1. Sensory receptors transduce stimulus energy and transmit signals to the nervous system Fig. 49.2

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2 1. Sensory receptors transduce stimulus energy and transmit signals to the nervous system Fig. 49.2

3 Sensory reception begins with the detection of stimulus energy by sensory receptors. Exteroreceptors detect stimuli originating outside the body. Interoreceptors detect stimuli originating inside the body. Sensory receptors convey the energy of stimuli into membrane potentials and then transmit signals to the nervous system. They are energy transducers.

4 2. Sensory receptors are categorized by the type of energy they transduce Fig. 49.3

5 Mechanoreceptors respond to mechanical energy. For example, muscle spindles are interoreceptors that respond to the stretching of skeletal muscle. For example, hair cells detect motion in your inner ear.

6 Pain receptors = nocioceptors. Different types of pain receptors respond to different types of pain. Prostaglandins increase pain by decreasing a pain receptors threshold. This tells you something is wrong. Anti-inflammatories like aspirin and Advil work by inhibiting prostaglandin synthesis.

7 Thermoreceptors respond to heat or cold. Respond to both surface and body core temperature. Paradoxical cold is a neat aspect of hot receptors.

8 Chemoreceptors respond to chemical stimuli. General chemoreceptors transmit information about total solute concentration. Specific chemoreceptors respond to specific types of molecules. Internal chemoreceptors respond to glucose, O 2, CO 2, amino acids, etc. External chemoreceptors are gustatory (taste) receptors and olfactory (smell) receptors. Try tasting something while you hold your nose and you will experience the connection.

9 Electromagnetic receptors respond to electromagnetic energy. Photoreceptors respond to the radiation we know as visible light. Electroreceptors: some fish use electric currents to locate objects.

10 1. A diversity of photoreceptors has evolved among invertebrates watch here Eye cups are among the simplest photoreceptors Detect light intensity and direction no image formation. The movement of a planarian is integrated with photoreception. Fig. 49.7

11 Image-forming eyes. Compound eyes of insects and crustaceans. Each eye consists of many ommatidia, each with its own light-focusing lens. This type of eye is very good at detecting movement. Flicker fusion rate? Fig. 49.8

12 Single-lens eyes of invertebrates such as jellies, polychaetes, spiders, and mollusks. The eye of an octopus works much like a camera and is similar to the vertebrate eye, even though it evolved independently (an example of what kind of evolution?). But the HOX gene is the same!!

13 Does someone you know have bug-eyes? Yes. More than you think!!! In a classic example of how evolution and development work, the Pax-6 hox gene for eye formation is shared by ALL animals, no matter what type of eye (compound, camera, etc.). The gene even remains as a fossil gene in eyeless animals.

14 So how do you go from simple eyes to complex ones??? Here is how it DOESN T work all at once. This is a BIG misconception about how evolution works. We have seen it before with that bacterial flagella example, but this idea that complex things evolve all at once is NOT how it works. The misconception still persists, however, which is why we need to EDUCATE. Example??? Watch here, starting at 24:30.

15 2. Vertebrates have single-lens eyes Short version of how it works. Ted Talk 19 min. Fig. 49.9

16 Photoreceptors of the retina. These are sensory neurons. About 125 million rod cells. Rod cells are triggered by low light intensity, but do not distinguish colors. About 6 million cone cells. Not as light sensitive as rods but provide color vision. Most highly concentrated on the fovea an area of the retina that lacks rods.

17 3. The pigment rhodopsin triggers a signaltransduction pathway Rhodopsin (retinal + opsin) is the visual pigment of rods. The absorption of light by rhodopsin initiates a signaltransduction pathway. Fig

18 Color reception is more complex than the rhodopsin mechanism. There are three subclasses of cone cells (red, blue and green) each with its own type of photopsin. Color perception is based on the brain s analysis of the relative responses of each type of cone. In humans, colorblindness is due to a deficiency, or absence, of one or more photopsins. Inherited as an X-linked trait.

19 4. The retina assists the cerebral cortex in processing visual information Visual processing begins with rods and cones synapsing with bipolar cells. Bipolar cells synapse with ganglion cells. Visual processing in the retina also involves horizontal cells and amacrine cells. Follow the path of the stimulus (light) and the nerve impulse it generates

20 Fig

21 The optic nerves of the two eyes meet at the optic chiasm. Where the nasal half of each tract crosses to the opposite side. Ganglion cell axons make up the optic tract. Most synapse in the lateral geniculate nuclei of the thalamus. Neurons then convey information to the primary visual cortex of the optic lobe. Fig

22 2. The inner ear also contains the organs of equilibrium Behind the oval window is a vestibule that contains the utricle and saccule. The utricle opens into three semicircular canals.

23 Fig

24 The utricle and saccule respond to changes in head position relative to gravity and movement in one direction. Hair cells are projected into a gelatinous material containing otoliths (hearing rocks). When the head s orientation changes the hair cells are tugged on, resulting in a nerve impulse along a sensory neuron.

25 The semicircular canals respond to rotational movements of the head. The mechanism is similar to that associated with the utricle and saccule.

26 This organ is involved in how one gets the spins when one drinks too much Alcohol diffuses into the gel of the inner ear. Let s pour some alcohol into some oil Mixed with alcohol, the gel in your inner ear swirls just like this. The swirling pushes the hair cells and our brain thinks we are moving. Now the you are moving message gets sent to our eyes

27 Policemen know their physiology! The brain sends the you re moving message to your eye muscles, which twitch in one direction (usually to the right) to try to track the objects which seem to be moving. This twitch is called nystagmus, and it is one thing police will look for in people they stop for driving erratically. Not done yet! The spins may return as your liver breaks down the alcohol in your blood, and the alcohol still in your inner ear starts to diffuse out, setting the gel to swirling again!

28 4. Muscles move skeletal parts by contracting Muscles come in antagonistic pairs. Hormones?? Fig

29 Find this in your book on-line. Or, see this from Texas A&M estruccontractswf/index.html The sarcomere is the functional unit of muscle contraction. Thin filaments consist of two strands of actin and one tropomyosin coiled about each other. Thick filaments consist of myosin molecules. Fig

30 5. Interactions between myosin and actin generate force during muscle contractions The sliding-filament model of muscle contraction. Fig

31 6. Calcium ions and regulatory proteins control muscle contraction At rest tropomyosin blocks the myosin binding sites on actin. When calcium binds to the troponin complex a conformational change results in the movement of the tropomyosintropinin complex and exposure of actin s myosin binding sites. Fig

32 But, wherefore art the calcium ions? Follow the action potential. When an action potential meets the muscle cell s sarcoplasmic reticulum (SR) stored Ca 2+ is released. Fig

33 Watch the action.. At the Neuro-Muscular Junction Where do our little friends the cone snails fit in?? See here and here.

34 Muscle fatigue: a new bad guy!! Lactic acid used to be thought of as the fatigue causing agent in muscles. How and when is it produced? New studies show that when a muscle is repeatedly contracted the sarcoplasmic reticlulum will get a bit leaky, and the calcium leaking into the sarcomeres will decrease their ability to contract. A drug was developed to counteract the leaking, and it gave rats up to 20% more endurance in treadmill tests. So, count on reading about this one soon when endurance athletes start taking it

35 Fast and Slow Muscle Fibers. Fast twitch (white) muscle fibers are adapted for rapid, powerful contractions. Fatigue relatively quickly. Great sprinters like FSU s Walter Dix, 7 time NCAA champion and Olympic bronze medalist, have a high % of them.

36 Slow twitch (red) muscle fibers are adapted for sustained contraction. Relative to fast fibers, slow fibers have. Less SR Ca 2+ remains in the cytosol longer. More mitochondria, a better blood supply, and myoglobin. Great marathoners have lots of these.

37 What s the difference between fat and slow twitch fibers??? It s the myosin. There are about 40 different kinds, and they vary in the speed at which they can attach to actin, pull, release and attach again. The fastest combinations are found in the flight muscles of insects, and the slowest are in the muscles of sloths and tortoises. You mainly get your particular combination from your parents via genes.

38 Other Types of Muscle. In addition to skeletal muscle, vertebrates have cardiac and smooth muscle. Cardiac muscle: similar to skeletal muscle. Intercalated discs facilitate the coordinated contraction of cardiac muscle cells. Can generate there own action potentials. Action potentials of long duration.

39 Fig. 40.4

40 Smooth muscle: lacks the striations seen in both skeletal and cardiac muscle. Contracts with less tension, but over a greater range of lengths, than skeletal muscle. No T tubules and no SR. Ca 2+ enters the cytosol from outside, via the plasma membrane. Slow contractions, with more control over contraction strength than skeletal muscle. Found lining the walls of hollow organs.