Nervous system Flashcards
How is visual acuity measured? What does the fractions of a VA of 6/24 represent?
By using a Snellen chart viewed at a distance of 6m (20 feet) Numerator/denominator (e.g. 6/6 - normal vision; 6/24 - reduced VA) Numerator is the distance at which the chart is read; denominator is the smallest line that can be read
What factors influence visual acuity?
Optical factors - the state of the image forming mechanisms / sharpness of focus
Retinal factors - the state of the cones
Stimulus factors - illumination, brightness of the stimulus, contrast between stimulus and background, length of time exposed to stimulus
Why is the fovea important for visual acuity?
Fovea is the point where VA is the greatest
Fovea is the centre of the macula, a thinned-out rod-free portion of the retina where the cones are densely packed and each synapses on a single bipolar cell
By what processes does the body lose heat?
Radiation and conduction (70% of loss at 21 C)
Vaporization of sweat (27%)
Respiration (2%)
Urination and defecation (1%)
How does the body produce heat?
Basal metabolic processes
Contraction of skeletal muscle
Food intake
What temperature-regulating mechanisms are activated by the cold?
Shivering
Hunger
Increased voluntary activity
Increased secretion of noradr and adr
Decreased heat loss mechanism
Cutaneous vasoconstriction
Curling up
Horripilation
What part of the brain controls the reflex responses activated by cold?
The posterior hypothalamus