Organisms Respond To Changes In Their Environment: - Receptors

- Receptors - 

A Pacinian corpuscle is a sensory neruone :

1. Specific to single type of stimulus - responds to mechanical pressure 
2. Produces a generator potential, acting as a transducer which converts the change in form of energy by stimulus into nerve impulses, that can be understood. Nerve Impulse = energy 

Receptors in nervous system convert energy of the stimulus into a nervous impulse = generator potential. 

- What does the structure of the Pacinian corpuscle look like? -

The sensory neurone ending at the centre of the Pacinian corpuscle has special sodium channel in the plasma membrane = stretch-mediated sodium channel. 

The permebility to sodium changes when it is deformed = i.e. stretching the pacinican corpuscle. 

- What is the function of the Pacinian corpuscle? -

1. Pacinian corpuscle contain the end of the sensory neurone - wrapped in many layers of connective tissue = lamellae
2. When it is stimulated the lamallae is deformed and presses on the sensory nerve endings. 
3. This causes the sensory neruone's cell membrane to stretch, defroming the stretch-mediated sodium ion channels. // channels open and sodium ions diffuse into the cell 
4. Influx of the sodium ions changes the potential of the membrane - becomes depolarised - a generator potential is created. 
5. If the generator potential reaches the threshold an action potential is triggered. 

- Differences between Rods and Cones -

Rods = sensitive // firing action potential in dim light. Many rods join to only one neurone, this means that a weak generator potential needed, as well as, a weak threshold to trigger the action potential. 

Rods have low visual acuity // many rods attached to one neurone 

Cones = less sensitive // enables to cones to differentiate whether an image is of two objects or one object. 

Cones have high visual acuity // one cone is attached to one neurone 

when the light hits two cones from two points two action potentials are produced and go to the brain. 

In other words, this enables the two points that were close together as two separate points.