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Reflexes and heart
AQA A-level biology year 13
| Term | Definition |
|---|---|
| Reflex | Automatic behaviours used to reduce the risk of of damage to all or part of an organism made without conscious decision. These are short circuits which can bypass the central nervous system |
| Reflex arc | The pathway of neurones in a reflex |
| Central nervous system (CNS) | A complex network of cells, tissues, and organs that is responsible for controlling and coordinating the functions of the body. Comprised of the brain and spinal cord |
| Order of reflex arc | Stimulus - receptor - sensory neurone - synapse - relay neurone - coordination centre - synapse - motor neurone - effector - response |
| Stimulus | A change in the internal or external environment |
| Receptor | Specialised neurone cell that detects a specific stimulus. Turns energy from stimulus into electrical impulse |
| Sensory neurone | Carry electrical impulses from receptors to the CNS |
| Relay neurone | Allow the communication of electrical impulses between the sensory neurone and the CNS & motor neurone |
| Motor neurone | Carry impulses from the CNS and relay neurone to the effector |
| Coordination centre | Formulates a suitable response to the stimulus |
| Synapse | The gap between neurones |
| Effector | An organ or cell that carries out a response to an electrical impulse |
| Response | A hormone is released from a gland or a muscle contracts in response to an electrical impulse |
| Periphery nervous system | The system of cells which connect the CNS with the rest of the body. Comprised of 2 main systems: the Somatic nervous system and the Autonomic nervous system |
| Somatic nervous system | Carries nerve impulses to body muscles under conscious control |
| Autonomic nervous system | Carries nerve impulses to glands, smooth muscle, and cardiac muscle under subconscious control. Comprised of 2 main systems: the Sympathetic and the Parasympathetic nervous systems |
| Sympathetic nervous system | Prepares the body for action, fight or flight |
| Parasympathetic nervous system | Calms the body down, rest and digest |
| Neurone | Specialised cells that are responsible for transmitting electrical and chemical signals in the nervous system |
| Spinal cord | A column of nervous tissue which runs along the back and lies inside the vertebral column for protection. Pairs of nerves emerge in intervals on each side of the spinal cord and each pair contains a sensory and motor neurone |
| Types of receptors in the body (7) | Thermoreceptor, chemoreceptor, baroreceptor, cone cell, rod cell, pacinian corpuscle, osmoreceptor |
| Thermoreceptor | Detects changes in temperature, located in the dermis, skeletal muscles, liver, and hypothalamus |
| Chemoreceptor | Detects chemical changes (normally PH), located in the brain stem, carotid sinus, aortic arch, taste buds and more |
| Baroreceptor | Detects changes in pressure, located in the carotid sinus and aortic arch |
| Cone cell | Detects colour, located in the retina |
| Rod cell | Detects brightness and contrast, located in the retina |
| Pacinian corpuscle | Detects vibrations and deep pressure, located almost everywhere in the body but most tightly clustered in the hands and feet |
| Osmoreceptors | Detects the presence of water, located in the hypothalamus and carotid artery but not in humans |
| How reflexes are inherited | Organisms with certain reflexes are more likely to survive and have a greater chance of passing on their alleles to the next generation. This applies selection pressure which favours organisms with more appropriate responses |
| Benefits of reflexes being involuntary | They are involuntary and therefore do not require decision making, this leaves the brain free to carry out more complex responses without being overloaded. The brain can also consciously override the reflex if necessary |
| Benefits of reflexes being innate | They are innate which means they don’t have to be taught or learned and can even protect infants which leads to a higher likelihood the organism will survive to adulthood |
| Benefits of reflexes being fast | They are extremely fast which means that response to the hazard is instantaneous. The reason they are so fast is because the neurone pathway is very short with their only being one or two synapses, also the lack of decision makes the response even faster |
| Role of chemoreceptors in control of the heart | The chemoreceptors in the carotid sinus, aortic arch and medulla can detect the PH in the blood lowering due to the increase in carbon dioxide which makes the heart best faster in order to increase respiration and vice versa |
| Role of baroreceptors in control of the heart | The baroreceptors in the aortic arch detect the increase in blood pressure and decrease the heart rate and stroke volume to reduce the chances of a cardiac event and vice versa |
| Sino-Atrial Node (SA/SAN) | A region of cardiovascular fibres in the right atrium which stretches across the heart muscle giving electrical impulses which cause it to contract and relax in order to beat. Also known as the pacemaker |
| Role of the sympathetic nervous system in control of the heart | It secrets the neurotransmitter noradrenaline to the SAN in order to engage the body in a fight or flight response by increasing heart rate and stroke volume |
| Role of the parasympathetic nervous system in controlling the heart | It secretes the neurotransmitter acetylcholine to the SAN in order to relax the body into a rest and digest state by decreasing the heart rate and stroke volume |
| Atrioventricular Node (AVN) | Acts as a relay between the atria and the ventricles, transmitting electrical impulses from the atria to the ventricles. It regulates the heart rate by slowing down the impulses to allow the ventricles to fill properly before contracting |
| Cardiovascular control centre | Part of the medulla that changes our heart rate and stroke volume according to our needs by sending electrical impulses down the sympathetic and parasympathetic neurones to the SAN |
| Cardiac skeleton/fibrous skeleton of the heart | The layer of connective tissue that runs between the atria and ventricles horizontally and insulates against electrical activity |
| Myogenic muscle | A type of muscle that can initiate its own contractions within the cell without help from the CNS |
| Stages of contraction: 1 | Electrical impulses spread out from the SAN through the myogenic cardiac muscle in a wave of coordinated motion |
| Stages of contraction: 2 | When the electrical impulse reaches the AVN, it is paused for a fraction of a second and then is transported down a bundle of His neurones in the septum |
| Stages of contraction: 3 | The electrical impulse spreads through Purkinje fibres from the apex upwards causing the heart to contract from bottom to top |
| Bundle of His | Muscle fibres that extend from the AVN to the apex (bottom) of the heart and carry electrical impulses to the Purkinje fibres |
| Purkinje fibres | Spread up the walls of the ventricles and cause the ventricles to contract from the bottom of the heart to the top |
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