Topic 8 Flashcards
Explain receptors and effectors
-Receptors detect stimuli, there are many types
-Receptors can be cells or proteins on cell surface membranes
-Receptors communicate to effectors by the nervous or hormonal system
-Effectors are cells that bring a response to a stimuli to produce an effect e.g muscle cells or glands
Explain the nervous system
-Sensory neurones - transmit E.I from receptors to CNS (brain and spinal cord)
-Relay neurones - transmit E.I between sensory and motor neurones
-Motor neurones - transmit E.I from CNS to effectors
-Stimulus: Dim light
-Receptors: light receptor detect this
-Information relayed across a sensory neurone
-Relay neurone passes it onto motor neurone from sensory
-Motor neurone passes information onto CNS which pass it to effectors to make a change
-Effectors contrart radial muscles to dilate/enlarge pupils
Explain hormonal system
-Hormonal system is made of glands and hormones
-Glands are a group of cells specialised to secrete useful substances e.g pancreas and insulin
-Hormones are chemical messengers
-When a gland is stimulated via a change in concentration of a substance or an E.I, hormones are secreted
-Hormones diffuse into the blood and are taken all over the body, diffusing anywhere
-Hormones can only bind to specific receptors on cell membranes known as target cells
-Hormones trigger a response in the target cells, the effectors
Explain difference of nervous and hormonal system
-Uses electrical impulses
-Faster response - E.I are rapid
-Localised response
-Short response
-Uses chemicals
-Slower response, hormones have to reach specific receptor
-Widespread response, hormones target cells all over the body
-Longer response, hormones break down slowly
Explain photoreceptors
-Light enters the eye through the pupil, amount is controlled by iris muscles
-Light rays absorb by photoreceptors in the retina
-Nerve impulses are carried from the retina to the brain by the optic nerve - a bundle of neurones
-Two types: Rod and Cones
-Rod receptors are found in the retina peripheral and gives information in black and white
-Cone cells are found packed together in the fovea (back of the eye) and gives information in colour
-They convert light to electrical impulses
-When absorbed, pigments are bleached causing a chemical charge
-This triggers a nerve impulse along a bipolar neurone which connects the photoreceptors to the optic nerve which sends information to the brain
Explain rod cells
-Type of photoreceptor which gives information in black and white
-Rod cells contain light-sensitive rhodopsin pigment
-Rhodopsin is made of retinal and opsin chemical joined together
-In the dark, your rods aren’t stimulated
-Na ions are pumped out of rod cell via active transport
-Na ions diffuse back in through open sodium channels
-This makes the inside slightly more negative then the outside, creating a depolarised membrane
-This triggers neutransmitter release which inhibit the bipolar neurone
-Bipolar neurone cannot fire an A.P to send information to the optic nerve thus to the brain
-In light, rod cells are stimulated
-Light energy breaks/bleaches rhodopsin into retinal and opsin
-Causing Na ion channels to close, preventing Na ions in and Na ions actively transporting out
-Na ions build up on outside, inside is much more negative - the cell membrane becomes hyperpolarised
-When the rod cell is hyperpolarised, neutransmitters release is inhibited preventing its inhibition of the bipolar neurone therefore an A.P is sent to the optic nerve and to the brain
Structure of Sensory neurone
-One long dendron that carries E.I to the cell body, in the middle of the neurone
-One short axon carries nerve impulse to the CNS
Structure of a Motor neurone
-Many short dendrites to carry E.I from CNS to cell body
-One long axon to carry E.I from cell body to effector cells
Structure of Relay neurone
-Many short dendrites to carry E.I from sensory neurone to the cell body
-Axon to carry nerve impulses from the cell body to motor neurones
Explain neurone cell membrane
-Polarised at rest, outside of a neurone’s membrane is more positively charged than the inside as more +ve ions are on the outside than inside
-Membrane is polarised, there is a difference in charge
-Voltage across the membrane at rest is the resting potential and its at -70mv
-Resting potential is created and controlled by sodium potassium pumps and potassium ion channel
-Sodium potassium pump moves 3Na ions out for every 2K ions in using ATP
-Na-K pump moves sodium ions out, and cannot diffuse back in due to membrane impermeable to Na whereas K ions can be pumped in and diffuse out via K channel
-This makes outside positively charged than inside
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Explain action potential effect on neurone
-When an A.P occurs, Na ions enter a neurone diffusing sideways causing sodium ion channels in the next region to open for Na ions to diffuse into that part.
-This creates a wave of depolarisation/A.P to travel along the neurone
-A.P moves away from parts of a membrane in the refratory period as they cannot fire an A.P
-Preventing movement of sodium ion channels stop A.Ps
-Local anaesthetics stop you feeling pain by binding to sodium ion channels to prevent sodium ions moving into neurones preventing depolarisation, preventing A.Ps from conducting and information of pain reaching the brain
Explain myelinated neurones
-Allows A.Ps to transmit faster
-Some neurones are myelinated which is an electrical conductor
-Made of schwann cells
-Between schwann cells are bare membrane named nodes of ranvier in which Na ion channels are concentrated
-In myelinated neurones, depolarisation only occurs at the nodes on ranvier, where Na ions can enter the membrane
-The neurone’s cytoplasm conducts enough charge to depolarise the next node so the impulse jumps from node to node named saltatory conduction which is rapid
-In non-myelinated neurones, the impulse travels as a wave through the axon membrane
-It is slower than saltatory conduction but is still quick
Explain synapses
-A synapse is a junction between a neurone and another cell e.g neurone of effector cell
-A tiny gap between the cells at a synapse is a synaptic cleft
-Presynaptic neurones (one before the synapse) has synaptic knob with synaptic vesicles filled with chemicals known as neurotransmitters
-When an A.P reaches the end of a neurone it causes synaptic vesicles to release into the synaptic cleft to diffuse to the postsynaptic membrane (one after the synapse) and bind to specific receptors
-When neurotransmitters bind to a receptor, they can trigger an A.P or muscle contraction or hormone secretion
-Receptors are only found on postsynaptic membranes, synapses make sure impulses are unidirectionaL
-Synapses allow information to be dispersed or amplified i.e one neurone connects to many or many neurones connect to one
Explain neurotransmitters – BETWEEN NEURONES
-Neurotransmitters transmit nerve impulses between neurones
-An A.P arrives at the presynaptic neurone which stimulates calcium ion gated channels to open
-Calcium ions then diffuse into the presynaptic knob
-Influx of calcium ions causes synaptic vesicles to move into the presynaptic membrane to be released into the synaptic cleft
-Neurotransmitters diffuse across the synaptic cleft to the specific receptors on the postsynaptic membrane
-This causes sodium ions on the postsynaptic membrane to open
-Na ions enter the postsynaptic membrane causing depolarisation
Explain plants response to stimuli
-Plants sense direction of light and grow towards it to maximise light absorbtion
-Plants sense gravity so they can shoot their roots and grow in the right direction (upwards)
-Climbing plants have a sense of touch to find things and reach for sunlight
