Receptors,

Question 1

Two key facts of a receptor
(From spec)

Answer 1

receptors respond only to specific stimuli
stimulation of a receptor leads to the establishment of a generator potential.

Question 2

How does a pacinian corpuscle demonstrate that a receptor is specific to a single type of stimulus

Answer 2

It responds only to mechanical pressure
Will not respond to other stimuli like heat, light, sound

Question 3

How does the pacinian corpuscle demonstrate that the stimulation of a receptor leads to the establishment of a generator potential.

Answer 3

All stimuli involve a change in some sort of energy (heat, light, sound, mechanical)
Nerve impulses are also a form of energy
Receptors act as a transducer (convert mechanical energy into nerve impulses)
Nerve impulses are known as a generator potential

Question 4

Basic structure of pacinian corpuscle

Question 5

Example of a mechanical stimuli

Answer 5

Pressure change

Question 6

Where are pacinian corpuscles found

Answer 6

Deep in the skin
Most abundant on fingers, soles of feet, external genitalia
Joints, ligaments, tendons (enable organisms to know which joints are changing direction)

Question 7

Stretch mediated sodium channel

Answer 7

The sensory neurone ending at the centre of the PC has a special type of sodium channel in its plasma membrane.
Their permeability to sodium changes when they are deformed (eg by stretching)

Question 8

Function of PC

Answer 8

Resting state: stretch mediated sodium channels are too narrow to allow sodium ions to pass along them, so PC has a resting potential
Pressure applied to PC: deformation, membrane stretches. Widens the sodium channels so sodium ions diffuse into the neurone
This influx of sodium ions changes the potential of the membrane (depolarises). Produces a generator potential
The generator potential creates an action potential (nerve impulse) that passes along the neurone and to others then to CNS

Question 9

Taxis

Answer 9

Simple response
Direction determines by direction of stimulus
Motile organism responses to a change in environment by moving its whole body either towards or away from the stimulus

Question 10

Receptors in the eye

Answer 10

Light receptors found in the retina
Two types: rod and cone cells
Act as transducers by converting light energy into a nerve impulse

Question 11

How receptors in the eye work

Answer 11

Light hits photo receptors in the eye
Absorbed by optical pigments which are bleached
Causes a chemical change that alters permeability of membrane to sodium ions
Generator potential created
Nerve impulse travels along bipolar neurone to the optic nerve

Question 12

Rods

Answer 12

Peripheral parts of retina

Question 13

Structure of CNS

Answer 13

Brain and spinal cord

Question 14

peripheral nervous system

Answer 14

Nerves that branch out from the brain and spinal cord

Question 15

Somatic nervous system

Answer 15

Controls conscious activities

Question 16

Autonomic nervous system

Answer 16

Controls unconscious activities
Split into sympathetic and parasympathetic nervous systems which have opposite effects on the body

Question 17

Sympathetic nervous system

Answer 17

Fight or flight response

Question 18

Parasympathetic nervous system

Answer 18

Control of heart rate
Rest state

Question 19

How light enters the eye

Answer 19

Light enters the eye through the pupil, and the amount of light that enters is controlled by the muscles of the iris. Light rays are focused by the lens onto the retina

Question 20

Bipolar neurone

Answer 20

Connects photoreceptors to optic nerve

Question 21

Cones

Answer 21

Packed together in fovea

Question 22

Rods vs cones in terms of colours

Answer 22

Rods and cones contain different optical pigments making them sensitive to different wavelengths
of light. Rods only give information in black and white (monochromatic vision), but cones give
information in colour
(trichromatic vision).

Question 23

Types of cones

Answer 23

contain
a different optical
pigment
red-sensitive,
green-sensitive
blue-sensitive.
When they’re stimulated in different proportions you see different colours.

Question 24

Visual acuity

Answer 24

the ability to tell apart points that are close together

Question 25

Visual acuity of rods vs cones

Answer 25

Rods give low visual acuity because many rods join the same bipolar neurone, which means light from two points close together can’t be told apart.

Cones give high visual acuity because cones are close together and one cone joins one bipolar neurone. When light from two points hits two cones, two action potentials (one from each cone) go to the brain — so you can distinguish two points that are close together as two separate points.