BMSC11002 Lecture Notes - Lecture 4: Endocrine System, Cardiac Muscle, Threshold Potential

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26 May 2018

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Muscle and nerve tissue and physiology: Neurons and muscle cells have much

in common, in that they both are excitable, conduct electric impulses by allowing

sodium ions to enter and potassium ions to exit, and both function by allowing

calcium ions to move back and forth across membranes. Most cells contain more

potassium and magnesium, while the surrounding tissue fluids contain more

sodium and calcium. When at rest, muscle and neuron cell membranes

are polarized (more positively charged on the outside, and more negatively

charged on the inside due to negative charges on the inner membrane proteins),

and are said to have a resting potential, (see material on cell membrane

structure and physiology). The brain sends a message (impulse or action

potential) to muscles through motor neurons that may innervate from one to

nearly 2000 muscle cells, depending on how much the neurons diverge within

and outside the brain. Once an impulse reaches the neuromuscular

(myoneural) junction, Ca++ ions must enter the synaptic knobs before the

neuron can release its neurotransmitter (usually acetylcholine) to stimulate the

muscle cell. Know the sequence of events that follows this step, allowing a muscle

to contract, then relax. What are synaptic vesicles, and what is their

function? Describe a Motor unit. What is acetylcholinesterase (Ach'ase), and

what is its role in muscle physiology?

In terms of associated connective tissues, we also see similarities

between muscles and nerves. Both are surrounded by connective

tissue (epimysium and epineurium, respectively), both are subdivided into

groups of cells (called fascicles, or fasciculi) surrounded by connective

tissue (perimysium and perineurium), and each cell is surrounded by

connective tissue (endomysium and endoneurium). However, a muscle fiber is

the same as a muscle cell, while many authors describe a nerve fiber as a neuron

and its associated Schwann cell (neurilemma). Neurons consist of three major

structural types, unipolar (sensory cells that have one process entering and

leaving the cell body), bipolar (sensory cells containing one dendrite leading to

the cell body, and one axon leading away from the cell body),

and multipolar (cells with many dendrites entering the cell body (soma), and

one axon leaving the cell body (that may later subdivide into as many as 2-2000

branches). The larger the diameter of the neuron, the faster it conducts an

impulse, especially if it is myelinated.

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Study, in detail, the types and characteristics of muscle tissue, its

microscopic anatomy, and physiology. What is a triad? What are the similarities

and differences in a muscle contraction and a nerve impulse? What

is/are: summation (spatial & temporal), facilitation, isotonic and isometric

contraction, tetanus, atrophy? What causes muscle fatigue? …nerve

fatigue? Distinguish by structure and function the differences in slow- and fast-

twitch fibers. What are the energy sources for muscles? What is oxygen

debt, what are its causes, and how is it paid off? What is meant by aerobic and

anaerobic respiration? What are the roles of ATP in muscle and

neurophysiology? What are the roles of myoglobin, hemoglobin,

mitochondria, and creatine phosphate (phosphocreatine) in muscle

function? What are gap junctions, and what is their role in smooth and cardiac

muscle function?

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Document Summary

Most cells contain more potassium and magnesium, while the surrounding tissue fluids contain more sodium and calcium. The brain sends a message (impulse or action potential) to muscles through motor neurons that may innervate from one to nearly 2000 muscle cells, depending on how much the neurons diverge within and outside the brain. Once an impulse reaches the neuromuscular (myoneural) junction, ca++ ions must enter the synaptic knobs before the neuron can release its neurotransmitter (usually acetylcholine) to stimulate the muscle cell. Know the sequence of events that follows this step, allowing a muscle to contract, then relax. In terms of associated connective tissues, we also see similarities between muscles and nerves. Both are surrounded by connective tissue (epimysium and epineurium, respectively), both are subdivided into groups of cells (called fascicles, or fasciculi) surrounded by connective tissue (perimysium and perineurium), and each cell is surrounded by connective tissue (endomysium and endoneurium).

Related Questions

Which of the following statements is TRUE regarding sea anemones?

	None of the answer options is correct.
	Spongesânot sea anemonesâpossess what is considered to be the âsimplestâ nervous system found in animals.
	Because sea anemones are âsimpleâ organisms, these animals only possess motor neurons; sensory neurons or interneurons are never found in sea anemones.
	Although sea anemones possess ânet-likeâ nervous systems, these animals have brains located at their bases (near where they would attach to rocks).
	Although sea anemones lack definitive brains, they do possess ganglia that serve a similar function to the paired ganglia of flatworms.

Some people have low levels of calcium circulating in the blood, a condition known as hypocalcemia. While for many this disorder has little to no effect, for some it can be life-threatening. How could low levels of calcium harm an individual?

	Low levels of calcium would not have any effect on synaptic transmission.
	Low levels of calcium would cause sustained depolarization of the presynaptic cell.
	Low levels of calcium would result in fewer signals sent between the pre- and postsynaptic cell.

Cephalization is: the

	All of these choices are correct.
	development of a brain within the head of an animal.
	concentration of sensory organs within the head end of an animal.
	development of a âhead endâ in an organism.

Which of the following are TRUE about the resting membrane potential? (Select all that apply.)

	It results from voltage-gated sodium channels remaining open for long periods of time.
	It results from K⁺ ions diffusing out of the cell.
	It results from the sodium-potassium pump moving more Na⁺ ions out of the cell than K⁺ ions into the cell.

Afferent and efferent neurons differ in:

	their size.
	the directionality of the information they send.
	their pattern of myelination.

A neuron that responds to the environment is a(n):

	interneuron.
	homeostatic neuron.
	motor neuron.
	sensory neuron.

Which of the following is NOT the role of an interneuron?

	stimulating a muscle to contract
	conveying information from the internal environment of an animal
	relaying information from sensory to motor neurons
	maintaining homeostasis

Where are postsynaptic cell receptor proteins synthesized?

	the Golgi apparatus
	the lysosome
	the cytoplasm
	the rough endoplasmic reticulum

Inhibition of the flexor muscle during the knee-extension reflex is an example of:

	homeostasis.
	reciprocal inhibition.
	negative feedback.
	All of these choices are correct.

10.

What type of cells produce myelin for sensory neurons?

	pyramidal neurons
	glial cells
	melanocytes
	astrocytes

3. a) The neurotransmitter that is responsible for âcommunicationâ at the neuromuscular junction between motor nerve cells and skeletal muscle fibers is acetylcholine (ACh). The ACh receptor protein is a channel that opens when ACh binds. Upon the opening of this channel, the membrane at the motor end plate region of the muscle cell becomes depolarized, resulting in the generation of an action potential in the muscle fiber membrane. The ACh receptor channel is equally permeable to both Na⁺ and K⁺ ions. Explain how opening a channel that allows both potassium and sodium to cross the membrane results in membrane depolarization. (2 points)

b) In normal individuals, a single end-plate potential (EPP) is always sufficient to elicit an action potential (and hence contraction) in a skeletal-muscle fiber. This is not the case in individuals suffering from myasthenia gravis (MG). MG is an autoimmune disorder in which antibodies are produced that attack the AChRs at skeletal-muscle endplates reducing their number. Patients suffering from the disease present with significant muscle weakness. Explain why patients with MG would exhibit muscle weakness. (2 points)

c) Treatment strategies for myasthenia gravis include thymectomy (removing the source of the antibody producing cells) or immunosuppressant drug therapy (inhibiting the synthesis and release of the antibodies). In addition, the drug neostigmine administered at carefully monitored doses is highly effective in treating myasthenia gravis. Investigate the actions of neostigmine, and discuss in detail why it may be an effective treatment. (2 points)

1)What type of cell allows the immune system to respond morequickly if the same antigen is encountered a second time?

A)leukocytes

B)memory cells

C)macrophages

D)neutrophils

E)natual killer cells

2)why is the heart divided funtionally into two separate pumpsthat work in series?

A)because arteries carry blood away from the pump and veinsbring blood back to the pump

B)because blood decreases in pressure as it travels throughcirculation

C)because vessles in the vasculature keep blood moving in onedirection'

D)because there are four chambers to the heart

E)none of the above-the heart contracts in unison and is notdivided into two pumps

3)which of the following statements is correct?

A)Na+,K+, Ca2+ and Cl- are all more concentrated in theEXTRACELLULAR fluid

B)Na+, K+, Ca2+ and Cl- are all more concentrated in theEXTRACELLULAR fluid

C)Na+, Ca2+, and Cl- are all more concentrated in theEXTRACELLULAR fluid

D)K+, ca2+ are more concentrated in the EXTRACELLULAR fluid

E)K+, Ca2+ are more concentrated in the EXTRACELLULAR fluid

3)During skeletal muscle contraction:

A)the width of the H-zone decreases

B)the actin heads bind to myosin chain

C)ATP hydrolysis requires Ca2+ as a cofactor

D)tropomyosin changes conformation when Ca2+ binds

E)all of the above occur during skeletal muscle contraction

4)The rapid depolarization phase of myocardial contratile cellaction potential is due to the movement of which ion(s)?

A)Ca2+ flows into the cytosol

B)K+ flow out of the cytosol

C)Na+ flow into the cytosol

D)Ca2+ flow out of the cytosol

E)K+ flow into the cytosol

5)You are a physiology graduate student asked to study theeffect of ion permeability on the initiation of action potentials.You have isolated a cell with resting membrane potential of -70mVand have determined that the cell's threshold voltage is -55mV. Youthen change the cell to make it less permeable to K+ ions(Eions=-90mV)

With all ther condition staying the same, has cell's restingmembrane potential been DEPOLARIZED or HYPERPOLARIZED; and will thecell require a greater or smaller stimulus to reach threshold?

A)hyperpolarize; smaller

B)depolarize;greater

C)hyperpolarize;greater

D)depolarized; smaller

E)none of the above answers are possibe

6)Skeletal muscle cells are UNUSUAL in that they :

A)lack smooth endoplasmic reticulum

B)have no mitochondria

C)depend entirley on anaerobic respiration

D)have MULTIPLE nuclei

E)none of the baove are found in the skeletal muscle cells

7)What is the name for the autonomic nervous system synapses atthe neuroeffector?

A)electrical synapses

B)axon viscosities

C)bidirectional synapses

D)axon varicosities

E)light bulb synapse

8)Which cytokines are involvedin making cells resistant toviruses?

A)colony-stimulating actors

B)interferons

C)erythrpoietin

D)major histocompatibility complex

E)none of the above can make a cell resistant to a virus

9)If a person switiches from normal breathing to more shallowbreathing, whcih statement is true

A)tidal volume decreases

B)alveolar PO2 decreases

C)alveolar ventilation decreases

D)"a" and "b"

E)"a", "b', and "c"

10)Which scenerio supports hyperpolarization of pre-synapticcell?

A)allowing Cl- ions into the cell

B)allowing K+ ions to leave the cell

C)allowing Ca2+ ions into the cell

D)"a" and "b"

E)"a", "b", and "c"

11)The gap junctions in cardia muscle are part of specializedcell junctions that are localized to the__________.

A)transverse tubules

B)intercalated discs

C)Interdigitated fingers

D)desmosomes

E)high-end shppoinf malls

12)What role does myosin light chain kinase (MLCK) play insmooth muscle cell contraction?

A)dephosphorylates myosin

B)phosphorylates actin

C)phosphoylates myosin

D)dephosphorylates actin

E)both "a" and "c"Given that your forearm is 30cm long and yourbiceps inserts 2 cm away from your elbow joint, how much force mustyour biceps exert to hold up a 10kg weight?

A)0.67kg

B)6.0kg

C)20kg

d)150kg

e)600kg

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BMSC11002 Lecture Notes - Lecture 4: Endocrine System, Cardiac Muscle, Threshold Potential

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