Quiz 116 · Synaptic Transmission in Central Nervous System

Answers to Quiz 115 · Functional Organization of Nervous System

1. In an adult, the spinal cord ends at the level of the:

   Answer: Body of the first lumbar vertebra

   The cord runs from the base of the skull, as the continuation of the medulla, to the body of L1. So in adults it is shorter than the vertebral column. Revise divisions of the nervous system

2. The brainstem is made up of the:

   Answer: Midbrain, pons and medulla

   Midbrain, pons and medulla together form the brainstem. The cerebellum shares the metencephalon with the pons but is not part of the brainstem. Revise divisions of the nervous system

3. The metencephalon consists of the:

   Answer: Pons and cerebellum

   The hindbrain is the metencephalon (pons and cerebellum) plus the myelencephalon (medulla). Thalamus and hypothalamus are diencephalon; the corpora quadrigemina and peduncles are midbrain. Revise divisions of the nervous system

4. The central pattern generator for locomotion and the nuclei for the righting reflexes lie in the:

   Answer: Midbrain

   Your book places both in the mesencephalon (midbrain), which also holds part of the reticular formation. Revise divisions of the nervous system

5. How many pairs of spinal nerves arise from the spinal cord?

   Answer: 31

   The cord has 31 segments, each with a motor and a sensory root. The roots of each segment join to form one pair of spinal nerves, so there are 31 pairs. Revise divisions of the nervous system

6. When a sensory signal reaches the brain, where is it relayed first, before the sensory cortex processes it?

   Answer: Thalamus

   The signal is relayed in the thalamus, processed in the sensory cortex and then transformed in the brain's sensory networks. Relaying information to the cortex is a main job of the diencephalon. Revise divisions of the nervous system

7. Which of these is a glial cell of the brain?

   Answer: Ependymal cell

   Ependymal cells, which line the ventricles and central canal, are one of the four CNS glia. Stellate cells are neurons, named for their star-shaped spread of dendrites. Revise neurons and glial cells

8. The myelin sheath of axons in the brain and spinal cord is formed by:

   Answer: Oligodendrocytes

   Oligodendrocyte processes wrap many times round CNS axons to form myelin. Schwann cells do the same job for peripheral nerves, not in the CNS. Revise neurons and glial cells

9. The scavenger cells of the brain are the:

   Answer: Microglia

   Microglia, the smallest CNS cells, enlarge into mononuclear phagocytes when nervous tissue is damaged or infected. Astrocytes give support and nutrition, not phagocytosis. Revise neurons and glial cells

10. Which statement about glial cells is correct?

    Answer: They can multiply, and excess multiplication causes gliomas

    Glia neither conduct action potentials nor form functional synapses, and they outnumber neurons 10–30 times. Unlike neurons they can divide, which is why gliomas arise from them. Revise neurons and glial cells

11. In a neuron, Nissl bodies are absent from the:

    Answer: Axon hillock

    Nissl bodies are modified rough ER that make proteins. They fill the soma and reach into the proximal dendrites, but the axon hillock and the axon have none. Revise neurons and glial cells

12. The spike initiation zone of a neuron, where the action potential normally begins, is the:

    Answer: Initial segment of the axon

    The initial segment is the unmyelinated first stretch of the axon, just beyond the hillock. Activity from the soma and dendrites summates there to fire the action potential. Revise neurons and glial cells

13. A dorsal root ganglion cell, whose single axon divides into a central and a peripheral branch, is classed as:

    Answer: Pseudounipolar

    An axon that splits into central and peripheral branches is the mark of a pseudounipolar neuron. The retinal bipolar cell is bipolar; the spinal motor neuron is multipolar. Revise neurons and glial cells

14. What share of a neuron's total surface area do its dendrites make up?

    Answer: More than 90%

    Dendrites make up more than 90% of the surface area. With the soma they form the neuron's receiving zone. Revise neurons and glial cells

15 questions on chapter 116. Pick one answer for each, then save. Your answers stay in this browser, and the right ones are shown at the top of the next quiz.

1. Classified by the parts of the neurons that meet, the commonest synapse in the CNS is:

DendrodendriticAxoaxonicAxosomaticAxodendritic

2. The width of the synaptic cleft is about:

200–500 nm20–50 nm2–5 nm2–5 µm

3. Tetanus toxin blocks transmitter release by acting on:

SNAP-25ClathrinSynaptobrevinSyntaxin

4. In a spinal motor neuron, graded potentials (EPSPs and IPSPs) are generated mainly at the:

Dendrites and cell bodyAxon terminalsInitial segmentNodes of Ranvier

5. Which change in the postsynaptic membrane would produce an IPSP?

Opening of Cl⁻ channelsClosure of K⁺ channelsOpening of Ca²⁺ channelsOpening of Na⁺ channels

6. The Renshaw cell circuit of the spinal cord is an example of:

Negative feedback inhibitionFeedforward inhibitionPresynaptic inhibitionReciprocal inhibition

7. The synaptic delay at a single synapse is about:

5 ms50 ms0.05 ms0.5 ms

8. In presynaptic (indirect) inhibition, transmission fails because:

The postsynaptic membrane is hyperpolarizedThe postsynaptic receptors are destroyedLess transmitter is released from the excitatory terminalThe presynaptic axon can no longer conduct an impulse

9. Long-term potentiation differs from post-tetanic potentiation in that it depends on:

A rise in Ca²⁺ in the postsynaptic neuron through NMDA channelsExtra Ca²⁺ left behind in the presynaptic knobA fall in K⁺ conductance in the presynaptic terminalProlonged inactivation of presynaptic Ca²⁺ channels

10. GABA is formed from:

Glycine, by transaminationTryptophan, by hydroxylation and decarboxylationGlutamate, by glutamate decarboxylaseGlutamine, by glutaminase

11. Which statement about the GABA-B receptor is correct?

It is the receptor on which benzodiazepines actIt is a Cl⁻ channel made of five subunitsIt is the GABA receptor of the retinaIt is coupled to a G protein and raises K⁺ conductance

12. Benzodiazepines produce sedation and relieve anxiety by:

Blocking NMDA and AMPA receptorsRaising K⁺ conductance through GABA-B receptorsRaising Cl⁻ conductance through GABA-A receptorsBlocking Na⁺ channels in peripheral nerves

13. Atropine blocks:

All five muscarinic subtypesNicotinic receptors at the motor end plateOnly the M1 muscarinic subtypeNicotinic receptors at the autonomic ganglia

14. Glutamate in high concentration acts as an excitotoxin because:

It blocks the vesicular transporter BNP1It stops astrocytes from making glutamineIt drives a large Ca²⁺ influx into neurons and kills themIt raises Cl⁻ conductance so much that neurons are silenced

15. During long-term potentiation, which transmitter carries the signal from the postsynaptic neuron back to the presynaptic neuron?

Nitric oxideNeuropeptide YAdenosineSubstance P

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