Lab 1 - Nervous System/Sensory Physiology

Why does an action potential normally flow only in one direction along a nerve fiber?

During the absolute refractory period, voltage-sensitive Na+ channel cannot be reactivated

Post-Lab: What is the peripheral nervous system comprised of?

Enteric nervous system, somatic nervous system, autonomic nervous system

Size perception, describe what you see in figure 2?

It appears that the blue line is definitely longer than the red line, but they are in fact equal in lengths

Which cones are affected in protan type color blindness?

Red

Pre-Lab: Vertebrates rely on information from which sensory structure to keep their balance?

Semicircular canal; one of the three interconnected tubes found in each ear; it is part of the vestibular system which provides sensation on movement and balance

Is our taste sensitivity uniform across the tongue?

Sensitivity of taste receptors to different tastes varies with regions across the tongue.

Pre-Lab: In muscles, tendons, and ligaments, which receptor type informs the central nervous system of the position of loads on parts of the body?

Stretch receptors; type of mechanoreceptors located in various organs in the body

Given the number of blood vessels in the retina, why do you suppose that you are not able to see them normally?

The brain suppresses the image of the retinal blood vessel

Emmetropia

The near response of the eye for normal vision

Post-Lab: For the activity regarding the semi-circular canals of the ear, when the subject stopped spinning, which of the following phenomena was observed?

The subject's eyes kept looking quickly in the direction of the spin in jerky movements

T/F - The somatic nervous system is also known as the voluntary nervous system?

True

Was it easy to tell the direction when each of the following scenarios occurred?

a) The chair had just started spinning.b) The chair had been spinning for some time. c) The chair had stopped spinning.

The Ishihara color test is:

(full test consist of 38 images or plates) is a test for red-green color deficiencies, which is the most common kind of color blindness. It was named after Dr Shinobu Ishihara (1879-1963) of the University of Tokyo, who published these tests in 1917.

If the same nerve fiver was myelinated (like it is in the human body), the conduction velocity would be 50 m/s. Now, how long would it take you to withdraw your foot from that hot object?

0.1 seconds; If the same 10 um nerve fiber was myelinated, conduction speed would increase to 50 m/s. The resulting reflex withdrawal of the foot would be much quicker (100 milliseconds)

The cell uses ATP to power the Na+/K+-ATPase pumps in the cell membrane and moves:

3 Na+ OUT of the cell; 2 K+ INTO the cell each cycle to maintain an uneven distribution of ions

If the conduction velocity of a human nerve fiber was 0.5 m/s, how long would it take you to withdraw your foot from a hot object?

4 seconds; answer is based on a distance from the foot to the spinal cord of one meter, and the distance back to the muscle being approximately the same distance

Saltaory Conduction

AP conduction along the lengths of myelin is very fast, and then slow at the nodes of Ranvier where the action potential regenerates. As a result, the action potential is described as "jumping" between the nodes of Ranvier

The eye can accommodate (change focus) for far or near vision, by varying the shape of the lends...

Accommodation is the reflex in which the optical power of the eye changes to maintain focus on an object as the distance between eye and object changes. There are three parts to the accommodation reflex. Consider how the eye adjusts to focus on near objects.

Pre-Lab: An electrode is inserted into a chemosensory nerve fiber leading away from a taste bud in the mouth of a dog. A mild acid solution is then flushed continuously over the taste buds associated with this nerve. Initially the nerve responds to this stimulation, but over time ceases to carry action potentials. This observation would best be explained by which of the following?

Adaptation of the sensory cells

Semicircular canals, describe your observations regarding the affect of rotation?

After several rotations, you should be relatively inaccurate when trying to identify your new orientation

In Visual Information Experiment, who do you see?

Albert Einstein

An impossible geometric object, describe what you see in figure 3?

Although at first glance, this image "makes sense", it quickly becomes obvious that it is an impossible structure

All-Or-None Events True Statements

An action potential will ALWAYS fire once the threshold potential is met; All action potentials are the SAME SIZE

Do action potentials in the body travel in one direction only or in both?

An axon can experimentally pass action potentials in either direction

What is meant by binocular vision? Why do you suppose this is useful?

Binocular vision means that you have two eyes with overlapping visual fields; this allows depth perception

Which cones are affected in tritan type color blindness?

Blue

Describe what you saw during the negative afterimage activity?

Color change is what is most important here

Autonomic Nervous System (ANS) = involuntary

Contains sensory and motor components; Information from the CNS travels to smooth muscles, cardiac muscles, and glands along a TWO-NEURON EFFERENT PATHWAY

The amplitude of accommodation that our eyes can achieve decreases as we age, shown by

Duane's Classical Curve - The graph below has been recreated using data from 4200 eyes, including 500 patients, which was obtained by Dr Alexander Duane and published in 1922 [1]. Note that accommodation is measured in diopters.

Describe and explain your observations on eye movement for saccadic masking experiment?

During saccadic (rapid) movements of the eye, the brain suppresses processing of visual information in such a way that the motion is not detectable. The movement should be apparent to another observer.

Post-Lab: Sensation is the conscious meaning we derive from our senses about our internal and external environment, T/F?

FALSE; Perception is the meaning or interpretation of our senses

Describe your observation regarding two-point discrimination?

Fingertips have the shortest distance for two-point discrimination

Which cones are affected in deutan type color blindness?

Green

Describe your observations of retinal blood vessels?

Here, sufficient light should enter the eye through the sclera (white of the eye) if the small, bright light is held close enough to the volunteer's eye in such a way that little light enters via the pupil

Even with the neural implant, Ian has no sensation in his hands. How else might he tell if he was producing grasping or pinching movements with his fingers?

Ian uses other sensory information (for example, he watches his hand move) to know if he is producing the appropriate movements with his fingers

If the neuron is stimulated at the middle of the axon, which direction would the action potential travel?

In both directions (to the left and right); Axons can experimentally pass action potentials in either direction

Somatic Nervous System (SNS) = voluntary

Information from the periphery travels to the CNS along AFFERENT SENSORY NERVES; Responses travel directly to SKELETAL MUSCLES along EFFECTOR MOTOR NERVES

Post-Lab: Which of the following regarding proprioception is true?

It allows us to know where our head and limbs are relative to each other without having to look at them

How can explain the Hermann Illusion?

It has been argued that this illusion can be explained by reference to retinal receptive fields. However, very recent research indicates that the explanation lies in cortical interpretation of the information, not retinal signaling.

Action potential events - what does the purple line represent?

K+ permeability

Why is it harder to fire a second action potential in the relative refractory period?

Many voltage-gated Na+ channels are inactivated and the cell is permeable to K+

What did you observe when you mechanically stimulated your retina?

Mechanical stimulation of the eye causes random firing of cells in the retina, which produces visual effects similar to light stimulating the retina. This type of entopic phenomenon (that is, visual effects produced by the eye itself), which is known as a "phosphene"

The Hermann Illusion describe what you see in the figures that Tyndall had arranged in a matrix?

Most people see gray spots in the intersections of the spaces between the squares. Every space in the grid has the same white intensity, and yet the intersection appear gray.

The rate of conduction of an action potential along a nerve fiber is affected by a range of things. Which of the following affects the rate of conduction?

Myelin, Nerve diameter, Temeprature

Consider the relative size of humans, and the speed at which we must react to our environment. What is the most important factor for increasing conduction speed in the human body?

Myelination

Action potential events - what does the green line represent?

Na+ permeability

The result is that much of that change in membrane permeability and current flow occurs at the

Nodes of Ranvier; these nodes contain high concentrations of Na+ channels which allow for the regeneration of the AP as it travels along the axon

Sense are physiological bases of:

Perception

What do your results from the afterimage activities suggest about the response time of photoreceptors to light?

Photoreceptors have a fast and a slow response to light

From your results, what do you conclude about the blind spot?

Results should prove the existence of the blind spot; there is a portion of the field of vision that is missing due to the optic disk not containing photoreceptors

Describe your observations regarding the accommodation activity. How does the near point differ between people with normal vision and those who are nearsighted?

Students who are nearsighted (myopic) should have a significantly shorter near point than those with normal vision.

What is the anatomical basis for the blind spot?

The blind spot is where the optic nerve exits the retina; there are no photoreceptors there

What can you say about the distribution of the different types of taste receptors?

The classical interpretation of taste distribution is that various regions of the tongue are sensitive to different taste; the "tongue map" theory. This has now been disproved. It is believed that all areas of the tongue can detect all tastes, but some areas are more sensitive than others to particular tastes.

Pre-Lab: Which statement about sensory systems is false?

The more intense a stimulus, the greater the magnitude of each action potential fired by a sensory neuron.

When you change your focus from a near object to a far object, what occurs in the eye to allow you to focus on the object?

The muscles that control the curvature of the lens (ciliary muscles) relax, increasing the tension on the suspensory ligaments (zonule fibers), which stretches the lens to a thinner shape.

How can you explain the size perception illusion?

The perceived size of objects is affected by a number of influences, of which the most important is the angle subtended by the object at the eye. However, many other cues are used by the visual system. For example, to decide if an object is small and near or large and distant. The cues given by the black line ends in the image above confuse our judgment of the line length.

How can you explain the impossible geometric object illusion?

The shadowing cues used here lure the brain into attempting to interpret this as a real structure, but no such physical structure can exist.

Joint position sense, could the volunteer determine joint position?

The volunteer should be able to easily identify the joint position

The neural implant acts to replace Ian's motor function to his hand. What is the normal function of motor neurons?

They carry signals from the spinal cord to the muscles to produce movement

Post-Lab: Why are the representations of some body parts larger compared to others in the somatosensory cortex?

They have a greater proportion of specialized sensory receptors; A larger region of somatosensory cortex to one body part reflects a greater proportion of specialized sensory receptors. Compare the skin that covers the back with that over the hands, especially the fingertips.

Three basic functions of the nervous system:

To sense changes internal and external to the body; To process (integrate) this sensory information; To initiate a response

If the neuron is stimulated at the sensory nerve endings in the periphery, which direction would the action potential travel?

To your right; Electrical impulses travel in one direction along sensory neurons. That is, impulses travel from the sensory receptor (on the left) to the spinal cord (on the right)

Describe and discuss your observations regarding the thermal illusion?

Typically after immersion of separate hands in either hot or cold water, the lukewarm water will feel cold to the hand immersed in hot water, and hot to the hand immersed in cold water. For the second activity, the metal pipe will feel colder to the touch than the wooden rod due to the different thermal conductive properties of each material.

Where was your tactile discrimination best? What can you say about the density of tactile receptors on your arm?

Typically, tactile discrimination is best on the fingertips. The areas that have the best tactile discrimination have the highest density of receptors.

Describe what you saw when you performed the convergence of gaze activity?

When performing the convergence of gaze activity, our volunteer focused on a smoke detector on a wall about six feet above the ground. The smoke detector was seen as doubled when the volunteer did not cover either eye. After covering the right eye, the right smoke detector disappeared. After covering the left eye, the left smoke detector disappeared.

Does smell influence taste?

Without the sense of smell, the identification of a flavor would be extremely difficult.

Describe what you saw during the positive afterimage activity?

Your observations should be similar to the description given for this activity: bright features of the scene remain visible for an appreciable time (a substantial fraction of a second)

In the relative refractory period,

a stimulus of greater than normal intensity can elicit a response

The presence of myelin decreases membrane,

capacitance (ability to store electrical energy) and increases membrane resistance

Indicate the structures of the eye that contract to release tension on the lens, which allows its curvature to increase for near vision. What are these structures called?

ciliary muscles

We can regard resting membrane potential (RMP) as a

diffusion potential dominated by the contribution of K+ diffusion; membrane is more permeable to K+ than Na+ because there is a greater tendency for K+ to DIFFUSE OUT of the cell than Na+ to DIFFUSE INTO the cell

Neurons carrying sensory information to the spinal cord have their cell bodies in the

dorsal root ganglia

In the absolute refractory period,

it is impossible to initiate a second action potential

Axons with a larger diameter have,

lower internal resistance; as a result, conduction of an action potential is faster along axons with larger diameters

Unmyelinated axon (3 things)

lower membrane resistance, regeneration occurs continuously along the axon, slow conduction velocity

Efferent divison (motor)

motor nerves carry information away from the CNS to skeletal muscle fibers to bring about an appropriate response to the stimulus

For an individual to form a clear image, an object needs to lie between the

near point and the far point

Myopia

nearsightedness

somatic nerve fibers running to and from the periphery are collected together into bundles called

peripheral nerves

Myelinated axon (5 things)

regeneration occurs at the nodes of Ranvier, fast conduction velocity, high membrane resistance, less electrical current loss across the membrane, saltatory conduction

Afferent divison (sensory)

sensory nerves carry information towards the CNS (brain or spinal cord) in response to stimulation such as pain, pressure, or stretch

During the refractory period,

the cell may either be unable to fire a second action potential (ABSOLUTE) , or be more resistant to firing a second action potential (RELATIVE)

Far point

the maximum distance from the eye at which an individual can see a clear image of an object

Near point

the minimum distance from the eye at which an individual can form a clear image of an object

Binocular vision requires that,

the separate images in the left and right eyes be "fused" to give a single view. Fusion of the images of an object is possible only if the images fall on corresponding parts of the left and right retinas.

Neurons carrying information from the spinal cord to skeletal muscles have their cell bodies in the

ventral horn of the spinal cord