Peripheral Nervous System
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Transcript Peripheral Nervous System
Chapter 13
Sensory Receptor Types
Nociceptors
Respond to excess heat, pressure, or
chemicals
Tissue damage
All parts of the body but brain
Thermoreceptors
Temperature of skin and blood
Maintains homeostatic control via
the hypothalmus
Photoreceptors
Light absorbing pigments
Light detection
Sensory Receptor Types
Mechanoreceptors
Chemoreceptors
Touch, pressure, & vibrations
Chemicals in the internal &
Bend or stretch PM of
external environment
O2 in arterioles
Osmoreceptors - changes in
[blood solute]
Pheromone detection
receptor cell = changing
permeability
Stretch receptors – position
of body parts
Hair cells - sound waves and
H2O movements
Sensory Receptor Locations
Exteroceptors
Stimuli outside the body
Skin and special sense organs
Interoceptors
Stimuli within the body
Chemical messengers, tissue stretch, and temperature
Proprioceptors
Internal stimuli
Monitor position and stretch of joints, tendons, and
muscles
Sensory Receptor Structures
Unencapsulated
Free nerve endings
Most body tissues
Temperature and painful
stimuli
Capsaicin and itch
Merkel discs
Deeper epidermal layers
Light touch
Hair follicle receptors
Shaft of hair follicle
Light touch and hair bending
Encapsulated
Meissner’s corpuscles
Dermal papillae of sensitive and
hairless skin
Discriminative touch
Pacinian corpuscles
Deep in the dermis
Deep pressure initially, vibration
Ruffini endings
Deep dermis and hypodermis
Deep continuous pressure
Muscle spindles
Perimysium of skeletal muscle
Detect muscle stretch & initiate a reflex
Golgi tendon
Insertion tendons
Activation inhibits contracting muscle
Sensory Input
All senses trigger the same TYPE of signal
Distinction occurs in activated brain area
Typically graded response, but AP’s possible
Sensory receptors detect sensations and carry to the
brain
Awareness of environmental change
Brain constructs perceptions by integrating sensations
with other information
Neuronal communication involving multiple brain areas
The Working Brain
Sensory Adaptation
Sensory receptors
become less responsive
Fewer action potentials
Limits reactions to
normal background
stimuli
Shower or hot tub
temperature
Odors over time
Decoding Nerves
PNS organ consisting of parallel bundles of
axons enclosed by connective tissue layers
Epineurium
Perineurium
Endoneurium
Direction of transmission
Afferents: only to CNS
Dorsal root ganglia
Efferents: only from CNS
Sympathetic & parasympathetic ganglia
Mixed: carry both; most
Classified as cranial or spinal
Nerve Fiber Regeneration
Mature neurons don’t divide*
Cell body damage = death
Cut/compressed axons regenerate
Separated ends seal off and swell
Distal end of injury disintegrates
Lack of nutrients
Neurilemma maintained in endoneurium
Schwann cells proliferate & encourage
axon growth
Guide ‘sprouting’ axons to original contacts
Greater distance decreases chances
Regrowth never exact = retraining
Extremely rare in CNS
Cranial Nerves
Ventral portion of the
brain
1st 2 pairs attach to
forebrain
Remainders originate on
brainstem
Numbers
Cranial Nerve
Function
I
OLFACTORY
Smell (sensory)
II
OPTIC
Vision (sensory)
III
OCULOMOTOR
Eye movement (motor)
(medial, inferior, superior rectus muscle
& inferior oblique muscle)
IV
TROCHLEAR
Eye movements (motor)
(superior oblique muscle)
V
TRIGEMINAL
Temperature, pain, crude touch of face
(sensory) & mastication (motor)
VI
ABDUCENS
Eye movement (motor)
(lateral rectus muscle)
VII
FACIAL
Taste (2/3 of anterior tongue) (sensory)
Facial expressions (motor)
VIII
VESTIBULOCOCHLEAR
Hearing & Equilibrium (sensory)
IX
GLOSSOPHRAYNGEAL
Taste (1/3 of posterior tongue) (sensory)
Pharynx (swallowing & gag reflex)
(motor)
X
VAGUS
Senses blood pressure (sensory)
Stimulate heart rate and digestive organs
(motor)
XI
ACCESSORY
Head and neck movement (motor)
e.g. trapezius, levator scapula
XII
HYPOGLOSSAL
Tongue movement (motor)
Testing Cranial Nerves for Disorders
Olfactory
Smell substances
Anosima
Optic
Eye chart
Anopsias
Oculomotor
Follow object; pupil reflex
Strabismus, double vision, ptosis
Trochlear
See oculomotor
Trigeminal
Close/move jaws; touch face with
objects
Abducens
See oculomotor
Facial
Make various faces; tasting substances
Bell’s palsy, loss of taste, can’t close eye
Vestibulocochlear
Tuning fork; distance of sound
Deafness, vertigo, tinnitus
Glossopharyngeal
Swallowing & gag reflex; say ‘ah’
Vagus
See glossopharyngeal
Horseness, swallowing problems, death
(Spinal) accessory
Move head/shoulders against resistance
Hypoglossal
Stick out, retract, & move tongue to sides
Spinal Nerve Anatomy
Roots: medial & afferent OR
efferent
Dorsal root: peripheral receptors to
spinal cord
Ventral root: ventral horn to skeletal
muscles
Branches: laterally pass through
intervertebral foramen
Dorsal ramus: dorsal trunk
Ventral ramus: limbs & rest of trunk
Meningeal branch: meninges and
blood vessels
Plexus
Criss cross joining of ventral rami
Excludes T2 – T12
31 Pairs of Spinal Nerves
8 cervical
Cervical plexus
Brachial plexus
12 thoracic
Intercostal nerves & enlargements
5 lumbar
Lumbar plexus
5 sacral
Sacral plexus
1 coccygeal
Tailbone & perineum
Cervical Nerves
Cervical plexus
Phrenic nerve: diaphragm
Irritation causes hiccups
Brachial plexus C5 – C8
Median nerve: flexor muscles of the anterior forearm
and small hand muscles
Carpal tunnel syndrome and suicide attempts
Radial nerve: extensor muscle of posterior forearm and
triceps brachii
‘Saturday night paralysis’
Ulnar nerve: similar to median nerve
‘Funny bone’ and paralysis/distortion of medial fingers
Lumbosacral Plexus
Innervates lower limbs, buttocks, and pelvic muscles
Lumbar plexus L1 – L4
Femoral nerve: quadriceps and sartorius
Branches to saphenous
Obturator nerve: adductor muscles
Sacral plexus L4 – S4
Sciatic nerve: entire lower leg (except anteriomedial thigh)
Tibial: hamstrings
Common fibular nerve: anterior tibialis
Reflex Arc
Receptor
Senses stimulus
Sensory neuron (afferents)
Message to the CNS
Integration center
Synapses in CNS
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Monosynaptic (single motor or sensory neuron)
Polysynaptic (multiple interneurons)
Motor neuron (efferents)
Message to effectors
Effector
Muscle fibers or glands
Reflexes are rapid, predictable motor responses to a
stimulus
Classifying Reflexes
Somatic: activate skeletal muscle
Spinal: integration center is spinal cord
Stretch: ensures muscle length maintained (knee-jerk reflex)
Crossed extensor: withdrawl from painful stimuli (pin prick)
Superficial: cutaneous stimulation (plantar reflex)
Cranial nerve: integration center is brain stem
Corneal: stimulation causes blinking
Autonomic (visceral): activate smooth or cardiac muscle
Pupillary light: controls diameter of pupil (inside/outside)
Ciliospinal: ipsilateral pupil dilation from pain