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Biology > 10 — nervous system & the eye > Flashcards

10 — nervous system & the eye Flashcards

1
Q

Define reflex action

A

A reflex action is an immediate response to a specific stimulus without conscious control. There r 2 types of reflex action. Cranial reflexes are controlled by the brain. Spinal reflexes r controlled by spinal cord. Brain and spinal cord r reflex centres.

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2
Q

Define reflex arc

A

shortest pathway by which nerve impulses travel from the receptor to effector in a reflex action. The nerve impulses generated by the receptor r transmitted along the reflex arc.

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3
Q

Voluntary action + arc

A

an action under conscious control. It is a deliberate action.

Nerve impulses r initiated and generated in the brain -> transmitted via RN from brain to spinal cord, across a synapse to the motor neurone, to the effector muscle contracts and arm/leg picks up.

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4
Q

Involuntary actions

A

Involuntary actions r activities that r not controlled consciously

Eg breathing, shivering, reflex actions

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5
Q

Define accommodation

A

Focusing, also called accommodation, is the adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina.

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6
Q

Define stimulus

A

any change in the environment that causes an organism to react

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7
Q

Define Response

A

an organism’s reaction to a stimulus

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8
Q

Examples of cranial reflexes

A

Pupil reflex, blinking, salivation (usually occur in head region)

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9
Q

Central nervous system (CNS)

A

Consists of
- brain
- More sophisticated. It integrates visual, auditory, touch, olfactory n taste info from our sensory organ
- Spinal cord
- Involved mostly in automatic actions known as reflex actions
- Works to integrate nerve impulses from various parts of the body

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10
Q

Peripheral nervous system (PNS)

A
  • cranial and spinal nerves
    • Nerves r tissues
  • Sense organs
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11
Q

Reflex arc Answ formula

A

Stimulus → stimulates receptors in sense organs to produce nerve impulses → transmitted by sensory neurones to spinal cord → across a synapse to relay neurone to spinal cord -> nerve impulses transmitted across another synapse to motor neurones () -> transmits nerve impulses to effectors (muscles or glands) (->bicep muscles contracts n causes ur hand to withdraw)
()At the same time, nerve impulses transmitted via relay neurone parallel to the spinal cord to the brain for pain sensation

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12
Q

Types of neurones

A
  • neurones r nerve cells

Sensory neurones transmits nerve impulses (secretes hormones) from the receptors to relay neurones in the spinal cord or brain. (structure:
- Circular cell body
- One long nerve fibre betw receptor n cell body
- One short nerve fibre betw cell body n CNS

Relay neurones in the CNS receive nerve impulses from sensory neurones and transmits nerve impulses along CNS to motor neurones.

Motor neurones transmits nerve impulses from CNS to effectors for an action to occur
- Irregular-shaped cell body
- Location of cell body diff from
sensory neurone
- One long nerve fibre betw cell body n effector

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13
Q

Voluntary action characteristics

A
  1. Under conscious will
  2. Does not require a stimulus
  3. Regulated by the brain
  4. Produced by choice
  5. Choice-dependent spd
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14
Q

Reflex (involuntary) action characteristics

A

1.an immediate action
2. Requires a stimulus
3. Regulated by the brain or spinal cord
4. Produced during an emergency
5. Without conscious control

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15
Q

Endocrine control vs nervous control

A

EC: involves hormones as signals
NC: involves nerve impulses as signals

EC: hormones transported by blood
NC: nerve impulses transmitted by neurones

EC: usually slow responses
NC: usually quick responses

EC: responses may be short-lived or long-lived
NC: responses r short-lived

EC: alw involuntary
NC: may be voluntary/involuntary

EC: may affect more than 1 target organ
NC: usually localised

Similarities:
Both have receptors that detect stimulus.
Both involve transmission of a signal or message.
Both involve an effector that carries out a response.

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16
Q

Cornea

A

cornea
- Dome-shaped transparent layer that is able to refract light, bending light rays towards pupil of eye

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17
Q

Sclerotic coat

A
  • outermost layer of the eye
    • Tough, white outer covering of the eyeball which is continuous with the cornea
    • Protects the delicate inner structures
    • Eye muscles (rectum muscles) attached to this layer facilitates the movement of the eyeball
    • Maintains the shape of the eyeball
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18
Q

Fovea

A
  • contains highest density of photoreceptors to receive refracted light rays and generate nerve impulses to be transmitted via SN and generate NI to be transmitted via SN in optic nerve to the brain to interpret the image
    • site where images r focused.
    • Contains highest conc of cones but no rods
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19
Q

Cones vs rods

A

Types of photoreceptors:
Cones: red, blue, green
Rods: 1 type

Types of pigment:
Cones: each type of photoreceptor contains diff pigment which absorbs light of diff wavelengths
Rods: contain pigment called visual purple which is bleached when exposed to bright light n nerve impulses cannot be transmitted to brain

Role:
Cones: works well only in bright light; is responsible for colour vision n formation of sharp images
Rods: works well only in dim light; responsible for black n white images we see

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20
Q

In bright light

A
  1. Circular muscles of iris contract
  2. Radial muscles of iris relax
  3. Pupil becomes smaller or constricts, reducing amt of light entering the eye
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21
Q

In dim light

A
  1. Radial muscles of iris contract
  2. Circular muscles of iris relax
  3. Pupil enlarges or dilates, increasing amt of light entering the eye
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22
Q

Focusing on distant objects:

A
  1. Ciliary muscles relax, pulling on the suspensory ligaments
  2. Suspensory ligaments becomes taut, pulling on the edge of lens
  3. Lens becomes thinner and less convex, increasing its focal length.
  4. Light rays from distant objects bend less and focus to a point on the retina, forming a clear and sharp image.
  5. Photoreceptors r stimulated
  6. Nerve impulses produced r transmitted by the sensory neurone in the optic nerve to the brain. The brain interprets the nerve impulses, the person sees the distant object.
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23
Q

Focusing on a near object:

A
  1. Ciliary muscles contract, relaxing their pull on Suspensory ligaments
  2. Suspensory ligaments slacken, relaxing their pull on the lens
  3. The elastic lens becomes thicker n more convex, decreasing its focal length.
  4. Light rays from near object bend more and r sharply focused on retina (fovea), forming a clear and sharp object
  5. Photoreceptors r stimulated
  6. Nerve impulses produced r transmitted by the sensory neurones in the optic nerve to the brain. The brain interprets the nerve impulses n person sees the near object.

The point at which the image of a near object becomes blurred is called the near point of vision where the lens reaches its maximum curvature.

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24
Q

Voluntary action vs non-voluntary action

A
  1. Involuntary action does not involve conscious control but VA does.
  2. IV is an immediate response but VA may not have an immediate response
  3. VA NI is generated at the brain but IV NI is generated at the receptors.
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25
Q

Describe the sequence of events occuring when a person enters a dark room. [6]

A

Response of pupil to a change in light intensity is a reflex action known as pupil reflex. Decrease in light intensity is detected by photoreceptors on the retina which will generate nerve impulses [1]; which is transmitted via the sensory neurone in optic nerve to the relay neurones in the brain across a synapse [1] and then across another synapse to the motor neurone to the effector iris muscles [1]; the circular muscles of the iris relax while the radial muscles of the iris contracts, [1] causing the pupil to dilate [1]; increasing amount of light entering the eye. [1]

26
Q

Describe how the parts of the eye produce a focused image of an object. [5]

A
  • Cornea – is dome-shaped to refract light, bending the light rays towards the pupil [1]
  • Aqueous humour – viscous fluid, refracts light entering the pupil [1]
  • Lens – most refraction of light; adjust thickness and curvature to vary the angle of refraction to focus light rays from near / far objects onto the fovea [1]
  • Vitreous humour - jelly like substance, refract light towards the fovea on the retina [1]
  • Fovea – high density of photoreceptors to receive refracted light rays and generate nerve impulse to be transmitted via the sensory neurone in the optic nerve to the brain to interpret the image. [1]
27
Q

Describe the sequence of events occuring when a person shifts his attention from the distant signboard to his watch and to the incoming train. [6]

A
  • To produce a focused image of near objects on the retina, ciliary muscles contract and suspensory ligaments slackens [1]; relaxing the pull on the lens, making the lens thicker and more convex [1], decreasing the focal length. Light rays from near objects bend more and are focused onto the
    fovea of the retina [1], forming a clear image.
  • To produce a focused image of distant objects on the retina, ciliary muscles relax and suspensory ligaments pulls taut [1]; Lens becomes thinner and less convex [1], increasing the focal length. Light rays from the distant object bend less and are focused onto the fovea of the retina, forming a clear image. [1]
28
Q

Cataracts are gradual clouding of the lens in the eye. Suggest how this condition may affect vision. [4]

A
  • Less light rays able to pass through [1], dimmer image formed [1] at retina
  • Less refraction of light [1], light rays not focused at fovea, blurred image formed. [1]
29
Q

Describe how myopia affects vision. [4]

A
  • Myopia affects far object accommodation [1]
  • The ciliary muscles is not able to sufficiently relax and suspensory ligaments is not able to pull taut [1]; Lens remain thick and convex [1],
  • The focal length is short. Light rays from the distant object focus to a point before the fovea of the retina, thus forming a blurry image on the retina. [1]
30
Q

Compare and contrast between voluntary and reflex actions. [6]

A

Similarities:
- Both involve the transmission of nerve impulses via electrical and chemical signals.[1]
- Both involve motor neurones and effector muscles [1]

Differences (any 4):
- Voluntary action is initiated at the brain but reflex action is initiated at the receptors [1]
- Voluntary action does not need a stimulus but reflex action requires a stimulus [1]
- Voluntary action does not require sensory neurone but reflex action does require sensory neurone [1]
- Voluntary action is under conscious control but reflex action is not under conscious control [1]

31
Q

Using a named example, describe the mechanism of a reflex response. [6]

A
  • Thermoreceptors in the skin of the hand are stimulated by the hot object. [1]
  • Nerve impulses are generated [1] and transmitted along the sensory neurone [1] across a synapse to the relay neurone in the spinal cord [1] of the central nervous system.
  • The nerve impulse is then transmitted across another synapse to the motor neurone [1] and then to the effector which is the arm muscles and the hand is withdrawn. [1]
  • At the same time, nerve impulses are transmitted to the brain via the relay neurone and the person feels the pain sensation. [1] (Any 6 points)
32
Q

Compare and contrast between hormonal and nervous control. [6]

A

Similarities:
- Both require stimulus. [1]
- Both initiate a response. [1]
- A signal is transmitted in both cases, nerve impulses in nervous control and hormones in hormonal control. [1]
Differences:
- Nervous coordination is a faster response than hormonal coordination. [1]
- Nervous coordination involves transmission of electrical impulses while hormonal coordination involves the transmission of chemical hormones. [1]
- Nervous coordination produces short-term effects, while hormonal coordination can produce short-term or long–term effects. [1]
- Nervous coordination is usually localised, while hormonal coordination may affect more than one target organs. [1]
- Nervous coordination is transmitted by the neurones while hormonal coordination is transmitted by the blood plasma. [1]
- Nervous coordination is either voluntary or involuntary, while hormonal coordination is involuntary. [1] (Any 3 differences)

33
Q

Describe and explain how the pupil of the eye responds to an increase in light

A

^ in light intensity -> pupil reflex occurs. The pupil changes size according to changes in light intensity.
When LI ^ -> too much light enters the eye thru pupil and stimulates photoreceptors in retina -> producing NI that is transmitted in SN in optic nerve across a synapse to RN in brain, across another synapse to MN to iris. Circular muscles of iris contract, radial muscles of iris relax to make the pupil constricts -> less light enters the retina.

34
Q

Describe the role of lens in an eye [3]

A
  1. Refract light that enters the eye
  2. Helps to produce a focused image on the photoreceptors on the retina by changing its thickness.
  3. Thickness and curvature of the lens can be controlled by the suspensory ligament and ciliary muscles to change the focal length of the lenses and thus produced a focused image on the retina.
35
Q

Anaesthetic is injected in xxx within the CNS. Suggest why this helps to reduce pain.

A

The anaesthetic inhibits the relay neurone in the spinal cord, preventing the transmission of nerve impulses from relay neurone to the brain.

36
Q

Peripheral neural receptors functions r impaired. State and explain whether the patient can react to touching hot objects.

A

No. The receptor is unable to generate NI to be transmitted along the SN across a synapse to RN in spinal cord. No nerve impulses will be transmitted to MN and to effector to initiate a response.

37
Q

Blind person can read Braille, raised marks on surface of paper. Explain.

A

Pressure receptors in finger stimulated, generating NI, and is transmitted along SN across a synapse to RN parallel to spinal cord to the brain for interpretation.

(To brain: parallel to spinal cord; to effector muscle: in spinal cord)

38
Q

Sclerotic coat ruptured,clear jelly like substance escapes. Explain why vision blur. Explain why distorted vision.

A

Blur:
Clear jelly like substance is vitreous humour. Light passing thru VH is not properly refracted towards fovea, image is blur.

Distorted vision:
Vitreous humour pushes the retina against choroid and holds it in place. Loss of VH may cause retina to become detached from the choroid resulting in distorted vision.

39
Q

Neurones

A

Nerve cells that function to transmit nerve impulses within the nervous system. They differ in shapes and sizes. They consists of a cell body containing the nucleus and organelles, where essential metabolic processes occur to maintain cell survival; nerve fibres which are strands of cytoplasm extending from cell body that transmit nerve impulses to other neurones or effectors, and terminal nerve fibres that are short-branched nerve fibres that convert chemical info from other neurones or receptor cells into electrical nerve impulses.

40
Q

Synapse

A

A junction or connection between 2 neurones by chemical means through neurotransmitters

41
Q

Pupil reflex

A

Involuntary action of the muscles in the iris in response to a change in light intensity by changing the size of the pupil. This action is controlled by 2 sets of involuntary muscles in iris, the circular and radial muscles.

42
Q

Seeing objects downwards

A

Rectum muscles contracts to pull the eyeball downwards. Ciliary muscles in the ciliary body contract, suspensory ligaments slackens, lens become thicker and more convex. Focal length decreases and light rays are focused on the retina.

43
Q

Drawing of lens when light rays are parallel

A

Light rays parallel -> distant object -> lens thinner less convex

Light rays diverge -> near object -> lens thicker more convex

44
Q

Conjunctiva

A
  • Mucus membrane, covering the sclera
  • Secretes mucus to keep the front of the eyeball moist
45
Q

Pupil

A
  • A hole in the centre of the iris, allowing light to enter the eye
46
Q

Iris

A
  • Circular sheet of muscles, consisting of 2 sets of involuntary muscles — circular and radial muscles
    • Also contains a pigment which gives the eye its colour
47
Q

eyelid

A
  • Protects cornea from mechanical dmg
  • Squinting prevents excessive entry of light
  • Blinking spreads tears over the eyes so that dust can be wiped off
48
Q

eyelash

A

Shields the eye from dust particles

49
Q

Tear gland

A

Secretes tears to
- Wash away dust particles
- Keep the cornea moist for atmospheric oxygen to dissolve
- Lubricate the conjunctiva, reducing friction when the eyelids move.

50
Q

Choroid

A
  • middle layer of the eye
    • Black pigmented middle layer which prevents the internal reflection of light
    • Contains blood vessels that transports oxygen and nutrients to eyeball n remove metabolic waste products from the eyeball
51
Q

Retina

A
  • Innermost layer of the eye wall
    • Contains light-sensitive cells known as photoreceptors which consist ‘rods’ and ‘cones’ that detects light and where images are formed
      • Cones (responsible for colour vision and formation of sharp images)
        • 3 types: Red blue green, each type contains diff pigment, which absorbs light off diff wavelengths → Work tgt to enable us to see a variety of colours in bright light
        • > /1 cone(s) missing → colour blindness
      • Rods r stimulated even by v dim light → enable us to see in dim light but only in black or white
        • Contain a pigment called visual purple (requires vitamin A)
        • Visual purple is bleached when exposed to bright light n nerve impulses cannot be transmitted to the brain
    • Connected to nerve fibres from the optic nerve
    • Images r formed n detected here
52
Q

Blind spot

A
  • site whr optic nerve leaves the eye
    • Does not contain photoreceptors, therefore not sensitive to light. It transmit nerve impulses via SN to brain.
53
Q

Optic nerve

A
  • Transmits nerve impulses to the brain when photoreceptors r stimulated
54
Q

Lens

A
  • Transparent, circular n biconcave structure
    • curvature or thickness can be adjusted to vary angle of refraction to control refraction of light and focus light rays to form a clear and sharp image on the retina at varying distances.
55
Q

Suspensory ligament

A
  • Attaches the edge of the lens to the ciliary muscles
56
Q

Iris

A

Iris is a circular sheet of muscles consisting of circular and radial muscles, working antagonistically which controls the size of the pupil and amt of light entering the pupil. It contains pigment which gives eye its colour.

57
Q

Ciliary body

A
  • Contains ciliary muscles which control the curvature n thickness of lens
58
Q

Aqueous chamber

A
  • Filled w aqueous humour, a transparent, watery fluid
    • Aqueous humour keeps the front of the eyeball firm n refracts light into the pupil
59
Q

Vitreous chamber

A
  • Space behind the lens
    • Filled w vitreous humour, a transparent jelly-like substance
    • Vitreous humour keeps eyeball firm n refracts light onto the retina
    • Floaters r bits of cellular debris which drift within the vitreous humour n may temporary show up in our field of view
60
Q

As a person ages, the muscles in the ciliary body become loose and cannot contract as much as when the person was younger. How does this affect vision? [1]

A

The lens becomes unable to focus on near objects. [1]

Biology (18 decks)

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