PNB Lab Questions

What stretch resulted in the highest contraction force? What is happening in the muscle at the highest stretch levels?

5 mm resulted in the highest contraction force, at this length the resting and twitch force reach it's maximum threshold and will no longer increase at a great rate. Feedback from grader what is happening in the muscle?

What is the new resting membrane potential (R.P. or Vrest)?

52.34 mV

What is plantar flexion? Which two muscles are the most powerful plantar flexors?

Plantar flexion is the action of pointing your toes inferiorally or downwards (tip toes). Two muscles that are the most powerful plantar flexors are the soleus and gastrocnemius.

What is the reversal potential (Nernst potential) for Na+ based on the simulation result?

The Nernst potential for Na+ has to be 52.34 mV because conductance in this chart is only for Na+ and K+, therefore closing K+ channels would make membrane potential only Na+'s Nernst potential.

What happens to Vrest if the internal K+ increases? What happens to Vrest if the internal K+ decreases?

K+ increases than V rest will become more negative. If K+ decreases than V rest will become less negative, or more positive.

Which regions of the spinal cord (e.g. cervical, thoracic, lumbar, sacral) have enlarged areas that reflect innervation of the upper and lower extremities, respectively?

The cervical region of the spinal cord contains eight cervical nerves which processes information related to the upper and lower limbs.

Name two important factors that contribute to the stability of the knee. How do they stabilize the knee?

The collateral ligaments help to stabilize the knee medially and laterally. The cruciate ligaments (ACL & PCL) help to stabilize the knee anteriorly and posteriorly.

Describe two aspects of the female pelvis that allow for easier childbirth.

The pubic arch in a female is larger than the pubic arch of a male. During birth, the pubic symphysis softens to allow the female to give birth. The pubic symphysis is usually immobile otherwise.

What does the threshold stimulus voltage and maxmum excitation voltage values signify in terms of muscle preparation?

The threshold stimulus voltage is the minimum voltage needed to create an action potential while the maximum excitation voltage is the stimulus in which the force will no longer increase exponentially.

Which of the following statements is true about EMG?

While flexing during reciprocal activation, some signal will be seen in the antagonist muscle, along with that seen in the agonist muscle

what feature will you use to identify hyaline cartilage?

glassy-appearing matrix: cells hosted in lacunae

When you chew gum, which muscle is not used

masseter

true or false, the supraspinatus and infraspinatus are named for their origins/insertions on the spine of the scapula

true

In light of the "all or none" law of muscle contraction, how can you explain the graded response?

"All or none" refers to the occurrence of the threshold being reached. If the stimulus is above threshold, the muscle or nerve fiber will either produce a complete response or no response at all. To explain the graded response, I can use this concept to presume that above 500 mV I will either get a response or none at all but when observing our results it appears that we reached a complete response at each stimuli increase. Feedback from grader: graded response is adding all the individual responses together from multiple motor units

general features of all connective tissue

1. Ground substance in an extracellular matrix 2. Protein fibers in an extracellular matrix

List at least three structural differences that you observed in the lab regarding sheep and human brain.

1. The human brain has more surface area 2. the olfactory bulbs in the sheep are larger 3. the sheep also has a larger pineal gland

Provide a possible mechanism for why the muscle was unable to maintain a prolonged contraction during fatigue.

A possible mechanism for why the muscle was unable to maintain a prolonged contraction during the fatigue is that the action potential is being fired repeatedly and therefore opening potassium channels into the t-tubules which causes depolarization of the cell and therefore conduction failure. When this occurs, action potential won't be able to be generated.

Which 3 cranial nerves are responsible for eye movements? b) What is the name of fissure in the skull where they exit?

A) The three cranial nerves that are responsible for eye movements are the oculomotor (CNIII), abducens (VI), and trochlear nerve (IV) B) the name of the fissure: superior orbital fissure

You will have seen that an action potential generated very soon after a preceding one is not full-size. Explain this observation.

An action potential occurs when the sodium ions enter through sodium channels causing depolarization and then the channels have to be reset to cause re-polarization and during this time an action potential cannot be generated.

In this exercise, you had decreased the stimulus interval (increased frequency of the two pulses). According to your data, how did the muscle respond to shorter intervals?

As the intervals decreased the force of the muscle contraction merged into one and the force of the first and second responses became relatively close in mN. In comparison to the longer intervals which gave us two noticeable contractions and therefore two distinguishable forces in mN.

You will have seen that as you stimulated at higher voltages, there was an increase in the number of fibers responding. What is this phenomenon called?

As the stimulus increased, the number of fibers responding also increased and this is due to the phenomenon called "recruitment." Recruitment is the activation of additional motor units in order to get an increase in contractile strength.

Which muscle is attached to the radial tuberosity, and what are the actions of that muscle?

Biceps Brachii attach to the radial tuberosity and perform flexion of the elbow joint.

Describe the articulation between the scapula and the humerus. a) What parts of the bones articulate, b) what type of joint is it, and c) what is the name of this joint?

Glenoid fossa of the scapula and the humeral head of the humerus articulate. This forms ball-and-socket joint. It is called the glenohumeral joint.

Describe the three articulations in the elbow joint. Specifically, a) which bones articulate (include the bone markings involved), and b) which movements do each of these articulations allow?

Hinge - radiohumeral and Hinge - ulnahumeral, flexion/extension. Pivot - radius and ulna, pronation/supination.

Rickets is a skeletal disorder that can be caused by a deficiency in Vitamin D, which is necessary for calcium and phosphate absorption in the intestines. A deficiency in Vitamin D, particularly during ages of rapid bone growth, can lead to stunted bone development. Based on what you know about bone formation, how would you expect the long bone you had observed in lab to have looked if the cow had a Vitamin D deficiency during adolescence? Why?

I know that calcium is a main component for bone growth. Therefore a deficiency of Vitamin D and therefore a deficiency in calcium would result in softer, less dense bones. This is due to the lack of calcium absorption that would allow for calcification/ossification of bones.

From your data, the theoretical maximum frequency at which nerve impulses can be generated by the median giant fiber was calculated. Do you think that the nerve fiber would be able to generate impulses continuously at this rate?

I would not think that the nerve fiber would be able to generate impulses continuously at this rate because eventually the supply of ATP will deplete and ATP is required to pump ions in and out to get the resting potential.

Write your hypotheses that explains how batrachotoxin acts on voltage-gated sodium ion channels, and design experiment that will test its action. 1.5 / 1.5

If TTX is not able to depolarize and send stimuli due to the blocked passage way of sodium ions in (causing sensory and motor symptoms) than bactratoxin must effect the sodium ion channels in a way where it selectively does not allow enough sodium channels to exit the cell and therefore lack of/no repolarization because unlike TTX there is a depolarization meaning the nervous system is able to send out a message but then it is not completely able to send the entire message because repolarization cannot occur and hence the sensory symptoms but no motor symptoms. Thought process: TTX does not have the ability to depolarize and therefore therefore preventing the nervous system to carry messages, resulting in the muscles not flexing because of a lack of stimuli being detected. Bactratoxin IS able to depolarize, so the nervous system is detecting a stimuli, hence the lack of paralysis from contact with bactratoxin, but because of the fact that the toxin will only allow partial or no repolarization at all this results in the numbness. Experiment: We can test my hypothesis using the squid program. Viewing what will occur to the action potential as a result of more or less sodium input

The word "sartorius" is a Latin word that means pertaining to a tailor. The muscle contracts to rotate your thigh in order to sit down on the floor in a cross-legged position, which tailors had to do frequently many years ago. Give one other muscle that contracts to rotate your thigh in the opposite direction in order to stand up from this position.

If you are sitting down cross legged, that means that your thigh had to move laterally. So, the opposite direction would mean to move medially. To stand up you have to move with your hips and thigh muscles. So, arguably I can say that the gluteus minimus or medius are two other options to assist in medially rotating the hip or I can say that the adductor longus assists in medially rotating the femur at the hip joint. Feedback from grader gluteus medius and minimus

If you were to palpate your olecranon process, where would you find it? Where would you find the styloid process of the ulna? The styloid process of the radius?

If you palpate your olecranon process you would find it posteriorly and promixal end of your ulna. The styloid process of the ulna would be medial, in line with your pinky on the distal end. The styloid process of the radius is lateral, in line with your thumb on the distal end.

In your own words what is co-contraction? Describe co-contraction using the exercise in class as an example; what happens in each of the muscles during this exercise?

In my own words, co-contraction is the action of two muscle groups contracting at the same time while performing the same action. In class when Andrew was moving his arm into a 90 degree angle, both the bicep and the tricep contracts, although the EMG shows us that the bicep has more electrical activity than the tricep because the tricep in this action is more relaxed.

An intracellularly recorded nerve action potential approximates 80 mV. Why is your recorded action potential so much smaller? 1 / 1

Our recorded action potential is so much smaller because we recorded our nerve action potential extracellularly. Because of this there is a possibility that, the extracellular electrode did not have internal access to the internal electrical current and therefore, giving us a smaller action potential recording. The extracellular electrode is also sensitive to small potential difference.

The typical shape of the response we see in this lab is biphasic with two peaks of opposite sign. In your own words, explain why we see this shape.

Outside is negative so therefore negative repels negative and positive attracts negative. Which is why the negative goes up and the positive goes down.

What is the reversal potential for K+ based on the simulation result?

Reversal potential for K+ is -91.07 due to the conductance only being open to K+ so V rest looks like K+.

Capillaries, alveoli in the lungs, and glomeruli in the renal system are lined by simple squamous epithelial cells. Meanwhile, the skin, inside lining of the mouth, and the lining of the esophagus are made up of stratified squamous epithelial cells. How do the required functions of these tissues relate to the type of epithelial cells found there?

Simple squamous cells are located in places that don't require as much protection as places in which stratified squamous epithelial cells are found. Places that contain stratified squamous usually are exposed to more risks of abrasion. Feedback from grader: Simple squamous allows diffusion to occur in these places too.

Explain why did Dr. Westwood experienced both of sensory and motor symptoms?

TTX inhibits the firing of an action potential but when it binds to the voltage gated sodium channels, it blocks the pathway of sodium ions which are responsible for the rising action potential (depolarization) into the neuron and this therefore prevents the nervous system from carrying messages (sensory) and as a result of this the muscles in our body would not flex because there is no stimuli in the nervous system being detected/ sent out.

Explain how tetrodotoxin would affect communication between neurons and what its mechanism is (what channels are affected with TTX). 1 / 1

Tetrodotoxin (TTX) affects the communication between neurons by binding to the voltage-gated sodium channels, preventing sodium from entering the cell membrane and therefore preventing an action potential from occurring because there can be no depolarization if sodium is not entering the cell membrane.

How are the atlas and axis vertebrae morphologically different from "typical" vertebrae? Be sure to mention two features for each.

The atlas holds the head up while the axis is responsible for movement. The axis vertebrae (C2) is the vertebrae that contains the dens and the atlas (C1) has no vertebral body and no spinous process. Feedback from grader: axis also has atypical body

. How does the experimental value compare with your calculated Na+ Nernst potential in Table 1? What might be the reason for the difference?

The experimental value compared to calculated is less, this could be due to a different temperatures being used.

Name two cranial nerves primarily responsible for our perception of taste.

The facial nerve (CN VII) which is responsible for the two thirds of the tongue and the glossopharyngeal which (CN IX) is responsible for taste and other sensations of the tongue

What functions do mammillary bodies serve in the brain?

The function of the mammillary bodies are to aid the process of memory recognition and it may also link smell to memory.

Name all of the muscles of the quadriceps group, and all of the muscles of the hamstrings group. What are the muscle actions of these two groups

The hamstring muscles consist of the semimembranosus, semiteninosus and biceps femoris. the quadriceps muscles consist rectus femoris, vastus medias, lateralis and intermedias.

How would be able to differentiate the anterior and posterior views of the femur? How would you use this information to help you tell if you were looking at a left or right femur

The head faces medially, the greater trochanter faces laterally and the femoral condyles need to be posteriorly curved.

Which joint is more stable (and less mobile) and for what purpose? The hip joint or the glenohumeral joint? What are the structural features that make one of these joints more stable and one joint less stable? 1 / 1

The hip joint is more stable, less mobile because it has to withstand the weight of the body. The acetabulum (hip) is deeper than the glenoid fossa (glenohumeral) which makes the structure more stable. The osseous acetabulum is much deeper in the hip and provides stability to the hip joint.

A student was trying to measure the amplitude of an EMG trace. As you can see, the marker and cursor were shown on the trace. Name one mistake he made.

The marker was placed on the raw data instead of the integrated data. The correct way to measure the amplitude of the EMG is to place the pointer on the peak of the raw (RMS) data and the marker on the valley of the integrated data.

The medial malleolus is similar to which bone marking of the forearm? What can the lateral malleolus be compared to?

The medial malleolus of the tibia/ fibula is similar to the styloid process of the forearm. The lateral malleolus is similar to the radial tuberosity , in that it is a surface that articulates with the tibia. Feedback from grader: later malleolus - styloid process and medial malleolus - styloid of ulna

When you are looking at a cross section of the spinal cord, in which region will you observe motor neurons? (White/gray matter is not a sufficient answer). 1 pt

The motor neurons will be located in the peripheral region of the spinal cord.

Unlike the discrete waveform from an electrocardiogram, the electromyogram waveform is irregular. Why do you suppose this is? 1 / 1

The waveform of an electrocardiogram is discrete because it measures the heart's electrical activity which is usually a consistent heartbeat (the entire muscle is contracting in a synchronized fashion). An electromyogram measures the electrical activity of the muscles and I suppose it has an irregular waveform because unlike the heart which contracts all at once, the skeletal muscle does not; which is why the waveform is irregular because an EMG measures the activity of multiple muscle fibers.

Briefly describe the cellular events responsible for the refractory period (Hint: Discuss the mechanism of repolarization).

There is a buildup of potassium during hyperpolarization which make it harder for stimulus to reach threshold. The refractory period shown in our graph is shown by the largest interval in which a second spike cannot be produced.

How did your EMG traces change when you added weights to your arm? Based on your data, what would you infer is happening in your muscles as more weight is added?

When weight was added to the arm, the muscle contracted causing the EMG to spike. In comparison to the lower weights, the heavier weights caused the peaks to be larger; this shows that when weight is added, it causes the muscle to contract with more force.

Did you observe a difference in the conduction velocity values produced by the two methods for the median nerve?

Yes, the further the distance, the greater the velocity. Although the difference method should give a slower, but more accurate reading.

You will have noticed that each osteon (Haversian system) consists of a central canal with several concentric lamellae, and lacunae interspersed throughout. Based on what you learned in lab and in the prelab video, a) what leads to the formation of these lacunae, and b) what purpose do they (or what resides in them) serve afterward?

a) As bone grows it creates new lamellae around old lamellae until different osteons fuse together. Each lamellae contains lacunae which houses an osteocyte. As the pre-lab introduced to us,"Osteocytes are former osteoblasts that have been trapped in the matrix they form." (which leads to the formation of the lacunae) b) the lacunae are small spaces in between the lamellae that contains osteocytes and canaliculi; which connect to other lacunae. Tissue fluid in the lacunae allow the transfer of materials between bone cells and capillaries.

a) Define Tetanus. b) At which stimulus interval did you observe tetanus? c) Explain the mechanism behind this phenomenon.

a) Tetanus is defined as a sustained muscle contraction resulting from rapid series of nerve impulses. b) At 0.4s is when i began to observe tetanus (incomplete tetanus), it is at 0.02 s when the reading showed one smooth sustained muscle contraction (complete tetanus). c) Tetanus occurs when the motor nerve exerts an action potential at a very high rate. Here the muscle fibers have reached a state of maximum contraction.

a) Which color line should be comparable to the length tension curve? b) Does your trace roughly match with a typical length tension curve? If not, could you provide some explanations?

a) The green line should be comparable to the length tension curve. b) Our trace does roughly match with a typical tension curve, the line increases and then decreases as the length increases.

a) What is the function of the ventricular system of the brain? b) Identify the location of each ventricle (and cerebral aqueduct) in relation to brain structures.

a) the function of the ventricular system of the brain is to produce the cerebrospinal fluid b) the ventricular system of the brain is a set of canals (ventricles). The lateral ventricle is located in between the corpus callosum and the fornix when looking at a midsagittal cut of the brain. The third ventricle is located underneath the fornix and above the thalamus (in the midsagittal view). The fourth ventricle is in between the pons and the cerebullum and communicates with the third ventricle via the cerebral aqueduct (connects the third and fourth ventricle).

only these ribs articulate with thoracic vertebrae

all ribs

which type of joints has the greatest freedom of movement?

ball and socket joint

what is the first thing you will do if your recorded EMG looks like a flat line?

click auto scale button

which of the following bone does not articulate with any other bone?

hyoid bone

What happens to Vrest if the internal NA+ concentration decreases?

it becomes more negative

In anatomical position the radius is___ to the ulna and the radial tuberosity faces the ____ direction

lateral; medial

Which part would you adjust in order to examine a specimen under light microscope with two eyes at the same time?

ocular lenses to adjust the inter-pupillary distance

What are the two largest "soft spots" in the newborn skull?

posterior and anterior fontanelle

True ribs

ribs 1-7 and only these ribs connect directly to the sternum

False ribs

ribs 8-12, false ribs are also known as floating ribs

Kyphosis is a curving of the spine that causes a bowing or rounding of the back, which leads to a hunchback or slouching posture. Which part of the spinal column has the exaggerated curve in people with kyphosis?

thoracic vertebrae