Sensory and Motor Mechanisms Chapter 49

Sensing and Acting Bats use sonar to detect their prey Moths  can detect the bat’s sonar and attempt to flee Both of these organisms have complex sensory systems that facilitate their survival

Types of Sensory Receptors Based on the energy they transduce, sensory receptors fall into five categories  Mechanoreceptors  Chemoreceptors  Electromagnetic receptors  Thermoreceptors  Pain receptors

Mechanoreceptors Mechanoreceptors sense physical deformation  Caused by stimuli such as pressure, stretch, motion, and sound The mammalian sense of touch  Relies on mechanoreceptors that are the dendrites of sensory neurons

Figure 49.4 Mechanoreception by a hair cell

Chemoreceptors General receptors that transmit information about the total solute concentration of a solution Specific receptors that respond to individual kinds of molecules EX: Taste, Smell

Figure 49.5 Chemoreceptors in an insect: Female silk moth Bombyx mori releasing pheromones; SEM of male Bombyx mori antenna

Figure 49.x1 Chemoreceptors: Snake tongue

Electromagnetic Receptors Electromagnetic receptors detect various forms of electromagnetic energy  Such as visible light, electricity, and magnetism Some snakes have very sensitive infrared receptors  That detect body heat of prey against a colder background

Figure 49.6 Specialized electromagnetic receptors: Rattle snake with infrared recpters, beluga whale pod

Figure 49.6bx Beluga whale pod Many mammals appear to use the Earth’s magnetic field lines  To orient themselves as they migrate

Thermoreceptors Thermoreceptors, which respond to heat or cold  Help regulate body temperature by signaling both surface and body core temperature

Pain Receptors In humans, pain receptors, also called nociceptors  Are a class of naked dendrites in the epidermis  Respond to excess heat, pressure, or specific classes of chemicals released from damaged or inflamed tissues

The mechanoreceptors  hearing and equilibrium detect settling particles or moving fluid Hearing and the perception of body equilibrium  are related in most animals Three regions of the human ear  The outer ear  The middle ear  The inner ear

Ear Structure The outer ear  external pinna and the auditory canal Collects sound and directs it to the tympanic membrane (eardrum)

Middle Ear Three small bones  malleus (hammer), the incus (anvil) and stapes (stirrup)  collect vibrations The eustacian tube  equalizes air pressure between the outer and middle ear

The Cochlea Snail shaped structure  organ of corti Cochlea Stapes Oval window Apex Axons of sensory neurons Round window Basilar membrane Tympanic canal Base Vestibular canal Perilymph

Hearing Vibrating objects create percussion waves in the air  That cause the tympanic membrane to vibrate The three bones of the middle ear  Transmit the vibrations to the oval window on the cochlea These vibrations create pressure waves in the fluid in the cochlea  That travel through the vestibular canal and ultimately strike the round window

The pressure waves in the vestibular canal  Cause the basilar membrane to vibrate up and down causing its hair cells to bend The bending of the hair cells depolarizes their membranes  Sending action potentials that travel via the auditory nerve to the brain

Figure How the cochlea distinguishes pitch

Figure Organs of balance in the inner ear

Senses of Taste and Smell Are closely related in most animals The perceptions of gustation (taste) and olfaction (smell)  Are both dependent on chemoreceptors that detect specific chemicals in the environment

Taste in Humans The receptor cells for taste in humans  Are modified epithelial cells organized into taste buds Five taste perceptions involve several signal transduction mechanisms  Sweet, sour, salty, bitter, and umami (elicited by glutamate)

Figure 49.2 Sensory transduction by a taste receptor

Smell in Humans Olfactory receptor cellsAre neurons that line the upper portion of the nasal cavity When odorant molecules bind to specific receptors  A signal transduction pathway is triggered, sending action potentials to the brain

Olfaction in Humans

Vision in the Animal Kingdom Two major types of image-forming eyes have evolved in invertebrates  The compound eye and the single-lens eye Compound eyes are found in insects and crustaceans  And consist of up to several thousand light detectors called ommatidia Single-lens eyes  Are found in some jellies, polychaetes, spiders, and many molluscs  Work on a camera-like principle

Simplest Eye The eye cup of planarians  provides information about light intensity and direction but does not form images

Figure 49.8 Compound eyes (a)

Vertebrate Eyes Camera-like  they evolved independently and differ from the single-lens eyes of invertebrates The main parts of the vertebrate eye are  The sclera, which includes the cornea  The choroid, a pigmented layer  The conjunctiva, that covers the outer surface of the sclera  The iris, which regulates the pupil  The retina, which contains photoreceptors  The lens, which focuses light on the retina

Structure of the Human Eye

Focusing of the Mammalian Eye

Photoreceptors The human retina contains two types of photoreceptors  Rods are sensitive to light but do not distinguish colors  Cones distinguish colors but are not as sensitive

Figure From light reception to receptor potential: A rod cell’s signal-transduction pathway

The effect of light on synapses between rod cells and bipolar cells

Figure The vertebrate retina

Neural pathways for vision

The Human Skeleton Functions in support, protection, & movement Animal movements result from muscles working against some type of skeleton The mammalian skeleton is built from more than 200 bones  Some fused together and others connected at joints by ligaments that allow freedom of movement

The Human Skeleton

Muscles contraction Move Skeletal Parts The action of a muscle  always to contract Skeletal muscles are attached to the skeleton in antagonistic pairs  With each member of the pair working against each other

Vertebrate Skeletal Muscle Is characterized by a hierarchy of smaller and smaller units A skeletal muscle consists of a bundle of long fibers  Running parallel to the length of the muscle A muscle fiber  Is itself a bundle of smaller myofibrils arranged longitudinally Skeletal muscle is also called striated muscle  Because the regular arrangement of the myofilaments creates a pattern of light and dark bands

The myofibrils are composed to two kinds of myofilaments  Thin filaments, consisting of two strands of actin and one strand of regulatory protein  Thick filaments, staggered arrays of myosin molecules Each repeating unit is a sarcomere  Bordered by Z lines The areas that contain the myofilments  Are the I band, A band, and H zone

Skeletal Muscle

The sliding-filament model of muscle contraction The filaments slide past each other longitudinally, producing more overlap between the thin and thick filaments As a result of this sliding  The I band and the H zone shrink The sliding of filaments is based on  The interaction between the actin and myosin molecules of the thick and thin filaments The “head” of a myosin molecule binds to an actin filament  Forming a cross-bridge and pulling the thin filament toward the center of the sarcomere

The sliding-filament model of muscle contraction

One hypothesis for how myosin-actin interactions generate the force for muscle contraction

Hypothetical mechanism for the control of muscle contraction

Review of skeletal muscle contraction

Types of Skeletons The three main functions of a skeleton are  Support, protection, and movement The three main types of skeletons are  Hydrostatic skeletons, exoskeletons, and endoskeletons

Hydrostatic Skeletons A hydrostatic skeleton  Consists of fluid held under pressure in a closed body compartment This is the main type of skeleton  In most cnidarians, flatworms, nematodes, and annelids Annelids use their hydrostatic skeleton for peristalsis  A type of movement on land produced by rhythmic waves of muscle contractions

Exoskeletons An exoskeleton is a hard encasement  Deposited on the surface of an animal  Are found in most molluscs and arthropods

Endoskeletons An endoskeleton consists of hard supporting elements  Such as bones, buried within the soft tissue of an animal Endoskeletons  Are found in sponges, echinoderms, and chordates