Chapter 13

Sensory Receptor TypesNociceptors

Respond to excess heat, pressure, or chemicals

Tissue damageAll parts of the body but brain

ThermoreceptorsTemperature of skin and bloodMaintains homeostatic control

via the hypothalmusPhotoreceptors

Light absorbing pigmentsLight detection

Sensory Receptor TypesMechanoreceptors ChemoreceptorsTouch, pressure, &

vibrationsBend or stretch PM of

receptor cell = changing permeabilityStretch receptors –

position of body partsHair cells - sound waves

and H2O movements

Chemicals in the internal & external environment

O2 in arteriolesOsmoreceptors -

changes in [blood solute]Pheromone detection

Sensory Receptor LocationsExteroceptors

Stimuli outside the bodySkin and special sense organs

InteroceptorsStimuli within the bodyChemical messengers, tissue stretch, and

temperature Proprioceptors

Internal stimuliMonitor position and stretch of joints, tendons,

and muscles

Sensory Receptor StructuresUnencapsulated Encapsulated

Free nerve endingsMost body tissuesTemperature and painful

stimuliCapsaicin and itch

Merkel discsDeeper epidermal layersLight touch

Hair follicle receptorsShaft of hair follicleLight touch and hair

bending

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 InputAll senses trigger the same TYPE of signal

Distinction occurs in activated brain areaTypically graded response, but AP’s possible

Sensory receptors detect sensations and carry to the brainAwareness of environmental change

Brain constructs perceptions by integrating sensations with other informationNeuronal communication involving multiple

brain areas

The Working Brain

Sensory AdaptationSensory receptors

become less responsiveFewer action

potentials

Limits reactions to normal background stimuliShower or hot tub

temperatureOdors over time

Decoding NervesPNS organ consisting of parallel

bundles of axons enclosed by connective tissue layers

EpineuriumPerineuriumEndoneuriumDirection of transmission

Afferents: only to CNS Dorsal root ganglia

Efferents: only from CNS Sympathetic & parasympathetic ganglia

Mixed: carry both; mostClassified as cranial or spinal

Mature neurons don’t divide*Cell body damage = deathCut/compressed axons regenerate

Separated ends seal off and swellDistal end of injury disintegrates

Lack of nutrients Neurilemma maintained in

endoneuriumSchwann cells proliferate &

encourage axon growth Guide ‘sprouting’ axons to original

contactsGreater distance decreases chancesRegrowth never exact = retrainingExtremely rare in CNS

Nerve Fiber Regeneration

Cranial NervesVentral portion of the brain

1st 2 pairs attach to forebrain

Remainders originate on brainstem

Numbers Cranial Nerve FunctionI 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

Roots: medial & afferent OR efferentDorsal root: peripheral

receptors to spinal cordVentral root: ventral horn to

skeletal musclesBranches: laterally pass

through intervertebral foramenDorsal ramus: dorsal trunkVentral ramus: limbs & rest of

trunkMeningeal branch: meninges

and blood vesselsPlexus

Criss cross joining of ventral rami

Excludes T2 – T12

Spinal Nerve Anatomy

31 Pairs of Spinal Nerves8 cervical

Cervical plexusBrachial plexus

12 thoracicIntercostal nerves &

enlargements5 lumbar

Lumbar plexus5 sacral

Sacral plexus1 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 PlexusInnervates lower limbs, buttocks, and pelvic

musclesLumbar plexus L1 – L4

Femoral nerve: quadriceps and sartorius Branches to saphenous

Obturator nerve: adductor musclesSacral plexus L4 – S4

Sciatic nerve: entire lower leg (except anteriomedial thigh) Tibial: hamstrings Common fibular nerve: anterior tibialis

Reflex ArcReceptor

Senses stimulusSensory neuron (afferents)

Message to the CNSIntegration center

Synapses in CNS Monosynaptic (single motor or sensory neuron) Polysynaptic (multiple interneurons)

Motor neuron (efferents)Message to effectors

EffectorMuscle fibers or glands

Reflexes are rapid, predictable motor responses to a stimulus

http://a248.e.akamai.net/7/248/430/20080327144023/www.mercksource.com/ppdocs/us/common/dorlands/dorland/images/arc_reflex%20a.(1).jpg

Classifying ReflexesSomatic: 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 musclePupillary light: controls diameter of pupil

(inside/outside)Ciliospinal: ipsilateral pupil dilation from pain