- excitability - conductivity - infatiguability - all or none rule

Muscles And Nerves Flashcards by Umu Koroma

How do nerves and muscles react to stimulus

By changing their electrical properties

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The structural and functional units of the nervous system are

Nerve cells or neurons

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Dendrites

branched thick extensions of the cytoplasm of the cell body which function to receive signals from other nerve cells and conduct them toward the cell body

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What is the first part of axon called

Initial segment

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The axon ends by forming

Synaptic knobs or terminal buttons

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Function of myelin sheaths

Protect and insulate nerve fibers
Increases speed of transmission of nerve impulse

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Myelin sheaths are formed by

Schwann cells wrapping around axon processes

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Myelin sheaths are separated by

Nodes of ranvier

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Stimulus can be

Mechanical
Electrical
Chemical
Thermal

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In studying nerves, electrical stimuli are preferred because:

it is similar to the natural stimuli of the body
Its intensity and duration can be controlled and measured
Do not readily damage the nerve and so can be repeated.

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Properties of nerves

excitability
conductivity
infatiguability
all or none rule

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All or None law

: a stimulus must reach a certain threshold before being transmitted, if sub-threshold, only a local non-propagated change will result; if however the nerve cell is stimulated by a supra-threshold stimulus, the resulting effect is similar to that of a threshold stimulus irrespective of the strength of the stimulus.

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Factors affecting effectiveness of a stimulus

strength
rate of rise in intensity
duration

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Stimuli of short duration (outside it limit) will not excite the nerve no matter it intensity. True or false

True

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The mini MSK current that excites the nerve is called

Rheobase

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Time needed by rheobase to excite the nerve is called

Utilization time

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Stimuli that causes local response

Sub threshold

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What is Chronaxie

Chronaxie is a concept in neuroscience and physiology that refers to the minimum amount of time required to stimulate a nerve or muscle to contract when an electric current of double the rheobase (the minimum current needed to just elicit a response) is applied.

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Define membrane potential

An electrical potential (voltage difference) between the inside and the outside of the cell membrane

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Membrane potentials are caused by

Diffusion potential

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How is diffusion potential measured

This is measured by 2 electrodes; 1 in the fiber and 1 on the fiber, with both electrodes connected via an amplifier to a cathode ray oscilloscope; which functions to measure very minute and very rapid electrical changes.

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Types of membrane potential

resting membrane potential
action potential
localized electronic potential

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What forces and of what percent produce the resting membrane potential

Passive force (93%) and active force (7%)

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The embrace is about ________ times more permeable to potassium than sodium

100 times

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What constitutes the 7% of active force in attaining resting membrane potential?

Na/K pump

What is action potential?

This is a transient rapid reversal in the membrane polarity of an excitable membrane in response to a threshold stimulus.

When the stimulus is applied, there is a short irregular deflection of the baseline, this is called

Stimulus

The four phases of action potential:

- latent phase - Depolarization phase - depolarization phase - Hyperpolarization

What restores balance from Hyperpolarization to resting membrane potential

Na / K pump

The speed of propagation is proportional to:

The speed of propagation = square root of nerve diameter

The jump of (+ve) charges from the resting node to the activated node in myelinated nerve fibres is called

Saltatory conduction

Importance of saltatory conduction

1. Increases velocity of conduction up to 50 folds 2. It conserved energy to be used only at nodes of ranvier

The speed of propagation in myelinated nerve tubes is proportional to

Proportional to fiber diameter and internodal distance

Conduction of impulse in one direction from receptors along afferent path is called

Orthodromic conduction

Abnormal direction of nerve impulse propagation .i.e. from axon terminal to cell body is called

Antidromic conduction

the time following the initiation of an action potential during which no new action potential can be generated, regardless of the strength of the stimulus

Absolute refractory period

the phase after the absolute refractory period during which a new action potential can be initiated, but only by a stimulus that is stronger than usual.

Relative refractory period

Function of refractory period

1. It protects the nerve from extremely rapid repetitive stimulation which could compromise it function 2. Also to prevent backward propagation of impulse

Factors that affect excitability of nerve

1. Anything that increases or decreases permeability to Na 2. Anything that increases or decreases permeability to k 3. Na / K pump

Conditions that increase nerve permeability to Na

1. Veratrine 2. Low Ca in ECF

Conditions that decrease nerve permeability to Na

1. Local anesthetic like cocaine 2. High concentration of Ca in the ECF

What decreases nerve excitability by blockading Na

Tetrodotoxin

When tetra ethyl ammonium blockade (TEA) K what happens ?

Action potential is prolonged due to prolonged depolarization. Hyperpolarization is absent

Factors that decrease membrane excitability are called

Membrane stabilizers

Thickness of A fibers

2 - 20 microns

Thickness of B fibers

1 - 5 microns

Thickness of C fibres

< 1 micron

Velocity of C fibers

0.5 - 2 m/sec

Velocity of B fibers

5 - 15 m/sec

Velocity of B fibers

5 - 15 m/sec

Velocity of A fibres

20-120 m/sec

Spike duration of A, B and C fibers

0.5msec 1 msec 2 msec

What are the A fibres

myelinated somatic fibers

What are the B fibers

Myelinated Preganglionic autonomic fibres

What are the B fibers

Myelinated Preganglionic autonomic fibres

What are the C fibers

Unmyelinated postgamglionic autonomic fibers

What percentage of body weight does skeletal muscle make up? a) 30% b) 40% c) 50% d) 60%

b) 40%

2. What is the diameter range of skeletal muscle fibers? a) 5-20 micrometers b) 10-80 micrometers c) 20-100 micrometers d) 50-120 micrometers

b) 10-80 micrometers

3. What is the membrane surrounding the skeletal muscle fiber called? a) Myofibril b) Sarcoplasm c) Sarcolemma d) Endomysium

c) Sarcolemma

4. What is the primary structural unit of a myofibril between two Z-discs? a) Sarcoplasm b) Sarcomere c) H-zone d) M-line

b) Sarcomere

5. Which protein makes up the thick filament in skeletal muscle? a) Actin b) Myosin c) Troponin d) Tropomyosin

b) Myosin

Name the components of actin filament

Actin Tropomyosin Troponin

Which subunit of troponin binds to calcium ions to initiate contraction? a) Troponin I b) Troponin T c) Troponin C d) Troponin M

C) Troponin c

Where is the calcium stored in the skeletal muscle fiber? a) Sarcoplasmic reticulum b) Transverse tubules c) Synaptic cleft d) Motor end plate

a) Sarcoplasmic reticulum

What is the functional unit of contraction in skeletal muscle? a) Muscle fiber b) Sarcomere c) Myofilament d) Motor end plate

b) Sarcomere

What causes the release of calcium ions from the terminal cisterns during muscle contraction? a) Action potential b) ATP depletion c) Acetylcholinesterase activity d) Rigor mortis

a) Action potential

What type of receptor is found on the transverse tubules? a) Acetylcholine receptor b) DHP receptor c) Ryanodine receptor d) Troponin receptor

b) DHP receptor

Which molecule covers the actin active sites at rest? a) Tropomyosin b) Troponin c) Myosin d) Titin

a) Tropomyosin

What happens during the power stroke of muscle contraction? a) Myosin detaches from actin b) Myosin head bends, pulling actin filaments c) ATP binds to myosin d) Calcium binds to tropomyosin

b) Myosin head bends, pulling actin filaments

Which enzyme destroys acetylcholine in the synaptic cleft? a) Acetylcholine transferase b) Acetylcholinesterase c) DHP kinase d) ATPase

b) Acetylcholinesterase

Which enzyme destroys acetylcholine in the synaptic cleft? a) Acetylcholine transferase b) Acetylcholinesterase c) DHP kinase d) ATPase

b) Acetylcholinesterase

What is the local depolarization caused by sodium influx called? a) Action potential b) End plate potential c) Membrane potential d) Synaptic potential

b) End plate potential

Which protein holds actin and myosin filaments in place? a) Titin b) Tropomyosin c) Troponin d) Myosin

a) Titin

What happens during rigor mortis? a) Excess ATP causes prolonged contraction b) Lack of ATP prevents detachment of myosin heads c) Calcium ions are actively pumped back into the SR d) Muscle fibers are destroyed

b) Lack of ATP prevents

What happens to the Z-discs during muscle contraction? a) They move further apart b) They are destroyed c) They move closer together d) They do not change position

c) They move closer together

Which structure increases the surface area for acetylcholine action at the synaptic cleft? a) Motor end plate b) Subneural folds c) Synaptic vesicles d) Synaptic gutter

b) Subneural folds

What is the Fenn effect? a) The mechanism of muscle relaxation b) The relationship between muscle work and ATP usage c) The process of calcium reuptake d) The breakdown of acetylcholine in the synaptic cleft

b) The relationship between muscle work and ATP usage

What is the role of the Z-disk in muscle fibers? a) Stores calcium ions b) Anchors actin filaments c) Produces ATP d) Regulates muscle relaxation

b) Anchors actin filaments

Which component of the myosin molecule forms the cross-bridges? a) Heavy chains b) Light chains c) Globular heads d) Helical tails

c) Globular heads

Which structure transmits the action potential from the sarcolemma to the muscle interior?

Transverse tubules

What connects the sarcoplasmic reticulum to the transverse tubules for calcium release?

Ryanodine receptors

What is the term for the structure formed by two terminal cisterns and one transverse tubule?

Triad

What occurs during the detachment of myosin heads from actin?

ATP binds to the myosin head

What is the first step of the muscle contraction cycle? a) Calcium binding to troponin-C b) ATP binding to the myosin head c) Power stroke d) Actin filament detachment

b) ATP binding to the myosin head

What process occurs during rigor mortis?

ATP depletion prevents myosin detachment

What is the lighter region in the center of the A-band called? a) Z-disc b) H-zone c) I-band d) M-line

b) H-zone

What structural protein anchors myosin to the Z-disc? a) Tropomyosin b) Titin c) Troponin d) Actin

b) Titin

What molecule is attached to G-actin and forms the active site for myosin binding?

b) ADP

What happens to ATP during the power stroke of muscle contraction?

It is hydrolyzed into ADP and Pi

What is the primary function of acetylcholinesterase?

Break down acetylcholine stops ach binding to ach receptors. Therefore stops Na influx

Which step of muscle contraction is energy-dependent?

Pumping calcium ions back into the sarcoplasmic reticulum

What causes rigor mortis after death?

Depletion of ATP

What is the primary component of the Z-disc?

Filamentous proteins distinct from actin and myosin

What is the primary component of the Z-disc?

Filamentous proteins distinct from actin and myosin

What is the functional unit of a myofibril called?

Sarcomere

What happens to the A-band during muscle contraction?

It remains the same length

Which part of the sarcomere shortens the most during contraction?

H-zone

What structural feature of the myosin head allows it to perform a power stroke?

Hinged tail and neck

Which step follows ATP hydrolysis during the cross-bridge cycle?

Kinking of the myosin head

Which component of the muscle cell stores large quantities of potassium and magnesium?fri

Sarcoplasm

Muscles And Nerves Flashcards

(100 cards)