladder

Stomach

Kidneys

Ovaries

Small intestine

Ureters

Urinarybladder

Colon

Pancreas

Liver

Heart

Appendix

Gallbladder

Peripheral Nervous System. Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright...

Documents

Transcript of Peripheral Nervous System. Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright...