Physiology notes for competitive examinations

Dr. Ajith Kumar D S
Dept. of Physiology & Biochemistry, GHMC, Calicut.
Email : ajithdevarajan@yahoo.co.in 

Muscle Physiology

• Muscle form 40 to 50% of body mass.
• About 600 muscles are identified.

Classification of Muscles:

• Depending on striations: Striated(Skeletal & Cardiac) & Nonstriated(smooth)
• Depending on Control: voluntary(Skeletal) & Involuntary(Cardiac & smooth)
• Depending on situation: Skeletal, Cardiac & Smooth.
• Muscle fiber or cell has a length b/w 1 – 4cm (Average 3cm) & diameter from 10 – 100microns.
• 1 myofibril contains 1500 myosin filaments & 3000 actin filaments
• Sarcomere is the structural & functional unit of skeletal muscle.
  • Length – 2.5 to 3.2 mm.
  • Sarcomere lies b/w two ‘Z’ lines
• Each myofibril consists of alternate light (I or J band) & dark band (A or Q band).
• Each sarcomere consist of thin (Actin) & thick (myosin) filaments.
  • Myosin filament is present throughout the ‘A’ band.
  • No movement of myosin during muscular contraction.
• Actin filaments are formed by 3 types of proteins called actin, tropomyosin & troponin.
• The skeletal muscle is formed by 75% of water, 20% of proteins & 5%of organic substances.
• Troponin: is formed by 3 subunits; Troponin I – attached to F actin; Troponin T – attached to tropomyosin; Troponin C – attached to calcium ions.
• Following are the muscle proteins; Myosin; Actin; Tropomyosin; Troponin; Actinin; Titin; Desmin; Myogen & Myoglobulin.
• There is no movement in the myosin filament during muscle contraction.
• Actin filaments slide over the myosin filament during muscle contraction.
• Tropomyosin covers the active sites of actin.

• Rheobase: this is the least possible, i.e. (minimum) strength (Voltage) of stimulus which can excite the tissue.
• Chronaxie: it is the minimum time, at which a stimulus with double the rheobasic strength (voltage) can excite the tissue.
  • Chronaxie of skeletal muscle is shorter than that of cardiac and smooth muscles.
  • Cold lengthens chronaxie. whereas vagal stimulation shortens chronaxie.
• Refractory period is the period at which the muscle does not show any response to a stimulus.
• Skeletal muscles are purely aerobic & don’t have any fuel reserve.
• Dark, light bands & troponin are absent in smooth muscle.
• The study of electrical activity of the muscle is done by electromyography.
• The muscle ruptures when it is stretched to about 3 times its equilibrium length. 

Cardiovascular system

• The syncytium of called physiological syncytium because there is no anatomical continuity of the fibers.
• SA node the pace maker is a small strip of modified cardiac muscle is situated in the superior part of lateral wall of right atrium, just below the opening of superior vena cava.
• AV node is situated in the right posterior portion of interatrial septum.
• Bundle of his run on either side of the interventricular septum.
• Rhythmicity of different parts of heart:
  • SA node                      : 70 to 80 / min
  • AV node                      : 40 to 60 / min
  • Atrial muscle               : 40 to 60 / min
  • Ventricular muscle      : 20 to 40 / min
• Velocity of impulse at different parts of the conductive system.
  • Atrial muscle fibres     : 0.3 meter / second
  • Internodal fibers          : 1.0 meter / second
  • AV node                      : 0.05 meter / second
  • Bundle of his               : 0.12 meter / second
  • Purkinje fibers             : 4 meter / second
  • Ventricular muscle fibers : 0.5 meter / second
• Cardiac cycle includes systole & diastole which practically includes the events of ventricles.
• When heart beats at the normal rate of 72/min, the duration of cardiac cycle is 0.8 sec.
• The duration of systole is 0.27 sec & that of diastole is 0.53 sec.
• The subdivision with duration are
  • Systole
    • Isometric contraction  = 0.05 sec
    • Ejection period            = 0.22 sec
  • Diastole
    • Protodiastole               = 0.04 sec
    • Isometric relaxation    = 0.08 sec
    • Rapid filling                 = 0.11 sec
    • Slow filling                   = 0.19 sec
    • Atrial systole                = 0.11 sec
    • Total duration of cardiac cycle = 0.27 + 0.53 = 0.8 sec.
• Atrial systole: atrial contract & a small amount of blood enter the ventricles.
• Isometric contraction: all the valves are closed, ventricles undergo isometric contraction & pressure in the ventricles is increased.
• Ejection period: semilunar valves opened, ventricles contract & blood is ejected out.
• Protodiastole: this is the first diastole. The semilunar valves are closed at the end of this period.
• Isometric relaxation: all the valves are closed, ventricles undergo isometric relaxation & pressure in the ventricles is reduced.
• Rapid & slow filling: Atrioventricular valves are opened, ventricles relax & filling occurs.

• Pressure difference

• End systolic volume is 70 – 90 ml
• End diastolic volume is 130 – 150 ml.

• Cause for cardiac murmurs 

• Electrocardiography:

Duration

• • Interval B/W 2 thick lines: (5mm) = 0.2 second
  • Interval B/W 2 thin lines (1mm) = 0.04 second

Amplitude

• • Interval B/W 2 thick lines: (5mm) = 0.5 mV
  • Interval B/W 2 thin lines (1mm) = 0.1 mV

Speed of the paper

• • 25 mm  or 50 mm / second

• Normal heart rate is 72 / min
• Tachycardia: increase heart rate above 100 / min.

Waves of normal ECG

• In hyperkalemia, ECG shows a tall T wave.
• In hypokalemia, ECG shows depressed S-T segment.
• Heart sounds.

• Bradycardia: decrease in rate below 60 / min.
• Sinus tachycardia: increase in discharge of impulse from SA node, upto 100 / min
• Sinus bradycardia: reduction in the impulses from SA node, about 40 / min
• Atrial flutter: Atrial rate is about 250 – 350 / min
• Atrial fibrillation: rate of 300 – 400 beats / min
• Ventricular fibrillation: rate is about 400 – 500 / min
• Bain Bridge reflex (venous reflex) is characterized by reflex increase in Heart rate on venous engorgement of the right atrium.
• Mary’s law states that the Heart rate and Blood pressure have inverse relationship.
• Stokes Adams syndrome is characterized by repeated fainting attacks associated with complete heart block.

• Arrhythmia: irregular heart beat.

• Cardiac Output:
  • The amount of blood pumped from each ventricle.
• Stroke volume: the amount of blood pumped out by each ventricle during each beat – 70ml.
  • Stroke volume at rest is 80 – 100 ml.
• Minute volume: amount of blood pumped out by each ventricle in one minute. Minute volume = stroke volume X heart rate. – 5 liters/per ventricle/minute.
• Cardiac Index: the minute volume from ventricle expressed in relation to square meter of body surface area. Normal value: 2.8 ± 0.3 liters / 1 square meter of body surface area / minute.
• Ejection fraction: the fraction of end diastolic volume that is ejected out by each ventricle. Normal – 60 to 65%.
• Cardiac reserve: the maximum amount of blood that can be pumped out by the heart above normal value. Normal healthy adult: 300 – 400%.
• Variations in Cardiac output: (Physiological)
  • Less in children, females, early morning, changing from recumbent to upright position & in sleep.
  • Increased in males, greater body build, day time, emotional upset, after meals, after exercise, high attitude, and later months of pregnancy.
• Distribution of  Cardiac output:

Organ	Amount of blood	Percentage
Liver	1500ml	30%
Kidney	1300ml	26%
Skeletal muscles	900ml	18%
Brain	800ml	16%
Skin, bone & GIT	300ml	6%
Heart	200ml	4%
Total	5000ml	100%

• Factors maintaining  Cardiac output:

• 1. Venous return

• Respiratory pump; Muscle pump; Gravity; Venous pressure; Vasomotor tone.

• 2. Force of contraction
  3. Heart rate
  4. Peripheral resistance

•  Regulation of Heart rate:

1. 1.    Vasomotor center: bilaterally situated in the reticular formation of medulla oblongata & lower part of pons.
2. 2.    Motor nerve fiber of heart.
3. 3.    sensory nerve fiber

• Haemodynamics:

Factors maintaining volume of flow of blood.

• Pressure gradient; Resistance to blood flow; Viscosity of blood; Diameter of blood vessels; Velocity of blood flow:
• Arterial Blood pressure:
  • Systolic pressure: maximum pressure exerted in the arteries during the systole of heart. Normal: 120 mmHg. (range 110 – 140)
  • Diastolic Blood Pressure: minimum pressure in the arteries during the diastole of the heart. Normal: 80 mmHg (range 60 – 90)
  • Pulse pressure: Difference between the systolic pressure & diastolic pressure. Normal: 40 mmHg.
  • Mean arterial blood pressure: this is the diastolic pressure plus one-third of pulse pressure. Normal: 93 mmHg.
  • Variations (Physiological)
    • Lessin children, females before menopause, early morning & in sleep.
    • Increased in males, greater body build, and day time, after meals, after exercise, sleep with dreams.
  • Determinants of Arterial blood pressure:

Cardiac output; Heart rate; Peripheral resistance; Venous return; Elasticity & Diameter of blood vessels; Velocity of blood flow; Viscosity of blood

• Regulation of Arterial blood pressure:
  • Nervous mechanism: by vasomotor center & impulse from periphery
  • Renal mechanism: by regulation of ECF volume & rennin-angiotensin mechanism.
  • Local mechanism

                        Local vasoconstrictors & Local vasodilators

• Hormonal mechanism:

Hormones increase BP	Hormones decrease BP
AdrenalineNoradrenalineThyroxine Aldosterone Vasopressin Angiotensin Serotonin	Vasoactive intestinal polypeptide(VIP)BradykininProstaglandin Histamine Acetylcholine Atrial natriuretic peptide

•  Venous pressure:
• • Venous pressure in Jugular vein: 5.1 mmHg (6.9 cm H₂O)
  • Venous pressure in superior vena cava: 4.6 mmHg (6.2 cm H₂O)
  • Portal venous pressure: 10 mm Hg
  • Hepatic venous pressure: 5 mm Hg.
  • Capillary pressure:
    • Capillary pressure in the arterial end is about 30 – 32 mmHg & venous end is about 15 mmHg.
    • It is high in Kidney (glomerular capillary pressure), about 60 mmHg – responsible for filtration.
    • Low in lungs (pulmonary capillary pressure), about 7 mmHg.
    • Venous pulse: (it is the pressure changes transmitted in the form of waves from right atrium to the veins near the heart)
      • Recording of JVP is called phlebogram.
      • Phlebogram has 3 positive waves – a, c & v and 3 negative waves – x, x₁ & y.
      • ‘a’ wave – 1^st positive wave & it’s due to atrial systole.
      • ‘x’ wave – fall of pressure in atrium, coincides with atrial diastole
      • ‘c’ wave – its due to rise in atrial pressure during isometric contraction during which the AV valves bulges into atrium.
      • ‘x₁’ wave – occurs during ejection period, when AV ring is pulled towards ventricles causing distension of atria.
      • ‘v’ wave – occurs during isometric relaxation period or during atrial diastole.
      • ‘y’ wave – due to opening of AV valve & emptying of blood into ventricle. 

Nervous system

• Neuron is defined as the structural & functional unit of nervous system.
• Neuron does not have Centrosome so it cannot undergo division.
• Nissl bodies are organelles containing ribosomes & are concerned with synthesis of protein in neurons.
• Dendrites are conductive in nature & transmit impulses towards the nerve cell body.
• Axons are longer process of the nerve cell concerned with transmission of impulse away from the nerve cell body.
• The myelin sheath envelops the axon except at its ending and at the nodes of Raniver.
• Myelin sheath is responsible for faster conduction of impulse through the nerve fiber & also acts as an insulating material.
• Neurotrophins are the substances, which facilitate the growth, survival & repair of the nerve cells.
• A alpha (Type Ia) nerve fiber is said to be the fastest nerve with a velocity of conduction of 70 to 120 meters / second.
• Glial cells are very abundant and as many as 10 to 50 times as neurons.
• Astrocytes form supporting network in brain & spinal cord, form basis for blood brain barrier.
• Microglia is phagocytic in function.
• Oligodendrocytes are responsible for the formation of myelin sheath in CNS because schwann cells are absent there.
• Receptors:
  • Exteroceptors: give response to stimuli arising from outside the body. (Cutaneous, Chemoreceptors & Telereceptors)
  • Interoceptors: give response to stimuli arising from within the body.
  • Cutaneous receptors:

• Touch receptors: Meissner’s corpuscle & Merkel’s disc (max in lips & fingers)
• Pressure receptors: Pacinian corpuscles
• Temperaturereceptor
  • Cold: Krause’s end organ
  • Warm: Raffini’s end organ
  • Warm receptors respond at body temperature of— 30 – 45°C.
  • Cold receptors are activated at body temperature of— 10°C or below.
  • Warm Sensation is carried by — C Fibres.
  • Cold Sensation is carried by — A. & C fibres.
    •  Pain receptors: free (naked) nerve ending. (sensation which return earliest on recovery)

• • Chemoreceptors:
    • Taste: Taste buds
    • Smell: Olfactory receptors
    • Hearing: hairs cells of organ of corti in the internal ear.
    • Vision: Rods & Cones in retina – for visual sensation.
  • Viseroreceptors:
    • Stretch receptors, baroreceptors, chemoreceptors & Osmoreceptors
  • Proprioceptors: give response to change in position – labyrinthine, muscle spindle, golgi tendon, pacinian corpuscle, muscle, tendon & fascia.
• Neurotransmitters:
  • Excitatory neurotransmitter: is responsible for the conduction of impulse from the presynaptic neuron to the postsynaptic neuron.
  • Inhibitory neurotransmitters: inhibits the conduction of impulse from the presynaptic neuron to the postsynaptic neuron.

Group	Name	Action
Amino acids	GABA	Inhibitory
	Glycine	Inhibitory
	Glutamate	Excitatory
	Aspartate	Excitatory
Amines	Adrenaline	Inhibitory & Excitatory
	Noradrenaline	Inhibitory & Excitatory
	Dopamine	Inhibitory
	Serotonin	Inhibitory
	Histamine	Excitatory
Others	Nitric oxide	Excitatory
	Acetylcholine	Excitatory

• Superficial reflexes:

Reflex	Stimulus	Response	Center
Corneal	Irritation of cornea	Blinking of eye	Pons
Conjunctival	Irritation of conjuctiva	Blinking of eye	Pons
Nasal	Irritation of nasal mucus membrane	Sneezing	Motor nucleus of V cranial nerve
Pharyngeal	Irritation of pharyngeal mucus membrane	Retching of gagging	Nuclei of X cranial nerve
Uvular	Irritation of Uvula	Raising of Uvula	Nuclei of X cranial nerve

• Superficial cutaneous reflexes

Reflex	Stimulus	Response	Center – spinal segment involved
Scapular	Irritation of skin at the interscapular space	Contraction of scapular muscles & drawing in of scapula	C5 to T1
Upper abdominal	Stroking the abdominal wall below the costal margin	Ipsilateral contraction of abdominal muscle & movement of umbilicus towards the site of stroke	T6 to T9
Lower abdominal	Stroking the abdominal wall at umbilical & iliac level	Ipsilateral contraction of abdominal muscle & movement of umbilicus towards the site of stroke	T10 to T12
Cremasteric	Stroking the skin at upper & inner aspect of thigh	Elevation of testicles	L1, L2
Gluteal	Stroking the skin over glutei	Contraction of glutei	L4 to S1, S2
Plantar	Stroking the sole	Plantar flexion & adduction of toes	L5 to S2
Bulbocavernous	Stroking the dorsum of glans penis	Contraction of bulbocavernous	S3, S4
Anal	Stroking the perianal region	Contraction of anal sphincter	S4, S5

• Deep reflexes

Reflex	Stimulus	Response	Center – spinal segment involved
Jaw jerk	Tapping middle of the chin with slightly opened mouth	Closure of mouth	Pons – V cranial nerve
Biceps jerk	Percussion of biceps tendon	Flexion of forearm	C5, C6
Triceps jerk	Percussion of triceps tendon	Extension of forearm	C6 to C8
Supinator jerk or radial periosteal reflex	Percussion of tendon over distal end (Styloid process) of radius	Supination & flexion of forearm	C7, C8
Wrist tendon or finger flexion reflex	Percussion of wrist tendons	Flexion of corresponding finger	C8, T1
Knee jerk or Patellar tendon reflex	Percussion of patellar ligament	Extension of leg	L2 to L4
Ankle jerk or Achilles tendon reflex	Percussion of Achilles tendon	Plantar flexion of foot	L5 to S2

• Pathological reflexes:
  • Babinski’s sign: there is dorsiflexion of great toe & fanning of other toes. Seen in UMN lesion, also in infants & normal persons with deep sleep.
• Spinal cord:
  • Extends from foramen magnum to 1^st lumbar vertebra.
  • Length – 45 cm in male & 43 cm in females.
  • Below the lumbar enlargement, the spinal cord rapidly narrows to a cone shaped termination called Conus medullaris.
  • Spinal corresponds to 31 pairs of spinal nerves. (C-8; T-12; L-5; S-5; C-1)
  • Grey matter is the collection of nerve cell bodies, dendrites & parts of axons.
  • White matter is a collection of myelinated & nonmyelinated nerve fibers.
  • Neurons in the grey matter of spinal cord
    • Neurons in Anterior gray horn

• Alpha motor neurons; Gamma motor neurons & Renshaw cells
• Intermediolateral horn cells
• Substania gelatinosa of Rolando; Marginal cells; Chief sensory cells & Clarke’s column of cells.

• • • Neurons in lateral gray horn

• • • Neurons in posterior gray horn

Ascending tracts of Spinal cord:

 Descending tracts of Spinal cord:

Effect of upper motor neuron & lower motor neuron lesion:

Action of sympathetic & parasympathetic divisions of ANS:

Resting membrane potential of various cells of the body.

• Resting membrane potential of a skeletal muscle is -90mV.
• Resting membrane potential of a smooth muscle is -50 to -75mV.
• Resting membrane potential of a cardiac muscle is -85 to -95mV.
• The resting membrane potential in the nerve fiber is -70mV.
• The resting membrane potential in the rods is -40mV.
• The resting membrane potential of inner ear cell is -60mV.

Brain stem: (medulla oblongata, Pons & Midbrain)

• Pathway for ascending & descending tracts b/w brain & spinal cord.
• Important centers for regulation of vital functions in body.

Medulla oblongata

• Respiratory centers: inspiratory & expiratory.
• Vasomotor center: B.P & Heart rate.
• Deglutition center: Pharyngeal & Oesophageal stage.
• Vomiting center: induce vomiting.
• Superior & inferior salivatory nuclei: controls secretion of saliva.
• Cranial nerve nuclei: nuclei of 10, 11 & 12 cranial nerves.
• Vestibular nuclei:

Pons

• Bridge b/w medulla & midbrain.
• Forms pathway connecting cerebellum with cortex.
• Nuclei of 5 to 8^th cranial nerve.
• Pneumotoxic & apneustic centers for regulation of respiration.

     Midbrain: (Consist of 2 parts Tectum & cerebral peduncles)

• Tectum: center for light & auditory reflexes.
• Cerebral peduncles: control of muscle tone
• Control of complex  & skilled muscular movements, movement of eye balls

     Thalamus: Ovoid mass of gray matter, situated B/L in diencephalons)

• Relay center: for sensations (also called functional gateway).
• Center for integration of sensory impulses: determining the quality of sensations(discriminative & affective nature)
• Center for sexual sensations.
• Role in arousal & alertness reactions.
• Center for reflex activity
• Center for integration of motor functions.

       Hypothalamus:

• Control the secretion of Ant. & Post Pituitary hormones & adrenal cortex & medulla.
• Control of Autonomic nervous system; Heart rate; B.P; Body temp; Food intake (satiety, hunger &thirst); water balance; sleep & wakefulness.
• Role in behaviour & emotional changes.
• Regulation of sexual function & response to smell.
• Role in circadian rhythm.

       Cerebellum:

• Vestibulocerebellum: regulates tone, posture & receiving impulse for vestibular apparatus.
• Spinoncerebellum: regulates tone, posture & equilibrium by receiving impulses from proprioceptors in muscles, tendons & joints, tactile receptors, visual receptors & auditory receptors.
• Corticocerebellum: concerned with the integration & regulation of well coordinated muscular activities.
• Different parts are represented in an upright manner in cerebellum. (opp: in cerebrum)

       Basal ganglia: (concerned with motor activities of extra-pyramidal system)

• Control of voluntary motor activity, muscle tone, reflex muscular activity, associated movements.
• Role in arousal mechanism.

       Cerebral cortex:

Frontal lobe	Pre central cortex(Post. Part)	Primary motor area(concerned with initiation of voluntary movements & speech)	Area 4 – center for movement
			Area 4S – suppressor area. Inhibits movements initiated by area 4.
		Pre motor area	Area 6 – concerned with coordination of movements initiated by area 4.
			Area 8 – frontal eye field.
			Area 44 & 45(broca’s area) – motor area for speech.
		Supplementary motor area	Concerned with co-ordinated skilled movements.
	Pre –frontal cortex(Ant. Part)	Silent area or association areaCenter for higher functions – emotion, learning, memory.	Area – 9 to 14, 23, 24, 29 & 32. Center for planned action.Seat of intelligence. Personality of individual.
Parietal lobe	Somesthetic area I		Area 1 – concerned with sensory perception
			Area 2 & 3 – integration of these sensations. Spatial recognition. Recognition of intensity, similarities & diff. B/W stimuli
	Somesthetic area II		Concerned with perception of sensation.
	Somesthetic association area		Synthesis of various sensations perceived by S.Area-I. Stereognosis.
Temporal lobe	Primary auditory area		Area 41, 42 & wernicke’s area – concerned with perception of auditory impulses, analysis of pitch, determination of intensity & source of sound
	Auditopsychic area		Area 22 – interpretation of auditory sensation
	Area of equilibrium		Maintenance of equilibrium
Occipital lobe	Primary visual area		Area 17 – perception of visual impulse
	Visual association area		Area 18 – Interpretation of visual impulses
	Occipital eye field		Area 19 – Movements of eye

Limbic system: (It is a group of cortical & sub cortical structures which form a ring around the hilus of cerebral hemisphere)

• Regulation of olfaction, autonomic functions (B.P, water balance & body temp).
• Control of circadian rhythm.
• Regulation of sexual function.
• Role in emotional state, memory & motivation.
• Retention of recent memory.
• Most developed part of Limbic System — Hippocampal formation
• Major efferent from Limbic system goes to — Mid brain reticular formation.
• Main function of Limbic system is to — Control the emotional behaviour.

Proprioceptors: (These are receptors which give response to change in the position of different parts of the body).

• Muscle spindle: gives response to change in length of muscle.
• Golgi tendon organ: gives response to change in force developed in muscle.
• Pacinian corpuscle: pressure receptor in fascia, tendon & joints.
• Free nerve endings:

Vestibular apparatus:

• Give response to rotatory movements or angular acceleration of the head.
• Responsible for detecting the position of head during different movements.

EEG: (ELECTROENCEPHOLEGRAM)

• Alpha rhythm:
  • Frequency: 8 to 12 waves / sec
  • Amplitude: 50µU.
  • Most marked in parieto-occipital area.
  • Obtained in inattentive brain as in drowsiness & light sleep.
• Beta rhythm:
  • Frequency: 15 to 60 waves / sec
  • Amplitude: 5 – 10µU.
  • Recorded during mental activity or mental tension or arousal state.
• Delta rhythm:
  • Frequency: 1 to 5 waves / sec
  • Amplitude: 20 – 200µU.
  • Seen in tumour, epilepsy, increased intracranial pressure & mental depression.
• Theta rhythm:
  • Frequency: 4 to 8 waves / sec
  • Amplitude: 10µU.
  • Seen in children below 5 years. 

SLEEP:

• Sleep requirement:
  • Newborn infants: 18 to 20 hours.
  • Growing children: 12 to 14 hours.
  • Adults: 7 to 9 hours.
  • Old persons: 5 to 7 hours.
• Types of sleep:

Rapid eye movement sleep(REM)	Non rapid eye movement sleep(NREM)
Eye balls move	Absent
Dreams occur	Absent
Muscle twitching	Absent
20 to 30% of sleep	70 to 80% of sleep

• Normal amount of C.S.F. in man is 150 C.C,
• Sympathetic nervous system is controlled by — Posterior hypothalamic nuclei
• Parasympathetic nervous system is controlled by — Anterior nuclei and part of middle nuclei of hypothalamus.

EYE:

• Refractory power is measured in dioptre (D).
• Refractory power of cornea is 42D.
• Refractory power of lens is 23D.
• Refractory power of eye at rest is 59D.
• Focal length of cornea is 24mm.
• Focal length of lens is 44mm.
• The wave lengths of visible light are approximately 397 to 723 nm.
• There are about 6 million cones & 12 million rods in human eye.
• Rods are responsible for dim light or night vision or scotopic vision.
• Cones are responsible for colour vision, sensitive to day light & acuity of vision.
• Rhodopsin is the photosensitive pigment of rods cells.
• Photosensitive pigment in cones are
  • Porpyropsin – Red
  • Iodopsin – Green
  • Cyanopsin – Blue
• Electroretinogram is the instrument to record the electrical basis of visual process.
• Test for visual acuity – snell’s chart (distant vision) & Jaeger’s chart (near vision).
• Test for color blindness – Ishihara’s colour chart.
• Mapping of visual field – perimetry.
• Nearest point at which the object is seen clearly is about 7 to 40cm.
• Farthest point is infinite.
• Myopia (short sightedness) is corrected by concave lens.
• Hypermetropia (long sightedness) is corrected by convex lens.
• Astigmatism is corrected by cylindrical lens.
• Presbyopia is corrected by convex lens.

EAR:

• Ear is sensitive to sound between 1000 to 4000Hz range.
• Hairs cells in organ of corti are the receptors for auditory sensation.
• Sound becomes painful above 140db.
• Auditory centers – 41, 42 & also auditopsychic area 22.

TONGUE:

• Sense organ of taste sensation is taste buds.
• There are about 10,000 taste buds & each taste bud is replaced in every 10 days.
• Each taste bud consists of 4 types of cells and is supplied by about 50 nerve fibres.
• Receptors are type III cells of taste buds.
• Taste center – opercular insular cortex (lower part of post central gyrus).
• Bitter taste has very low threshold – 1 in 2,000,000.
• Sweet taste has high threshold – 1 in 200.
• Locations of taste buds are: sweet – tip; salt – dorsum; sour – side; bitter – posterior.

SMELL:

• Olfactory mucus consists of 10 to 20 million olfactory receptor cells.
• Human nose can distinguish 2000 to 4000 different odours.

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