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Flashcards in Neurophysiology Deck (52):
1

Neuron

Excitable cells with specialised projections which transmit info around the body by electrochemical transmission

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Dendrites

Bring info to cell body

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Axons

Take info away from cell body

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Myelin sheath

Lipid covering most axons, produced by Schwann cells (membrane = regular intervals)

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Node of Ranvier

gaps in myelin sheath

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Interneurons

Spinal cord + brain, signals from sensory neutrons or other interneurons

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Sensory neurons

Run to spinal cord and brain from stimuli receptors (cell bodies in clusters at spinal cord => ganglia)

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Motor neurons

Impulses from CNS to effectors (muscles and glands)

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Spinal cord

31 pairs of spinal nerves - both sensory and motor axons -
All sensory axons -> dorsal root ganglion -> spinal cord
All motor axons -> ventral root -> sensory axons -> mixed nerves

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Resting potential

Electrical charge across plasma membrane - interior more negative -> -70mV
Sodium/potassium ATPase pump pushes 2K+ in for every 3Na+ out -> net loss of +ve charge within cell
K+ leaky channels so slow facilitated diffusion of K+ out

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Depolarisation

Reduce charge across membrane . Mechanically gated sodium channels open -> ligand-gated Na+ channels open -> excitatory postsynaptic potential (EPSP) -> reduced to threshold violates (~-50mV) -> action potential (nerve impulse). Na+ close and K+ open out -> normal polarity. All or none. Strength = frequency

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In myelinated areas...

Action potential jumps form node to node (myelin = insulator) by saltatory conduction which speeds up the propagation of the action potential

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Autonomic nervous system

Controls smooth muscle, cardiac muscle, glands and some adipose tissue

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Sympathetic nerovous system

Fight or flight response

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Parasympathetic nervous system

Everyday responses

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Neuromuscular junction

The synapse between a somatic motor neuron and skeletal muscle fibre
Arrival of AP
Depolarisation of presynaptic membrane
Voltage-Gated Ca2+ channels open
Influx of Ca2+ ions
Vesicles fuse presynaptic membrane
Release of Ach
Diffusion to postsynaptic receptors (ligand-gated Na+ channels)
Activation of postsynaptic receptors
Generation of end-plate potential (EPP)
Transmitted intact - Achesterare

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Neurotransmitters

Chemical signal released by a neurone that influences the neurones largest cell -> amino acids (GABA), amines (Acetylcholine), peptides, others (adenosine, ATP)

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Synaptic plasticity

Can change functionally or structurally
Molecular and structural changes at synapse -> learning and memory deficits e.g. memory encoding -> storage -> retrieval
Training = gain of function

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Contribution of NS to homeostasis: all body systems

And hormones (endocrine) = communication and regulation of body tissues

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Contribution of NS to homeostasis: integumentary system

Sympathetic nerves ANS - control os SM to hair follicles and secretion of perspiration from sweat glands

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Contribution of NS to homeostasis: skeletal system

Pain receptors in bone tissue -> brain trauma and damage

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Contribution of NS to homeostasis: muscular system

Somatic motor neutrons - contract SM - body moves basal ganglia and reticular system = muscle tone, cerebellum co-ords skilled movement

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Contribution of NS to homeostasis: endocrine system

Hypothalamus regulates secretion of hormones from pituitary gland, ANS from adrenal gland and pancreas

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Contribution of NS to homeostasis: CV System

Medulla oblongata -> nerve impulses ANS => heart rate. ANS regulates bp and blood flow through vessels

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Contribution of NS to homeostasis: Lymphatic system and immunity

NTs regulate immune respones - increase and decrease

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Contribution of NS to homeostasis: respiratory system

Brain stem controls rate and depth. ANS airways diameter

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Contribution of NS to homeostasis: digestive system

ANS and enteric NS regulate, parasympathetic ANS stimulates process

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Contribution of NS to homeostasis: urinary system

ANS blood flow in kidneys -> urine formation

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Contribution of NS to homeostasis: Reproductive system

Hypothalamus and limbic system - sexual behaviour, NAS - erection and ejaculaton. Hypothalamus - hormones controlling gonads. Touch stimuli suckling infant - oxytocin and milk ejection

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Sclera

Outermost layer of the eye - posterior proportion (5/6 eye) (anterior = cornea)

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Episclera

Sclera: outermost layer, contacts eye socket, loose CT

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Sclera proper

Sclera: middle layer, collages, tendons, attach to Tenan's capsule

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Lamina fuscula

Sclera: Inner layer, adjacent to choroid, collagen and elastin, pigmented cells

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Uvea: choroid

Largest
Blood vessels, Bruch's membrane - supports retinal pigmented epithelia

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Uvea: ciliary body

Projections close to lens producing aqueous humour

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Uvea: iris

Covers lens and regulates light -> retina and protects from sunlight

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Tear film

Provides nutrients to cornea, contains antibacterial agents and provides a clear optical surface
Outer, oily layer - tears don't evaporate quickly, prevents dryness
Middle aqueous layer nourishing cornea and conjunctiva
Bottom mucin layer

38

Aqueous humour

Maintains intracellular pressure, contributes to ocular transparent, provides metabolic support for lens, cornea and vitreous
Similar to plasma body but only 1% plasma protein

39

Itra-ocular pressure (IOP)

10-21 mmHg, dynamic balance of secretion and draining of aqueous humour
High = glaucoma - loss of visual light field => blindness

40

Eye lens

Oldest cells and proteins in the body - fully formed at week 4-5
Avascular tissue - low O2 tension, 8mm diameter, central cells, no organelles
Refract light, low light scatter, all life
Disease: age related, environment, diabetes, drugs

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Avascular tissue facilitates image focus

Lens capsule - BM -> homogenous translucen CT matrix - glycoprotein
Subcapsular epithelium - single layer of cuboidal cells
Lens fibres - elongated cells from near lens equator
Cells grow - optical axis, lose many organelles
at optical acs - hexagonal and pack tightly - highly organised
Few organelles - high in proteins (60-70%) - major protein = cystallins which increases refractive index of cytosol

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Accommodation of lens

Thinner focussing distance - relaxed ciliary muscles
Presbyopia - with age (47+) lens less elastic - muscle contraction and less accomodation

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Cataract

With age, lens fibres less transparent, not sufficient light for clear image - replace with plastic

44

Human retina

Transparent, at least 11 layers, converts light energy -> nervous impulses - signal transduction, photoreceptors, 120 million rods, 6 million cones, muller glia, retinal pigmented epithelia
0.5mm thick
Photoreceptors outermost pigment against epithelium and choroid
Absorption of photons by visual pigment of photoreceptors -> biochemical message -> electrical message -> neurons of retina
3 layers of nerve cell bodies
2 layers of synapses
Outer nuclear layer - cell bodies of rods and cones
Inner nuclear layer - cell bodies of bipolar, horizontal, amacrine cells
Ganglion cell layer - cell bodies of ganglion and displaces amacrine cells
Dividing nerve cell layers - 2 neuropils -> synaptic contacts occur over 1m fibres - only myelinated after leaving eye

45

Photoreceptors

Outer segment - stacks of membranes with visual pigment molecules
Inner segment - mitochondria, ribosomes and membranes where opsin molecules assemble
Cell body - nucleus
Synaptic terminal - neurotransmission - 2nd order neurons

46

Rod cells

Rhodopsin
Sensitive to blue/green light -> 500nm peak, highly sensitive -> dark/dim conditions - monochromatic
Thiner
Peripheral retina

47

Cone cells

Cone opsin
3 types:
1 - max sensitive to either long wavelength of light (red)
2 - medium wavelength (green)
3 - short (blue)
Colour perception
Thicker
At fovea

48

Muller cells

Guide light to rods and cones - tram lines and putative stem cells

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Retinal pigmented epithelium cells

Prevent retinal degradation - consume damaged cells e.g. UV damage - no knock on effects like phagocytosis. Cell barrier

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Optic nerve

Centre of retina - circular, oval white area 2x1.5mm -> major blood vessel
Ganglion cell axons - brain and incoming vessels
Innermost retina closest to lens

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Fovea

Centre of macula, only cones

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Optic disc

Entry of optic nerve into eye = blind spot - no photoreceptors, only axons