Survival and Response Flashcards
What’s a stimulus?
- detectable change in internal or external environment of organism that leads to a response
- e.g. (internal) blood glucose levels or (external) touching hot surface
What’s a response?
- change brought about due to a stimulus e.g. sweating
What are receptors?
- cell or organ that detects change in internal/external environment
What are co-ordinators?
- connects info between receptor and appropriate effector (may be on molecular level or even involve the brain)
What is an effector?
- a cell, tissue, organ or system that carries out a response e.g. sweat glands
From a stimulus to a response state the route it takes
stimulus - receptor - sensory neuron - intermediate neuron - intermediate neuron - motor neuron - effector - response
What is a taxis? (plural: taxes)
- response that involves movement in a specific direction
- positive taxis is towards the stimulus and negative taxis is away from the stimulus
example: positive chemotaxis is mobile bacteria moving to an area where there’s a higher conc. of glucose
Give an example of taxis
- single-celled algae will move towards light (positive phototaxis)
- increases chances of survival since being photsynthetic they require light to manafacture food
What’s kineses? (singular: kinesis)
- response that involves movement in random directions
- speed and frequency of direction change increase
- response is carried out in order to increase the chance that the organism will enter different conditions more rapidly.
Describe what happens in a kinesis response
- if organism crosses sharp dividing line between favorable and unfavorable environment, its rate of turning increases - raises chance of quickly returning to favorable environment
- however, if it moves a considerable distance into an unfavorable environment rate of turning slowly decreases so it moves in long straight lines before it turns (often sharply)
Why is a kinesis response important?
- because its important when a stimulus is LESS directional
e. g. humidity + temp (dont produce clear gradient from one extreme to another)
The kinesis response tends to what?
- bring organism into new region with favorable conditions
What is tropism?
- the growth of part of a plant in response to a directional stimulus
- most cases plant grows towards (positive response) or away from (negative response) the stimulus.
What is tropism?
- growth of part of a plant in response to a directional stimulus
- most cases plant grows towards (positive response) or away from (negative response) the stimulus.
Example of tropisms in plant shoots
- plant shoots grow towards light (positive phototropism) and away from gravitiy (negative gravitropism)
- so leaves are in most favorable conditions to capture light for photsynthesis
Example of tropism in plant roots
- plant roots grow away from light (negative geotropism) and towards gravity (positive gravitotropism).
- In both cases response increases probability that roots will grow into the soil, where they are better able to absorb water and mineral ions
Suggest advantages of simple reflexes
- rapid
- protect against damage to body tissues
- do not have to be learnt
- help escape from predators
- enable homeostatic control
Give one similarity and one difference between a taxis and a tropism
Similarity:
- directional response to a stimulus
Difference:
- taxis (whole) organism moves and tropism a growth (response)
How do plants respond to light and why?
- shoots grow towards light (positively phototropic)
- because light is needed for photosynthesis
How do plants respond to gravity and why?
- roots are sensitive to gravity and grow in the direction of their pull (positively gravitropic)
- because they need to be firmly anchored in the soil
How do plants respond to water and why?
- almost all plant roots grow towards water (positively hydrotropic)
- in order to absorb it for the use in photosynthesis and other metabolic processes, as well as for support
What are plant growth factors?
- hormone-like substances involved in plant responses to external stimuli
- they’re produced in small quantities
What is IAA (indoleacetic acid)?
- a plant growth factor that belongs to auxins
- control plant cell elongation
What is unilateral light?
light from only one side
the process of positive phototropism in flowering plants
1 cells in tip of shoot produce IAA - transported down shoot. IAA initially transported evenly as it moves down shoot
2 Light causes movement of IAA from light side to shaded side of shoot - greater conc build up on shaded side of shoot than light side
3 IAA causes elongation of shoot cells and so cells on shaded side of shoot elongate more
4 shaded side of shoot elongates faster than light side - causes shoot tip to bend towards light
How does IAA differ in effect on cells in shoots and roots?
- high conc of IAA in shoots increases cell elongation
- high conc of IAA in roots inhibits cell elongation
the process of positive gravitropism in flowering plants
1 cells in tip of root produce IAA - which is transported along root. IAA initially transported to all sides of root
2 gravity influences movement of IAA from upper side to lower side of root - greater conc of IAA builds up on lower side of root than on upper side
3 IAA inhibits elongation of root cells and greater conc of IAA on lower side so they elongate less than the cells on upper side
4 relatively greater elongation of cells on upper side compared to lower side - causes root to bend downwards towards force of gravity
Why do shoots grow upwards away from force of gravity?
- in shoots greater conc of IAA on lower side increases cell elongation - causes side to elongate more than upper side
- so shoots grows upwards away from gravity
Transport of IAA is in what direction?
- ONE DIRECTION
- away from tip of shoots and roots where it’s produced
Describe effect of IAA on plant cells
- ## increases plasticity (ability to stretch) of their cell walls
What type of cell walls dos plasticity occur?
- only occurs on young cell walls where cells can elongate
- mature cell develop greater rigidity so older parts of shoot/root won’t be able to respond
What is the acid growth hypothesis?
- explanation of how IAA increases plasticity of cells
- involves active transport of H+ ions from cytoplasm into spaces in cell wall causing cell wall to become more plastic…allowing cell to elongate by expansion
Nervous Organisation
two major divisions:
CNS - brain and spinal cord (sc)
PNS - made up of pairs of nerves that orginate from brain or SC
PNS made up of: sensory neurons (sensory nervous system -SNS ) and motor neurons (MNS)
MNS:
- voluntary nervous system
- autonomic nervous system
what do sensory neurons do (SNS)?
- carry nerve impulses (electrical signals) from receptors towards the CNS
what do motor neurons do (MNS)?
- carry nerve impulses away from CNS to effectors
role of the voluntary nervous system
- carries nerve impulses to body muscles and is under conscious (voluntary) control
role of the autonomic nervous system
- carries nerve impulses to glands, smooth muscle and cardiac muscle and involuntary (subconscious)
What is the spinal cord?
- column of nervous tissue that runs along back
- lies inside vertebral column for protection
describe a simple reflex using a hot object as an example
stimulus - heat from hot object
receptor - temp receptors in skin on back of hand - generates nerve impulses in sensory neuron
sensory neuron - passes nerve impulses to spinal cord
coordinator (intermediate neuron) - LINKS sensory neuron to motor neuron in spinal cord
motor neuron - carries nerve impulses from spinal cord to muscle in upper arm
effector - muscle in upper arm - stimulated to contract
response- pulling hand away from hot object
state 4 reasons why reflex actions are important
- involuntary so don’t require decision therefore brain free for more complex responses
- protect body from harm
- fast - neuron pathway is short with few synapses (slowest link in neuron pathway)
- absence of decision-making process means action is RAPID
What is the pacinian corpuscles?
- nerve endings in the skin responsible for sensitivity to vibration and pressure
(it’s a sensory receptor)
pacinian corpuscles responds to what?
- changes in mechanical pressure
Features of the pacinian corpuscles
- specific to single type of stimulus (mechanical pressure), not others like heat
- produces generator potential by acting as a transducer
(transduces mechanical energy of stimulus into generator potential)
what does the Pacinian Corpuscle respond to and where do they occur?
- mechanical stimuli such as pressure
- occur deep in skin, abundant in fingers, soul of feet and external genitalia
- occur in joints, ligaments and tendons so they enable organism to know which joints are changing direction
describe how an action potential is triggered
- when stimulus detected, cell membrane is more excited and permeable - alters potential difference
- change in potential difference due to stimulus called the generator potential
- bigger stimulus excites membrane more = bigger change in P.D. = bigger generator potential produced
- if generator potential reaches threshold level an action potential will be triggered
(action potentials all 1 size so strength of action potential measured by its frequency
describe the structure of the pacinian corpuscle
- have a single sensory neurone, located in the centre of connective tissue called lamellae which form layers separated by a gel
describe the role of receptors and discuss different types
- detect changes in the internal and external environment
- there are many types (all specific to different stimuli)
e. g. some receptors are cells (photoreceptors are receptor cells that connect to NS), some are proteins (glucose receptors found on cell membrane of some pancreatic cells)
describe how deformation of stretch-mediated sodium ion channels in pacinian corpuscle leads to establishment of a generator potential
- pacinian corpuscle contains stretch mediated sodium channels in the cell surface
membrane - when not under pressure these channels are closed, however under pressure these become deformed
- so they open and allow rapid influx of sodium ions to occur.
- positive charge on the sodiums changes the membrane potential, causing the membrane to
become depolarised - results in generator potential being created which goes on to create an action potential in the axon
what does acuity mean?
- ability to distinguish between 2 separate stimuli
describe the role of the photoreceptors in the eye and all the subsequent roles of the other eye structures
- photoreceptors are light receptors in the eye
- light enters the eye through the pupil and amount of light entering is controlled by muscles in a structure called the iris
- lens of the eye focuses the light on the retina where the photoreceptors are located (specifically the
fovea) - so the nerve impulses received by the photoreceptors cells are then carried via the optic nerve to the brain
- point where optic nerve leaves the eye is known as the blind spot as there are no photoreceptor cells located there
(ensure you are able to label eye diagram)
role of the ciliary muscles
- pulls the lens for focusing
ensure you are able to label eye diagram
role of the cornea
- lets light into the eye and begins focusing
ensure you are able to label eye diagram
role of the iris
- controls amount of light entering the eye
ensure you are able to label eye diagram
role of the lens
- focuses light onto the retina
ensure you are able to label eye diagram
role of the optic nerve
- sends signal to the brain
role of the pupil
- lets light through the lens
role of the retina
- light-sensitive, sends signals to the optic nerve
role of the suspensory ligaments
- holds the lens in the place
what are the two types of photoreceptors?
- rods and cones
what are cone cells and describe their features?
- cone cells involve colour vision
- most conc in fovea of the eye and contain pigment iodopsin
- cone cells aren’t sensitive to light so require quite bright light in order to work
- there are three different types, each sensitive to the primary colours of light (red, green or blue)
- cone cells provide good visual
acuity
why do cone cells provide good visual acuity?
- because each cone cell has its own synapse via a bipolar neurone which connects to the
optic sensory neurone
e.g. when light from 2 points hits 2 cones 2 action potentials (1 from each) go the brain - so 2 points can be distinguished easily
what are rod cells and describe their features?
- rod cells involve monochromatic vision
- rod cells mainly concentrated in highest density outside of fovea
- contain the pigment rhodopsin so they are very sensitive to light and stimulated in low light conditions
- rod cells provide low visual acuity
why do rod cells have poor visual acuity?
- more than one rod cell shares the same synapse with a bipolar cell
- so multiple rods need to be stimulated to cause creation of a generator potential
shape of rod cells
rod-shaped
shape of cone cells
cone-shaped
describe how photoreceptors convert light into an electrical impulse
1 light enters eyes and hits photoreceptors and is absorbed by light-sensitive optical pigments
2 light bleaches pigments, causing chemical change and altering membrane permeability to Na+ ions
3 generator potential is created and if it reaches threshold, nerve impulse is sent along bipolar neurone
4 bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain
5 rods mainly found in peripheral parts of retina and cones packed together in fovea (they contain different optical pigments making them sensitive to different wavelengths of light)
6 when they’re stimulated in different proportions you see different colours
why are rods and cones sensitive to different wavelengths of light?
- they contain different optical pigments (iodopsin and rhodopsin) making them sensitive to different wavelengths of light
discuss sensitivity to light in terms of rods
- rods sensitive to light (work well in dim light) because many rods join 1 neurone so many weak generator potentials combine to reach threshold and trigger an action potential
discuss sensitivity to light in terms of cones
- less sensitive to light (work best in bright light) than rods
- because 1 cone joins 1 neurone, so it takes more light to reach threshold and trigger an action potential
the cardiac muscle (heart) is ‘myogenic’, what does this mean?
- contract and relax w/o receiving signals from nerves
- patterns of contractions controls regular heartbeat
so heart initiates its own contraction
what is the autonomic nervous system?
- controls involuntary (subconscious) activities of internal muscles and glands, further subdivided into two divisions:
- sympathetic nervous system
- parasympathetic nervous system
what is the sympathetic nervous system’s role?
- stimulates effectors so speeds up any activity
- helps cope with stressful situations by heightening awareness and preparing us for activity
(FIGHT OR FLIGHT response)
what is the parasympathetic nervous system’s role?
- inhibits effectors, so slows down activity
- controls activities under normal resting conditions
- concerned with conserving energy and replenishing body’s reserves
(REST AND DIGEST)
why are the actions of the sympathetic and parasympathetic NS described as antagonistic?
- because they oppose each other
e. g. if one system contracts a muscle, the other will relax it - activities of internal glands and muscles are therefore regulated by the balance of the 2 systems
what is ‘neurogenic’?
- contractions of muscle initiated by nerve impulses outside
what is the sinoatrial node (SAN)?
- distinct group of cells within wall of right atrium
- area that initial stimulus for contraction originates
why is the SAN referred to as a pacemaker?
- because has a basic rhythm of stimulation that determines beat of the heart
describe the pattern of contractions that control the regular heartbeat
- wave of electrical excitation spreads out from SAN across both atria, causing them to contract
- layer of non-conductive tissue (atrioventricular septum) prevents wave crossing the ventricles
- wave of the excitation enters a 2nd group of cells AVN (atrioventricular node), which lies between atria
- AVN node, after a short delay, conveys a wave of electrical excitation between ventricles along purkyne tissue
- bundle of His conducts wave through atrioventricular septum to base of ventricles, where bundle branches into smaller fibres of purkyne tissue
- wave of excitation released from purkyne tissue, causing ventricles to contract quickly at same time, from bottom of heart upwards.
what is the purkyne tissue?
series of specialised muscle fibres which collectively make up structure: ‘bundle of his’
why is there a slight delay before AVN reacts?
- make sure atria have emptied before the ventricles contract
how is the heart increased and decreased, (discuss the accelerator nerve and vagus nerve) ?
- SAN connected to 2 nerves from medulla oblongata in brain
- accelerator nerve (part of sympathetic NS), delivers higher freq of impulses to SAN to increase heart rate
- vagus nerve does opposite (part of parasympathetic NS), and delivers slower freq of impulses to slow down heart rate
resting heart rate of average adult human
70 bpm
why would resting heart rate ever need to be modified?
- to meet varying demands for oxygen e.g. during exercise
the function of the SAN
sinoatrial node acts as pacemaker of heart/sets the rhythm of the heartbeat
the function of the purkyne tissue
purkyne tissue conducts electrical impulses through the ventricle walls
what is a pacemaker? (for context)
- electronic device that send out electrical impulses to control heart rate
describe how the heart responds to the stimulus: high blood pressure, by stating the receptor, neurone and transmitter, effector and response
stimulus: high blood pressure
receptor: baroreceptors detect high BP
neurone and transmitter: impulses sent to medulla, which sends impulses along parasympathetic neurones. they secrete acetylcholine (neurotransmitter) which binds to receptors on SAN
effector: cardiac muscle
response: heart rate slows down to reduce BP back to normal
describe how the heart responds to changes in blood pressure
- changes in blood pressure, monitored by baroreceptors in the sinus
- blood pressure increases then increased frequency of impulses are sent from the medulla oblongata via parasympathetic pathway to the SAN
- causes heart rate to decrease, lowering
blood pressure
describe how the heart responds to changes in pH caused by high CO2 concentration
changes detected by chemoreceptors
- receptors send impulses to the
medulla oblongata more frequently as a result via the sympathetic pathway
- so more frequent impulses are sent to the SAN, which results in an increase in heart rate
- speeds up blood flow to the lungs where the CO2 can be expelled
(the opposite occurs for high O2 and low CO2)
where are chemoreceptors found?
found in the wall of carotid arteries, aorta and brain
state two chemical stimuli that cause heart rate to increase during exercise
- low blood O2 level
- low blood pH level (caused by increased CO2 level)
vaguely describe how stimuli can increase/decrease heart rate
- electrical impulses from sent to medulla along sensory neurones
- medulla processes info and sends impulses to SAN along sympathetic/parasympathetic neurones (part of autonomic nervous system)
- which determine frequency of impulses to SAN (slower = decreased HR, faster = increased HR)
