nervous system and the eye Flashcards
sensory neurone
-receptor neurone
-transmits nerve impulses from the sense organs/receptors to the CNS
relay neurone
-intermediate neurone
-transmits nerve impulses from the sensory neurone to the motor neurone
motor neurone
-effector neurone
-transmits nerve impulses from the CNS to the effectors
structure of motor neurone
-irregular shaped cell body
-long nerve fibre extending from the cell body
structure of sensory neurone
-circular cell body
-long nerve fibre extending towards the receptor and a shorter one extending to the relay neurone
synapse
-the junction between 2 neurones
-allows nerve impulses to be transmitted when chemicals are released by neurones
spinal nerve
- ‘mixed’ nerve
-contains both sensory and motor neurones
central nervous system
consist of brain and spinal cord
peripheral nervous system
consist of cranial nerves [from brain], spinal nerves and sense organs
reflex action [define]
the immediate subconscious response to a specific stimuli without conscious control
voluntary action [define]
a deliberate action that is done under conscious control
reflex action [touch hot object]
-[receptor] heat from the object stimulates the nerve endings in willy’s skin, producing nerve impulses
-[SN] sn transmits nerve impulses across a synapse to rn in the spinal cord
-[RN] rn transmits nerve impulses across a synapse to mn
-[MN] mn transmits nerve impulses across a synapse to bicep muscles
-[effector] bicep muscles contract, withdrawing hand suddenly
reflex arc [define]
the shortest pathway by which the nerve impulse travels from the receptor to the effector in a reflex action
cranial reflex
-controlled by the brain [not conscious] and usually occur in head region
-e.g. pupil reflex, blinking, salivation
spinal reflex
-controlled by spinal cord
-e.g. sudden withdrawal of the hand touching a hot object, knee jerk reflex
characteristics of endocrine control
-involves hormones as signals
-hormones are transported to the blood
-usually slow responses
-responses can be short or long lived [eg adrenaline and growth hormone]
-always involuntary
-may affect more than one target organ [effector]
-ductless
characteristics of nervous control
-involves nerve impulses as signals
-nerve impulses are transported by neurones
-usually quick responses
-responses are short lived
-can be voluntary or involuntary
-usually localised [affect one particular part of the body]
sclera/sclerotic coat
-tough white outer covering of the eyeball which is continuous with cornea
-protects the eye from mechanical damage
conjunctiva
-thin transparent membrane covering the sclera
-it is a mucous membrane; secretes mucous to keep the front of the eyeball moist
eyelash
shield eye from dust particles
tear gland
-wash away dust particles
-keep cornea moist for atmospheric o2 to dissolve into cornea
-lubricate conjunctiva; reduce friction when eyelids move
-exploited when doing bio
eyelids
-protect cornea from mechanical damage
-allows squinting; prevents too much light entering eyelid and damaging retina
-allows blinking; spreads tears over cornea and conjunctiva, wipes dust particles off cornea
iris
-circular sheet of muscles
-controls size of pupil which controls amount of light entering the eye
-contains a pigment that gives the eye its colour
pupil
-hole in the centre of the iris
-allows light to enter the eye
ciliary body
-contains ciliary muscles; control the curvature/thickness of the lens
suspensory ligament
-connective tissue that attaches the edge of the lens to the ciliary body
cornea
-dome shaped transparent layer continuous with the sclera
-refract/bend light rays into the eye
-causes the greatest refraction of light into the eye
aqueous chamber
-filled with aqueous humour [transparent watery fluid]
-aqueous humour keeps the front of the eyeball firm and helps to refract light into the pupil
lens
-transparent, circular and biconvex structure
-elastic; change its shape/thickness to focus light onto retina
retina
-light sensitive layer where images are formed
-contains photoreceptors [light sensitive cells] which are connected to nerve endings from optic nerve
choroid
-pigmented black; prevent internal reflection of light
-contains blood vessels; bring o2 and nutrients to eyeball and remove metabolic waste products
vitreous chamber
-filled with vitreous humour [transparent jelly-like substance]
-vitreous humour keeps eyeball firm and helps to refract light onto the retina
fovea
-small yellow depression in the retina stimulated directly behind the lens
-images are focused here
-contains the greatest concentration of cones, but no rods
-allows people to have detailed colour vision in bright light
optic nerve
-transmits nerve impulses to the brain when photoreceptors in the retina are stimulated
blind spot
-region where optic nerve leaves the eye
-does not contain rods or cones, thus not sensitive to light
cones
-found only in fovea
-allows us to see colours in bright light
rods
-found throughout retina, just not in fovea
-more sensitive to light than cones
-allows us to see in dim light, but only black and white
pupil reflex [bright light]
-circular muscles of the iris contract
-radial muscles of the iris relax
-pupil becomes smaller and constricts, reducing amount of light entering the eye
pupil reflex [dim light]
-circular muscles of the iris relax
-radian muscles of the iris contract
-pupil enlarges and dilates, increasing amount of light entering the eye
benefits of pupil reflex
-automatic, no learning is required
-prevents excessive light from entering the eye and damaging the retina
-immediate response
-allows enough light to enter the light for us to see
transmission of nerve impulses for pupil reflex [bright light]
-when bright light is shone into the eyes, photoreceptors in the retina is stimulated
-SN in optic nerve transmits nerve impulses across a synapse to RN in the brain
-RN in the brain transmits nerve impulses across a synapse to MN
-MN transmits nerve impulses across a synapse to iris
-circular muscles of iris contract and radial muscles of iris relax, causing pupil to constrict, reducing amount of light entering the eye
formation of image on the retina
-light rays are refracted through the cornea and the aqueous humour onto the lens
-lens cause further refraction and the rays are brought to a focus on the retina
-image on the retina stimulates rods/cones [depend on light intensity]
characteristics of the image formed on the retina
-upside down/inverted
-laterally inverted
-diminished/smaller than actual
focusing/accommodation
-the adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina
focusing [distant object]
-ciliary muscles relax, pulling on the suspensory ligaments
-suspensory ligaments become taut, pulling on the edge of the lens
-lens become thinner and less convex
-light rays from the distant object are sharply focused on the retina
-photoreceptors are stimulated
-nerve impulses are produced and transmitted by the optic nerve to the brain
-brain interprets nerve impulses, allowing willy to see the distant object
focusing [near object]
-ciliary muscles contract, relaxing pull on the suspensory ligaments
-suspensory ligaments slacken, relaxing their pull on the edge of the lens
-lens, being elastic, become thicker and more convex
-light rays from the near object are sharply focused on the retina
-photoreceptors are stimulated
-nerve impulses are produced and transmitted by the optic nerve to the brain
-brain interprets nerve impulses, allowing willy to see the near object
