14: Responses to stimuli Flashcards
What is a stimulus?
Detectable change in the internal or external environment of an organism that leads to a response
What is a receptor?
Something which detects the presence of a stimulus
Specific to a type of stimulus
What is a response produced by?
Effector
Response at molecular level or whole organism
What is a coordinator?
Formulates a suitable response to a stimulus
Coordination is at a molecular or organ level
What does the ability to respond to stimuli do?
Increases the chances of survival for an organism
Allows for alleles to be passed on and by natural selection
What are the two types of response to a stimuli?
Hormonal response
Nervous response
How does coordinators work?
Connects information from each receptor with appropriate effector
What is the sequence of events starting with a stimulus?
stimulus -> receptor -> coordinator -> effector -> response
What is a taxis?
Simple response whose direction is determined by moving its whole body
In which direction is a taxis done?
Either whole body is turned towards a favourable stimulus or away form an unfavourable stimulus
What are the simplest forms of response to stimuli?
Taxes
Kinesis
Tropisms
What is a positive taxis?
Movement of the organism towards the stimulus
What is a negative taxis?
Movement of the organism away from the stimulus
What is an example of positive phototaxis?
Single-celled algae move towards light, increases survival rate as they are photosynthetic cells
What does positive phototaxis mean?
Positive - towards stimulus
Phototaxis - response to light
What does positive chemotaxis mean?
Positive - towards stimulus
Chemotaxis - response to a chemical concentration
What is kinesis?
Form of response in which the rate of movement and rate of direction change is altered
What occurs in kinesis when an organism goes to an unfavourable environment?
Rate of turning increases
Increases chance of return to a favourable environment
What occurs to the rate of turning in kinesis after a long period of time in the unfavourable environment?
Rate of turning slowly decreases so it moves in a straight line before it turns very sharply
Brings into favourable conditions
When is kinesis important?
When the stimulus is less directional
What types of stimulus are thought as non-directional?
Temperature
Gradient
What occurs to woodlice when they move from damp to dry areas?
Move more rapidly and change direction more often
Once back in damp they move slower and change direction less often
What is a tropism?
Growth of part of a plant in response to a directional stimulus
What is positive and negative tropism?
Positive - plant grows towards the stimulus
Negative - plant grows away from the stimulus
What is a phototropism?
Tropism when light is involved
What tropism do plant shoots show?
Positive phototropism
Negative gravitotropism
Grow towards light and away from gravity
Allows leaves in most favourable position for photosynthesis
What tropism do plant roots show?
Negative phototropism
Positive gravitotropism
Increase probability the roots grow in the soil, where they can absorb water and mineral ions
Do plants have nervous systems?
None present
What do plants respond to?
Light
Gravity
Water
How do plants respond to light?
Shoots grow towards light
As light needed for photosynthesis
(positive phototropism)
How do plants respond to gravity?
Roots respond to gravity and grow in direction of its pull
positive gravitotropism
How do plants respond to water?
Almost all plant roots grow towards water to absorb for use in photosynthesis and other metabolic processes
(positively hydrotropic)
How do plants respond to external stimuli?
Involves hormone-like substances or plant growth factors
Why is the term plant growth factors descriptive?
Exert influence by affecting growth, made by cells throughout plant rather than particular organs
Can affect the tissues that release them rather than acting on specific organ (like animal organ)
How much of plant growth factors are produced?
Small quantities are produced
What is indoleacetic acid (IAA)?
Plant growth factor which is an auxin
Controls plant cell elongation
How does IAA affect phototropism in plants?
Cell in tip of shoot produces IAA which is transported down the shoot, which build up on shaded side of the shoot
Greater [IAA] causes shoot cells on shaded side to elongate
Shaded side elongates, causing shoot tip to bend towards the light
How does IAA work in the roots?
High [IAA] results in inhibition of elongation of shaded side
Causes light side to grow more and bends away from the light
How is IAA used in gravitotropism?
Cells in root tip produce IAA
Gravity causes IAA to move from the upper to lower side of the root
IAA inhibits elongation so greater elongation on upper side causes root to bend downwards to force of gravity
What happens to IAA in shoots for gravitotropism?
Greater [IAA] on lower side increases cell elongation
Causes this side to elongate more than upper side
Shoots grow upwards away from the force of gravity
How is IAA transported?
IAA always transported away from shoots and roots where its produced
When does IAA work?
Only works on young cell walls where cells can elongate
Known to increase the cells ability to stretch
Why do older cells of plants not respond to IAA?
Rigidity of cells increase
So cannot stretch/elongate
What is the theory by which IAA increases plasticity of cells?
Acid growth hypothesis
What is the acid growth hypothesis?
Active transport of hydrogen ions from cytoplasm into spaces in the cell wall
This causes cell wall to become more plastic and allows elongation
Do plants respond to stimuli quickly?
Elongation occurs rapidly
Due to IAA uneven distribution
What are the two major divisions of the nervous system?
Central nervous system (CNS)
Peripheral nervous system (PNS)
What are the constituents of the CNS?
Brain and spinal cord
What are the constituents of the PNS?
Made of pairs of nerves that originate from either the brain or spinal cord
What does the peripheral nervous system consist of?
Sensory neurones
Motor neurones
What is a sensory neurone?
Carries nerve impulse (electrical signals) from receptors to the CNS
What is a motor neurone?
Carries nerve impulses away from the CNS to the effectors
What is the motor nervous system divided into?
Somatic nervous systems
Autonomic nervous system
What is the somatic nervous system?
Carries nerve impulses to body muscles and is under voluntary (conscious) control
What is the autonomic nervous system
Carries nerve impulses to glands, smooth and cardiac muscle
Involuntary (subconscious)
What is the spinal cord?
Column of nervous tissue that runs along the back and lies inside the vertebral column for protection
What is the characteristic of a reflex?
Rapid, short-lived, localised and totally involuntary
What is a reflex arc?
Pathway of neurones involved in a reflex
How many neurones are involved in a reflex?
Three neurones
What is the alternative name of a reflex and why?
Spinal reflex
One of the 3 neurones is in the spinal cord
What is an examples of a stimulus which causes a spinal reflex arc?
Withdrawing hand from a hot object
What are the stages of a spinal reflex arc?
Stimulus Receptor Sensory neurone Coordinator (intermediate neurone) Motor neurone Effector Response
What are examples of the stages of the reflex arc?
Stimulus - heat from hot object
Receptor - temp receptor in skin which generates nerve impulse in sensory neurone
Sensory neurone
Coordinator (intermediate neurone)
Motor neurone - carries nerve impulses from spinal cord to a muscle in the upper arm
Effector - muscle in upper arm is caused to contract
Response - hand pulled away from hot object
What is the function of a sensory neurone in a spinal reflex?
Passes nerve impulse to spinal cord
What is the function of the coordinator/intermediate neurone in a spinal reflex?
Links sensory neurone to motor neurone in spinal cord
What is the function of the motor neurone in a spinal reflex?
Carries nerve impulse to muscle/effector
Why are reflex actions important?
Involuntary - doesn’t require brain to decide, meaning it can do more complex responses. Brain not overloaded when the response is the same
Protect body from harm - don’t have to be learnt, there from birth
Fast - short neurone pathway (1 or 2 synapses)
Absence of any decision making process means action is rapid
Why are few synapses important in a reflex arc?
Synapses are the slowest link in a neurone pathway
How is sensory information from internal and external environments?
Variety of receptors
Each type responds to different and specific type of stimulus
What is sensory reception?
Function of the receptor - broadcast of a nerve impulse
What is sensory perception?
Involves making sense of the info from the impulse from the receptor
Where is sensory perception done?
Mostly a function of the brain
What are Pacinian corpuscles?
Receptors in the skin which respond to changes in mechanical pressure
How do Pacinian corpuscles show they are sensory neurones?
Specific to a single type of stimulus - only responds to mechanical pressure
Produces a generator potential by acting as a transducer
What is a transducer?
Convert one form of energy into another
E.g. heat,light,sound,mechanical energy to electrical nervous impulse
How do receptors act as a transducer?
Converts one form of energy to the nerve impulse
Nerve impulse called a generator potential
What is a generator potential?
Nerve impulse created by a receptor
What does the Pacinian corpuscle respond to?
Responds to mechanical stimuli such as pressure
Where are the Pacinian corpuscles found?
Deep in the skin
Most abundant on fingers, soles of feet and external genitalia
Joints, ligaments, tendons
Why are Pacinian corpuscles found in joints, ligaments and tendons?
Enables organism to know which joints are changing directions
Where is the sensory in the Pacinian corpuscle?
Centre of layers of tissue
Each layer is separated by a gel
How does a Pacinian corpuscle function?
Stretch mediated sodium channels in membrane of sensory neurone
Permeability increases when pressure applied as stretches membrane
Na+ flow in and changes the potential of the membrane, creates a generator potential
Generator potential creates action potential that passes along neurones to CNS
Where are the light receptors of the eye found?
Innermost layer - the retina
What are the types light receptors in the eye?
Rod cells
Cone cells
How do light receptors work as transducers?
Transduces light energy into electrical energy of a nerve impulse
What does visual acuity mean?
Clarity of the image seen by the eye
Measured by an eye chart 20 feet away
What is the pupil?
Black dot - hole through which light can enter the eye
What is the iris?
Colour in the eye - muscle that controls how much light enters the eye
What is the cornea?
Colourless curved front of the eye that helps to diffract light onto the retina
Why can rod cells only contribute B&W images?
Cannot distinguish different λ of light
How many light receptors are there compared to each other?
More rod cells than cone cells
How are light receptors connected?
Light receptors are connected to bipolar cells
Bipolar cells are connected to a sensory neurone
Sensory neurone sends impulse to the brain
How are rod cells connected to a single sensory neurone?
Many rod cells connected to a single bipolar and sensory neurone
What is required for a light receptor to create an impulse?
Threshold value has to be exceeded before a generator potential is created in the bipolar cell
What is retinal convergence?
Many rod cells are connected to a single bipolar cell
Why are rod cells sensitive to very low intensity of light?
Many rod cells connected to a bipolar cell
Greater chance the threshold value will be exceeded than if only a single rod cell were connected to each bipolar cell
What is the photopigment in rod cells?
Rhodopsin
How is a generator potential induced in a rod cell?
Rhodopsin broken down by even low-intensity light
Breakdown causes a potential difference to form and a generator potential is formed in a bipolar cell
Why do rods give low visual acuity?
Many rod cells linking to a single bipolar cell
Therefore only one impulse created regardless of number of neurones stimulated
Brain cannot distinguish between separate sources of light that stimulated them
Two dots close together cannot be resolved
How many types of cone cells are there?
Three different types
Respond to: short, medium and long wavelengths of light
How are full colour images formed?
Different proportions of different stimulation of different cone cells
How are cone cells connected to the CNS?
One cone cell connected to one bipolar cell
Bipolar cell is connected to sensory neurone to the brain
Why can cone cells only respond to high light intensity?
Stimulation of cone cells cannot be combined to exceed threshold variable to create generator potential
One cone cell connected to one bipolar cell
What pigments are found in cone cells?
Iodopsin
Each type of cone cell has a specific type of pigment
What is a feature of iodopsin?
Requires higher light intensity for breakdown
Only responds to a specific λ of light
Why do cone cells have a high visual acuity?
One cone connected to one bipolar cell
Brain receives separate impulses from adjacent cone cells, can distinguish as two separate sources
Two dots can be resolved
What is the fovea?
Location on the retina where light is focused the most
Receives the highest intensity of light
What is the distribution of cone cells?
High intensity of cone cells found at the fovea
Concentration of cone cells diminishes further away from the fovea
What is the distribution of rod cells?
No rod cells at the fovea
Conc of rod cells increase further from fovea, only rod cells at the peripheries
What part of the nervous system is responsible for the control of heart rate?
Autonomic nervous system
What is the two divisions of the autonomic nervous systems?
Sympathetic nervous system
Parasympathetic nervous system
What is the sympathetic nervous system?
Motor neurones that stimulate effectors so speeds up activity
Used in emergency controller or in stressful situations as heightening awareness (fight or flight)
What is the parasympathetic nervous system?
Motor neurones that inhibits effectors so slows down any activity
Controls activity in normal resting conditions, conserves energy
Why is the parasympathetic and sympathetic nervous system said to be antagonistic?
Actions normally oppose one another
What muscles control heart rate?
Cardiac muscles
Why is contraction of muscles said to be myogenic?
Contraction is initiated from within the muscle itself
What is neurogenic?
Contractions caused by nervous impulses from outside
What is the sinoatrial node (SAN)?
Group of cells responsible for producing initial stimulus for contraction of cardiac muscles
Found in the wall of the right atrium
Why is the SAN known as a pacemaker?
Has a basic rhythm of stimulation that determines the beat of the heart
What are the sequences of events which controls the basic heart rate?
Wave of electrical excitation from SAN moves across both atria, causing atrial systole
Atrioventricular septum prevents wave crossing to the ventricles
Wave of excitation moves to AVN
AVN produces electrical excitation along ventricles after a short delay
Wave passes along Purkyne tissue which make up the Bundle of His
Bundle conducts wave through atrioventicular septum to base of ventricles, where the bundle branches off
Wave of excitation causes ventricular systole from bottom upwards
What is the normal resting heart rate of an adult?
~70 bpm
What is the equation for cardiac output?
Cardiac output = Stroke volume * Heart rate (beats per minute)
What are chemoreceptors?
Receptors which can detect concentrations of different chemicals
Where are chemoreceptors found which control heart rate?
Carotid arteries and aortic arteries
What are the carotid arteries?
Arteries that serve the brain
What are the chemoreceptors in the carotid arteries sensitive to?
pH of the blood as a result of [CO2]
How does [CO2] affect pH?
Increased [CO2] lowers the pH
How are chemoreceptors used to control heart rate?
Decrease in pH causes chemoreceptors to send nervous impulse to centre in brain that increases heart rate
Center increases frequency of impulses the sympathetic nervous system to the SAN
This increases rate of production of electrical waves, therefore heart rate
Increased blood flow causes more CO2 removed by lungs
[CO2] goes back to normal, chemoreceptors detect this
Then leads to reduction of nerve impulses so back to normal
Where is the center for the control of both the increase and decrease of heart rate?
Medulla oblongata
What are the two nervous systems which are used to control heart rate?
Sympathetic - increases heart rate
Parasympathetic - decreases heart rate
How do responses from chemoreceptors affect heart rate?
Controls rate
Doesn’t control whether it beats
Where are pressure receptors to control the heart rate?
Walls of the carotid arteries and aorta
How is blood pressure controlled if it is too high?
Pressure receptors transmit nervous impulses to centre that decreases heart rate
Center sends impulses via parasympathetic nervous system to SAN
Leads to decrease in rate at which heart beats
How is blood pressure controlled if it is too low?
Pressure receptors transmit nervous impulses to centre that increases heart rate
Center sends impulses via sympathetic nervous system to SAN
Leads to increase in rate at which heart beats
Define fibrillation
When the contraction of the heart is not synchronised
Why is the SAN referred to as the pacemaker?
Sets the rhythm of the heart rate
What are the names of pressure receptors in the carotid artery and aorta?
Baroreceptors
