Download Peripheral Nervous System

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
• Touch, pressure, & vibrations
• Bend or stretch PM of
receptor cell = changing
permeability
– Stretch receptors – position of
body parts
– Hair cells - sound waves and
H2O movements
Chemoreceptors
• Chemicals in the internal &
external environment
– O2 in arterioles
– Osmoreceptors - changes in
[blood solute]
– Pheromone detection
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
•
•
•
•
Epineurium – covers nerve
Perineurium – covers fascicle
Endoneurium – cover axon
Direction of transmission
– Sensory afferents go to CNS
• Dorsal root ganglia
– Motor efferents come from CNS
• Sympathetic & parasympathetic
ganglia
– Mixed carry both; most nerves
• 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
• Sensory, motor, or mix
• 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
(SPINAL) ACCESSORY
Head and neck movement (motor)
e.g. trapezius, levator scapula
XII
HYPOGLOSSAL
Tongue movement (motor)
Testing Cranial Nerves for Disorders
• Olfactory
• Facial
– Smell substances
– Anosima
• Optic
– Make various faces; tasting substances
– Bell’s palsy, loss of taste, can’t close eye
• Vestibulocochlear
– Eye chart
– Anopsias
• Oculomotor
– Follow object; pupil reflex
– Strabismus, double vision, ptosis
• Trochlear
– Tuning fork; distance of sound
– Deafness, vertigo, tinnitus
• Glossopharyngeal
– Swallowing & gag reflex; say ‘ah’
• Vagus
– See glossopharyngeal
– Horseness, swallowing problems, death
– See oculomotor
• Trigeminal
• (Spinal) accessory
– Corneal reflex; close/move jaws; touch
face with objects
•
• Abducens
– See oculomotor
– Move head/shoulders against resistance
Hypoglossal
– Stick out, retract, & move tongue to sides
Spinal Nerve Anatomy
• Roots
– Dorsal root: peripheral receptors (sensory)
to spinal cord
– Ventral root: ventral horn to skeletal
muscles (motor)
• 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 femoral
innervation)
• Tibial: hamstrings
• Common fibular nerve: anterior tibialis
Reflex Arc
• Receptor
– Senses stimulus
• Sensory neuron (afferents)
– Message to the CNS
• Integration center
– Synapses in CNS
• Monosynaptic (single motor or sensory neuron)
• Polysynaptic (multiple interneurons)
• Motor neuron (efferents)
– Message to effectors
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• Effector
– Muscle fibers or glands
• Reflexes are rapid, predictable responses to a stimulus
– Somatic and autonomic
Classifying Reflexes
• Somatic: activate skeletal muscle
– Spinal: integration center is spinal cord (brain not required)
• Stretch: ensures muscle length maintained (knee-jerk reflex)
– All monosynaptic and ipsilateral
• Flexor reflex: withdrawl from painful stimuli (glass or hot stove)
– Polysynaptic and ipsilateral
– Common pairing with crossed extensor in weighted limbs (contralateral)
• 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/stimuli