The eye and muscle Flashcards
What happens when light enters the eye?
It is refracted slightly by the cornea
What happens when the ciliary body relaxes?
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
What is the process of the lens becoming thicker and thinner called?
Accommodation
How does the eye focus on a near object?
Ciliary muscle contracts
Suspensory ligaments slacken
Lens is thick
How does the eye focus on a distant object?
Ciliary muscle relaxes
Suspensory ligaments stretch
Lens pull thin
What two types of muscle does the iris consist of?
Radial and circular
What happens to the radial and circular muscles in low light?
Radial muscle contracts, circular muscle relaxes - pupil becomes larger
What happens to the radial and circular muscles in bright light?
Circular muscles contract, radial muscle relaxes - pupil smaller
What are the two specialised photoreceptors in the eye?
Rods and cones
What does rhodopsin consist of?
Opsin and Retinal - vitamin A for
What happens when light strikes a Rod cone?
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.
What is special about Rod cones?
Rod cells are sensitive and a readily broken down in low light intensities
What is dark adaption?
All the Rhodopsin is broken down (bleached) and it takes time for it to be re-synthesised.
Describe cone cells
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)
Describe the distribution of rods and cones in the retina
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.
What is summation?
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.
What is binocular vision?
The use of both eyes to create a single image
What is stereoscopic vision?
The ability to form 3D images
Describe the structure of skeletal muscle
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.
What are the two proteins in skeletal muscle?
Actin (Thin) and myosin (thick) filaments
Draw a labelled diagram of filaments in the transverse section
in book
Describe the process of muscle contraction
The sliding filament theory
- An action potential stimulates muscle fibre as it travels through the extensive system of T tubules
- The AP causes calcium ion channels in the sarcoplasmic reticulum to open
- This causes Ca2+ ion that have been stored in the sarcoplasmic reticulum to open to diffuse into the sarcoplasm down a concentration gradient
- 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
- Once attached, the myosin heads rotate and pull the actin filaments over the mysoin
- An ATP molecule attaches and the energy released from its hydrolysis causes the head to detach and return to its normal position
- The cycle of attachment, rotation and release continues as long as stimulation occurs (Ca2+ ions present)
What happens to the different zones during contraction?
Sarcomere shortens, H zone shortens, I band shortens, A band remains the same length.
