BSCI201: LEx4

Goytia | Only on Endocrine and Sensory System

How do sensory systems function?

By the process called transduction, which is the detection of stimuli and transforming the signal into an electrical message that is sent to the central nervous system (CNS).

What receptor detects light energy?

photoreceptors

Where is the location of photoreceptors?

Retina (vision)

What is the signal transduction of photoreceptors?

Light → chemical → electrical

What receptors detects mechanical forces (touch, pressure, stretch, vibration)?

Mechanoreceptors

Where are the locations of mechanoreceptors?

hair cells in ear (hearing) and pacinian corpuscles (touch)

What is the signal transduction of mechanoreceptors?

mechanical → electrical

What receptors detect chemicals in solution (odorants/tastants)?

Chemoreceptors

What are the locations of chemoreceptors?

olfactory cells (smell) and gustatory cells (taste)

What is the signal transduction of chemoreceptors?

chemical → electrical

What are some other receptors?

thermoreceptors, osmoreceptors, and noiceptors

What are the receptor cells for olfaction?

olfactory receptor cells

What is the requirement for olfaction to occur?

odorants must be dissolved in mucus

What are the key structures for olfaction?

olfactory epithelium, olfactory gland (produces mucus)

What is the transduction of olfaction?

odorants bind to G-protein coupled chemoreceptors

What is the pathway to CNS for olfaction?

Olfactory tract goes straight to the cerebral cortex (limbic system), bypassing the thalamus

What can replace olfactory receptor cells and gustatory cells?

differentiated basal cells

What is the receptor cells for gustation? Where are they found?

gustatory cells in taste buds

What is the requirement for gustation to occur?

tastants must be dissolved in saliva

What is the key structures for gustation?

taste buds located on lingual papillae (except filiform papillae, which lacks taste buds)

What is the transduction for gustation?

Salty/Sour (ions: Na+, H+) pass through ion channels. Sweet/Bitter/Umami bind to G-protein coupled chemoreceptors.

What is the pathway to CNS for gustation?

Pathway goes through the thalamus

How are olfactory and gustation connected?

The appreciation of flavor 80% dependent on the sense of smell - why food taste bland when sense of smell is impaired.

When sound waves enter the external auditory canal what does it do?

vibrates the tympanic membrane

What does the vibration do when it hits the tympanic membrane?

The vibration is amplified across the three ossicles (Malleus → Incus → Stapes)

When the vibration reaches the stapes, what does it do?

stapes pushes on the oval window, creating pressure waves in the perilymph found in scala vesticuli

After the waves reach the scala vestibuli, where does it move to?

moves through the cochlea to the endolymph in the cochlear duct

When the ear converts vibrations into fluid vibrations, what does it activate?

organ of Corti and are perceived as sounds

As fluid waves travel, what moves at a specific location that corresponds to the frequency of the sound?

basilar membrane

After the basilar membrane, what relative motion does it hit? What does that do?

tectorial membrane, bends the stereocilia of the hair cells

The endolymph is rich in K+, why is that important for the bending of stereocilia?

bending of stereocilia mechanically opens ion channels, causing K+ to enter the hair cell, which causes depolarization (EPSP).

Depolarization opens what in the ear?

Depolarization opens voltage-gated Ca2+ channels, leading to neurotransmitter release onto the cochlear nerve - sensing sound!

What senses the head position and motion?

the vesticular apparatus using mechanoreceptor hair cells

Linear acceleration/deceleration (position) are sensed by what?

utricle and saccule (in the vestibule)

What does motion rely on?

heavy otoliths (CaCO3 crystals) in the otolithic membrane

Rotational acceleration/deceleration are sensed by what?

semicircular canals

What does rotation cause?

causes the endolymph inside the canals to flow against and bend the Cupula located in the Ampulla, activating the hair cells

What are the two main types of photoreceptors in the retina?

rods and cones

What do rods sense?

dim light, images of shades of gray

What do cones sense?

bright light, concentrated in the fovea, color vision

What is the fovea centralis?

central region of retina providing color vision

What is the path of light when entering the eye?

Light enters the eye and is refracted (bent) primarily at the cornea and then by the lens

What are problems with refraction?

myopia and hyperopia

What is myopia known as? What is it?

nearsightedness; focal point is in front of the retina with concave lens to decrease curvature

What is hyperopia known as? What is it?

farsightedness; focal point is behind retina with convex lens to increase curvature

Where does light need to reach to present vision?

Light must reach the deepest cellular layer of the retina, where the photoreceptors are located

What is the electrophysiology (signal transmission) when your in the dark (resting state)?

Photoreceptors are depolarized and continuously release glutamate. Glutamate hyperpolarizes bipolar cells, which prevents the depolarization of retinal ganglion cells, meaning no AP is sent.

What is the electrophysiology (signal transmission) when your in the light?

Light hyperpolarizes photoreceptor cells. They stop releasing glutamate and bipolar cells are released from inhibition, depolarize, and excite retinal ganglion cells. RGCs generate APs that travel down the optic nerve.

What is the chronology of vision signal?

1. Light is sensed by photoreceptors

2. Receptor cells hyperpolarize by closing sodium and calcium channels

3. The neurotransmitter is not delivered to the bipolar cells

4. Bipolar cells are depolarized

5. The neurotransmitter delivers an activating signal to the ganglion cells

What is the visual pathway to cortex?

What does the visual deficit (lesion) at the left optic nerve cause?

blindness in the left eye

What does the visual deficit (lesion) at the optic chiasma cause?

loss of peripheral vision in both eyes (tunnel vision)

What does the visual deficit (lesion) at the left optic tract/radiations (CNS) cause?

loss of entire right visual field

What is the difference in signaling between the endocrine system and nervous system?

Endocrine system is chemical (hormones) while Nervous system is electrical and chemical

What is the difference in transport between the endocrine system and nervous system?

Endocrine system is bloodstream (long distance) while Nervous system is neurons (short distance)

What is the difference in action between the endocrine system and nervous system?

Endocrine system action takes time, triggers long-lasting actions while Nervous system action is immediate, triggers quick, brief actions.

What is the main function of primary endocrine glands?

Ductless glands; hormone production and secretion directly into the blood (ie. pituitary, adrenal, etc.)

What is the main function of secondary endocrine glands?

have primary functions outside of hormone production but secretes hormones (ie. Heart, kidneys, etc)

What are the two signal chemicals that diffuses to target?

Autocrine and Paracrine

Autocrine signals

Acts on same cell → potentiation

Paracrine signals

Secreted by one cell and diffuse to adjacent cells, ie. neurotransmitters

What is an example of Paracine secretion?

Pancreas secretion of glycotic and lipolytic enzymes to the small intestine

What are the messenger classifications of chemical messengers?

Neurotransmitters, hormones, neurohormones, and cytokines

What system are Neurotransmitters for?

messenger molecule of nervous system

How are neurotransmitters released?

released from neuron by exocytosis

Where do neurotransmitters diffuse through?

diffuses through synaptic cleft to very close target cell

What do neurotransmitters induce?

I/EPSP for long-distance communication (NS)

What are examples of neurotransmitters?

acetylcholine, epinephrine, norepinephrine

What system are hormones for?

messenger molecule of endocrine system

How are hormones expressed?

expressed by endocrine glands

What do target cells of hormones must express?

accessible and functional hormone-specific receptors (cognate receptor)

When are hormones produced?

produced in advance, stored in vesicles for secretion

What system are neurohormones for?

messenger molecule of nervous system

How are neurohormones released?

released from neuron into blood: axosecretory synapse

What are examples of neurohormones?

anti-diuretic hormone and oxytocin

What are cytokines?

peptides or proteins

What released cytokines?

most cell types

How do cytokines get transported?

through blood

What are cytokines involved in?

cell development, proliferation, differentiation and immune response

What do the target cells of cytokines must express?

accessible and functional receptor

Hormones can be chemically classified as…

Biogenic Amines, Peptide, Protein, Glycoprotein, Steroids

Biogenic Amines, Peptide, Protein, Glycoprotein are all…

generally hydrophilic (polar); requires cell surface receptor and are stored in vesicles

Steroids derive from what? What polarity are they?

derive from cholesterol; hydrophobic/lipophilic and diffuse through cell membranes. They are transported in blood by carrier protein

Where is the receptor location(s) of hydrophobic hormone types?

Cytosolic or Nuclear

What is the response speed of hydrophobic hormone types?

Slower

What is the mechanism of hydrophobic hormone types?

regulates gene expression

Where is the receptor location(s) of hydrophilic hormone types?

Cell Membrane

What is the response speed of hydrophilic hormone types?

Faster

What is the mechanism of hydrophilic hormone types?

Activates second messenger systems, leading to signal amplification

What are the receptor properties?

Must be expressed, accessible, and functional

Receptors must exhibit…

saturation, specificity and competition

Agonism

Binds to the receptor and mimics the normal response

Inverse Agonism

A hormone (ligand) that binds to the same receptor, and imposes the inverse effect of the agonist

Additive/Cooperative

Effects of two hormones favor each other and sum

Antagomism

Binds to the receptor, blocking the cognate hormone and producing no response

Synergism

Two hormones together produce an effect that exceeds the sum of their individual effect

Permissiveness

One hormone is required for another to exert its full effects

What is an example of permissiveness?

Estrogen causes expression of oxytocin receptors and oxytocin induces expression of prostaglandins (PG) which induces expression of oxytocin

Receptor agonist

chemicals that bind to a receptor mimicking normal response

Receptor antagonists

chemicals that bind to a receptor producing no response