topic 6 Flashcards
What is a receptor?
cells/proteins that detect stimuli
what is an effector?
muscles/glands that produce a response to a stimulus
What are the 3 main types of neurones found in the nervous system?
sensory - transmit electrical impulses from receptors to CNS
relay - transmit electrical impulses between sensory and motor neurones
motor - transmit electrical impulses from the CNS to effectors
Describe the divisions of the nervous system
central nervous system (brain and spinal cord) + peripheral nervous system (connects CNS to rest of body)
peripheral nervous system = somatic nervous system (conscious activities) + autonomic nervous system (unconscious activities)
autonomic nervous system = sympathetic nervous system (fight or flight) + parasympathetic nervous system (rest and digest)
What is a reflex?
the body responds to a stimulus without making a conscious system
Describe the reflex arc if you touch something hot
Thermoreceptors in hand detect the heat stimulus
the sensory neurone carries impulses to the relay neurone
the relay neurone connects to the motor neurone
the motor neurone sends impulses to the effector (muscle in arm)
muscle contracts to withdraw hand and avoid damage
if there’s a relay neurone involved then it is possible to override the reflex - your brain could tell your hand to withstand the heat
Describe the characteristics of a reflex
neurotransmitters directly secreted onto target cells - localised
neurotransmitters quickly removed when their job is done - short-lived
-little neurones/synapses involved so response is rapid
How do plants respond to changes in their environment?
sense direction of light and grow towards it to maximise photosynthesis
sense gravity - roots and shoots can grow in the right direction
some plants have a sense of touch - can climb and reach the sunlight
What is a tropism? give examples
the response of a plant to a directional stimulus
- a positive tropism - growth towards the stimulus
- a negative tropism - growth away from stimulus
phototropism = growth of a plant in response to light (shoots are positively phototropic, roots are negatively phototropic)
gravitropism = growth of a plant in response to gravity (shoots are negatively gravitropic, roots are positively gravitropic)
How do plants produce responses to stimuli?
-use growth factors (hormone-like chemicals that speed up/slow down plant growth)
-produced in growing regions of plants and move around to where they’re needed
-growth factors called auxins stimulate the growth of shoots by cell elongation
-high concentrations of auxins inhibit growth in roots
Explain the function of indoleacetic acid (IAA) in plant growth
IAA is a type of auxin produced in the tips of shoots
IAA is moved around the plants to control tropisms - moves be diffusion and active transport over short distances, and via the phloem over long distances
-results in different parts of the plant having different concentrations of IAA - this uneven distribution results in uneven growth in the plant
Phototropism - IAA moves to shaded parts of shoots and roots :
-shoots = IAA conc increases on shaded side, cells elongate and shoot bends towards light
-roots = IAA conc increases on shaded side, growth is inhibited so root bends away from light
How do animals respond to stimuli?
Tactic responses (taxes) - organisms move towards or away from a directional stimulus
e.g. woodlice show a tactic response to light (phototaxis) - move away from light to keep them safe from predators
Kinetic responses (kinesis) - the organism’s movement is affected by a non-directional stimulus
e.g. woodlice move slowly and turn less often in higher humidity so they stay where they are. As the air gets drier, they move faster and turn more often so they’ll move to a new area
Describe the steps involved in a reflex arc. Describe the characteristics of a reflex
-receptors detect a stimulus
- impulse transmitted along a sensory neurone , to a relay neurone in the CNS, the relay neurone will analyse the stimulus and decide on a response
-the relay neurone transmits electrical impulse to a motor neurone, which will transmit the impulse to an effector to produce a response
if a relay neurone is involved it is possible to override the reflex, e.g. your brain could tell your hand to withstand the heat
Reflexes are:
- rapid - as only a few neurones/synapses are involved
- localised - neurotransmitters are directly secreted onto target cells
- short-lived - neurotransmitters are removed when they are no longer needed
Describe how general receptors work
Receptors are specific - only detect particular stimulus
Resting state - potential difference across membrane
Stimulus detected - membrane is excited + more permeable, allowing more ions in/out - altering the potential difference (generator potential)
If generator potential is big enough it will trigger an action potential - only if threshold level is reached
- if stimulus is too weak the generator potential won’t reach threshold, so no action potential
Describe how pressure is detected by Pacinian Corpuscle receptors
-skin receptors called Pacinian Corpuscles detect pressure
- the receptors contain the end of a sensory neurone
-when stimulated, the lamellae surrounding the neurone are deformed and press on the nerve ending
- causes neurone’s membrane to stretch, deforming the stretch-mediated sodium ion channels
-channels open and sodium ions diffuse into cell, creating a generator potential
-if threshold is reached, an action potential is triggered.
