Phys II Exam I

Types of sensory receptors

Machanoreceptors, nociceptors, thermoreceptors, other free nerve endings

CNS nuclei

Thalami nuclei, medullary nuclei, pontine nuclei, midbrain nuclei

How is pain perceived?

Acute v chronic, associated with emotion, context, and memory

Sensitization

More aware of pain, small things may be higher on pain scale for those who are more sensitized

Somatic sensation

Nervous mechanism that collect sensory information from all over body except for special and visceral (deep) senses

Modality

Unique type of sense- vibration, touch, smell

Transduction

Conversion of environmental stimulus into a normal stimulus

Adaptation

How quickly acceptor gets used to a stimulus

Decussation

Crosses body at some point

Basic concepts for somatic sensation

Sensory information muster be sufficiently strong to excite (depolarize) each neuron in pathway, stimuli that don’t make it to brain are not processed, we classify each neuron in pathway as 1st-4th order, a synapse occurs between each neuron, the synapse is where we find the axon terminal of a pre-synaptic neuron and the dendrites/cell body of post-synaptic neuron

All somatic sensory receptors are

Highly sensitive to a single specific nucleus, must transduce the environmental stimulus, are located in a specific location, relay to a specific and repeated location, are pseudo-unipolar neurons within cell body in dorsal root ganglia/CNS nuclei

Sensory transduction

The language of information, conversion of environmental stimulus into an electrical impulse, will differ between different types of receptors, I’m cat= ion channels open/close→ mechanical stimulus deforms receptor membrane→ chemical change occurs when light is absorbed→ chemicals react and activated G-protein and 2nd messengers inside receptor cell→ temperature change changes permeability of membrane

Activation occurs if

Change in membrane permeability results in Na+ influx (depolarization)

No activation occurs if

Change in membrane permeability results in Cl- influx or K+ out flux, threshold is not reached

Exteroreceptors

Sensitive to external stimuli- Meissner, pacinian, Ruffini, free nerve endings (Markell, nociceptors, temperature, hair follicle receptor)

Interoreceptors

Sensitive to internal stimuli- free nerve endings, pacinian

Proprioceptors

Sensitive to internal stimuli for body position- free nerve endings, pacinian, ruffini, muscle spindles, golgi tendon organ

Machanoreceptor modalities

Touch, vibration, pressure, stretch, equilibrium, audition

Nociceptors modalities

Pain (free nerve endings), extreme intensity

Photoreceptor modality

Vision

Chemoreceptor modalities

Taste, smell, osmolality, O2/CO2

Thermoreceptor modalities

Warm and cold (free nerve endings)

Mechanoreceptors

Respond to mechanical deformation of cell membrane, classified by how quickly they adapt- rapidly (phasic) v slowly (tonic)

Rapidly adapting (phasic) mechanoreceptors

Pacinian (lamellar) corpuscle, Meissner (tactile) corpuscle

Pacinian lamellar) carpuscle

Fastest adapting mechanoreceptors, deep dermis and intramuscular, detect vibration- large receptive field

Meissner (tactile) corpuscle

Rapidly adapting, superficial dermis (especially fingertips and lips, precise touch - small receptive field

Slow adapting (tonic) mechanoreceptors

Ruffini corpuscle, Markell disc, tactile disc

Ruffini corpuscle

Slowly adapting, deep dermis and joint capsules, detect stretch- large receptive field

Markell receptor disc

Slowly adapting, superficial dermis-epidermis junction, light touch/pressure- small receptor field

Adaptation

Decrease in receptor action potential over time with a constant stimulus, basically how quickly the receptor gets “used” to a stimulus

Strong stimulus intesity

Increases frequency of action potentials

Weak stimulus intensity

Decreases frequency of action potentials

Non-encapsulated free nerve endings

Present basically everywhere in body, most common in epithelia and connective tissue, connected to A-delta and C fibers (non-myelinated),, nociceptors, thermoreceptors, tickle/itch receptors

Nociceptors

Receptors that detect potentially harmful stimulus, stimulus is capable of tissue damage, threshold should be high, multimodal, mechanical, thermal, chemical, dense concentration in- skin, joints, periosteum, arterial walls,flax, low concentration in- deep tissue, (brain, GI tract)

Mechanical nociceptors

Transduce extreme mechanical intensity- extreme force, presssure, stretch, pinching, cutting, outside body

Multimodal nociceptors

Capable of transduction mechanical, thermal, and chemical

Thermal nociceptors

Transduce extreme temperatures- greater than 120F or less than 42F

Chemical nociceptors

Stimulated by Inflammatory chemicals, markers of ischemia, strong acids/bases - lactic acid, bradykinin prostaglandins, proteolytic enzymes, K+

Fast pain

Pricing/sharp/acute/localized, stimuli- skin cut, heavy impact of object, bone fracture, needle stick; characteristics- sharp and well localized, travels in. A-delta fibers- small receptive field, faster than C fibers

Slow pain

Deep/aching/chronic, stimuli- inflammation, ischemia, burns, chronic injury, deep/visceral structure; characteristics- diffuse and poorly localized, travels in C fibers- large receptive field, slower than A-delta fibers, particularly annoying and intolerable

Warmth themoreceptors

Free nerve endings, A-delta fibers, transduce between termperatures 50C/over 120F, utilizes vanilloid transient receptor potential channels (TRP), TRPV transduces heat and capsaicin in spicy foods

Cool thermoreceptors

Free nerve endings, C-fibers, transduce temperatures between 6C/below 42F, utilizes metastatic transient receptor potential channels (TRPM), TRPM transduces col and methanol found in additives/topical pain relievers

Tickle receptors

Almost exclusive to superficial skin, very thin, very low threshold, sensitive to very light touch (mosquito on arm)

Itch receptors

Almost exclusive to superficial skin, very thin, reasoned to chemical stimuli- histamine and other products on inflammation

Erlanger’s system

Both motor and sensory receptors, AAAABC fibers

Erlangers A-alpha fibers

Muscle spindles- sensory, alpha motoneurons

Erlangers’s A-beta fibers

Discriminative touch, vibration, 2-point discrimination, fine touch

Erlanger’s A-gamma fibers

Muscle spindles- motor(intramural) muscle fibers

Erlanger’s A-delta fibers

Fast pain, crude touch, deep pressure, cold temprature

Erlanger’s beta fibers

N/a, pre-ganglionic autonomic

Erlanger’s C fibers

Slow pain, heat, post-ganglionic autonomic, olfaction

Lloyd’s system

Only sensory, mostly used in proprioception, type Ia, Ib, II, III, IV fibers

Lloyd’s type Ia fibers

Muscle spindle afferents

Lloyd’s type Ib fibers

Golgi tendon organ afferents

Lloyd’s type II fibers

Discriminative touch, vibration

Lloyd’s type III fibers

Crude touch, pressure, fast pain, temperature

Lloyd’s type IV fibers

Slow pain, olfaction

Gate control theory

When slow pain gets interrupted and overridden by fast pain fibers, fast A-beta fibers give off communicating interneurons in spinal cord which inhibit synapses of slower/smaller C & A-delta fibers for spinothalamic tracts via lateral inhibition through hyperpolarization of 2nd order neuron in dorsal horn

Dorsal column-medial lemniscus

Fine discriminative touch, vibration, proprioception from joints, muscles, gracilis- info below T6 from lower extremities, cuneatus- info from above T6 from upper extremities, A-beta fibers, rapid speed, well localized (except vibration), 1st order neurons enter cord and dorsal columns and ascend to medulla, neurons are ipsilateral → synapse on nuclei in medulla, cross & ascend to thalamus in medial lemniscus→ synapse in VPL of thalamus

Spinothalamic (anterolateral) pathway

Lower degree of speed, 2 subdivisions- Neo and Paleo, pain, temperature, crude touch that’s poorly localized, tickle and itch, sexual sensation

Anterior spinothalamic pathway

Mostly A-delta fibers, crude touch poorly localized, tickle and itch sensation, sexual sensation; fibers synapse in dorsal horn ipsilaterally→ cross immediately to contra lateral side and ascend → synapse in VPL of thalamus

Lateral spinothalamic pathway

A-delta fibers carry fast pain and cold temp, C fibers carry slow pain and heat, same pathway as anterior spinothalamic (except neo and paleo pain pathways)

Neo spinothalamic pathway

A-delta fibers carry fast pain, glutamate neurotransmitter, ascend to VPL of thalamus, stimulated by mechanical and thermal nociceptors

Paleo spinothalamic pathway

C fibers carry slow pain, synapse on small inter neuron before crossing and ascending, 90% terminate in reticular formation of brain stem, Substance P neurotransmitter, stimulated by chemical, mechanical, and thermal nociceptors

Reticular formation

Extends from medulla to midbrain, increases arousal of CNS, stimulation by chronic pain known to interfere with sleep, slow pain fibers that synapse here do __not__ ascend to cortex

Thalamus function in somatic sensation

Relay station for all somatosensory fibers on way to cortex, all synapse in VPL, nuclei of thalamus house cell bodies of 3rd order neurons

Somatosensory cortex

Located in post-central gyrus in parietal lobe, consists of somatosensory area 1- primary region where sensory info is processed and localized(excision only disable localization), sensory homonculus, contains 6 layers of neurons

Sensory homonculus

Located in post-central gyrus in parietal lobe, consists of somatosensory areas 1 and 2, contains 6 layers of neurons

Somatosensory area 1

Consists of broadmann’s areas 1, 2, 3a, 3b

Broadmann area 1

Receives stimuli from rapidly adapting cutaneous receptors

Broadmann area 2

Receives stimuli from deep pressure receptors

Broadmann area 3a

Most anterior portion of postcentral gyrus, closest to pre central gyrus, receives stimuli from muscle spindles

Broadmann area 3b

Receives stimuli from cutaneous receptors

Sensory association areas

PCP- provide context for sensation, create memories, provide emotional context

Somatosensory area 2

Poorly understood

Nociceptors pain

Traditional view of pain, activated nociceptors via tissue injury due to potentially damaging stimulus may be up regulated by inflammatory products derived from prostaglandins

Neuropathic pain

Damage to sensory nerves themselves, altered firing of nociceptors due to unhealthy neurons, peripheral neuropathy (diabetes) and multiple sclerosis are examples

Nociplastic pain

Altered processing of pain signals within CNS, maybe altered by fatigue, stress, mental status, pain pathway more sensitive than it should be, recent additional category

Muscle pain

Thought to be combination of 2 factors- mechanosensitive nociceptos stimulated by excessive force, chemosensitive nociceptors stimulated by products of ischemia (lactic acid, bradykinin proteolytic enzymes, K+)

Headache sensitive structures

Dura, dura venous sinuses, blood vessel walls, tentorium

T/F brain tissue is sensitive to pain

F- it’s almost totally insensitive to pain, swelling causes discomfort

Extracranial headaches

Referred to head, cervical spine dysfunction, muscle spasm- connection to dura in upper cervical spine, sinus pressure/irritation through CN5

Cervical myodural bridge

Anatomical connection between suboccipital muscles/fascia and dura matter, significant in extracranial headaches

Cervicogenic headache

Cervical spine dysfunction, nociceptors from cervical afferents (occipital - C2/3) especially greater occipital nerve, relayed to sensory nucleus of CN5 (trigeminal nucleus caudalis), trigemino cervical complex (TCC)

Trigemino cervical complex (TCC)

Occipital-C1, C1-C2, C2-C3, share common sensory pathway with ophthalmic nerve

Intracranial headaches

Migraine- old theory- vasoconstriction/dilation of middle cerebral artery, prolonged so spasm may lead to ischemia of brain, prodromal ‘sura’ symptoms; meningitis- inflammation of meninges (most commonly from infections), very abnormally severe headache, neck rigidity/nausea

Referred pain types

Visceral and parietal localization- visceral= membrane offering each organ, parietal= membrane lining body cavity

Visceral localization of referred pain

Pathway will refer pain to surface of body (skin) via dermatology pattern where organ originated embryologically- not directly on top of organ, mechanism is both visceral and skin pain pathways share/synapse on some 2nd order neuron

Parietal localization of referred pain

Pathway will refer pain to surface of body near organ- more on top of organ, referrred via highly sensitive nociceptors located in parietal layer of pleura, pericardium, peritoneum

Central sensitization of pain

Increased membrane excitability in central nociceptors pathways (not at receptor), smaller stimulus will be able to cause a depolarization

Allodynia

Pain with a normally non-painful stimulus, occurs when sensitization is high

Descending analgesic system

Pain signals that reach higher centers then send signal back down, when stimulated 3 regions of brain stem nuclei (periaqueducatl gray matter, raphe magnus nucleus, nucleus reticularis paragiganocellularis) send fibers to dorsal horn- these inhibit synapses for spinothalamic tracts (pain signals) through endorphins and enkephalins

Sensory innervation of joints

Conscious Proprioception (heavily innervated, mechanoreceptors, large myelinated fibers, found in joint capsules, low threshold) and pain (heavily innervated, nociceptors, very high threshold, completely inactive through- significant mechanical pressure, increased capsular pressure, chemical irritation

Sensory proprioception innervation of muscles

Intramural muscle fibers- minimally/non-contractile, type 1a fibers monitor speed of changing length (large & myelinated innervated both nuclear bag and chain), type 2 fibers monitors only length (static position, are intermediate and myelinated, and innervate only nuclear chain

Muscles spindles are innervated by

Both sensory and motor neurons

Motor proprioceptive innervation of muscles

A-gamma motor fibers (smaller than alpha motor), should be in coordination with extramural muscle fibers, job is to keep muscle spindle same length as rest of muscle

Golgi tendon organs

Found in tendons, part of proprioceptive innervation of muscles, relays info to inhibitory interneurons that synapse on alpha motoneurons- resulting in relaxation of homonymous muscle, Type 1a fibers (slightly smaller than 1a fibers) in muscle spindles monitor tension of muscle/tendon

T/F dorsal columns allow for conscious interpretation of proprioception

T

Do spinocerebrellar tracts allow for conscious processing of proprioception?

No it allows for subconscious processing

Dorsal spinocerebellar tracts

Carries majority of proprioceptive input- muscle spindles, tactile/golgi tendon organs, informs cerebellum instantly of changes in muscle (length, tension, position), and outside forces put on body, composed of 2nd order neurons, originate from T12-L5, cross cord and ascend, crosses twice to remain ipsilateral