Infrared Detection in Snakes

Question 1

what do humans feel infrared as?

Answer 1

heat

Question 2

What is the frequency range of infrared rays?

Answer 2

760 nm - 1 million nm

Question 3

Why might snakes have evolved a system for the detection of infrared?

Answer 3

compare response to warm targets in complete darkness

Question 4

What kind of snakes are the most sensitive to IR radiation?

Answer 4

crotaline snakes

Question 5

Where are the infrared sensors in boas? pythons?

Answer 5

• boas = upper and lower jaws
• pythons = upper and lower jaws; more on upper jaw that form pits

Question 6

How many and where are the infrared sensors in crotaline snakes?

Answer 6

a single deep loreal pit between the eye and nostril

Question 7

What is another name for crotaline snakes?

Answer 7

pit vipers

Question 8

draw the shapes of the pits in boas, pythons, and pit vipers.

Answer 8

slide 9

Question 9

TRUE or FALSE: snakes can hear well

Answer 9

FALSE: very poor hearing bc no middle ear bones

Question 10

How does the loreal pit resemble an eye?

Answer 10

• pinhole to detect directionality (i.e. where the heat is coming from)
• multiple pits work like a compound eye

Question 11

Where is the topographic map for the loreal pit? What does it detect?

Answer 11

• optic tectum (TeO)
• detect both IR radiation and visual

Question 12

Which cranial nerve innervates the infrared sensors in snakes?

Answer 12

trigeminal nerve

Question 13

Which branches of the trigeminal nerve innerve infrared sensors for boas, rattlesnakes, and pythons?

Answer 13

• boas and pythons: maxillary and mandibular
• rattlesnakes/vipers: maxillary and ophthalmic

Question 14

Draw the infrared pathway in the brain for the rattlesnake and python.

Answer 14

slide 15; rattlesnake has a nucleus reticularis caloris (RC)

Question 15

Which nucleus in the infrared pathway of the brain is topographically organized?

Answer 15

nucleus of the lateral descending trigeminal tract (LTTD)

Question 16

What is the equivalent of the snake’s optic tectum in mammals? What is it generally responsible for?

Answer 16

• TeO = superior colliculus in mammals
• orienting movements

Question 17

What kind of integration occurs in the optic tectum?

Answer 17

visual infrared integration in the optic tectum?

Question 18

What kind of temperature is TRPA1 more sensitive to in mammals vs snakes?

Answer 18

• mammals = cold
• snakes = hot

Question 19

Is the caloric threshold of crotaline snakes higher or lower than other snakes? What does this imply about activation of IR response in different types of snakes?

Answer 19

• caloric threshold lower in crotaline snakes
• takes more heat to activate python and boa IR response
• crotaline can detect prey from further away

Question 20

Do rattlesnakes and pythons see infrared?

Answer 20

no; thermal transduction