PHSL 3051 Unit 1 Learning Objectives

diagram the body plan, showing the various organ systems and their interrelationships with one another and with the external environment

*look in notes

Differentiate between presynaptic inhibition and postsynaptic inhibition

Postsynaptic inhibition involves the flux of K+ and/or Cl through the membrane of a receiving postsynaptic cell. This prevents the cell from generating an action potential. Presynaptic inhibition involves the inhibition of an axon terminal by preventing an influx of Ca2+. With decreases in Ca2+ influx associated with presynaptic inhibition, less neurotransmitter is released from the terminal, resulting in decreased stimulation of the postsynaptic cell.

Describe Two Factors That Encode Stimulus Intensity.

(1) the frequency of action potentials generated in response to the stimulus and (2) the number of sensory receptors activated by the stimulus. As stimulus intensity increases, the amplitude of the receptor potentials formed in the sensory receptor increases.

Give two reasons why we are unaware of our blind spots during normal visual experiences.

1) Eyes are constantly moving, so the blind spot is constantly changing; the brain fills in the little missing bits for us (pieces image together like a puzzle by constantly moving) 2) The blind spot one eye perceives is/may not be the same blind spot for the other eye; therefore what one eye misses, the other will detect

Describe the 4 attributes of a stimulus that the central nervous system can distinguish: 1) modality (type of stimulus), 2) location, 3) intensity, and 4) duration.

1. Modality- type of stimulus that optimally activates the receptors, Mechanoreceptors: EX: touch, deep pressure, stretch, tension Nociceptor: receptor activated by chemicals EX: Pain Thermoreceptors: EX: <37 degrees C or >37 degrees C Chemoreceptors: EX: pH, CO2, O2 2. Location:- Receptive field of a primary sensory neuron Acuity: sharpness of perception, the ability to precisely locate and distinguish one stimulus from another. In the somatic sensory and visual systems, two major factors affect acuity: (1) the size of the receptive field (2) lateral inhibition. 3. Intensity: · Encoded by the frequency of action potentials generated in response to the stimulus and by the number of sensory receptors activated by the stimulus· As stimulus intensity increases, the amplitude of the receptor potentials formed in the sensory receptor increases.· Frequency coding: The use of action potential frequency to determine stimulus intensity 4. Duration: encoded by the duration of action potentials in the sensory neuron, the longer the stimulus lasts, the longer the sensory neuron produces action potentials. If the stimulus persists, however, most sensory neurons do not continue to generate the same frequency of action potentials because their sensory receptors adapt.

Define excitatory postsynaptic potential (epsp) and inhibitory postsynaptic potential (ipsp)

A depolarizing postsynaptic potential is called an excitatory postsynaptic potential (EPSP). A hyperpolarizing postsynaptic potential is termed an inhibitory postsynaptic potential (IPSP).

Explain how a receptor potential in a sensory neuron can lead to the initiation of an action potential at the trigger zone of the sensory axon.

A stimulus causes a receptor potential in a sensory neuron by opening up transduction channels in the membrane of the sensory receptor. It is generally a depolarizing event resulting from inward current flow. To communicate information from one part of the body to another, action potentials in a neuron must travel from the trigg

Explain the mechanism by which the opening and closing of ligand-gated ion channels is regulated. opens or closes in response to a specific ligand (chemical) stimulus.

A wide variety of ligands—including neurotransmitters, hormones, and chemicals in food or an odor—can open or close ligand-gated channels. For example, the neurotransmitter acetylcholine opens cation channels that allow Na+ and Ca2+ to diffuse inward and K+ to diffuse outward. Ligand-gated channels participate in the generation of graded potentials.

Compare and contrast the autonomic and somatic divisions of the peripheral nervous system, considering the type of targets, neurotransmitters, and general functions with which they are involved

Autonomic: effectors include smooth muscle, cardiac muscle, and glands. The motor neuron pathway is usually a 2 neuron pathway, 1- a preganglionic neuron that extends from the CNS to an autonomic ganglion and 2 a postganglionic neuron that extends from the autonomic ganglion to the effector. Most autonomic motor neurons release either acetylcholine or norepinephrine. Chromaffin of the adrenal medulla releases epinephrine and NE into the bloodstream as hormones. Usually cholinergic or adrenergic receptor type on effector organ. The action of neurotransmitter on effector may be excitatory (causes contraction of smooth muscle, increase rate and force of contraction of cardiac muscle, or increase secretion of glands) or inhibitory ( causes relaxation of smooth muscle, decreases rate and force of contraction of cardiac muscle, or decreases secretion of glands). Has an involuntary control from hypothalamus, brain stem, and spinal cord. Somatic: the effectors are skeletal muscle. The motor neuron pathway is a one neuron pathway, a single somatic motor neuron extends from the CNS to synapse directly with the effector. The neurotransmitters all release ACh. The receptor type on the effector organ is cholinergic. The action of neurotransmitter on the effector is always excitatory (causes contraction of skeletal muscle). The control of motor output is voluntary control from the cerebral cortex, with contributions from the basal nuclei, cerebellum, brain stem, and spinal cord.

Compare and contrast the sympathetic and parasympathetic branches of the autonomic nervous system based on: neurotransmitters and receptors at the ganglionic and target organ synapse, and general functional effects on the target organs

BOTH branches can have different effects on the same target cells. BOTH have preganglionic neurons that release ACh on nicotinic cholinergic receptors (which have ligand-gated Na channels) on postgang neurons; the opening of the Na channel creates an action potential down postgang neuron; while the specific target cell receptors vary, they are usually all GPCRs. Parasympathetic: parasymp ganglia are located on or near target organs; long preganglionic and short postgang; slow heart rate and constricts airway, increases digestion; preganglionic parasympathetic release ACh onto postgang nicotinic receptor; postgang parasymp releases ACh again which is received via a muscarinic receptor (GPCR) on target cell. Sympathetic: postgang symp releases norepinephrine (NE) onto adrenergic (GPCR) receptor on target cell. most originate in thoracic and lumbar regions of the spinal cord; short preganglionic and long postgang; increase heart rate and contractility, relaxes airway, inhibits digestion; preganglionic symp releases ACh into postgang nicotinic receptor.

Explain how one might determine the location of a spinal cord injury based on the modality sensation datis lost and the region of the body (both the side of the body and body part) where sensation is lost

Below area where complete loss of sensation is evident = affected region b/c sensory pathways ascend the spinal cord (thus they enter at lower spinal levels and travel up). Fine touch, proprioception, and vibration would all be affected on the same side that the injury occurred, because they do not cross the midline in the spinal cord (cross @ medulla); therefore they travel up the spinal cord on the side that has been affected (thus leading to a lack of sensation on that side). Pain, temp, and coarse touch would not be affected on this side because these neurons do cross at spinal level and thus do not travel on the affected side. Nociception, temp, and coarse touch would all be affected on the opposite side that the injury occurred, because they cross the midline in the spinal cord (therefore they travel up the spinal cord on the side opposite of the injury). Damage to the spinal cord would lead to damage of secondary axons that crossed in spinal cord level; therefore the signal would not be able to successfully travel up to the thalamus and whatnot. This would lead to decreased sensation of nociception, temp, etc. on the opposite side of the spinal cord injury. Fine touch, proprioception, and vibration on this side would not be affected because the primary sensory neurons travel up to the medulla on the side opposite of the original injury.

Compare and contrast the properties of voltage-gated Na+ and voltage-gated K+ channels, and understand how voltage influences their activation and inactivation (do they both have inactivation gates?

Both are located at the first node of sensory axons, mediate action potentials, activated by cell depolarization of the membrane potential from RMP to -55mV, play important roles in invitation and conduction of electrical signals They contrast: Voltage gated Na: opens first, two gates, activation gate closed at RMP, depolarization to -55mV causes gate to open and Na enters cell, opens more VG Na channels and causes further depolarization, inactivation gate closes and Na entry stops, repolarization resets the gates. Voltage gated K: only has activation gate, no inactivation gate, at RMP activation gate is closed, depolarizing stimulus opens gate, K leaves cell, repolarization causes activation gate to close

Understand how the activity of voltage-gated Na+ and K+ channels generates an action potential and the roles of these channels in each phase of the action potential (i.e. depolarization/rising phase, overshoot, repolarization, afterhyperpolarization/undershoot).

Depolarization and rising phase: Na and K channels begin to open, rapid entry of Na depolarizes Overshoot: Na channels close and slower K channels open Repolarization: K moves out of cell Afterhyperpolarization: More K out of cell causes hyperpolarization, K channels close and return to RMP

Define the concepts of electrochemical equilibrium and equilibrium potential. Calculate the equilibrium potential for Na+, K+, and Ca2+ using the Nernst equation (with a calculator or MetaNeuron) and explain what accounts for the differences between them. Use diagrams to explain conceptually why the equilibrium potentials are what they are.

Electrochemical equilibrium is reached when the movement of ions down their electrical gradient is equal and in the opposite direction to the movement of ions down their concentration gradient. Equilibrium potential is the membrane potential in a cell when electrochemical equilibrium is reached. K+ equilibrium potential = -90mV (ONLY K+ channels open) Na+ equilibrium potential = +60mV ways that these values differ from one another is charge and magnitude. Sodium has a positive equilibrium potential and potassium has a negative equilibrium potential, also potassium has a greater charge than sodium. Potassium is 5 on outside and 150 (30x) on the inside while sodium is 150 on the outside and 15 on the inside (10x)

Explain the factors that contribute to stimulus localization and two-point discrimination; consider factors in the periphery (e.g. in the skin), and at the various levels of the somatosensory pathways.

Factors that contribute to stimulus localization are the Receptive field: associated with one sensory neuron which in turn synapses on one CNS neuron. These fields frequently overlap with neighboring receptive fields, and Sensory receptors. Two point discrimination is When two stimuli activate separate pathways to the brain, they are perceived as distinct stimuli and hence there is two-point discrimination. Somatosensory pathways are different levels of perception are attributed to the fact that some areas of the body require more sensory perception than others. The fingers are used for perception much more often than the back of the neck is for example.

Explain the different cues the brain uses to compute depth perception (Fig. 10.34). Include a discussion of binocular disparity, as well as other contextual cues.

Field of depth is created by constricting the pupil so that only a narrow beam of light enters the eye. In this way, a greater depth of the image is focused on the retina. Monocular cues include: size. Binocular cues include: eye convergence, disparity, 3D structure, and displacement (parallax). Binocular disparity is the difference in image location of an object seen by the left and right eyes, resulting from the eyes' horizontal separation (parallax). The brain uses binocular disparity to extract depth information from the two-dimensional retinal images in stereopsis. Contextual cues state that depth perception arises from a variety of depth cues. These are typically classified into binocular cues that are based on the receipt of sensory information in three dimensions from both eyes and monocular cues that can be represented in just two dimensions and observed with just one eye.

Explain how an increase in extracellular K+ concentration can have a dramatic effect on the EK, the resting membrane potential, and the neural status of a person.

Increase in extracellular [K] has a larger effect because permeability of K ions is 30x that of Na. Also [K]out is relatively low to begin with and an increase in [K]out causes a bigger difference in ratio. If there is an increase in potassium ions outside the cell (extracellular) then the resting membrane potential will become less negative.

Explain how an increase or decrease in the permeability (i.e. opening or closing channels permeable) to K+, Na+, Ca2+, or Cl- would change the membrane potential from rest.

Increase in permeability of K: Membrane potential will become more negative (closer to -90) (hyperpolarization) Increase in permeability of Na: Membrane potential will become more positive from rest (closer to +60) (depolarization) Increase in permeability Ca: membrane potential will become more positive because Ca will move down gradient into the cell. (depolarization) Increase in permeability Cl: membrane potential will become more negative because Cl will move down its gradient into the cell (hyper polarization)

Explain How The Gating (activation ) characteristics of ion channels (e.g.mechanically gated versus chemically gated) in sensory receptors contributes to the modality of sensory receptors.

Ion channels that open in response to mechanical movement of adjacent structures include touch sensors in the skin and vibration sensors in the inner ear that respond to sound. Also, most hollow organs, such as the bladder, intestines and heart, have stretch sensors that respond to expansion of the organ. Respond to stimuli produced outside the body. Chemically gated = ligand-gated... respond to stimuli produced by the body. Mechanically- respond to pressure, deformation of the channel causes reaction; pressure/touch. Nociceptors- release of chemicals like ATP from injured cells.Thermoreceptors- increase/decrease in temperature

Explain what determines whether or not a postsynaptic neuron will generate an action potential at its trigger zone.

It depends on the amount of neurotransmitter released and the sensitivity of the postsynaptic cell. When a depolarizing postsynaptic potential reaches threshold, it triggers an action potential in the axon of the postsynaptic neuron.

List the intracellular and extracellular concentrations of the following ions: K+, Na+, Cl-, Anions (A-), and Ca2+ ions, and draw a diagram of a cell showing these concentration gradients

K+ = I:150mM E:5 mM Na+ = I:15 mM E:145mM Cl- = I:5 mM E:115 mM anions = I:100 mM E:10mM Ca2+ = I:0.0002mM E:2 mM

Explain which type of channels are responsible for the resting membrane potential (note their gating characteristics and the ion selectivity)

Most potassium channels are open at rest (leak channels), with a small number of sodium channels open. Leak channels are not gated, but rather are open all the time (more or less). The resting membrane potential is close to the potassium equilibrium potential (-90mV) but is slightly less negative because of the small number of open Na leak channels. NaK ATPase maintains sodium and potassium gradients across the membrane.

Compare the distribution of ion channels along unmyelinated versus myelinated axons and explain how this accounts for the difference in conduction velocity between these two types of axons. Predict the effects on action potential propagation of demyelinating diseases, such as multiple sclerosis.

Myelinated axons- leak channels are insulated by myelin leading to less loss of current flow and better conduction velocity. Ion channels only located at Nodes of Ranvier; thus signal has saltatory conduction along myelin sheaths and "jumps" and moves much quicker. Demyelinating diseases: along locations where myelin sheath once was, current leak occurs and conduction slows. The signal cannot make it very far because it loses energy as it travels through the axon. In an unmyelinated axon, ion channels are sequentially placed all along the axon; thus it takes longer to send a signal down the axon. the energy isn't leaked out, it still contains the same signal, but it is simply slower. Distance between voltage gated channels needs to be small enough so local current flow can depolarize the membrane **Harder to generate action potential in demyelinating diseases **Axon diameter (bigger diameter = less resistance = faster current)

Contrast the change in EK caused by a 5mM increase in extracellular K+ concentration with the change in ENa caused by a 5mM increase in extracellular Na+ concentration. Explain how this difference can be accounted for.

Na = 61 K = -71 with the 5mM increase in the extracellular concentrations, sodium increased by approximately 1, while potassium increased by approximately 18mV. Potassium had a greater change.

List the conditions that must exist and which proteins must be present in order for a cell to have a negative resting membrane potential (i.e. think about ion channels, carrier proteins, etc.)

Need appropriate combination and number of leak channels (need way more K+ leak channels compared to Na channels). More K leak channels open so more movement of K out of cell down concentration gradient. Proteins: NaKATPase pump: maintains gradient by moving 3 Na out of cell and 2 K into cell (-1 net charge inside)

Explain why postsynaptic potentials are transient (i.e. short lived). In other words, what terminates the action of the neurotransmitter on the postsynaptic cell

Neurotransmitters can be returned to axon terminals for reuse or transported into glial cells. Enzymes inactivate neurotransmitters. Neurotransmitters diffuse out of synaptic cleft

Describe how incoming sensory inputs from primary sensory axons can be modified at the level of the spinal cord and relate this to the mechanism of action of some common pain medications

Pain neurons which have opiate receptors at the axon terminal. When opiate neurotransmitters are released and bind to the opiate receptors, blocks the release of substance P by not allowing Ca2+ to enter. The primary afferent is then unable to transfer it's info onto the secondary afferent due to the internal pain reduction pathway. An exogenous chemical (morphine) works at the same receptors, inhibiting the neurotransmitter release, stopping pain.

Describe chemical neurotransmission, listing in correct temporal sequence events beginning with the arrival of an action potential at the pre-synaptic axon terminal and ending with a graded potential generated at the postsynaptic membrane

Presynaptic axon terminal: synaptic vesicles filled with neurotransmitters are docked at active zones along synaptic cleft waiting for signal to release their contents; neurotransmitters are made in the cell body and brought to the axon terminal; When depolarization of action potential reaches the axon terminal, the change in membrane potential sets off: 1) axon terminal membrane has voltage gated Ca+ channels that open in response to depolarization 2) Ca moves into cell, down its concentration gradient, and binds to regulatory proteins which initiates exocytosis of synaptic vesicle 3) Synaptic vesicle fuses with cell membrane, opens, and neurotransmitter inside vesicle moves into synaptic cleft 4) neurotransmitters diffuse across the gap to bind with membrane receptors in postsynaptic cell, initiating a response inside the postsynaptic cell 5) Unbound neurotransmitters can be taken back up into axon terminal/glial cells(via secondary active transport that takes in Na and neurotransmitter), can be metabolized by enzymes in post synaptic cleft, or diffuse out of neurotransmitters 6) Bound neuromodulators/neurotransmitters may activate GPCR(slow) (which alter gating channel, modifies proteins, changes concentration gradients, etc) or may bind to and open a receptor channel (fast) which allows ions in (if these ions cause depolarization they are excitatory and if hyperpolarizing they are inhibitory) 7) opening and closing of ion channels causes changes in membrane potentials (called graded potentials in neurons-these depend on the amount of neurotransmitter released and the # of receptors)

Describe how it is possible for us to differentiate between stimuli of different modalities the same body part (i.e. fingertip). Consider this at the level of 1) the sensory receptors and 2) the neurons onto which they synapse in the ascending sensory systems.

Primary sensory neurons of different receptive fields in the fingertip synapse with their own secondary sensory neurons (1:1 ratio of primary to secondary neurons). Each of these different secondary sensory neurons travel in their own separate but parallel pathways, which are respective to their original receptive fields.

Explain how action potentials are propagated along an axon and compare this to the passive conduction like the local current flow in dendrites.

Propagation of action potential: depolarization causes voltage gated Na+ and K+ channels to open and local current flow to initiate more voltage gated channels to open at the next Node of Ranvier. The propagation of an action potential is accomplished by local current flow. Local current flow refers to the passive movement of charges from one membrane region to adjacent membrane regions due to differences in membrane potential in these areas. In a neuron, an action potential can propagate along the axon away from the cell body only—it cannot propagate back toward the cell body because any region of membrane that has just undergone an action potential is temporarily in the absolute refractory period and cannot generate another action potential.

Explain why the resting membrane potential is closer to EK than to ENa and explain two reasons why changes in extracellular K+ concentration have more dramatic effects on resting membrane potential than do changes in extracellular Na+ concentration.

Resting membrane potential is closer to Ek than Ena because more K leak channels are open, therefore net movement of K down its concentration gradient out of the cell leads to negative membrane potential. [K] has more dramatic effects on RMP because K is 30x more permeable than Na because many more K leak channels are open than Na leak channels.

Explain the concept of selective permeability of the plasma membrane, and describe the chemical characteristics of molecules that are most likely to diffuse across the lipid bilayer

Selective permeability is a property of cellular membranes that only allows certain molecules to enter or exit the cell. Selectively permeable to nonpolar, small and uncharged molecules can regularly move through lipids as they are uncharged, anything that is lipid can move across the membrane. Nonpolar molecules most readily diffuse why small, uncharged polar molecules are only slightly able to diffuse. Charged molecules such as ions and large uncharged, polar molecules can not pass through the lipid bilayer.

Differentiate between sensory receptor activation and perception of a stimulus.

Sensory receptor activation occurs any time there is a stimulus that reaches threshold and thus allows for a receptor potential large enough to set off an action potential (primary) Perception only occurs when there stimulation reaches the perceptual threshold (level of stimulus intensity necessary for you to be aware of a particular situation); some info just doesn't go to a conscious part of the brain (ie sensory info that initiates visceral reflexes); also, some receptors adapt to stimulus and thus tune out stimulus for a period of time. (secondary/tertiary)

Define a sensory receptor and recognize the difference between this and a plasma membrane receptor

Sensory receptors have transduction channels that are opened by a specific type of stimulus (mechanical, thermal, or chemical). And evaluates information from a stimulus on or around the skin and sends a graded potential to a neuron to create an action potential. Plasma membrane receptors are gated by a ligand that is activated by molecules that initiate a graded potential, and electrochemical gradients.

Explain why two-point discrimination is better in some areas of the body surface than others, e.g., lips, fingertips versus back of the neck.

Some areas of the body, such as the fingertips, have smaller receptive fields with as little as a 1:1 relationship between primary and secondary sensory neurons. Two pins separated by as little as 2mm can be perceived as two separate touches.

Explain spatial summation of postsynaptic potentials.

Spatial summation is summation of postsynaptic potentials in response to stimuli that occur at different locations in the membrane of a postsynaptic cell at the same time. For example, spatial summation results from the buildup of neurotransmitter released simultaneously by several presynaptic end bulbs

List the types of sensory receptors that are found in the skin (Figure 9.11) and explain what determines the optimum type of stimulus that will activate each

Tactile receptors in the skin or subcutaneous layer include Meissner corpuscles, hair root plexuses, Merkel discs, Ruffini corpuscles, pacinian corpuscles, and free nerve endings. Merkel disc (slowly adapting, touch & pressure) Meissner corpuscle (rapidly adapting, touch & low frequency vibration) Ruffini corpuscle (slowly adapting, stretch & pressure) Hair root plexus (rapidly adapting, touch, i.e. movement of hair) Free nerve endings (itch, pain, temperature, tickle) Pacinian corpuscle (rapidly adapting, high frequency vibration)

Define a chemical gradient, an electrical gradient, and an electrochemical gradient across the plasma membrane of a typical cell.

The electrochemical gradient is the concentration gradient plus the electrical gradient. The electrical gradient is the inside of the plasma membrane is slightly negative relative to the outside (negative membrane potential). Potassium ions, which are positively charged, are attracted to the inside of the cell, therefore the potassium electrical gradient is inward (ECF to ICF). a chemical gradient refers to the concentration gradient of an ion or molecule.

Describe the fovea and the blind spot, and explain their functional significance

The fovea is a small depression in the center of the macula lutea (high density of cone receptors). The fovea is the area of highest visual acuity or resolution (sharpness of vision). The main reason that you move your head and eyes to look directly at something is to place images of interest on your fovea. Because photoreceptors are not present in the optic disc, it is also known as the blind spot. Therefore, you cannot see an image that strikes this region. Normally, you are not aware of having a blind spot because visual processing in the brain "fills in" the missing information.

Explain how a primary sensory neuron transmits information about the intensity of a stimulus to a secondary sensory neuron at a chemical synapse (i.e. explain temporal summation of postsynaptic potentials).

The frequency of the AP - higher frequency = more intense. Temporal summation is the summation of postsynaptic potentials in response to stimuli that occur at the same location in the membrane of the postsynaptic cell but at different times. For example, temporal summation results from buildup of neurotransmitter released by a single presynaptic end bulb two or more times in rapid succession.

Compare and contrast the properties of leak channels and mechanically-gated channels found on sensory receptors.

The gates of leak channels randomly alternate between open and closed positions. Typically, plasma membranes have many more potassium ion (K+) leak channels than sodium ion (Na+) leak channels, and the K+ leak channels are leakier than the Na+ leak channels. A mechanically-gated channel opens or closes in response to mechanical stimulation in the form of touch, pressure, tissue stretching, or vibration (such as sound waves). The force distorts the channel from its resting position, opening the gate.

Define a sensory receptor potential and explain how it is generated. Explain how the size of a receptor potential can be increased by a larger stimulus.

The graded potentials that occur in sensory receptors are termed receptor potentials . A receptor potential is often produced by sensory transduction. It is generally a depolarizing event resulting from inward current flow.The coding of stimulus intensity by the size of the receptor potential means the larger the stimulus, more transduction channels are open, larger receptor potential.

Describe the chemical characteristics and functions of the following components of the plasma membrane: lipid bilayer, proteins (include the following types of proteins: channels, carriers (also known as transporters), receptors, enzymes, and linkers

The lipid bilayer forms a significant barrier between extracellular fluid and intracellular, and is a selective barrier. Plasma membrane proteins have various functions. Ion channels are integral and form a pore through which a specific ion can flow to get across a membrane, there water channels are aquaporins. Most plasma membranes include specific channels for several common ions. Carriers are also integral and transport a specific substance across membranes by undergoing a change in shape. Receptors are also integral and recognize specific ligands and alters cells function in some way. Enzymes are integral and peripheral as a catalyzed reaction inside or outside the cell (depending on what direction the active site faces). Linker proteins are rigid and function to prohibit unwanted interactions between the discrete domains.

Understand the interplay between parasympathetic and sympathetic innervation of a target organ and when one is more likely to be active than the other.

The parasympathetic is dominant in taking command of routine. The sympathetic branch is dominant in stressful situations.

Explain The Concept Of Receptive Field.

The receptive field of a sensory neuron can be defined as the stimulated physical area, specific group of chemicals, or particular set of sound frequencies that causes a response in that neuron. The receptive field of a neuron is the stimulated physical area, specific group of chemicals, or particular set of sound frequencies that causes a response in that neuron.

Describe the homunculus and explain the significance of the size of the region of the somatosensory cortex devoted to a particular body part

The sensory homunculus is the distorted map of the body that exists in the primary somatosensory cortex. The size of the region in the SSC that receives information about a specific body part is proportional to the density of innervation of the body part (not to the size of the body part)

Describe the 3 main types of somatic sensations: 1. tactile: light touch, deep pressure, vibration, cold, hot, etc., 2. pain, 3. Proprioception

The tactile sensations encompass a variety of sensations—touch, pressure, vibration, itch, and tickle. Several types of encapsulated mechanoreceptors attached to large-diameter myelinated A fibers mediate sensations of touch, pressure, and vibration. Tactile receptors in the skin or subcutaneous layer include Meissner corpuscles, hair root plexuses, Merkel discs, Ruffini corpuscles, pacinian corpuscles, and free nerve endings. Pain is indispensable for survival. It serves a protective role by signaling the presence of noxious stimuli that are causing or are about to cause tissue damage. By contrast, pain perception may be suppressed in an injured person who is trying to escape a burning building. From a medical standpoint, the subjective description and indication of the location of pain may help pinpoint the underlying cause of disease. Proprioceptive sensations allow us to know where our limbs are located and how they are moving even if we are not looking at them, so that we can walk, type, or dress without using our eyes. Because most proprioceptors adapt slowly and only slightly, the brain continually receives action potentials related to the position of different body parts and makes adjustments to ensure coordination.

Write the Nernst equation, and indicate how this equation accounts for both the chemical and electrical driving forces that act on an ion.

This is used to calculate the equilibrium potential for a specific ion (ie the membrane potential that would be reached at electrochemical equilibrium if the membrane were permeable to only this specific ion) Ek = (RT/ZkF)ln(Kout/Kin) R=8.31 J(mol-deg) T = 310K F= 96500coul/mol ln to log (x2.303) Zk = valence (+1)

Write the Goldman-Hodgkin-Katz equation and explain what the relative ion permeability (P) represents. Explain which variables in this equation are generally quite stable and which can vary on a moment to moment basis in a neuron (i.e. explain which membrane proteins contribute to these).

This reflects the real world situation of finite and variable ionic permeabilities. The relative permeability represents the comparison between the ions in reference to one another, this is rapidly changing due to ion channel gating. The ion gradients on the other hand are quite stable due to NaK ATPase. (look in notes for equation)

Define threshold, and relative and absolute refractory period. Explain the state of ion channels and the stimulus amplitude required to generate an action potential during each

Threshold: membrane potential required to cause an action potential. If a point is not reached, nothing will happen. Absolute refractory period: no stimulus can trigger another action potential (Na close and K channels open). It represents the time required for Na to return to its resting position or reset itself. Relative refractory period: only larger than normal stimulus can initiate new action potential (Na reset and K still open)

Compare and contrast simple diffusion of a molecule across the lipid bilayer to the movement of an ion through an ion channel. Consider the 1) chemical characteristics of the molecules moving across the membrane, 2) whether or not a membrane protein is required, and 3) the driving force for the movement.

Uncharged molecules are not affected by the electrical gradient across the plasma membrane (membrane potential).The structure of the lipid bilayer allows small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass through the cell membrane, down their concentration gradient, by simple diffusion. Ion channels are macromolecular pores made up of multiple protein subunits through which ions may move passively across the cell membrane. Large-scale ion movement across the membrane changes not only the ion concentrations on either side of the membrane, but also the electrical gradient (movement down the electrochemical gradient)

Draw a diagram illustrating lateral inhibition and explain how this process modifies sensory information.

Understand how this process permits precise localization of boundaries (edges) of stimuli. in lateral inhibition, input from sensory receptors along the border of a stimulus is substantially inhibited compared to input from sensory receptors at the center of the stimulus. Because of lateral inhibition, (1) there is a further decrease in the number of action potentials transmitted by the pathways from the peripheral area and (2) the pathway from the center area is only slightly inhibited and continues to transmit a higher frequency of action potentials than the peripheral area. Both of these effects allow the brain to determine exactly where the pencil point is located

Compare and contrast the properties of mechanically-gated channels and voltage-gated channels (consider what causes them to open and close, where they are located, what kind of membrane potentials they mediate).

Voltage gated channels are opened by a change in membrane potential, which is a depolarization from -70 up to -55mV. This happens at the first node. Mechanically gated channels are Gated channels that open in response to a mechanical stimulus (such as touch, pressure, tissue stretching, or vibration). The force distorts the channel from its resting position, opening the gate. This is located in the Dendrites of some sensory neurons such as touch receptors, pressure receptors, and some pain receptors.

differentiate between the afferent and efferent division of the PNS and describe the general function and direction of info flow

afferent is how the world and stimuli affect us, while efferent causes an effect. the afferent division is where somatic senses and special senses send signals to the brain through sensory input. the efferent division is where the somatic nervous system sends signals to skeletal muscles casing us to move. afferent neurons only take info to the CNS, and efferent neurons only take it away from the CNS

describe the main functions of the brainstem, diencephalon, cerebellum, and cerebrum

cerebrum- involved in perception, initiation and control of movement, cognitive function (cortex and basal nuclei) cerebellum- involved in sensory and motor function, and motor learning brain stem- involved in the regulation of autonomic functions, and mid level sensory and motor processes (is critical for survival) ( pons, medulla oblongata, midbrain diencephalon- involved in sensory motor processing (thalamus) and control of thirst, satiety, sex hormones, and other hormones (thalamus, hypothalamus, pineal gland, pituitary gland)

describe the interrelationships between molecules, cells, tissues, organs, and organ systems in the body

collections of molecules in living organisms form cells. collection of cells that carry out related functions are called tissues. the four main types of tissues are epithelial, connective, muscle, and nerve. structural and functional units composed of tissues are called organs. groups of organs integrate their function to create organ systems.

describe the form and function of the different components of a neuron: dendrites, soma, axon

dendrites receive inputs (synapses) and integrate (sum) inputs they are branches on the end of the neuron. soma inputs flow into soma from dendrites, and contain a nucleus. axons are an output structure, they send electrical signals (action potentials) propagated long distances, the tail of the neuron. action potentials trigger release of chemical signals (neurotransmitter) that activate or inhibit other neurons or target cells

explain the four main themes: homeostasis, integration, mechanism of action, and communication

homeostasis maintains our body internal conditions; the maintenance of relatively stable conditions in the body internal environment, a dynamic steady state. EX: blood glucose. integration is how our cell types (and actions) are put together to figure out what must be done, can lead to communication, cells must coordinate their work with other cells in order to accomplish their functions EX: interaction of nervous and endocrine signals and to regulate blood flow. communication is one neuron releasing neurotransmitters to communicate, seeks must communicate with one another to function EX: sympathetic neurons communicate with the pacemaker cells in the SA node to cause an increase in heart rate. mechanism of action is when a sympathetic neuron will release a neurotransmitter, which will bind to a receptor, basically think about how does something happen in our body, what is that cell doing, how is that organ accomplishing that?

Draw a picture of a primary sensory (afferent) neuron, and label its components and their location in the body. Include the sensory receptor (dendrites), soma, and the peripheral and central branches of the axon. Use an arrow to indicate the direction of information flow.

image in notes

compare and contrast the morphology of sensory neurons (unipolar) with that of motor neurons and interneurons (multipolar)

most sensory neurons have only one process that extends from their cell bodies. this single process is an axon that has dendrites at its peripheral end. most motor neurons have numerous dendrites and one main axon extending from their cell bodies. like motor neurons, interneurons usually have numerous dendrites and one main axon extending from their cell bodies. sensory neurons convey action potentials into the CNS. motor neurons convey action potentials away from the CNS to effectors in the periphery. interneurons are responsible for integration, they process incoming sensory information from sensory neurons

compare and contrast negative and positive feedback and feedforward systems, and give examples of each, and what are each of these types of systems designed to

negative feedback loops are designed to maintain relative constancy while positive feedback loops are designed to reinforce change negative: as the controlled parameter decreases, its response is to increase the controlled parameter. EX: blood pressure positive: as the controlled parameter is increased the response also increases the controlled parameter EX: the stretch of the cervix during birth free forward: as the controlled parameter decreases the response helps prevent that change EX: you are cold so your body shivers to get warm free forward systems are designed to anticipate a change in a condition or parameter

Describe the two different modality-specific ascending somatosensory pathway end notes which modalities are carried in each

nociception, temp, coarse touch: primary neuron enters spinal cord > synapses with secondary neuron > secondary neuron crosses midline @ spinal level > synapses with tertiary in thalamus > tertiary synapses at primary somatosensory cortex. fine touch, proprioception, vibration: primary sensory neuron enters spinal cord > synapses with secondary neuron in medulla > secondary neuron crosses midline @ medulla > synapses with tertiary in thalamus > tertiary synapses at primary somatosensory cortex. Anterolateral Pathway- (spinothalamic pathway); first synapse between the sensory receptor neuron and a second neuron located in the gray matter. Dorsal Column Pathway- sensory don't cross but ascend to the brainstem

Define sensory transduction and explain the mechanism by which this process occurs (i.e. what type of channels mediate it, how are they activated, etc.)

sensory transduction is the conversion of one type of stimulus energy (pressure, temperature) to an electrical signal. This is carried out by mechanically gated transduction channels, which are closed at rest and with the influx of Na and Ca cause a depolarizing receptor potential, opening the cation channel. This is represented by a membrane deformation (mechanical stimulus) into a receptor protein.

Explain two ways that activation of a G protein-coupled receptor (GPCR) can regulate opening and closing of ion channels

the G protein directly opens the ion channel by binding to it. In other cases, the G protein indirectly opens the ion channel by activating a second messenger pathway

describe the main components of the central nervous system and their general functions

the brain is focused on integration and high order functions. it initiates thoughts and intentions, initiates and coordinates movement, senses and percepts, regulates hormones, blood pressure and other critical body functions. the spinal cord is more concerned with signal transmission and local circuits. it also transmits signals from cells in the body into the brain, contains local circuits that integrates signals to and from the brain and the body, and transmits signals from brain to body. the peripheral nervous system represents nerves which are collections of axons and ganglia which are collections cell body of neurons. the nervous system is functionally organized. the main function of the PNS is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body.

Understand How Stimulus Intensity Is Encoded By Neurons.

the greater the stimulus strength above threshold, the greater the frequency of the action potentials until a maximum frequency is reached as determined by the absolute refractory period

describe the segmental organization of the spinal cord

the spinal cord is enclosed within the meninges and vertebrae. each spinal nerve is broken up into segments that send and receive messages from specific regions of the body. neurons in different spinal cord segments innervate different regions of the body. the 4 sections are cervical, thoracic, lumbar, and sacral spinal cord

describe the organization of the spinal cord with respect to the dorsal and ventral roots and their relationships to the efferent and afferent divisions of the PNS

the ventral root is efferent and carries motor info to muscles and glands via efferent signals through ventral horns. the two types of horns are somatic motor and autonomic nuclei. the dorsal root is afferent and carries sensory info to the CNS. dorsal root ganglia contains cell bodies of sensory neurons (somatic and visceral info)

describe the main components of a feedback system

they start with a stimulus which disrupts homeostasis by decreasing the controlled condition (ie blood pressure) then the receptors or baroreceptors in blood vessels input the decrease in action potentials to the control center(brain) which outputs action potentials in sympathetic nerves which reaches the effective (here and blood vessels) which its response is an increase in heart rate and the constriction of the blood pressure back to normal. *stimulus > variable > receptor senses change in variable > control center compares against set point > effectors make adjustments