Flashcards in U1T3 - Coordination & Control (2) Deck (71):
What does coordination in animals rely on?
Hormones and nervous impulses which travel through neurones.
What are the 3 types of neurones?
Sensory, motor + relay neurones.
What are the 3 common features of neurones?
Cell body/centron, dendrons + axons.
Describe the general structure of nerves in mammals?
Mostly myelinated which speeds up nerve impulse transmission + protects neurone.
What does the presence of a cell membrane result in in all cells?
Uneven distribution of charged ions across membrane.
What do neurones have in response to their resting potential?
Electrochemical gradient across membrane (+ ions want to move to - region + vice versa) Ions can't flow across membrane as required transmembrane proteins closed.
What happens when a stimulus is applied to the neurone + it reaches threshold potential?
The transmembrane proteins open + positively charged ions flood into cell so it's pot diff rises. When it reaches threshold potential, more voltage gated ion channels open + neurone becomes depolarised. PD reaches peak of +40mV (Action Potential)
What happens when a stimulus is applied to the neurone + doesn't reach threshold potential?
Transmembrane proteins open + positively charged ions flood into cell so it's PD rises. As it doesn't reach threshold potential, then action potential isn't fired + stimulus is referred to as sub threshold stimulus. Neurones display all or nothing principle.
How does a nerve impulse work?
There are transmembrane proteins which are voltage gated ion channels + localised circuits generated along membrane. Areas with - charges attract + charges + vice versa. Localised circuits flow in both directions but only result in action potentials in areas of membrane which have resting potential returned. Voltage Gated Ion Channels do their job so depolarisation occurs, making action potential more likely and this continues along neurone resulting in impulse.
Why do localised circuits only result in actions potentials in areas where resting potential has returned?
Due to refractory period.
What happens to impulse transmission speed in myelinated neurones?
Speed increased as local current can only exist at nodes of Ranvier.
What affects speed of impulse transmission?
Whether neurone is wrapped in myelin + temperature as rate of diffusion directly affected + axon diameter.
Give 2 examples of neurotransmitters.
Acetylcholine + GABA.
What is GABA's mode of action?
Open chloride ion channels rather than usual sodium ion channels. As chloride ions carry - charge, interior of neurone becomes more negative in contrast to surrounding fluid.
What allows us to provide coordinated responses to range of stimuli?
Integration of IPSPs + EPSPs by CNS.
What is the negative effect of bright light?
Can damage the light sensitive cells of the retina.
What is the issue with low light intensities?
Eye can have difficulty forming an image.
What is the solution to the issues of light and the eye?
Size of pupil can be altered through the action of muscles in iris.
What happens when bright light is detected?
Circular muscles contract, radial muscles relax, pupil constricted so amount of light entering eye reduced so preventing damage to light sensitive cells of retina.
What happens when dim light is detected?
Circular muscles relax, radial muscles contract, pupil dilates allowing more light to enter eye so enough light reaches light sensitive cells to form image.
What are 2 functions of the eye?
Change pupil size to prevent damage + allow sight.
Ability to change lens shape to focus on near + distant objects.
What components are involved in changing lens shape?
Ciliary muscles, suspensory ligaments + lens.
What is necessary to form a sharp image?
Light rays must be refracted to single point on retina. Lots of light refraction at cornea. Lens completes refraction by bending rays by appropriate amount depending on distance from object.
When happens when viewing a distant object?
Ciliary muscles relax, tension in eye ball wall transferred to suspensory ligaments, pulling them taut, lens pulled into thinner shape + refractive power of lens reduced.
What happens when viewing a near object?
Ciliary muscles contract, eyeball tension not transferred to suspensory ligaments so they slacken, less pressure exerted on lens so it bulges, becoming thicker, refractive power of lens increased.
Describe the structure of rods.
Inner segment with nucleus + many mitochondria, rod shaped outer segment containing membrane discs packed with light sensitive pigment.
Describe the structure of cones.
Inner segment with nucleus + many mitochondria, cone shaped outer segment containing membrane discs packed with light sensitive pigment.
What is the light sensitive pigment in rods?
What is the light sensitive pigment in cones?
Iodopsin (one of each of the 3 types found in each cell)
What is the number of types of rods?
Only 1 - all contain rhodopsin.
What is the number of types of cones?
3 - each with iodopsin sensitive to different wavelength.
What is the sensitivity of rods?
High - can operate in low light intensities due to retinal convergence so used for night vision.
What is the sensitivity of cones?
Low - require high light intensities to function + so used for day vision.
What is the visual acuity of rods?
Low - lower resolution.
What is the visual acuity of cones?
High - detailed coloured info provided.
What vision is provided by rods?
Only provide monochromatic vision.
What vision is provided by cones?
Can sense blue, green or red light depending on form of iodopsin present in membrane discs.
How does light reach the membrane discs containing light sensitive pigments?
It must pass through ganglion cells, bipolar cells + bulk of rod + cone cells. Permitted due to transparent nature of these cells.
What is the process of how an image is formed in the eye using rods?
Light reaches membrane discs containing light sensitive pigments through ganglion + bipolar cells + rod + cone cells. When it reaches there, changes occur leading to visual transduction. When light strikes rhodopsin, bleaching occurs so change in membrane potential is passed onto neighbouring bipolar cell which releases neurotransmitter into synaptic cleft between it and the ganglion cell of optic nerve. Retinal convergence occurs.
What intensity of light is necessary for neurotransmitters to be released into the synaptic cleft?
Low intensity but another factor that results in high sensitivity of rods is retinal convergence.
Describe how an image is formed in the eye using cones.
Process of visual transduction is similar but cones don't display retinal convergence + so require higher light intensity to release enough neurotransmitter. Explains why they have high visual acuity as each bipolar cell synapses to 1 cone so brain can tell which part of retina. Provide colour as diff amounts of coloured cones are stimulated. Relative amounts of each type result in diff colours.
What must happen before rhodopsin can be reused?
It must be resynthesised after bleaching. Requires ATP energy from mitochondria in inner segment of rod. In light conditions, it's almost entirely broken down. Takes 30 mins upon entering darkness for it to reform to allow rods to be sensitive hence why you see little when you initially enter dark room and then improves as time passes.
What is the structure of skeletal muscles?
Muscle covered in tough outer coating of connective tissue. Muscle tissue composed of many bundles of muscle fibres which could be considered as 1 large cell with many nuclei but is multiple cells together, each fibre being made of multiple myofibrils, fibre has sarcoplasmic reticulum. Many mitochondria.
Describe the process of muscle contraction.
Binding sites on actin in muscle blocked by tropomyosin, action potential stimulates muscle fibre, releases Ca ions in sarcoplasmic reticulum into sarcoplasm down conc gradient which unblock binding sites so myosin heads can attach to actin binding sites to form actomyosin bridges, myosin heads change angle sliding actin filament past myosin towards sarcomere centre, hydrolysis of ATP used to detach myosin heads from actin + reposition heads so they attach further along actin + myosin heads change angle, sliding actin again. Repeat process so cycle of attachment, rotation + release repeated.
What is the comparison between nervous and hormonal control?
Nervous control is faster + more precise.
How does axon diameter affect nerve impulse speed?
Thicker axon, faster impulse as less leakage of ion. Leakage makes diff to maintain potential gradients to form resting + action potentials. Not issue in myelinated neurones as they have few ion channels under sheath.
How does temperature affect nerve impulse speed?
Affects rate of ion diffusion so affects speed neurones can conduct impulses.
How are impulses transmitted across a synapse?
Transmitted by neurotransmitters which diffuse across synaptic cleft.
Describe the process of transmission at synapses.
When impulses arrives at synaptic bulb, CA ion channels open, allowing CA ions to diffuse into bulb, causing synaptic vesicles to move towards pre-synaptic membrane + fuse with it, releasing neurotransmitter by exocytosis into synaptic cleft which it diffuses across + binds to receptors in post-synaptic membrane, causing opening of Na ion channels in membrane. As + ions diffuse in, membrane becomes depolarised + EPSP generated. If sufficient depolarisation, EPSP reaches threshold intensity to produce AP in PoS neurone. Enzyme breaks down neurotransmitter into multiple products to prevent it generating new AP. Products diffuse across cleft + reabsorbed into SB where they're resynthesised + stored in vesicles. ATP required produced by mitochondria.
What are the advantages of synapses?
Enable nerve impulses to pass from neurone to neurone even when they're not continuous.
Ensure unidirectionality as transmitter only at 1 side of synapse.
Prevent effector overstimulation to avoid synapse fatigue.
Provide Integration allowing flexibility.
How do you obtain a focused image?
Light rays enter + pass through cornea, some refraction occurs automatically but most takes place in cornea. Further refraction occurs as light passes through lens.
What is the arrangement of rods + cones in the retina?
Rods + cones form layer immediately inside choroid, layer of bipolar neurones lie immediately inside photosensitive cells + beyond these is a layer of ganglion cells. Their axons group together to make up optic nerve.
What is the pattern of myosin + actin like?
Regular. Each myosin filamente is surrounded by 6 actin filaments in regular hexagonal pattern.
What happens whilst the muscle is contracting?
Sarcomere shortens (distance between Z-lines decreases), H-zone + I-band become shorter. A-band stays same length.
What is the power of muscle contraction due to?
Many parallel myofibrils lined side by side in muscle fibre all contracting at same time. Its strength depends on how long muscle stimulated + num of muscle fibres stimulated + contracting.
What are the 3 types of muscle?
Skeletal, Smooth + Cardiac.
Describe the appearance of skeletal muscle.
Striated with multinucleate fibres. Long, threadlike cells.
Describe the appearance of smooth muscle.
Discrete uninucleate cells which are spindle shaped + non striated. Shorter cells.
Describe the appearance of cardiac muscle.
Striated but branched with intercalated discs seen as discrete lines between cells. 1 nucleus.
Describe the distribution of skeletal muscle.
Attached to bone throughout body (most of muscle in body)
Describe the distribution of smooth muscle.
Lining gut + blood vessels, iris + ciliary body in eye. Walls of hollow internal organs.
Describe the distribution of cardiac muscle.
Describe the nervous control of skeletal muscle.
Voluntary/conscious control of skeletal parts.
Describe the nervous control of smooth muscle.
Involuntary/automatic control of internal organs.
Describe the nervous control of cardiac muscle.
Myogenic + involuntary control heart movements.
Give a basic description of how nerve impulses travel across a synapse.
Nerve impulse travels down neurone to presynaptic cell + triggers Ca ion channels to open. Ions diffuse in + trigger vesicles to release ATC by exocytosis into synapse. ATC travels across cleft + attaches to receptors on postsynaptic cell to open ion channels so Ca ions diffuse in + continue nerve impulse.
What is the purpose of peer review?
Improves validity + objectivity as it involves experts in the field.
Why is the mammalian eye described as being inverted?
Light must first travel through ganglion and bipolar cells before it reaches rod and cone cells. Formation of cells results in blind spot so detection of light is compromised.
What is the neurone arrangement that leads to high sensitivity in low light intensities?
What is the type of vision that makes 3D images possible?