The eye and muscle

Question 1

What happens when light enters the eye?

Answer 1

It is refracted slightly by the cornea

Question 2

What happens when the ciliary body relaxes?

Answer 2

The tension in the walls of the eyeball is transferred through the suspensory ligaments to the lens, which means the lens will be thinner and have little refractive potential

Question 3

What is the process of the lens becoming thicker and thinner called?

Answer 3

Accommodation

Question 4

How does the eye focus on a near object?

Answer 4

Ciliary muscle contracts
Suspensory ligaments slacken
Lens is thick

Question 5

How does the eye focus on a distant object?

Answer 5

Ciliary muscle relaxes
Suspensory ligaments stretch
Lens pull thin

Question 6

What two types of muscle does the iris consist of?

Answer 6

Radial and circular

Question 7

What happens to the radial and circular muscles in low light?

Answer 7

Radial muscle contracts, circular muscle relaxes - pupil becomes larger

Question 8

What happens to the radial and circular muscles in bright light?

Answer 8

Circular muscles contract, radial muscle relaxes - pupil smaller

Question 9

What are the two specialised photoreceptors in the eye?

Answer 9

Rods and cones

Question 10

What does rhodopsin consist of?

Answer 10

Opsin and Retinal - vitamin A for

Question 11

What happens when light strikes a Rod cone?

Answer 11

Rhodopsin breaks down into retinal and opsin, this result in a change in membrane potential and a generator potential is produced. If a threshold level is reached a bipolar neurone becomes depolarised - action potential.

Question 12

What is special about Rod cones?

Answer 12

Rod cells are sensitive and a readily broken down in low light intensities

Question 13

What is dark adaption?

Answer 13

All the Rhodopsin is broken down (bleached) and it takes time for it to be re-synthesised.

Question 14

Describe cone cells

Answer 14

Contain Iodopsin - less readily broken down, only produce a generator potential in bright light. Cones provide colour vision. Different types of iodopsin absorb different wavelengths of light - blue, green and red (trichromatic theory of colour vision)

Question 15

Describe the distribution of rods and cones in the retina

Answer 15

Rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lie immediately inside that. Ganglion cells lie inside them. Each cone cell has its own bipolar neurone - provides high visual acuity. The rods show retinal convergence - a number of rods have the same bipolar neurone, this allows summation - rods show a lack of visual acuity.

Question 16

What is summation?

Answer 16

With low light-intensity stimuli, generator potentials have an additive effect and there is enough transmitter released to reach the threshold value for an action potential to be generated and an impulse propagated to the optic nerve.

Question 17

What is binocular vision?

Answer 17

The use of both eyes to create a single image

Question 18

What is stereoscopic vision?

Answer 18

The ability to form 3D images

Question 19

Describe the structure of skeletal muscle

Answer 19

Consists of bundles of muscle fibres, each surrounded by a sarcolemma. Each fibre is multinucleate. The nuclei lie just beneath the sarcolemma and out of the way of the myofibrils.

Question 20

What are the two proteins in skeletal muscle?

Answer 20

Actin (Thin) and myosin (thick) filaments

Question 21

Draw a labelled diagram of filaments in the transverse section

Answer 21

in book

Question 22

Describe the process of muscle contraction

Answer 22

The sliding filament theory

1. An action potential stimulates muscle fibre as it travels through the extensive system of T tubules
2. The AP causes calcium ion channels in the sarcoplasmic reticulum to open
3. This causes Ca2+ ion that have been stored in the sarcoplasmic reticulum to open to diffuse into the sarcoplasm down a concentration gradient
4. The Ca2+ ions cause ancillary proteins which normally cover the binding sites on the actin filaments to move, enabling the myosin heads to form actomyosin bridges
5. Once attached, the myosin heads rotate and pull the actin filaments over the mysoin
6. An ATP molecule attaches and the energy released from its hydrolysis causes the head to detach and return to its normal position
7. The cycle of attachment, rotation and release continues as long as stimulation occurs (Ca2+ ions present)

Question 23

What happens to the different zones during contraction?

Answer 23

Sarcomere shortens, H zone shortens, I band shortens, A band remains the same length.