Physiology Lab Exam 2
Muscle twitch??? Diff between twitch response?
-??? -Myosin combines with actin forming a complex called actomyosin. -no other protein can substitute for actin. -When actin and myosin combine the muscle produces force. Myosin is an enzyme that hydrolyzes ATP. Hydrolysis of ATP to ADP causes a conformational change in the actomyosin complex, leading to muscle shortening. -a brief contraction -Reuptake of the released Ca2+ into stores then lowers cellular Ca2+ levels, and the muscle relaxes again.
Define a withdrawal reflex
-moves affected parts of the body away from a painful stimulus
Muscle contractile force
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???Be able to identify and describe the functions of the components of the knee-jerk reflex. ???
-??? -Striking the patellar tendon stretches the quadriceps muscle. This stimulates sensory receptors in the muscle that trigger an impulse in a sensory axon whose cell body lies in the dorsal root ganglion in the lumbar region of the spinal cord. The sensory axon synapses directly with a motor neuron that conducts the impulse to the quadriceps, triggering contraction. This reflex that you have artificially activated here, helps maintain the upright posture in everyday life.
Twitch response???
-??? Myosin combines with actin forming a complex called actomyosin. -no other protein can substitute for actin. -When actin and myosin combine the muscle produces force. Myosin is an enzyme that hydrolyzes ATP. Hydrolysis of ATP to ADP causes a conformational change in the actomyosin complex, leading to muscle shortening. -a brief contraction
Verbal encouragement and muscle fatigue
-??? (decreases muscle fatigue and increases reaction time?)
Tetanus
-At extremely high stimulation frequencies, the muscle has no time to relax between successive stimuli. The result is a smooth contraction many times stronger than a single twitch -a "tetanic" contraction
Muscle summation
-At stimulation intervals between 75-200 ms, Ca2+ in the muscle is still above baseline levels when the next action potential arrives -the muscle fiber has not completely relaxed and the next contraction is stronger than normal -additive effect
Define a pupillary light reflex
-More complex reflex- involves additional cells called interneurons, and more than one population of motor neurons -This results in a longer delay between stimulus reception and the more complex response -involves four neurons that connect the retina to the midbrain
Muscle fatigue
-Skeletal muscle contraction requires energy from the breakdown of ATP to ADP -depletion of ATP stores can result in fatigue -ATP can be remade from ADP by the addition of a phosphate group (3 pathways): -Aerobic glycolysis: when enough O2 is present, pyruvate (from the breakdown of fats, glycogen, or glucose) can enter the citric acid cycle and is broken down to CO2 and H2O. This process generates large amounts of ATP. -Anaerobic glycolysis: if O2 supplies are insufficient, pyruvate cannot enter the citric acid cycle and instead is converted to lactic acid. This makes a small amount of ATP, but does not require O2. -Phosphocreatine: in resting muscle, some ATP transfers a phosphate to creatine, creating a store of phosphocreatine. During intense exercise, phosphocreatine can be used to resynthesize ATP, and allows contraction to continue. ***Some muscle fibers are more resistant to fatigue than others. They may have more mitochondria and hence a greater capacity for oxidative metabolism, or they may have greater stores of phosphocreatine. -In animals and humans fatigue occurs primarily because the motor drive from the brain (or the "central drive") is reduced, rather than as a result of depletion of the muscle energy reserves. The role of the "central drive" also explains why, some people can show "super-human" strength for brief periods in extreme situations. -Factors explaining the fall in force during prolonged contraction include the following: -Changes in the "sense of effort". -Loss of the "central drive". -Failure of neuromuscular propagation. -Reduction in Ca2+ release in excitation-contraction coupling. -Metabolic changes in the muscle cell (such as build up of lactic acid which can make the skeletal muscle acidic, inhibiting any further anaerobic glycolysis). -Reduction in muscle blood flow owing to compression of blood vessels.
Comparison between auditory and visual reaction times
-The Auditory RT is faster than the Visual RT
Be able to define a Jendrassik maneuver and its importance.
-The Jendrassik maneuver is a medical maneuver wherein the patient clenches the teeth, flexes both sets of fingers into a hook-like form, and interlocks those sets of fingers together. The tendon below the patient's knee is then hit with a reflex hammer to elicit the patellar reflex. -caused increased reflex amplitude and decreased total reflex time -reinforces reflexes
Muscle recruitment
-The control of a whole muscle can involve the firing of hundreds of motor axons. These motor nerves control movement in a variety of ways. One way is by adjusting the number of motor axons firing, thus controlling the number of twitching muscle fibers.
Define motor unit
-The motor neuron, together with all of the individual muscle fibers that it innervates
Define a reaction time
-Voluntary reactions to a cue
Define electromyography
-a technique that measures the electrical activity of the muscles and the nerves controlling the muscles. The data recorded is an electromyogram; also known as an "EMG" or "Myogram". -There are two methods of recording: -Intramuscular: needle electrodes inserted through the skin into the muscle. -Surface: electrodes placed on the skin surface. Importance: -The size and shape of the waveform measured provide information about the ability of the muscle to respond when the nerves are stimulated. -EMG is most often used when people have symptoms of weakness, and examination shows impaired muscle strength. It can help to differentiate muscle weakness caused by neurological disorders from other conditions. -provides a depiction of the timing and pattern of muscle activity during complex movements. -raw surface EMG signal reflects the electrical activity of the muscle fibers active at that time. Motor units fire asynchronously. With exceedingly weak contractions, there may be very few motor units activated or "firing". This means that only a single motor unit is firing at any time. So it is possible that the activity of a single motor unit can be seen in an EMG. As the strength of the muscular contraction increases, the density of action potentials increases and the raw signal at any time may represent the electrical activity of perhaps thousands of individual fibers.
Differences between a reaction time and a reflex
-considerably more complicated than reflexes -require higher brain functions, rather than relying on low-level neuronal circuitry
Activity of antagonist muscles and phenomenon of coactivation
-contraction of a muscle leads to minor activity in the antagonistic muscle -the physiological significance of this is not entirely clear, but it has been suggested that it helps to stabilize the joint during isotonic contractions -example such as lifting a weight with your arm. The biceps muscle contracts to lift the weight, and the triceps also contract to help control this lifting movement.
Understand the responses evoked by nerve stimulation at the elbow
-ex. of evoked EMGs -produced by electrical stimulation of a motor nerve supplying a muscle -results in contraction of the abductor pollicis brevis muscle, which causes the thumb to twitch. -brief electrical pulses are administered through the skin to the nerve, and the time it takes for the muscle to contract in response to the electrical pulse is recorded. The speed of the response is dependent on the conduction velocity. -faster than in wrist because nerve is close to the skin
Understand the stimulation of the median nerve at the wrist
-example of evoked EMGs -produced by electrical stimulation of a motor nerve supplying a muscle -results in contraction of the abductor pollicis brevis muscle, which causes the thumb to twitch. -brief electrical pulses are administered through the skin to the nerve, and the time it takes for the muscle to contract in response to the electrical pulse is recorded. The speed of the response is dependent on the conduction velocity. -takes longer than elbow because nerve is deeper
Be able to identify and describe the functions of the components of the pupillary light reflex.
-involves four neurons that connect the retina to the midbrain -When light is focused upon the eye, the pupillary sphincter muscle in the iris constricts reducing the aperture (diameter) of the pupil. At the same time, the pupillary sphincter muscle of the other eye constricts too, which is known as the consensual light reflex. Pupillary constriction is known as miosis, pupillary dilatation is called mydriasis. Accommodation, which involves changes in ciliary muscle activity, often occurs at the same time as the pupillary light reflexes to maintain visual acuity.
Be able to identify and describe the functions of the components of the withdrawal reflex.
-involves several synaptic links -stimulation of pain (nociceptive) sensory neurons leads to stimulation of flexor muscles and reciprocal inhibition of extensor muscles. The reaction of the stimulated limb is accompanied by an opposite reaction in the other limb. This crossed extension reflex serves to enhance postural support during withdrawal of the affected limb from the painful stimulus.
Define a knee-jerk reflex
-produced by a tap on the tendon under the kneecap -a.k.a. "myotatic" reflex -Striking the patellar tendon stretches the quadriceps muscle. This stimulates sensory receptors in the muscle that trigger an impulse in a sensory axon whose cell body lies in the dorsal root ganglion in the lumbar region of the spinal cord. The sensory axon synapses directly with a motor neuron that conducts the impulse to the quadriceps, triggering contraction. This reflex that you have artificially activated here, helps maintain the upright posture in everyday life. -2 neurons involved, sensory and motor
Nerve conduction rate
-the speed at which an electrochemical impulse propagates down a neural pathway -affected by a wide array of factors, including age, sex, and various medical conditions. -allow for better diagnoses of various neuropathies, especially demyelinating conditions -In general, the normal range will be approximately 40-60 meters per second -may vary from one individual to another and from one nerve to another.
Identify the factors that affect a reaction time
Age ± For both males and females, reaction time shortens from infancy into the late 20s. It then increases slowly until the 50s and 60s, and then lengthens faster as the person gets into their 70s and beyond. Arousal ± Reaction time is fastest with an intermediate level of arousal, and deteriorates when the volunteer is either too relaxed or too tense. Distraction + Distractions increase reaction time significantly, especially in younger individuals. Sex ± Males generally have faster reaction times than females. Practice - Practice at a task decreases reaction time. Errors + When a volunteer makes an error (like pressing the button before the stimulus is presented), subsequent reaction times are slower likely due to the subject being more cautious. Fatigue + Reaction time deterioration due to fatigue is more marked when the task is complicated than when it is simple. Mental fatigue (especially sleepiness) has the greatest effect. Punishment - Shocking a volunteer when he or she reacts slowly does shorten reaction time (we will not replicate these experiments for obvious reasons). Drugs ± Stimulants tend to decrease reaction times to a point, but see the comment above for Arousal. Depressants often increase reaction times. Warnings - Generally, reaction times are faster when the volunteer has been warned that a stimulus will arrive soon.
Latent period, contraction period, relation period
Latent Period: time it takes for the muscle to contract Contraction Period: time period where 1+ motor units are contracted? Relation Period:???
