NEET MDS Lessons
Physiology
- Sensory:
- Somatic (skin & muscle) Senses:
Postcentral gyrus (parietal lobe). This area senses touch, pressure, pain, hot, cold, & muscle position. The arrangement is upside-down (head below, feet above) and is switched from left to right (sensations from the right side of the body are received on the left side of the cortex). Some areas (face, hands) have many more sensory and motor nerves than others. A drawing of the body parts represented in the postcentral gyrus, scaled to show area, is called a homunculus . - Vision:
Occipital lobe, mostly medial, in calcarine sulcus. Sensations from the left visual field go to the right cortex and vice versa. Like other sensations they are upside down. The visual cortex is very complicated because the eye must take into account shape, color and intensity. - Taste:
Postcentral gyrus, close to lateral sulcus. The taste area is near the area for tongue somatic senses. - Smell:
The olfactory cortex is not as well known as some of the other areas. Nerves for smell go to the olfactory bulb of the frontal cortex, then to other frontal cortex centers- some nerve fibers go directly to these centers, but others come from the thalamus like most other sensory nerves - Hearing:
Temporal lobe, near junction of the central and lateral sulci. Mostly within the lateral sulcus. There is the usual crossover and different tones go to different parts of the cortex. For complex patterns of sounds like speech and music other areas of the cortex become involved.
- Somatic (skin & muscle) Senses:
- Motor:
- Primary Motor ( Muscle Control):
Precentral gyrus (frontal lobe). Arranged like a piano keyboard: stimulation in this area will cause individual muscles to contract. Like the sensory cortex, the arrangement is in the form of an upside-down homunculus. The fibers are crossed- stimulation of the right cortex will cause contraction of a muscle on the left side of the body. - Premotor (Patterns of Muscle Contraction):
Frontal lobe in front of precentral gyrus. This area helps set up learned patterns of muscle contraction (think of walking or running which involve many muscles contracting in just the right order). - Speech-Muscle Control:
Broca's area, frontal lobe, usually in left hemisphere only. This area helps control the patterns of muscle contraction necessary for speech. Disorders in speaking are called aphasias.
- Primary Motor ( Muscle Control):
- Perception:
- Speech- Comprehension:
Wernicke's area, posterior end of temporal lobe, usually left hemisphere only. Thinking about words also involves areas in the frontal lobe. - Speech- Sound/Vision Association:
Angular gyrus, , makes connections between sounds and shapes of words
- Speech- Comprehension:
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Damage to Spinal Nerves and Spinal Cord |
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Damage |
Possible cause of damage |
Symptoms associated with innervated area |
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Peripheral nerve |
Mechanical injury |
Loss of muscle tone. Loss of reflexes. Flaccid paralysis. Denervation atrophy. Loss of sensation |
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Posterior root |
Tabes dorsalis |
Paresthesia. Intermittent sharp pains. Decreased sensitivity to pain. Loss of reflexes. Loss of sensation. Positive Romberg sign. High stepping and slapping of feet. |
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Anterior Horn |
Poliomyelitis |
Loss of muscle tone. Loss of reflexes. Flaccid paralysis. Denervation atrophy |
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Lamina X (gray matter) |
Syringomyelia |
Bilateral loss of pain and temperature sense only at afflicted cord level. Sensory dissociation. No sensory impairment below afflicted level |
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Anterior horn and lateral corticospinal tract |
Amyotrophic lateral sclerosis |
Muscle weakness. Muscle atrophy. Fasciculations of hand and arm muscles. Spastic paralysis |
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Posterior and lateral funiculi |
Subacute combined degeneration |
Loss of position sense. Loss of vibratory sense. Positive Romberg sign. Muscle weakness. Spasticity. Hyperactive tendon reflexes. Positive Babinski sign. |
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Hemisection of the spinal cord |
Mechanical injury |
Brown-Sequard syndrome |
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Below cord level on injured side |
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Flaccid paralysis. Hyperactive tendon reflexes. Loss of position sense. Loss of vibratory sense. Tactile impairment |
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Below cord level on opposite side beginning one or two segments below injury |
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Loss of pain and temperature |
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Functional Divisions of the Nervous System:
1) The Voluntary Nervous System - (ie. somatic division) control of willful control of effectors (skeletal muscles) and conscious perception. Mediates voluntary reflexes.
2) The Autonomic Nervous System - control of autonomic effectors - smooth muscles, cardiac muscle, glands. Responsible for "visceral" reflexes
The Parathyroid Glands
The parathyroid glands are 4 tiny structures embedded in the rear surface of the thyroid gland. They secrete parathyroid hormone (PTH) a polypeptide of 84 amino acids. PTH increases the concentration of Ca2+ in the blood in three ways. PTH promotes
- release of Ca2+ from the huge reservoir in the bones. (99% of the calcium in the body is incorporated in our bones.)
- reabsorption of Ca2+ from the fluid in the tubules in the kidneys
- absorption of Ca2+ from the contents of the intestine (this action is mediated by calcitriol, the active form of vitamin D.)
PTH also regulates the level of phosphate in the blood. Secretion of PTH reduces the efficiency with which phosphate is reclaimed in the proximal tubules of the kidney causing a drop in the phosphate concentration of the blood.
Hyperparathyroidism
Elevate the level of PTH causing a rise in the level of blood Ca2+ .Calcium may be withdrawn from the bones that they become brittle and break.
Patients with this disorder have high levels of Ca2+ in their blood and excrete small amounts of Ca2+ in their urine. This causes hyperparathyroidism.
Hypoparathyroidism
This disorder have low levels of Ca2+ in their blood and excrete large amounts of Ca2+ in their urine.
Abnormalities of Salt, Water or pH
- Examples:
- Hyperkalemia: caused by kidney disease & medical malpractice
- High K+ in blood- can stop the heart in contraction (systole)
- Dehydration: walking in desert- can lose 1-2 liters/hour through sweat
- Blood becomes too viscous to circulate well -> loss of temperature regulation -> hyperthermia, death
- Acidosis: many causes including diabetes mellitus and respiratory problems; can cause coma, death
- Hyperkalemia: caused by kidney disease & medical malpractice
Nucleic Acids:
- Two major types: DNA
- RNA (including mRNA, tRNA, & rRNA)
- Both types have code which specifies the sequence of amino acids in proteins
- DNA = archival copy of genetic code, kept in nucleus, protected
- RNA = working copy of code, used to translate a specific gene into a protein, goes into cytoplasm & to ribosomes, rapidly broken down
- Nucleic acids are made of 5 nucleotide bases, sugars and phosphate groups
- The bases make up the genetic code ; the phosphate and sugar make up the backbone
- RNA is a molecule with a single strand
- DNA is a double strand (a double helix) held together by hydrogen bonds between the bases
- A = T; C= G because:
- A must always hydrogen bond to T
- A = T; C= G because:
C must always hydrogen bond to G
Respiration occurs in three steps :
1- Mechanical ventilation : inhaling and exhaling of air between lungs and atmosphere.
2- Gas exchange : between pulmonary alveoli and pulmonary capillaries.
3- Transport of gases from the lung to the peripheral tissues , and from the peripheral tissues back to blood .
These steps are well regulated by neural and chemical regulation.
Respiratory tract is subdivided into upper and lower respiratory tract. The upper respiratory tract involves , nose , oropharynx and nasopharynx , while the lower respiratory tract involves larynx , trachea , bronchi ,and lungs .
Nose fulfills three important functions which are :
1. warming of inhaled air .
b. filtration of air .
c. humidification of air .
Pharynx is a muscular tube , which forms a passageway for air and food .During swallowing the epiglottis closes the larynx and the bolus of food falls in the esophagus .
Larynx is a respiratory organ that connects pharynx with trachea . It is composed of many cartilages and muscles and
vocal cords . Its role in respiration is limited to being a conductive passageway for air .
Trachea is a tube composed of C shaped cartilage rings from anterior side, and of muscle (trachealis muscle ) from its posterior side.The rings prevent trachea from collapsing during the inspiration.
From the trachea the bronchi are branched into right and left bronchus ( primary bronchi) , which enter the lung .Then they repeatedly branch into secondary and tertiary bronchi and then into terminal and respiratory broncholes.There are about 23 branching levels from the right and left bronchi to the respiratory bronchioles , the first upper 17 branching are considered as a part of the conductive zones , while the lower 6 are considered to be respiratory zone.
The cartilaginous component decreases gradually from the trachea to the bronchioles . Bronchioles are totally composed of smooth muscles ( no cartilage) . With each branching the diameter of bronchi get smaller , the smallest diameter of respiratory passageways is that of respiratory bronchiole.
Lungs are evolved by pleura . Pleura is composed of two layers : visceral and parietal .
Between the two layers of pleura , there is a pleural cavity , filled with a fluid that decrease the friction between the visceral and parietal pleura.
Respiratory muscles : There are two group of respiratory muscles:
1. Inspiratory muscles : diaphragm and external intercostal muscle ( contract during quiet breathing ) , and accessory inspiratory muscles : scaleni , sternocleidomastoid , internal pectoral muscle , and others( contract during forceful inspiration).
2. Expiratory muscles : internal intercostal muscles , and abdominal muscles ( contract during forceful expiration)