Response to stimuli

What is taxis?

directional movement towards/ away from the stimulus

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What is kinesis?

random movement, increasing number of turns, non directional

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explain the process of phototropism on shoots

IAA produced in the tip of shoot, it accumulates on shaded side, this causes cell elongation , so the shaded side of the shoot elongates faster than the light side which causes the shoot to bend towards the light

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explain the process of gravitropism in roots

IAA is transported to the lower side of the root, it inhibits cell elongation in roots, so the cells on the upper side elongate more, causing the root to bend downward towards gravity

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How does IAA cause cells to elongate?

there is active transport of hydrogen ions from the cytoplasm into the cell wall, which increases its plasticity it becomes more loose and stretch allowing the cells to elongate by expansion, this mostly occurs in young cells

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Describe how the nervous system is split

the Nervous system splits into the peripheral NS and the CNS( brain and spinal chord). the peripheral nervous system splits into motor and sensory NS, Motor NS is split into the voluntary and autonomic NS

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What do the sensory neurones and motor neurones do ?

sensory- carry impulses from receptors to CNS Motor- carry impulses away from CNS to effectors

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Describe the process of the reflex arc

stimulus, receptor detects stimulus, impulse sent to sensory neurone, coordinator, motor neurone then effector which responds

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What happens after the response of the reflex arc?

the brain processes the information, the nerve impulses are sent to the sensory area in the brain called the cerebral hemesphere, to interpret and process the information by the association area

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What is the importance of the reflex arc?

It is involuntary , doesn't require the brain, fast, protects the body from harm

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describe the structure of pacicinian corpuscle

sensory neurone with the capsule of connective tissue (lamellae) surrounding it and a blood capillary, the sensory neurone ending which has a stretch mediated sodium channel in its plasma membrane

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How does the pacinian corpuscle function?

pressure applied, lamellae deforms, membrane stretches, sodium ion channel opens, sodium ions diffuse in, membrane becomes depolarised, generator potential, threshold= action potential in sensory neurone

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Why is there higher acuity in cone cells?

each cone joins to one bipolar neurone, so the brain can distinguish between the two different sources of light that stimulate the two cone cells and two action potentials go to the brain

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Where are rod and cone cells?

cone cells are on the fovea and rod cells on the rest of the retina

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Why are rod cells more sensitive/ easier to trigger an action potential?

many rod cells connected to one bipolar cell so many weak generator potentials can be combined to reach the threshold and trigger an action potential (spatial summation)

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How is a generator potential created from light?

light enters eye through pupil, hits the photoreceptors and bleaches the pigments which causes the membrane to become more permeable to sodium ions. This creates a generator potential and then if that reaches the threshold an action potential

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What happens when you move from a well lit room to a dark room?

if you try move, you will bump into things because your rod cells need time to adjust to the low light. Because in light the rhodopsin is inactivated and need to be fully regenerated again when your in the dark.

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How is heart rate controlled?

SAN initiates heartbeat, sends wave of electrical activity across atria which contracts, AVN delays impulse so atria can empty before ventricles contract, AVN sends impulse down bundle of his to purkyne fibres, ventricles contract from base up

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where are chemoreceptors and pressure receptors found?

In the wall of carotid arteries and aortic arch

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What do chemoreceptors do when they detect a low blood PH?

increased action potentials sent along SN to cardioacceleratory centre in medulla, and then along sympathetic NS to SAN, SAN increases rate of electrical waves which increases heart rate, blood flow increase=more co2 removed,

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What neurotransmitter is released at SAN to increase heart rate and what does it bind to ?

Noradrenaline is released at SAN and binds to adrenergic receptors

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What do pressue (baro) receptors do when there is a high blood pressure?

increased action potentials sent along SN to cardioinhibitory centre in medulla, and then along parasympathetic NS to SAN, SAN decreases rate of electrical waves which decreases heart rate, cardiac output decreases, blood pressure decreases

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What neurotransmitter is released at SAN to decrease heart rate and what does it bind to ?

acetylcholine is released which binds to cholinergic receptors

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What happens once the blood pressure has been decreased/ Ph increased?

receptors reduce frequency of impulses to medulla which reduces frequency of impulses to SAN. which will act accordingly to reduce/increase heart rate back to normal

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What are the two types of nervous systems that control heart rate?

Parasympathetic nervous system decreases heart rate and sympathetic nervous system increases heart rate

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what is the optical pigment in cone and rod cells?

rhodopsin for rod cells responds to low light intensity, iodopsin in cone cells , there are 3 different types of it, each sensitive to either red, green or blue

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Response to stimuli

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