HUMAN ANATOMY

LECTURE TWELVE

PERIPHERAL NERVOUS SYSTEM

PERIPHERAL NERVOUS SYSTEM

• PNS consists of all the neuron cell bodies and process located outside the brain and spinal cord

• Collects info from sources inside and on the surface of the body

• Relays info by way of afferent fibers to the CNS

• Efferent fibers relay info from CNS to muscles and glands

• Divided into two parts:

- 12 pairs of cranial nerves

- 31 pairs of spinal nerves

PERIPHERAL NERVE STRUCTURE

• Consists of:

- dendrites

- cell bodies

- axon bundles

- Schwann cells

- connective tissue

ENDONEURIUM - surrounds individual neurons

PERINEURIUM - surrounds axon groups to form fascicles

EPINEURIUM - surrounds the entire nerve fibre

CRANIAL NERVES• Indicated by:

- Roman numerals I – XII from

anterior to posterior

- names

• May have one or more of three functions:

- sensory (special or general)

- somatic motor (control of

skeletal muscle)

- parasympathetic (regulation of

glands, smooth muscles, cardiac

muscle)

Olfactory Nerves (I) - sensory

• Specialized receptors for smell found in roof of nasal cavity

• Axons pass through cribform plate of ethmoid bone to the olfactory bulbs

• Attach directly to cerebrum (others attach to brain stem)

Optic Nerves (II) - sensory

• Carry visual info from special ganglia in eyes

• Pass through optic canals of sphenoid bone, at optic chiasm they cross and move toward opposite sides of the brain (occipital lobe)

Oculomotor Nerves (III) - motor and parasympathetic

• Each nerve innervates four of six extra-ocular muscles that move the eye and raise the upper eyelid

• Also controls intrinsic eye muscles that change the diameter of the pupil (adjust amount of light entering) and change shape of lens

Trochlear Nerves (IV) - motor

• Innervates superior oblique eye muscles - eye movement up/down

Trigeminal Nerves (V) – sensory and motor

• Sensation to face

• Innervates muscles of mastication

Abducens Nerves (VI) - motor

• Innervates 6th pair of eye muscles - make eye move to side

Facial Nerves (VII) – sensory, motor, parasympathetic• Deep pressure sensations of face and taste information from receptors in

the tongue• Innervate muscles of scalp, face and near ear• Parasympathetic to salivary glands, lacrimal glands, and glands of nasal

cavity

Vestibulocochlear Nerves (VIII) - sensory

• Receives sensory receptors from inner ear

• Concerned with balance sensations, equilibrium, hearing

Glossopharyngeal Nerves (IX) – sensory, motor, parasympathetic• Sensory responses to tongue, pharynx, and palate• Motor responses control swallowing

Vagus Nerves (X) – sensory, motor, parasympathetic

• Sensory information from acoustic canal, diaphragm, pharyngeal taste receptors, also along esophagus, respiratory tract and abdominal viscera (as far away as large intestine)

• Motor functions affect the heart, stomach, intestines, gall bladder

Accessory Nerves (XI) - motor

• Voluntary swallowing muscles of soft palate and pharynx

• Control vocal cords

• Also innervates muscles of neck and back

Hypoglossal Nerves (XII) - motor

• Innervates skeletal muscles of tongue - controls voluntary movements

SPINAL NERVES• 31 pairs of mixed (sensory and motor)

nerves

• First pair exit vertebral column between skull and atlas

• Last four exit via sacral foramina

• Others exit through intervertebral foramina

• 8 pair-cervical, 12 pair-thoracic,

5 pair-lumbar, 5 pair-sacral,

1 pair-coccygeal

• Most organized into 3 PLEXUS - where nerves come together and then separate (cervical plexus, brachial plexus, lumbosacral plexus)

DERMATOMAL MAP

• Spinal nerves indicated by capital letter and number

• DERMATOMAL MAP - skin area supplied with sensory innervation by spinal nervers

DISTRIBUTION OF SPINAL NERVESEach nerve has a dorsal and ventral

RAMUS (branch)

DORSAL RAMUS – around the back

• sensory and motor neurons that innervate deep muscles of the trunk

VENTRAL RAMUS – around the front

• Innervation depends upon which part of the spinal cord they leave from

Cervical plexus – C1-C4

Brachial plexus – C5-T1

Lumbar plexus – T1-L4

Sacral plexus – L4-L5

Cooccygeal plexus – S4-S5

PLEXUS (braid)

• Spinal nerves are organized into one of three plexuses - where nerves come together and then separate (all except T2 - T11 which extend around the thorax between the ribs to innervate intercostal muscles)

Cervical Plexus (C1-C5)• Innervates superficial neck

structures, skin of neck, posterior portion of head

PHRENIC NERVE C3-C5

• innervates diaphragm

Brachial Plexus (C5-T1)• Innervates pectoral girdle and

upper arm

• Five rami divide into 3 trunks that further separate into 6 cords that

branch off into 5 specific nerves:

- axillary nerve

- radial nerve

- musculocutaneous nerve

- median nerve

- ulnar nerve

AXILLARY NERVEC5, C6

Muscle innervation:

• Laterally rotates arm - teres minor

• Adducts arm - deltoid

Skin Innervation:

• Inferior lateral shoulder

RADIAL NERVEC5-T1

Muscle Innervation:

• Muscles located in posterior of arm

• Movements at elbow, wrist and thumb

Skin Innervation:

• Posterior surface of arm and forearm, lateral 2/3 on back of hand

MUSCULOCUTANEOUS NERVE

C5-T1

Muscle Innervation:

• Muscles located at anterior of arm

• Movements at shoulder, elbow and wrist

Skin Innervation:

• Lateral surface of forearm

ULNAR NERVEC8-T1

Muscle Innervation:

• Two anterior forearm muscles and most of hand muscles

• Movements at wrist, fingers, and hand

Skin Innervation:

• Medial 1/3 of hand, little finger, medial1/2 of ring finger

MEDIAN NERVEC6-T1

Muscle Innervation:

• Anterior forearm muscle and some hand muscles

• Movements of wrist, hand, fingers, thumb

Skin Innervation:

• Lateral 2/3 palm, thumb index and middle fingers, lateral ½ of ring finger and dorsal tips of same fingers

Thoracic Region T1-T12

THORACIC NERVES - not organized into a plexus

Muscle Innervation:

• Intercostal muscles

Skin Innervation:

• Thoracic dermatomes

•

Lumbosacral Plexus• Originates from nerves of the

lumbar plexus (L1-L4)

- obturator nerve

- femoral nerve

- saphenous branch

• Also nerves from the sacral plexus (L4-S4)

- tibial nerve

- peroneal nerve

OBTURATOR NERVEL2-L4

Muscle Innervation:

• Muscles of medial thigh

• Adduction of the thigh and knee

Skin Innervation:

• Superior middle side of thigh

FEMORAL NERVEL2-L4

Muscle Innervation:

• Anterior thigh muscles

• Movements of hip, knee, sartorius, quadriceps femoris

Skin Innervation:

• Anterior and lateral thigh, medial leg and foot

SAPHENOUS BRANCH• Branches off fermoral nerve

Muscle Innervation:

• Anterior and medial thigh

Skin Innervation:

• Anterior and medial thigh, medial leg

TIBIAL NERVE• Together with peroneal nerve

make up SCIATIC NERVE

L4-S3

Muscle Innervation:

• Posterior thigh muscles, anterior and posterior leg muscles

• Movement of hip, knee, foot, toes

Skin Innervation:

• Sole of foot

PERONEAL NERVE

(COMMON FIBULAR)L4-S3

Muscle Innervation:

• Muscles of lateral thigh and leg, some foot muscles

Skin Innervation:

• Lateral, anterior leg and sole of foot

Coccygeal Plexus S4-S5

• Muscles of pelvic floor

• Sensory info from skin over coccyx

PNS DISORDERSGeneral Disorders:Anesthesia - loss of sensation

• Hyperesthesia - increased sensitivity to pain, pressure, light

• Paesthesia - tingling, prickling, burning

• Neuralgia - nerve inflammation causing stabbing pain

• Sciatica - pain radiating down back of thigh and leg

Infections:• Herpes - skin lesions

• Shingles (herpes zoster) - adult chickenpox

• Poliomyelitis - infantile paralysis

• Anesthetic leprosy - bacterial infection of peripheral nerves

Genetic and Autoimmune Disorders:• Myasthenia gravis - results in fatigue and muscular weakness due to

inadequate ACh receptors