Peripheral Nervous System

Peripheral Nervous System (PNS)

• Connects the CNS to the

rest of the body

• Includes nerves and

ganglia

• Transmit sensory input

and motor output

Functional Divisions of the PNS

• Divided into sensory (input) and motor (output)

pathways

• Somatic (body surface, muscles) and visceral

(internal organs)

• General (widespread) and special (localized senses)

Autonomic Nervous System (ANS)

• General visceral motor division of the PNS

• Regulates involuntary functions (ex. heart rate,

digestion)

• Main divisions:

1. Parasympathetic: rest and digest

2. Sympathetic: fight or flight

PNS Pathway Picture

Cranial Nerves

• Originate from the brain and pass through specific

foramina of the skull

• Numbered from I-XII

• Cranial nerves I and II: attach to the forebrain

• Cranial nerves III–XII: attach to the brainstem

• Serve head and neck structures

• Only vagus nerve (X) extends into the abdomen

Cranial Nerves Table

Cranial Nerves Mnemonic

Open One Or Two Textbooks And Find Very Generic Vague Study Habits

1. Open = Olfactory

2. One = Optic

3. Or = Oculomotor

4. Two = Trochlear

5. Textbooks = Trigeminal

6. And = Abducens

7. Find = Facial

8. Very = Vestibulocochlear

9. Generic = Glossopharyngeal

10. Vague = Vagus

11. Study = Spinal Accessory

12. Habits = Hypoglossal

I - Olfactory Nerves

• Special visceral sensory

• Smell

• Origin: olfactory receptor cells located in olfactory

epithelium of nasal cavity

• Pathway: pass through cribriform foramina of the

ethmoid bone

II - Optic Nerves

• Special somatic sensory

• Vision

• Origin: retina of the eye

• Pathway: pass through the optic canals of the

sphenoid bone

III - Oculomotor Nerves

• Somatic motor: innervates extrinsic eye muscles

1. Superior rectus

2. Medial rectus

3. Inferior rectus

4. Inferior oblique

• Visceral motor: constricts pupil, controls lens shape

• Origin: oculomotor nucleus of midbrain

• Pathway: pass through the superior orbital fissure

IV - Trochlear Nerves

• Somatic motor

• Innervate superior oblique muscle

• Origin: trochlear nucleus of midbrain

• Pathway: pass ventrally and laterally around midbrain

• Exit through superior orbital fissure

V - Trigeminal Nerves

• Largest cranial nerve, sensory and motor functions

• Ophthalmic Division (V1): sensory, upper face

• Maxillary Division (V2): sensory, midface

• Mandibular Division (V3): sensory and motor,

lower face

• Origin: sensory cell bodies in the trigeminal ganglion

and motor nucleus of trigeminal nerve

V - Trigeminal Nerve Pathways

• V1 – passes through superior orbital fissure

• V2 – passes through foramen rotundum

• V3 – passes through foramen ovale; enters

mandible through mandibular foramen

VI - Abducens Nerves

• Somatic Motor

• Innervates the lateral rectus muscle

• Origin: abducens nucleus in the pons

• Pathway: travels through the superior orbital fissure

to the eye

VII - Facial Nerves Somatic

• Special visceral sensory:

• Taste (anterior two-thirds of tongue)

• Somatic motor:

• Innervates five branches of facial muscles

1. Temporal

2. Zygomatic

3. Buccal

4. Mandibular

5. Cervical

VII - Facial Nerves Visceral

• Visceral motor

• Innervates lacrimal glands, submandibular and

sublingual salivary glands

• Origin: facial nucleus of pons in brain stem

• Pathway: enters temporal bone through the internal

acoustic meatus

• Travels through facial canal to target glands

VIII - Vestibulocochlear Nerves

• Sensory nerve for hearing and balance

• Vestibular Branch: equilibrium

• Cochlear Branch: hearing

• Origin: vestibular apparatus and cochlea

• Pathway: Passes through the internal acoustic meatus

to the brainstem

IX - Glossopharyngeal Nerves Sensory

• Posterior third of tongue

Special Visceral Sensory:

• Taste

General Visceral Sensory:

• Pharyngeal mucosa

• Chemoreceptors in the carotid body

• Baroreceptors in the carotid sinus

IX - Glossopharyngeal Nerves Motor

Somatic Motor:

• Elevate pharynx during swallowing

Visceral Motor:

• Innervate the parotid salivary gland

• Origin: Medulla oblongata

• Pathway: fibers exit through the jugular foramen

X - Vagus Nerves Sensory

Sensory Functions

• General Visceral Sensory: from thoracic and

abdominal viscera

• Special Visceral Sensory: taste from taste buds on the

epiglottis

X - Vagus Nerves Motor

Somatic Motor Functions

• Innervates skeletal muscles of pharynx and larynx

Visceral Motor (Parasympathetic innervation)

• Heart, lungs, abdominal viscera

• Origin: Medulla oblongata

• Pathway: fibers exit the skull through the jugular

foramen

XI - Accessory Nerves

• Somatic motor

• Innervates the trapezius and sternocleidomastoid

muscles

• Formed from ventral rootlets of spinal cord (C1–C5)

• Pathway:

• Enter skull through foramen magnum

• Exit skull through jugular foramen

XII - Hypoglossal Nerves

• Somatic motor

• Innervates the tongue muscles

• Formed from ventral rootlets of medulla oblongata

• Pathway: Exits skull through the hypoglossal canal

Cranial Nerve Function Mnemonic

Spinal Nerves

• 31 pairs connect to spinal cord

• Cervical (C1–C8): 8 pairs

• Thoracic (T1–T12): 12 pairs

• Lumbar (L1–L5): 5 pairs

• Sacral (S1–S5): 5 pairs

• Coccygeal (Co1): 1 pair

Spinal Nerve Root Connections

• Dorsal Root: sensory fibers, cell bodies in dorsal root

ganglion

• Ventral Root: motor fibers from the anterior gray

column

Spinal Nerve Branches

• Dorsal & Ventral Rami: both carry sensory and motor

fibers

• Rami Communicantes: connect ventral ramus to

sympathetic chain ganglia

Innervation of the Back

• Dorsal rami supply

back muscles and

skin in segmented

strips

• Follow emergence

points of the

vertebral column

Thoracic and Abdominal Wall Innervation

• Ventral Rami: simple, segmented pattern

• Intercostal Nerves: supply intercostal muscles, skin,

and abdominal wall

• Branches: lateral and anterior cutaneous

Introduction to Nerve Plexuses

• Networks of ventral rami

(except T2–T12)

• Found in cervical,

brachial, lumbar, and

sacral regions

• Serve limbs; fibers

crisscross for redundancy

The Cervical Plexus

• C1-C4

• Deep to the

sternocleidomastoid

• Mostly cutaneous

nerves; some serve

anterior neck muscles

Cervical Plexus Sensory Branches

• Lesser Occipital Nerve

• Great Auricular Nerve

• Transverse Cervical Nerve

• Supraclavicular Nerves

• Mnemonic: “Let’s Go To Sleep”

Cervical Plexus Motor Branches

• Muscular branches

• Ansa cervicalis

• Phrenic nerve

• Acronym: "MAP"

Phrenic Nerve

• Key nerve of the cervical

plexus

• Formed by C3, C4, and C5

fibers

• Controls the diaphragm

• “C3,4,5 keeps the

diaphragm alive”

Brachial Plexus

• Located in the neck and

axilla

• Formed by C5–C8 ventral

rami

• Cords give rise to main

upper limb nerves

Upper Limb Innervation

• Components (medial to lateral):

1. Ventral rami

2. Trunks

3. Divisions

4. Cords

Brachial Plexus Structure

• Ventral Rami: form the roots of the brachial plexus

• Trunks: 3 trunks formed from merging rami

• Divisions: Each trunk splits into anterior and posterior

divisions

• Cords: 6 divisions converge to form 3 cords

Terminal Branches from Lateral and Medial Cords

1. Musculocutaneous: from lateral cord, innervates

biceps brachii and brachialis

2. Median: from lateral and medial cords, innervates

anterior forearm muscles and lateral palm

• Muscular and digital branches

3. Ulnar: from medial cord, innervates intrinsic hand

muscles and medial hand skin

• Dorsal, superficial, and digital branches

Terminal Branches from the Posterior Cord

• Axillary: innervates deltoid and teres minor

• Deep and superficial branch

• Radial: continuation of posterior cord, largest branch,

innervates posterior upper limb muscles

• Deep and superficial branch, posterior cutaneous nerve

Terminal Branches Mnemonic:

Most Alcoholics Must Really Urinate

Musculocutaneous Axillary Muscular Radial Ulnar

Mnemonic for the Brachial Plexus

3 Musketeers Assassinated 5 Rats, 4 Mice and 2 Unicorns

• C5, C6, C7 fingers = Musculocutaneous nerve

• C5 and C6 form a gun shape = Axillary nerve

• C5 to T1 = Radial nerves

• C6 to T1 = Median nerves

• C8 and T1 = Ulnar nerve

Muscular Innervation of the Upper Limb MME

• Musculocutaneous Nerve: Coracobrachialis, Biceps

Brachii, Brachialis

• Median Nerve: Forearm flexors, 3 Thenar muscles,

Lumbricals (digit 2 and 3)

• Ulnar Nerve: Flexor Carpi Ulnaris, Flexor Digitorum

Profundus, 3 Hypothenar Muscles, Lumbricals (digit 4

and 5)

• Radial Nerve: Triceps, Brachioradialis, Extensors

(Wrist, Digits), Supinator, Abductor Pollicis Longus,

Aconeus

• Axillary: Teres Minor, Deltoid

Cutaneous Innervation of the Upper Limb RAM

• Medial Cutaneous Nerve: sensory input to

Musculocutaneous, Ulnar, and Median Nerves

• Axillary Nerve: provides sensory input to the shoulder

• Radial Nerve: provides sensory input to the posterior

arm, forearm, and hand

Lumbar Plexus

• L1 to L4

• Smaller branches:

innervate posterior

abdominal wall and psoas

muscle

• Femoral Nerve:

innervates anterior

thigh muscles

• Obturator Nerve:

innervates adductor

muscles

Ventral Rami & Major Branches

• Iliohypogastric: L1

• Ilioinguinal: L1

• Genitofemoral: L2

• Lateral Femoral Cutaneous: L2-L3

• Obturator: L2-L4

• Femoral: L2-L4

• Lumbosacral Trunk: L4-L5

Muscular Innervation of the Lower Limb

Femoral Nerve

• Anterior thigh

• Innervates: Iliacus, Sartorius, Pectineus, Rectus Femoris,

Vastus Lateralis, Vastus Intermedius, Vastus Medialis

Obturator Nerve

• Medial thigh

• Innervates: Pectineus, Obturator Externus, Adductor

Brevis, Adductor Longus, Adductor Magnus, Gracilis

Cutaneous Innervation of the Thigh

• Lateral Femoral Cutaneous Nerve: lateral sensory

innervation

• Obturator Nerve: medial sensory innervation, upper

thigh

• Femoral Nerve: anterior thigh, medial thigh, knee

Sacral Plexus

• Arises from spinal nerves L4–S4

• Located caudal to the lumbar

plexus

• Often considered together with

the lumbar plexus

• “Lumbosacral plexus”

Ventral Rami and Major Branches

• Superior Gluteal Nerve: L4-S1

• Inferior Gluteal Nerve: L5-S2

• Posterior Femoral Cutaneous Nerve: S1-S3

• Sciatic Nerve: L4–S3

• Pudendal Nerve: S2-S4

• Nerve to Quadratus Femoris: L4-S1

• Nerve to Obturator Internus: L5-S2

Mnemonic: Some Irish Sailors Pester Polly Quite Often

Innervation of the Pelvis

• Superior and Inferior

Gluteal Nerves:

innervate gluteal

muscles

• Superior: gluteus

medius, minimus,

and tensor fasciae

latae

• Inferior: gluteus

maximus

• Pudendal Nerve:

innervates perineum

Innervation of the Lower Limb

• Sciatic Nerve

• Largest nerve of the sacral

plexus

• 2 nerves in one sheath:

1. Tibial Nerve:

innervates posterior

lower limb

2. Common Fibular

(Peroneal) Nerve:

innervates

anterolateral leg

Tibial Nerve

• Passes through popliteal fossa, innervates posterior leg

and foot muscles and skin

• Divides into:

• Medial Plantar Nerve

• Lateral Plantar Nerve

Common Fibular Nerve

• Innervates anterolateral leg

• Divides into:

• Superficial Fibular Nerve: Fibularis Longus and

Fibularis Brevis

• Deep Fibular Nerve: Tibialis Anterior, Extensor

Hallucis Longus, Extensor Digitorum Longus, and

Fibularis Tertius

Cutaneous Innervation of the Lower Leg

• Common Fibular Nerves: dorsum of foot and

anterolateral leg

• Tibial Nerve: posterior leg and sole of foot

Innervation of the Skin

• Dermatome: area of skin innervated by cutaneous

branches of a single spinal nerve

• Pain along dermatome indicates nerve root damage

• General pattern similar, precise area innervated unique

like fingerprints