Ch. 50 Sensory and Motor Mechanisms

Sensory Receptor

converts stimulus energy into a change in the membrane potential

• motor response generated = simple reflex

• 4 pathways: Sensory Reception, Transduction, Transmission, Perception

Sensory Reception

Begins sensory pathway, detection of stimuli by sensory receptors

• sensory cells or organs

• interact with stimuli inside/outside of body

Transduction

conversion of stimulus energy into a change in the membrane potential of a sensory receptor

• receptor potential (graded, magnitude varies with strength of stimulus)

Transmission

Sensory information travels through the nervous system as action potentials

• Inc receptor potential with inc of intensity of stimulus

Perception

are the brain’s construction of stimuli

• travel along certain neural pathways

Amplification and Adaptation

Amp: the strengthening of a sensory signal during transduction

Adapt: decrease in responsiveness to continued stimulation

• EX: amoeba

Types of Sensory Receptors (5)

1. Mechanoreceptors

2. Chemoreceptors

3. Electromagnetic receptors

4. Thermoreceptors (detect heat + cold: snakes, capsaicin)

5. Pain receptor

Mechanoreceptors

sense physical deformation caused by forms of mechanical energy

• consists of “hairs” (cilia) outside the cell + relies on dendrites of sensory neurons

• EX: hearing + perception (moving fluid)

Chemoreceptors

transmit information about the total solute concentration of a solution or respond individually

• becomes more/less permeable to ions when stim mole binds

• EX: antennae of silkworm moth

Electromagnetic Receptors

detect electromagnetic energy such as light, electricity, and magnetism

• EX: platypus bill + migration

Pain Receptor/Nociceptors

detect stimuli that reflect harmful conditions

• respond to excess heat, pressure, chemicals released by damaged/inflamed tissue

Statocysts

how most invertebrates maintain equilibrium using mechanoreceptors

• Can detect movement of statoliths (info about body position + gravity)

Tympanic Membrane

Localized organs that detect sound + stretched over an internal air chamber

• EX: insects

Hearing in mammals (9)

• Mechanoreceptors

1. Vibrating objects create pressure waves in the air

2. Ear turns into nerve impulses

3. Sounds heard by hair cells that detect motion

4. air in outer ear causes vibration of tympanic membrane

5. 3 bones in middle ear transmit vibs to oval window

6. Pressure waves created in fluid inside cochlea

7. Push down on cochlear duct + basilar mem (hair cell up/down)

8. Action potential sent to auditory nerve

9. Wave dissipates after striking round window at end of tympanic canal

What information does ear capture? (2)

1. Volume: amplitude of sound wave

2. Pitch: freq of sound wave

Organs in inner ear (2)

1. Utricle + Saccule: hair cell project into gelatinous material

2. Otoliths

Otoliths

granule embedded in gel, allow us to perceive position relative to gravity or linear movement

• if lacking, have poor ability to sense motion + orient gravity

• EX: estimate age of fish (lateral line for H2O move)

Light detectors

simple clusters of cells that detect direction + intensity of light to complex organs that form images

• Contain photoreceptors (contain light-absorbing pigment moles)

• EX: invertebrates (Planarians = ocelli “eyespots”)

Compound eyes

Insects, crustaceans, and some polychaete worms have ommatidia (several thousand light detectors )

• Can see into ultraviolet range

Single-lens eyes

Invertebrates: jellies, polychaete worms, spiders, molluscs

Iris changes diameter of pupil to control amount of light

Vertebrate Visual System (6)

• photoreceptor

1. Choroid (thin, pigment (photopsins) layer) contains retina

2. Lens: transparent disk of protein

   1. Front: clear, water aq humor

   2. Behind: Jelly vitreous humor

3. Rod (light) + Cones (color- red,green,blue “Ishihara color test”)

4. Optic Nerve (at cerebral cortex )sends visual info to brain

5. Optic disk = blind spot

Retinal

a light-absorbing pigment bound to a opsin (membrane protein)

• EX: Rhodopsin

• light causes change in shape of retinal proteins

Abnormal color vision

results from mutations in the genes for one or more photopsin proteins

• studied squirrel monkeys = red-green color blind

Fovea

center of the visual field and contains no rods, but a high density of cones

• Nearsighted: long eyeballs/rounded corneas that focus light in front retina

• Farsighted: short eyeballs/flat corneas that focus light behind retina

Gustation and Olfaction

1. (taste) is dependent on the detection of chemicals called tastants

2. (smell) is dependent on the detection of odorant molecules

• Aquatic animals have no distinct

Taste buds

Receptor cells for taste in mammals are modified epithelial cells in several areas of tongue + mouth

• papillae are the projections

• sweet, sour, salty, bitter, umami

Olfactory receptor cells

neurons that line the upper portion of the nasal cavity

• binding odorant molecules trigger action potentials

Muscle Activity

response to input from the nervous system = contraction

• Thin filaments: actin

• Thick filaments: staggered mysoin

Skeletal Muscle

“striated muscle”

moves bones and the body and is characterized by a hierarchy of smaller and smaller units

• Long fiber to myofibrils (protein filaments)

• Sarcomere runs from one z-line to another + attaches to thin filament

Steps of Muscle Contraction (8)

1. Signal sent to motor neuron (action potential)

2. Releases neurotransmitters in synaptic gap near sarcolemma

3. Cause Ca²⁺ to be released in sarcoplasmic reticulum (SR) in transverse (T) tubules

4. Ca²⁺ causes tropomyosin to change shape + troponin frees actin binding sites

5. Now open, myosin binds to actin to form cross bridge

6. ATP (from glycolysis, aerobic respiration, or lactic acid fermentation) used for cross-bridge

7. Myosin moves actin along = sliding filmanent mechanism

8. Low calcium causes muscle to relax

Amyotrophic lateral sclerosis (ALS)

formerly called Lou Gehrig’s disease, interferes with the excitation of skeletal muscle fibers; this disease is usually fatal

Myasthenia gravis (MG)

an autoimmune disease that attacks acetylcholine receptors on muscle fibers; treatment exist for this disease

Graded Contractions classified (2)

1. Varying the number of fibers that contract

2. Varying the rate at which fibers are stimulated

• each fiber is controlled by ONE motor neuron = motor units

Recruitment

process by which more and more motor neurons are activated

• force developed by muscle increases throughout process

• Twitch: single action potential in neuron

  • More produced through summation

Tetanus

a state of smooth and sustained contraction produced when the rate of stimulation is so high that muscle fibers cannot relax between stimuli

Types of Skeletal Muscles (2)

classified by the source of ATP powering the muscle activity or by the speed of muscle contraction

1. Oxidative Fibers

2. Glycolytic Fibers

Oxidative Fibers

rely mostly on aerobic respiration to generate ATP

• mitochondria, a rich blood supply, and a large amount of myoglobin (protein, binds O2 tightly)

• EX: dark meat

Glycolytic Fibers

use glycolysis as their primary source of ATP

• less myoglobin, large diameter, tire easiely

• EX: light meat

Fast vs Slow Twitch Fibers

Fast: brief, powerful contractions (oxidative or glycolytic)

Slow: slow, sustained contractions (oxidative)

• less SR + slow pump of Ca²⁺

Cardiac Muscle

only in the heart, consists of striated cells electrically connected by intercalated disks

• generate action potentials w/out neural input

Smooth Muscle

in walls of hollow organs such as those of the circulatory, digestive, and reproductive system

• slow contractions (from neurons in autonomic nervous system)

Skeletal Muscle/Skeleton

attached in antagonistic pairs; actions are coordinated by the nervous system

• for support, protection, movement

1. Hydrostatic skeleton (fluid-based support)

2. Endoskeleton

3. Exoskeleton

Hydrostatic Skeleton

consists of fluid held under pressure in a closed body compartment

• EX: cnidarians, flatworms, nematodes, and annelids (use for peristalsis = rhythmic waves of contractions)

Swimming Locomotion

friction is a bigger problem than gravity

• need sleek, shape to min friction

• EX: paddling, undulating

Flying Locomotion

requires that wings develop enough lift to overcome the downward force of gravity

• must reduce body mass