Kin 460 Exam 1

Which of the following type of glial cell myelinates peripheral axons? a. Schwann cells b. Oligodendrocytes c. Astrocytes d. Microglia e. All of the above

a. Schwann cells

List the steps involved in chemical neurotransmission, from the synthesis of neurotransmitter through responses in the postsynaptic neuron.

1. Action potential depolarizes terminal membrane, causes calcium to flow into cell 2. Calcium causes vesicles to bind with cell membrane 3. Release of NT by exocytosis into synaptic cleft 4. NT binds with receptor 5. Ion channels open or close 6. Conductance change causes current flow 7. Postsynaptic potential changes 8. Postsynaptic cells excited or inhibited 9. Summation determines whether AP occurs or not

What criteria define a neurotransmitter?

1. Must be synthesized and stored in the presynaptic terminal 2. Must be released in response to presynaptic electrical activity 3. Interact with receptors specific for the NT in the post-synaptic membrane 4. Elicit same response when artificially applied

What prevents action potentials from turning around and going back up the axon?

After sodium channels opened in AP, they become inactivated as membrane potential becomes more positive. Sodium channels cannot open again until hyper polarization resets them at end of AP. Refractory period where Na+ channels are inactivated prevents back flow of AP

Why are lower motor neurons referred to as the "final common path" for movements? Are the motor neurons that innervate head muscles upper or lower motor neurons?

All commands for movement whether reflexive or voluntary are conveyed to muscles by activity of lower neurons. The lower motor neurons send their axons out of the spinal cord and brainstem to innervate the skeletal muscles of the head (and body)

What are the main types of glial cells, and what is the main function of each?

Astrocyte: maintain appropriate chemical environment for neuronal signaling, blood-brain barrier (BBB) restricts diffusion of bacteria and large molecules in the blood from entering the neural tissue Microglial cells: like macrophages of the immune system, modulate local inflammation, remove damaged cells from injured sites Oligodendrocytes: myelinate axons in the brain and spinal cord (CNS), myelin wraps around some axons, speed up propagation of electrical signals, Schwann Cells are same but PNS

Compare the pros and cons of electrical versus chemical synapses.

Chemical synapse: synaptic cleft (20-49 nm b/w cells) chemical transmitter synaptic delay (1-5 ms) Electrical synapse: continuity b/w cells (bidirectional) ion current no delay

List major stimulus types that can open various kinds of ion channels.

Ligand (chemical) Electrical (voltage) Stretch Heat

Diagram a neuron and label its components. In what ways are neurons specialized for communication? Do these specializations distinguish neurons from other types of cells?

Neuron: dendrite, nucleus, soma, myelin sheath, axon terminal Specialized because of extensive branching of dendrites, use of synapses (communication b/w cells, can be excitatory or inhibitory). Yes this distinguishes them from other cells.

Suppose you are recording action potentials from a neuron. How will the action potential be affected if you remove Na+ from the external medium? How will the action potential be affected if you remove external K+?

Sodium: removing sodium from the external medium will cause absence of AP and membrane will become hyperpolarized Potassium: removing potassium from external medium will not affect propagation of AP, outward current of potassium ions is unaffected

What is the purpose of myelin? Explain how myelin speeds the conduction of the action potential.

The main purpose of myelin is to increase the speed at which AP propagates along the fiber. It does this by acting as an electrical insulator

What is the "neuron doctrine"?

The principle that each neuron is a discrete cell with distinctive processes arising from its cell body and that neurons are the signaling units of the nervous system

A motor pool (as opposed to a motor unit) consists of a. all of the motor neurons that project to a given muscle. b. all of the motor neurons within a single segment of spinal cord. c. all of the motor neurons that project to a given limb. d. a single motor neuron and all of the muscles it innervates. e. a single motor neuron and all of its afferent interneurons.

a. All of the motor neurons that project to a given muscle

Listed below are the individual events that make up chemical synaptic transmission. a. Diffusion of transmitter across the synaptic cleft b. Depolarization of the presynaptic terminal c. Vesicle fusion with plasma membrane d. Opening of voltage-gated ion channels e. Activation of presynaptic, calcium-sensitive proteins Which of the following is the correct sequence of these events? a. a; b; c; d; e b. b; d; e; c; a c. b; e; d; c; a d. e; d; b; c; a e. a; b; d; e; c

b. B; D; E; C; A 1. Depolarization of the presynaptic terminal 2. Opening of voltage-gated ion channels 3. Activation of presynaptic, calcium-sensitive proteins 4. Vesicle fusion with plasma membrane 5. Diffusion of transmitter across the synaptic cleft

Typically, neurons firing action potentials encode a signal's intensity by a. changing the size of their action potentials. b. changing the frequency of their action potentials. c. firing at precise moments so as to signal different sized signals. d. sending signals of different sizes down different axonal branches. e. All of the above

b. Changing the frequency of their action potentials

Action potentials are generated a. at most subthreshold voltages. b. only when the cell reaches threshold. c. only when the membrane potential exceeds threshold by 5 to 10 millivolts. d. intermittently, but usually when the membrane potential exceeds threshold. e. only after all of the sodium channels are open.

b. Only when the cell reaches threshold

Which of the following best describes nerve cells? a. Nerve cells are exceptionally good conductors of electricity (much better than copper wires). b. Nerve cells are similar in their electrical conduction properties to copper wires. c. In comparison to copper wires, nerve cells are relatively poor conductors of electricity. d. Nerve cells are unable to conduct electricity under any circumstances. e. Nerve cells are electron sinks: they absorb many electrons, but no electricity comes out of them.

c. In comparison to copper wires, nerve cells are relatively poor conductors of electricity

Which of the following is an accepted criterion for defining a molecule to be a neurotransmitter? a. It must be present in the presynaptic terminal. b. It must be released in response to presynaptic electrical activity. c. It must exert an effect on the postsynaptic cell. d. All of the above e. None of the above

d. All of the above

Gap junctions (electrical synapses) may exhibit all of the following features except for the ability to a. pass small metabolites, including some second messengers. b. pass electrical current bidirectionally. c. pass electrical current unidirectionally. d. amplify small incoming electrical signals into large regenerative potentials. e. synchronize the activity of populations of nerve cells.

d. Amplify small incoming electrical signals into large regenerative potentials

Which of the following is not integral to the action potential waveform? a. A change in permeability of the membrane to sodium b. A change in permeability of the membrane to potassium c. A transient increase in the sodium current d. An initial decrease in the potassium current e. A "self-activating" aspect to the rise in the sodium current

d. An initial decrease in the potassium current

The motor neurons innervating the medial gastrocnemius muscle are found a. concentrated with a single segment of cervical spinal cord. b. concentrated within a single segment of lumbar spinal cord. c. spanning several segments of medial lumbro-sacral spinal cord. d. spanning several segments of lateral lumbro-sacral spinal cord. e. distributed diffusely throughout the dorsal and ventral horns of lumbro-sacral spinal cord.

d. Spanning several segments of lateral lumber-sacral spinal cord

Acetylcholine is used as a neurotransmitter at a. the neuromuscular junction. b. preganglionic synapses of the autonomic (visceral motor) nervous system. c. postganglionic synapses of the sympathetic nervous system. d. widely distributed synapses in the central nervous system. e. All of the above

e. All of the above