T8: Grey Matter Flashcards
Reflex arc general stages
Rapid, involuntary response
Stimulus (environment change)
Receptor (detect stimulus)
Sensory neurone (ventral route)
Synapse
Relay neurone
Coordination (determine response)
Synapse
Motor neurone (dorsal route)
Effector (muscle/gland)
Response (action)
Nervous system subsections and their functions
Central (brain/spinal cord)
Peripheral (sensory/motor)
- somatic (voluntary/skeletal muscles)
- autonomic (involuntary smooth/cardiac muscle/glands)
— sympathetic (fight/flight)
— parasympathetic (rest/digest)
Nerve
Bundle of neurones wrapped in a protective coating
Neurone structure
Cell body: nucelus and other organelles
Dendrites: extensions that conduct impulses to cell body
Axon: transmit impulses away from cell body
- myelin sheath, Schwann cells, lipid, insulating layer, increase transmission speed, nodes of Ranvier)
3 types of neurone
Motor: cell body end of axon, relay - motor
Relay: cell body inside axon, sensory - motor
Sensory: cell body off axon, receptor - relay
Receptors
Detect stimuli
Convert energy source input —> electrical signals/nerve impulses
Cells that synapse sensory neurones
Part of a specialised sensory neurone
Name and describe 4 types of receptors
Chemoreceptors, chemical stimulae, taste, smell, blood conc
Mechanoreceptors, force stimulae, balance, touch, hearing
Photoreceptors, light stimulae, sight
Thermoreceptors, temperature stimulae
Spinal cord matter
Nerve cell bodies, grey matter
Axons and myelin sheaths, white matter
Iris light control mechanism
Autonomic nervous system
Strike retina photoreceptors
Nerve impulses —> optic nerve —> midbrain
Impulse —> midbrain —> parasympathetic Iris motor neurones
Circular muscles contract
Radial muscles relax
Smaller pupil, less light in
Compare the radial and circular muscles in the Iris
Antagonistic
Radial, sympathetic, contract, larger Iris
Circular, parasympathetic, contract, smaller Iris
Summation role
Control nerve pathways
Flexible responses
Integrate different electrical impulses —> coordinated response
What does the likelihood of a postsynaptic membrane depolarisation depend on
Type of synapse (inhibitory/excitatory)
Frequency of impulses
NOT the strength of the impulses
Spatial - several impulses from different neurones
Temporal - several impulses from one neurone
Compare excitatory and inhibitory synapses
Excitatory: more Na+ permeable, temporal/spatial, depolarisation +40mV
Inhibitory: less Na+ permeable, reduce AP likelihood, neurotransmitters open K+/Cl- channels in postsynaptic membrane, Cl- diffuse down conc grad into cell, K+ diffuse down conc grad out of cell, -90mV Hyperpolarisation
Synaptic process
AP arrives
Membrane depolarises
Ca2+ channels open and enter
Synaptic vesicles fuse to pre synaptic membrane
Neurotransmitters enter synaptic cleft via Exocytosis and diffuse across
Neurotransmitters bind to post synaptic membrane transmitters
Cation channel opens and Na+ eneters
Post synaptic membrane in depolarised
Initiates AP
Neurotransmitters released from receptor
Taken up by pre synaptic membrane/diffuse away to be broken down
Acetylcholine
First neurotransmitter discovered
Ca2+ facilitated diffusion into cytoplasm
Increase Ca2+ conc
Several impulses need to stimulate neurostramitter
Acetylcholine fuse to pre synaptic membrane and release via Exocytosis
Diffuse across synaptic cleft
Bind to complementary receptors
Receptor shape changes
Cation channels open
Membrane more permeable
Threshold met
AP generated
Reuptaken by pre synaptic membrane/broken down by acetylcholinesterase
Resting potential
Inside more negative than outside cell
-70mV resting PD/polarisation
Na+ out via pump
K+ in via pump
Against conc grad (ATP/NRG)
Organic molecules too big to move
Cl- follows conc grad
K+ out via channel diffusion
PD pulls K+ back in
Conc/elec hard counteract
No net K+ movement
Electrochemical equilibrium
Action potential process
Depolarisation - VD Na+ channels open, Na+ flow into axon, PD threshold positive feedback, +40mV
Polarisation - VD Na+ channels close, VD K+ channels open, K+ leave axon, down EC gradient, -90mV
Hyperpolarisation - VD K+ channels close, K+ diffuse back into axon, restore resting potential
Compare nervous vs hormonal responses
Nervous - electrical impulses, nerves/neurones, fast, short term, use muscles, localised responses
Hormonal - chemicals/hormones, blood, slower, long term, only target cells can respond, widespread response
Refractory period
Partially depolarised membrane
Local current as Na+ goes to adjacent region
Wave of depolarisation passes along membrane
New AP can’t be generated for 5ms
VD channels close, RP restored, unidirectional travel
What varies impulse speed
Faster
Wider diameter
Myelination (insulated, depolarise nodes of Ranvier, circuit depolarises next node, AP triggered, saltatory conduction)
Photoreceptors generally
Retina
Rods: black and white, dim light
Cones: colour, bright light, fovea/centre
Photochemical pigments absorb light, chemical change
Photoreceptors structure
Light
Retina
Ganglion axon (lead to optic nerve)
Bipolar cells
Rod/cone cells
Inner segment
Outer segment (photoreceptor vesicles)
Choroid
Sclera
Photoreceptors in the dark
Na+ —> non specific cation channels —> outer segment
Na+ diffuse down conc grad —> inner segment
Pumps push Na+ back out cell
Na+ influx causes -40mV depolarisation
Trigger glutamine release
Bind to bipolar cells
Stop depolarisation
Photoreceptors in light
Light
Rhodopsin —> opsin + retinal
Opsin activates membrane bound reactions
Outer segment cations channels close
Na+ influx decreases
Inner segment pumps out Na+
Inside cell —> hyperpolarised
No glutamate released
Bipolar cells depolarise
Create AP
Plants nervous system
None
Use tropism, directional stimulus response
Positive/negative
Coleoptile
Protective sheath
Simple structure
Easily grown
Used for tropism investigation
What 3 things can be determined about phototropism from Coleoptile experiments
Need diffusion
Auxin elongates cells
Auxin made in tip
Cholodny-Went model
Auxins (eg. IAAs)
Transported by phloem
Bind to target cell receptors
Activate messenger signalling molecules
Control auxin regulated transcription genes
Synthesised proteins control cell expansion/division/replication
Cell wall acidified (pump moves H+ Into cell wall)
Expansion activated
Disrupt microfibrils/hemicellulose bonding
Polysaccharide slippage
Allow cell expansion
Phytochrome structure
Protein bonded to light absorbing pigment
2 non protein isomers
Pr/Phytochrome red (600nm)
Pfr/Phytochrome far red (730nm)
Phytochrome photoreversability
Inactive/night Pr
Far red light synthesised
Red light converted
Isotopes apart
Active/day Pfr
Red light synthesised
Far red light converted
Isotopes together
Rise fast in day
Decrease slowly at night
Germination
Seeds need light/optimum conditions
Red light triggers germination
Far red light inhibits it