The Peripheral Nervous System

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The PeripheralNervous System

• PART 3

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Peripheral Nervous System
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The Peripheral Nervous System

• Nervous structures outside the brain and 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

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Sensory Input and Motor Output

• 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

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PNS Afferent Division

• Afferent (sensory) division transmits impulses
  from receptors to the CNS.
• Somatic afferent fibers carry impulses from
  skin, skeletal muscles, and joints
• Visceral afferent fibers transmit impulses from
  visceral organs

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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

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Types of Sensory and Motor Information
Figure 12.3
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Sensory

• General somatic senses include touch, 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)

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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

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Divisions of the ANS

• Sympathetic - fight or flight
• Catabolic (expend energy)
• Mass activation prepares for intense activity.
• Heart rate (HR) increases.
• Bronchioles dilate.
• Blood glucose increases.
• Parasympathetic - feed breed, rest digest
• Maintain homeostasis
• Normally not activated as a whole, stimulation of
  separate parasympathetic nerves.
• Relaxing effects
• Decreases HR.
• Dilates visceral blood vessels.
• Increases digestive activity.
• Dual innervation of many organs having a brake
  and an accelerator provides more control

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Sympathetic Division Organization

• Preganglionic neurons in segments T1 to L2
• Ganglia near the vertebral column
• Sympathetic ganglia
• Paired sympathetic chain ganglia
• Unpaired collateral ganglia
• Preganglionic fibers to adrenal medullae
• Epinephrine (adrenalin) into blood stream

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The Autonomic Nervous System

• Effects of Sympathetic Activation
• Generalized response in crises
• Increased alertness/energy
• Increased cardiovascular activity
• Increased respiratory activity
• Increased muscle tone

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Parasympathetic Division Organization

• Preganglionic neurons in brain stem and sacral
  spinal segment
• Ganglionic neurons (peripheral ganglia) in or
  near target organ
• Sacral fibers form pelvic nerves

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The Autonomic Nervous System

• Effects of Parasympathetic Activation
• Relaxation
• Food processing
• Energy absorption
• Brief effects at specific sites

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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

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Nerves

• Nerves cablelike organs in the PNS
• Consists of numerous axons wrapped in connective
  tissue
• Endoneurium layer of delicate 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

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Cranial Nerves

• Attach to the brain and pass through foramina of
  the skull
• Numbered from IXII
• 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

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The 12 Pairs of Cranial Nerves
Figure 14.5
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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)
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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)
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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)
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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)
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Trigeminal Nerve (V)

• 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
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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)
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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)
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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)
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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)
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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)
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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)
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Hypoglossal Nerve (XII)

• Runs inferior to the tongue - innervates the
  tongue muscles

Table 14.3 (12 of 12)
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Spinal Nerves

• 31 pairs contain thousands of nerve fibers
• Connect to the spinal cord
• Named for point of issue from the spinal cord
• 8 pairs of cervical nerves (C1C8)
• 12 pairs of thoracic nerves (T1T12)
• 5 pairs of lumbar nerves (L1L5)
• 5 pairs of sacral nerves (S1S5)
• 1 pair of coccygeal nerves (Co1)

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Spinal Nerves

• Connect to the spinal cord by the dorsal root and
  ventral root
• 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

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 Spinal Nerves
White matter
Ventral root
Gray matter
Dorsal root
Dorsal root ganglion
Dorsal and ventral rootlets of spinal nerve
Dorsal ramus of spinal nerve
Ventral ramus of spinal nerve
Spinal nerve
Rami communicantes
Sympathetic trunk (chain) ganglion
(a)
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Innervation of the Back

• Dorsal rami
• 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

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Innervation of the Thoracic region

• Ventral rami arranged in simple, segmented
  pattern
• Intercostal nerves supply intercostal muscles,
  skin, and abdominal wall
• Each gives off lateral and anterior cutaneous
  branches

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Introduction to Nerve Plexuses

• Nerve plexus a network of nerves
• Ventral rami (except T2 T12)
• Branch and join with one another
• Form nerve plexuses
• Cervical
• Brachial
• Lumbar
• Sacral
• Primarily serve the limbs
• Fibers from ventral rami crisscross

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The Cervical Plexus

• 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

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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
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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 L4S4
• 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