1. Sensory and Motor Mechanisms
AP Chapter 50

2. Notice
You do not need to know the specific neuroanatomy of the sensory organs, rather the mechanisms of how they work, ie: type of receptors, generally how signal is carried (by vibrations, photopigments, etc), signaling mechanisms or opening of ions channels. Even though more information is included in the power point, just read for information purposes.

3. However….. Please review the structure of the ear and eye in case you are asked questions about structure and function!

4. The brain’s processing of sensory input and motor output is cyclical rather than linear
The way it ISN’T: sensing  brain analysis  action.
The way it is: sensing, analysis, and action are ongoing and overlapping processes.
Sensations begin as different forms of energy that are detected by sensory receptors.
This energy is converted to action potentials that travel to appropriate regions of the brain.
The limbic region plays a major role in determining the importance of a particular sensory input.

5. Sensory receptors transduce stimulus energy and transmit signals to the nervous system

6. 4 Functions common to all sensory pathways
Sensory Reception
Sensory transduction
Transmission
Perception

7. Sensory receptors are categorized by the type of energy they transduce.

8. Categories of sensory receptors
Mechanoreceptors – pressure, touch, motion, sound, hair cells
Chemoreceptors
general – solute conc
specific – molecules; gustatory (taste),
olfactory (smell)
Electromagnetic - electrical
Thermoreceptors – heat/cold
Photoreceptors - light
Pain receptors – in humans, nociceptors in epidermis, located in skin and other areas, aspirin/ibuprofen blocks prostaglandins

9. Mechanoreceptors for hearing and equilibrium
Utilize moving fluid and settling particles
Mammals – pressure waves picked up by ears (fluid in canals) and converted into nerve impulses
Fish – lateral line systems
Invertebrates – statocysts with ciliated receptor cells with sand granules
Insects – body hairs that vibrate, some have ears

10. Statocysts in invertebrates

11. Cricket hairs used in sensing

12. Our Hearing and Balance
Energy of fluid into energy of action potentials
Uses sensitive hair cells
True organ of hearing – the organ of Corti located in the cochlea
Balance – semicircular canals
Hearing animation

13. Be familiar with the structures.

14. Hearing The three small bones transmit vibrations
To the inner ear which contains fluid-filled canals.

15. Air pressure vibrates fluid in canals which vibrate the basilar membrane, bending the hairs of its receptor cells against the tectorial membrane which opens ion channels and allows K+ to enter the cells and cause a depolarization and releases neurotransmitters to continue to the auditory nerve to the brain.

16. Figure 50.9 Sensory reception by hair cells
“Hairs” of hair cell
Neuro- trans- mitter at synapse
More neuro- trans- mitter
Less neuro- trans- mitter
Sensory neuron
–50
–50
Receptor potential
–50
–70
–70
–70
Membrane potential (mV)
Membrane potential (mV)
Membrane potential (mV)
Action potentials
Signal
Signal
Signal
–70
–70
–70
Figure 50.9 Sensory reception by hair cells
Time (sec)
Time (sec)
Time (sec)
(a) No bending of hairs
(b) Bending of hairs in one direction
(c) Bending of hairs in other direction

17. Frequency (pitch) determined by areas of basilar membrane that vibrate at different frequencies; areas are thick and thin

18. Volume is controlled by amplitude of wave – stronger bends hair cells more and more action potentials

19. The inner ear also contains the organs of equilibrium
Balance in the semicircular canals is also a response to hair cells; different head angles stimulate different.
Hair cells; lateral line systems in fish and some amphibians work like this too.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

22. Many invertebrates have gravity sensors and are sound-sensitive
Statocysts are mechanoreceptors that function in an invertebrates sense of equilibrium.
Statocyst function is similar to that of human semi-
circular canals
Use ciliated (hair-
like cells)
Fig
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

23. Photoreceptors

24. A diversity of photoreceptors has evolved among invertebrates.
Planaria – eyecup for
light and direction
Insects/crustaceans-
compound eyes
(ommatidia)
Jellyfish, spider, mollusks – single lens eye

25. Grasshopper compound eye

26. Single-lens eyes
Box jellyfish have
24 eyes!

27. Vertebrate eyes
Rods and cones are photoreceptors located in the retina of the eye.
Rods are more light sensitive and are concentrated toward the edge of the retina.
Cones are more color sensitive and are concentrated in the center of the visual field called the

28. Vertebrates have single-lens eyes
Is structurally analogous to the invertebrate single-lens eye.

29. How does this work?
Rods and cones synapse with bipolar cells in the retina, which synapse with ganglion cells, whose axons form the optic nerve.
R/C BP Ganglion Cells

30. Light hits the retina
and then comes back
through the cells to the
optic nerve.

31. Photoreceptors

32. Rods and cones have visual pigments embedded in a stack of folded membranes or disks in each cell.
Retinal is the light-absorbing
pigment and is bonded to a membrane
protein – opsin. Combo – rhodopsin.

33. When retinal absorbs light, it changes shape and separates from opsin
When retinal absorbs light, it changes shape and separates from opsin. In the dark, the retinal is converted back to its original shape.

34. Opsin activates a G protein and opens/closes Na channels to continue/discontinue the nerve impulse.
Fig
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

35. Notice in the
light, the Na+
channels are
closed.

37. Taste and Smell
Odor molecules bind to ciliated receptor cells and taste molecules bind to receptor cells in taste buds and trigger a signal-transduction pathway that involves a G-protein and, often, adenylyl cyclase and cyclic AMP’s.
cAMP to open Na+ channels, depolarizing the membrane and sending action potentials to the brain.

38. Fig
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

39. Sensory receptor cells
Fig
Sugar molecule
G protein
Sweet receptor
Tongue
Phospholipase C
SENSORY RECEPTOR CELL
Sugar molecule
Taste pore
PIP2
Taste bud
Sensory receptor cells
IP3 (second messenger)
Sodium channel
Sensory neuron
IP3-gated calcium channel
Nucleus
Figure Sensory transduction by a sweet receptor ER
Ca2+ (second messenger)
Na+

40. remember…
The ultimate perception of the stimulus depends on the area of the brain that is stimulated!

41. In summary:
Smell, taste – chemoreceptors, gen (solute conc), specific (individual molecules), G protein activates a second messenger that controls a Na or K ion channel Sight (light) – photoreceptors (pigment molecules) change structure, activates a G protein cascade that opens/closes Na channels Hearing, balance – mechanoreceptors, moving fluid, settling particles, bending of hair cells open ion channels

42. Locomotion and muscle action

43. The muscle cell’s structure is conducive to its purpose which is to contract upon receiving a stimulus.

44. How the muscle cell is organized
for energy
This is ONE
muscle cell,
called a
muscle fiber.
Animations
The muscle fiber (cell) is made up of many myofibrils
which in turn are made up of sarcomeres, the units of
contraction.

45. The sarcoplasmic reticulum (SR) is a special type of smooth ER found in smooth and striated muscle.
The SR contains large stores of calcium ions, which it releases when the cell is depolarized.
Action potential
Is spread in the
T tubules

46. The contracting unit is the sarcomere.
Fig b
The contracting unit is the sarcomere.
TEM
0.5 µm
M line
Thick filaments (myosin)
Thin filaments (actin)
Figure The structure of skeletal muscle
Z line
Z line
Sarcomere
This is what gives skeletal muscles and heart muscles their striated appearance.

47. The sliding filament model
When the
sarcomere
contracts,
the filaments
slide over each
other.
Animation: Sarcomere Contraction

48. How does this happen? a closer look: Myosin
Myosin is made of polypeptides twisted to form a fiber helix with a globular end,  which has ATPase activity & an affinity to bind to actin.

49. a closer look: Actin
Actin is a globular protein; each globular actin unit contains a myosin binding site. 
Remember – Actin – Ac”thin”

50. Mechanism of action 1. The Neuromuscular Junction – neuron to muscle
Signal travels from motor neuron by acetycholine (excitatory) to the skeletal muscle cell and depolarizes it.
An action potential is spread in the T tubules and changes the permeability of the sarcoplasmic reticulum which releases Ca+.

51. Actin involvement Myosin-binding sites are blocked by a strand
of tropomyosin whose
position is controlled by
Troponin complex molecules.
Ca+ ions bind to the complex
and move the tropomyosin and
expose the binding sites for
myosin.

52. 3. Myosin Involvement
The globular heads of the myosin are energized by ATP and bind to actin forming a cross-bridge
When relaxing to its low-energy state, the myosin head bends and pulls the attached actin toward the center of the sarcomere

53. 4. Completion
When its’s over, Ca+ returns to the sarcoplasmic reticulum and tropomyosin recovers binding sites on actin.
Acetylcholine is degraded at the synapse.

54. Mechanism of Filament Sliding at the Neuromuscular Junction
Animation: Action Potentials and Muscle Contraction

55. http://highered. mheducation

56. Interactions between myosin and actin generate force during uscle contractions
The sliding-filament model of muscle contraction.
Fig
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

58. Protein models of muscle action

59. Contraction
Many muscle fibers (cells) make up a muscle. The strength of the muscle contraction depends on how many fibers are stimulated by their motor neurons.
If some muscle fibers do not “fire” then the muscle will contract more weakly.
Of single muscle fiber – all or none

60. Fibers must have many mitochondria, a good blood supply (myoglobin better which picks up O2 better and stores it)
Tetanus – smooth, sustained contraction; action potentials arrive rapidly

61. In the disease tetanus, the bacterial toxins block GABA receptors, causing sustained stimulation of the muscles.

62. Muscle Fatigue
Depletion of ATP, loss of ion gradient, accumulation of lactic acid

63. Does not allow for running or walking.
Skeletons support and protect the animal body and are essential to movement
Hydrostatic skeleton: consists of fluid held under pressure in a closed body compartment.
Form and movement is controlled by changing the shape of this compartment.
Advantageous in aquatic environments and can support crawling and burrowing.
Does not allow for running or
walking.

64. Exoskeletons – supportive, protective but do not grow (molted)
Endoskeletons – supportive, grow with the organism, less protective