THE PERIPHERAL NERVOUS SYSTEM AND REFLEX ACTIVITY

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THE PERIPHERAL NERVOUS SYSTEM AND REFLEX
ACTIVITY
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PNS in the Structural Organization of the Nervous
system
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SENSORY RECEPTORS AND SENSATION
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SENSORY RECEPTORS

• Sensory receptors are specialized to respond to
  changes in their environment called stimuli
• Receptors my be classified according to the
  activating stimulus
• Receptors may be classified based on their
  location or the location of the activating
  stimulus
• Receptors may be classified based on their
  overall structural complexity

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SENSORY RECEPTORS

• Free, or naked, nerve endings are present
  everywhere in the body and respond primarily to
  pain and temperature
• Encapsulated Dendritic Endings
• Meissners corpuscles are receptors for
  discriminatory and light touch in hairless areas
  of the body
• Pacinian, or lamellated, corpuscles, are
  stimulated when deep pressure is first applied
• Ruffinis corpuscles respond to deep and
  continuous pressure
• Muscle spindles detect when a muscle is being
  stretched and initiate a reflex that resists the
  stretch
• Golgi tendon organs are stimulated when the
  associated muscle stretches the tendon
• Joint kinesthetic receptors monitor the stretch
  in the articular capsules of synovial joints

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OVERVIEW FROM SENSATION TO PERCEPTION

• The somatosensory system, the part of the sensory
  system serving the body wall and limbs, involve
  the receptor level, the circuit level, and the
  perceptual level
• Processing at the receptor level involves a
  stimulus that must excite a receptor in order for
  sensation to occur
• Processing at the circuit level is involved with
  delivery of impulses to the appropriate region
  of the cerebral cortex for stimulus localization
  and perception
• Processing at the parceptual level involves
  interpretation of sensory input in the cerebral
  cortex

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SOMATOSENSORY SYSTEM
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TRANSMISSION LINES NERVES AND THEIR
STRUCTURE AND REPAIR
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NERVES AND ASSOCIATED GANGLIA

• A nerve is a cordless organ consisting of
  parallel bundles of peripheral axons enclosed by
  connective tissue wrappings
• Ganglia are collections of neuron cell bodies
  associated with nerves in the PNS
• If damage to a neuron occurs to the axon and the
  cell body remains intact, cut or compressed axons
  can regenerate

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NERVE STRUCTURE
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NERVE REGENERATION
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CRANIAL NERVES

• Olfactory nerves are responsible for smell
• Optic nerves are responsible for vision
• Oculomotor nerves play a role in eye movement
• Trochlear nerves play a role in eye movement
• Trigeminal nerves are general sensory nerves of
  the face
• Abducens nerves play a role in eye movement
• Facial nerves function as the chief motor nerves
  of the face
• Vestibulocochlear nerves are responsible for
  hearing and equilibrium
• Glossopharyngeal nerves innervate part of the
  tongue and pharynx
• Vagus nerves innervate the heart, lungs, and the
  abdominal organs
• Accessory nerves move structures associated with
  the head and neck
• Hypoglossal nerves are mixed nerves that arise
  from the medulla and serve the tongue

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CRANIAL NERVES
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CRANIAL NERVES
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SPINAL NERVES

• Thirty-one pairs of mixed spinal nerves arise
  from the spinal cord and serve the entire body
  except the head and neck
• Innervation of Specific Body Regions
• Each spinal nerve connects to the spinal cord by
  a dorsal root and a ventral root
• Rami lie distal to and are lateral branches of
  the spinal nerves that carry both motor and
  sensory fibers
• The back is innervated by the dorsal rami with
  each rami innervating the muscle in line with the
  point of origin from the spindle column
• Only in the thorax are the ventral rami arranged
  in a simple segmental pattern corresponding to
  that of the dorsi rami
• The cervical plexus is formed by the ventral rami
  of the first four cervical nerves
• The brachial plexus is situated partly in the
  neck and partly in the axilla and gives rise to
  virtually all the nerves that innervate the upper
  limb
• The sacral and lumbar plexuses overlap and
  because many fibers of the lumber plexus
  contribute to the sacral plexus via the
  lumbosacral trunk, the two plexuses are often
  referred to as the lumbosacral plexus
• The area of skin innervated by the cutaneous
  branches of a single nerve is called a dermatone
• Hintons law states that any nerve serving a
  muscle that produces movement at a joint also
  innervates the joint and the skin over the joint

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SPINAL NERVES
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FORMATION OF SPINAL NERVES
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RAMI DISTRIBUTION OF THE SPINAL NERVE
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CERVICAL PLEXUS
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BRACHIAL PLEXUS
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BRACHIAL PLEXUS
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LUMBAR PLEXUS
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SACRAL PLEXUS
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DERMATOMES
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MOTOR ENDINGSANDMOTOR ACTIVITY
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PERIPHERAL MOTOR ENDINGS

• Peripheral motor endings are the PNS element that
  activates effectors by releasing
  neurotransmitters
• The terminals of the somatic motor fibers that
  innervate voluntary muscles form elaborate
  neuromuscular junctions with their effector cells
  and they release the neurotransmitter
  acetylcholine
• The junctions between autonomic motor endings and
  the visceral effectors involve varicosities and
  release either acetylcholine or epinephrine as
  their neurotransmitter

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OVERVIEW OF MOTOR INTEGRATIONFROM INTENTION
TO EFFECT
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LEVELS OF MOTOR CONTROL

• The segmental level is the lowest level on the
  motor control hierarchy and consists of the
  spinal cord circuits
• The projection level has direct control of the
  spinal cord
• The precommand level is made up of the cerebellum
  and the basal nuclei and is the highest level of
  the motor system hierarchy

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LEVELS OF MOTOR CONTROL
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REFLEX ACTIVITY
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THE REFLEX ARC

• Reflexes are unlearned, rapid, predictable motor
  responses to a stimulus, and occur over highly
  specific neural pathways called reflex arc

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THE REFLEX ARC
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SPINAL REFLEXES

• Spinal reflexes are somatic reflexes mediated by
  the spinal cord
• In the stretch reflex the muscle spindle is
  stretched and excited by either an external
  stretch or an internal stretch
• The Golgi tendon reflex produces muscle
  relaxation and lengthening in response to
  contraction
• The flexor, or withdrawal, reflex is initiated by
  a painful stimulus and causes automatic
  withdrawal of the threatened body part from the
  stimulus
• They crossed extensor reflex is a complex spinal
  reflex consisting of an ipsilateral withdrawal
  reflex and a contralateral extensor reflex
• Superficial reflexes are elicited by gentle
  cutaneous stimulation

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Anatomy of the Spindle and Golgi Tendon Organ
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Operation of the Muscle Spindle
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STRETCH REFLEX
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DEEP GOLGI TENDON REFLEX
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CROSSED EXTENSOR REFLEX
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PAIN TRANSMISSIOM
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DEVELOPMENTAL ASPECTS OF THE PERIPHERAL NERVOUS
SYTEM

• The Spinal Nerves branch from the developing
  spinal cord and adjacent neural crest and exit
  between the forming vertebrate
• Each nerve becomes associated with the adjacent
  muscle mass
• Cranial Nerves innervate muscles of the head in a
  similar way
• Sensory Receptors atrophy to some degree with
  age, and there is a decrease in muscle tone in
  the face and neck, reflexes occur a bit more
  slowly