Download Nerves

The Peripheral
Nervous System
PART 3
Peripheral Nervous System
The Peripheral Nervous System
• Nervous structures outside the brain and
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•
spinal cord
Nerves allow the CNS to receive
information and take action
Functional components of the PNS
• Sensory inputs and motor outputs
•
categorized as somatic or visceral
Sensory inputs also classified as general or
special
Sensory Input and Motor Output
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Sensory (afferent) signals picked up by sensor receptors,
carried by nerve fibers of PNS to the CNS
Motor (efferent) signals are carried away from the CNS,
innervate muscles and glands
Divided according to region they serve
• Somatic body region
• Visceral body region
•
Results in four main subdivisions
• Somatic sensory
• Visceral sensory
• Somatic motor
• Visceral motor
PNS Afferent Division
•
Afferent (sensory) division – transmits impulses from
receptors to the CNS.
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Somatic afferent fibers – carry impulses from skin, skeletal
muscles, and joints
Visceral afferent fibers – transmit impulses from visceral
organs
PNS Efferent Division
• Motor (efferent) division – transmits impulses from the CNS to
effector organs. Two subdivisions:
• Somatic nervous system – provides conscious control of skeletal
muscles
• Autonomic nervous system – regulates smooth muscle, cardiac
muscle, and glands
Types of Sensory and Motor Information
Figure 12.3
Sensory
• General somatic senses – include touch,
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pain, vibration, pressure, temperature
Proprioceptive senses – detect stretch in
tendons and muscle provide information on
body position, orientation and movement of
body in space
Special Senses - hearing, balance, vision,
olfaction (smell), gustation (taste)
Motor
• General somatic motor
• Signals contraction of skeletal muscles
• Under our voluntary control
• Visceral motor
• Makes up autonomic nervous system (ANS)
• Regulates the contraction of smooth and
cardiac muscle, controls function of visceral
organs
• ANS has two divisions
• Parasympathetic
• Sympathetic
Divisions of the ANS
•
Sympathetic - “fight or flight”
• Catabolic (expend energy)
• Mass activation prepares for intense
activity.
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Heart rate (HR) increases.
Bronchioles dilate.
Blood [glucose] increases.
Parasympathetic - “feed & breed”, “rest
& digest”
• Maintain homeostasis
• Normally not activated as a whole,
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stimulation of separate
parasympathetic nerves.
Relaxing effects:
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Decreases HR.
Dilates visceral blood vessels.
Increases digestive activity.
Dual innervation of many organs —
having a brake and an accelerator
provides more control
Sympathetic Division Organization
•
Preganglionic neurons in
segments T1 to L2
•
Ganglia near the vertebral
column
•
Sympathetic ganglia
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Paired sympathetic chain
ganglia
•
Unpaired collateral ganglia
Preganglionic fibers to adrenal
medullae
•
Epinephrine (adrenalin) into
blood stream
The Autonomic Nervous System
• Effects of Sympathetic Activation
• Generalized response in crises
• Increased alertness/energy
• Increased cardiovascular activity
• Increased respiratory activity
• Increased muscle tone
Parasympathetic Division Organization
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Preganglionic neurons in
brain stem and sacral
spinal segment
Ganglionic neurons
(peripheral ganglia) in or
near target organ
Sacral fibers form pelvic
nerves
The Autonomic Nervous System
• Effects of Parasympathetic Activation
• Relaxation
• Food processing
• Energy absorption
• Brief effects at specific sites
Basic Structural Components of the PNS
• Sensory receptors – pick up stimuli from inside or outside the body
• Motor endings – axon terminals of motor neurons innervate effectors
•
(muscle fibers and glands)
Nerves and ganglia
• Nerves – bundles of peripheral axons
• Ganglia – clusters of peripheral neuronal cell bodies
Nerves
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Nerves – cablelike organs in the
PNS
Consists of numerous axons
wrapped in connective tissue
• Endoneurium – layer of delicate
•
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connective tissue surrounding the axon
Perineurium – connective tissue wrapping
surrounding a nerve fascicle
Nerve fascicles – groups of axons bound into
bundles
• Epineurium – whole nerve is surrounded
by tough fibrous sheath
•
Axon is surrounded by Schwann
cells
Cranial Nerves
• Attach to the brain and pass through
•
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foramina of the skull
Numbered from I–XII
Cranial nerves I and II attach to the
forebrain
• All others attach to the brain stem
• Primarily serve head and neck structures
• The vagus nerve (X) extends into the
abdomen
The 12 Pairs of Cranial Nerves
Figure 14.5
Olfactory Nerves (I)
• Sensory nerves of smell
olfactory nerve (I)
Olfactory bulb
Olfactory tract
Optic nerve (II)
Optic chiasma
Optic tract
Oculomotor nerve (III)
Trochlear nerve (IV)
Trigeminal nerve (V)
Abducens nerve (VI)
Cerebellum
Medulla
Table 14.3 (1 of 12)
Optic Nerve (II)
• Sensory nerve of vision
Filaments of
olfactory nerve (I)
Olfactory bulb
Olfactory tract
Optic nerve (II)
Optic chiasma
Optic tract
Oculomotor nerve (III)
Trochlear nerve (IV)
Trigeminal nerve (V)
Abducens nerve (VI)
Cerebellum
Medulla
Table 14.3 (2 of 12)
Oculomotor Nerve (III)
• Innervates four of the extrinsic eye muscles
Filaments of
olfactory nerve (I)
Olfactory bulb
Olfactory tract
Optic nerve (II)
Optic chiasma
Optic tract
Oculomotor nerve (III)
Trochlear nerve (IV)
Trigeminal nerve (V)
Abducens nerve (VI)
Cerebellum
Medulla
Table 14.3 (3 of 12)
Trochlear Nerve (IV)
•
Innervates the superior oblique muscle (an
extrinsic eye muscle)
Filaments of
olfactory nerve (I)
Olfactory bulb
Olfactory tract
Optic nerve (II)
Optic chiasma
Optic tract
Oculomotor nerve (III)
Trochlear nerve (IV)
Trigeminal nerve (V)
Abducens nerve (VI)
Cerebellum
Medulla
Table 14.3 (4 of 12)
Trigeminal Nerve (V)
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•
Provides sensory innervation to the face
Motor innervation to chewing muscles
Filaments of
olfactory nerve (I)
Olfactory bulb
Olfactory tract
Optic nerve (II)
Optic chiasma
Optic tract
Oculomotor nerve (III)
Trochlear nerve (IV)
Trigeminal nerve (V)
Abducens nerve (VI)
Cerebellum
Medulla
Abducens Nerve (VI)
• Abducts the eyeball – innervates lateral
rectus muscle
Filaments of
olfactory nerve (I)
Olfactory bulb
Olfactory tract
Optic nerve (II)
Optic chiasma
Optic tract
Oculomotor nerve (III)
Trochlear nerve (IV)
Trigeminal nerve (V)
Abducens nerve (VI)
Cerebellum
Medulla
Table 14.3 (6 of 12)
•
Facial Nerve (VII)
Innervates muscles of facial expression
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Table 14.3 (7 of 12)
Vestibulocochlear Nerve (VIII)
• Sensory nerve of hearing and balance
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Table 14.3 (8 of 12)
Glossopharyngeal Nerve (IX)
• Innervates structures of the tongue and
pharynx
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Table 14.3 (9 of 12)
Vagus Nerve (X)
• A mixed sensory and motor nerve - “Wanders” into thorax and abdomen
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Table 14.3 (10 of 12)
Accessory Nerve (XI)
•
An accessory part of the vagus nerve -innervates
trapezius muscle
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Table 14.3 (11 of 12)
Hypoglossal Nerve (XII)
•
Runs inferior to the tongue - innervates the tongue
muscles
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Table 14.3 (12 of 12)
Spinal Nerves
• 31 pairs – contain thousands of
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nerve fibers
Connect to the spinal cord
Named for point of issue from the
spinal cord
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8 pairs of cervical nerves (C1–C8)
12 pairs of thoracic nerves (T1–T12)
5 pairs of lumbar nerves (L1–L5)
5 pairs of sacral nerves (S1–S5)
1 pair of coccygeal nerves (Co1)
Spinal Nerves
• Connect to the spinal cord
by the dorsal root and
ventral root
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Dorsal root – contains
sensory fibers
Dorsal root ganglion – of
afferent cell bodies
Ventral root – contains
motor fibers arising from
anterior gray column
• Branch into dorsal ramus
•
and ventral ramus both
contain sensory and motor
fibers
Rami communicantes
connect to the base of the
ventral ramus and lead to
the sympathetic chain
ganglia
Spinal Nerves
Ventral root
Dorsal root
Dorsal root
ganglion
Dorsal ramus
of spinal nerve
Ventral ramus
of spinal nerve
Spinal nerve
Rami communicantes
Sympathetic trunk
(chain) ganglion
(a)
White matter
Gray matter
Dorsal and ventral
rootlets of spinal
nerve
Innervation of the Back
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Dorsal rami
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Innervate back muscles
Follow a neat, segmented pattern
Innervate a horizontal strip of muscle and skin
In line with emergence point from the vertebral column
Innervation of the Thoracic region
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Ventral rami arranged in simple, segmented pattern
Intercostal nerves – supply intercostal muscles, skin, and
abdominal wall
• Each gives off lateral and anterior cutaneous branches
Introduction to Nerve Plexuses
• Nerve plexus – a network of
•
nerves
Ventral rami (except T2 – T12)
• Branch and join with one
another
• Form nerve plexuses
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Cervical
Brachial
Lumbar
Sacral
• Primarily serve the limbs
• Fibers from ventral rami
crisscross
The Cervical Plexus
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Buried deep in the neck under the sternocleidomastoid muscle
Formed by ventral rami of first four cervical nerves (C 1 – 4)
Most are cutaneous nerves
Some innervate muscles of the anterior neck
Brachial Plexus
• Brachial plexus lies in the neck and axilla
• Formed by ventral rami of C5 – C8 give rise to cords
• Cords give rise to main nerves of the upper limb
Figure 14.9d
•
Lumbar Plexus
Arises from L1– L4
• Smaller branches innervate the posterior abdominal wall and psoas
•
muscle
Main branches innervate the anterior thigh
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The Sacral Plexus
Arises from spinal nerves L4–S4
Often considered with the lumbar plexus referred to as the lumbosacral plexus
Sciatic nerve – the largest nerve of the sacral plexus is actually two nerves in one sheath
• Tibial nerve – innervates most of the posterior lower limb
• Common fibular (peroneal) nerve – innervates muscles of the anterolateral leg