Chapter 2

alpha 7 vs. alpha4beta2

Alpha 7 open quickly, desensitize quickly vs. alpha4beta2

Motor Neuron

Motor neurons carry commands from the brain or spinal cord to muscles and glands (efferent information).

Axon signal length

.1mm to 2mm

21. Summarize the two major mechanisms by which voltage-gated ion channels become inactivated (see figure 5-7).

Change in membrane potential- many channels enter a refractory period after briefly opening when the membrane is depolarized. They recover only after the membrane potential is restored. Calcium Binding- Some voltage-dependent Ca-channels inactivate when the internal Ca level increases following channel opening. The internal Ca binds to calmodulin, a specific regulatory protein associated with the channel.

Chemoreceptor what are these responsible for?

In class he used the example of olfactory receptor cells being depolarized as a result of oderant molecules binding receptors that open (or close) ion channels. This changes receptor potential. Chemoreceptors are responsible for olfaction, gustation, itch, pain, and many visceral sensations.

principles applying to neuronal integration

Integration site HIghest density of voltage-gated Na+ channels Summation occurs here Trigger zone, Axon Hillock. All the inputs summate here (both temporal and spatial summation). IF you reach threshold, you get a positve feedback cycle that lets massive amounts of sodium in to start the action potential

Transmitter-gated ion channels ()

Ionotropic Both IPSP and EPSP The receptor and the ion channel are the same molecule Receptors that open to allow the ion through

Summarize important principles applying to neuronal input

Local change in membrane potential --Right at the synapse, ion channels open, current flows and membrane potential is locally changed Graded (amplitude and duration is variable) --Large amplitude input or small --Long lasting or short lasting Degrades with distance (spreads passively) --As the current flows from the synapse, it disipates Degrades with time Depolarizing or hyperpolarizing Received from a sensory receptor or another neuron

19. Describe how the __________ of ACh receptors contributes to the channel's selectivity and gating (see figures 9-14 and 9-15 and textbook pages 200-202). How would the M2 region of GABAA and Glycine receptors differ?

M2 region The M2 helices line the inside of the pore, it is the selectivity filter. When the pore is closed, there are valine and leucine preventing ion passage. After binding of ligand, this portion moves out of the way and opens up, allowing the ion to pass through. In a channel that allows positive ions through, the pore needs to be lined with negatively charged amino acids --GABA and glycine allow chloride through, so they must have positive charges on the M2 region

Mechanoreceptors where are these found?

Mechanical stretch of the membrane, ion channels open which cause current to flow. Result is depolarization which notifies the brain that the muscle has been stretched. Happens in muscles and in hair cells of the ear

Multipolar —Where found

Multipolar neurons predominate in the nervous system of vertebrates. A spinal motor neuron with a relatively modest number of dendrites receives about 10,000 contacts 1,000 on the cell body and 9,000 on dendrites. The dendritic tree of a Purkinje cell in the cerebellum is much larger and bushier, receiving as many as a million Multipolar cells have a single axon and many dendrites

16. State the general structure/composition of muscle ACh receptors, neuronal ACh receptors and ClC channels.

Muscle - alpha, beta, delta, alpha, gamma in that order Neuronal - Alpha 2-10 and beta 2-4 subunits. Bunch of different combinations of these subunits. ClC - "Two" channels linked together, each half acting independent of the other. Look at slide 5-21 to look at structure and current readings for this type of channel.

Oligodendrocytes

Oligodendrocytes are found in the central nervous sys-tem; each cell envelops from one to 30 axonal segments (called internodes), depending on axon diameter.

Astrocytes Types, Function

Protoplasmic astro-cytes are found in the gray matter; their many processes end in sheet-like appendages. The sheet-like processes of protoplasmic astrocytes envelop nerve cell bodies and synapses, Fibrous astrocytes are found in the white matter and have long, fine processes that contain large bundles of tightly packed intermediate filaments. Their end feet contact axons on nodes of Ranvier Both types of astrocytes have end-feet, dilatations that contact and surround capillaries and arterioles throughout the brain. 1. Astrocytes separate cells, thereby insulating neuronal groups and synaptic connections from each other. 2. Because astrocytes are highly permeable to K + , they help regulate the K + concentration in the space between neurons. As we shall learn below, K flows out of neurons when they fire. Repetitive firing may create excess extracellular K + that could interfere with signaling between cells in the vicinity. Astrocytes can take up the excess K + and thus maintain the efficiency of signaling between neurons. 3. Astrocytes perform other important housekeeping chores that promote efficient signaling between neurons. For example, as we shall learn later, they take up neurotransmitters from synaptic zones after release. 4. Astrocytes help nourish surrounding neurons by releasing growth factors

23. Explain the molecular structure and the functioning of the bacterial K+ channel KcsA as determined by________________ (see textbook pages 116-119 and figure 5-15).-- GO BACK TO SHARED

Rod MacKinnon -Four identical subunits arranged around a central pore. -Each subunit has two membrane spanning helices that are connected by the P loop- selectivity filter. -Lined by negative ions to attract cations. -Electronegative oxygens strip off the hydration shell 2 spanning regions and a pore loop Analagous to S5 pore loop S6 on the real molecule 4 subunits Inner helix the gate (similar to S6) Pore loop is the selectivity filter --First half is helix, 2nd half is selectivity filter --Selectivity filter Amino acids -- red dots are oxygens ----from carbonyl groups/hydroxyl groups ---------Electronegative oxygens the perfect distance from each other to let potassium out, but too far apart to allow sodium

Photoreceptor — how do they work?

Rods and cones Inside they have membrane disks/invaginations. On those disks are photoreceptors. As light hits them, it changes that receptors shape and changes a signaling cascade which decreases the level of cAMP which causes the channel to close which changes membrane (receptor) potential.

Schwann Cells

Schwann cells occur in the peripheral nervous system, where each envelops a single seg-ment of one axon.

Interneuron Types -length of types -subtypes

Short: Interneu-rons are the most numerous and are subdivided into two classes: relay and local. Relay or projection interneurons have long axons and convey signals over consider-able distances, from one brain region to another. Local interneurons have short axons because they form con-nections with nearby neurons in local circuits. Each functional classfication can be subdivided further. Sensory system interneurons can be classified according to the type of sensory stimuli to which they respond; these initial classifications can be broken down still further, into many subgroups according to location, density, and size. For example, the retinal ganglion cell interneurons, which respond to light, are classified into 13 types based on the size of the dendritic tree, the branching density, and the depth of its location in specifc layers of the retina

Sensory Neuron Length What it does and purpose

Short: Sensory neurons carry information from the body's peripheral sensors into the nervous system for the purpose of both perception and motor coordination. Some primary sensory neurons are called afferent neurons, and the two terms are used interchangeably.

12. Explain how stimulus intensity is encoded in action potential frequency, leading to changes in transmitter release at the synapse. (See figure 2-10)

The amount of secretion (transmitter release) is dictated by the frequency of action potentials Neural signaling is encoded by action potential frequency, leading to variable release of neurotransmitter at the synapse Bigger stretch = bigger frequency of action potentials = more neurotransmitter released If you keep that big stretch going for a long time, you're getting MORE action potentials because its a longer time at the frequency which also results in more neurotransmitter release.

Pseudo-unipolar What they are and where they're found

The receptor neurons that convey touch, pressure, and pain signals to the spinal cord, Both segments function as axons; one extends to peripheral skin or muscle, the other to the central spinal cord.

11. Summarize important principles applying to action potential conduction and neuronal output (as discussed in class). How long does an action potential last propagation velocity

They are initiated at the trigger zone when threshold is reached Stereotypical event lasting 1-2 milliseconds The action potential itself is similar in almost all cases. Mediated by voltage-gated channels Stereotypical one at least All-or-none Always about the same height -- no mini action potentials Self-propagating/regerative Once initiated it is going to go all the way to the end Propagation velocity is variable...up to 120 meters/second Bigger and myelinated is fastest

Unipolar neurons — what they are and where found

are the simplest because they have a single primary process, which usually gives rise to many branches. One branch serves as the axon; other branches function as receiving structures. These cells predominate in the nervous systems of invertebrates; in vertebrates they occur in the autonomic nervous system. Unipolar cells are characteristic of the invertebrate nervous system.

Feed-Forward Inhibition

enhances the effect of the active pathway by suppressing the activity of pathways mediating opposing actions. Feed-forward inhibition is common in mono-synaptic reflex systems. For example, in the knee-jerk reflex circuit (Figure 2-6) afferent neurons from extensor muscles excite not only the extensor motor neurons but also inhibitory interneurons that prevent the firing of the motor cells innervat-ing the opposing flexor muscles. In the knee-jerk reflex, feed-forward inhibition is reciprocal, ensuring that the flexor and extensor pathways always inhibit each other so that only muscles appropriate for the movement and not those opposed to it are recruited.

glia breakdown (including percentage)

glia in the vertebrate nervous system can be divided into two major classes: microglia and macroglia. Macroglia: oligodendrocytes, Schwann cells, and astrocytes In the human brain about 80% of all the cells are macroglia. Of these, approxi-mately half are oligodendrocytes and half are astrocytes.

Feed-Back Inhibition

is a self-regulating mechanism. Here extensor motor neurons act on inhibitory interneurons that in turn act on the extensor motor neurons themselves and thus reduce their probability of firing. The effect is to dampen activity within the stimulated pathway and prevent it from exceeding a certain critical level For example, a motor neuron may have excitatory connections with both a muscle and an inhibitory interneuron that in turn inhibits the motor neuron. The inhibitory interneuron is thus able to limit the ability of the motor neuron to excite the muscle

G-protein-linked ion channels ()

metabotropic receptors Receptor and ion channel are separate molecules Several steps until ion channel is actually opened or closed Sometimes an ion channel being opened isn't the final result, but instead second messangers are formed Second messangers could change METABOLISM or even the cells genetic profile/expression

Connectional specificity

nerve cells do not connect randomly with one another in the formation of networks. Rather each cell makes specific connections at particular contact points with certain postsynaptic target cells but not with others.

Negative current

is positive ion coming in

IPSP and molecule

Inhibitory Post Synaptic Potential Cloride makes it more negative.

All 5 subunits with 4 transmembrane regions

] ligand-gated channels (ACh, 5-HT3, GABAA, Glycine receptor channels).

Where action potentials start

action potentials, are initiated at a specialized trigger region near the origin of the axon initial segment

Microglia

immune system cells that are mobilized to present antigens and become phagocytes during injury, infection, or degenerative diseases.

Review the anatomy and physiology of the knee-jerk reflex.

1. Sensory information is conveyed to the central nervous system (the spinal cord) from muscle. 2. Motor commands from the central nervous system are issued to the muscles that carry out the knee jerk. 3. Inhibitory commands are issued to motor neurons that innervate opposing muscles, providing coor-dination of muscle action. 4. Information about local neuronal activity related to the knee jerk is sent to higher centers of the central nervous system, permitting the brain to coordinate different behaviors either simultane-ously or in series.

Bipolar What they are and where they're found

Bipolar neurons have an oval soma that gives rise to two distinct processes: a dendritic structure that receives signals from the periphery of the body and an axon that carries information toward the central nervous system. Many sensory cells are bipo-lar, including those in the retina and in the olfactory epithelium of the nose. —in general, sensory pathway cells

Convergence

Conversely, a single motor cell in the knee jerk circuit receives 200 to 450 input con-tacts from approximately 130 sensory cells. This pat-tern of connection is called convergence It is common at the output stages of the nervous sys-tem; a target motor cell that receives information from many sensory neurons is able to integrate information from many sources. Convergence also ensures that a motor neuron is activated only if a sufï¬cient number of sensory neurons become activated together.

EPSP and molecule

Excitatory Post Synaptic Potential Sodium

explain Synaptic potentials

Input comes from another neuron. Involves neurotransmitters going across a synaptic cleft to hit the receptors on the other side

Principle of Dynamic Polarization

It states that electrical signals within a nerve cell flow only in one direction: from the receiving sites of the neuron, usually the den-drites and cell body, to the trigger region at the axon. From there the action potential is propagated along the entire length of the axon to its terminals.

22. Explain what is known about the structure of voltage-gated Na+ channels and voltage-gated K+ channels. In your answer, include the number of subunits and the number of transmembrane regions in each subunit. (See figure 5-11C, figure 5-12A, and pictures from the lecture handout)

Na - Large subunit that contains four repeating motifs. Each motif contains 6 transmembrane regions named S1-S6. S5, pore loop, S6 make the selectivity filter. K - Four separate subunits. Six transmembrane regions in each subunit with a pore loop that forms the selectivity filter.

20. Explain the different gating properties of voltage-gated Na+ channels and voltage-gated K+ channels. Name a potent blocker of each channel.

Na- open quickly but are also inactivated quickly by an inactivation gate that closes the channel. -Toxin-TTX K- Opens slowly and closes slowly. No second gating mechanism. -Toxin- TEA

desensitization

The cell regulates individual channels so that if you apply the ligand multiple times in a short amount of time, you get less current going through.

Divergence

The stretching of just one muscle, the quadriceps, activates several hundred sensory neurons, each of which makes direct contact with 45 to 50 motor neu-rons. This pattern of connection, in which one neu-ron activates many target cells, is called divergence It is especially common in the input stages of the nervous system; by distributing its signals to many target cells, a single neuron can exert wide and diverse influence.