Reflex, Responses, Receptors

Question 1

Reflexes?

Answer 1

• reflex - rapid automatic response to protect animals from danger
• reflex arc made up of three neurons - sensory, relay, motor
• Rapid - only two synapses

Question 2

Simple responses - taxes and kinesis?

Answer 2

• keep organisms within favourable conditions of their environment (light, moisture, chemicals)
• Taxes - move entire body towards favourable stimulus (positive taxis) or away from unfavorable stimulus (negative taxis)
• kinesis - changes speed of movement and rate it changes direction

Question 3

Receptors?

Answer 3

• Detect stimuli
• each receptor responds only to specific stimuli - stimulation leads to establishment of an action potential which can cause a response
  Three receptors to know:
• Pacinian corpuscle
• rods
• cones

Question 4

Pacinian corpuscle?

Answer 4

• deep in skin, mainly in fingers and feet
• sensory neurons in Pacinian corpuscle has special channel proteins in plasma membrane
• membranes have stretch-mediated sodium ion channels - open and allow Na+ ions to enter sensory neurons when stretched and deformed
• when pressure is applied it deforms neuron plasma membrane, stretches and widens Na+ ion channels so it can diffuse in - leads to action potential

Question 5

Rod Cells?

Answer 5

• process images in black and white
• to create action potential, pigment of rod cells (rhodopsin) must be broken down into light energy
• detect light of very low intensity as many rod cells connect to one sensory neuron (retinal convergence) - means brain can’t distinguish between separate sources of light that stimulated it - low visual acuity

Question 6

Cone cells?

Answer 6

• process images in colour
• three types that contain different types of iodopsin pigment (red, green, blue) which all absorb different wavelengths of light
• Iodopsin broken down if high light intensity - action potentials can only be generated with enough light
• One cone cell connects to a bipolar cell - cones can only respond to high light intensity - why we can’t see in the dark
• connected to a bipolar cell - distinguish between separate sources of light - high visual acuity

Question 7

Distribution of rods and cones?

Answer 7

• uneven distribution in retina
• light focused by lens on the fovea - received highest light intensity
• most cone cells located near fovea
• rods cell further away