Organisms Respond to Changes in their Internal and External Environments Flashcards
Effector
An organ or a cell that carries out a response to an electrical impulse.
Stimulus
A change in the environment that can be detected and will provoke a response
Receptor
A cell that will detect a change in the environment (stimulus)
Sensory neurone
A nerve cell that carries an electrical impulse from a receptor to the central nervous system
Synapse
A gap between two neurones
Coordinator
Formulates a suitable response to a stimulus
Relay neurone
A nerve cell that acts as a coordinator between sensory and motor neurone
Motor neurone
Nerve cell that carries electrical impulses from the central nervous system and the effector
Response
A hormone released by a gland, or a muscle contraction as a result of an electrical impulse.
What does the sympathetic system do?
Increases heart rate and stroke volume
What chemical does the sympathetic nervous system release on the SAN?
Noradrenaline
What does the parasympathetic nervous system do?
Decreases heart rate and stroke volume
What chemical does the parasympathetic nervous system releases on the SAN?
Acetylcholine
What type of receptors detect changes in CO2 levels in the blood, and where are they found?
Chemoreceptors in the aortic arch (blood always passes through aorta) and carotid arteries (ones that go to the brain so constant blood flow).
What activity would cause an increase in CO2 levels in the blood?
Exercise as increased respiration
Describe the reflex arc for changing heart rate
Receptors detect a rise in CO2 levels in blood and send electrical impulse via sensory neurone to relay neurone and coordinator (medulla). Motor neurone then takes electrical impulse to ventricular muscle which release chemical onto SAN and increase heart rate and stroke volume to get normal concentration of CO2 in blood
Describe how the sinoatrial node (SAN) controls heart rate
The SAN generates an electrical impulse that spreads over the atrium, causing them to contract, and blood to leave the atrium to the ventricles.
The impulse reaches the AVN (atrioventricular nerve where it is delayed to allow all of the blood to leave the atrium.
The impulse passes down the bundle of His to the purkinje fibres which cause the ventricles to contract.
Saltatory conduction
When the electrical impulse jumps from one node of ranvier to the next.
What are the three factors that affect rate of nerve impulse?
Temperature (faster diffusion)
How wide the axon is (more surface area so more protein channels on the membrane for diffusion)
Myelinated or not (if myelinated there will be saltatory conduction which is quicker as less action potentials generated)
Resting potential
The potential across the plasma membrane of a cell that isn’t conducting an impulse
What is occurring when an axon is at resting potential? (where are ions moving and what charge is generated where)
The potassium ion channel protein is open so potassium ions are moving out of the axon.
The sodium-potassium pump is actively transporting sodium ions out and potassium ions into the axon.
The sodium ion channel is shut, so sodium ions are trapped outside axon
There are more positively charged ions out of the axon.
Depolarisation
When an action potential is created
What happens in depolarisation?
The sodium channel opens, so sodium ions move into the axon.
The potassium channel is shut, so potassium ions are trapped wherever they are.
This means there is a more positive charge in the axon.
Repolarisation
When a membrane is polarised again (a resting potential is re-established)
Why is repolarisation important?
An impulse cannot be generated if the membrane of an axon is not at resting potential
What happens in repolarisation?
Potassium ion channels open so potassium ions move out.
Sodium ion channel closes so sodium trapped wherever.
Sodium ions are actively transported out of axon.
More positively charged outside of axon
What is the type of conduction happens in unmyelinated axons? Why is it slower?
Continuous. Much slower as action potential has to be generated across the axon
What type of receptor detects pressure?
Mechanoreceptors
Transducer
Converts energy in a stimulus (e.g. light) into an impulse
Why will a thermoreceptor not transduce light?
Receptors are specific and thermoreceptors are for heat not light
What is the name of a mechanoreceptor that detects changes in pressure in the skin?
Pacinian corpuscle
What is the pacinian corpuscle made of?
An unmyelinated axon surrounded by layers of lamellae separated by gel. Attached to a sensory neurone with a myelinated axon
What causes an impulse to be generated at the pacinian corpuscle?
Pressure distorts the naked axon, opening the stretch-mediated sodium ion channels to allow sodium ions into the axon (depolarisation/a generator potential)
Why is an impulse not generated when constant pressure is applied? Why is this important?
The gel repositions itself to relieve the pressure. Prevents the brain being overloaded with information.
What stimulus does the parasympathetic nervous system respond to?
Baroreceptors detect an increase in blood pressure
What stimulus does the sympathetic system respond to?
Chemoreceptors detect an increase in CO2 in the blood due to respiration
What happens to rhodopsin when light shines on it?
It breaks down to retinal and opsin
A series of reactions occur
An action potential is generated
What are retinal and opsin converted back to?
Rhodopsin
Requires ATP
Homeostasis
Regukation of the internal conditions in the blood
