B14- Response to Stimuli Flashcards
What is kinesis?
a non-directional response to a stimulus
What is taxes
a directional response to a stimulus
What is Indoleacetic acid
Indoleacetic Acid (IAA) is the most common naturally occurring plant hormone of the auxin class.
Phototropism
is a growth response to light
- Synthesised at root tips and shoot tips → affects cell elongation
- If the shaded side of the plant experiences greater cell elongation, the shaded side will grow faster → plant bends towards the light
- In shoots, higher concentrations of IAA on the shaded side results in a greater rate of cell elongation
- The shoot bends towards the light - positive phototropism
What is gravitropism
is a growth response to gravity
- In shoots, higher concentrations of IAA results in a reduced cell elongation on the LOWER side of the root
- The upper side of the root grows, and bends in the direction of gravity - positive gravitropism
Types of neurons
- Sensory neurones carry impulses from receptors to the CNS
- Relay neurones are found within the CNS, and connect sensory and motor neurones
- Motor neurones carry impulses from the CNS to effectors (muscles or glands)
What are reflex arcs
Reflex arc = pathway along which impulses are transmitted from a receptor to an effector without involving ‘conscious’ regions of the brain - Very quick, protective response
What is the reflex pathway
- A pin (the stimulus) is detected by a pain receptor in the skin
- The sensory neurone sends electrical impulses to the spinal cord (the coordinator)
- Electrical impulses are passed on to relay neurone in the spinal cord
- The relay neurone connects to the motor neurone and passes the impulses on
- The motor neurone carries the impulses to the muscle in the leg (the effector)
- The impulses cause the muscle to contract and pull the leg up and away from the sharp object (the response)
What is Pacinian Corpuscles and how do they work?
Pacinian corpuscles are a type of receptor found deep in the skin - respond to changes in pressure.
There is an excess of Na+ ions surrounding the axon
- Pressure is exerted on the pacinian corpuscle
- Membrane layers become distorted
- Stretched-mediated Na+ channels OPEN
- Na+ ions enter the axon via facilitated diffusion
- Influx of ions changes the potential difference (voltage) of the membrane
- Depolarisation occurs….
The Human Eye & Retina
- A sense organ that contains receptors:
- Rod cells which are sensitive to light intensity
- Cone cells which are sensitive to different wavelengths of visible light (colour)
Rod Cells
Rod cells contains rhodopsin, Cone cells contains iodopsin
The breakdown of these pigments results in a generator potential being produced
Rhodopsin breaks downs in dim light, Iodopsin breaks down in bright light
Rods are very sensitive to low-intensity light - allows humans to distinguish between light and dark objects in dim light.
Cone cells
Cones are less sensitive to light - instead, they are sensitive to different wavelengths of light
- There are three cone types found in human eyes, each contains a different optical pigment
- Red sensitive cones are sensitive to wavelengths of light that correspond to the colour red
- Blue sensitive cones are sensitive to wavelengths of light that correspond to the colour blue
- Green sensitive cones are sensitive to wavelengths of light that correspond to the colour green
The combined effect of all three pigments allows humans to observe all the other colours that are on the visible spectrum
What is visual acuity?
being able to distinguish between two separate points
Why do rod cells provide lower visual acuity?
- Multiple rod cells synapse with a single bipolar cell
- Multiple bipolar cells synapse with a single ganglion cell
- The brain is not able to interpret which impulses are sent by specific rods
The brain receives a general, not specific, understanding of the fields of vision that are light or dark
Has to have a high enough potential to reach threshold
CONE cells provide HIGHER Visual acuity
- A single cone cells synapses with a single bipolar cell
- A single bipolar cells synapse with a single ganglion cell
- If two cones are stimulated to send an impulse, the brain is able to interpret these as two different spots of light
As cone cells detect only one of three colours (red, green or blue) the brain will receive information about the colour of light detected.
Sinoatrial node (SAN)
a group of cells in the wall of the right atrium that can initiate waves of despoliation
Atrioventricular node (AVN)
a region of conducting tissue between atria and ventricles
Bundle of His
a collection of conducting tissue in the septum (middle) of the heart
Purkyne fibres
spread around the ventricles & initiate depolarisation of the ventricles from the apex (bottom) of the heart
Describe how a heartbeat is initiated and coordinated?
SAN sends a wave of electrical activity
Non-conducting tissue prevents immediate contraction of ventricles
AVN delays whilst blood leaves the atria
AVN sends a wave of electrical activity down the bundle of his
Causing the ventricles to contract from apex.
Autonomic Nervous System & Heart Rate
The cardioregulatory centre in the brain controls heart rate, and is called the medulla (part of the self-controlling, autonomic nervous system)
- Made up of two distinct parts (both of which are connected to the SAN via nerves):
- The acceletory centre - causes the heart to speed up
- The inhibitory centre
- causes the heart to slow down
The Acceleratory centre
- Acceletory centre activated
- Impulses are sent along the sympathetic neurones, to the SAN
- Noradrenaline is secreted in the synapse
- SAN increases the frequency of impulses it produces
- Increased heart rate
The Inhibitory centre
- Inhibitory centre activated
- Impulses are sent along the parasympathetic neurones, to the SAN
- Acetylcholine is secreted in the synapse
- SAN reduces the frequency of impulses it produces
- Increased heart rate returns to the rest heart rate
Chemoreceptors, pressure receptors & The heart
Exercise causes several internal conditions to change, creating internal stimuli:
- Carbon dioxide concentration in the blood increases
- There is an initial fall in blood pressure caused by the dilation of muscle arterioles
The internal stimuli is detected by chemoreceptors & pressure receptors in the aorta and carotid arteries
- These receptors release nerve impulses → sent to acceltory & inhibitory centres in the brain
