Sensing, Acting, and Brains
1. Differentiate between Sensation and Perception.
Sensation involves converting energies to a change in the membrane potential of sensory
receptor cells and thereby regulating the output of action potentials to the central nervous
system. Turning stimuli into action potentials. We sense the stimulus.
Perception (Colors, smells, sounds, and tastes) are constructions formed in the brani and
do not exist outside it. Action potentials reach brain, bringing awareness of stimulus.
Ex: When someone is poking you. You first sense a poking (sensation), then you
immediately know that someone is poking you (perception).
Introduction to Sensory Reception
2. Explain the difference between exteroreceptors and interoreceptors.
Exteroreceptors detect stimuli outside the body (heart, light, pressure, chemicals)
Interoreceptors detect stimuli inside the body (blood pressure/body postion)
3. Describe the four general functions of receptor cells as they covert energy stimuli
into changes in membrane potentials and then transmit signals to the nervous
system.
The four general functions of receptor cells as they convert energy stimuli into changes in
membrane potentials and then transmit signals to the nervous system is
1) Sensory Transduction: The conversion of stimulus energy into electrochemical activity
of nerve impulses. Receptor potential: The initial response of the receptor to the stimulus
is a graded potential.
2) Amplification: The stimulus energy is often too weak to be carried into the nervous
system and must be amplified.
3) Transmission: Receptor/sensory cell: the intensity of the receptor potential will affect
the frequency of action potentials that travel as sensations to the CNS. Receptor →
sensory cell: Many sensory spontaneously generate signals at a low rate. A stimulus does
not really switch the production of action potentials no or off; it modulates their
frequency – CNS is sensitive not only to the presence or absence of a stimulus but also to
change in stimulus intensity.
4) Integration: summation. Sensory adaptation: a decrease in sensitivity during continued
stimulation-receptors are selective in the information they send to the CNS. The threshold
for transduction by receptor cells varies with conditions: sugar level
4. List and describe the energy stimulus of the five types of receptors.
The five types of receptors:
1) Mechanoreceptors – sense physical deformation caused by forms of mechanical
energy sych as pressure, touch, stretch, motion, and sound. Consist of ion channels that
are linked to structures that extend outside the cell (hair/Cilia), as well as internal cell
structure (cytoskeleton). *Detects muscle movements.
2) Chemoreceptors – transmit information about total solute concentration and specific
receptors that respond to individual kinds of molecules. Stimulus molecule binds to the
specific chemoreceptor on the membrane of the sensory cell and initiates changes in ion
permeability.
3) Electromagnetic Receptors – Detect various forms of electromagnetic energy (visible
light, electricity, and magnetism).
Ex: Photoreceptors, electromagnetic receptors that detect energy in the form of light, are
often organized into eyes.
4) Thermoreceptors – detect heat and cold. Located in the skin and in the anterior
hypothalamus. They send information to the body’s thermostat, located in the posterior
hypothalamus.
5) Pain Receptors – Extreme pressure or temperature, as well as certain chemicals, can
damage animal tissues. To detect stimuli that reflects noxious (harmful) conditions.
Photoreceptors and Vision
5. Compare and structure of, and the processing of light by, the eye cups of Planaria,
the compound eyes of insects, and the single-lens eyes of mollusks.
Planaria (eye cups) – Located in the head region and are surrounded on three sides of a
layer of darkly pigmented cells that block light. Light shining on the planarian stimulates
light-sensitive cells called photoreceptors in each ocellus only through the opening where
there are no pigmented cells. They are bilateral structures partly shielded from light by
layer of pigmented cells lining cup and responds to light by moving away from source
toward darkness.
Insects - Evolved compound eyes that provide info about patterns or images in
environment, each compound eye consists of many optical units called ommatidia; each
ommatidium has lens structure that directs light onto photoreceptor cells called retinula
cells. inner borders of retinula cells covered with microvilli that contain rhodopsin and
thus trap light. Microvilli of different retinual cells overlap and appear to form central rod
(rhabdom) down center of ommatidium. Axons from retinual cells communicate with
nervous system. Then crude, broken image communicated from compound eye to CNS of
insect.
Single lens – focuses light onto retina which consists of light-transducing receptor cells.
Muscles move lens forward or backward to focus images on the retina. Has small
opening (pupil) though which light enters eye. Adjustable iris (analogous to camera’s
shutter) changes diameter of pupil.
6. Using a Diagram of vertebrate eye, identify and give the function of each structure.
Sclera – a tough white outer layer of connective tissue.
Choroid – a thin pigmented inner layer
Cornea – lets light into the eye and act as a fixed lens.
Retina – forms the innermost layer of the eyeball and contains layers of neurons and
photoreceptors.
Lens and ciliary body – divide the eye into two cavities: an anterior cavity between the
cornea and the lens and a much larger posterior cavity behind the lens.
Aqueous humor – fills the anterior cavity (clear and watery).
Vitreous humor – constitutes most of the volume of the eye.
7. Describe the functions of the rod cells and cone cells of the vertebrate eye.
Rod cells are more sensitive to light but do not distinguish colors; they enable us to see at
night, but only in black and white.
Cones provide color vision, but, being less sensitive, contribute very little to night vision.
There are three types of cones, which however, acts differently to sensitivity across the
visible spectrum, providing an optimal response to red, green, or blue light.
8. Explain and compare how the rods and cones of the retina transducer the stimuli
into action potentials.
The rods and cones of the retina transduces the stimuli into action potentials by a bipolar
cell neuron called Ganglion cells which transmit the action potentials to the brain via
axons in the optic nerves. Together, the rods or cones that feed information to one
ganglion cell define a receptive field. The fewer rods or cones that supply a single
ganglion, the smaller the receptive field. A small receptive field results in a sharper
image, because the information as to hwere light struck the retina is more precise.
9. Explain how the retina assists the cerebral cortex in the processing of visual
information.
The retina assists the cerebal cortex in the processing of the visual information by taking
part in formulating what we actually “see”. Determine how these centers integrate such
components of our vision as color, motion, depth, shape, and detail. A point-by-point
information in the visual field is projected along neurons onto the visual cortex.
Hearing and Equilibrium
10. Using a diagram of the human ear, identify and give the function of each structure.
Outer ear consists of the external pinna and the auditory canal, which collect sounds
waves and channel them to the tympanic membrane (separating the outer and middle ear).
Middle ear has three bones – the malleus (hammer), incus (anvil), and stapes (stirrup)
transmit vibrations to the oval window, which is a membrane beneath the stapes.
Eustachian tube connects to the pharynx and equalizes pressure between the middle ear
and atmosphere. Inner ear consists of fluid-filled chambers, including the semicircular
canal, which function in equilibrium. Cochlea (snail) which is involved in hearing.
11. Explain how the mammalian ear functions as a hearing organ.
Ear pinnae (our “ear”) collects sound waves and directs them into auditory canal: leads
to actual hearing apparatus in middle and inner ear. Tympanic membrane (eardrum)
covers the end of auditory canal and vibrates in response to pressure waves traveling
down auditory canal. The middle ear (air filled cavity) lies on other side of tympanic
membrane. It open to throat at back of mouth via Eustachian tube(pressure equilibrates
between middle ear and outside world). The tympanic membrane will not vibrate
properly unless pressure is equalized on both sides. The middle ear contains three delicate
bones called ear ossicles: malleus (hammer), incus (anvil), and stapes (stirrup). Ossicles
transmit vibrations of eardrum to another flexible membrane called oval window (behind
oval window lies FLUID-FILLED inner ear), movements of oval window results in
pressure changes in inner ear; these pressure changes converted into action potentials.
The inner ear is long, tapered, coiled chamber called cochlea and are composed of three
parallel chambers separated by two membranes: Reissner’s membrane and basilar
membrane. Sitting on basilar membrane is organ of Corti which transduces pressure
waves into action potentials in auditory nerve. Organ of Corti contains hair cells whose
stereocilia are in contact with overhanging, rigid shelf called the tectorial membrane.
When basilar membrane flexes, tectorial membrane will bend hair cell stereocilia; hair
cells either depolarize or hyperpolarize thereby altering rate of action potentials sent to
brain by associated sensory neurons.
12. Explain how the mammalian ear functions to maintain body balance and
equilibrium.
Mammalian inner ear has two equilibrium organs that use hair cells to detect position of
body with respect to gravity.
- semicircular canals and vestibular apparatus
1) semicircular canals contain gelatinous capulae that are pushed one way or another
when changes in position of head causes the fluid in canals to shift. A capula is
gelatinous cap containing cluster of hair cells and detects head rotation and/or changes in
head rotation.
2) vestibular apparatus composed of utricle and saccule. It contain hair cells and tell body
which way is up but also inform of body’s fixed space or of any linear acceleration with
movement.
13. Compare the hearing and equilibrium systems found in nonmammalian vertebrates.
An ear of a fish does not open to the outside of the body and has no eardrum or cochlea.
The vibrations of the water caused by sound waves are conducted through the skeleton of
the head to a pair of inner ears, setting otoliths in motion and stimulating hair cells. The
fish perceives its movement through water or the direction and velocity of water currents
flowing over its body.
Most fishes/aquatic amphibians also have lateral line system along both sides of body.
Mechanoreceptors detect low-frequency waves ad water enters lateral line through pores
and flows along tube past mechanoreceptors.
14. Describe the structure and function of statocysts.
Statocysts is to sense gravity (hair cells) and maintain equilibrium. They consist of a
layer of ciliated receptor cells surrounding a chamber that contains one or more statoliths,
which are grains of sand or other dense granules. They can be found at the fringe of
jellies and at the base of antennules in lobsters and crayfish.
15. Explain how many insects detect sound.
Insect detect sound by the means of “ears” consisting of a tympanic membrane
(eardrum) stretched over an internal air chamber. Sound waves vibrate the ear drum,
stimulating receptor cells attached to the inside of the membrane and resulting in nerve
impulses that are transmitted to the brain.
Chemoreception: Taste and Smell
16. Explain how the chemoreceptors involved with taste and smell perform their
functions.
Perceptions of taste (gustation) and smell (olfaction) depend on chemoreceptors that
detect specific chemicals in environment. In terrestrial animals, taste is detection of
certain chemicals in solution and smell is detection of airborne chemicals; these
chemicals senses closely related and there is NO distinction in aquatic environments.
Taste receptors of insects located within sensory hairs called sensillae on feet and
mouthparts; tasting hair contains receptors responsive to particular class of chemicals.
Insects also smell airborne chemicals using olfactory sensillae usually located on
antennae, in humans and other mammals, senses of taste and smell are functionally
similar and interrelated. In both cases, small molecule must dissolve in liquid to reach
receptor cell and trigger the sensation molecule binds to specific protein in receptor cell
membrane, triggering depolarization of membrane and release of a neurotransmitter.
Receptor cells for taste are modified epithelial cells organized into taste buds scattered on
tongue and in mouth; most are on tongue associated with nipplelike projections called
papillae. Humans recognize four basic taste: sweet, sour, salty, and bitter. They create
action potentials that brain interprets, olfactory sense of mammals detects certain airborne
chemicals and are neurons that line upper portion of nasal cavity (send impulses directly
to olfactory bulb of brain).Receptive ends of cells contain cilia that extend into mucus
coating the nasal cavity and binds to specific receptor molecule on PM of olfactory cilia.
They also signal transduction pathway-->cAMP-->Na+-->action potential. Humans can
distinguish 1000s of different odors.
Movement and Locomotion
17. List the advantages and disadvantages associated with moving through
a) An aquatic environment
b) A terrestrial environment
c) Air
a) An aquatic environment: Overcoming gravity is less of problem in aquatic
environment because most animals are reasonably buoyant in water. Water is much
denser than air so resistance (friction) is a BIG problem. It’s sleek, fusiform (torpedolike)
shape is common adaptation of fast swimmers; swimming tends to be most energyefficient means of locomotion. Swimming has diverse forms like using legs as oars, jet
propelled (taking in water and squirting it out in bursts), moving body and tail side to
side, and undulating body and tail up and down.
b) A terrestrial environment: terrestrial locomotion requires animal to support itself and
move against gravity. Leg muscles expend energy to propel animal and keep it from
falling down with each step, leg muscles must overcome inertia. Movement on land
(walk, run, hop, or crawl) requires powerful muscles and strong skeleton. Crawling
animal must exert considerable force to overcome friction.
c) Air: Flying animals has to overcome gravity. Uses more energy than swimming or
running animals even with the same body mass. Have structural adaptations that
contribute to low body mass.
18. Describe three functions of a skeleton.
Three functions of a skeleton:
1) Hydrostatic Skeleton: Consist of fluid held under pressure in a closed body
compartment. Main type of skeleton in most cnidarians, flatworms, nematodes, and
annelids. Control their form and movement by using muscles to change the shape of
fluid-filled compartments. Annelids use their hydrostatic skeleton for peristalsis; a type of
movement produced by rhythmic waves of muscle contractions passing from front to
back.
2) Exoskeleton: Hard encasement deposited on an animal’s surface. Muscles are attached
to knobs and plates if the cuticle that extend into the interior of chitin, a polysaccharide
similar to cellulose (are embedded in a protein matrix, forming a composite material that
combines strength and flexibility). The cuticle is hardened with organic compounds that
cross-link of the exoskeleton.
3) Endoskeleton: Consist of hard supporting elements, such as bones, buried within the
soft tissues of an animal. They are found in sponges, echinoderms, and chordates. They
mammalian skeleton is built from more than 200 bones, some fused together and others
connected at joints by ligaments that allow freedom of movement.
19. Describe how hydrostatic skeletons function and explain why they are not found in
large terrestrial organisms.
Hydrostatic function as a fluid held under pressure in a close body compartment. They
are not found in large terrestrial organisms because it cannot support terrestrial activity in
which an animal’s body is held off the ground, such as walking or running.
20. Explain how the structure of the arthropod exoskeleton provides both strength and
flexibility.
The structure of the arthropod exoskeleton provides both strength and flexibility because
the muscles are attached to knobs and plates of the cuticle that extend their interior of the
body which consists 30-50% of chitin, a polysaccharide similar to cellulose. When a
fibrils of chitin are embedded in a protein matrix, it forms a composite material that
combines strength and flexibility.
21. Distinguish between an exoskeleton and endoskeleton.
Exoskeleton – a hard encasement deposited on an animal’s surface.
Endoskeleton – a hard supporting elements, such as bones, buried within the soft tissues
of an animal.
22. Explain how the skeleton combines with an antagonistic muscle arrangement to
provide a mechanism for movement.
The skeleton combines with an antagonistic muscle arrangement to provide a mechanism
for movement is based on contraction of muscles working against some type of skeleton.
In endoskeleton of vertebrates is internal scaffolding to which muscles can attach and
against which they can pull; do NOT provide protection that exoskeleton does, but
advantage is that it can GROW because bones are inside body, the body can enlarge
without shedding its skeleton. Action of a muscle is always to CONTRACT and the
ability to move parts of body in opposite direction requires that muscles be attached to
skeleton in antagonistic pairs; means each muscle works against the other of the pair.
Flex our arm by contracting the biceps with hinged joint of elbow acting as the fulcrum
of a lever to extend the arm, we relax the biceps while triceps on opposite side contracts.
23. Explain how body proportions and posture impact physical support on land.
The strength of a building support depends on its cross-sectional area, which increases
the square of its diameter. And the strain on the supports depends on the building’s
weight, increases as the cube of its height or other linear dimension.
24. Using a diagram, indentify the components of the skeletal muscle cell.
Vertebrate skeletal muscle attached to bones and responsible for movement and are
characterized by hierarchy of smaller and smaller parallel units. Skeletal muscle consists
of bundle of long fibers running length of muscle. Each fiber is single cell with many
nuclei and each fiber is itself a bundle of smaller myofibrils arranged longitudinally.
Myofibrils are composed of two kinds of myofilaments: thin filaments composed of two
strands of actin and one strand of regulatory protein and thick filaments are staggered
arrays of myosin molecules; also called striated muscle because regular arrangement of
myofilaments creates repeating pattern of light and dark bands. Each repeating unit is a
sarcomere, the borders of the sarcomere, Z LINES, are lined up in adjacent myofibrils
and contribute to striations visible with scope. The thin filaments (actin) are attached to Z
lines and project toward center of the sarcomere. The thick filaments (myosin) are
centered in the sarcomere. At rest, thick and thin filaments DO NOT overlap completely.
25. Explain how muscles contract.
When muscle fibers activated by nervous system, cross bridges on myosin attach to
myosin binding sites on the thin filaments (actin). Each cross bridge attaches and
detaches several times during contraction and pulls thin filaments toward the center of
sarcomere. As this event occurs simultaneously in sarcomeres throughout cell, muscle
cell shortens, Z lines move closer together, H zone disappears, and A bands move closer
together but do NOT change in length. The contraction of millions of sarcomeres in
millions of fibers results in contraction of entire skeletal muscle
26. Explain how muscle contraction is controlled.
Muscle contraction is controlled by motor neurons triggering release of CA2+ into the
cytosol of muscle cells with which they form synapses. When motor neuron input stops,
the muscle cell relaxes. As it relaxes, the filaments slide back to their starting position.
27. Explain how the nervous system produces graded contractions of whole muscles.
The nervous system produces graded contractions of whole muscles by varying the
number of muscle fibers that contract and by varying the rate at which muscle fibers are
stimulated.
28. Explain the adaptive advantages of slow and fast muscle fibers.
The adaptive advantage of slow muscle fibers is that they have les sarcoplasmic
reticulum and pumps CA2+ more slowly than a fast fiber. Because CA2+ remains in the
cytosol longer, a muscle twich in a slow fiber lasts about five times as a long as one in a
fast fiber. While fast muscle fibers are used for brief, rapid, powerful contraction.
29. Distinguish between skeletal muscle, cardiac muscle, and smooth muscle.
Skeletal muscle fibers: oxidative or glycolytic fibers, by the source of ATP. As fasttwitch or slow-twitch fibers, by the speed of muscle contraction. They are packaged into
organs called skeletal muscles that attach to body’s skeleton; known as striated muscle
because fibers appear
Cardiac muscle: only in heart; striated, branched. Intercalated discs are gap junctions that
electrically couple all the muscle cells in the heart. Cardiac muscle cells can generate
action potential on their own, without any input from the nervous system.
Smooth muscle : Lacking the striations: actin and myosin filaments are not all aligned
along the length of the cell - spiral arrangement. Smooth muscles do not have either a Ttubule system or a well-developed sarcoplasmic reticulum.
Vocabulary
Sensations – Action potentials that reach the brain via sensory neurons
Perception – The interpretation of sensory system input by the brain.
Sensory Reception – the detection of the energy of stimulus by sensory cells.
Sensory Receptor – An organ, cell, pr structure within a cell that responds to specific stimuli
from an organism’s external or internal environment.
Exteroreceptor - detect external stimuli, such as heat, pressure, light, and chemicals.
Interoreceptor – Detect internal stimuli, such as blood pressure and body position
Sensory Transduction – The conversion of stimulus energy to a change in the membrane
potential of a sensory receptor cell.
Receptor Potential – A graded change in the membrane potential
Amplification – The strengthening of stimulus energy during transduction.
Transmission – The passage of nerve impulse along the axons.
Integration – Sensory information begins as soon as the information is received.
Sensory Adaptation – The tendency of sensory neurons to become less sensitive when they
are stimulated repeatedly.
Mechanoreceptor – Stimulated by physical deformation caused by pressure, touch, stretch,
motion, sound—all forms of mechanical energy
Muscle Spindle – Stretch receptors (a type of interoreceptor) that monitor the length of
skeletal muscles, as in the reflex arc.
Hair Cell – Detect motion
Pain Receptor – A sensory receptor that responds to noxious or painful stimuli, also called a
nocirecptor.
Nociceptor – A class of naked dendrites that function as pain receptors
Thermoreceptor – A receptor stimulated by either heat or cold
Chemoreceptor – A sensory receptor that responds to a chemical stimulus, such as a solute
or an odorant.
Gustatory Receptor – Respond to electromagnetic radiation such as light (photoreceptors),
electricity, and magnetic fields
Olfactory Receptor – They are the receptors for smell.
Electromagnetic Receptor – A receptor of electromagnetic energy, such as visible light,
electricity, or magnetism.
Photoreceptor – An electromagnetic receptor that detects radiation known as visible light.
Eye Cup – Simple light receptor that responds to light intensity and direction without
forming an image
Compound Eye – A type of multifaceted eye in insects and crustaceans consisting of up to
several thousand light-detecting, focusing ommatidia; especially good at detecting
movement.
Ommatidia – The plural form of ommatidium. One of the facets of the compound eye of
arthropods and some polychaete worms.
Single-lens eye – The camera-like eye found in some jellies, polychaetes, spiders, and many
mollusks.
Sclera – A tough, white outer layer of connective tissue that forms the globe of the vertebrate
eye.
Choroid – A thing, pihmented inner layer of the vertebrate eye.
Conjuctiva - A thin layer of cells and covers the sclera and keeps the eye moist.
Lens – The structure in an eye that focuses light rays onto the photoreceptors.
Ciliary Body – A portion of the vertebrate eye associated with the lens. It produces the clear,
watery aqueous humor that fills the anterior cavity of the eye.
Aqueous Humor – Plasma-like-liquid in the space between the lens and the cornea in the
vertebrate eye; helps maintain the shape of the eye, supplies nutrients and oxygen to its
tissues, and disposes of its waste.
Vitreous humor – Fills the cavity behind the lens and comprises most of the eye's volume.
Accommodation – The change of the optic lens into a spherical shape caused by focus upon
a close object
Rod cell – The photoreceptors of the eye; sensitive to light but do not distinguish colors
Cone Cell – The photoreceptors of the eye; daytime color image
Fovea – The place on the retina at the eye’s center of focus, where cones are highly
concentrated.
Retinal – Transduce stimuli (caused by the lens focusing a light image onto the retina) into
action potentials.
Opsin – A membrane protein bound to a light absorbing pigment molecule.
Rhodopsin – A visual pigment consisting of retinal and opsin. When rhodopsin absorbs
light,the retinal changes shape and dissociates from the opsin, after which it is converted
back to its original form.
Bipolar Cell – A neuron that relays information between photoreceptors and ganglion cells
in the retina.
Photopsin – The perception of color in humans is based on three types of cones, each with a
different visual pigment – red, green, or blue; are formed from the binding of retinal to three
distinct opsin proteins.
Ganglion Cell – A type of neuron in the retina that synapses with bipolar cells and transmits
action potentials to the brain via axons in the optic nerve.
Horizontal Cell – A neuron of the retina that helps integrate information before it is sent to
the brain.
Amacrine Cell – Neurons in the retina that help integrate the information before it is sent to
the brain.
Lateral Inhibition – A process that sharpens the edges and enhances the contrast of a
perceived image by inhibiting receptors lateral to those that have responded to light.
Optic Chiasm – The place where the two optic nerves meet and where the sensations from
the left visual field of both eyes are transmitted to the right side of the brain and the
sensations from the right visual field of both eyes are transmitted to the left side of the brain.
Lateral Geniculate Nuclei – One of a pair of structures in the brain that are destination for
most of the ganglion cell axons that form the optic nerves.
Primary Visual Cortex – the destination in the occipital lobe of the cerebrum for most of
the aons from the lateral geniculate nuclei.
Outer Ear – One of three main regions of the ear in reptiles (including birds) and mammals;
made up of the auditory canal and, in many birds and mammals, the pinna.
Tympanic Membrane – Another name for the eardrum, the membrane between the outer
and middle ear.
Middle Ear – One of three ancestral and embryonic regions of the vertebrate brain; develops
into sensory integrating and relay centers that send sensory information to the cerebrum.
Malleus – The first of three ones in the middle ear of mammals; also called the hammer.
Incus – The second of three bones in the middle ear of mammals; also called the anvil.
Stapes – The third of three bones in the middle ear of mammals; also called the stirrup.
Oval Window – In the vertebrate ear, a membrane-covered gap in the skull bone, through
which sound waves pass from the middle ear to the inner ear.
Eustachian Tube – The tube that connects the middle ear to the pharynx.
Inner Ear – One of three main regions of the vertebrate ear; includes the cochlea (which in
turn contains the organ of Corti) and the semicircular canals.
Cochlea – The complex, coiled organ of hearing that contains the organ of Corti.
Saccule – In the vertebrate ear, a chamber in the vestibule behind the oval window that
participates in the sense of balance.
Semicircular Canals – A three-part chamber of the inner ear that functions in maintaining
equilibrium.
Lateral Line System – A mechanoreceptor system consisting of a series of pores and
receptor units along the sides of the body in fishes and aquatic amphibians; detects water
movements made by the animal itself and by other moving objects.
Statocyst – A type of mechanoreceptor that functions in equilibrium in invertebrates by use
of statotliths, which stimulate hair cells in relation to gravity.
Statolith – In invertebrates, the grain or other dense granule that settles in response to gravity
and is found in sensory organs that function in equilibrium.
Taste Buds – A collection of modified epithelial cells on the tongue or in the mouth that are
receptors for taste in mammals.
Locomotion – Active motion from place to place.
Hydrostatic Skeleton – A skeletal system composed of fluid held under pressure in a closed
body compartment; the main skeleton of most cnidarians, flatworms, nematodes, and
annelids.
Peristalsis – Alternating waves of contraction and relaxation in the smooth muscles lining
the alimentary canal that push food along the canal. A type of movement on land produced
by rhythmic waves of muscle contractions passing from front to back, as in many animals.
Exoskeleton – A hard encasement of the surface of an animal, such as the shell of a mullusc
or the cuticle of an arthropod, the provides protection and points of attachment for muscles.
Chitin – A structural polysaccharide, consisting of amino sugar monomers, found in many
fungal cell walls and in the exoskeletons of all arthropods
Endoskeleton – A hard skeleton buried within the soft tissues of an animal, such as the
spicules of sponges, the plates of echinoderms, and the bony skeletons of vertebrates.
Skeletal Muscle – Muscle that is general responsible for the voluntary movements of the
body; one type of striated muscle.
Myofibril – A fibril collectively arranged in longitudinal bundles in muscle cells (fibers);
composed of thin filaments of actin and a regulatory protein and thick filaments of myosin.
Myofilaments - Thin filaments consist of two strands of actin and one strand of regulatory
protein coiled together. Thick filaments are staggered arrays of myosin molecules.
Thin Filament – A filament consisting of two strands of actin and two strands of regulatory
protein coiled around one another; a component of myofibrils in muscle fibers.
Thick Filament – A filament composed of staggered arrays of myosin molecules; a
component of myofibrils in muscle fibers.
Sarcomere – The fundamental, repeating unit of striated muscle, delimited by the Z lines.
Z Lines – The borders of the sarcomere; aligned in adjacent myofibrils
I Band – Areas near the edge of the sarcomere containing only thin filaments.
A Band – Regions where thick and thin filaments overlap and correspond to the length of the
thick filaments.
Sliding-filament Model – The theory explaining how muscle contracts, based on change
within a sarcomere, the basic unit of muscle organization. According to this model, thin
(actin) filaments slide across thick (myosin) filaments, shortening the sarcomere. The
shortening of all sarcomeres in a myofibril shortens the entire myofibril.
Tropomyosin – The regulatory protein that blocks the myosin-binding sites on actin
molecules.
Troponin Complex – The regulatory proteins that control the position of tropomyosin on the
thin filament.
Sarcoplasmic Reticulum – A specialized endoplasmic reticulum that regulates the calcium
concentration in the cytosol of muscle cells.
T (transverse) tubules – An infolding of the plasma membrane of skeletal muscle cells.
Tetanus – The maximal, sustained contraction of skeletal muscle, caused by a very high
frequency of action potentials elicited by continual stimulation.
Motor Unit - A single motor neuron and all the muscle fibers it controls.
Recruitment – The process of progressively increasing the tension of muscle by activating
more and more of the motor neurons controlling the muscle.
Fast Muscle Fibers – A muscle fiber used for rapid, powerful contractions.
Slow Muscle Fibers – A muscle fiber that can sustain long contractions.
Cornea – The transparent frontal portion of the sclera, which admits light into the vertebrate
eye.
Iris – The colored part of the vertebrate eye, formed by the anterior portion of the choroid.
Pupil – The opening in the iris, which admits light into the interior of the vertebrate eye.
Muscles in the iris regulate its size.
Retina - the innermost layer of the eyeball; it contains photoreceptor cells which transmit
signals from the optic disc, where the optic nerve attaches to the eye.
Organ of Corti – The actual hearing organ of the vertebrate ear, located in the floor of the
cochlear duct in the inner ear; contains the receptor cells (hair cells) of the ear.
Round Window – In the mammalian ear; the point of contract between the stapes and the
cochlea, where vibrations of the stapes create a traveling series of pressure waves in the fluid
of the cochlea.
Pitch – A ground tissue that is internal to the vascular tissue in a stem; in many monocot
roots, parenchyma cells that form the central core of the cascular cylinder.
Utricle – In the vertebrate ear, a chamber in the vestibule behind the oval window that opens
into the three semicircular canals.
Myoglobin- An oxygen-storing, pigmented protein in muscle cells.
Cardiac Muscle – A type of muscle that forms the contractile wall of the heart. Its cells are
joined by intercalated disks that relay each heart beat.
Intercalated Discs – A special junction between cardiac muscle cells that provides direct
electrical coupling between the cells.
Smooth Muscle – A type of muscle lacking the striations of skeletal and cardiac muscle
because of the uniform distribution of myosin filaments in the cell; responsible for
involuntary body activities.