Transcript lecture twelve – peripheral nervous system

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 NERVES
Each 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 NERVE
C5, C6
Muscle innervation:
• Laterally rotates arm - teres minor
• Adducts arm - deltoid
Skin Innervation:
• Inferior lateral shoulder
RADIAL NERVE
C5-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 NERVE
C8-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 NERVE
C6-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 NERVE
L2-L4
Muscle Innervation:
• Muscles of medial thigh
• Adduction of the thigh and knee
Skin Innervation:
• Superior middle side of thigh
FEMORAL NERVE
L2-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 DISORDERS
General 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:
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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