Peripheral

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Peripheral
Nervous System
Ch 13
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____Cranial nerves attach to brain
___Spinal nerves attach to spinal cord
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• Sensation
• The conscious or subconscious awareness of
  external or internal stimuli.
• Perception
• The conscious awareness and the interpretation of
  meaning of sensations.

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Peripheral sensory receptors

• By location
• Exteroceptors
• Sensitive to stimuli arising from outside body
• Interoceptors
• Or visceroreceptors, from internal viscera
• Proprioceptors
• Monitor degree of stretch in skeletal muscles,
  tendons, joints and ligaments

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General Senses vs. Special Senses

• Pain
• Temperature
• Light touch
• Pressure
• Sense of body and limb position

• Taste
• Smell
• Vision
• Hearing
• Balance

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Sensory Receptors

• Mechanoreceptors
• Thermoreceptors
• Photoreceptors
• Chemoreceptors
• Nociceptors
• Osmoreceptors

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General Senses
Unencapsulated Nerve Endings
Encapsulated Nerve Endings
vs
Naked nerve endings surrounded by one or more
layers
Free nerve endings
Pacinian corpuscle
skin, bones, internal organs, joints
Deeper tissue, muscles
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Unencapsulated Nerve Endings
pain, light touch, and temperature

• Free Nerve Endings - Pain Temperature
• Merkels Discs - Light Touch Pressure
• Root Hair Plexuses - Light Touch

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Encapsulated Nerve Endings

• Pacinian Corpuscles - Deep Pressure
• Meissners Corpuscles - Discriminative Touch in
  Hairless Skin Areas
• Krauses End-Bulbs - Discriminative Touch in
  Mucous Membranes
• Ruffinis Corpuscles - Deep Pressure Stretch
  (Proprioception)

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The Epidermis
Merkel cell
Merkel Cells- slow mechanoreceptors (basal layer)
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Skin Receptors
free nerve endings
Merkel disc
Meissners corpuscles
Ruffini corpuscle
root hair plexus
Pacinian corpuscles
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Encapsulated Nerve Endings
Proprioceptors

• Muscle Spindles - Skeletal Muscle Stretching
• Golgi Tendon Organs - Tendon Stretching
• Joint kinesthetic receptors monitors stretch in
  synovial joints sends info to cerebellum and
  spinal reflex arcs

• to cerebrum,
• cerebellum and
• spinal reflex arcs

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Muscle Spindle
Tendon Organ
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Peripheral motor endings

• Innervation of skeletal muscle
• Innervation of visceral muscles and glands

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• Motor axons innervate skeletal muscle fibers at
  neuromuscular junctions motor end plates
• 
  
  
• 
  

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Motor unit motor neuron all the muscle fibers
it innervates

• All muscles in motor unit contract together when
  neuron fires
• Stimulation of single motor unit causes weak
  contraction of entire muscle (spread out)

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Innervation of visceral muscles glands

• Near end organ visceral motor axon swells
  presynaptic terminals (vesicles with
  neurotransmitters) action slow (NT diffuses)

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Somatic Pain-results from injuries to skin,
muscle, joints, tendon
vs.Visceral Pain-
pain in body organs
Pain- protective function
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Referred Pain-felt on the body surface
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Nerve Damage Repair in PNS

• Mature neurons are amitotic
• If the soma of a damaged nerve is intact, axon
  will regenerate
• Involves coordinated activity among
• Macrophagesremove debris
• Schwann cellsform regeneration tube and secrete
  growth factors
• Axonsregenerate damaged part
• CNS oligodendrocytes bear growth-inhibiting
  proteins that prevent CNS fiber regeneration

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Endoneurium
Schwann cells
The axon becomes fragmented at the injury
site.
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Droplets of myelin
Fragmented axon
Site of nerve damage
Figure 13.4 (1 of 4)
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Macrophages clean out the dead axon distal to
the injury.
2
Schwann cell
Macrophage
Figure 13.4 (2 of 4)
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Axon sprouts, or filaments, grow through
a regeneration tube formed by Schwann cells.
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Aligning Schwann cells form regeneration tube
Fine axon sprouts or filaments
Figure 13.4 (3 of 4)
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The axon regenerates and a new myelin sheath
forms.
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Site of new myelin sheath formation
Schwann cell
Single enlarging axon filament
Figure 13.4 (4 of 4)
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Cranial Nerves

• On Old Olympus Towering Tops A Fat Voracious
  German Viewed A Hop
• Olfactory- smell
• Optic- vision
• Oculomotor- 4 of the 6 extrinsic eye muscles
• Trochlear- extrinsic eye muscles
• Trigeminal- sensory fibers to the face and motor
  fibers to the chewing muscles
• Abducens- controls eye muscles that turn the eye
  laterally
• Facial- facial expression
• Vestibulocochlear- hearing and balance
• Glosopharyngeal- tongue and pharynx
• Vagus- parasympathetic control of heart, lungs
  abdominal organs
• Accessory- accessory part of vagus nerve, neck
  throat muscles
• Hypoglossal- moves muscles under tongue

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Cranial Nerves
Olfactory
Optic
Oculomotor
Trochlear
Trigeminal
Abducens
Facial
Vestibulocochlear
Glossopharyngeal
Vagus
Accessory
Hypoglossal
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Olfactory Nerves I
Olfactory bulb
Olfactory tract
Filaments of olfactory nerve
Olfactory receptor cell
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Optic Nerves II
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Oculomotor Nerves III
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Trochlear Nerves IV
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Trigeminal Nerves V
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Abducens Nerves VI
Lateral rectus muscle cut
Abducens nerve
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Facial Nerves VII
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Vestibulocochlear Nerves VIII
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Glosopharyngeal Nerves IX
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Vagus Nerves X
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Accessory Nerves XI
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Hypoglossal Nerves XII
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Nerve Pathways into the Spinal Cord
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Spinal nerves
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Spinal nerves

• Dorsal roots sensory fibers arising from cell
  bodies in dorsal root ganglia
• Ventral roots motor fibers arising from
  anterior gray column of spinal cord

Ventral root ganglia
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• Dorsal and ventral roots join in an
  intervertebral foramen forming spinal nerve
• Outside foramen, re-branch as rami (sing.,
  ramus) Dorsal and ventral rami (somatic) Rami
  communicantes (visceral)

Spinal nerve
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• Dorsal rami serve the muscles and skin of the
  posterior trunk
• Back, from neck to sacrum, innervated in a neatly
  segmented pattern horizontal strip at same level
  as emergence from spinal cord
• Ventral rami serve the muscles and skin of the
  lateral and anterior trunk
• In thorax only, a simple segmented pattern as
  intercostal nerves
• Also serve the limbs

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• Cross section of thorax showing main roots and
  branches of a spinal nerve
• In the thorax, each ventral ramus continues as an
  intercostal nerve

Dorsal ramus
Ventral ramus
Intercostal nerve
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Spinal Nerves
Nerve plexuses

• Networks of successive ventral rami that exchange
  fibers (crisscross redistribute)
• Mainly innervate the limbs
• Thoracic ventral rami do not form nerve plexuses

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Cervical Plexus

• Formed by ventral rami of C1C4
• Innervates skin and muscles of the neck, ear,
  back of head, and shoulders
• Phrenic nerve
• Major motor and sensory nerve of the diaphragm
  (receives fibers from C3C5)

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Cervical Plexus
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Brachial Plexus

• Formed by ventral rami of C5C8 and T1 (and often
  C4 and T2)
• It gives rise to the nerves that innervate the
  upper limb
• Major branches of this plexus
• Rootsfive ventral rami (C5T1)
• Trunksupper, middle, and lower
• Divisionsanterior and posterior
• Cordslateral, medial, and posterior

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Brachial Plexus
Roots (ventral rami)
C4
Dorsal scapular
C5
Nerve to subclavius
C6
Suprascapular
Upper
Posterior divisions
C7
Middle
Trunks
C8
Lateral
Lower
Cords
T1
Posterior
Long thoracic
Medial pectoral
Medial
Lateral pectoral
Axillary
Upper subscapular
Musculo- cutaneous
Lower subscapular
Thoracodorsal
Radial
Medial cutaneous nerves of the arm and forearm
Median
Ulnar
(a) Roots (rami C5 T1), trunks, divisions, and
cords
Anterior divisions
Posterior divisions
Trunks
Roots
Figure 13.9 (a)
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Brachial Plexus Nerves

• Axillaryinnervates the deltoid, teres minor, and
  skin and joint capsule of the shoulder
• Musculocutaneousinnervates the biceps brachii
  and brachialis and skin of lateral forearm
• Medianinnervates the skin, most flexors and
  pronators in the forearm, and some intrinsic
  muscles of the hand
• Ulnarsupplies the flexor carpi ulnaris, part of
  the flexor digitorum profundus, most intrinsic
  muscles of the hand, and skin of medial aspect of
  hand
• Radialinnervates essentially all extensor
  muscles, supinators, and posterior skin of limb

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Axillary nerve
Anterior divisions
Posterior divisions
Trunks
Roots
Humerus
Radial nerve
Musculocutaneous nerve
Ulna
Radius
Ulnar nerve
Median nerve
Radial nerve (superficial branch)
Dorsal branch of ulnar nerve
Superficial branch of ulnar nerve
Digital branch of ulnar nerve
Muscular branch
Median nerve
Digital branch
(c) The major nerves of the upper limb
Figure 13.9 (c)
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Note distribution of cutaneous nerves
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Sensory innervation, palm

1. Ulnar nerve
2. Median nerve
3. Radial nerve

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Thoracic Nerves

• T3-T12
• 11 intercostal nerve
• 1 subcostal nerve

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Lumbar Plexus

• Arises from L1L4
• Innervates the thigh, abdominal wall, and psoas
  muscle
• Femoral nerveinnervates quadriceps and skin of
  anterior thigh and medial surface of leg
• Obturator nervepasses through obturator foramen
  to innervate adductor muscles

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Lumbar Plexus
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Sacral Plexus

• Arises from L4S4
• Serves the buttock, lower limb, pelvic
  structures, and perineum
• Sciatic nerve
• Longest and thickest nerve of the body
• Innervates the hamstring muscles, adductor
  magnus, and most muscles in the leg and foot
• Composed of two nerves tibial and common fibular

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Sacral Plexus
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Functional Divisions of the Peripheral Nervous
System

• Afferent Division
• Sensory (advances) neuron goes toward CNS
• Efferent Division
• Motor (exits) neuron- leaves CNS
• Somatic Nervous System
• Autonomic Nervous System

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REFLEXES

• Rapid, predictable response to a stimulus.
• Unlearned, involuntary, "hard-wired" into our
  neuroanatomy at the cellular tissue level.
• The simplest type of nerve circuit regulates a
  reflex (or autonomic response) and is called a
  reflex arc.

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Methods of Classifying Reflexes
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Reflex classifications

• Innate reflexes
• Result from connections that form between neurons
  during development
• Acquired reflexes
• Learned, and typically more complex

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More reflex classifications

• Cranial reflexes
• Reflexes processed in the brain
• Spinal reflexes
• Interconnections and processing events occur in
  the spinal cord

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still more reflex classifications

• Somatic reflexes
• Control skeletal muscle
• Visceral reflexes (autonomic reflexes)
• Control activities of other systems

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and more reflex classifications

• Monosynaptic reflex
• Sensory neuron synapses directly on a motor
  neuron
• Polysynaptic reflex
• At least one interneuron between sensory afferent
  and motor efferent
• Longer delay between stimulus and response

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Spinal Reflex Arc
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1
Quadriceps strongly contracts. Golgi tendon
organs are activated.
Interneurons
Quadriceps (extensors)
Spinal cord
Golgi tendon organ
Hamstrings (flexors)

Excitatory synapse

Inhibitory synapse
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1
2
Quadriceps strongly contracts. Golgi tendon
organs are activated.
Afferent fibers synapse with interneurons in
the spinal cord.
Interneurons
Quadriceps (extensors)
Spinal cord
Golgi tendon organ
Hamstrings (flexors)

Excitatory synapse

Inhibitory synapse
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1
2
Quadriceps strongly contracts. Golgi tendon
organs are activated.
Afferent fibers synapse with interneurons in
the spinal cord.
Interneurons
Quadriceps (extensors)
Spinal cord
Golgi tendon organ
Hamstrings (flexors)
3a
The motor neurons (red) send activating impulses
to the quadriceps causing it to contract,
extending theknee.

Excitatory synapse

Inhibitory synapse
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1
2
Quadriceps strongly contracts. Golgi tendon
organs are activated.
Afferent fibers synapse with interneurons in
the spinal cord.
Interneurons
Quadriceps (extensors)
Spinal cord
Golgi tendon organ
Hamstrings (flexors)

The interneurons (green) make inhibitory synapses
with ventral horn neurons (purple) that prevent
the antagonist muscles (hamstrings) from
resisting the contraction of the quadriceps.
3a
3b
The motor neurons (red) send activating impulses
to the quadriceps causing it to contract,
extending theknee.
The motor neurons (red) send activating impulses
to the quadriceps causing it to contract,
extending theknee.

Excitatory synapse

Inhibitory synapse
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Reflex Arc
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Baby Reflexes

• Palmar Grasp reflex
• Suckling reflex
• Rooting reflex
• Babinski/plantar reflex

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Pupillary Reflex
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Mammalian Dive Reflex

• An automated response system for diving in cold
  water (less than about 21C / 70F).
• Bradycardia
• Vasoconstriction to extremities
• Apnea

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INQUIRY

1. What is a reflex?
2. Damage of the spinal cord above C3 can result
   in_____?
3. In which portion of the spinal cord do the
   interneurons lie?
4. What kind of peripheral nerve fiber carries motor
   impulses outward to smooth muscles and glands of
   internal organs?