Nervous System – Sensory Systems

1. Nervous System – Sensory Systems Biol 105 Lecture 11 Chapter 9

2. Concepts to Know: • Depolarization is caused by ______ ions entering or leaving (which one) the axon • The gap in between two neurons is called the ________. • What is the name for the chemicals that are held in vesicles and released from one neuron, and bind to receptors of the next neuron? • What part of the autonomic nervous system stimulates digestion? • What is the thin outer layer of the cerebrum where most of the higher thinking and processing takes place called • The part of the brain that processes sensory information (except smell) is called the ______.

3. Outline • Senses • Sensory receptors • Touch • Vision • Hearing and balance • Smell

4. Senses • Major senses – touch, hearing, smelling, taste, and seeing. • All the sensory nerves are routed through the thalamus except the nerves for smell.

5. Sensory receptor cells • Sensory receptors are specialized structures that detect stimuli (stimulus) • Sensory receptor cells change the stimulation into an electrical response that is transmitted through the nerves • If a sensory receptor is continuously stimulated, it will stop responding = sensory adaptation

6. 12.2 The Central Nervous System 12-18

7. 12-28

9. Touch • We can sense different things through touch: • Thermal • Tactile • Pain • Vibration

10. Figure 9.2 Sense receptors of the skin

11. Figure 9.2 Sense receptors of the skin

12. Types of receptors in the skin • Free nerve endings • Merkel disks • Meissner’s corpuscles • Pacinian corpuscles • Ruffini corpuscles • Thermoreceptors

13. Free Nerve Endings • Free nerve endings – tips of dendrites of sensory neurons (free nerve endings may be wrapped around hair), detect touch and pain

14. Figure 9.2 Free nerve endings

15. Figure 9.2 Free nerve endings

16. Merkel Disks • Merkel disks – comprised of free nerve endings and Merkel cells, detect touch

17. Merkel disk

18. Meissner’s corpuscles • Meissner’s corpuscles – encapsulated nerve endings - detect light touch, tell us exactly where we were touched

19. Meissners corpuscle

20. Pacinian corpuscles • Pacinian corpuscles – layers of tissues surround the nerve ending, detects pressure when first applied, important in sensing vibration

21. Pacinian corpuscle

22. Ruffini corpuscles • Ruffini corpuscles – encapsulated nerve endings in deep layers that respond to continuous pressure

23. Ruffini corpuscle

24. Thermoreceptors • Thermoreceptors – specialized nerve endings, detects changes in temperature.

25. Vision • Sight is complex: • Light enters the eye, it is focused, then the light has to be transformed into it into an electrical signal that then has to be processed.

26. Vision • Light enters through the cornea • The lens focuses it to the back of the eye • The retina is a layer at the back of the eye where light is transformed into electrical signals

27. Optic nerve Optic disk (blind spot) Fovea Sclera Choroid Retina Vitreous humor (fills the posterior chamber) Lens Ciliary body Aqueous humor (fills the anterior chamber) Cornea Pupil Iris Sclera Figure 9.4

28. Layers of the Eye – Outer layer • The sclera • Protects and shapes the eye • Provides attachment for muscles • The cornea • Allows light to enter

29. Outer Layer of Eye Table 9.1 (1 of 4)

30. Middle Layer of Eye • The choroid • Contains blood vessels that supply nutrients and oxygen. • Contains melanin, absorbs light reflected from the retina • The ciliary body • A ring of muscle that functions to focus the lens on the retina

31. Middle Layer of Eye • The iris • The colored portion of the eye • Contains smooth muscle that dilates or constricts to regulate the amount of light entering the eye • The pupil • The opening in the center of the iris that lets light into the eye

32. Middle Layer of the Eye Table 9.1 (2 of 4)

33. Inner Layer of Eye • Contains: • Retina • Photoreceptors - Rods and Cones • Fovea

34. Inner Layer of Eye - Retina • The retina contains photoreceptors • Rods • Cones – detect color • The fovea is a pit in the retina with a high concentration of cones

35. Vision Depends on the Eye Table 9.1 (3 of 4)

36. Structures of the Eye • Optic Nerve • Fluid • Aqueous humor • Vitreous humor • Lens

37. Optic Nerve • The optic nerve • Carries visual information to the brain • Forms a blind spot where it leaves the retina

38. Fluid in the Eye • There are two fluid filled chambers in the eye • Vitreous humor – jelly like fluid in posterior chamber. Holds retina against the wall of the eye • Aqueous humor – clear fluid in anterior chamber. Supplies nutrients and oxygen to cornea and lens, removes the waste. Creates pressure in eye to maintain shape of eye.

39. Lens • The lens can change shape to focus on near and far objects. • Focuses the light onto the retina • Ciliary muscles are attached to lens by ligaments

40. Vision Depends on the Eye Table 9.1 (4 of 4)

41. Photoreceptors • Cones and Rods have pigments that absorb • Cones work best in bright light and provide color vision • Rods work in low light situations but can only provide black and white vision

42. Photoreceptors • The photoreceptors (rods and cones) have pigments that absorb light • When there is no light coming in, they are releasing neurotransmitters (opposite of most receptors) • When they absorb light they stop releasing neurotransmitters

43. Photoreceptors • The neurotransmitters are inhibitory • When the neurotransmitters diminish, cells that process the information are stimulated • This information from these cells (bipolar and ganglion cells) is transmitted to the optic nerve to the thalamus to the visual cortex

44. Light Choroid Sclera Retina Blind spot (a) Light enters the left eye and strikes the retina. Figure 9.8a

45. Light Vitreous humor Ganglion cell layer Electrical signals Bipolar cell layer Retina Cone Photoreceptor cells Rod Pigment layer Axons Choroid Sclera Figure 9.8b

46. Light Retina Optic nerve Visual cortex (c) The axons of the ganglion cells leave the eye at the blind spot, carrying nerve impulses to the brain (viewed from below) by means of the optic nerve. Figure 9.8c

47. Rods and Cones Rod cell Cone cell Figure 9.9 (2 of 2)

48. Which part of the human eye detects colored light? • Pupil • Rods • Cones • Cornea

49. A ring of muscle that functions to focus the lens on the retina is the: • Iris • Choroid • Ciliary body • Sclera

50. Figure 9.10 A standard test for color blindness