6A - Stimuli and Responses Flashcards
What do sensory neurones do?
- transmit impulses from receptors to CNS (brain and spinal cord)
What do motor neurons do?
- transmit impulses from CNS to effectors
What do relay neurones do?
- transmit impulses between sensory and motor neurones
What is the peripheral NS?
- made up of neurones that connect CNS to rest of the body
What is the somatic NS?
- one division of peripheral NS
- controls conscious activities
What is the autonomic NS?
- one division of peripheral NS
- controls unconscious activities e.g digestion
What does the autonomic NS divide into and what is the difference between them?
- sympathetic and parasympathetic NS
- sympathetic gets body ready for action e.g fight or flight
- parasympathetic calms body down e.g rest and digest
What is a reflex?
- a response to a stimulus without making a conscious decision to respond
How is nervous system communication localised, short-lived and rapid?
- localised as neurotransmitter are directly secreted onto target cells
- short-lived as neurotransmitters are quickly removed
- rapid as impulses are really fast
What is meant by a tropism?
- plant’s growth response to an external stimulus
What is the difference between a positive and negative tropism?
- positive grows towards stimulus
- negative grows away from stimulus
What type of tropisms do shoots have?
- positive phototropism
- negative gravitropism (grow upwards)
What type of tropisms do roots have?
- negative phototropism
- positive gravitropism
How is IAA transported around the plant?
- diffusion/active transport over short distances
- via the phloem over long distances
How does IAA affect phototropism in shoots and roots?
shoots - concentration increases on shaded side, cells elongate and shoot bends toward light
roots - concentration increases on shaded side, growth is inhibited so root bends away from light
How does IAA affect gravitropism in shoots and roots?
shoots - concentration increases on lower side, cells elongate so shoot grows upwards
roots - concentration increases on lower side, growth is inhibited so the root grows downwards
What is meant by a tactic response?
- organism move towards or away from a directional stimulus e.g. light
What is meant by a kinetic response?
- organisms’ movement is affected by a non-directional stimulus e.g. humidity
What happens when a receptor is at resting state?
- difference in charge inside and outside of cells - generated by ion pumps and channels
What happens when a stimulus is detected?
- cell membrane is excited and becomes more permeable, more ions move in and out of cell
- potential difference is altered, the change is called generator potential
How is an action potential triggered?
- if generator potential reaches threshold level
- if stimulus is too weak, generator potential doesn’t reach threshold level, so no action potential
What are Pacinian Corpuscles?
- mechanoreceptors (detect mechanical stimuli) in the skin e.g pressure and vibrations
What happens when a Pacinian Corpuscle is stimulated?
- lamellae are deformed and press on sensory nerve ending
- causes sensory neurone’s cell membrane to stretch, deforming sodium ion channels
- channels open and sodium ions diffuse into the cell creating a generator potential
- if gen. potential reaches threshold, triggers action potential
How do photoreceptors convert light into an electrical impulse?
- light is absorbed by light-sensitive optical pigments
- causes a chemical change and alters membrane permeability to sodium ions
- gen. potential is created and if it reaches threshold, a nerve impulse sent along bipolar membrane
- bipolar neurones connect photoreceptors to optic nerve, which takes impulses to the brain
Where are rods found and what type of vision do they have?
- found in peripheral parts of the retina
- monochromatic vision (black and white)
Where are cones found and what type of vision do they have?
- found clumped together in fovea
- trichromatic vision (colour)
What is the degree of sensitivity and visual acuity in rods?
- very sensitive to light; many rods join one neurone, many weak generator potentials combine to create action potential
- low visual acuity; many rods join one neurone, light from 2 points close together can’t be told apart
What is the degree of sensitivity and visual acuity in cones?
- less sensitive to light; one cone joins one neurone, more light is needed to trigger action potential
- high visual acuity; cones are close together, two action potentials go to brain
What happens in a regular heartbeat?
- sinoatrial node sends out regular waves of electrical activity to atrial walls
- causes right and left atria to contract at same time
- collagen tissue prevents electrical activity from being passed directly from atria to ventricles
- waves are sent to atrioventricular node (AVN)
- AVN passes waves on to bundle of His
- bundle splits into finer muscle fibres in right and ventricle walls, called Purkyne tissue
- Purkyne tissue carries waves into muscular walls of left and right ventricles, causing them to contract at same time
What are baroreceptors?
- pressure receptors in aorta and carotid arteries
- stimulated by high and low blood pressure
What are chemoreceptors?
- chemical receptors in aorta, carotid arteries and medulla
- monitor oxygen, carbon dioxide and pH levels in blood
Heart rate is unconsciously controlled in the brain by what?
- medulla oblongata
