Transcript THE PERIPHERAL NERVOUS SYSTEM AND REFLEX ACTIVITY

THE PERIPHERAL NERVOUS SYSTEM
AND
REFLEX ACTIVITY
PNS in the Structural Organization
of the Nervous system
SENSORY RECEPTORS
AND
SENSATION
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
SENSORY RECEPTORS
• Free, or naked, nerve endings are present everywhere in
the body and respond primarily to pain and temperature
• Encapsulated Dendritic Endings
– Meissner’s 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
– Ruffini’s 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
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
SOMATOSENSORY SYSTEM
TRANSMISSION LINES:
NERVES
AND
THEIR STRUCTURE
AND
REPAIR
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
NERVE STRUCTURE
NERVE REGENERATION
CRANIAL NERVES
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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
CRANIAL NERVES
CRANIAL NERVES
SPINAL NERVES
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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
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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
Hinton’s law states that any nerve serving a muscle that produces movement at a joint also
innervates the joint and the skin over the joint
SPINAL NERVES
FORMATION OF SPINAL NERVES
RAMI DISTRIBUTION OF THE
SPINAL NERVE
CERVICAL PLEXUS
BRACHIAL PLEXUS
BRACHIAL PLEXUS
LUMBAR PLEXUS
SACRAL PLEXUS
DERMATOMES
MOTOR ENDINGS
AND
MOTOR ACTIVITY
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
OVERVIEW
OF
MOTOR INTEGRATION:
FROM INTENTION TO EFFECT
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
LEVELS OF MOTOR CONTROL
REFLEX ACTIVITY
THE REFLEX ARC
• Reflexes are unlearned, rapid, predictable
motor responses to a stimulus, and occur
over highly specific neural pathways called
reflex arc
THE REFLEX ARC
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
Anatomy of the Spindle and Golgi
Tendon Organ
Operation of the Muscle Spindle
STRETCH REFLEX
DEEP GOLGI TENDON REFLEX
CROSSED EXTENSOR REFLEX
PAIN TRANSMISSIOM
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