Graded Contractions and Muscle Metabolism

The muscle twitch is a single response to a single stimulus. Muscle twitches vary in length according to the type of muscle cells involved. .

Fast twitch muscles such as those which move the eyeball have twitches which reach maximum contraction in 3 to 5 ms (milliseconds).  [superior eye] and [lateral eye] These muscles were mentioned earlier as also having small numbers of cells in their motor units for precise control.

The cells in slow twitch muscles like the postural muscles (e.g. back muscles, soleus) have twitches which reach maximum tension in 40 ms or so.

 The muscles which exhibit most of our body movements have intermediate twitch lengths of 10 to 20 ms.

The latent period, the period of a few ms encompassing the chemical and physical events preceding actual contraction.

This is not the same as the absolute refractory period, the even briefer period when the sarcolemma is depolarized and cannot be stimulated. The relative refractory period occurs after this when the sarcolemma is briefly hyperpolarized and requires a greater than normal stimulus

Following the latent period is the contraction phase in which the shortening of the sarcomeres and cells occurs. Then comes the relaxation phase, a longer period because it is passive, the result of recoil due to the series elastic elements of the muscle.

We do not use the muscle twitch as part of our normal muscle responses. Instead we use graded contractions, contractions of whole muscles which can vary in terms of their strength and degree of contraction. In fact, even relaxed muscles are constantly being stimulated to produce muscle tone, the minimal graded contraction possible.

Muscles exhibit graded contractions in two ways:

1) Quantal Summation or Recruitment - this refers to increasing the number of cells contracting. This is done experimentally by increasing the voltage used to stimulate a muscle, thus reaching the thresholds of more and more cells. In the human body quantal summation is accomplished by the nervous system, stimulating increasing numbers of cells or motor units to increase the force of contraction.

2) Wave Summation ( frequency summation) and Tetanization- this results from stimulating a muscle cell before it has relaxed from a previous stimulus. This is possible because the contraction and relaxation phases are much longer than the refractory period. This causes the contractions to build on one another producing a wave pattern or, if the stimuli are high frequency, a sustained contraction called tetany or tetanus. (The term tetanus is also used for an illness caused by a bacterial toxin which causes contracture of the skeletal muscles.) This form of tetanus is perfectly normal and in fact is the way you maintain a sustained contraction.

Treppe is not a way muscles exhibit graded contractions. It is a warmup phenomenon in which when muscle cells are initially stimulated when cold, they will exhibit gradually increasing responses until they have warmed up. The phenomenon is due to the increasing efficiency of the ion gates as they are repeatedly stimulated. Treppe can be differentiated from quantal summation because the strength of stimulus remains the same in treppe, but increases in quantal summation

Length-Tension Relationship: Another way in which the tension of a muscle can vary is due to the length-tension relationship. This relationship expresses the characteristic that within about 10% the resting length of the muscle, the tension the muscle exerts is maximum. At lengths above or below this optimum length the tension decreases.

Heart sounds

Heart sounds are a result of beating heart and resultant blood flow . that could be detected by a stethoscope during auscultation . Auscultation is a part of physical examination that doctors have to practice them perfectly.
Before discussion the origin and nature of the heart sounds we have to distinguish between the heart sounds and hurt murmurs. Heart murmurs are pathological noises that results from abnormal blood flow in the heart or blood vessels.
Physiologically , blood flow has a laminar pattern , which means that blood flows in form of layers , where the central layer is the most rapid . Laminar blood flow could be turned into turbulent one .

Turbulent blood flow is a result of stenotic ( narrowed ) valves or blood vessels , insufficient valves , roughened vessels` wall or endocardium ,  and many diseases . The turbulent blood flow causes noisy murmurs inside or outside the heart.

Heart sounds ( especially first and second sounds ) are mainly a result of closure of the valves of the heart . While the third sound is a result of vibration of ventricular wall and the leaflets of the opened AV valves after rapid inflow of blood from the atria to ventricles . 

Third heart sound is physiologic in children but pathological in adults.

The four heart sound is a result of the atrial systole and vibration of the AV valves , due to blood rush during atrial systole . It is inaudible neither in adults nor in children . It is just detectable by the phonocardiogram .

Characteristic of heart sounds :

1. First heart sound  (S1 , lub ) : a soft and low pitch sound, caused by closure of AV valves.Usually has two components ( M1( mitral ) and T1 ( tricuspid ). Normally M1 preceads T1.

2. Second heart sound ( S2 , dub) : sharp and high pitch sound . caused by closure of semilunar valves. It also has two components A2 ( aortic) and P2 ( pulmonary) . A2 preceads P2.

3. Third heart sound (S3) : low pitched sound.

4. Fourth heart sound ( S4) very low pitched sound.

As we notice : the first three sounds are related to ventricular activity , while the fourth heart sound is related to atrial activity.
Closure of valves is not the direct cause for heart sounds , but sharp blocking of blood of backward returning of blood by the closing valve is the direct cause.
 

Proteinuria—Protein content in urine, often due to leaky or damaged glomeruli.

Oliguria—An abnormally small amount of urine, often due to shock or kidney damage.

Polyuria—An abnormally large amount of urine, often caused by diabetes.

Dysuria—Painful or uncomfortable urination, often from urinary tract infections.

Hematuria—Red blood cells in urine, from infection or injury.

Glycosuria—Glucose in urine, due to excess plasma glucose in diabetes, beyond the amount able to be reabsorbed in the proximal convoluted tubule.

SPECIAL VISCERAL AFFERENT (SVA) PATHWAYS

Taste

Special visceral afferent (SVA) fibers of cranial nerves VII, IX, and X conduct signals into the solitary tract of the brainstem, ultimately terminating in the nucleus of the solitary tract on the ipsilateral side.

Second-order neurons cross over and ascend through the brainstem in the medial lemniscus to the VPM of the thalamus.

Thalamic projections to area 43 (the primary taste area) of the postcentral gyrus complete the relay.

SVA VII fibers conduct from the chemoreceptors of taste buds on the anterior twothirds of the tongue, while SVA IX fibers conduct taste information from buds on the posterior one-third of the tongue.

SVA X fibers conduct taste signals from those taste cells located throughout the fauces.

Smell

The smell-sensitive cells (olfactory cells) of the olfactory epithelium project their central processes through the cribiform plate of the ethmoid bone, where they synapse with mitral cells. The central processes of the mitral cells pass from the olfactory bulb through the olfactory tract, which divides into a medial and lateral portion The lateral olfactory tract terminates in the prepyriform cortex and parts of the amygdala of the temporal lobe.

These areas represent the primary olfactory cortex. Fibers then project from here to area 28, the secondary olfactory area, for sensory evaluation. The medial olfactory tract projects to the anterior perforated sub­stance, the septum pellucidum, the subcallosal area, and even the contralateral olfactory tract.

Both the medial and lateral olfactory tracts contribute to the visceral reflex pathways, causing the viscerosomatic and viscerovisceral responses.

CNS PROTECTION

- Bones of the Skull       Frontal, Temporal, Parietal, Sphenoid, Occipital

- Cranial Meninges         Dura mater, Arachnoid Space, Pia mater

- Cerebrospinal Fluid

Secreted by Chroid Plexi in Ventricles

Circulation through ventricles and central canal

Lateral and Median apertures from the 4th ventricle into the subarachnoid space

Arachnoid villi of the superior sagittal sinus return CSF to the venous circulation

Hydrocephalic Condition, blockage of the mesencephalic aqueduct, backup of CSF, Insertion of a shunt to drain the excess CSF

Gonadotropin-releasing hormone (GnRH)

GnRH is a peptide of 10 amino acids. Its secretion at the onset of puberty triggers sexual development.

Primary Effects

FSH and LH Relaese

Secondary Effects

Increases estrogen and progesterone (in females)

testosterone Relaese (in males)

Growth hormone-releasing hormone (GHRH)

GHRH is a mixture of two peptides, one containing 40 amino acids, the other 44.  GHRH stimulates cells in the anterior lobe of the pituitary to secrete growth hormone (GH).

Corticotropin-releasing hormone (CRH)

CRH is a peptide of 41 amino acids. Its acts on cells in the anterior lobe of the pituitary to release adrenocorticotropic hormone (ACTH) CRH is also synthesized by the placenta and seems to determine the duration of pregnancy.  It may also play a role in keeping the T cells of the mother from mounting an immune attack against the fetus

Somatostatin

Somatostatin is a mixture of two peptides, one of 14 amino acids, the other of 28. Somatostatin acts on the anterior lobe of the pituitary to

• inhibit the release of growth hormone (GH)
• inhibit the release of thyroid-stimulating hormone (TSH)

Somatostatin is also secreted by cells in the pancreas and in the intestine where it inhibits the secretion of a variety of other hormones.

Antidiuretic hormone (ADH) and Oxytocin

These peptides are released from the posterior lobe of the pituitary