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- Tetrodoxin blocks Na+ channels, nifedipine blocks Ca2+ channels

- voltage gated channel family – membrane spanning protein with 4 subunits with 6 membrane spanning domains each.

- S4 senses membrane voltage, S2 forms conducting pore

- opening/closing regulated by membrane potential

- other ion channels – cation – cellular activity, ion channel properties, spontaneous transmitter release, not regenerative

- ? is the length of an axon, the distance at which the voltage declines to ~37% of the original value (exponential decay). It depends on the diameter, membrane leakiness (Rm) and cytoplasmic crowdedness (Ri)

- active – the action potential, maintains full size (all or nothing) but is slow

- passive – fast, but decays quickly

- combined by mylination – active at the nodes of ranvier, passive between

- Na+ channels abundant in axon hillock, nodes of ranvier & soma, least in axon beneath myelin & dendrites

- K+ channels wide spread

- Ca2+ channels abundant in terminals, dendrites & areas of soma

- dimensions of color – visual system deals with variations in brightness, hue and saturation, independent of the levels of ambient light

- what you see about an object depends on the context in which it is placed

- reflects the same amount of light, but differs in perceived darkness

- illusory contours

- the visual image focused on the retina is inverted top to bottom and reversed left to right

- myopic- the image is formed before light reaches the eye

- hyperopic – plane of focus is behind the retina

- accommodation – the process by which curvature of the lens changes to allow the eye to focus on a nearby object

- near response – at the same time that accommodation occurs, the eyes converge and pupils constrict to increase depth of field of the focus

- presbyopia – the lens loses elasticity in older age, making accommodation difficult

- fovea – optimized for high acuity vision, the displacement of ganglion cells and the highest density of cone photoreceptors

- adaption to light levels by – adjustment of pupil size and adaptation of sensitivity of receptor cells

- photo receptor à bipolar cell à ganglion cell (modulated by horizontal and amacrine cells)

- cones – 4 million, three classes, low sensitivity, concentrated on fovea

- rods – 100 million, rhodopsin, high sensitivity, outside fovea

transduction in photoreceptors

1. light stimulated rhodopsin molecule activates 500 molecules of G-protein transducin. Cause GTP to bind, not GDP

2. G-protein activates a phosphodiesterase (PDE)

3. Each PDE hydrolyses 2000 molecules of cGMP

4. Reduction of cGMP causes closure of Na+ channels and hyperpolarisation of the receptor

– photoreceptors are somewhat depolarized and release glutamate in the dark

– illumination hyperpolarizes the photoreceptors, reducing glutamate release

– bipolar cells

o preserve the photoreceptor signal, glutamate is excitatory turning off ganglion cell

o invert the photoreceptor signal so that glutamate is inhibitory and ganglion cell on

decussiation of optic neurons

– the right half of the visual field projects to the left half of the brain

– the axons of ganglion cells in the nasal part of the retina cross in the optic chiasm (for information about light colors)

– the axons in the temporal part of the retina do not cross

lateral geniculate nucleus – receives projections for ganglion cells

· forms layers of cells (magnocellular from Y-cells, parvocellular from x cells.

· projections from the LGN to the cortex forms optic radiation (distinct fibre)

o topographically organized

- The hypothalamus generates homeostatic and behavioural responses to ‘interoreceptive’ stimuli

- humeral, secretion of hormones

- visceromotor, changes in the nervous system

- somatic motor, behavioral responses

- long term control of energy balance

- dual center model for regulation of feeding

- Frohlich’s syndrome – injury to the pituitary gland (WRONG!)

- role of the hypothalamus (Hetherington and Ranson)

- lesions of lateral hypothalamus – thin mouse

- lesions of anteromedial hypothalamus – fat mouse

- lipostatic theory

- the brain monitors the amount of body fat and defends this against change

- ob gene, expressed in fat cells

- db receptor, produced in brain

- leptin is produced in the fat cells and received in the brain

- decreased levels of leptin in starvation

- NPY/AgRP neurons of articulate nucleus – stimulate feeding behavior and inhibit secretion of hormones controlling ACTH & TSH

- increased levels of leptin in weight gain

- inhibit feeding behavior (MSH/CART neurons)

- stimulate release of ACTH and thyrrotropin

- NPY + AgRP – ‘oxexigenic’

- POMC + CART – ‘anorexigenic’

- Short term control of energy balance

- Ghrelin produced in stomach acts on feeding centers (NPY and AgRP), building up prior to a meal and then reduced following the meal

- Satiety signals – gastric distention and cholecystekinin and insulin

- Hedonistic feeding excites dopaminergic neurons

- language is a creative process using sounds, symbols and rules to create meanings

- language is innate, and has a specific development period (<6-7 years)

- animal sounds are steriotyped and not unique

- monkeys do not use cortical regions for communication, use brain stem

- critical period is bird song development, otherwise the sounds produced are meaningless

- language areas usually located in left hemisphere

- supramarginal gyrus, angular gyrus, Wernike’s area, Broca’s area

- deficits called aphasias

- paraphrasia – substitutions of a different word

- nonfluent speech – talking with effort (affected Broca’s area)

- agraphia – impairment in writing

- alexia – impairment in understanding written words

- Broca’s area – understand language, but can’t form or organise own sentances

- Wernike’s area – trouble understanding, but can talk

- conduction – can understand and speak well, but can’t repeat of make conversation (destruction of axons)

Classic Connectional Model

1. Sound is analysed in primary auditory cortex
2. Structure and meaning deoded by Wernike’s area
3. Motor plan for articulation is formed in Broca’s area
4. Primary motor cortex activates appropriate muscles

Left hemisphere dominant for language in right handed people.

Left handed people have less dominance.

If split brain occurs, the two hemispheres cannot determine what occurred in the other, so informtion in the right hemisphere cannot be processed into words.

Right hemisphere, involved in analysis and production of intonation and emotional content. It is used for understanding the pragmatics of language (such as interpreting jokes) in different contexts.

stimulus receptor/ action

Accessory Structures à Receptor Surface à output neurons à

energy generator potentials

potential

Translation à transduction à transmission à

Receptors

Type 1: specialized endings of sensory nerve fibers

transmit to somatosensory; proprioceptive and olfactory systems

Type 2: specialized receptor cells that connect via synapses to afferent nerve fibers

auditory, vestibular and gustatory systems

Type 3: specialized receptor cells that synapse with intermediatory cells, then nerve fibers

visual system

Stimulus à receptor cells à structural change à opening/closing

in membrane of ion channels

activated

molecules conductance change and

change in resting membrane potential

mechano receptors – mechanically gated ion channels

all other receptors – chemically gated ion channels

Coding of stimulus timing and duration à summation and adaption

Receptors fractionate (divide) the entire stimulus range into smaller blocks, allowing for coding of stimulus quality.

Temporal Summation – in order to produce a reaction, the first stimulus provides a hump for the second to leap off and reach threshold.

Spatial Summation – when there are two connections though a dendrite and the cell body (first provides hump)

Simultaneous Stimulation – two connections though the cell body make it easy to reach threshold

Facilitation – second ESP is larger than the first, then there is residual calcium in the bouton so the next stimulation has more of an action.

Metabotropic Receptors – presynaptic inhibits release

- postsynaptic slows synaptic responses and may not change membrane potential

- possess membrane spanning regions

- response transduced via G-proteins, then second messenger transduction pathways are activated

- change in membrane potential not required

Muscle Structure and Contractile Properties

- Muscle fibre – cellular element, multinucleate, each innervated, sarcomere as a functional division

- Sarcolemma – cell membrane

- Sarcoplamic reticulum – source of Ca2+ that surrounds each myofibril

- Myofibril – bundles of actin and myosin

- T-tubules – ramifying tubular system that carried the depolarization of the sarcolemma internally to each myofibril

- Sarcomere – myosin – 6 polypeptide chains, a hinge region, and ATPase activity – 400 myosin to each filament, half in one direction, half in the other

- actin – anchored to the 2-disc by protein liten – tropomysoin (covers the active sites) is regulated by troponin (calcium reactions)

Excitation-Contraction Coupling

a) motor neuron releases Ach onto skeletal muscle fiber activating the nicotinic receptors and opening K+ and Na+ channels (depolarization)

b) action potential moves away and down t-tubule system

c) dihydropyridine receptors are activated by voltage change

d) ryanodine receptors (lateral sacs of sarcolemic reticulum) open to release Ca2+

e) Ca2+ diffuses across microfilamentsa, then binds to troponin

f) Myosin heads can now bind to g-actin molecules, beginning CBC

Cross-Bridge Cycling

- Continues while nerve depolarizes membrane and ATP is present

- Shortens sarcomere to relax, Ca2+ is returned to sarcoplasmic reticulum and actin filament returns to resting position (this process occurs several times)

- Contraction velocity – ATPase activity and length of power stroke

- Contraction frequency – greater contraction strength builds piggyback response

- Muscle length – isotonic – concentric (muscle shortens) vs eccentric (muscle lengthens)

- isometric – muscle does not shorten/lengthen

- ATP provided by phosphate, anaerobic and aerobic respiration

- chemical senses – oldest and most common form of sensory system

- pheromones released for chemosensory information/communication

- reproductive behavior, identification, aggression

- chemoreceptors – generate neural signals on binding with particular chemicals

- provide quality control for injestion

Taste

- tongue, mouth, palate, pharynx, epiglottis

- taste and smell are intertwined to detect flavor

- all tastes are combinations of salt, sweet, sour, bitter (umami)

- taste preferences are inborm and present very early in life

- can develop a taste for certain types of food

- can recognize a deficiency and crave that nutrient

- whole of tongue sensitive to all basic tastes

- threshold concentration for taste

- higher concentration, less selective – specificity lies in the brain

- adaptation to higher levels of the same taste

- 2000 à 5000 taste buds on oral cavity and throat

- tastebuds located along the edge of the papillae

- receptor cell microvilli protrude from pore in chemoreceptor to contact fluid

- dissolved molecules bind to receptor, producing receptor potentials

- depolarizes à open Ca2+ channels à release neurotransmitter

- if large enough, action potentials signal taste to the brain stem

- taste stimuli

- pass through ion channels (sweet and sour)

- bind to and block ion channels (sour)

- bind to a-protein coupled receptors, not voltage gated

- are these neurons? They form synapses and transmit signals….

- saltiness – special Na+ selective channels, not voltage gated

- sourness – acidity with protons, bind to and block K+ channels

- action potentials travel along different pathways to the brain stem

- medulla of brain stem, ventral posterior medial nucleus, gustatory cortex

- population coding – integrate activity across all neurons from tastebuds

Olfaction

- oderants reach the nose through diffusion/sitting/eating

- olfactory nerves of thin unmylinated axons, only one signaling system, opening of cation channels activated Cl- channels to depolarise membrane

- response adapts quickly

- glomeruli ‘smell’ maps for olfactory discrimination

- skeletal muscle – highly efficient and adaptable

- energy and metabolism, heater, pump, movement and posture

- muscle fibres grouped into bundles

- somatic motor system – skeletal muscles and the part of the motor system that control them

- lower motor neurons – project from spinal cord

- alpha motor neurons – muscle force generation

- gamma motor neurons – sensory (spindles)

- neuromuscular junction – nerve-muscle interface

- motor unit – a single motor neuron (axon) and all the muscle fibers it innervates

- size is determined by the number of fibers attached to the neuron

- to increase force in a muscle – increase in frequency of motor neurons, recruitment of additional motor units (small first, large last)

Neuromuscular Transmission

1. nerve AP reaches axon terminal

2. axon terminal membrane depolarizes

3. calcium channels open, calcium flows into terminal

4. release of Ach and binding to muscle membrane

5. the permeability of muscle membrane increases, causing depolarization

Mechanism of Contraction

- a single muscle action potential is generated from a single neuron

- travels along muscle membrane then down t-tubules

- causes release of Ca2+ from the sarcoplasmic reticulum

- troponin blocks actin and myosin from reacting together, but calcium removes it (cross bridge attachment)