MCAT BIO CH. 8 PART 2 Flashcards
How does light enter the eye? What happens to light when it passes through the cornea?
Passing through the cornea
What happens to light when it passes through the cornea?
Refracted; refractive index of the cornea is higher than that of air
What is the sclera? (Based on vision)?
The white of the eye
Where is the choroid located? What does it contain? What’s it purpose? (Based on vision)?
Beneath the sclera; contains darkly pigmented cells; absorbs excess light within the eye
Where is the retina located? What is its purpose? (Based on vision)
Beneath the choroid; the surface upon which light focuses
What is just inside the cornea? What does it contain? (Based on vision)
The anterior chamber; fluid called aqueous humor
What does the iris do? (Based on vision)
Muscles in the iris regulate the diameter of the pupil
What is located just behind the iris? What does it contain? (Based on vision)
Posterior chamber; aqueous humor
What is located at the back of the posterior chamber?(Based on vision)
Lens
What is the purpose of the lens? (Based on vision)
Fine-tune the angle of incoming light so beams are perfectly focused on the retina
How is the curvatures of the lens varied (the refractive power)? (Based on vision)
By the ciliary muscle
As light passed through the lens, where does it go through to reach where? (Based on vision)
Goes through the vitreous chamber en route to the retina
What does the vitreous chamber contain? (Based on vision)
A thick jelly-like fluid called the vitreous humor
What does the retina contain? (Based on vision)
Photoreceptors known as rods and cones
What type of cells do the rods and cones of the retina synapse with? (Based on vision)
Bipolar cells
What are bipolar cells type of nerve cells? (Based on vision)
Only have one axon and one dendrite
What type of cells do bipolar cells from the rod and cones synapse, synapse with? (Based on vision)
Ganglion cells
Which nerve does the ganglion cells stimulate? (Based on vision)
The optic nerve which travels from each eye towards the occipital lobe of the brain
What is the optic disk of the retina? (Based on vision)
The point where many axons from ganglion cells converge to form the optic nerve
What is the blind spot (optic disk)? (Based on vision)
Contains no photoreceptors
What is the macula? (Based on vision)
Portion at the center of the retina that makes vision focused
What is in the center of the macula? (Based on vision)
Fovea centralis (focal point)
What does the fovea centralis only contain and what is it important for?
Contains only cones and responsible for extreme visual acuity
What are special about opsin that are located in rods and cones?
Special pigment proteins that change their tertiary structure upon absorbing light
What are opsin proteins bound to, based on vision?
Bound to one molecule of retinal, derived from Vitamin A
What happens in the dark when the rods and cones are resting, based on the opsin protein and retinal molecule? (Based on vision)
Retinal has several trans double bonds and one cis double bond to keep sodium channel open with opsin
Since the retinal has several trans double bonds and one cis double bone to keep sodium channels open, the cell remains…..? (Based on vision)
Depolarized
What happens when there is absorption of the photo light, based on retinal and opsin?
Retinal is covered to all trans-for which triggers reactions that close sodium channels and cell is hyper polarized
What neurotransmitter is released by rods and cones (photoreceptors) in the dark?
Glutamate onto the bipolar cells
What happens in the light to the photoreceptors rods and cones based on the neurotransmitter they release?
Glutamate is released less or stopped, cell is hyper polarized
Where can the bipolar cells be located?
On center or off center
The bipolar cells that are on center, what happens in the dark and in the light?
Dark: Glutamate released and inhibits on center bipolar cells
Light: Inhibition stops, bipolar cell increases release of neurotransmitter
The bipolar cells that are off center, what happens in the dark and in the light?
Dark: Stimulated by glutamate release
Light: Inhibited as glutamate stops being released
What is night vision accomplished by?
Rods
Why is night vision accomplished by rods?
More sensitive to dim light and motion and more concentrated in the periphery of the retina
What is color vision accomplished by?
Cones
Why is color vision accomplished by cones?
Require abundant light and are more concentrated in the fovea
Color depends on the presence of there different types of cones; what are they?
Absorb blue, tree and red light
What is normal vision?
Emmetropia
What is myopia?
Too much curvature causes light to be bent too much and to be focused in front of the retina (nearsightedness)
What is hyperopia?
Focusing of light behind the retina
How can myopia be corrected?
By concave lens which cause the light rays to diverge slightly before they reach the cornea
How can hyperopia be corrected?
By a convex lens which causes light rays to converge before reaching the Cornes
What is presbyopia?
Inability to accomodate (focus)
How does presbyopia happen?
Results from loss flexibility of the lens which occurs with aging
Where is the location of neurons that fir in response to visual information?
Visual cortex
What is the feature detection theory?
Why different areas of the brain are stimulated when looking at different things
What is parallel processing based on process of vast amounts of visual information?
Many aspects of a visual stimulus are processed simultaneously
What’s the absolute threshold based on general sensory processing?
Minimum stimulus intensity required to activate a sensory receptor
What is the difference threshold based on general sensory processing?
The minimum noticeable difference between any two sensory stimuli
What is Weber’s law?
Two stimuli must differ by a constant proportion in order for their difference to be perceptible
What is signal detection theory?
Predicting how and when someone will detect the presence of a given sensory stimulus amidst all other sensory stimuli in the background
What are the four possible outcomes of the signal detection theory?
- Hit
- Miss
- False alarm
- Correct rejection
What is the hit theory of the signal detection theory?
Signal is present and was detected
What is the miss theory of the signal detection theory?
Signal was present but not detected
What is the false alarm theory of the signal detection theory?
Signal was not present but the person thought it was
What is the correct rejection theory of the signal detection theory?
The signal was not present and the person did not think it was
What do gestalt psychologists believe?
Believe that the whole exceeds the sum of its parts
Revert the gestalt psychologists belief in regards to humans, what does it mean?
When humans perceive objects, rather than seeing lines angles and colors they perceive it as a whole
What is bottom-up processing?
Begins with the sensory receptors and works up to the complex integration fo information
What is top-down processing?
The brain applies experience and expectations to interpret sensory information
What does the endocrine system regular?
Physiology over a period of hours to days
What is a hormone and what does it do?
A molecule secreted into the bloodstream by an endocrine gland and has effect on distant large cells
What is the endocrine gland?
Ductless gland whose secretory products are piked up y capillaries supplying blood to the region
How do exocrine gland secrete its products?
Into the external environment by way of ducts, which empty into the gastrointestinal lumen of the external world
What is a hormone receptor?
A polypeptide that possesses a ligand-specific binding site
What is autocrine activity?
Some signaling molecules modify the activity of the cell which secreted them
What are the two groupings of hormones?
- Hydrophilic hormones
2. Hydrophobic hormones
What are hydrophilic hormones?
Peptides and amino-acid derivatives
What are hydrophobic hormones?
Steroid hormones bind to receptors in the cellular interior
Where are peptide hormones synthesized?
Into the rough ER and modified the Golgi
How are peptide hormones released?
Exocytosis
What happens when peptide hormones are released in the bloodstream?
Dissolve as they are hydrophilic
What does hydrophilicity of the peptide hormones prevent them from doing and what must they do?
They cannot cross biological membranes and required to communicate with the interior of the target cell by way of second messenger cascade
What is the receptor of the peptide hormone?
Polypeptide with a domain on the inner surface of the plasma membrane that contains the ability to catalytically activate a second messenger
What is the end result fo the second messenger based on peptide hormones and receptor?
Function of proteins in the cytoplasm is changed
What is a key feature of second messenger cascade, based on peptide hormones and receptors?
Signal amplification which allows a few activated receptors to change the activity of many enzymes in the cytoplasm
Because peptide hormones modality the activity of existing enzymes in the cytoplasm, how are their effects?
Done rapidly, minutes to hour from the time of secretion
What are the two subgroups within the peptide hormone category?
- Polypeptides
2. Amino acid derivatives
What is an important example of the polypeptide hormone?
Insulin
Along with a complex tertiary structure, what does insulin contain?
Disulfide bridges
What is insulin secreted by?
B cells of the pancreatic islets of Langerans in response to elevated blood glucose
What does insulin bind to and what does it cause?
Binds to a cell-surface receptor with a cytoplasmic domain possession protein kinase activity
What are amino acid derivatives?
Derived from single amino acids and contains no peptide bonds
What is an example of an amino acid derivative?
Tyrosine the parent amino acid for the catecholamines (epinephrine) and the thyroid hormones
What are catecholamines behave as?
Like peptide hormones while the thyroid hormones have more like steroid hormones
What is epinephrine?
A small cyclic molecule secreted by the adrenal medulla upon activation of the sympathetic nervous system
What does epinephrine do?
Binds to cell-surface receptors to trigger a cascade that makes second messenger cyclic adenosine monophosphate (cAMP) + activates protein kinases
What do thyroid hormones do?
Enter cells, bind to DNA and activate transcription of genes involved in energy mobilization
What does thyroid hormones incorporate in their structure?
Iodine
What are steroid hormones synthesized from?
Cholesterol in the smooth endoplasmic reticulum
Why can steroids diffuse through biological membranes?
Due to their hydrophobicity
Since steroids are hydrophobic they can be dissolved in plasma. T/F
False
Steroid hormones exerts its effects upon target cells by…?
Diffusing through the plasma membrane to bind with a receptor in the cytoplasm
What happens after the steroid hormones has bounded to the receptor?
The steroid-hormone receptor complex is transported into the nucleus where it acts as a sequence-specific regular of transcription
Why are steroid hormones effects exerted slowly, over a period of days and persist for days and weeks?
Because steroid hormones must modify transcription to change the amount and/or type of proteins in the cell
Steroids regulating sexuality, reproduction and development are secreted by…?
Testes, ovaries and placenta
Steroids regulating water balance and other processed are secreted by….?
Adrenal cortex
Endocrine glands other than steroid hormones, secrete….?
Peptide hormones
Although thyroid hormones is derived from an amino acids, its mechanism of action more closely resembles…?
That of the steroid hormones
What is a physiological endpoint?
Point that much be maintained at constant levels
What are tropic hormones?
Hormones that regulate hormones
What is the role of the adrenocorticotropic hormone (ACTH)?
To stimulate increased activity of the portion of the adrenal gland called the cortex
What is the cortex of the adrenal gland responsible for?
Secreting cortisol (and other steroid hormones)
What does ACTH stand for?
Adrenocorticotropic hormone
Why is ACTH considered a tropic hormone?
It regulates another regulator (cortisol)
What does cortisol regulate?
Regulates physiological endpoints, including cellular responses to stress and glucose
Most feedback in the endocrine system are____?
Negative feedbacks or feedback inhibition
The portion fo the brain which controls such of the endocrine system is the _______?
Hypothalamus
How does the hypothalamus control the endocrine system?
By releasing tropic hormones that regulate other tropic hormones; called releasing and inhibiting factors
What does the hypothalamus specifically control and why does that relate to the endocrine system?
Controls the anterior pituitary and the anterior pituitary controls most of the endocrine system
What is the name of the endocrine control center?
Hypothalamic-pituitary control axis
What’s the hypothalamic-pituitary portal system?
The blood supply, a special miniature circulatory system provided for efficient transport of hypothalamic releasing and inhibiting factors
What is a hypophysis?
Another name for pituitary gland
What is the arrangement of the capillaries in a portal system?
Consists of two capillary beds in sequence, allowing for direct communication between nearby structures
What are the two halves of the pituitary gland?
- Anterior pituitary: Adenohypophysis
2. Posterior pituitary: Neurohypophysis
What is the anterior pituitary and what does it do?
Normal endocrine gland; controlled by hypothalamic releasing and inhibiting factors (tropic hormones)
What is the posterior pituitary and what does it do?
Composed of axons with descend from the hypothalamus
Based on the posterior pituitary, where are the neurons that allow axons to descend?
The hypothalamic neurons that send axons down to the posterior pituitary; an example of neuroendocrine cells
What are neuroendocrine cells?
Neurons which secrete hormones into the bloodstream
What are the hormones from the posterior pituitary?
ADH (antidiuretic hormone or vasopressin)
What is the purpose of ADH?
Causes the kidney to retain water during times of this and oxytocin
What does the retaining of oxytocin help with, based n ADH function?
Causes milk let-down for nursing’s and uterine contractions during labour
Are hormones made by axon termini in the posterior pituitary or by somas in the hypothalamus?
Hypothalamic and pituitary hormones are peptides, and since there’s no protein synthesis at axon termini, the posterior pituitary doesn’t make any hormones but stores them
Thyroid hormone is produced from where?
Produce from the AA tyrosine in the thyroid gland
What is the structure of the thyroid hormone?
Comes in two forms, with three or four iodine atoms per molecule
How is the production of the thyroid hormone increased?
Increased by thyroid stimulating hormone from the anterior pituitary
What is the mechanism of action of thyroid hormone?
Bind to a receptor in the cytoplasm of cells that then regulates transcription in the nucleus
What is the effect of the regulation of thyroid hormone based on regulating transcription in the nucleus?
Increase the overall metabolic rate and body temperature, and in children stimulate growth
What is cortisol secreted by?
Adrenal cortex in response to ACTH from the pituitary
The effects of cortisol help the body deal with _____?
Stress
What does cortisol help mobilize and store?
Mobilize glycogen and store fat to provide energy during stress and increase protein consumption
