3.6.1 Stimuli,both internal and external are detected and lead to a response what

A detectable change in environment eg light/pressure/temp

Simple response whose direction is determined by direction of stimulus
Positive taxes = towards stimulus
Negative taxeis = away from stimulus

Response which organism changes its speed and rate it changes directions

When plants respond via growth to stimuli. Can be positive/negative
Phototropism = response to light
Geotropism = response to gravity
hydrotropism = response to water

Indolacetic acid - Type of auxin which stimulates cell elongation/ growth in shoots and inhibit growth in roots. Made in tips of roots and shoots

1)Shoot tips produce IAA, IAA will diffuse/move towards area of shade of shoots.
2)This causes the cells on shaded side to elongate more, causing plant to bend towards light source

SHOOTS:
IAA diffuses from upper to lower side, if plant is on its side it will cause shoot to bend upwards.
ROOTS
IAA moves to lower side of roots so roots bend down towards gravity

Touch/pressure receptor which has stretch-mediated Na channels.
When enough pressure applied Na channels open forming AP.

In the retina containing rod and cone cells

Used to detect light of very low intensity as many rods cells connect to one sensory neurone but gives low visual acuity(low resolution)

To form AP enough rhodopsin needs to be broken down which requires little light intensity and multiple rod cells connect to one neurone making it even easier to form AP via spatial summation

Three types of them which contain different types of iodopsin which absorb different wavelengths of light.(red,green,blue).
Iodopsin only broken if there is high light intensity
No spatial summation
High visual acuity

Most of cone cells at fovea as it absorbs highest amount of light while rod is distributed more evenly out

Sinoatrial node(SAN) located at right atrium
Atrioventricular node(AVN) located near border of right and left ventricle within atria still
Both known as pacemakers

Conductive and Runs through septum

1)SAN gives electrical impulse causing atria to contract, this then stimulates AVN
2)AVN delays impulse giving time for blood to go to ventricle.
3)Impulse passed down bundle of his being electrical insulating which forces impulse to carry along down to the apex of heart, delaying contraction of ventricles further.
4)Electrical impulse travels up and out the purkyne fibres from apex, causing ventricle to contract from bottom.

Medulla oblungata in brain via autonomic nersvous system which contains two parts linked to SAN.
One increases heart rate via sympathetic nervous system
One decreases heart rate via parasympathetic system

Found in carotid arteries(neck) and aorta
Chemoreceptors - Detect change in pH of blood ie CO2
Baroreceptors-Detect change in blood pressure

1)Baroreceptors detect this and causes more impulses sent to medulla.
2)More impulses sent via sympathetic nervous system to SAN to increase heart rate frequency
For high instead more impulse sent via parasympathetic

1)Chemoreceptor detect this and causes more impulse sent to medulla
2)More impulses sent via sympathetic nervous system to SAN to increase heart rate frequency
For high more impulse sent via parasympathetic