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The combined electrical activity of the different myocardial cells produces electrical currents that spread through the body fluids.
True
The action potentials recorded from atrial and ventricular fibers are the same as those recorded from nerves and skeletal muscle.
False
The cardiac action potential is composed of three phases: a rapid depolarization, a plateau depolarization, and a repolarization back to resting membrane potential.
True
On an ECG, the P-wave is produced by atrial depolarization.
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On an ECG, the QRS complex is produced by atrial depolarization; ventricular repolarization also occurs during this time.
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On an ECG, the T-wave is produced by atrial repolarization.
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On an ECG, the T-wave is produced by ventricular repolarization.
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Chest movements in humans may be recorded using any device that responds to the increase in chest circumference during inspiration.
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A stethograph is used to measure respiratory movements.
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In a stethograph, the rising of the pointer indicates expiration and the fall of the pointer indicates inspiration.
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A stethograph gives an indication of the respiratory rate only.
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A spirometer measures pulmonary volume changes occurring in the respiratory cycle.
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As the subject breathes through the mouthpiece into the spirometer, it causes a floating container to rise and fall with each respiratory cycle.
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The volume of gas which moves in and out of the lungs during each normal respiratory cycle is termed aspiratory volume.
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The average normal tidal volume is approximately 500 ml, however it is dependent on other factors such as sex, weight, and age.
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The volume of gas which can be drawn into the lungs during maximum inspiration after filling the lungs with tidal air is known as inspiratory reserve volume (IRV).
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Inspiratory capacity (IC) is the minimum amount of gas that can be inhaled after a normal expiration.
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The sum of the tidal and inspiratory capacity is generally around 3000 ml.
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The amount of air which can be inspired beyond the tidal volume is called expiratory reserve volume (ERV).
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Expiratory reserve volume (ERV) is normally measured at 100 ml.
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Residual volume (RV) is the amount of gas in the lungs that cannot be forcibly expelled.
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To calculate the vital capacity, minus the expiratory reserve from the expiratory reserve.
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The vital capacity is the maximum amount of gas that can be expired after a maximum inspiration.
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The sum of the expiratory reserve and residual volume will equal the functional residual capacity (FRC).
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The total lung capacity averages around 8 litres in an adult.
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Minute respiratory volume is the amount of tidal air that passes in and out of the lungs over 5 minutes.
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Functional residual capacity (FRC): This is the amount of gas which remains in the lungs after completing a normal respiratory cycle. It is the sum of the expiratory reserve and residual volumes.
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Expiratory reserve volume (ERV): This is the amount of air which can be expired beyond the tidal volume.
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Total lung capacity (TLC): This is the total volume of the lungs and is the sum of the vital capacity and the residual volume, averaging around 6 litres.
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Automatic responses to stimuli are generated by the nervous system and are called reflexes.
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All reflexes that result in automatic regulation of body function are visceral.
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Somatic reflexes involve smooth and cardiac muscle.
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Visceral reflexes involve adjustments of smooth and cardiac muscle, and response of glands to stimuli.
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A reflex arc is a neural pathway used in performing a reflex.
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The somatic reflex arc consists of all of the following components: a reactor neuron, an afferent neuron, a peripheral neuron, a motor neuron and an effector.
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A receptor responds to the stimulus by contracting.
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Examples of a receptor include a neuromuscular spindle and a cutaneous end-organ.
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A sensory neuron is also known as an efferent neuron.
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An afferent neuron carries impulses through a peripheral nerve and posterior root thus leaving relaying information to the spinal cord.
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An association neuron is also known as a motor neuron.
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An interneuron forms synaptic connections between the sensory and motor neuron in the gray matter of the spinal cord.
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An association neuron relays and processes a signal across only one synapse.
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A motor neuron transmits nerve impulses from the central nervous system through the posterior root to the effector via a peripheral nerve.
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An effector is a muscle or gland innervated by the motor neuron, responding to the stimulus by contracting.
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The knee jerk reflex is an example of a reflex arc with no interneuron.
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A reflex arc with no interneuron is termed polysynaptic.
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A single-sided reflex arc is termed ipsilateral. They only involve afferent and efferent pathways on one side of the brain and spinal cord.
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Contralateral reflexes use afferent pathways on the same side to the incoming stimulus.
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The five key features of somatic reflexes include: (a) function (b) radiation (c) synaptic excitement (d) inhibition (e) speed of reaction.
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Classical physiology experiments used to be performed using the frog as a model. A frog with its brain destroyed but retaining an intact spinal cord is known as a 'pithed' frog.
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The spinal frog preparation can be used to test either of the followings; reflex radiation, reflex inhibition, synaptic fatigue reaction time of reflexes or functional nature of reflexes.
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Functional nature of reflexes demonstrates that changes in muscle tone, movement, and coordinated action are dependent on cognition.
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Reaction time to a stimulus is influenced by the strength of the stimulus.
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Reflex radiation is a phenomenon observed when the foot of the spinal frog is subjected to increasing titrations of an acidic solution resulting in a change in reflex pattern.
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Reflex inhibition demonstrates how electrical stimulation can override a reflex action in the heart of the spinal frog observed in response to dipping the toes in an alkaline solution.
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Synaptic fatigue is a phenomenon observed when the sciatic nerve is overstimulated.
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Reflex testing is a fundamental clinical procedure used by physicians searching for possible systemic organ failure.
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Reflex studies can prove a useful aid in assessing a number of conditions including damage to intervertebral disks, tumors, polyneuritis and apoplexy.
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Clinically, reflexes are categorised as one of two types: (a) deep reflexes and (b) superficial reflexes.
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Deep reflexes include all reflexes elicited by a sharp tap on a tendon or muscle.
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Receptors for deep reflexes are located in tendon not muscle.
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When the tendon is tapped, the muscle relaxes which activates the muscle spindle therefore triggering the reflex response.
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Superficial reflexes are withdrawal reflexes elicited by noxious or tactile stimulation.
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Superficial reflexes can also be called jerk, stretch or myotactic reflexes.
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Stroking or scratching the skin will not induce a response in superficial reflexes.
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Hyporeflexia is a diminished response to stimuli often accompanied by marked muscle tone due to loss of inhibitory control by the motor cortex.
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Hyporeflexia is often due to malnutrition, neurological lesions, ageing or deliberate relaxation.
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Hyperreflexia is an exaggerated response to stimuli and can be induced by strychnine poisoning.
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Pathological reflexes are responses which occur in the muscle from which the stimulus originates.
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Hoffman's reflex is a superficial reflex in which the response occurs only in the muscle that is stretched.
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If the response to the stimulus to the Hoffman's reflex is broad then there is indication of pyramidal tract damage.
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To elicit the Hoffman's reflex, tap the patellar tendon just below the kneecap.
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When testing the Hoffman's reflex, if the thumb is abducted and relaxed but the fingers exhibit a twitch-like flexion, this indicates pathology.
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The patellar reflex is a monosynaptic reflex which is also known as the knee reflex/jerk or quadriceps reflex.
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The Jendrassic manoeuvre involves the subject locking the fingers of both hands behind the body and pulling each hand against each other.
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Clonus is characterised by a succession of spasms which follow a normal response to the patellar reflex and persist for a period of time.
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Clonus is a manifestation of hyporeflexia which indicates damage within the central nervous system.
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The patellar reflex functions through L3, L4 and L5 spinal nerves.
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The patellar reflex functions through L2, L3 and L4 spinal nerves.
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The Achilles reflex is characterised by plantar flexion when the Peroneus tendon is dealt a sharp blow.
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Stretching the Achilles tendon affects the muscle spindles in the triceps surae, causing it to contract.
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Hyporeflexia of the Achilles tendon is often associated with hyperthyroidism.
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The Achilles reflex functions through the S1 and S2 spinal nerves.
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Plantar flexion is a deep reflex.
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The normal reaction to stroking the sole of the foot in an adult is plantar flexion without adduction of the toes.
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Dorsiflexion starting in the big toe and spreading to the others (Babinski's sign) signifies damage to myelin in the fibers of the pyramidal tracts.
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Babinski's sign can occur in adults during sleep and in epileptics immediately after a seizure, but usually indicates a lesion in the corticospinal tracts or peripheral nerve damage.
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It is considered abnormal in sleeping infants up to six months and disappears once myelination of nerve fibers is complete.
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Plantar's flexion functions through S5 and S6 spinal nerves.
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A skeletal muscle fiber is innervated by a branch of a motor axon and under normal circumstances; a neuronal action potential activates all of the muscles innervated by the motor neuron.
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The activation of the motor neuron involves an action potential and relaxation of the muscle fibers.
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During a muscle contraction there is synchronised activity in a number of fibres in the same muscle.
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One way the nervous system controls a muscle is by adjusting the size of motor axons that fire, thus controlling the number of twitching muscle fibers.
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The nervous system can control a muscle contraction by varying the frequency of action potentials in the motor axons or by adjusting the number of motor axons firing.
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During continuous maximal muscle contraction all components required to maintain the contraction (from both nervous system and muscle itself) are used at rapid rate.
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The blood flow to the active muscle(s) is increased during maximal contractions to deliver oxygen and remove metabolites.
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The electrical signal recorded from a contracting muscle is called an electrocardiogram or ECG, and this activity can be detected by electrodes placed on the skin.
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An ECG is a series of regular waves whereas EMG activity is a chaotic burst of overlapping spike-like signals.
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Isotonic contraction of the muscle occurs when muscle contracts but does not shorten.
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Isometric contraction of the muscle occurs when muscle contracts and shortens.
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The first cardiovascular sound occurs simultaneously with the contraction of the ventricular myocardium and closure of the mitral and tricuspid valves.
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The second cardiovascular sound arises from the simultaneous closure of the ventricular and pulmonary valves at the start of ventricular systole.
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The third cardiovascular sound is believed to arise from the ventricular walls and atrioventricular (AV) valves during systole.
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Abnormal heart sounds are collectively referred to as murmurs and are usually indicative of damaged valves.
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A common cause of heart murmur results from damage to the tricuspid valve associated with rheumatic fever, with the mitral valve next susceptible to damage.
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Damaged valves often result in stenosis or regurgitation of blood flow.
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The four thoracic locations include the aortic area, the ventricular area, the pulmonic area and the mitral area.
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Listening to sounds within the body is referred to as auscultation. When considering auscultatory areas, it is important to note that they coincide with the anatomical locations of the various valves.
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The three methods used to monitor heart sounds are: (i) the stethoscope (ii) electronic recording and (iii) use of an audio monitor.
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Ventricles contract to push blood into the arterial system and then relax to fill with blood before pumping once more.
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The intermittent ejection of blood into the veins is balanced by a constant loss of blood from the arterial system through the capillaries.
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When the heart pushes blood into the arteries there is a sudden decrease in pressure, which slowly declines until the heart contracts again.
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Blood pressure is at its highest immediately after the ventricle contracts (systolic pressure) and at its lowest immediately prior to the pumping of blood into the arteries (diastolic pressure).
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A non-invasive way to measure systolic and diastolic pressures a small catheter can be inserted into an artery and the catheter attached to a pressure gauge.
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A blood pressure cuff is placed low on the arm and inflated to stop arterial blood flow to the arm from the brachial vein.
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When the systolic pressure in the artery exceeds the cuff pressure, blood slowly flows to the arm through the partially collapsed artery. This flow can be heard through the stethoscope as sharp, tapping sounds called Korotkoff sounds. At this stage, the cuff pressure approximates systolic pressure.
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As cuff pressure is reduced further, the sounds heard through the stethoscope increase in intensity and then suddenly become muffled. The cuff pressure at the point of sound muffling approximates diastolic blood pressure.
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The disappearance of sound is commonly used to determine diastolic pressure.
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The pressure in veins situated above a horizontal plane through the first costal cartilage is usually greater than atmospheric and the veins are distended.
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Venous pressure in a particular area may be raised if there is obstruction on any of the veins draining it, and may be lowered by movement of the adjacent muscles.
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The pressure in distended veins can be judged by palpitation. This pressure is mainly due to the hydrostatic effect of the blood column extending up to the heart.
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Note that relaxation of leg muscles squeezes blood into adjacent veins, and because the veins have valves helping maintain a single direction of flow blood, is moved onward towards the heart. This is often termed the muscle pump.
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When venous pressure rises it causes the capillary blood pressure to rise and fluid exudes from the capillaries into the tissues, resulting in swelling or edema.
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The pattern of electrical activity produced by each heartbeat is called the electrocardiogram (ECG).
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Blood enters the ventricle chambers of the heart at a low pressure and leaves the atria at a higher pressure.
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Blood returning from the body arrives at the right side of the heart and is pumped through the lungs to pick up oxygen and release carbon dioxide. This oxygenated blood then arrives at the left side of the heart, from where it is pumped back to the body.
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Study Notes
Reflexes
- Automatic responses to stimuli generated by the nervous system
- All reflexes that result in automatic regulation of body function are visceral
- Somatic reflexes involve skeletal muscle
- Visceral reflexes involve adjustments of smooth and cardiac muscle and response of glands
- A reflex arc is a neural pathway used in performing a reflex
- The somatic reflex arc consists of a receptor, an afferent neuron, an association neuron, a motor neuron and an effector.
- A receptor responds to the stimulus by initiating a nerve impulse
- Examples of a receptor include a neuromuscular spindle and a cutaneous end-organ
- A sensory neuron is also known as an afferent neuron
- An afferent neuron carries impulses through a peripheral nerve and posterior root to the spinal cord
- An association neuron is also known as an interneuron
- An interneuron forms synaptic connections between the sensory and motor neuron in the gray matter of the spinal cord
- A motor neuron transmits nerve impulses from the central nervous system through the anterior root to the effector via a peripheral nerve
- An effector is a muscle or gland innervated by the motor neuron, responding to the stimulus
- The knee jerk reflex is an example of a reflex arc with no interneuron
- A reflex arc with no interneuron is termed monosynaptic
- A single-sided reflex arc is termed ipsiateral
- Contralateral reflexes use afferent pathways on the opposite side to the incoming stimulus
- The five key features of somatic reflexes include: function, radiation, synaptic excitement, inhibition, speed of reaction
- A frog with its brain destroyed but retaining an intact spinal cord is known as a 'pithed' frog.
- The spinal frog preparation can be used to test either of the followings; reflex radiation, reflex inhibition, synaptic fatigue reaction time of reflexes or functional nature of reflexes
- Functional nature of reflexes demonstrates that changes in muscle tone, movement, and coordinated action are dependent on cognition
- Reaction time to a stimulus is influenced by the strength of the stimulus
- Reflex radiation is a phenomenon observed when the foot of the spinal frog is subjected to increasing titrations of an acidic solution resulting in a change in reflex pattern
- Reflex inhibition demonstrates how electrical stimulation can override a reflex action observed in response to dipping the toes in an alkaline solution
- Synaptic fatigue is a phenomenon observed when the sciatic nerve is overstimulted
- Reflex testing is a fundamental clinical procedure used by physicians searching for possible systemic organ failure
- Reflex studies can prove a useful aid in assessing a number of conditions including, damage to intervertebral disks, tumours, polyneuritis and apoplexy
- Clinically, reflexes are categorised as one of two types: deep reflexes and superficial reflexes
- Deep reflexes include all reflexes elicited by a sharp tap on a tendon or muscle
- Receptors for deep reflexes are located in muscle
- When the tendon is tapped, muscle stretches which activates the muscle spindle therefore triggering the reflex response
- Superficial reflexes are withdrawl reflexes elicited by noxious or tactile stimulation
- Superficial reflexes can also be called jerk, stretch or myotactic reflexes
- Stroking or scratching the skin will induce a response in superficial reflexes
- Hyporeflexia is a diminished response to stimuli often accompanied by reduced muscle tone due to loss of inhibitory control by the motor cortex
- Hyporeflexia is often due to malnutrition, neurological lesions, ageing or deliberate relaxation
- Hyperreflexia is an exaggerated response to stimuli and can be induced by strychnine poisoning
- Pathological reflexes are responses which occur in the muscle from which the stimulus originates
- Hoffman's reflex is a superficial reflex in which the response occurs in the muscle that is stretched and the fingers
- If the response to the stimulus to the Hoffman's reflex is broad then there is indication of pyramidal tract damage
- To elicit the Hoffman's reflex, tap the fingernail of middle finger
- When testing the Hoffman's reflex, if the thumb is abducted and relaxed but the fingers exhibit a twitch-like flexion, this indicates pathology
- The patellar reflex is a monosynaptic reflex which is also known as the knee reflex/jerk or quadriceps reflex
- The Jendrassic manoeuvre involves the subject locking the fingers of both hands behind the body and pulling each hand against each other
- Clonus is characterised by a succession of spasms which follow a normal response to the patellar reflex and persist for a period of time
- Clonus is a manifestation of hyperreflexia which indicates damage within the central nervous system
- The patellar reflex functions through L3, L4 and L5 spinal nerves
- The Achilles reflex is characterised by plantar flexion when the Achilles tendon is dealt a sharp blow
- Stretching the Achilles tendon affects the muscle spindles in the triceps suurae, causing it to contract
- Hyporeflexia of the Achilles tendon is often associated with hyperthyroidism
- The Achilles reflex is functions through the SI and S2 spinal nerves
- The Plantar flexion is a superficial reflex
- The normal reaction to stroking the sole of the foot in an adult is plantar flexion without adduction of the toes
- Dorsiflexion starting in the big toe and spreading to the others (Babinski's sign) signifies damage to myelin in the fibres of the pyramidal tracts
- Babinski's sign can occur in adults during sleep and in epileptics immediately after a seizure, but usually indicates a lesion in the corticospinal tracts or peripheral nerve damage.
- It is considered abnormal in sleeping infants up to six months and disappears once myelination of nerve fibres is complete
- Plantar's flexion functions through S5 and S6 spinal nerves
Muscle Contraction
- A skeletal muscle fibre is innervated by a branch of a motor axon and under normal circumstances; a neuronal action potential activates all of the muscles innervated by the motor neuron
- The activation of the motor neuron involves an action potential and contraction of the muscle fibres.
- During a muscle contraction there is synchronised activity in a number of fibres in the same muscle.
- One way the nervous system controls a muscle is by adjusting the number of motor axons firing, thus controlling the number of twitching muscle fibres.
- The nervous system can control a muscle contraction by varying the frequency of action potentials in the motor axons or by adjusting the number of motor axons firing.
- During continuous maximal muscle contraction all components required to maintain the contraction (from both nervous system and muscle itself) are used at a rapid rate.
- The blood flow to the active muscle(s) is increased during maximal contractions to deliver oxygen and remove metabolites.
- The electrical signal recorded from a contracting muscle is called an electromyogram or EMG, and this activity can be detected by electrodes placed on the skin.
- An ECG is a series of regular waves whereas EMG activity is a chaotic burst of overlapping spike-like signals.
Isotonic and Isometric Contraction
- Isotonic contraction of the muscle occurs when muscle contracts and shortens.
- Isometric contraction of the muscle occurs when muscle contracts but does not shorten.
Cardiovascular Sounds
- The first cardiovascular sound occurs simultaneously with the closure of the mitral and tricuspid valves at the start of ventricular systole.
- The second cardiovascular sound arises from the simultaneous closure of the aortic and pulmonary valves at the end of ventricular systole.
- The third cardiovascular sound is believed to arise from the ventricular walls and atrioventricular (AV) valves during systole.
- Abnormal heart sounds are collectively referred to as murmurs and are usually indicative of damaged valves.
- A common cause of heart murmur results from damage to the mitral valve associated with rheumatic fever.
- Damaged valves often results in stenosis or regurgitation of blood flow.
- The four thoracic locations include the aortic area, the pulmonary area, the tricuspid area and the mitral area.
- Listening to sounds within the body is referred to as auscultation.
- The three methods used to monitor heart sounds are: the stethoscope, electronic recording and use of an audio monitor.
Blood Pressure
- Ventricles contract to push blood into the arterial system and then relax to fill with blood before pumping once more.
- Blood pressure is at its highest immediately after the ventricle contracts (systolic pressure) and at its lowest immediately prior to the pumping of blood into the arteries (diastolic pressure).
- A non-invasive way to measure systolic and diastolic pressures a small catheter can be inserted into an artery and the catheter attached to a pressure gauge.
- A blood pressure cuff is placed low on the arm and inflated to stop arterial blood flow to the arm.
- When the systolic pressure in the artery exceeds the cuff pressure, blood slowly flows to the arm through the partially collapsed artery. This flow can be heard through the stethoscope as sharp, tapping sounds called Korotkoff sounds. At this stage, the cuff pressure approximates systolic pressure.
- As cuff pressure is reduced further, the sounds heard through the stethoscope increase in intensity and then suddenly become muffled. The cuff pressure at the point of sound muffling approximates diastolic blood pressure.
- The disappearance of sound is commonly used to determine diastolic pressure.
- The pressure in veins situated above a horizontal plane through the frist costal cartilage is usually greater than atmospheric and the veins are distended.
- Venous pressure in a particular area may be raised id there is obstruction on any of the veins draining it, and may be lowered by movement of the adjacent muscles.
- The pressure in distended veins can be judged by palpitation. This pressure is mainly due to the hydrostatic effect of the blood column extending up to the heart.
- Relaxation of leg muscles squeezes blood into adjacent veins, and because the veins have valves helping maintain a single direction of flow blood, is moved onward towards the heart. This is often termed the muscle pump.
- When venous pressure rises it causes the capillary blood pressure to rise and fluid exudes from the capillaries into the tissues, resulting in swelling or oedema.
Electrocardiogram (ECG)
- The pattern of electrical activity produced by each heart beat is called the electrocardiogram (ECG).
- Blood entering the ventricle chambers of the heart at a low pressure and leaves the atria at a higher pressure.
- Blood returning from the body arrives at the right side of the heart and is pumped through the lungs to pick up oxygen and release carbon dioxide. This oxygenated blood then arrives at the left side of the heart, from where it is pumped back to the body.
- The combined electrical activity of the different myocardial cells produces electrical currents that spread through the body fluids. These currents are large enough to be detected by recording electrodes placed on the skin. The regular pattern of peaks produced by each heart beat cycle is called the electrocardiogram or ECG.
- The action potentials recorded from atrial and ventricular fibers are the same as those recorded from nerves and skeletal muscle.
- The cardiac action potential is composed of three phases: a rapid depolarization, a plateau depolarization (which is very obvious in ventricular fibers), and a repolarization back to resting membrane potential.
- On an ECG, the P-wave is produced by atrial depolarization.
- On an ECG, the QRS complex is produced by ventricular depolarization.
- On an ECG., the T-wave is produced by ventricular repolarization.
Respiratory Movements
- Chest movements in humans may be recorded using any device which responds to the increase in chest circumference during inspiration.
- A stethograph is used to measure respiratory movements. It consists of a flexible corrugated tubing filled with air. On inspiration the tubing is stretched and the volume decreases; air is displaced from the rubber tambour and the lever carrying the ink pen rises.
Stethograph
- A stethograph is a device used to measure respiratory movements.
- The rising of the pointer indicates inspiration.
- The falling of the pointer indicates expiration.
Spirometer
- A spirometer is used to measure changes in lung volume.
- Air is exhaled through a mouthpiece into the spirometer which causes a floating container to rise and fall.
- Respiratory movements are recorded using a kymograph.
Lung Volumes
- Tidal Volume: This is the amount of air inhaled or exhaled during normal breathing. The average tidal volume is 500 ml, but this varies depending on sex, weight, and age.
- Inspiratory Reserve Volume (IRV): This is the maximum amount of air that can be inhaled after a normal tidal volume.
- Inspiratory Capacity (IC): This is the maximum amount of air that can be inhaled after a normal exhalation. It is the sum of the tidal volume and the inspiratory reserve volume.
- Expiratory Reserve Volume (ERV): This is the maximum amount of air that can be exhaled after a normal expiraiton. The average ERV is around 1100 ml.
- Residual Volume (RV): This is the amount of air remaining in the lungs after a forced exhalation. It cannot be exhaled and is approximately 1200 ml.
- Vital Capacity (VC): This is the maximum amount of air that can be exhaled after a maximum inspiration. This volume is dependent on age, height, and sex and the average is around 4500 ml.
- Functional Residual Capacity (FRC): This is the volume of air remaining in the lungs after a normal exhalation. It is the sum of the expiratory reserve volume and the residual volume.
- Total Lung Capacity (TLC): This is the total amount of air that the lungs can hold. It is the sum of the vital capacity and the residual volume. The average TLC is approximately 6 liters.
Respiratory Volumes & Capacity
- Minute Respiratory Volume: This is the amount of air inhaled or exhaled per minute. It is calculated by multiplying the tidal volume by the respiratory rate.
- Minute Ventilation: This is the total amount of air that moves into and out of the lungs per minute.
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Description
This quiz focuses on the automatic responses generated by the nervous system known as reflexes. It covers both somatic and visceral reflexes, including the components of a reflex arc and the role of different neurons involved. Test your understanding of how the nervous system regulates body functions through these quick responses.
