Chapter 10 Nervous System

neurofibrils

fine threads in an axon

dendrite

highly branched, multiple processes that may have spines

the ........ cells are capable of removing blood clots from the brain

microglia

3 types of neuroglial cells

microglia, astrocyte, oligodendrocyte

when a neuron reaches action potential it depolarizes and repolarizes in an amount of time in the order of

microseconds

a neuron with many nerve fibers arising from its cell body and that carries impulses away from the brain would be classified as

multipolar and motor

distinguish between neurons and neuroglia

neurons are the structural and functional cells reacting to the physical and chemical changes in their environment. neuroglia is the supporting cells necessary for nourishing and maintaining the neurons, among other functions

the ............... are the types of neuroglial cells that provide myelin in the central nervous system

oligodendrocytes

cell body

part of a neuron from which axon and dendrites extend

what type of neuroglial cells help regulate the composition of cerbrospinal fluid

ependyma

Distinguish between excitatory and inhibitory postsynaptic potentials.

Different neurotransmitters cause distinctly different responses in the postsynaptic neuron. If a neurotransmitter binding to the postsynaptic neuron causes sodium ion channels to open, the ions move inward and depolarize the membrane, possibly causing an action potential. Because this reaction causes the membrane to be closer to the threshold potential, it is said to be an excitatory postsynaptic potential (EPSP). If the neurotransmitter causes the potassium receptors to open, the postsynaptic membrane becomes hyperpolarized in response to an influx of potassium ions. This reaction makes an action potential less likely and is called an inhibitory postsynaptic potential (IPSP).

T or F : the strength of impulses carried along a single axon can vary with the strength of the initiating stimulus

False

explain how an injured neuron may regenerate

If the axon of a peripheral nerve is separated from the cell body, the distal portion deteriorates and the fragments are removed by macrophages. The proximal end then develops new sprouts, and nerve growth factors from surrounding neuroglia cause the sprouts to grow. At the same time, remaining Schwann cells proliferate and surround the new axon. If a sprout grows into the remaining basement membranes of the original tract, the new fiber may rejoin with its original connection. If the injured axon is from a neuron in the CNS, the lack of a myelin sheath prevents the new fiber from being guided to its original connection. Therefore, regeneration in the CNS is very unlikely. An injury to the cell body of a neuron usually causes death to the entire fiber, and no regeneration will occur.

explain how information is passed from a presynaptic neuron to a postsynaptic cell

Nerve impulses pass from neuron to neuron (or to other cells) at synapses. A presynaptic neuron brings the impulse to the synapse and, as a result, stimulates or inhibits a postsynaptic neuron (or a muscle or gland). A narrow space, or synaptic cleft, separates the two cells, which are connected functionally, not physically.

cut neurons in the PNS possess limited capabilities for regeneration. The type of neuroglial cells that aid in regeneration by forming a regeneration tube to help reestablish the former connection is the

Schwann cell

the myelin sheath around a neuron in the PNS is actually produced by the

Schwann cell

distinguish between myelinated and unmyelinated axons

a myelinated nerve fiber is one which is bound by schwann cells longitudinally along its length. the schwann cells wrap tightly around the nerve fiber and form a myelin sheath. unmyelinated nerve fibers lack these sheaths. In this case these schwann cells are not wound around the axons but simply form a grove or valley in which the axon sits. Myelinated nerve fibers appear white, unmyelinated nerve fibers appear grey.

which types of neurons are likely to increase muscular activites

accelerator neurons

myesthina gravis reflects a deficiency in communication by ............. because receptors for this neurotransmitter have been destroyed

acetlycholine

the most common neurotransmitter in the body is

acetylcholine

branched nerve fibers that convey local potential changes toward the cell body of a neuron are called

dendrites

In response to a stimulus, if the membrane potential becomes more negative than the resting potential, then the membrane is

depolarized

nerve impulses always travel to the brain through

axon fibers

the central nervous system is composed of

brain and spinal cord

diffusion of which of the following ions into the syanptic knob triggers the release of neurotransmitter

calcium ions

axon

conducts impulses

fibers that originate from different parts of the nervous system and lead to the same neuron are exhibiting

convergence

chromatophilic substance

rough endoplasmic recticulum

myelin sheaths on the outside of many axons on the peripheral nervous system are contributed by

schwann cells

cells that conduct messages towards the brain are the

sensory neurons

excessive sleeping is most likely due to the presence of too much of which neurotransmitter

serotonin

the levels of ....... are affected by the mood elevator cocaine

serotonin

at resting potential the ion distribution inside and outside of a neuron is such that ....... ions are most abundant on the outside of the cell while ........ ions are most abundant on the inside of the cell

sodium; potassium

list six functions neuroglia

structural support transport of substances communication between neurons induce synapse formation speed neurotransmission phagocytosis

what is true of when a neuron is at rest concerning the charge of that neuron

the outside is positive inside is negative