PSIO Block 5

List and describe (in order) the physiological events associated with synaptic transmission

An AP arrives at end of synaptic terminal of pre-synaptic cell. Electrical signal is converted to a chemical signal, it crosses the synaptic cleft to the post-synaptic cell. This chemical signal is converted back to an electrical signal in the post-synaptic cell, generating an AP in that cell (the chemical signal may cause ions to flood in, depolarizing the cell, i.e. electrical signal) - Could be excitatory or inhibitory depending on NT

Describe the factors that influence the speed of propagation of the action potential

The two factors that influence the speed of propagation of the action potential are size (bigger the axon diameter the faster), and myelination (insulation = faster)

Describe how differences in ionic gradients across the membrane contribute to electrical gradients (i.e. electrochemical gradients)

There is a concentration gradient that exists and an electrical gradient that results in charge separation (buildup of potential energy) across the membrane, and it is stored in the living cell at rest (this maintains resting membrane potential), as specific ion channels permeability changes, this will change the membrane potential (and alter the gradients).

Describe the mechanism of accommodation

1. The lends becomes more round (it rounds up) 2. The entering angle of the light increases 3. The light gets more refracted (bent) so the focused image now falls onto the retina - Ciliary muscles keep tension on the suspensory ligaments, when the ciliary muscle contracts, suspensory ligaments become slackened, causing the lens to be strong and rounded, used for up close objects

Describe the relevant general sense tests and explain important physiological terms related to these tests.

1. Two Point Discrimination Test: general test, where you poke your hand and calf to determine the minimum distance at which you can distinguish whether one or two points are in contact with the skin. You lower the distance until they can only feel one poke. Testing receptive field, fingertips should have smallest receptive field. 2. Tactile Localization Test: where you mark your hand and calf and must correctly identify where the marking was. Again tests receptive fields. 3. Temperature Adaptation Test: Submerge each hand in hot and cold water, then put both in room temperature bucket (letting hands adapt first), make sure proper feelings. Negative afterimage occurs here.

Define the terms receptive field and receptor potential

A receptive field is the area in which a receptor will respond to. It allows for discrimination between two similar stimuli. A receptor potential is a graded potential at the receptor. Receptor potentials influence the rate of action potential production in the sensory (afferent) neuron.

Describe the specific sensory events associated with gustation (i.e. the cellular events that occur when a stimulant molecule is detected)

A tastant binds to a chemoreceptor on the gustatory hair sticking out of the taste pore, stimulating the sensory neuron, which will carry that signal through a nerve depending on what portion of the tongue it is (upper to lower is vagus X nerve, glossopharyngeal IX nerve, or facial VII nerve), then the information is

List and describe the events that result in the propagation of the action potential

After one action potential the adjacent membrane area is depolarized to threshold, initiating a new action potential in the next 'new' region of the membrane. They only move in one direction due to refractory periods, the old area cannot be are-stimulated, so it goes down in one direction. They are also continuously regenerated along the axon.

Explain the concept of 'appropriate stimulus' with respect to interpretation within the CNS of incoming sensory information

All sensations are read in the CNS as electrical signals, regardless of the type of stimulus. We discriminate because the appropriate stimulus will activate a different receptor type, which lends to sensory discrimination in the brain. For example in vision, if a photoreceptor is stimulated and responds to light, that will be read as vision in the brain, as opposed to touch which would activate a different receptor (mechanoreceptor).

Describe how the activity of the Na+/K+ ATPase maintains ion gradients

At rest, Na+ wants to enter the cell and K+ wants to leave the cell. The ATPase uses one ATP to cause 3 Na+ ions to move out and 2K++ ions to move in, this keeps a potential difference from the inside and the outside of the cell, so that way when an action potential does come, the cell can much more easily respond with an action potential.

Define the terms depolarization, repolarization, and hyperpolarization

Depolarization occurs when the membrane potential becomes more positive or less negative. Repolarization occurs as the membrane potential falls back towards resting value (more negative). Hyperpolarization occurs when the membrane potential becomes more negative (less positive).

Draw a picture showing the structure of a synapse. Label the principal structure on the pre-synaptic neuron and post-synaptic neuron. Include an astrocyte in your picture

Do it.

Describe all of the important structures of the ear

External Ear: Oracle, external auditory canal, and the tympanic membrane Middle Ear: Ossicles (hammer, incus, stapes), oval window, auditory tube Inner Ear: Vestibule, semi-circular canals, cochlea, vestibulocochlear nerve

Define equilibrium potential and explain how the equilibrium potential for different ions relates to the membrane potential

For each ion, the equilibrium potential is the membrane potential where the net flow through any open channels is 0 (when chemical and electrical gradients are equal in magnitude, for that ion under the existing gradient.) The membrane potential shows the potential difference between the inside and outside of the cell in terms of potential difference. The equilibrium potential for K+ sets the negative limit for the membrane potential, whereas the equilibrium potential for Ca 2+ sets the positive limit for the membrane potential.

List the four general senses and the five special senses

General senses are for pain, temperature, touch/pressure/ body position, and chemical. Special senses are smell, taste, vision, hearing, equilibrium/balance.

Differentiate between general and special senses

General senses have receptors distributed throughout the body, general senses are not collected within specialized sense organs. Special senses are senses that have specialized organs devoted to them.

Compare and contrast the characteristics of graded vs action potentials

Graded potentials are post-synaptic electrical events and do not necessarily lead to an action potential. Graded potentials can be depolarizing (Na+ enters) or hyper polarizing (K+ leaves or Cl- enters), and result in EPSP's or IPSP's respectively. With enough EPSP's these can sum to produce an action potential, but not necessarily.

Define graded potential and describe the difference between EPSPs and IPSPs

Graded potentials occur in the post-synaptic cell and can be depolarizing (EPSP) or hyper polarizing (IPSP), they could lead to another action potential, but they must be added to reach threshold to do so.

Describe the basic mechanism of hair cells and explain how this relates to the general process of sensory transduction

Hair cells are within the organ of cortical and this is where transduction occurs. When the tallest stereo cilia moves, the tip link connects to the next stereo cilia, when it moves against the tympanic membrane the tip link moves, causing opening of K+ channels, K+ floods into the cell, causing depolarization and an AP (different ranges of the basilar membrane respond to different vibrations)

Predict what will happen to the membrane potential of a cell if the permeability of the membrane increases or decreases for Na+, K+, Cl-

If permeability for Na+ increases, Na+ will flood into the cell, making the membrane potential more positive. If permeability for Na+ decreases, Na+ will not be able to enter the cell, making the membrane potential more negative. If permeability for K+ increases, K+ will be able to leave the cell, making the membrane potential more negative. If permeability for K+ decreases, K+ will not be able to leave the cell, making the membrane potential more positive. If permeability of the membrane increases for Cl-, Cl- will be able to flow into the cell, making the membrane potential more negative. If permeability of the membrane decreases for Cl-, Cl- will not be able to flow into the cell, making the membrane potential more positive.

Compare and contrast 'continuous' and 'saltatory' conduction

In saltatory conduction, the AP can jump from the nodes of ranvier which boosts the signal and causes faster conduction. In continuous conduction, the axon is not myelinated, so the signal will just travel down the axon in an ordinary fashion (slower and less strong than saltatory).

Define spatial and temporal summation and describe how they contribute to neuron activation

In spatial summation, more neurons are recruited causing an increase in neuronal activation and response. In temporal summation, the frequency of neuron's firing increases, increasing neuronal activation

Describe the physiology of vision - how light influences sodium channel activity, neurotransmitter release, and action potential general

In the dark, rhodopsin is not activated, Na+ channels are open, the cell is depolarized, and there is a high rate of neurotransmitter released. In the light, rhodopsin is activated, Na+ channels close, the cell hyper polarizes, and there is a low rate of neurotransmitter released, high rate of AP Production.

Describe the normal concentration gradients for Na+ and K+ that exist across the membrane of all cells

Intracellular Na+ = about 10 mM Extracellular Na+ = about 140 mM Intracellular K+ = about 140 mM Extracellular K+ = about 2.5 mM

Compare and contrast the characteristics of leak-channels, voltage-gated, chemically-gated, and mechanically-gated channels

Leak-channels are channels that are routinely open (K+ leak channels are always open and the basis for the inside-negative resting membrane potential). Chemically-gated (ligand-gated) ion channels are channels that open once a particular ligand binds to the channel. Mechanically-gated ion channels are channels that respond to a physical stimulus like membrane stretch. The voltage-gated ion channels are channels that respond to depolarization, or when the membrane potential gets more positive.

List and describe the structures that light must refract/pass through in order to be detected by the eye

Light first goes through the cornea (refracted), the pupil, the lens (refracted), and continues through the vitreous humor, finally reaching the retina (back of the eye)

Identify the following general sense receptors and describe their functions: Merkel disc, nociceptor, Meissner's corpuscle, Pacinian corpuscle, hair root plexus, Golgi tendon organ, muscle spindle. Additionally, understand general receptor categories.

Merkel Disc: Responds to light touch and pressure Nociceptor: Responds to painful stimuli Meissner's Corpuscle: Responds to light touch and low frequency vibrations (close to surface) Ruffini's corpuscle: Responds to stretching of the skin and aids in proprioception Hair root Plexus: On hair bulb, responds when hairs on our skin are moved Pacinian Corpuscle: Responds to deep pressure and high frequency vibrations Golgi tendon organ: Respond to soft tissue organs Muscle Spindle: Responds to muscle excitation

Describe the importance of myelination and the function of oligodendrocytes and Schwann cells

Myelinated axons will have saltatory conduction and allow the potential to jump nodes which boosts the signal and leads to faster conduction. Oligodendrocytes extend processes that form the myelin sheath around axons in the CNS, while Schwann cells themselves form the myelin sheath around axons in the PNS.

Describe the specific sensory events associated with olfaction (i.e. the cellular events that occur when a stimulant molecule is detected)

Olfaction: Odorant binds to a receptor on the olfactory epithelium. When an odor molecule binds to the receptor, this causes signaling cascade (olfactory receptor protein is G-protein coupled), ATP is hydrolyzed, CAMP is produced, Na+ channel protein opens, sodium floods into the cell, results in EPSP (depolarization), triggering afferent action potential. This action potential is sent down the axon of olfactory neurons, synapsing to mitral cells, axons of those mitral cells carry signals to the brain through the olfactory tract.

Describe the following cells and structures related to olfaction and gustation: olfactory epithelium, olfactory receptors, olfactory nerve, olfactory bulb, taste buds, papillae, gustatory receptor cell, gustatory hair

Olfactory epithelium: Layer of mucus that sits on top, this is where the olfactory receptors are Olfactory receptors: Bind odorant and leads to sense of smell Olfactory nerve: Part of it exits cribriform plate, inferior to olfactory tract Olfactory tract: Bundle of nerve axons that exit to primary olfactory area in cerebral cortex Olfactory Bulb: Axons that exit cribriform plate in olfactory nerve extend to glomeruli here in olfactory bulb Taste Buds: On tongue, back of throat, roof of mouth, and cheeks, tucked down in papillae, have gustatory hair on it Papillae: Small, finger-like projections that increase surface area of the tongue Gustatory receptor cell: On gustatory hair, bind to different chemicals (tastings) in the food we eat, synapses onto a sensory neuron Gustatory hair: sticks out of taste pore on taste bud, has chemoreceptors on it

Describe presbyopia, hyperopia, and myopia, and the underlying issues that impair vision in each case

Presbyopia: Our lens loses elasticity with age. There is a loss of ability for the lens to accommodate, which is why it becomes harder to see objects up close. Hyperopia: Can see far objects just fine, can't see close up objects, can be corrected with a convex lens. Myopia: Can see close up objects just fine, can't see far objects, but can also be corrected with a concave lens

Describe the importance of refractory periods

Refractory periods establish the maximum rate (frequency) of action potentials. They also influence the characteristics of action potential propagation (ensures forward propagation from the axon hillock to the axon terminal)

Describe the principal differences between rods and cones and the basic structure of a rod photoreceptor including the function of rhodopsin

Rods are very sensitive to light and have large receptive fields, but do not allow us to see color. Cones are less sensitive to light and do allow us to see color. In rods, in light, rhodopsin gets activated. Outer segments of rod cells contain photopigments that change shape when they absorb light

List the steps associated with the transduction of sound stimuli and distinguish between how loudness and pitch of sound are detected

Sounds of various pitches will stimulate different regions of hair cells along the length of the cochlea.

List in order and describe the principal events associated with an action potential

Step 1: Local depolarization, must be local EPSP's to get to threshold. Step 2: Depolarization to threshold, opening of VG Na+ channels, which increases Na+ permeability, opening more channels. No turning back. Step 3: Na+ channels close, spontaneously inactivate. Step 4: Depolarization also opens VG K+ channels, inactivation of VG Na+ channels with this --> Repolarization of the membrane back toward resting value (aka "falling" or repolarizing phase). After this there is the after-hyperpolarizing phase where potassium ions are still leaving the cell so the cell turns back to rest.

Define the phrase 'all-or-none' in the context of the neuronal action potential

That phrase refers to the fact that once step 2 is reached, or once an action potential reaches the threshold, there is no going back, an action potential will occur. If the AP reaches the threshold, it WILL travel all the way to the end of the axon

Describe the basis of absolute and relative refractory periods

The absolute refractory period occurs immediately following inactivation of VG Na+ channels, and the membrane CANNOT be are-stimulated to produce another AP. This prevents overstimulation and ensures the signal will finish to completion. In the relative refractory period, a new action potential can be produced, but doing so requires a larger than normal stimulation (due to resetting of VG K+ channels).

Describe how receptive field size is related to sensory resolution/discrimination

The greater the receptor density, the greater the number of receptors within an area of 'sensory surface', the greater the sensory resolution and discrimination. The smaller the receptive field size generally the better sensory resolution/discrimination.

Describe, in general, how the intensity or duration of a stimulus is coded and relayed to the nervous system

The intensity and duration of the stimulus are conveyed through the frequency and pattern of incoming signals (higher frequency and pattern, higher response)

Describe the general mechanism of sensory transduction for equilibrium, including details related to the semicircular ducts, the utricle, and the saccule

The semicircular ducts, namely the utricle and the saccule help with sensory transduction for equilibrium and balance. Within that there is the ampulla, within ampulla there is cupulae which consists of a gelatinous substance that is secreted by supporting cells. Rotational acceleration is sensed by the semicircular ducts and linear acceleration is sensed by the utricle and saccule

Describe the features of the eye, what are the layers and important structures?

There are 2 cavities in the eye, the anterior cavity and the posterior cavity. The anterior cavity is the space between the cornea and the lens and it is filled with aqueous humor. It also has 2 chambers within it, the anterior chamber (which is between the cornea and the iris) and the posterior chamber (which is between the iris and the lens). The posterior cavity is the space between the lens and the retina, it is filled with vitreous humor which helps maintain the position of the retina against the choroid layer of the eye. Right underneath the cornea is the sclera, encircling the lens is the ciliary body, suspensory ligaments connect the ciliary body to the lens. Move the lens out of the way to see the pupil. On the posterior part of the eye you can see the choroid layer (black). Deep to the retina is the tapetum lucidum (looks blue and white). On the back of the external eye is the optic nerve.

Describe the following special sense tests and explain how each assesses function of sensory systems: visual acuity test (Snellen eye chart), astigmatism test, blind spot test, color blindness test, hearing (tone) test

Visual Acuity Test: Measures the ability of the lens to focus light reflected from an object on the central fovea of the retina Astigmatism test: Caused by irregularities in the curvature of the cornea or lens. Chart with radiating lines. Blind Spot Test: Making sure your blind spot is there, no photoreceptors in the optic disc causes this Color blindness Test: Tests if you are color blind if you can see the numbers Hearing (tone test): Humans can only hear tones within a certain range (20 - 20,000 Hz), tests that range and our ability to hear higher frequencies