ANP 1106 - 3 - class notes PDF

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Basic Definitions Na/K ATPase 3 Na out 2 K in

-ve inside , +ve outside Primary active transport Different charges drives ion mvmnt across membranes of excitable cells

Voltage

Measure of pot energy generated by potential difference - Measured un volts/ mV - Greater difference = higher voltage

Current

Flow of electrical charge (ions) between 2 points - Flow = dep on voltage + resistnce

Resistance

Hindrance to charge flow (current) - Insulator : substance w high electrical resistance - Conductor : subst w low resist

Role of membrane ion channels

Lrg proteins serve as selective membr ion channels - Leakage channels; always open - Gated channels: protein changes shape to open/close channel.

Chemically Only opened by specif chemical (ligand) gated - NT’s

Absolute refrac per.

Time betwn opening of Na channels until resetting of channels Ensures AP is all-or-none Enforces one-way transmiss of impulse

Relative refractory per.

Following ARP - Most Na gates closed - Some K gates still poen Repolarizing is occurring (threshold for AP gen is elevated)

Voltage-gated open in response to membrane pot Mechanically gated

open in response to physical deformation of sensory receptors

Electrochemi cal gradient

Ion flow creates electrical current & voltage changes across membrane

Important principles

Cell voltage is det by differences in [ion] but also conductance (permeability) for that ion across cell membr - Lrg diff in [ion] will have no effect on voltage unless there is conductance for that ion

Types of signals

Graded pot: incoming signals operating over short distances Action Pot: long-distnce axonal signl GRADED POTENTIALS

Stimulus intensity

Determined by FREQUENCY of impulses - #APs received - All AP intensities are equal Postsynaptic potentials (graded pot) Excitatory Short dist. w/in cell body towards axon hillock EPSP Moves membr pot towards threshold for AP No refractory P Simultaneously opens Na+ & K+ channels Na+ influx = greater than K efflux Creates local net graded pot (more positive) Inhibitory Hyperpolarizes, membr pot = further form AP IPSP No refractory P NT: opens K+ and Cl- channels K+ efflux & Cl- influx More neg. Charge (inhibitory)

1. Small patch of membr is depolarized 2. Depol. Area spreads by opp attract, creating local currents Short-lived, small distance, triggered by a stimulus that also opens fated ion channels Named according to location + function - Receptor pot; in sensory neurons - Postsynaptic pot: neuron graded pot ACTION POTENTIALS Occur in muscle Brief ~100mV change in membr pot + neurons Self propagating Dont decay over distance Req opening of specific voltage-gated channels Small depol area trigger next section of axon to dep.

Action Pot

Voltage triggered: First opens Na, then K channels Peak: +30-50 mV Conduction Velocity AP

Occur only in axons, NOT other neuronal areas AP Propagation rate depends on: 1. Axon diameter Lrg diam have less resistance to local current flow = faster impulse conduct’n 2. Degree of myelination Continuous cond; slow, on unmyelinated Saltatory cond; 30x faster, on myelinatd Myelin sheth insultaes + prevents charge lekage Voltage gated Na channels in myeln gaps

Bare Plasma membr - Voltage decays bc current leaks across Non myelinated axons (continous conduct’n)

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SLOW, so many channels = take time to open/close Myelinated axons (Saltatory conduct’n) - FAST, myelin maintain charge, jumps btwn gaps Clinical Examples - AP conduction Damaged myelin in CNS

Slows nerve conduction

Local Anesthetics

Block voltage Na channels

Cold temp. / pressure

Blocks blood circ.--> numb

Neuronal Pool Functional groups Integrate = forward info frm receptors/ of neurons othr pools Simple neuronal Simple presynaptic fiber branches & pool branches w several neurons in pool Discharge zone

Neurons closer to incoming fiber = more likely to generate impulse

Facilitated zone

Neurons on periphery of pool = farther frm incoming → no excited to threshold unless stim by other source

Classification of nerve fibers Diameter, degree of myelinat’n, & speed of conduction Group A Largest diameter Myelinated SS + motor fibers of skin, skeletal muscles + joints Transmit @ 150m/s Group B Intermediate diameter Lightly myelinated Transmit @ 15m/s Group C Smallest diameter Unmyelinated Transmit @ 1m/s The Synapse Junctions tht mediate info transfer

Include ANS visceral motor + sensory fibers (serve visceral organs)

Neron - neron Neuron - effector cell

Actions classif Direct Action NT binds directly + opens ion channels Rapid responses - ACh & AA’s Indirect Action

NT acts thru intracellular second messenger Longer lasting effects - G proteins, neuropeptides, dissolved gasses

Serial Processing Input travels along one pathway to specific destination

All or none manner Produce specific response - Spinal reflex

Reflexes

Rapid, automatic responses Particular stim always causes same response Pathways called reflex arcs

Reflex Arc

1 Receptor 2 Sensory neuron 3 CNS integration center 4 Motor neuron 5 Effector

Parallel Processing Input travels along One stim promotes numerous several pathways responses Important for higher-level mental functioning - Smell → odor + experience Circuits Patterns of synaptic cxns in neuronal pools Diverging

1 input, many outputs AMPLIFYING CIRCUIT - Brain neurons → muscle fibers

Converging

Many inputs, one output CONCENTRATING CIRCUIT - Sensory stim → one memory

Reverberating

Travels thru chain, each feeding back to a previous neuron OSCILLATING CIRCUIT - Breathing, sleep-wake cycle

Parallel after-discharge

Stim neurons arranged in parallel arrays tht eventually converge Input reaches output cells @diff times (AFTER DISCHARGE) - math

Receptors Channel-linked

G protein-linkd

G protein linkd mechanism

Ligand-gated Immediate + brief action Excitatory receptors = channels for small cations (Na+ ions) Inhibitory receptors allow Cl- influx Complex Indirect responses - Slow, prolonged Involves transmembr prot. Complexes Causes widespread metabolic changes - Muscarinic ACh recept - Biogenic amine recept - Neuropeptide recept NT binds to G prot receptor Activated G prot signals product’n of second messengers - Cyclic AMP, cyclic GMP, diacylglycerol, Ca2+ 2nd messengers open/close channels Activate kinase enzymes Phosphorylate channel prot. Activate genes + induce prot synthesis

Neural intergration Neuron grp work tog

Allow smooth operating

PNS Levels 1. Perception (cerebral cortex interpretat’n) 2. Circuit (ascending pathways) spinal cord 3. Receptor Level (sensory receptors) skin Nonencapsulated + encapsulated Nerves - affect sensitivity + physics THALA Relays info up MUS EVERYTHING PASSES THRU HERE PERIPHERAL AXONAL DAMAGE REPAIR

There are active mechanisms promoting + inhibiting growth

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Proliferat’n of schwann cells (growth hormone) No rewiring to reconnect to CNS neurons

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Transient Receptor Potential (TRP) proteins Free endings, permeability (AP rates) change w specif temps

Photoreceptors

Light energy (retina)

Chemoreceptors

Chemicals (smell, taste, blood chemistry)

Nociceptors

Painful stim

Proprioceptors

location in space (joint angle, muscle length) - Golgi tendon organ ( info abt muscle tension) Structural classif of receptors Sensory Territories

Sections of body organized into dermatomes “bands”

Somatotopic organization

To recog what part of body is being stim.

Trigeminal Nerve Control whole face

CRANIAL nerve 5 (not spinal) 3 gemini (roots) 1. Ophthalmic 2. Maxillary 3. Mandibular

Simple 1 step Complex 2 step

Sensory Receptors Stimulus here causes graded depolarizat’n → Triggers AP to CNS Reflex activity

Spinal cord

Sensat’n + Percept’n

Cerebral cortex

Transduction

Convert physical property into electrochemical property (physical stim → graded pot.

Receptor Potential

Transmembr difference produced by activated sensory receptor (most = depolarizing)

Pain perception (Nociception) Perception of stimuli that have potential to cause tiss damage. We avoid these stimuli by reflex + conscious responses Tiss release histamine, K, ATP, acid, bradykinin

Depolarize free nerve endings of nociceptors

Achieve pain relief

Electrical, pharmacological, inhib pathways release endog opioids (Enkephalin)

Majority Include encaps & nonencaps Transduction + transmission Special sense organs Receptor cell releases vesicles to stim afferent neuron - Retina ; nerve gathers info but does not transduct info into Potentials (instead, use a specialized cell to relay info to bipolar cell - photoreceptor cell) - Taste cells + taste nerve axons - Hair cells + auditory axons

AP frequency is directly proportional to stimulus intensity Adaptation Rapidly adapting ( phasic) - lots APs at (with first, no more, small burst at end continuous - Smells, put on shirt intensity) Slowly adapting ( tonic)- Stable APs all throughout (keeps you aware) - Pain, proprioreceptors Acuity Level of branching of nerves

Lower acuity: Highly branched nerves, reaches lots of area (thigh) higher acuity: Lip has concentrated, finer receptive field

Overlapping stim between adjacent receptive fields provides more precise info regarding locat’n of stim CIRCUIT LEVEL PROCESSING First order neurons

Soma reside in dorsal root/ ganglia Conduct frm skin → spine/ brain stem

Second order

Soma is in dorsal horn of spine Transmit impulses to thalamus/ cerebellum

Third order

Soma in thalamus Conduct impulses to somatosensory crtx

Enkephalin

Interferes+ blocks pain signals from periphery Location classif of sensory recept Extroreceptors Found near surface Touch, pressure, pain, temp Interoeptors

Found in viscera + blood vessels Chemical changes, stretch, temp, BP

Stimulus Type classif of Sensory Recep Mechanoreceptors

Touch + pressure, itch, stretch

Thermoreceptors Temp changes

Major Ascending pathways Decussation

Crosses midline in CNS

Chiasma

Crossing in PNS

Anterolateral Pathways Lateral Spinothalamic

Transmit pain + temp impulses to opposite side of brain to SS

Ventral Spinothalamic

Transmit touch + pressure impulses to opp side to SS

Main aspects of Sensory Perception mitral cells In Perceptual detection Detecting occurrence of sitmulus Olfactory bulbs MAgnitude estimation

How much of stimulus is acting

Spatial discrimination

Identifying pattern of stimulus (make out what objects are by touch)

PERCEPTUAL LEVEL PROCESSING Thalamus projects fibers to SS cortex + sensory association areas Feature abstraction

Identify substance w specific texture/ shape

Qualirt discrimination

Identify sumodalities of sensation - sweet vs sour

Pattern Recognize patterns in stimuli Recognition - Melody, familiar face Muscle Spindle (proprioception) Stretch receptors

Bundle of muscle fibers, Encapsulated Detect muscle length

Intrafusal muscle fibers

coiled by sensory fibers All surorunded by Extrafusal muscle fiber

Stretch

Results in more APs

Alpha motor neuron activation

(voluntary contraction) only extrafusal muscle fibers shorten Spindle becomes slack & no APs

1. Olfactory cortex (interpretation) 2. Limbic system (memories + associations)

Smell is the only input into cerebral cortex that does NOT pass thru thalamus first PHYSIOLOGY OF TASTE Dissolve in saliva

Contact Gustatory hairs

Binding of chemical

Depolarizes taste cell membr. → releases NT into sensory neuron

Initiates generator potential Taste nerves

Elicits AP in sensory neuron signal brainstem

Facial nerve XII

Carries signals frm Anterior ⅔ tongue

Glossopharyngeal

Carries taste afferents from Posterior ⅓ tongue

nerve IX

Taste Buds + Taste transduction 10 000 (mainly in papillae)

Each composed of 50+ epithelial cells - Gustatory (sensory taste cells) - Basal (stem cells) - Support cells (insul ate receptor)

Sweet

Sugars, saccharin, alcohol, AA’s - Cl influx → G proteins

Salt

Metal ions - influx Na channel)

Alpha gamma Both extrafusal and intrafusal fibers Sour coactivation shorten Tension is maintained in muscle & can still signal changes in length.

Hydrogen ions H+ - Direct diffusion of H+, or open cation (Na, Ca, K) channels, or block K+ channels

Bitter

Gustatory receptors Taste substances dissolved in saliva

Alkaloids (quinine, nicotine) - Cl influx → G proteins

Umami

Glutamate AA - Cl influx → G proteins

Olfactory receptors

Gustatory cells

SMELL + TASTE

Substances dissolcved in nasal fluids PHYSIOLOGY OF SMELL Air → nasal conchae

Mix air to even distribute smells across Olfactory epithelium - Supporting cell - Basal cell Epithelium contains receptor cells (replaced q4-8 wks)

Dendrite bends Branches into olfactory cilia (distal downwards endings of dendrite factory olfactory towards Mucosa receptor neuron) - Mucosa captures orderants Transduction

Transmission Synapse w

Olf receptr binds to G proteins → produces cAMP (2nd messenger) - Opens Na+ & Ca+ ligand gated channels - AP occurs in olf sensory receptor neurons

Contain gustatory Microvillae that extend thru pore into hairs saliva Membrane Receptors

Replaced every 7days

Taisant (taste “odorant”)

Binds to receptors on gust. Hairs. Trigger graded + APs Release NT → activates gustatory afferent fibers

Gustducin

G protein for sweet + bitter tastes

80% smell

Nociceptors, thermorecept, mechano can all affect taste

Gustatory Pathway Cranial Nerves VII + IX

Carry impulses frm buds → solitary nucleus of medulla

Cross midline + Reach thalamus

Branch to : 1. Gustatory cortex (in insula) 2. Hypothalamus + limbic systm

Move up thru holes in cribriform plate on ethmoid bone → cranial cavity

EYE STRUCTURES

Go to:

Eyebrows Coarse hairs tht overlie suproorbital margins

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Prevent perspiration from reaching eye Orbicularis muscle; depresses brows Corrugator muscles; moves brows medially (tog)

Palpebrae Protect eye anteriorily (eyelids) Palpebral fissure; separates eyelids Tarsal plates; CT supports eyelids internally Levator Palpebrae superioris; elevates upper eyelid Conjuncti Transparent membrane va - Lines eyelids (palpebral conjunctiva) - Covers whites of eyes ocular conjunctiva - Lubricates + protects eye Conjunctivitis; inflammation + dilation of vessels make whites appear red/ pink Tears - LACRIMAL GLANDS Produce + secrete tears Enter eye via excretory ducts Flow across + down

Drain into lacrimal sac

Exit eye, flow thru lacrimal puncta into lacrimal canaliculi Empty via nasolacrimal duct into (inf meatus) nasal cavity

Rods (most) 20 rods/ 1 cone Cones

1 visual pigment (non colour) Low light vision (high sensitivity) Low acuity (many rods converge→ 1 ganglion cell) Peripheral retina Colour (3 visual pigments) Higher light (lower sensitivity) High Acuity (1:1 w ganglion cell) Central retina

Retinal (Vit A) Combines w opsin (prot) to make Rhodopsin (essential photoreceptor for colour) 11-cis-retinal (dark) derived frm Vit A Rhodopsin absorbs light → All-trans-retinal (light) All-trans activates G proteins → convert cGMP → GMP Falling cGMP levels cause cation (Na/Ca) channels to close (hyperpolarize) Phototransmission - DARK cGMP-gated channels open

Allow Na//Ca influx Depolarization occurs

Voltage gated Ca channels open

In synaptic terminal of photoreceptor cell

NT release

Causes IPSP in bipolar cell

Hyperpolarization closes voltage Ca channels

Inhibits NT release frm bipolar cell

No ESPS occur in No AP along optic nerve ganglion cell Phototransmission - LIGHT cGMP-gated channels close

Hyperpolarization occurs

Voltage-gated Ca channels No NT release close

Retina Iris

Sphincter pupillae (constricts) PSNS Dilator pupillae (dilates) SNS

Ganglio Axons run along inner surface of retina n cell Leave eye as optic nerve

Lack of IPSP in bipolar cells cause depolarization

Opens voltage-gated Ca channels

NT released by bipolar c

EPSP in ganglion cell AP along optic nerve

OPTIC NERVE Nerves frm 2 eyes converge Fibers partially cross over in Optic chiasma Travel down optic tracts

Optic disc

Optic nerve exits eye Blind spot bc no photoreceptors

Synapse at 2 Lateral geniculate nuclei of thalamus

Thalamic fibers run as optic radiation to visual cortex for interpretation

Ciliary muscle

Opposite of Ciliary zonule Contraction - convex shape, more focus, close Relax - flatten, far vision

A few fibers contain melanopsin

circadian pigment Sets biological clock

Eyesight issues (Refraction) Nearsighted (myopic)

Eyeball too long Focal point in front of retina Concave lens to correct

Farsighted (hyperoptic)

Eyeball too short Focal point behind retina Need convex lens

Photoreceptors

AUDITORY External ear

Collects & passes sound waves inward Pinna (auricle) ; skin covered cartilage Acoustic Meatus (aud canal) Tympanic membrane (eardrum)

Ossicles

Malleus, Incus, Stapes Transmit vibrations onto oval window

Tensor tympani & Stapedius muscles CNS control - Protect auditory Receptor cells

Mechanism of Hearing Vibrations beat against Pushes ossicles → pressure tympanic membrane fluid against oval window

Inner ear

Shearing forces pull on Mvmnt stimulates cochlear hair cells nerve impulses

Bony Labyrinth - Many channels in temporal bone - Contain vestibule, cochlea + semicircular canals - Fillled w perilymph

Inner Ear

Membranous labyrinth - Series of membranous sacs w/in bony labyr. - Filled w Potassium-rich endolymph

Vestibule

Central egg-shaped cavity of bony lab. 2 sacs - House equilibrium receptors (Maculae) - Respond to gravity + head position

Semicircular canals W in vestibule

Cochlea

3 canals - Lined w membranous semicirc ducts Ampulla ; swollen end, houses Maculae in crista amullaris region - Respond to head mvmnt