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Bio 222

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Mechanoreceptors: Percentage of hand covered
Pascinian Corpuscle: 10-15% Ruffini's Ending: 20% Meissener's Corpuscle: 40% Merkel's Disk: 25%
Mechanoreceptors: Smallest and Largest
Merkel's Disk: smallest Pascinian Corpuscle: Largest
Mechanoreceptors: sensitivity
Pascinian Corpuscle: high frequency vibration Ruffini's Endings: skin stretch Meissner's Corpuscle: low frequency vibration Merkel's Disk: edges, points, curvature
Mechanoreceptors: spacial acuity
Pascinian Corpuscle: low Ruffini's Endings: low Meissner's Corpuscle: intermediate Merkel's Disk: high
Receptive Field
area of skin that significantly changes action potential firing rate when stimulated
Mechanoreceptors: adaptation speed
Pascinian Corpuscle: rapid Ruffini's Endings: slow Meissner's Corpuscles: rapid Merkel's Disk: slow
Pascinian Corpuscle Receptor Function
1) mechanical deformation of membrane at onset/offset 2) mechanosensitive cation channels open 3) generator potential depolarizes axon 4) if threshold is reached, AP Onion-like corpuscle confers sensitivity to high-frequency vibration but not steady pressure
Divisions of Spinal Cord and number of segments in each
Cervical: 8 Thoracic: 12 Lumbar: 5 Sacral: 5
Dermatome
skin innervated by right and left dorsal roots for a single spinal segment
Pathway which conveys touch info from body to cortex Kind of sensory axons used
Dorsal Column-Medial Lemniscal Pathway; Abeta fibers
Where do DCML 1st order neurons enter spinal cord, where do they go from there?
Dorsal roots, ascend via ipsilateral dorsal column
Topographic organization of dorsal columns
Lower Body: fasciculus gracilis, medial Upper Body: fasciculus cuneatus, lateral
Where do DCML 1st order neurons synapse?
Dorsal Column Nuclei of Medulla -nucleus gracilis and nucleus cuneatus
What is the 2nd order tract conveying touch info from body axons axons ascend via?
Medial lemniscus
Where do DCML 2nd order neurons synapse?
Ventral posterior nucleus of thalamus
What tract do 3rd order DCML neurons use to ascend to the cortex?
Internal capsule
Pathway for touch info from face to cortex?
Trigeminal Nerve Pathway, cranial nerve 5
Peripheral branches of cranial nerve which carries touch info from face to cortex?
opthalamic, maxillary, mandibular
Location of cell bodies in trigeminal nerve pathway (touch)
trigeminal ganglion, mid-pons
trigeminal nerve pathway: location of 1st order neuron synapse
ipsilateral trigeminal nucleus
Trigeminal nerve pathway: location of crossover
2nd order neurons crossover, forming trigeminal lemniscus
Trigeminal 2nd order neurons projection tract
trigeminal lemniscus
Trigeminal Nerve Pathway: location of 2nd order neuron synapse
VPM of thalamus
Location of Somatosensory Cortex
Parietal lobe of cerebral cortex
S1 Columnar Organization
Cortex has 3-6 layers Laver IV has stellate cells
Layer of Thalamic Inputs to cortex
IV stellate cells
Cortical Columns
neurons sharing inputs and responses stack vertically
Features of Somatotopic Map
-Not necessarily continuous -Body parts overrepresented -Density of sensory receptors -Smallest receptive fields -Importance of sensory input
Cranial Nerve(s): olfactory
I
Cranial Nerve(s): vestibulo-ocular reflex
III, IV, VI
Cranial Nerve(s): touch system
V
Cranial Nerve(s): Pain/Temperature
V
Cranial Nerve(s): Vestibular System
VIII
Cranial Nerve(s): Gustatory
VII, IX, X
Vestibular Labyrinth
organ of balance, vestibular portion of cranial nerve VIII
Cochlea
organ of hearing; auditory portion of cranial nerve VIII
Endolymph
fills membranous sacs within bony structure of vestibular labyrinth high [K+], low [Na+] similar to cytoplasm
Two types of structures in vestibular labyrinth
Two otolith organs Three semicircular canals Each has a sensory epithelium containing hair cells
Hair Cells
sensory cells for movement, have lots of cilia
Kinocilium
longest cilium of a hair cell
Organization of Sensory Epithelium
Polarized: groups of hair cells have their kinocilia oriented in the same direction; deflection of the cilia towards the kinocilium causes depolarization
Otolith Organ, function, epithelium, and two features
Detect head tilt and linear accelerations Epithelium: Macula Utricle and Saccule
Utricle
Macula oriented parallel to ground, connected to semicircular canals, sensitive to horizontal motion
Saccule
Macula oriented perpendicular to ground, connected to cochlea; sensitive to vertical movement
Macula Orientation in Otolith Organs
Kinocilia oriented in multiple directions; symmetrically represented
Semicircular Canals: function, epithelium, and three parts
Detection of angular accelerations (rotations) Sensory Epithelium is the Crista Three canals: superior, posterior, and lateral
Structure of Semicircular Canals
Each canal joins the utricle at an enlargement called the ampulla that houses the crista and cupula
Ampulla
Part of Semicircular Canal Contains: crista, hair bundle, cupula
Crista
Sensory epithelium of semicircular canals
Hair Bundle
cilia of hair cells
Cupula
gelatinous mass extending across ampulla
Crista Orientation in Semicircular Canals
Kinocilia are oriented in the same direction
Deflection of Hair Cells
Towards Kinocilia: depolarizing deflection --> increased transmitter release --> increased firing in vestibular ganglion cell Deflection away from kinocilia: hyperpolarizing deflection --> decreased transmitter release --> decreased firing in vestibular ganglion cell
Signal Transduction in Hair Cells
1) Stretch activated cation channels open when cilia are deflected towards kinocilia 2) Membrane depolarizes 3) Voltage-gated Ca+2 channels open 4) NT released at synapse with vestibular ganglion cell
Structure of the Macula
Hair cells of macula are covered by a gelatinous layer and a membrane embedded with otoliths
Tilt and Acceleration
Backward sustained tilt and foward acceleration (no tilt) --> similar cilia bending
Hair cell bending in crista
when a canal moves, endolymph lags and pulls on cupula, which then moves towards/away from kinocilia depolarizing/hyperpolarizing hair cells and increasing/decreasing vestibular axon firing
Activation of Semicircular Canals During Head Rotation
Increased firing during acceleration, adaptation in firing rate during constant velocity, and decreased firing during decelleration
Location of Vestibular Nuclei
Brainstem
Vestibular axon projection (cranial nerve)
Cranial nerve VIII Cerebellum and Lateral Vestibular Nucleus (otolith) and Medial Vestibular Nucleus (semicircular)
Otolith Projection
Lateral Vestibular Nucleus --> Limb motor neurons (maintains posture)
Semicircular Canal Projection
Medial Vestibular Nucleus --> Neck motor neurons (orient heat), Extraocular Motor Nuclei (III, IV, VI)
Vestibulo-Ocular Reflex
Maintains focus of vision during head motion Left semicircular canal hair cells excited --> excite muscles that move eyes rightward + inhibit muscles that move eyes leftward Opposite side inhibited, will not excite muscles
Pain
Does not require activation of nociceptors, subjective
Nociception
not necessarily percieved as painful
Thermoreceptor Activation
Do not increase firing rate when stimuli become noxious
Nociceptor Activation
Starts responding when stimuli becomes noxious
Nociceptors
Free nerve endings of A delta and unmyelinated C fibers Most polymodal
A delta and C receptors
Smallest diameter, least myelin A delta, pain and temp C fibers: temp, pain, itch
Chemicals that activate Nociceptors
Bradykinin: made by enzyme released from damaged cells, directly activates via depolarization through GPC receptors ATP: made by enzyme released from damaged cells, directly activates P2X receptors K+: released from nociceptors, depolarizes nociceptors
Hyperalgesia
following injury, injury site and surrounding area have increased perception of pain
Sensitization
exposure of nociceptors to products of tissue damage increases their activity and their sensitivity to stimuli
Chemicals that Sensitize Nociceptors
Bradykinin: increases sensitivity of ion channels like TRPV1 Prostaglandins: made by enzyme released from damaged cells Substance P: released from nociceptors, causes vasodilation, and release of histamine from mast cells
First Pain vs Second Pain
First Pain: Adelta fiber, fast and sharp Second Pain: C fibers, long-lasting and dull

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