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The Nervous System, Voluntary, Control, Signals - Coggle Diagram

- - - - Conjunctiva (covers sclera)
        Secretes mucus to keep front of eyeball moist
        
        Eyelashes
        Shields eye from dust particles
        
        Tear gland
        Above corner of upper eyelid. Secretes tears that
        
        wash away dust particles
        
        keep the cornea moist for atmospheric oxygen to dissolve so that the dissolved oxygen can diffuse into the cornea
        
        lubricates the conjunctiva to reduce friction when eyelids move.
        
        Eyelid
        Protect cornea from mechanical damage.
        
        Squinting (partially close) prevents too much light from entering the eye and damaging the retina.
        
        Blinking spread tears over the cornea and conjunctiva, and wipes dust particles off the cornea.
        
        Iris ☆
        Circular sheet of muscles, contains pigment that gives eyes its colour. Controls the size of the pupil and therefore the amount of light entering the eye.
        
        Pupil ☆
        Hole at center of iris which allows light to enter the eye.
  - - - Lens
        Transparent, circular and biconvex structure, Is elastic and changes its shape/thickness to focus light onto the retina
        
        Blind Spot
        Region where optic nerve leaves the eye. Doesn't contain any rods or cones, hence, not sensitive to light. Can't see if image object falls on this spot.
        
        Optic Nerve ♢☆
        Transmits nerve impulses to brain when photoreceptors stimulated.
        
        Fovea
        Small depression in retina directly behind lens. Focuses images, with most cones but no rods. Give detailed coloured vision in bright light.
        
        Vitreous Chamber
        Space behind the lens, filled with vitreous humour (transparent, jelly-like substance) which keeps eyeball firm and helps refract light onto retina
        
        Choroid
        Between sclera and retina.
        
        Is black to prevent internal refraction of light
        
        Has blood vessels that bring oxygen and nutrients to eyeball and remove metabolic waste products
        
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  - - - In Bright Light
        (make pupil smaller to dec amt of light entering eye)
        
        Circular muscles contract
        
        Radial muscles relax
        
        Pupil becomes smaller/constricts. Reduces amt of light entering the eye
      - In DimLight
        (make pupil larger to inc amt of light entering eye)
        
        Circular muscles relax
        
        Radial muscles contract
        
        Pupil becomes enlarges/dilates. Increases amt of light entering the eye
  - - - 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 on Distant Object
        
        Ciliary muscles relax, pulling on suspensory ligaments
        
        Suspensory ligaments become taut, pulling on the edges of the lens
        
        Lens becomes thinner and less convex
        
        Light rays from the distant object are sharply focused on the retina
        
        Photoreceptors are stimulated
        
        Nerve impulses produced are transmitted by the optic nerve to the brain. The brain interprets nerve impulses, and the person sees the distant object
        
        Focusing on Near Object
        
        Ciliary muscles contract, relaxing their pull on suspensory ligaments
        
        Suspensory ligaments slackens, relaxing their pull on the edges of the lens
        
        Lens, being elastic, becomes thicker and more convex
        
        Light rays from the near object are sharply focused on the retina
        
        Photoreceptors are stimulated
        
        Nerve impulses produced are transmitted by the optic nerve to the brain. The brain interprets nerve impulses, and the person sees the near object
- - - - The Spinal Nerve contains both sensory and motor neurones. Hence, it is a 'mixed' nerve.
    - - Sensory Neurone (receptor neurone): Transmits nerve impulses from the sense organs/receptors to the CNS.
        
        Relay Nurone (immediate neurone): Transmits nerve impulses from the sensory neurone to the motor neurone. Found in CNS.
        
        Motor neurone (effector neurone) : Transmits nerve impulses from the CNS to the effectors.
        
        from Cell Body, through Nerve Fiber, to Muscle Fibres
        Cell Body: contains a nucleus, cytoplasm, cell membrane and organelles. Irregular shape.
        Nerve Fibre: a strand of cytoplasm extending from the cell bo
        
        from Sense Organ through One Long Nerve Fibre extending from sense organ to Cell Body then through One Short Nerve Fibre with Terminal Nerve Fibres extending towards relay neurone in CNS
        Circular Cell Body: by the side of the nerve fibre, between long nerve fibre and short nerve fibre.
        
        Synapse: tiny space between sensory neurone and relay neurone. Due to this space, nerve impulses cannot directly cross. They are transmitted across the synapse by chemicals released by the neurones.
  - - - done under conscious control. It is a deliberate action.
        
        Brain -> Relay Neurone in Spinal Cord -> Motor Neurone -> Effector
    - - Reflex Action
        An immediate response to a specific stimulus without conscious control
        
        Cranial Reflexes
        (controlled by the brain but NOT the conscious will. Usually occur in the head region. eg. pupil reflex, blinking and salivation
        
        Reflex arc
        The shortest pathway by which nerve impulses travel from the receptor to the effector in a reflex action
        
        Receptor -> Sensory Neurone -> Relay Neurone (CNS, brain or spinal cord) -> Motor Neurone -> Effector
        
        Spinal Reflexes
        (controlled by spinal cord. eg. sudden withdrawal of the hand when touching a hot object and knee-jerk reflex)
    - - When receptors in skin are stimulated
        
        Receptor in Skin -> Sensory neurone -> Relay Neurone in Spinal Cord -> Brain
    - - Involuntary
        
        Reflex
        
        Sudden action in response to something
        
        Need stimulus
        
        Brain/Spinal Cord regulates
        
        Produced during emergency
        
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        Not controlled by will
        
        No need stimulus
        
        Brain regulates
        
        Occurs throughout lifetime
        
        May be slow/quick
        
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  - - - Nervous Control
      - Involves hormones (chemical substances) as signals
        
        Hormones are transported by blood
        
        Usually slow responses
        
        Responses may be short-lived (eg. adrenaline) or long-lived (eg. growth hormone)
        
        Always involuntary
        
        May affect more than one target organ
        
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        May be voluntary or involuntary
        
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        Responses are short-lived
        
        Usually quick responses
        
        Nerve impulses transmitted by neurones
        
        Involves nerve impulses as signals
- - - - Produced by choice
        
        Choice-dependant speed
- - - - Speed
- - - - Voluntarism
        
        Affect