I'm so totally determined to do well for my sciences this year! I don't really enjoy being in triple science as much as being in double humanities, since textbook science is so dead, but getting 9A1s is one of the more important goals I've set out this year. Thus, I'm forcing myself to enjoy science, but maybe I'm starting to appreciate how amazing life-forms are, and the wonder of symbiotic relationships of different species in Creation.
So I'm studying for my Coordination & Response test tomorrow, and I'm supposed to memorize the anatomy of the human eyeball and how each part enables us to see, as well as the topics on hormones and the nervous system.
Okay. So for internal structure of the eye:
(i) Sclera: tough white outer protective covering that protects the the eyeball from mechanical damage.
(ii) Choroid: middle layer of the eyeball. Two functions - (a) Pigmented black to prevent internal reflection of light; (b) contains blood vessels that bring O2 and nutrients to the eyeball and removes metabolic waste products.
(iii) Ciliary body: Contains the ciliary muscles that contract and relax to control the curvature of the lens. Connected to the suspensory ligament. Contracts when focusing far, relaxes when focusing on near objects (<7 m).
(iv) Lens: transparent, circular and biconvex. Elastic. Can change thickness in order to control the focal length (refracts light on the retina).
(v) Aqueous chamber: Filled with aqueous humour, a transparent and watery fluid that (a) keeps front of eyeball firmed and (b) helps light to refract into pupil.
(vi) Vitreous chamber: Filled with vitreous humour, a transparent and jelly-like substance that (a) keeps eyeball firm and (b) helps to refract light onto the retina.
(vii) Retina: innermost layer. Light sensitive, containing photoreceptors consisting of rod (black and white) and cone (colour) cells. This is where images are formed. (images are normally focused on the Fovea/Yellow Spot, which is rich in cone cells to aid in night vision.)
Proverbial 10-year series questions revisited:
What happens when you step from a dark room into bright light? (this is a reflex arc)
- Increase in light intensity
- Receptors in retina stimulated
- Sensory neurone in optic nerve transmits signal to the brain
- motor neurone acts on the effector (iris)
- circular muscles on the iris contract, radial muscles relax. (They are antagonistic)
- pupil constricts, allowing less light to enter the eye.
- is light intensity is high enough, squinting may occur to prevent excessive light from entering and damaging the light-sensitive tissues inside.
What happens when you read a book and look up to view a plane in the sky?
- Change in focus from short-distance to long-distance
- Ciliary muscles relax, pulling on suspensory ligaments. They become taught and pull on the lens.
- Lens becomes thinner, less convex and less refractive. Focal length is increased.
- Light rays from the faraway object enter the eye and are sharply focused on the retina.
- Photoreceptors are stimulated. Nerve impulses sent to the brain via optic nerve. Brain interprets the object.
(when focusing on near objects, ciliary muscles contract, suspensory ligaments slacken, lens becomes thicker, more convex, and focal length is decreased. Light rays enter, focused sharply on the retina, etc. etc.)
On the Nervous System:
Made up of two components:
1. Central nervous system
2. Peripheral nervous system
1. CNS:
Brain - controls voluntary actions by generating nerve impulses. Also controls cranial reflexes eg. salivation
Spinal cord - Transmits nerve impulses to the brain. Also controls spinal reflexes e.g. knee-jerk reflex.
2. PNS:
Cranial Nerves from the brain - Transmit impulses from receptors to the brain, motor nerves transmit impulses from brain to effectors.
Spinal Nerves - sensory nerves transmit impulses from receptors to spinal cord, motor nerves transmit impulses from spinal cord to effectors
Sense organs (receptors) - receives stimuli from the environment
NERVOUS TISSUE - consisting of neurons:
1) Sensory neurons: transmits nerve impulses from receptors to CNS
2) Relay neurons: found within CNS, transmits nerve impulses from sensory neurons to motor neurons
3) Motor neurons: transmits nerve impulses from CNS to effectors
REFLEX ARC
Sensory neurone -> relay neurone (spinal cord)* -> motor neurone
*signal also sent to brain.
yawn sleepy.
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