10 — nervous system & the eye

Question 1

Define reflex action

Answer 1

A reflex action is an immediate involuntary 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.

Question 2

Define reflex arc

Answer 2

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.

Question 3

Voluntary action definition + arc

Answer 3

Body activities carried out under conscious control and is a deliberate action.

Eg singing, walking, eating

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.

Question 4

Involuntary actions

Answer 4

Involuntary actions are automatic body activities not controlled consciously

Eg breathing, shivering, peristalsis, reflex actions

Question 5

Define accommodation

Answer 5

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.

Question 6

Define stimulus

Answer 6

a change in the environment that causes an organism to react.

Question 7

Define Response

Answer 7

an organism’s reaction to a stimulus

Question 8

Examples of cranial reflexes

Answer 8

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

Question 9

Reflex arc Answ formula

Answer 9

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

Question 10

Types of neurones

Answer 10

• 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

Question 11

Endocrine control vs nervous control

Answer 11

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.

Question 12

Cornea

Answer 12

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

Question 13

Sclerotic coat

Answer 13

• 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

Question 14

Fovea

Answer 14

• 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

Question 15

Cones vs rods

Answer 15

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

Question 16

Focusing on distant objects:

Answer 16

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.

Question 17

Focusing on a near object:

Answer 17

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.

Question 18

Voluntary action vs non-voluntary action

Answer 18

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.
4. VA does not require a stimulus but IV requires a stimulus

Question 19

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

Answer 19

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]

Question 20

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

Answer 20

• 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]

Question 21

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]

Answer 21

• 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]

Question 22

Cataracts are gradual clouding of the lens in the eye. Suggest how this condition may affect vision. [4] + Nuclear cataract impact on functioning of eye [3]

Answer 22

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

[3]:
It blocks the light rays passing through the lens hence reducing the light reaching the retina [1], making the image formed dimmer. [1] As less light is refracted onto the retina, the image formed is also blurred. [1]

Question 23

Describe how myopia affects vision. [4]

Answer 23

• 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]

Question 24

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

Answer 24

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]

Question 25

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

Answer 25

• 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)

Question 26

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

Answer 26

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)

Question 27

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

Answer 27

Response of pupil to an increase in light intensity is a reflex action known as pupil reflex.
Increase in light intensity is detected by photoreceptors on the retina which will generate nerve impulses [1]; which is transmitted via the sensory neurones in the optic nerve across a synapse to the relay neurone to the brain and then across another synapse, along the motor neurone to the iris muscles [1]; the circular muscles of
the iris contracts while the radial muscles of the iris relaxes, [1] causing the pupil to constrict; reducing the excessive amount of light entering the eye and damaging the retina [1]

Question 28

Describe the role of lens in an eye [3]

Answer 28

Thickness and curvature of the lens can be controlled and changed by the suspensory ligament and ciliary muscles during accommodation to change the focal length of the lenses and thus produced a focused image on the retina. [1] Refract and focus light rays [1] reflected from near and far objects onto the retina. [1]

Question 29

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

Answer 29

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

Question 30

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

Answer 30

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.

Question 31

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

Answer 31

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)

Question 32

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

Answer 32

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.

Question 33

Neurones

Answer 33

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.

Question 34

Synapse

Answer 34

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

Question 35

Pupil reflex

Answer 35

Involuntary action of the circular and radial muscles in the iris in response to a change in light intensity by changing the size of the pupil.

Question 36

Seeing objects downwards

Answer 36

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.

Question 37

Drawing of lens when light rays are parallel

Answer 37

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

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

Question 38

Conjunctiva

Answer 38

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

Question 39

Pupil

Answer 39

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

Question 40

eyelid

Answer 40

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

Question 41

eyelash

Answer 41

Shields the eye from dust particles

Question 42

Tear gland

Answer 42

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.

Question 43

Choroid

Answer 43

• 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

Question 44

Retina

Answer 44

• 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

Question 45

Blind spot

Answer 45

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

Question 46

Optic nerve

Answer 46

• comtains sensory neurone that Transmits nerve impulses to the brain when photoreceptors r stimulated

Question 47

Lens

Answer 47

• 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.

Question 48

Suspensory ligament

Answer 48

• Attaches the edge of the lens to the ciliary muscles

Question 49

Iris

Answer 49

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.

Question 50

Ciliary body

Answer 50

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

Question 51

Aqueous chamber

Answer 51

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

Question 52

Vitreous chamber

Answer 52

• 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

Question 53

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]

Answer 53

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

Question 54

Describe how a focused image is produced on the retina of the eye. [6]

Answer 54

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

Question 55

Describe the sequence of events occuring when a person touches a hot object. [6]

Answer 55

Eg; touching a hot object
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 ALONG the relay neurone parallel to the spinal cord and the person feels the pain sensation.

Question 56

Describe and explain the pathway for the closure of the eyelids during a sneeze. [4]

Answer 56

Dust stimulates the receptor cells and nerve impulse generated. [1]
Nerve impulses transmitted via sensory neurone to the brain [1]
Nerve impulse transmit across a synapse to the relay neurone in the brain and transmit across another synapse to the motor neurone [1]
Motor neurone transmit nerve impulses to the muscles of the eyelids and causing them to close. [1]

Question 57

Suggest one possible change in human activities overly the years and explain how this change could make a person less able to see far objects clearly. [2]

Answer 57

more time/ more often/ more frequently/ increased usage/ more time/ prolonged period of time spent looking at near objects [1]
Ciliary muscles contract for a long period of time / ciliary muscles constantly contract when looking at near objects, resulting in fatigue and cause strain to the eye [1]