PHYSIOLOGY TUTORIAL
What are the angles formed by extra ocular muscles with the visual axis in primary position? Explain the movements on the different direction of visual axis.
The relative importance of primary and secondary actions of extra ocular muscles depends on the direction of visual axis.
Medial and lateral recti lie on the horizontal meridian of the globe. Their functions are relatively simple and antagonistic. Contraction of medial rectus adducts and lateral rectus abducts the globe.
Superior and inferior recti subtend a 23° angle with the visual axis when the eye is in primary position.
When the eye is abducted 23°
The superior rectus acts solely as an elevator,
The inferior rectus acts solely as depressor.
When the eye is adducted 67°
The superior rectus acts solely to incyclotort the globe
The inferior rectus acts solely to excyclotort the globe.
Superior oblique –this vector plane subtends a 54° angle with the visual axis when the eye is in primary position.
When the eye is adducted 54°
Superior oblique acts solely to depress the globe
When the eye is abducted 36°
Superior oblique acts to incyclotort the globe.
Inferior oblique-subtends a 51° angle with visual axis when the eye is in primary position.
When the eye is adducted 51°
Inferior oblique solely elevates the globe.
When the eye is abducted 39°
Inferior oblique solely excyclotort the globe.
BIOSONAR: seeing with sound
Echolocation, also called biosonar, is the biological sonar used by several animals such as dolphins, shrews, most bats, and whales. They use their own emitted sounds, along with their auditory systems to perceive and localize objects in their environment. Pulses of emitted sound reflect from objects in the animal’s path and may be interpreted by the auditory system. This ability to localize objects with echoes was termed echolocation.
Human echolocation
It is the ability of humans to sense objects in their environment by hearing echoes from those objects. Blind and blindfolded sighted human subjects were in fact able to learn to use echolocation to detect objects in their environement.They actively create sounds ,such as tapping their canes or by making clicking noises with their mouths. Some blind people have described the phenomenon not as a learned method of navigation, but as an inherent and intuitive extra sense. For example, a blind person could walk past a line of trees and feel a “pressure “at their sides as they passed each tree. The cause of this would be the echo of the sound of their footsteps; however they may not consciously be aware of this mechanism, only that the phenomenon exists and can often be relied upon to detect obstacle.
Facial vision
Before it was known to be based on localization of echoes, human echolocation was sometimes described as “facial vision”. It is described as, ability to judge the nearness of bodies by the action of the air against the face.
Two major sets of theories evolved regarding the nature of this sense. One set constituted the tactile or skin sense theory by Diderot in 1749, that the blind were sometimes able to sense, through the skin of their face, some systematic change in subtle properties of nature that alerted them to the presence of objects in their vicinity.
A second set of theories comprised the audition theory which implicated auditory processing as responsible for the perception of objects. These fell in to 2 main classes -the pressure theory which stated that tympanic membrane was sensitive to subtle changes in air pressure caused by the presence of objects, and the auditory theory which asserted that the auditory system can perceive subtle variations in sound waves as they bounce off objects. Thus the term facial vision is little understood phenomenon implying that sensory mechanisms in the face provided some pseudo visual perception of space.
Later the investigators clearly established a definitive relationship between the presence of perceptible sound and the ability to detect obstacles, and they confirmed that no such relationship exists, involving tactile sensation. It was concluded that auditory perception is necessary and sufficient for the detection of obstacles. The perception of obstacles without vision depends on a rise in the pitch of sounds as they are reflected or echoed from approaching surfaces, and this rise in pitch is only perceptible with frequencies around 10 kHz and above. Since these 3 reports, terms that refer to the perception of echoes -echo detection, echolocation and echo ranging have come in to common use in references to the non visual perception of obstacles by humans.
Mechanism
Vision and audition are close cousins in that both can process reflected waves of energy. Vision processes photons (waves of light) as they travel from their source, bounce off surfaces throughout the environment, and enter the eyes. Similarly the auditory system can process waves of sound as they travel from their source, bounce off surfaces and enter the ears. Both systems can extract a great deal of information about the environment by interpreting the complex patterns of reflected energy that they receive.
3 components must be present for the perception of echoes to take place-sound (an incident wave), a surface or surfaces to reflect sound, and an observer with auditory perception. The quality at which echoes are perceived depends upon characteristics of each of these 3 components and the spatial relationship and interactions among them.
With echoes, a blind traveler can perceive very complex, detailed and specific information from distances far beyond the reach of the longest cane or arm. Echoes make information available about the nature and arrangement of objects and environmental features such as overhangs, walls, doorways and recesses, poles, steps, parked or moving vehicles, trees and other foliage and much more. Echoes can give detailed information about location, dimension, and density. By understanding the quality the nature of the object can be detected.
Echolocation in Bats
Bats use echolocation to orient themselves and to locate objects; their auditory systems are adapted for this purpose. This specialization is evident from the inner ear up to the highest levels of information processing in the auditory cortex. Bats have specialized inner ears which allow them selves to hear sounds in the ultrasonic range. The basilar membrane within the cochlea contains specialized neurons for echo information processing. These neurons are specifically tuned to different frequency of returning echoes. Neurons in the inferior colliculus are highly sensitive to time differences, respond even to weak stimuli. Auditory cortex is quite large in comparison with other mammals. The cortex contains series of maps of auditory information, organized systematically based on sound frequency and amplitude. Neurons in these areas respond only to a specific combination of frequency and timing known as combination-sensitive neurons.
Notable individuals who employ echolocation
James Holman
Daniel Kish
Ben Underwood
Dr.Lawrence Scadden
HEART
In what way might cardiac hypertrophy with pressure overload (resistance training) affect oxygenation of myocardial tissue?
Myocardium depends on an adequate oxygen supply; unlike skeletal muscle this tissue has limited anaerobic energy generating capacity. The important factors that affect myocardial oxygen consumption are the development of tension within the myocardium and its contractility and heart rate. During exercise, with increase in each of these factors, the myocardial blood flow adjusts to balance the oxygen supply with demand.
The myocardial work load can be calculated by using Rate-Pressure Product-RPP-the index of cardiac work.
RPP=SBP (systolic blood pressure) xHR (heart rate).this RPP relates closely to directly measured myocardial oxygen consumption and coronary blood flow.
Aerobic over load training.
The heart mass and volume increases with long term aerobic training. It induces significant adaptations in a variety of functional capacities related to oxygen transport and use. These adaptations also occur in coronary heart disease. Highly trained endurance athletes have larger slow twitch fibers than fast twitch fibers in the same muscle. Slow fibers generate more ATP aerobically which increases the o2 delivery to tissues.
Resistance training (Strength training-Weight training exercises)
Resistance training and upper body exercises produce substantially higher HR and BP and hence high RPPs than more rhythmic exercises with lower body. This added myocardial work causes a risk for coronary heart disease patients with compromised myocardial o2 supply.
Cardiac hypertrophy in hypertension.
Diseases can also induce considerable cardiac enlargement. In hypertension the heart works against after load. (Excessive resistance to blood flow.)This stretches the heart muscle, which, in accordance with Frank-starling mechanism, generates compensatory force to overcome resistance. In untreated hypertension, myocardial fiber stretches beyond the optimal length, dilated heart weakens and unable to deliver enough blood to satisfy minimal resting requirements
Possible explanation
Endurance training produces eccentric hypertrophy-ventricular enlargement. In contrast resistance trained athlete posse’s concentric hypertrophy-thickening of ventricular walls. They do not have volume overload but, elevated arterial pressure. An increase in wall thickness compensates for additional after load on the left ventricle without affecting the cavity size. There is no evidence indicates that specific forms of arduous exercise can damage a normal heart.
