Ability to distinguish stimuli depends on the brain:

Transcription

1 1 Chapter 50: Sensory / Motor Mechanisms Campbell et al. Figure 50.2 Ability to distinguish stimuli depends on the brain: Sensations: Electrical impulses that reach the brain via sensory neurons Perceptions: Interpretation of electrical impulses by the brain Pathway of a stimulus: Amplification Strengthening of stimulus signal Intensity = AP frequency Low intensity Sensory Adaptation Decrease in responsiveness over time Exteroreceptors (external) Interoreceptors (internal) High intensity (1) Reception Receptor detects stimuli (2) Transduction Stimuli converted to electrical impulse (3) Transmission Signal conducted to CNS (4) Summation Integration of signal by CNS Page 1

2 Sensory receptors are categorized by the type of energy they transduce: 1) Mechanoreceptors: Stimulated by physical deformation (e.g., touch) Muscle spindles = stretch receptors monitoring skeletal muscle length Hair cells = receptors detecting motion (e.g., hearing) 2) Nociceptors (pain receptors): Stimulated by inflamed / damaged tissue 3) Thermoreceptors: Stimulated by heat / cold 4) Chemoreceptors: Stimulated by specific molecule types Osmoreceptors = detect changes in [solute] Gustatory (taste) / Olfactory (smell) receptors 5) Electromagnetic receptors: Stimulated by electromagnetic energy Magnetic Field Heat Light Campbell e t al. Figure Photoreceptors and Vision: Invertebrates: A) Light Detection Eyes: Planaria Ocellus Allows for detection of light intensity / directionality B) Image-Forming Eyes: 1) Compound Eye (insects / crustaceans) Consists of multiple ommatidia (facets) Accurate at detecting movement 2) Single-lens Eye (Spiders / mollusks) Campbell et al. Figure Page 2 2

3 3 Campbell et al. Figure Photoreceptors and Vision: Vertebrates: A) Single-lens Eye: Cornea: Transparent; allows light into eye Pupil: Regulates amount of light entering eye Lens: Focuses image onto back of eye Fish = move lens forward / back Mammals = change shape of lens Retina: Inner surface of eye; contains photoreceptors Rods (125 million) = light sensitive Cones (6 million) = color sensitive Color vision common in lower vertebrates but rare in mammals WHY? Campbell et al. Figure Physiology of Vision (example = rods): A) Rhodopsin (light absorbing structure) triggers signal-transduction pathway: Opsin = membrane protein Retinal = light-absorbing pigment When rhodopsin absorbs light, the retinal changes shape and separates from opsin Why does it take several minutes for eyes to adjust to dark? Bleaching Separation of retinal Page 3

4 Physiology of Vision (example = rods): A) Rhodopsin (light absorbing pigment) triggers signal-transduction pathway: Altered opsin (minus retinal) triggers enzymatic pathway (similar to Figure 50.21): IMPORTANT FACT: Light does not depolarize rod cell, but hyperpolarizes it Campbell et al. Figure Physiology of Vision (example = rods): B) Retina assists cerebral cortex in processing visual information Vertical Pathway: Rod Bipolar Cell Ganglion Cell Lateral Pathway: Horizontal / Amacrine cells link neighboring cells Lateral Inhibition: Horizontal cells inhibit nearby rods from firing (sharpens edges / enhances contrast) Campbell et al. Figure Page 4 4

5 5 Skeletal System: Supporting framework for the body Types of Animal Skeletons: 1) Hydrostatic Skeleton Fluid-filled compartments provide support (via pressure) Movement = contraction of: 1) Circular muscles 2) Longitudinal muscles Peristalsis Ideal for aquatic life Limited vertical support Who: Cnidarians Flatworms Nematodes Annelids Campbell et al. Figure Page 5

6 6 Skeletal System: Supporting framework for the body Types of Animal Skeletons: 2) Exoskeleton (e.g., insects, crustaceans) Rigid, encasement deposited on surface of organism Chitin (modified polysaccharide) / Calcium carbonate Muscles attach from outer shell to interior of body Chitin Must be periodically shed 3) Endoskeleton (e.g., mammals) Rigid, internal skeleton supporting body (e.g., plates / bones) Benefits: Can grow with organism; relatively lightweight Human Skeleton = 206 bones Axial skeleton Skull, vertebral column, rib cage Appendicular Skeleton Upper / Lower limbs Tissue Types: 1) Cartilage (flexible support / connections) 2) Bone (rigid support - matrix) Bones connected at joints: 1) Hinge joint: 2 - dimensional movement (e.g., elbow) 2) Ball-and-socket joint: 3 - dimensional movement (e.g., hip) Page 6

7 Function of Muscle: 1) Produce movement Locomotion / manipulation (skeletal) Campbell et al. Figure Blood pressure (cardiac) Propulsion (smooth) 2) Maintain posture 3) Support soft tissue (e.g., abdominal wall) 4) Guard entrance / exit (e.g., lips / anus) 5) Maintain body temperature (endotherms) Prune Belly Syndrome Page 7 7

8 Gross Anatomy of Muscle: Connective Tissue Layers: Epimysium: Outside muscle covering Form tendons Perimysium: Compartments Divides muscle into fascicles Contains blood vessels/nerves Endomysium: Surrounds individual muscle fibers & ties them together Page 8 8

9 9 Microanatomy of Muscle: Muscle Fiber (cell): Functional Unit of Muscle Multi-nucleated Sarcolemma: Cell membrane Sarcoplasma: Cytoplasm Triad Transverse Tubules: Network of passageways through fiber Continuous with outside of cell Sacroplasmic Reticulum: Specialized endoplasmic reticulum Contain calcium ions (Ca ++ ) Myofibrils: Cylindrical structures containing contractile fibers Microanatomy of Muscle: Myofibrils contain myofilaments (protein) : 1) Actin (Thin filament) 2) Myosin (Thick filament) Sarcomere: Repeating units of myofilaments (~ 10,000 / cell) Sarcomere Actin Myosin I Band M line Z line A Band Page 9

10 10 Microanatomy of Muscle: Sliding Filament Theory Interactions between the thick and thin filaments of sarcomeres are responsible for muscle contraction Thick filaments: Composed of many myosin molecules Tails: Attach molecules together Heads: Bind with thin filament Hinge Page 10

11 11 Microanatomy of Muscle: Sliding Filament Theory Interactions between the thick and thin filaments of sarcomeres are responsible for muscle contraction Thick filaments: Composed of many myosin molecules Thin filaments: Composed of interwoven actin molecules Tails: Attach molecules together Heads: Bind with thin filament Tropomyosin: Cover active sites Troponin: Bind tropomyosin to actin Microanatomy of Muscle: Sliding Filament Theory Interactions between the thick and thin filaments of sarcomeres are responsible for muscle contraction Page 11

12 Neuron Synaptic Knob ACh ACh ACh Neuromuscular Junction: Neuron Muscle fiber 1 connection / muscle fiber T-tubule Sarcolemma Motor End Plate Sarcoplasmic Reticulum Sarcoplasm Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Muscle Contraction Events: Sarcomere of myofibril 1) Acetylcholine (ACh - neurotransmitter) released from synaptic knob 2) ACh binds to receptors on motor end plate; generates AP 3) Action potential (AP - electrical impulse) conducted along sarcolemma Neuron Synaptic Knob ACh ACh ACh Neuromuscular Junction: Neuron Muscle fiber 1 connection / muscle fiber T-tubule Sarcolemma Motor End Plate Sarcoplasmic Reticulum Sarcoplasm Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Ca ++ Sarcomere of myofibril Muscle Contraction Events: 4) AP descends into muscle fiber via T-tubules 5) AP triggers release of Ca ++ from sarcoplasmic reticulum 6) Ca ++ initiates cross-bridging (actin / myosin) Page 12 12

13 Cross-Bridging in Action: 1) Ca ++ binds with troponin; exposes active sites on actin Cross-bridging Events: Ca ++ Actin Troponin Tropomyosin Myosin Head Page 13 13

14 Cross-Bridging in Action: 1) Ca ++ binds with troponin; exposes active sites on actin 2) Myosin head (cocked) binds with active site 3) Myosin head pivots pulls actin forward Cross-bridging Events: Page 14 14

15 Cross-Bridging in Action: 1) Ca ++ binds with troponin; exposes active sites on actin 2) Myosin head (cocked) binds with active site 3) Myosin head pivots pulls actin forward 4) ATP binds to myosin head; head detaches and re-cocks Cross-bridging Events: Re-cock ATP ADP P ATP Page 15 15

16 Cross-Bridging in Action: Cross-bridging Events: 1) Ca ++ binds with troponin; exposes active sites on actin 2) Myosin head (cocked) binds with active site 3) Myosin head pivots pulls actin forward 4) ATP binds to myosin head; head detaches and re-cocks 5) Myosin head binds to active site; Process repeated Energy = Creatine phosphate Re-cock ATP Re-cock ATP ADP ADP P ATP P Page 16 16

17 Cross-Bridging in Action: Cross-bridging Events: 1) Ca ++ binds with troponin; exposes active sites on actin 2) Myosin head (cocked) binds with active site 3) Myosin head pivots pulls actin forward 4) ATP binds to myosin head; head detaches and re-cocks 5) Myosin head binds to active site; Process repeated Energy = Creatine phosphate 6) Process ends when APs cease ACh broken down by acetylcholinesterase (AChE) Ca ++ returned to sarcoplasmic reticulum (active transport) Campbell et al. Figure Rigor Mortis Lou Gerig s Disease (ALS) Tetanus Botulism Page 17 17

18 Tension Stimulus Muscle Mechanics: Muscle Tension: Force exerted on an object by a contacting muscle What Regulates Muscle Tension Production? 1) Number of muscle fibers activated: Diverse body movements require variation in muscle activity Motor Unit: A single motor neuron and all the muscle fibers innervated by it Recruitment: Addition of motor units to produce smooth, steady muscle tension (small large motor units) Motor unit size dictates control: Fine Control = 1-5 fibers / MU (e.g., eye) Gross Control = 1000 s fibers / MU (e.g., leg) All-or-none response Muscle Mechanics: Muscle Tension: Force exerted on an object by a contacting muscle 2) Frequency of stimulation: What Regulates Muscle Tension Production? Twitches alone are not a useful contraction Twitch = Single stimulus-contraction-relaxation sequence Latent Period: Time between stimulus and tension development CP RP Contraction Phase: Period where tension rises to peak level Ca ++ release; cross-bridge formation Relaxation Phase: Period where tension falls to resting level Ca ++ uptake; cross-bridge detachment LP Time Page 18 18

19 Tension Tension Stimulus Stimulus 19 Muscle Mechanics: Muscle Tension: Force exerted on an object by a contacting muscle What Regulates Muscle Tension Production? 2) Frequency of stimulation: Incomplete Tetanus: Rapid cycles of contraction & relaxation Maximum Tension Summation: Addition of twitches to produce a more powerful contraction Time Muscle Mechanics: Muscle Tension: Force exerted on an object by a contacting muscle What Regulates Muscle Tension Production? 2) Frequency of stimulation: Complete Tetanus: Rapid stimulation erases relaxation phase Maximum Tension SR can not reclaim Ca ++ (stimulation too rapid) Most normal muscle contraction involves complete tetanus Time Page 19

20 Degree of Muscle Stretch can also Affect Muscle Performance: Too contracted = no room for movement; poor cross-bridge formation Resting length = # of cross-bridges; distance to slide Too stretched = no cross-bridge formation (maximal muscle force is near / at normal resting length) Property Skeletal Muscle: Cardiac Muscle: Smooth Muscle: Filament Organization Sarcomeres along myofibrils Sarcomeres along myofibrils Scattered in sarcoplasm Control Mechanism Neural Automaticity (pacemaker cells) Automaticity, neural, hormonal Calcium Source Sarcoplasmic reticulum SR / across sarcolemma Across sarcolemma Contraction Rapid onset; tetanus can occur; rapid fatigue Slower onset; no tetanus; fatigue-resistant Slow onset; tetanus can occur; fatigue-resistant Energy Source Aerobic / Anaerobic metabolism Aerobic metabolism Aerobic metabolism Page 20 20