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12-coordination and response - Coggle Diagram
12-coordination and response
the human nervous system
it is made of special cells, "neurons"
they all have a nucleus, cytoplasm and a cell membrane
their peculiar structure neables them to carry electric signals very quickly
to do this, thin fibres of cytoplasm stretch out from the cell body, with the longest one being called an "axon" and the shorter ones "dendrites"
the dendrites pick up electric signals (called "nerve impulses") from other neurons
hundreds of neurons make up a "nerve"
there are sensory neurones, relay neurones and motor neurones
sensory neurones transmit electrical impulses from a receptor to the CNS
relay neurones transmit electrical impulses within the CNS
motor neurones transmit electrical impulses from the CNS to an effector
a group of all these neurones is called "reflex arc"
the reaction that takes place after the impulse has sped around the reflex arc is called "reflex action"
like many other animals, mammals have a Central Nervous System and a Peripheral Nervous System
the CNS is made up of neurons, the brain and the spinal cord
the PNS is made up of the neurons that spread out from the CNS, as well as the receptors in our sense organs
sense organs
in animals, they are groups of specialized receptor cells that respond to a particular stimulus
the eye is a sense organ because it contains receptor cells in the retina
the retina is at the back of the eye
when light hits a receptor cell, it sends an electrical impulse along the optic nerve to the brain
if light hits where the optic nerve leaves the retina (the blind spot), then no information is passed on
the part where the most cells are placed close together is called "fovea"
there are two types of receptor cells in the retina
rods, which are sensitive to dim light but do not respond to colour and are loosely packed and therefore do not show a very detailed image
cones, which are able to distinguish between red, green and blue light only when the light is bright and are quite tightly packed in the fovea and therefore show a more detailed image
the eye has a coloured piece of tissue called "iris", in the middle of which there is a gap, the "pupil"
the pigments in the iris block light from passing
the iris contains muscles that contract or relax depending on how much light there is
circular muscles, in circles around the pupil, contract to make the pupil smaller
radial muscles, which run outwards from the edge of the pupil, contract to make the pupil larger
they are antagonistic muscles
this is a reflex action
the cornea and the lens bend (refract) light rays onto the retina so that it gets a clear image
the refracted image is upside down, but the brain reinterprets it
objects at different distances need different amounts of refraction
the lens gets thinner or thicker depending on how much light needs to be bent
the thinner it is, the less light is bent
the thicker it is, the more light is bent
this change is called "accomodation"
the lens is kept in position by a ring of suspensory ligaments, moved by the ciliary muscle
when it relaxes, the ligaments are pulled tight
when it contracts, they are loosened
close objects need more refraction, far objects need less refraction
coordination in plants
plants are able to respond to changes in the surrounding environment, albeit at a slower pace
plants respond to stimuli through tropism, the growth response away or towards a stimulus
growth towards a stimulus is called "positive response"; growth away from a stimulus is called "negative response"
growth responses to light are called "phototropism"; growth responses to gravity are called "gravitropism"
hormones
they are chemicals used to transmit information from one part of the body to another
they are made in special glands called "endocrine glands"
they are carried around the body thanks to blood plasma
they alter the activity of target organs
there are many of them
insulin reduces the concentration of sugar in blood; it is made secreted by the pancreas
glucagon increases the concentration of sugar in blood; it is secreted by the pancreas
testosterone causes the devolpment of male secondary sexual characteristics; it is secreted by the testes
oestrogen causes the development of female secondary sexual characteristics and helps in the control of the menstrual cycle; it is secreted by the ovaries
adrenaline is secreted in dangerous situations and helps the body to cope with them
it is secreted by the two adrenal glands, each placed above one of the two kidneys
it causes the release of glucagon in the bloodstream, alongside a faster heartbeat, breathing rate (to accomodate for an increased metabolic activity) and widened pupils (to enable better vision)