chapter 14 - responses to stimuli Flashcards
What is a stimulus
A stimulus is a detectable change in the internal or external environment of an organism that leads to a response in the organism.
Describe the overall method when a change(stimulus) is detected
Stimulus
Receptor
Coordinator [central nervous system]
Effector
Response
What is a taxes
A taxes is a simple response who’s direction is determined by the direction of the stimulus. It is a directional response
Give an example of a taxes response
For example when earth worms move away from sunlight [negative phototaxis] this increases the chance of survival because it takes them into the soil where they are better able to conserve water, find food and avoid predators.
What is kinesis
It is a response in which the organism does not move towards or away from a stimulus instead it changes the speed at which it moves and changes the rate at which it changes direction.
Give an example of a kinesis response
For example wouldlice lose water from their bodies and dry conditions, when they move from a damp area to a dry area they move more rapidly and change direction more often this increases the chance of moving into a favorable condition [damp areas].
Tell me about the hormonal system
Main communication is by chemical is called hormones
Transmission is by the blood system and is usually relatively slow
Hormones travel to all parts of the body but only target cells respond
The responses often long-lasting and the effects could be permanent and irreversible.
Tell me about the nervous system
Main communication is by nerve impulses
Transmission is by neurons and is usually very fast
Nerve impulses only travel to specific parts of the body that for the response is localized
The response is short-lived and the effect is usually temporary and reversible
What is a tropism
A tropism is the growth of part of a plant in response to a directional stimulus.
Give an example of a tropism
For example plant shoots great towards light [positive phototropism] and away from gravity [negative gravitropism]
Plant roots grow away from the light [negative phototropism and they grow towards gravity [positive gravitropism]
Plants have no nervous system but they respond to changes in their internal and external environment. Give three examples of things plants respond to
Light - plant shoots grow towards light because light as needed for photosynthesis
Gravity - plants need to be firmly anchored into the soil.
Water - plant roots grow towards water [positively Hydrotropic] in order to absorb it for the use of photosynthesis and all the metabolic processes as well as for support.
What do plants use to respond to external stimuli
Plant growth factors
What are plant growth factors made from and why are they made
They are made by the cells located throughout the plant rather than in a specific organ.
However on like animal hormones, some plant growth factors affect the tissues that release them rather than acting on a distinct target Oregon.
What is IAA
IAA is indoleacetic acid
It belongs to auction switch control cell elongation
Describe phototropism and flowering plants
Cells in the tip of the shoot produce IAA which is then transported down the shoot
IAA is initially transported evenly throughout all regions as it begins to move down the shoot
Light causes the movement of IAA to the shaded side of the shoot
A high concentration of IAA builds up on the shaded side
IAA causes elongation oh shoot cells, the shaded side elongates more
The shaded side of the shoot elongates faster than the light side causing the shoot to bend towards light.
What does IAA do in roots
IAA inhibits cell elongation in the roots. Therefore elongation is greater on the light side than the shaded side causing the roots to bend away from light that for the roots are negatively phototropic.
Describe gravitropism in flowering plants
Cells in the tip of the root produce IAA. IAA is initially transported to all sides of the shoot.
Cravity influences the movement of the hormone from the upper side to the lower side of the root
A greater concentration of the hormone builds up on the lower side
Therefore the upper side will elongate faster than the lower side causing roots to bend down towards the force of gravity.
What is the acid growth hypothesis
IAA increases plasticity to the cell walls. However the response only occurs on young cell walls. As cells mature they developed greater rigidity therefore parts of the shoot/roots will not be able to respond.
The active transport of hydrogen ions from the cytoplasm to the cell wall causes the cell wall to become more plastic allowing the cell to elongate by expansion.
What is the central nervous system and what is it made up of
It is made up of the brain and the spinal cord
What is the peripheral nervous system [PNS]
Is made up of pairs of nerves that come from either the brain or spinal cord
What can the peripheral nervous system be divided into
Sensory neurons [which carry nerve impulses (electrical signals) from receptors towards the central nervous system]
Motor neurons [which carry nerve impulses away from the central nervous system to effectors]
What can the motor nervous system be divided into
The voluntary nervous system [carries nerve impulses to body muscles and is under voluntary [conscious control]].
The autonomic nervous system [which carries nerve impulses to glands and smooth muscle and cardiac muscle and is not on the voluntary control this is involuntary [subconscious]].
What is the spinal cord
The spinal cord is a column of nervous tissue that runs along the back and lies inside the vertebral column for protection.
What is a reflex arc
It is a type of involuntary response to a sensory stimulus which is called a reflex. The pathway of neurons involved in a reflex is known as a reflex arc
Give an example of a reflex and a reflex arc
When you place your hand over a fire. your hand Involuntarily moves away from the stimulus.
Describe the pathway of a reflex arc
Stimulus [hot object]
Receptor [temperature receptors on the hand]
Sensory neurone [passes nerve impulses to the spinal cord]
Coordinator [links the sensory neuron to the motor neuron in the spinal cord]
Motor neuron [carries nerve impulses from the spinal cord to the 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]
What are the importance of reflex arcs
They are involuntary and don’t require any decision making therefore the brain is not overloaded leaving the brain to carry out more complex responses
They are effective from Birth and do not have to be Learnt, they protect you from harm
They are fast because the neuron pathway is short this is important and withdrawal reflexes
what is a Pacinian Corpuscle
It response to changes in mechanical pressure
Features of a Pacinian corpuscle
It is specific to a single type of stimulus [pressure]
It’s produces a generator potential by acting as a transducer, the transducer converts a change in energy to a nervous impulse which is also known as a generator potential.
What is the function of a Pacinian corpuscle and where are they located
They are located deep in the skin and almost abundant on fingers, soles of feet, external genitalia. They are also located in joints, ligaments and tendons.
They resist changes in pressure and Ease them
What happens/what is the process when a pacinian corpuscle detects a stimulus [pressure]
During the resting state stretch mediated sodium ion channels are too narrow to allow sodium ions to pass through them. In this state the neuron has a resting potential.
When pressure is applied the pacinian corpuscle is deformed and the membrane around the neuron becomes stretched.
Stretching widens stretch mediated sodium ion channels and sodium ions diffuse into the neuron.
There is an influx of sodium ions and this changes the potential of the membrane/the membrane depolarize is producing a generator potential.
This generator potential produces an action potential [nerve impulse] that passes on the neuron and then via other neurons to the central nervous system [CNS]]
Give a summary of rod cells
The more rod cells and cone cells
They are distributed more at the for periphery of the retina. they are absent at the foeva.
They give Poor visual acuity
They are sensitive to low intensity light
Non-color
Only one type of rod cell exists
Give a summary of cone cells
There are fewer cone cells than rod cells
There are fewer at the periphery of the retina and more concentrated at the foeva
They give a good visual acuity
They are sensitive to high intensity light
There are three types responding to different wavelengths of light
What is synaptic convergence
One to many
What is synaptic divergence
Many to one
Why can’t the brain distinguish between separate sources of light with a rod cells
Because many rod cells, link to a single bipolar cell. The light received by Rod cells will only generate a single impulse traveling to the brain. The brain cannot distinguish between separate sources of light. Two separate dots cannot be resolved. This appears as a single blob giving low visual acuity.
What is the importance of rod cells
They detect light of low intensity and are highly sensitive. They are important for night vision as a small amount of light striking several rod cells provides summation to produce a generator potential.
Why can cone cells provide good visual acuity [can distinguish between two separate sources of light]
Each cone cell has its own connection to a single bipolar cell. Therefore if two adjacent cone cells are stimulated, the brain receives two separate impulses so the brain can distinguish between two separate sources of light. Two dots close together can be resolved and distinguished as two separate dots providing good visual acuity.
what is iodopsin
There are three different types of cone cells each containing a specific type of iodopsin. This requires a high light intensity for its breakdown. As a result a cone cell is sensitive to a different specific range of wavelengths.
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What is the autonomic nervous system
Autonomic nervous system controls the involuntary activities of internal muscles and glands, it has two divisions.
What is the sympathetic nervous system
It is a division of the autonomic nervous system
Stimulates effectors
Controls actions under stress/activity
Speeds up activity linked to [SAN]
Fight or flight
What is the parasympathetic nervous system
It is a division of the autonomic nervous system
It inhibits effectors
It controls actions under rest
Slows down activity linked to [SAN]
Conserves energy
The cardiac muscle/heart muscle is known as
Myogenic [it’s contraction is initiated from within the muscle itself]
Where is the sinoatrial node [SAN] located
It is located within the wall of the right atrium of the heart
Describe the sequence of events that controls the basic heart rate
A wave of electrical excitation spreads out from the SAN to both atria. Causing them to contract
A layer of non-conductive tissue [atrioventricular septum] prevents the waves crossing to the ventricles.
The wave of excitation enters the atrioventricular node [AVN] which lies between the atrium.
The AVN after a short delay conveys a wave of electrical excitation between the ventricles along a series of muscle fibers called the purkyne tissue. [Which collectively make up a structure called the bundle of His]
the bundle conducts the wave through the Atrioventricular septum to the base of the ventricles, with a bundle branches into smaller fibers of the purkyne tissue.
This wave of excitation is released from the tissue causes the ventricles to contract quickly at the same time from the bottom of the heart upwards.
Changes to the heart rates are controlled by what region in the brain
The medulla oblongata
What happens when you need to increase heart rate
The sympathetic nervous system is linked to the SAN which increases heart rate
What happens when you need to decrease heart rate
The parasympathetic nervous system is linked to the SAN which decreases heart rate
Describe the process of controlling blood pH via chemo receptors
When there is more CO2 in the blood pH is lowered as carbon dioxide forms an acid.
Chemo receptors in the carotid arteries and the aorta detect this increase and the frequency of nervous impulses to the medulla oblongata increases heart rate.
The medulla oblongata increases the frequency of impulses by the sympathetic nervous system to the SAN. Increasing the rate of production of electrical waves by the SAN and increasing the heart rate.
This increases blood flow leading to more carbon dioxide being removed by the lungs therefore CO2 concentration returns to normal.
Blood pH returns to normal. Chemo receptors reduce the frequency of nervous impulses to the medulla oblongata and the medulla oblongata reduces the frequency of impulses to the SAN leading to a reduction in heart rate.
What happens when blood pressure is higher than normal
Pressure receptors transmit more nervous impulses to the medulla oblongata that decrease his heart rate. This center sends nervous impulses via the parasympathetic nervous system so the SAN which decreases the rate at which the heart beats.
What happens when blood pressure is lower than normal
Pressure receptors transmit more nervous impulses to the medulla oblongata the increase heart rate. The centre sends nervous impulses by the sympathetic nervous system to the SAN which increases the heart rate.
