Assignment 14

True or false? Cone cells are color photoreceptors that use different retinal molecules to absorb different wavelengths of light.

False

Which part of the eye contains the densest concentration of cone cells?

Fovea

How would hearing be affected by a punctured eardrum?

Hearing loss would occur at all pitches. The eardrum would not vibrate correctly and thus any pitch sound would be affected.

Which of the following statements correctly describe(s) the relationship between Ca2+ concentration in the cytosol and the response in the sarcomere? Select all that apply.

Increasing Ca2+ concentration causes movement of tropomyosin, exposing myosin-binding sites on actin. Decreasing Ca2+ concentration causes dissociation of Ca2+ from troponin.

Which of the following occurs when light hits the retina in a rod cell?

It changes from cis to trans conformation.

Which of the following statements does not describe a vertebrate eye?

It contains many light-sensing columns called ommatidia.

Which part of the eye bends light to focus it on the retina?

Lens

Why is it difficult to taste food after burning your tongue?

The heat damages taste receptors

Which part of the eye is the opening through which light initially passes?

Pupil

If the structure of retinal is identical in the three opsin forms, how can different wavelengths of light be detected?

The rest of the protein has a different structure

Which of the following statements about photoreception is true?

The retinal molecule changes shape when it absorbs light.

How are other organisms able to see in wavelengths that humans cannot?

They possess different types of opsins

True or false? The "blind spot" in vertebrate eyes is a region of the retina that contains no photoreceptors.

True

Which of the following statements correctly describes why a series of closely spaced action potentials causes a sustained contraction rather than a series of closely spaced twitches?

When a series of action potentials is closely spaced, there is not sufficient time for Ca2+ uptake into the sarcoplasmic reticulum between action potentials, and Ca2+ remains bound to troponin throughout the series.

Which of the following statements correctly describe(s) T tubules and their role in conducting action potentials in muscle cells? Select all that apply.

Without T tubules, the muscle cell would not be able to contract. T tubules carry action potentials into the interior of the muscle cell via voltage-gated Na+ and K+ channels. T tubules are infoldings of the plasma membrane that encircle the myofibrils and are in contact with the sarcoplasmic reticulum.

The cycle diagram below shows the sequence of events that affect Ca2+ levels in a muscle cell, beginning with the propagation of an action potential down a T tubule (top of the diagram). Drag the labels to their appropriate locations on the cycle diagram below. Note that SR stands for sarcoplasmic reticulum.

a. Ca2+ channels in SR open b. Ca2+ diffueses out of SR c. cytosolic Ca2+ level rises d. Ca2+ diffuses into myofibril e. Ca2+ channels in SR close f. Ca2+ pumped into SR g. cytosolic Ca2+ level drops h. Ca2+ diffuses out of myofibril In muscle cells, the cytosolic Ca2+ concentration is kept low by active transport of Ca2+ from the cytosol into the sarcoplasmic reticulum. When an action potential moves down the T tubules, it triggers Ca2+ channels in the sarcoplasmic reticulum to open. As a result, Ca2+ ions rush into the cytosol. Once in the cytosol, the Ca2+ ions diffuse into the myofibrils, where they enable muscle contraction to begin. When the action potential is completed, the Ca2+ channels in the sarcoplasmic reticulum close, and Ca2+ ions are again pumped back into the sarcoplasmic reticulum. As the cytosolic level of Ca2+ drops, Ca2+ ions diffuse out of the myofibrils, stopping muscle contraction.

Drag the labels to their appropriate locations on the diagram below, indicating the function of each structure during muscle contraction.

a. filament that is pulled toward the center of the sarcomere b. filament that pulls the other filament toward the center of the sarcomere c. motor protein head that hydrolyzes ATP and drives contraction d. sites at which Ca2+ ions are bound e. binding site for motor protein head f. protein that controls access to motor protein binding sites

Each muscle cell is in contact with a single motor neuron that controls the contraction of that cell. The diagram below shows a single muscle fiber and its motor neuron. Understanding the unique structural components of a muscle cell and its interaction with its motor neuron is a prerequisite for understanding muscle contraction and how it is regulated. Drag the labels to their appropriate locations on the diagram below.

a. motor neuron b. T tubule c. sacromere d. synaptic terminal e. sacroplasmic reticulum f. myofibril g. plasma membrane

An action potential on the muscle cell plasma membrane initiates contraction of the sarcomeres from this relaxed state. Drag the labels to their appropriate locations on the cycle diagram below.

a. myosin head forms a cross-bridge with actin b. myosin releases P c. myosisn pulls actin toward center of sarcomere d. myosin binds ATP e. cross-bridge between myosin and actin is broken f. myosin hydrolyzes ATP to ADP and P g. myosin head extends (pivots)

A tear in the fovea would result in _____.

blurred vison

Which of the following animals has eyes that include many lenses?

butterfly All insects have compound eyes.

The release of _____ ions from the sarcoplasmic reticulum is required for skeletal muscle contraction.

calcium

When an action potential from a motor neuron arrives at the neuromuscular junction (NMJ), a series of events occurs that leads to muscle contraction. Which of the following events will occur last (that is, after all of the others)?

conformational change in troponin

The _____ is the region of the eye where photoreceptors are most highly concentrated.

fovea

Bat echolocation (sonar) is most closely related to which human sensory system?

hearing

The sour taste of a grapefruit results from the binding of which of the following to chemoreceptors on the tongue?

hydrogen ions

The sour taste of a grapefruit results from the depolarization of taste cell membranes triggered by the presence of which substance?

hydrogen ions Sour sensations result from the activity of the hydrogen ion channels

Red-green colorblindness is caused by _____.

lack of a functional allele for one or more types of opsin molecules

The _____ changes shape to focus light on the retina.

lens

Olfaction occurs when airborne molecules trigger _______ in the nose, which send signals to regions in the olfactory bulb called _______.

olfactory neurons; glomeruli Each of the nose's chemosensory neurons has one type of odor receptor protein; neurons with the same type of receptor are linked to glomeruli in the olfactory bulb.

What name is given to the opening that allows light into the interior of the eye?

pupil

Sensory transduction of light in the vertebrate retina is accomplished by _____.

rods and cones

Which of the following structures shortens when a muscle contracts?

sarcomeres

What name is given to the tough layer that forms the "white" of the eye?

sclera

What would occur if the uptake of calcium ions was blocked in the sarcoplasmic reticulum?

sustained muscle contraction

During the course of muscle contraction the potential energy stored in ATP is transferred to potential energy stored in _____.

the myosin head

Of these events, the first to occur when a motor neuron stops sending an impulse to a muscle is _____.

the pumping of calcium ions out of the cytoplasm and back into the sarcoplasmic reticulum

Myosin heads bind to _____, which they then pull and cause to slide toward the center of the sarcomere.

thin filaments

Bats use which of the following types of sensation when flying?

ultrasonic hearing