A&P- Chapter 8: The Nervous System

Why are spinal nerves also called mixed nerves?

All spinal nerves are classified as mixed nerves because they contain both sensory and motor fibers.

Identify the three meninges surrounding the CNS.

The three meninges surrounding the CNS are the dura mater, arachnoid mater, and pia mater.

Which type of glial cell would increase in number in the brain tissue of a person with a CNS infection?

Small phagocytic glial cells called microglia would typically be found in increased numbers in infected (or damaged) areas of the CNS.

Name the structural components of a typical neuron.

Structural components of a typical neuron include a cell body (which contains the nucleus and nucleolus), an axon, dendrites, Nissl bodies, axon hillock, collaterals, and axon terminals.

Two axons are tested for propagation velocities (speeds). One carries action potentials at 50 meters per second, the other at 1 meter per second. Which axon is myelinated?

The axon carrying action potentials at 50 meters per second is myelinated. Myelinated axons propagate action potentials by saltatory propagation at speeds much higher than those by continuous propagation along unmyelinated axons.

A person with polio has lost the use of his leg muscles. In which area of his spinal cord could you locate the poliovirus-infected motor neurons?

You would find poliovirus in the anterior gray horns of the spinal cord, because that is where the cell bodies of somatic motor neurons are located.

What effect would decreasing the concentration of extracellular potassium ions have on the membrane potential of a neuron?

If the extracellular potassium ion concentration decreased, more potassium ions would leave the cell, increasing the electrical gradient across the membrane (the membrane potential). This effect is called hyperpolarization.

Describe the general structure of a synapse.

A synapse is the site where a neuron communicates with another cell. It is composed of presynaptic and postsynaptic cells whose plasma membranes are separated by a narrow synaptic cleft.

Identify the neuroglia of the central nervous system.

CNS neuroglia include ependymal cells, astrocytes, oligodendrocytes, and microglia.

What type of neural circuit permits both conscious and subconscious control of the same motor neurons?

Convergence permits both conscious and subconscious control of the same motor neurons.

What would be the effect of damage to the afferent division of the PNS?

Damage to the afferent division of the PNS would affect nerves carrying sensory information to the brain and spinal cord. It would interfere with a person's ability to experience a variety of sensory stimuli.

Damage to which root of a spinal nerve would interfere with motor function?

Damage to the anterior root of a spinal nerve, which carries visceral and somatic motor fibers, would interfere with motor function.

What effect would blocking calcium ion channels at a cholinergic synapse have on synapse function?

Blocking calcium channels at the presynaptic terminal of a cholinergic synapse would prevent the influx of calcium ions that triggers the release of acetylcholine. As a result, no communication would occur across the synapse, and the postsynaptic neuron would not be stimulated.

What effect would a chemical that blocks the voltagegated sodium ion channels in the excitable axon membrane of a neuron have on its ability to depolarize?

If the voltage-gated sodium ion channels in a neuron's excitable axon membrane were blocked, the neuron would not be able to depolarize because sodium ions could not flow into the cell.

In the PNS, neuron cell bodies are located in ______________ and surrounded by neuroglial cells called ______________ cells.

In the PNS, neuron cell bodies (gray matter) are located in ganglia and are surrounded by satellite cells.

List the steps involved in the generation of an action potential.

The steps in the generation of action potentials are Step 1: depolarization to threshold; Step 2: activation of voltagegated sodium channels and rapid depolarization; Step 3: inactivation of sodium channels and activation of voltage-gated potassium ion channels; and Step 4: closing of potassium channels and return to normal permeability.

Identify the two anatomical divisions of the nervous system.

The two anatomical divisions of the nervous system are the central nervous system (CNS), consisting of the brain and spinal cord, and the peripheral nervous system (PNS), consisting of all nervous tissue outside the CNS.

Identify the two functional divisions of the peripheral nervous system, and describe their primary functions.

The two functional divisions of the peripheral nervous system are the afferent division, which brings sensory information to the CNS from receptors in peripheral tissues and organs, and the efferent division, which carries motor commands from the CNS to effectors, such as muscles and glands.

Examination of a tissue sample reveals unipolar neurons. Are these more likely to be sensory neurons or motor neurons?

Unipolar neurons are most likely sensory neurons of the PNS.