Glossary of Neuro Greenspan
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- Classifications of receptors based on microscopic structure
- Unencapsulated Receptors
- Free nerve ending and loses its myelin sheath and is only separated from tissue by the Schwann cell and a BM. Many of these respond to NOXIOUS stimuli and HIGH THRESHOLD mechanical stimuli.
Examples: thermoreceptors, nociceptor
- Encapsulated Receptors
- Consits of an elabortate arrangement of specialized cells that receive the peripheral endings of nerve fibers.
Examples: Pacinian corpuscle and Meissner's corpuscle
- Specialized Receptors
- ELECTROGENIC cells that become involved in the process of SENSORY TRANSDUCTION and their response depolarizes the attached nerve ending.
Ex: cochlear hair cells and photoreceptors
- Sherrington's Classification of Receptors
- detect EXTERNAL stimuli (5 senses = visual, touch, hearing, taste, smell)
- detect INTERNAL stimuli (stomachache, visceral receptors)
- Detect body position or movement (ex: muscle and joint mechanoreceptors, vestibular system)
- Functional classification of receptors (based on physiological function)
nociceptor (** can respond to mechanial, thermal, or even chemical stimulation)
- Auditory Sensory system
- Modality: hearing
Stimulus energy: sound
Receptor class: mechanoreceptor
Receptor cell type: hair cells (cochlea)
- Visual sensory system
- Modality: vision
Stimulus energy: light
Receptor class: photoreceptor
Receptor cell type: rods, cones
- Vestibular sensory system
- Modality: balance
Stimulus energy: gravity
Receptor class: mechanoreceptor
Receptor cell type: hair cells (vestibular labyrinth)
- Gustatory sensory system
- Modality: taste
Stimulus energy: chemical
Receptor class: chemoreceptor
Receptor cell type: taste buds
- Olfactory sensory system
- Modality: smell
stimulus energy: chemical
Receptor class: chemoreceptor
Receptor cell type: olfactory sensory neurons
- Touch [submodality]
- stimulus energy: pressue
receptor class: mechanoreceptor
receptor cell type: cutaneous mechanoreceptors
- Proprioception [submodality]
- Stimulus energy: displacement
Receptor cell type: muscle and joint receptors
- Temperature sense [submodality]
- stimulus energy: thermal
receptor class: themoreceptor
Receptor cell types: cold and warm receptors
- Pain [submodality]
- stimulus energy: chem, thermal, or mechanical
receptor class: chemo,thermo, mechanoreceptor
- Itch [submodality]
- stimulus energy: chemical
receptor class: chemoreceptor
Receptor cell type: chemical NOCICEPTOR
- Rapidly adapting receptors
- application of a stimulus may result in a few or only 1 action potential even if the stimulus is maintained.
ex: pacinian corpuscle
- slowly adapting receptors
- application of a stimulus results in a repetitive discharge in the primary afferent neuron as long as the stimulus is maintained.
ex: most nociceptors
- Stimulus intensity
- Refers to the strength of a stimulus. It is encoded at the receptor by FREQUENCY (nerve impulse/sec) and POPULATION (# of receptors activated).
- Frequency coding
- The strength of the stimulus is directly related to the firing rate of the sensory unit -- this is true for many slow adapting receptors.
- Spatial or Population responses
- more intense stimuli activate more sensory units at the point the stimulus is applied.
- Why do large myelinated nerve fibers conduct action potentials more rapidly than smaller myelinated/unmyelinated fibers?
- - increased diamater of myeline sheath produces a LOWER INTERNAL LONGITUDINAL RESISTANCE
-Myelinated fibers propagate impulses by SALTATORY CONDUCTION--> longer internodes so conduction is more efficient.
- Relationship between conduction velocity and fiber diamater of myelinated fibers.
- Conduction velocity increases by about 6 m/s per 1 micrometer increase in fiber diameter.
- Fiber Type I
diameter: 12-20 microns
conduction velocity: 72-120 m/s
receptor associations: mechanoreceptors: muscle spindles; golgi tendon organs
- Fiber Type II
diameter: 6-12 microns
conduction velocity: 36-72 m/s
receptor associations: mechanoreceptors: muscle spindles; Meissner, Pacinian, etc.
- Fiber Type III
- Agamma and Adelta
diameter: 1-6 microns
cond. velocity: 6-36 m/s
receptor associations: thermoreceptors (COOL); nociceptors
- Fiber Type IV
- C fibers
diameter: 0.4-1.2 microns
cond. velocity: 0.5-2.0 m/s
receptor associations: thermoreceptors (WARM); nociceptors
- Fast-adapting Type I
Only on non-hairy part of hand
Small, sharp borders
43% meissner corpuscle; edge sensitive
- Slow-adapting Type I
25% merkel cells
Found in hairy skin
Small, sharp borders
- Fast-adapting Type II
Large, obscure borders
13% Paccini (Golgi-Mazzoni)
Large receptive field (deep in skin)
- Slow-adapting Type II
Large receptive field
Deep in skin
Sensitive to lateral skin stretch
- Pacinian Corpuscles
- Most sensitive to vibration, particularly in the 100-400Hz range. At 250 Hz vibration, PC can detect skin displacement of 0.10 micrometers.
- Types of receptors found in the PDL
- several types of modified Ruffini nerve endings and a variety of free nerve endings.
Ruffini: slowly adapting mechanoreceptors
- Threshold sensitivity
- Often tested with monofilaments; varies across body; determined by sensitivity of RAPIDLY adapting mechanoreceptors (although perception of PRESSURE is mediated by slowly adapting mechanoreceptors).
- Types of input of DC-ML system
slowly and rapidly adapting cutaneous mechanoreceptors as well as muscle and joint mechanoreceptors
- Which encapsulated mechanoreceptor is the FAST-adapting one(s)?
- Pacinian corpuscle, then Meissner.
- Which encapsulated mechanoreceptor is found on GLABROUS skin?
- Meissner's corpuscle
- Which encapsulated mechanoreceptor functions for the stretching of skin?
- Ruffini's corpuscle
- DC-ML pathway: where are the second order neurons?
- gracile nucleus: MEDIAL; fibers that convey infromation from LOWER limbs
cuneate nucleus: LATERAL: fibers that convey information from UPPER limbs, trunk, neck.
- Internal arcuate tract
- Right after contacting the 2nd order neurons; axons project in the dorsal portion of each side of the lower branstem; subsequently cross the midline.
- Medial Lemniscus
- Elongated dorsoventrally (after the internal arcuate axons cross the midline).
Info. from lower limbs located ventrally; info. from upper limbs located dorsally.
- When does hte medial lemniscus rotate 90 degrees laterally?
- when it ascends through the pons and midbrain.
Upper body: medial
Lower body: lateral
- DC-ML pathway: 3rd order neurons
- cells of ventral posterior lateral (VPL) nucleus of thalamus.
- TRIGEMINAL SOMATIC SENSORY SYSTEM
- -these are mechanosensory receptors from FACE
-principal nucleus (2nd order)
-trigeminal lemniscus (trigeminothalamic tract)
-VPM (ventral posterior medial) nucleus of thalamus
- Primary somatic sensory cortex
- aka SI
Located in the postcentral gyrus of the parietal lobe and comprises 4 regions:
Broadmann's areas 3a, 3b, 1, and 2.
- Which laminae do the Adelta fibers and C fibers synapse in?
- Adelta: laminae 1 and 5
C: laminae 1 and 2
- The MAJOR ascending pathway for information abotu pain and temperature (for below face)
- Spinothalamic tract
- At what level of the brainstem does the first-order axons enter? This is for noxious and thermal stimulation of the FACE.
- Enter at the PONS, then descend to the MEDULLA forming the spinal trigeminal tract.
- First-order axons for pain/thermal stimulation for FACE originate where?
- trigeminal ganglion cells and from ganglia associated with VII, IX, X
[geniculate gang, sup/inf gang, sup/inf gang]
- What are 2 subdivions of the spinal [descending] nucleus of V?
- Pars interpolaris
- What is the major ascending pathway for inforamtion about pain/temp from the FACE?
- trigeminothalamic tract
- Neurons in the parabrachial nucleus project where?
- Hypothalamus & amygdala --> motivation and affect; also sends projections to the periaqueductal gray matter which has to do with descending modulation of the pain circuits.
- Where do projections of affective-motival pain pathway NOT in the parabrachial nucleus go?
- Other projections go to older parts of the thalamus such as the INTRALAMINAR nad MEDIAL THALAMIC NUCLEI (medial to ventral posterior nucleus)
- Projections from the anterolateral system to the medial thalamic nuclei provide nociceptive signals to which areas?
- Frontal lobe, insula, and cingulate cortex
- Nociception vs. pain
- Sensibility is the ability to detect noxious stimuli. Sensation is how the brain interprets that sensory information. Generally, sensation has two components: recognition of the location, form and intensity of the stimulus and the affective-emotional responses to the noxious stimulus.
- how does capsaicin create pain?
- capsaicin activates responses in a subset of nociceptive polymodal C fibers by opening ligand-gated ion channels (like VR-1) that permit the entry to Na+ and Ca2+.
- abnormal unpleasant sensations
- characteristics of persistent pain (7):
pain in the absence of detectable tissue damage
pain in a region of sensory deficit
summation and after-reaction with repetitive stimuli
- The analgesic effects of stimulating the periaqueductal gray are mediated through which brainstem sites?
- parabrachial nucleus, medullary reticular formation, locus coeruleus, raphe nuclei
- Referred pain: anginal pain (pain arising from heart muscle that is not adequately perfused with blood)
- upper chest wall, radiation into left arm and hand.
- referred pain: gallbladder pain
- scapular region
- referred pain: esophogeal pain
- chest wall
- referred pain: ureteral pain
- lower abdominal wall
- referred pain: bladder pain
- referred pain: inflamed appendix
- anterior abdominal wall around the umbilicus
- Gate control theory: activation of the small fibers
- leads to inhibition of SG (substantia gelatinosa) fibers which are inhibitory interneurons and this leads to increased activation of teh transmission cells and opening of the gate.
- Gate control theory: activation of the large fibers along with the small fibers
- leads to excitation of SG neurons and more inhibition of the T cells and closing of the gate.
- 3 families of endogenous peptides and their receptors
- endorphin: mu
- Serotonin pathways of descending control originate where?
- medulla: mainly the nucleus raphe
- Norepinephrine pathways of descending control originate where?
- in the pons locus coeruleus and subcoeruleus regions.
- Chemical mediators of CENTRAL sensitization
- excitatory amino acids
CGRP (calcitonin gene-related peptide)
- Management of hyperalgesia and pain following TISSUE injury (peripheral + central)
- This is INFLAMMATORY hyperalgesia.
Peripheral: local anesthetics & NSAIDS
Central: opioids & NMDA receptor antagonises
- Management of hyperalgesia and pain following NERVE injuery (peripheral + central)
- This is NEUROPATHIC hyperalgesia.
Peripheral: Local anesthetics & capsaicin analogs
Central: Opioids, NMDA receptor antagonists, and tricyclic antidepressants.
- Chemical mediators for descending control (3)
- 5-HT (serotonin)
- What are the EAA (excitatory amino acid) receptors of central sensitization?
- NMDA - Ca++ influx
AMPA - Ca++ influx (?)
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