nervous system Flashcards
how to synapse work
-presynaptic cell secretes neurotransmitters which crosses the synaptic cleft and binds to a specific receptor on the surface of a receiving cell
function of relay neurone
-form synapses with motor and sensory neurones
-enable nerve impulses to transmit from sensory neurone to motor neurone
-conduct nerve impulses from sensory neurone to brain, and brain to motor neurone
what is a reflex action
-reflex action is an immediate response to a specific stimulus without conscious control
describe reflex action when you touch something hot
-heat stimulates receptors in the skin, nerve impulses are produced which travel along sensory neurones to spinal chord
-in spinal chord, nerve impulses are transmitted across synapse to relay neurone, then across another synapse to motor neurone. At the same time, nerve impulses are transmitted to the brain
-upon receiving nerve impulses from relay neurone, motor neurone transmit nerve impulses to the effector
-effector muscle contracts, withdrawal of hand from hot object
what happens in bright light
circular muscle of iris contracts while radial muscles relax, pupils constrict so less light enters the eye
describe the formation of an image on the retina
light rays are refracted when it passes through the cornea and aqueous humour, and further refracted through the lens
-image on retina either stimulates the rods or cones
state the role of brain in vision
image formed on retina is inverted, laterally inverted and smaller in size than object in real life, brain has corrective mechanism
focusing on distant object
ciliary muscle relax, pulling on suspensory ligaments which become taut, pulling on the edge of lens
-lens becomes thinner and less convex, increasing focal length
-light rays are focused on the retina which stimulates photoreceptors,
nerve signals are transmitted to the brain which interprets the image and allow the person to correctly see the object
focusing on near object
-ciliary muscle contracts, relaxing their pull on suspensory ligaments which slacken, relaxing pull on edge of lens
-lens becomes thicker and more convex, decreasing focal length
features of rods
-extremely sensitive to light
-allows person to see in dim light but only in black and white
-contains visual purple that gets bleaches when exposed to bright light, preventing nerve signals from entering the brain so person cannot see in bright light
-time is taken for visual purple to reform in rods to see in the dark so person who exits a brightly lit room to a dim room cannot see for a while
-formation of visual purple requires vitamin A, so person suffering from vitamin A deficiency will have night blindness
features of cones
-enables us to see colour in bright light
-three types containing red, blue and green pigments, absorbs light of different wavelength and together allows us to see a variety of colours
-do not work well in dim light
