Chapter 13: Peripheral Nervous System and Reflex Activity Flashcards
PNS includes all neural structures…
OUTSIDE the CNS
Sensory Receptors
structures specialized to detect stimuli
Sensory receptors are classified by…
type of stimulus detected; location of stimulus; receptor structure
Mechanoreceptors
detect touch, pressure, vibration, and stretch
Thermoreceptors
detect temperature changes
Photoreceptors
detect wavelengths of light
Chemoreceptors
detect chemicals in a solution
Nociceptors
detect damaging stimuli (pain receptors)
Exteroceptors
detect external stimuli; found near body surface, within skin and special senses
Interoceptors
aka visceroceptors; detect interval stimuli; located within viscera and blood vessels
Proprioceptors
detect internal stimuli originating within muscles, tendons, joints, and ligaments; monitor degree of stretch
Receptors for the Special Senses
receptors for the special senses; specialized cells located in the head; found within complex sense organs
Receptors for General Senses
modified dendrites of sensory neurons; widely distributed in body; are either nonencapsulated (free) or encapsulated
Free Nerve Endings of Sensory Neurons
nonencapsulated; location- extroceptors, interoceptors, and proprioceptors; stimulus type- thermoceptors (warm and cool), chemoceptors (itch, pH, etc), mechanoreceptors (pressure), nociceptors (pain); body location- most body tissues; most dense in connective tissues and epithelia
Modified Free Nerve Endings
epithelial tactile complexes (Merkel cells and discs); nonencapsulated; location- exteroceptors; Stimulus type- mechanoreceptors (light pressure), slowly adapting; body location- basal layer of epidermis
Hair Follicle Receptors
nonencapsulated; location- exteroceptors; stimulus type- mechanoreceptors (hair deflection), rapidly adapting; body location- surrounding hair follicles
Tactile (Meissner’s) Corpuscles
encapsulated; location- exteroceptors; stimulus type- mechanoreceptors (light pressure, discriminative touch,vibration of low frequency), rapidly adapting; body location- dermal papillae of hairless skin, particulary nipples, external genitalia, fingertips, soles of feet, eyelids
Lamellar (Pacinian) Corpuscles
encapsulated; location- exteroceptors, interoceptors, and proprioceptors; stimulus type- mechanoreceptors (deep pressure, stretch, vibration of high frequency), rapidly adapting; body location- dermis and hypodermis; periostea, mesentery, tendons, ligaments, joint capsules; most abundant on fingers, soles of feet, external genitalia, nipples
Bubous Corpuscles (Ruffini Endings)
encapsulated; location- exteroceptors and proproceptors; stimulus type- mechanoreceptors (deep pressure and stretch), slowly or nonadapting; body location- deep in dermis, hypodermis, and joint capsules
Muscle Spindles
encapsulated; location- proprioceptors; stimulus type- mechanoreceptors (muscle strength, length); body location- skeltal muscles, particulary in the extremeiteis
Tendon Organs
encapsualted; location- proprioceptors; stimulus type- mechanoreceptors (tendon stretch, tension); body location- tendons
Joint Kinesthetic Receptors
encapsulated; location- proprioceptors; stimulus type- mechanoreceptors and nociceptors; body location- joint capsules of synovial joints
Processing of Sensory Information
occurs at 3 levels; receptor level, circuit level, and perceptual level
Receptor Level (1)
sensation (awareness of a stimulus) occurs when sensory receptor responds to a stimulus; sensory receptor transduces (converts) stimulus energy into electrical energy of an action potential; most sensory receptors exhibit adaptations (diminished sensitivity to a constand stimulus) ; which allows the body to ignore unimportant info
What are the exceptions to adaptations?
nociceptors and proproceptors are non adaptive because of the protective importance of their info
Circuit Level (2)
ascending pathways route impulses to appropriate region of cerebral cortex
Perceptual Level (3)
preception (conscious interpretation of a stimulus) occurs; brain organizes and interprets info
What is referred pain?
pain stimuli originating in one part of the body are perceived by the brian to come from another part of the body; occurs bc visceral sensory neurons travel along the same pathways as somatic sensory neurons (brain gets confused)
Structure of Nerves
bundles of Axons in the PNS encased within connective tissue wrappings; epineurium: around nerve; perineurium: around fascicle; endoneurium: around each axon
Nerve Classification
based on where they originate; cranial nerves- originate from brain; spinal nerves- originate from spinal cord; based on direction of impulse: sensory (afferent) nerves conduct impulses toward CNS; motor (efferent) nerves conduct impulses away from CNS; mixed nerve contain both afferent and efferent fibers (Most nerves are mixed-> all spinal nerves are)
Regeneration of Nerve Axons
damaged CNS axons cannot regenerate (oligodendrites suppress axon regeneration); damaged PNS axons can but ONLY if the cell body remains intact
ADD REGENERATION CHART
How many cranial nerves are there?
12 (I-XII)
Olfactory Nerve
I; filaments in teh olfactory mucosa that synapse with the olfactory bulb; sensory nerve (no motor); transmit afferent impulses for sense of smell; fracture of ethmoid bone may result in anosmia (loss of smell)
Optic Nerves
II; sensory (no motor); transmit afferent impulses for sense of vision; damage to optic nerve results in vision being lost in the respective eye; damage beyond optic chiasma results in reduced vision in BOTH eyes
Oculomotor Nerves
III; motor nerves (no sensory); transmit somatic (skeletal) motor impulses to 4 extrinsic eye muscles (superior, inferior, and lateral rectus and inferior oblique); transmit autonomic motor impulses to sphincter pupillae of iris and ciliary muscles of lens (intrinsic); if damaged, eye can not move up, down or inward; exhibits diplopia (double vision); trouble focusing on close objects
Trochlear Nerve
IV; motor nerve; transmit somatic motor impulses for superior oblique muscles of the eye; if damaged, eye cannot rotate inferolateraly; exhibits diploplia
Trigeminal Nerve
V; both (mixed;sensory and motor); transmits sensory impulses from cornea, face, and teeth; transmit motor impulses to muscles of mastication (chewing); inflammation of trigeminal nerve (trigeminalneuroglia); prodcues most excruciating pain known
Abducens Nerves
VI; motor; transmit motor impulses to lateral rectus muscle of eyes; if abducens damaged, eye cannot be moved laterally
Facial Nerves
VII; both (sensory and motor; mixed); transmit sensory impulses from taste buds in anterior 2/3 of tongue; transmit somatic motor impulses to muscles of facial expression; transmits autonomic motor impulses to lacrimal glands (tears) and submandibular and sublingual salivary glands; inlfammation of facial nerve (bells palsy) believed to be caused by herpes simplex I viral infection
Vestibulocochlear Nerves
VIII; both (mostly sensory though); transmit afferent impulses for sense of equlibrium (vestibular) nerve and sense of hearing (cochlear nerve); damage to vestibular nerve results in dizziness, loss of balance, nausea and vomiting; damage to cochlear nerve results in sensorineural deafness
Glossopharyngeal Nerve
IX; both; transmit sensory impulses from taste buds in posterior 1/3 of tongue and pharynx; transmits somatic motor impulses to swallowing muscle; damage to nerve impairs swallowing and taste; transmit autonomic motor impulses to parotid salivary glandsV
Vagus Nerve
X; only cranial nerve that leaves the head; both; transmit sensory impulses from thoracic and abdominal viscera; transmit somatic motor impulses to larynx and muscle of pharyns (swallowing); transmit autonomic motor impulses to thoracic and abdominal viscera; damage to vagus nerve results in hoarseness or loss of voice, difficulty swallowing and impaired digestive motility
Accessory Nerves
XI; motor; transmits somatic motor impulses to sternocleidomastoid and trapezius; damage to nerve causes head to turn toward injured side; only “cranial” nerve that doesnt originate form te brain (originates from spinal cord)
Hypoglossal Nerve
XII; motor; transmit somatic motor impulses to tongue muscles involved with chewing, speaking, and swallowing; if one nerve is damaged, tongue deviates toward affected side; if both nerves damaged can not protrude tongue
Mnemonic for Remembering the Order of the Cranial Nerves
Only One Of The Two Athletes Felt Very Good Victorious And Healthy
Mnemonic for Remembering which Cranial Nerves are Sensory, Motor, or Both
Some Say Marry Money But My Brother Believes (its) Bad Business (to) Marry Money
Spinal Nerves
31 pairs (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccyx); all are mixed (sensory and motor neurons)
Ventral Roots
contain motor (efferent) fibers
Dorsal Roots
contain sensory (afferent) fibers
Dorsal and Ventral Roots…
merge to form spinal nerve (mixed)
Spinal Nerves Branches to…
form a dorsal ramus and ventral ramus
Rami Communicantes
contains autonomic (visceral) nerve fibers
Dorsal Rami
mixed; supply skeletal muscles and skin of posterior trunk
Ventral Rami
T2-T12 form intercostal nerves taht go between ribs
Ventral Rami of cervical, lumbar and sacral nerves…
form nerve plexuses (interlacing nerve networks)
Cervical Plexus
formed from ventral rami of C1-C4 nerves; phrenic nerve stimulates diaphragm to contract
Brachial Plexus
formed from C5-T1 nerves; axillary nerve stimulates deltoid muscle; radial nerve stimulates posterior muscles in arm and forearm; musculocutaneous nerve stimulates flexor muscles in anterior arm; ulnar nerve stimulates flexor muscles in anterior forearm; median nerve stimulates flexor muscles in anterior forearm
Lumbar Plexus
formed from ventral rami of L1-L4 nerves; femoral nerves stimulates anterior muscles of the thigh; obturator nerve stimulates adductor muscles of medial thigh
Sacral Plexus
formed from ventral rami of L4-S4 nerves; sciatic nerve branches to form common fibular nerve and tibial nerve; common fibular nerve stimulates fibular muscles of lateral leg and tibialis anterior; tibial nerve stimulates posterior muscle of thigh, leg, and foot
Dermatomes
cutaneous branches of all spinal nerves except C1 innervate dermatomes; each dermatome is innervated by a single spinal nerve; dermatomes are used to pinpoint region of spinal cord injury
PNS motor endings…
connect motor neurons to effectors
Innervation of Skeletal Muscles
somatic motor nerve endings split to form multiple axon terminals; synaptic vesicles release acetylcholine
Innervation of Smooth Muscles and Glands
autonomic motor neurons branch forming multiple varicosities (knoblike swellings containing mitochondria and synaptic vesicles) along its length; synaptic vesicles release acetylchline OR norepinephrine that diffuses across a wide synaptic cleft
Processing of Motor Informatino
occurs at three levels; segmental, projection, precommand
Segmental Level
lowest; involves spinal cord; consists of reflexes and central pattern generators (CPGs) that stimulate groups of muscles—> networks of cells that produce rythmic outputs in the absence of brain or sensory inputs (like walking)
Projection Level
involves primary motor cortex and brain stem nuclei; conveys instructions to spinal cord motor neurons via projection fibers and sends a copy of that info to the precommand level
Precommand Level
highest; involves cerebellum and basal nuclei; modulates outputs of the precommand area; permits desired movements; prevents unwanted movements; refines moto plans from motor cortex on detailed sensory input
Reflex Activity
inborn (innate) reflexes are rapid, predictable responses to stimuli; learned (acquired) reflexes result from practice or repetition; test reflexes to determine if motor connects between CNS and effector are intact; somatic reflexes activated skeletal muscles (somatic reflex arc) ;autonomic (visceral) reflexes activate smooth muscle, cardiac muscle or glands
Spinal Reflexes
somatic reflexes mediated by spinal cord; such as stretch reflex, tendon reflex, flexor (withdrawal) reflex, abdominal reflex, plantar reflex
Stretch Reflex
initiates skeletal muscle contraction in response to increased muscle stretch; all are monosynaptic and ipsilateral; ie patellar reflex
Patellar Reflex
knee jerk reflex; stimulus: hitting the patellar ligament, receptor: muscle spindle, integration center: spinal cord, effector: quadriceps muscle
Reciprocal Inhibition
relaxing the muscle that is the antagonist of the muscle being stretched; hamstrings in patellar reflex (ADD BETTER DEFINITION)
Tendon Reflex
initiates relaxation and lengthening of skeletal muscles in response to muscle tension (NOT stretch); all are polysynaptic and ipisilateral; opposite of patellar reflex
RECIPRICAL ACTIVATION
ADD PARTS OF TENDON REFLEX
Flexor Reflex
withdrawal reflex; initiates withdrawal of a body part in response to pain; poly synaptic and ipsilateral; usually accompanied by the crossed extensor reflex which stimulates extensors on oppostite side to contract (polysynaptic and contralateral)
Abdominal Reflex
superficial reflex initiated by stroking skin above, lateral, or below the umbilicus; abdominal muscles contract moving umbilicus toward stimulated area; tests integrity of spinal cord from T8 to T12
Plantar Reflex
superficial reflex initiated by drawing a blunt object from heel to toe; initiates flexion (curling) of toes; tests integrity of spinal cord from L4-S2; Babinskis sign (abnormal response) indicates damage to motor areas of brains or spinal cord
