Physiology 🫁 Flashcards
what are excitable tissues?
- Tissues which respond to adequate stimulation by an electrical response, Nerve and muscle tissues are the most excitable tissues in the body.
Nerve: Respond by action potential (Depolarization &repolarization).
Muscle: Respond by muscle contraction (contraction followed by relaxation i.e., SMT)
What are the types of stimuli according to Strength?
- Subminimal (subthreshold) stimuli
- Minimal (threshold) stimulus
- Superminimal (super-threshold) stimuli
- Maximal stimulus
- Super-maximal stimuli:
Subminimal (subthreshold) stimuli
stimuli of low intensity which produce no response (even if applied for a very long time).
Minimal (threshold) stimulus
is the weakest stimulus which produces a response.
Superminimal (super-threshold) stimuli
Increasing the intensity of the stimulus gradually above the threshold value leads to gradual increase in the response till it becomes maximum
Maximal stimulus
- the stimulus that produces a maximal response. When the stimulus reaches a certain value, the response becomes maximum and fixed i.e. there is no further increase in the response with greater intensities.
Super-maximal stimuli
stimuli of greater intensities than the maximal stimulus. These stimuli produce the same response as the maximal stimulus.
statement of all or none rule
The response either occurs maximally or it does not occur at all, provided that all other conditions remain constant.
*So, All subminimal stimuli do not produce response
*And, Minimal (threshold) stimulus produces a maximal response
*Further increase in the intensity of the stimuli (superminimal, maximal, supermaximal) do not produce any further increase in the response
Is there any contradiction between gradation of skeletal muscle contraction and all or none role ?
NO, as All or non law is applied in the single nerve fiber or single muscle fiber while gradation is applied in the nerve trunk or the whole muscle.
what is the definition of simple muscle twitch (SMT)?
A single contraction followed by relaxation due to simulation of skeletal muscle by single maximal stimulus .
what are the phases of simple muscle twitch?
- The latent phase
- Contraction phase
- Relaxation phase
latent phase of simple muscle twitch
The interval from stimulus application until the muscle begins
to shorten.
contraction phase of simple muscle twitch
The muscle fibers shorten
relaxation phase of simple muscle twitch
The muscle return to its original length
what are the factors affecting simple muscle twitch?
- Temperature
- fatigue
- Stimulus frequency
how does warming affect simple muscle twitch?
- (by using a warm ringer’s solution) “30-40”
-
Effect:
1-Increase amplitude of SMT
2-Decrease duration of all phases of SMT -
Causes:
1.Temperature reduces muscle viscosity.
2.Temperature activates muscle enzymes.
_________
- NB: Severe ≥ 42: Heat rigor
how does cooling effect simple muscle twitch?
- (by using a cool ringer’s solution) “>20”
-
Effect:
1-decrease amplitude of SMT
2-increase duration of all phases of SMT -
Causes:
1. Temperature increases muscle viscosity.
2. Temperature reduces muscle enzymes activity
what are other types of Rigor?
- Ca rigor (arrest of heart in systole)
- Rigor mortis (stiffening of muscles after death due to Depletion of ATP)
what is the definition of fatigue?
- It is a state of decreased muscular activity due to rapid repeated stimuli, the muscle may not show any response to stimuli.
what are the manifestations of muscle fatigue?
1-Decrese amplitude of SMT
2-Increase duration of all phases of SMT
3- Contracture
what is contracture?
a state of sustained weak muscle contraction followed by incomplete relaxation due to depletion of ATP which occurs when the muscle become extremely fatigued.
effects of increased stimulus frequency
- Effects of stimulation with Very Low frequency
- Effects of stimulation with Low frequency
- Effects of stimulation with intermediate frequency
- Effects of stimulation with high frequency
effects of stimulation of muscle with very low frequency
- Leads to separate twitches as this allows enough time for the muscle to complete relaxation.
effects of stimulation of muscle with low frequency
Leads to separate twitches as this allows enough time for the muscle to complete relaxation, but staircase appears
effects of stimulation of muscle with intermediate frequency
Leads to Clonus (incomplete tetanus) As the stimuli falls during the relaxation time.
effects of stimulation of muscle with high frequency
Leads to tetanus. As the stimuli falls during the contraction time.
what is the definition of staircase (treppe) phenomenon?
- When a muscle is stimulated with the maximal stimulus at a slow rate so that each stimulus occurs after the previous muscle twitch is complete, there is an increase in the height of each twitch until a constant height is reached after several twitches
what is the cause of staircase (treppe) phenomenon?
- The cause of this phenomenon is that the 2nd stimulus finds the muscle in a better physiological condition (more warm and more Ca ++ ions are present inside the muscle fibers).
where does staircase phenomenon occur?
Staircase phenomenon can occur with separate twitches, clonus and tetanus
what is the definition of clonus (incomplete tetanus)?
- Repeated contractions of the muscle with incomplete relaxation.
(If the frequency is increased, stimuli will fall during the relaxation phases of the previous twitches)
what is the definition of tetanus?
- A continuous contraction without relaxation which results from fusion of successive contractions produced by the rapid successive stimulation due to persistent release of Ca++ ions which lead to continuous contractions.
(With the frequency further increased, stimuli will fall during the contraction phases of the preceding twitch)
what is the value of the tension developed during a complete tetanus?
The tension developed during a complete tetanus is about 4 times that developed by a simple muscle twitch.
what is the frequency of Stimulation needed to produce tetanus?
The frequency of stimulation needed to produce tetanus is around 20-60 HZ for most skeletal muscles.
Which is the commonest type of contraction in the human body stair case, clonus or tetanus ?
tetanus
With low frequency stimuli, how can you produce tetanus ?
Increaseing the duration of SMT, may be by cooling
what is the most commonly used stimuli in laboratory experiments? And why?
Electrical stimuli as:
- their onset, duration and strength are easily controlled
- similar to physiological process of excitation,
- cause no or minimal tissue damage so, can be repeated.
what are the apparatuses used to record muscle contraction?
- kymograph
- Biopac
what does each apparatus for recording of skeletal muscle response include?
- Organ bath for tissue
- Rotating drum and pen for recording
- Electrical stimulator
what are the two types of electric currents that can be used in Physiological experiments?
Galvanic current
- long duration
- low amplitude
Faradic current
- short duration
- high amplitude
what controls the degree of muscle contraction?
- Activating a desired number of motor units within the muscle.
- Controlling the frequency of motor neuron impulses in each motor unit.
- When an increased muscle contraction is necessary, the brain increases the number of simultaneously active motor unit within the muscle. This is known as “motor unit recruitment”.
what are the causes of delayed muscle fatigue inside the body?
Cardiovascular system: supplies the muscles with 02 and nutrients and removes the metabolites from the muscle.
CNS: regulates the muscle contraction so that not all the muscle fibers are contracted at the same time, but instead, there is alternation between contracted and relaxed muscle fibers.
Hormones: e.g. adrenaline, noradrenalin, cortisol, thyroxin and insulin. They delay onset fatigue by increasing the metabolic rate, glycogen stores, blood pressure and excitability of the nervous system
what are the disadvantages of perfusion of tissues with pure water?
- Perfusion of tissues with pure water destroys the cells.
- It draws from the cells important crystalloids
- It also leads to rupture of the cell membrane duo to accumulation of water inside the cells.
what are the solutions used instead of water?
- The following solutions (physiological saline, Tyrod’s solution, Ranger’s solution) are used instead of water for perfusion or for preventing the tissues from drying.
- They are isotonic with the cells and they contain the essential crystalloids constituents in the same concentration as the plasma and tissue fluids.
physiological saline
- 0.6% sodium chloride solution for frog’s tissues.
- 0.9% Sodium Chloride for mammalian tissue
ringer’s solution
- Ringer’s solution typically contains NaCI, KCI, CaCl2 and NaHCO3
- Sometimes with other minerals such as MCI2, dissolved in distilled water.
- The precise proportions of these vary from species to species
Tyrode’s solution
- It resembles lactated Ringer’s solution, but contains magnesium, a sugar (usually glucose) as an energy source and uses bicarbonate and phosphate as a buffer instead of lactate.
- It must be gassed with oxygen and carbon dioxide when used for cell culture applications and physiology
