Animal Physiology Flashcards
List the processes involved in animal physiology
- Energy
- Maintenance
- Moving
- Sensing & Coordination
What is the term used to describe the inside of an internal environment?
-Extracellular fluid
Where did the word ‘Homeostasis’ come from?
- 1872 Claude Bernard ‘Constancy of the internal environment is the condition of free life’
- Walter Cannon then coined ‘Homeostasis’
What are the proportions of total body water in vertebrates?
- 1/5 is blood plasma
- 4/5 is interstitial fluid
- 1/3 is extracellular fluid in non-vertebrates
What is the resting membrane potential?
- A difference in electrical voltage across a cell membrane, forming a ‘cell battery’
- The inside is maintained at 60 to 80 mV to the outside
- Measured using a intracellular microelectrode
Why is the ‘Cell battery’ important?
- Used to make electrical signals
- Move things across the membrane, absorption in gut, water and salt balance in teleost fish, regulate cell volume…
How is the cell’s resting potential maintained?
- Unequal distribution of K+ ions between inside and outside of cel;
- Selective permeability of resting cell membrane to K+
- There is a equilibrium between the two gradients across the membrane, electrical gradient and concentration gradient
Which proteins Maintain the cell resting potential?
- Sodium-potassium exchange pump - uses ATP to export 3 Na+ ions and import 2 K+ ions in the cell
- Potassium channel - no ATP required just allows for K+ ions are able to pass through the aqueous pore, use diffusion
What did Walther Nernst win the Nobel prize for?
- The Nernst equation - to work out the K+ equilibrium
- Problem is that resting membrane is slightly permeable to Na+
What is the function of neurons?
- Receive, sort out and transmit electrical signals
- Signals produced by currents flowing through ion channels in cell membrane
- Signals within a single neuron are called spikes/action potentials/impulses
What is the major difference in dendrite and axon channel activation?
- Dendrite is chemically activated
- Axon is voltage activated
What are cells that make cause spikes called?
-‘Excitable’
Describe a spike
- Brief, pulse-like electrical event
- Travels by propagating
- Triggered when local electrical signal is strong enough/exceeds threshold
- Stereotyped event (all-or-none)
- Membrane potential reverses in polarity, inside becomes more +ive than outside
Describe the nature of stimulating a spike
- Spikes usually around 1ms
- Amplitude of stimulus doesn’t affect the mV of spike
What are the structure of a axon?
- Dendrite
- Cell Body
- Axon hillock
- Axon
- Axon terminals
What are dendrites used for?
- Collect signals from other neurons
- If signals from dendrites is enough to excite the axon hillock, spike it formed
What is the function of a spike?
- Boosts the size of a small signal
- Carries electrical excitation along axon
- Without spikes signals would fade in a short distance
How long does a spike take to travel from the base of your spine to your toe?
-1/100s
What are the factors that affect the speed of which a spike travels?
- Axon width
- Temperature
- Myelin
What type of travel does myelin sheath cause?
-Saltatory conduction - jumping from node to node
What are the 5 phases of a spike?
- Resting potential
- Threshold
- Rising phase
- Falling phase
- Recovery
Which ion channels are involved in causing a spike?
- Potassium ion channels
- Voltage-gated Sodium ion channels
Describe how Voltage-gated Sodium ion channels act during a spike
- If excited Na+ channels open
- Na+ enters via diffusion
- This makes axon less negative, opening more Na+ channels.
- Na+ channels then close and become inactive
Describe how Potassium ion channels act during a spike
- Open after the Na+ channels are closed and K+ leaves the axon via diffusion
- Different to the K+ channels used to maintain resting potential
- Open more slowly than the Na+ channels, to allow for spike to occur
How long is a refractory period?
-1/2 ms
Where has most spike information come from?
-A giant axon from squid in the english channel used to cause jet propulsion in squid
What did Hodgkin and Huxley find?
- The resting potential of +50mV
- The cytoplasm ion composition was different than bathing fluid
- Intracellular recording found polarity reversed
- Separate out currents carried by Na+ and K+
- Sequence of events
List three types of neurons
- Cerebral cortex (Pyramidal cell) - Some neurons brand over a broad area, communicate over long distances via long axons
- Retina (bipolar cell) - Short axon with few dendrites
- Cerebellum (purkinje cell) - Bushy dendrites collect information from many other cells
List 4 structure specialised to synapses
- Junctional fold
- Synaptic cleft
- Active zone with synaptic vesicles
List two neurotransmitters
- Acetylcholine
- Glutamic acid
How does a synapse work?
- Neurotransmitter is released when presynaptic terminal is excited
- Vesicles fuse with presynaptic membrane
- Transmitter crosses narrow synaptic cleft
- Some bind to and opens ion channels on surface of post-synaptic membrane
- Ions carry electrical current through channels
What evidence is there for most synapses being chemical?
- Physical gap between 2 neurons at a synapse
- Applying a particular chemical to a postsynaptic site causes an electrical response
- Vesicles in presynaptic terminals contain the same chemical that produces the postsynaptic cell’s electrical response
How do electrical synapses work?
-Electric current flows directly between neurons
What triggers the release of neurotransmitters?
- Excitation in the presynaptic terminal causes voltage-gated Ca2+ channels
- Ca2+ enters the presynaptic terminal under a strong electrochemical gradient
- A increase in Ca2+ triggers a cascade of enzyme-like events that cause vesicles to fuse with presynaptic membrane and release neurotransmitter
Evidence for neurotransmitter release
- Squid giant synapse
- Involved in jet propulsion
- Stained two axons in a ‘relay’ synapse
- Measured presynaptic and postsynaptic terminals
- Found that pre-potential regulates the amount of neurotransmiter and that regulates size of postsynaptic potential
What is the evidence for Ca2+ entering the presynaptic terminal?
- (Linas and Nicholson 1975)
- Found that protein Aequorin form jelly fish glows blue in the presence of Ca2+
- Found light emitted was proportional to postsynaptic potential size
How do ‘non-spiking neurons work?
- Spikes aren’t required and only electrical excitation to open Ca2+ channels in the presynaptic terminal
- E.g retina
How long is the small delay at the chemical synapse?
- 0.5ms
- Time for Ca2+ channels to open
How do neurotransmitters cause PSPs?
- Neurotransmitters bind to receptor site, causing channel to open
- Several kinds of neurotransmitter and some inhibit neuron instead of excite
How can we tell if a post-synaptic terminal is excited?
- Patch clamping
- Take one fine channel protein which can be used to measure electrical pulses which run through the neuron
Compare a spike and a psp
- Spike - Voltage-gated channels, 1/10 V, Discrete and fixed amplitude and travel via propagation
- Psp - Chemical-gated channels, generally few mV, adds with other psps and cannot travel far
How do psps form a spike?
-Several psp join to form a spike, which enables nervous system to amke descisions - intergration
How do inhibitory synapses work?
- GABA opens Chlorine channels, allowing for Cl- ions to diffuse into the Post-synaptic terminal
- Cl- binds with Na+ to reduce psp amplitude
Which toxins target Na+-K+ exchange pump?
- Ouabain and digoxin
- Alkaloid which sticks to the ATPase site on the protein
- Used clinically for heart treatment
- Slow-acting around 1.5 hours to reach maximum
Which toxins target voltage-gated Na+ channels?
- Tetrodotoxin, found in pufferfish and other
- Weird biochemical, produced by bacteria in organs and skin
- Saxitoxin is similar and produced by dinoflagellates
- TTX forms a strong bond in the ion channel and ‘corks’ the channel
Which toxins target Na+ channel inactivation?
- Atracotoxin, found in funnel-web spider
- Toxic to apes
Which toxins target voltage-gated K+ channels?
- Tetraethylammonium
- Apamine, found in bees
- Dendrotoxin - mambas
What are cone snails?
- Largest marine invertebrate genus of 500 spp
- Diversified rapidly
- Sub-tropical
- Dangerous
- Varied diet-worms, molluscs and fish
- Modified radula as a toxin-bearing harpoon
Which toxins target voltage-gated Ca2+ channels?
- Conotoxins
- 15-30 amino acid peptides
- Lots of disulphide bridges
- ~100 distinct toxins per species
- 50,000 toxins in genus
What types of conotoxins are there?
- Alpha-conotoxins, nAch receptor
- mu-conotoxins, muscle v-gated Na+ channels
- Omega-conotoxins, v-gated Ca2+ channels
Which toxins target neurotransmitter release?
- Exocytosis inhibited
- Botulinum toxin blocks exocytosis
- Black widow spider venom causes uncontrolled exocytosis
What are the various neurotransmitters used?
- Vertebrates - Acetylcholine
- Arthropods - Glulatic acid
How does alkaloid curare work?
- Stops acetylcholine form binds to receptors
- Muscle relaxant used in clinics
- E.g Alpha bungarotoxin
Give a brief description of snake venoms
- 2,700 spp but only 300 toxins
- Can either be haemotoxic or neurotoxic
Give a brief description of spider venoms
- Multi-component polypeptides which block glutamate receptors
- E.g Strychnine, blocks glycine receptors
What does Eserine do?
- Interacts with acetylcholinesterase
- A potentiator
Define ‘transduction’
-Conversion of one form of energy into another
What is special about sensory neurons?
-Contain dendrites which specialise in transduction of particular stimuli e.g pressure, heat and light
How does stimulus transduction work?
-Alters the ion flow across cell membrane to cause a receptor potential
Describe the abdominal stretch receptor in a crayfish
- ‘Muscle receptor organ’
- Mechanoreceptor
- 4 per segment
- Detects downward tail bending in specialised receptor muscle
- If stimulus is sufficient then axon hillock will produce a spike
Define a ‘proprioceptor’
-A sense organ that monitors the position or a change in position of an animal’s body parts
What is linked to spike strength?
-The stronger the spike the higher the spike rate
What is adaptation? (sensory neuron)
- Allows sensitivity to changing stimuli
- ‘Anti-tickle’
- Be able to distinguish from fatigue and habituation
What are hair cells in vertebrates?
- Found in lateral line system of fish
- Signals about water movement
- Found in balance organs of other vertebrates
- Cells with cilia that are able to be excited
How are hair cells used to detect sound?
- Sounds are pressure waves
- Need to distinguish between tone (tonotropic organisation), loudness (amplitude of potentials) and source
List the range of tones for Humans, Dogs and Bats
- Humans - 10 Hz to 20 kHz
- Dogs - 40 Hz to 60 kHz
- Bats - 20 Hz to 150 kHz
List the structures of the mammalian inner ear
- Tectorial membrane
- Outer hair cells
- Inner hair cells
- Basilar fiber
How do hair cells transduct sound?
- Detect vibrations from the tympanic membrane
- 3,500 inner hair cells directly release transmitter
- 40,000 sensory axons in brain which cause spikes to occur
- 12,500 outer hair cells, regulating the sensitivity of the ear
- The basilar membrane can regulate it’s stiffness
What is tonotopic organisation?
-When the best tone for a receptor cell depends on it’s location along the basilar membrane
Define ‘metabotropic’ and ‘ionotropic’
- Metabotropic - Receptors which are indirectly linked to the ion channels
- Ionotropic - Receptors which are directly linked to the ion channels
What are photoreceptor cells?
- Cells that transduce light into receptor potentials
- Vertebrates have 2 types: Rods - Broad colour sensitivty and low light levels, Cone - Particular colours (three types) and good for detail in bright light
- Contain photo-pigments called discs
- Metabotropic receptors
Describe the function of a photoreceptor cell
- In dark, Na+ channels are kept open, resting potential is kept at -35 mV (held open by cGMP)
- Light causes the transducin to change shape, activating phosphodiesterase (PDE)
- PDE hydrolyses cGMP to GMP, closing the Na+ channels
Define ‘rhodopsins’
- The photo-pigments
- Two parts - Opsin (protein) and 11-cis-retinal (light-absorbing aldehyde) turns to all-trans-retinal with absorption of light
List the enzyme-like reactions that rhodopsins induce
- Activates transducing in disc membrane
- Activating phosphodiesterase, which hydrolyses cGMP
- Causing hyperpolarisation in vertebrates, depolarisation occurs in invertebrates
How does a photoreceptor adapt to dark light?
- One photon of light causes 1-5mV receptor potential
- But under normal like, hundreds of thousands of photon/per sec
- As light intensity increases, sensitivity decreases
How are photoreceptor cells coded?
-Equal contrasts in stimulus strength cause equal increments in response
How are images processed in the retina?
- 5 layers of neurons with photoreceptors at the back
- Front have retinal ganglion cells, long axons which go into the brain (use spikes), more ganglion cells then photoreceptor cells
- Bipolar cells connect photoreceptor cells to ganglion cells
- Horizontal cell, which modify signals to bipolar cells
- Amacrine cell modify signals passing from bipolar to retinal ganglion cells
What is lateral inhibition?
- Responses in one area inhibit responses in neighbouring areas
- Small spots generate larger responses than blobs
- Enhances the detection of edges in images
- Basis of several illusions
List 7 areas of the mammalian brain and their functions
- Cerebral hemisphere
- Thalamus - Relay station for sensory information
- Hypothalamus and Pituitary - control centre for hormones
- Cerebellum - ‘Little brain’ coordinates movement sequences
- Pons and Medulla - Autonomic function
What is the cerebrum?
- 2 cerebral hemispheres
- Small in fish, amphibia and reptiles
- Larger but smooth in birds
- Large and folded in mammals and cetaceans
- L and R hemisphere receive sensory information from opposite sides of body
- Major roles in sensory perception, learning, memory and conscious behavior
- 6 layers of neurons
Describe the pyramidal neuron
-Pyramid-shaped cell body
-Most numerous excitatory cell type in cerebrum
-Inputs from thousands of excitatory and inhibitory synapses
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Describe the spindle neuron
- Fewer dendrites than a pyramidal neuron and a smaller cell body
- Very rare
- 2 brain regions of apes, they are very prevalent
What is a sensory homunculus?
-A ‘nerve-weighted man’
What are mirror neurons?
- Visual neurons which respond to the sight of objects moving in particular ways
- Certain action doesn’t have to be committed by oneself
How does facial recognition work?
-Part of temporal lobe as it becomes active when subject is shown faces
What is the ‘Grandmother cell’ concept and what is a more accepted concept of facial recognition?
- Somewhere in your brain there is a neuron which allows you to recognise your grandmother
- More likely it’s the combining of several features in the brain
Define ‘receptive field’
-The area of space within which a stimulus causes a response in the neuron
Describe a Retinal ganglion receptive field
- Two parts, the centre and surround, which have opposite effects on the ganglion cell’s response
- Centre-surround receptive field shown by Kruffler 1953
- Define where edges and boarders
- Some are ‘on-centre’ and some ‘off-centre’
What did Hubel & Wiesel find? (1959)
- Found that light spots and dark spots didn’t give much response
- Found line and edges give vigorous response
What types of primary cortex cells are there and what are their functions?
- ‘Simple’ cells to see edges and lines
- ‘Complex’ cells to see orientation
- ‘Hypercomplex’ cells tp see shapes more complex than a single bar
How do muscle spindles work?
- Act as a mechanoreceptor for muscles
- Stretch to cause a receptor potential
What is spatial summation?
-The process of multiple psps joining together to form a spike
Why are antagonistic muscles important?
-To prevent any damage from occurring in the muscle cells
What is temporal summation?
-The process of multiple psps joining together over a period of time to form a spike
Describe the gill withdrawal process in Aplysia
- Graded in strength with stimulus
- Temporal & spatial summation
- 24 sensory neurons
- 6 motor neurons
- Direct chemical synapses
Describe the inking process in Aplysia
- Same sensory neurons as gill withdrawal but different muscles and motor neurons used
- Strong signal needed due to shared electrical neurons
Describe ‘habituation’ and ‘facilitation’
- ‘Habituation’ - wane in response with repeated stimulus
- ‘Facilitation’ - increased response when preceded by a different noxious stimulus
What are muscle cells specialised in?
-Generation of force and movement using ATP, require switching on and off
What various types of muscles are there?
- Skeletal muscles - used for voluntary movements
- Muscle fibres - cylindrical cells fuse end-to-end, formed from fibre bundles called myofibrils
What do myofibrils contain?
-Contractile proteins,, actin, myosin and control proteins
What are sarcomeres?
- Reapeating units along myofibrils, basic functional units of muscle
- 2.0-2.6um long in vertebrate skeletal muscle
- Z lines border adjacent sarcomeres, provide an anchor for actin filaments and for titin
How the contractile proteins function?
- Myosin head site binds to actin, forming ‘cross bridge’
- Myosin head has ATPase activity
How to take a muscle to bits
-‘Skinning’ - place in cold glycerol to remove cell and other lipid membranes, so you can alter the fluid bathing the filaments
-Separate actin and myosin from each other when no Ca2+ is present
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What did Huxley and Huxley find?
-Length of thick and thin filaments does not change when muscles contract and the extent of their overlap does change
How does the cross bridge cycle work?
- A cross bridge attaches actin to myosin giving the sarcomere strength
- The cross bridges rotate, moving actin past myosin and shortening the sarcomere
- The greater the number of cross bridges formed the stronger the sarcomere is
Explain the sliding filament theory
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