CHAPTER 13 PERIPHERAL NERVOUS SYSTEMclasspages.warnerpacific.edu/bdupriest/BIO 221/Chapter 13 PNS.pdf · CHAPTER 13 PERIPHERAL NERVOUS SYSTEM . ... of spinal nerve Dorsal ramus ...

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CHAPTER 13

PERIPHERAL NERVOUS SYSTEM



Organization


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

Motor (efferent) division Sensory (afferent)

division

Somatic nervous

system

Autonomic nervous

system (ANS)

Sympathetic

division

Parasympathetic

division

Figure 13.1 Place of the PNS in the structural organization of the nervous system.



Sensory Receptors


Table 13.1 General Sensory Receptors Classified by Structure and Function (1 of 3)






A receptor which responds to changes in

temperature is a…

1) mechanoreceptor

2) thermoreceptor

3) photoreceptor

4) chemoreceptor

5) nociceptor



Sensory Perception – CNS Integration


Figure 13.2 Three basic levels of neural integration in sensory systems.

1

2

3

Receptor level

(sensory reception and transmission to CNS)

Circuit level

(processing in ascending pathways)

Spinal cord

Cerebellum

Reticular formation

Pons

Muscle spindle

Joint kinesthetic receptor

Free nerve endings (pain, cold, warmth)

Medulla

Perceptual level (processing in cortical sensory centers)

Motor

cortex Somatosensory

cortex

Thalamus


Which level of sensory integration is the level

at which the reticular formation and thalamus

distribute signals to appropriate cortical

regions?

1) Circuit level

2) Receptor level

3) Perceptual level



NERVES: Structure


Figure 13.3b Structure of a nerve.

Blood

vessels

Fascicle

Epineurium

Perineurium

Endoneurium

Axon

Myelin sheath

(b)


Figure 13.3a Structure of a nerve.

Fascicle

Perineurium

Endoneurium (a)

Nerve fibers

Blood vessels


The membrane surrounding a nerve is the...

1) endoneurium

2) epineurium

3) perineurium



NERVES: Classification & Location



Nerves: Ganglia


A nerve is…

1) A neuron

2) A group of neuron cell bodies

3) A group of neuron axons wrapped in

connective tissue in the peripheral nervous

system

4) A group of neuron axons wrapped in

connective tissue in the central nervous

system

5) All of the above



Nerves: Regeneration and Repair


Figure 13.4 Regeneration of a nerve fiber in a peripheral nerve (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 Macrophage Macrophages

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



Cranial Nerves


Figure 13.5a Location and function of cranial nerves.

Frontal lobe

Temporal lobe

Infundibulum

Facial

nerve (VII)

Vestibulo-

cochlear

nerve (VIII)

Glossopharyngeal

nerve (IX)

Vagus nerve (X)

Accessory nerve (XI)

Hypoglossal nerve (XII)

(a)

Filaments of

olfactory

nerve (I)

Olfactory bulb

Olfactory tract

Optic chiasma

Optic nerve

(II)

Optic tract Oculomotor

nerve (III)

Trochlear

nerve (IV)

Trigeminal

nerve (V)

Abducens

nerve (VI)

Cerebellum

Medulla oblongata


Figure 13.5b Location and function of cranial nerves.

*PS = parasympathetic (b)

Cranial nerves

I – VI

I

II

III

IV

V

VI

Olfactory

Optic

Oculomotor

Trochlear

Trigeminal

Abducens

Yes (smell)

Yes (vision)

No

No

Yes (general

sensation)

No

No

No

Yes

Yes

Yes

Yes

No

No

Yes

No

No

No

Cranial nerves

VII – XII

Sensory

function

Motor

function

PS*

fibers

Sensory

function

Motor

function

PS*

fibers

VII

VIII

IX

X

XI

XII

Facial

Vestibulocochlear

Glossopharyngeal

Vagus

Accessory

Hypoglossal

Yes (taste)

Yes (hearing

and balance)

Yes (taste)

Yes (taste)

No

No

Yes

Some

Yes

Yes

Yes

Yes

Yes

No

Yes

Yes

No

No


Cranial nerve I is also known as the…

1) Hypoglossal nerve

2) Olfactory nerve

3) Optic nerve

4) Vagus nerve



Spinal Nerves


Figure 13.6 Spinal nerves.

Cervical nerves

C1 – C8

Thoracic nerves

T1 – T12

Lumbar nerves

L1 – L5

Sacral nerves S1 – S5

Coccygeal nerve Co1

Cervical plexus

Intercostal nerves

Cervical enlargement

Lumbar enlargement

Cauda equina

Brachial plexus

Lumbar plexus

Sacral plexus



Spinal Nerves: Branches


Figure 13.7a Formation of spinal nerves and rami distribution.

Dorsal root ganglion

Gray matter

White matter

Ventral root

Dorsal root

Dorsal and ventral rootlets of spinal nerve

Dorsal ramus of spinal nerve

Ventral ramus of spinal nerve

Sympathetic trunk ganglion

Spinal nerve

Rami communicantes

(a) Anterior view showing spinal cord, associated nerves, and vertebrae.

The dorsal and ventral roots arise medially as rootlets and join

laterally to form the spinal nerve.


Figure 13.7b Formation of spinal nerves and rami distribution.

Dorsal ramus

Ventral ramus

Intercostal nerve

Spinal nerve

Rami communicantes

Dorsal root ganglion Dorsal root Ventral root

Sympathetic trunk ganglion

Sternum

(b) Cross section of thorax showing the main roots and

branches of a spinal nerve.

Branches of intercostal

nerve

• Lateral cutaneous • Anterior cutaneous


True or false: information only flows toward

the spinal cord in a dorsal ramus.

1) True

2) False



Spinal Nerves: Plexuses (Plexi?)


Figure 13.8 The cervical plexus.

Hypoglossal nerve (XII)

C1

C2

C3

C4

C5

Segmental

branches

Lesser occipital nerve Greater auricular nerve

Ansa cervicalis

Phrenic nerve

Supraclavicular

nerves

Accessory nerve (XI)

Transverse cervical nerve

Ventral

rami:

Ventral rami


Figure 13.9a The brachial plexus.

Upper

Middle Trunks

Lower

Roots (ventral rami):

Upper subscapular

Lower subscapular

Thoracodorsal

Medial cutaneous

nerves of the arm

and forearm

Long thoracic

Medial pectoral

Lateral pectoral

Nerve to subclavius

Suprascapular

Dorsal scapular

Posterior divisions

Anterior

divisions

Lateral

Posterior Cords

Medial

Axillary

Musculo- cutaneous

Radial

Median

Ulnar

Posterior

divisions

Trunks Roots

C4

C5

C6

C7

C8

T1

(a) Roots (rami C5 – T

1), trunks, divisions, and cords


Figure 13.9b The brachial plexus.

Musculocutaneous nerve Lateral

cord

Posterior cord

Medial cord

Radial nerve

Ulnar nerve

Axillary nerve

Biceps brachii

Coracobrachialis

Median nerve

Radial nerve branches to triceps

(b) Cadaver photo


Figure 13.9c The brachial plexus.

Median nerve

Musculocutaneous nerve

Radial nerve

Humerus

Ulna

Ulnar nerve

Median nerve

Radius

Radial nerve (superficial branch)

Superficial branch of ulnar nerve Dorsal branch of ulnar nerve

Digital branch of ulnar nerve

Muscular branch

Digital branch

(c) The major nerves of the upper limb

Axillary

nerve Anterior divisions

Posterior divisions

Trunks Roots


Figure 13.9d The brachial plexus.

Anterior

divisions

(d) Flowchart summarizing relationships within the

brachial plexus

Major terminal

branches

(peripheral nerves) Cords Divisions Trunks

Roots

(ventral

rami)

Musculocutaneous

Median

Ulnar

Radial

Axillary

Anterior

Posterior

Anterior

Posterior

Posterior

Anterior

Upper

Middle

Lower

Lateral

Medial

Posterior

Posterior

divisions

Trunks Roots

C5

C6

C7

C8

T1


Figure 13.10 The lumbar plexus.

(a) Ventral rami and major branches

of the lumbar plexus

Iliohypogastric

L1

L2

L3

L4

L5

Ilioinguinal

Genitofemoral

Lateral femoral

cutaneous

Obturator

Femoral

Lumbosacral

trunk

Lateral femoral

cutaneous

Anterior femoral

cutaneous

Saphenous

Obturator

Iliohypogastric

Ilioinguinal

Femoral

Ventral rami Ventral

rami:

(b) Distribution of the major nerves from

the lumbar plexus to the lower limb


Figure 13.10a The lumbar plexus.


of the lumbar plexus

Iliohypogastric

L1

L2

L3

L4

L5

Ilioinguinal

Genitofemoral

Lateral femoral

cutaneous

Obturator

Femoral

Lumbosacral

trunk

Ventral rami Ventral

rami:


Figure 13.10b The lumbar plexus.

Lateral femoral cutaneous

Anterior femoral cutaneous

Saphenous

Obturator

Iliohypogastric

Ilioinguinal

Femoral

(b) Distribution of the major

nerves from the lumbar

plexus to the lower limb


Figure 13.11a The sacral plexus.

Superior gluteal

Lumbosacral trunk

Inferior gluteal

Common fibular

Tibial

Posterior femoral cutaneous

Pudendal

Sciatic


of the sacral plexus

L4

L5

S1

S2

S3

S4

S5

Co1

Ventral rami Ventral rami:


Figure 13.11b The sacral plexus.

Superior gluteal

Inferior gluteal

Common fibular

Deep fibular

Superficial fibular

Plantar branches

Tibial

Sural (cut)

Posterior femoral cutaneous

Pudendal

Sciatic

(b) Distribution of the major nerves from

the sacral plexus to the lower limb


Figure 13.11c The sacral plexus.

Pudendal nerve

Gluteus maximus (medial portion removed)

Piriformis

Inferior gluteal nerve

Greater trochanter of femur

Common fibular nerve

Tibial nerve

Sciatic nerve

Posterior femoral cutaneous nerve

Ischial tuberosity

(c) Cadaver photo



Spinal Nerves: Dermatomes


Figure 13.12 Map of dermatomes.

C2

C3

C4

C5

T1

T2

T2

T3

T4

T5

C6

C8

C7 C7

C6

T6

T7

T8

T9

T10

T11

T12

L1

S2

S3

L1

L2

L3

L4

L5

L2

L3

L4

L5

S1

C5

C6

C8

T2

C5

C6

S1

(a) Anterior

view

C2

C3

C4

C5

C6

C7

C8

C8 C8

C7 C7

T1

T2

T3

T4

T5

T6

T7

T8

T9

T10

T11

T12

L1

L2 L3

S1

(b) Posterior

view

L5 S2

S1

S1

S3

S2 S1 S2

S4

S5

L5 L5

L4

L5 L5

L4

C6 C6

C5

L4

L3

L2

L1

L4


True or false: Pain felt on the surface of a body

region is always related to skin problems.

1) True

2) False



MOTOR ENDINGS



MOTOR INTEGRATION


Figure 13.13 Hierarchy of motor control.

Feedback

Reflex activity Motor output

Sensory input

(a) Levels of motor control and their interactions

Precommand Level

(highest)

• Cerebellum and basal nuclei • Programs and instructions (modified by feedback)

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

• Convey instructions to spinal cord motor neurons and send a copy of that information to higher levels

Segmental Level (lowest)

• Spinal cord • Contains central pattern generators (CPGs)

Internal feedback

(b) Structures involved

Precommand level

• Cerebellum • Basal nuclei

Projection level

• Primary motor cortex • Brain stem nuclei

Segmental level

• Spinal cord



REFLEX ARC


Figure 13.14 The five basic components of all reflex arcs.

Receptor

Sensory neuron

Integration center

Motor neuron

Effector

Spinal cord

(in cross section)

Interneuron

Stimulus

Skin

1

2

3

4

5


Figure 13.15 Anatomy of the muscle spindle and Golgi tendon organ.

Secondary sensory

endings (type II fiber)

Efferent (motor)

fiber to muscle spindle

Primary sensory

endings (type Ia

fiber)

Connective

tissue capsule

Muscle spindle

Tendon

Sensory fiber

Golgi tendon

organ

Efferent (motor)

fiber to extrafusal

muscle fibers

Extrafusal muscle

fiber

Intrafusal muscle

fibers


Figure 13.16 Operation of the muscle spindle.

(a) Unstretched

muscle. Action

potentials (APs)

are generated at

a constant rate in

the associated

sensory (la) fiber.

Muscle

spindle

Intrafusal

muscle fiber

Primary sensory (la) nerve fiber

Extrafusal

muscle fiber

Time

(b) Stretched

muscle. Stretching

activates the muscle

spindle, increasing the rate of APs.

Time

(d) - Coactivation.

Both extrafusal and

intrafusal muscle

fibers contract.

Muscle spindle

tension is main-

tained and it can

still signal changes

in length.

Time

(c) Only motor

neurons activated.

Only the extrafusal

muscle fibers contract.

The muscle spindle

becomes slack and no

APs are fired. It is

unable to signal further length changes.

Time


Figure 13.17 The Stretch Reflex (1 of 2)

1 When muscle spindles are activated by stretch, the associated sensory neurons (blue) transmit afferent impulses at higher frequency to the spinal cord.

2 The sensory neurons synapse directly with alpha motor neurons (red), which excite extrafusal fibers of the stretched muscle. Afferent fibers also synapse with interneurons (green) that inhibit motor neurons (purple) controlling antagonistic muscles.

The events by which muscle stretch is damped

3a Efferent impulses of alpha motor neurons cause the stretched muscle to contract, which resists or reverses the stretch.

3b Efferent impulses of alpha motor neurons to antagonist muscles are reduced (reciprocal inhibition).

Initial stimulus

(muscle stretch)

Cell body of sensory neuron

Sensory neuron

Muscle spindle

Antagonist muscle

Spinal cord


Figure 13.17 The Stretch Reflex (2 of 2)

The patellar (knee-jerk) reflex – a specific example of a stretch reflex

Muscle

spindle

Quadriceps

(extensors)

Hamstrings

(flexors)

Patella

Patellar

ligament

Spinal cord

(L2 – L4)

3a

2

1

3b 3b

1 Tapping the patellar ligament excites

muscle spindles in the quadriceps muscle.

2

3a The motor neurons (red) send

activating impulses to the quadriceps

causing it to contract, extending the

knee.

Afferent impulses (blue) travel to the

spinal cord, where synapses occur with

motor neurons and interneurons.

3b The interneurons (green) make

inhibitory synapses with ventral horn

neurons (purple) that prevent the

antagonist muscles (hamstrings) from

resisting the contraction of the

quadriceps.

Excitatory synapse Inhibitory synapse –

+


Figure 13.19 The crossed-extensor reflex.

Afferent

fiber

Efferent

fibers

Extensor

inhibited

Flexor

stimulated

Site of stimulus: a noxious stimulus causes a flexor

reflex on the same side, withdrawing that limb.

Site of reciprocal

activation: At the same time, the extensor muscles on the opposite side are activated.

Arm

movements

Interneurons

Efferent

fibers

Flexor inhibited

Extensor stimulated

+ Excitatory synapse

– Inhibitory synapse


True or false: The flexor-crossed extensor

reflex involves multiple integration neurons.

1) True

2) False

CHAPTER 13 PERIPHERAL NERVOUS SYSTEMclasspages.warnerpacific.edu/bdupriest/BIO 221/Chapter 13 PNS.pdf · CHAPTER 13 PERIPHERAL NERVOUS SYSTEM . ... of spinal nerve Dorsal ramus ...

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