response to stimuli- chapter 14 Flashcards
1
Q
what is the stimulus
A
a detectable change in the internal or exchange environment of an organism that leads to a response in the organism
2
Q
why is it a good characteristic of life to have a response to stimuli
A
- increases the changes of survival for an organism.
- The organisms that survive have a greater chance of raising offspring and of passing their alleles to the next generation, this creates selection pressure favouring organisms with more appropriate responses.
3
Q
explain the process of the stimulus
A
- Stimuli are detected by receptors which are specific to one type of stimulus.
- A coordinator formulates a suitable response to a stimulus. May be at a molecular level or involve a large organ.
- A response is produced by an effector- may be molecular or involve the behaviour of the whole organism.
4
Q
what has a slow process of stimulus
what has a faster process of stimulus
A
hormonal communication
nervous system
5
Q
what is taxes
A
- Taxis is a simple response which direction if determined by the direction of the stimulus.
- Taxes are classified according to whether the movement is towards the stimulus (positive taxis) or away from the stimulus (negative taxis) and also by the nature of the stimulus.
6
Q
what is kineses
A
A form of a response in which the organism does not move towards or away from the stimulus, instead changing the speed at which it moves and the rate at which is changes direction
7
Q
what are tropisms
A
- The growth of part of a plant in response to a directional stimulus.
- Plants grow towards (positive response) or away from (negative response) the stimulus.
8
Q
what do plants respond to
A
- Light- shoots grow towards light
- Gravity- roots are sensitive to gravity and grow in the direction of its pull.
- Water- almost all plant roots grow towards water (positive hydrotrophic)
9
Q
what are plant growth factors
A
- Plants responses to external stimuli involve plant growth hormones which:
1. Exert their influence by affecting growth
2. Affect the tissues that release them rather than acting on a distant target organ - Plant growth factors are produced in small quantities.
10
Q
what is Indoleacetic acid (IAA)
A
belongs to a group of substances called auxins which controls plant cell elongation
11
Q
explain phototropism in flowering plants
A
- Cells in the tip of the shoot produce IAA, which is then transported down the shoot.
- The IAA is initially transported evenly throughout all regions as it begins to move down the shoot.
- Light causes the movement of IAA from the light to the shaded side of the shoot.
- A greater concentration of IAA builds up on the shaded side of the shoot than on the light side.
- There is a greater concentration of IAA on the shaded side of the shoot, causing the cells to elongate more.
- The shaded shade of the shoot elongates faster than the light side, causing the shoot tip to bend towards the light.
12
Q
explain gravitropism in flowering plants
A
- Cells in the tip of the root produce IAA, which is then transported along the root.
- The IAA is initially transported but gravity influences the movement of IAA from the upper side to the lower side.
- A greater concentration of IAA builds up on the lower side of the root than on the upper side.
- Cells on the lower side of the root elongate less than those on the upper side.
- The relatively greater elongation of cells on the upper side compared to the lower side causes the root to bend downwards towards the force of gravity.
13
Q
what is the role of IAA in elongation growth
A
- IAA has a number of effects on plant cells including increasing the plasticity (ability to stretch) of their cells walls.
- This only occur on young cell walls, as cells mature they develop greater rigidity.
14
Q
what is the acid growth hypothesis
A
Active transport of hydrogen ions from the cytoplasm into spaces in the cell wall causing the cell wall to become more plastic allowing the cell to elongate.
15
Q
what are the two divisions of the nervous organisation
A
- Central nervous system (CNS), which is made up of the brain and spinal cord.
- Peripheral nervous system (PNS), which is made up of pairs of nerves that originate from either the brain or the spinal cord.
16
Q
what is the peripheral nervous system divided into
A
- Sensory neurones, which carry nerve impulses (electrical signals) from receptors towards the central nervous system.
- Motor neurones, which carry nerve impulses away from the central nervous system to effectors.
17
Q
what is the motor system subdivided into
A
- The voluntary nervous system, which carries nerve impulses to body muscles and is under voluntary (conscious) control.
- The autonomic nervous system, which carries nerve impulses to glands, smooth muscle and cardiac muscles and is not under voluntary control, that is, it is involuntary (subconscious)
18
Q
what is the spinal cord
A
- Column of nervous tissue that runs along the back and lies inside the vertebral column for protection.
- Emerging at intervals along the spinal cord are pairs of nerves.
19
Q
what is a reflex
A
an involuntary response to a sensory stimulus
rapid, short-lived, localised and total involuntary
20
Q
give the example of a reflex
A
- Stimulus- heat from the hot object
- Receptor- temperature receptors in the skin on the back of the hand, which generates nerve impulses in the sensory neurone.
- Sensory Neurone- passes nerve impulses to the spinal cord
- Coordinator (intermediate neurone)- links the sensory neurone to the motor neurone in the spinal cord.
- Motor neurone- carries nerve impulses from the spinal cord to a muscle in the upper arm.
- Effector- the muscle in the upper arm, which is stimulated to contract.
- Response- pulling the hand away from the hot object.
21
Q
what is the importance of the reflex arc
A
- They are involuntary and therefore do not require the decision-making powers of the brain, thus leaving it free to carry out more complex responses.
- They protect the body from harm. They are effective from birth and do not have to be learnt.
- They protect the body from harm. They are effective from birth and do not have to be learnt.
- They are fast, because the neurone pathway is short with very few, typically one or two, synapses where neurones communicate with each other.
- The absence of any decision-making process also means the action is rapid.
22
Q
what are the features of sensory reception- Pacinian corpuscle
A
- Is specific to a single type of stimulus responding only to mechanical pressure.
- Produces a generator potential by acting as a transducer- convert the change in form of energy by the stimulus into a form (nerve impulses) that can be understood by the body
23
Q
what are the structures and functions of a Pacinian corpuscle
A
- Respond to mechanical stimuli such as pressure.
- Occur deep in the skin and most abundant on the fingers, the soles of the feet and external genitalia.
- Also occur in joints, ligaments and tendons enabling the organism to know which joints are changing direction.
- Single sensory neurone of a Pacinian corpuscle is at the centre of layers of tissue, separated by gel.
- Sensory neurone ending at the centre has a sodium channel in its plasma membrane called a stretch-mediated sodium channel.
- Their permeability to sodium changes when they are deformed.
24
Q
how does a Pacinian corpuscle work
A
- Normal resting state- the stretch-mediated sodium channels are too narrow to allow sodium ions to pass along them- it has resting potential.
- When pressure is applied to the Pacinian corpuscle, it is deformed and the membrane around its neurone becomes stretched.
- This widen the sodium channels in the membrane and sodium ions diffuse into the neurone.
- Influx of sodium ions changes the potential of the membrane (depolarised) thereby producing a generator potential.
- The generator potential in turn creates an action potential (nerve impulse) that passes along the neurone and then via other neurones to the CNS.
25
Q
how to receptors work together in the eye
A
- Light receptor cells of the mammalian eye are found on its innermost layer, the retina.
- The millions of light receptor cells found in the retina are of two main types: rod cells and cone cells.
- These both act as transducers by conserving light energy into the electrical energy of a nerve impulse.
26
Q
how do rod cells work
A
- Rod cells cannot distinguish different wavelengths of light and lead to images being seen in black and white.
- More numerous than cone cells- there are around 120 million in each eye.
- Rod cells are connected to a single sensory neurone in the optic nerve.
- Used to detect light of very low intensity.
- A certain threshold value has to be exceeded before a generator potential is created in the bipolar cells.
- As a number of rod cells are connected to a single bipolar cell (retinal convergence) there is a greater chance that the threshold value will be exceeded.
- In order to create this potential, the pigment in the rod cells (rhodopsin) must be broken down. There is enough energy from low-intensity light to cause this to happen.
- A consequence of many rod cells linking to a single bipolar cell is that light received by many rod cells sharing the same neurons only generates a single impulse. This means that the brain cannot distinguish between separate sources of light. i.e. two dots close together cannot be resolved and so appear as a single dot. Low visual acuity.
27
Q
how do cone cells work
A
- Three different types, each containing a specific type of iodopsin , so each responding to a different wavelengths of light.
- Depending under the proportion of each type that is stimulated, we can perceive images in full colour.
- In each human eye, there are around 6 million cone cells, often with their own separate bipolar cell connected to a sensory neurone in the optic nerve. This means that if two adjacent cone cells are stimulated, the brain receives two separate impulses, so two dots close together can be resolved and will appear as two dots. Therefore cone cells give very accurate vision, good visual acuity.
- This means that the stimulation of a number of cone cells cannot be combined to help exceed the threshold value and create a generator potential. So they only respond to high light intensity and not to low light intensity. The pigment in cone cells (iodopsin) requires a higher light intensity for its breakdown.
28
Q
compare rod and cone cells
A
- Distribution of rod and cone cells on the retina is uneven.
- Light is focused by the lens on the part of the retina opposite the pupil, this point is known as the fovea, so it receives the highest intensity of light. Cone cells, but not rod cell are found at the fovea. The concentration diminishes further away from the fovea.
- At the peripheries of the retina, where light intensity is at its lowest, only rod cells are found.
29
Q
what is the autonomic nervous system
A
Autonomic means self-governing so it controls the involuntary (subconscious) activities of internal muscles and glands.
30
Q
what is the autonomic nervous system split into
A
- Sympathetic Nervous System- stimulates effectors and so speeds up any activity. It controls effectors when we exercise strenuously or experience powerful emotions. Helps us for flight or fight response.
- Parasympathetic nervous system- this inhibits effectors and so slows down any activity. It controls activities under normal resting conditions. It is concerned with conserving energy and replenishing the body’s reserves.
-These two systems are antagonistic.
31
Q
what is the cardiac muscle like
A
myogenic, its contraction is initiated from within the muscle itself rather than by nervous impulses from outside (neurogenic)
32
Q
where is the SAN and what does it do
A
- Within the wall of the right atrium of the heart is a distinct group of cells known as the sinoatrial node (SAN). The initial stimulus for contraction originates here.
- The SAN determines the beat of the heart, so is often referred as a pacemaker
33
Q
explain the sequence of events that controls the basics of the heart rate
A
- A wave of electrical excitation spreads out from the sinoatrial node across both atria, causing them to contract
- A layer of non-conductive tissue (atrioventricular septum) prevents the wave crossing to the ventricles.
- The wave of excitation enters a second group of cells called the atrioventricular node (AVN), which lies between the atria.
- The AVN conveys a wave of electrical excitation between the ventricles along a series of specialised muscle fibres called Purkyne tissue which collectively make up a structure called the bundle of His.
- The bundle of His conducts the wave through the atrioventricular septum to the base of the ventricles, where the bundle branches into smaller fibres of Purkyne tissue.
- The wave of excitation is released from the Purkyne tissue, causing the ventricle to contract quickly at the same time, from the bottom of the heart upwards.
34
Q
how is the resting heart rate modified
A
- Changes to the heart rate are controlled by a region of the brain called the medulla oblongata.
- The has two centres concerned with heart rate:
1. A centre that increase heart rate, which is linked to the sinoatrial node by the sympathetic nervous system.
2. A centre that decreases heart rate, which is linked to the sinoatrial node by the parasympathetic nervous system. - Which of these centres is stimulated depends upon the nerve impulses they receive from two types of receptor, which respond to stimuli of either chemical or pressure changes in the blood
35
Q
what are chemoreceptors
A
- Found in the wall of the carotid arteries (the arteries that serve the brain).
- They are sensitive to changes in the pH of the blood that result from changes in carbon dioxide concentration.
36
Q
what is the process of chemoreceptors
A
- Blood has a higher than normal concentration of carbon dioxide, its pH is lowered.
- The chemoreceptors in the wall of the carotid arteries and the aorta detect this and increase the frequency of nervous impulses to the centre in the medulla oblongata that increases heart rate.
- This centre increases the frequency of impulses via the sympathetic nervous system to the sinoatrial node. This increases the rate of production of electrical waves by the sinoatrial node and therefore increases the heart rate.
- The increased blood flow that this causes leads to more carbon dioxide being removed by the lungs and so the carbon dioxide concentration of the blood returns to normal.
- As a consequence in the pH of the blood rises to normal and the chemoreceptors in the wall of the carotid arteries and aorta reduce the frequency of nerve impulses to the medulla oblongata.
- The medulla oblongata reduces the frequency of impulses to the sinoatrial node, which therefore leads to a reduction in the heart rate.
37
Q
where are the pressure receptors
A
within the walls of the carotid arteries and the aorta
38
Q
what happens when the blood pressure is higher than normal
A
pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that decreases heart rate. This centre sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart, which leads to a decrease in the rate at which the heart beats
39
Q
what happens when blood pressure is lower than normal
A
pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that increases heart rate. This centre sends impulses via the sympathetic nervous system to the sinoatrial node, which increases the rate at which the heart beats
