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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