Nervous Tissue - Chapter 14

Regeneration of severed axons has a lesser chance to succeed in the CNS because

(1) oligodendrocytes do not secrete a nerve growth factor to stimulate axonal outgrowth, and (2) oligodendrocytes do produce secretions that inhibit axonal outgrowth.

PNS axon regeneration is dependent on:

(1) the amount of damage, (2) the secretion of nerve growth factors, and (3) the distance between the damaged axon and the effector organ.

Structural classification of neurons:

Anaxonic - looks like no axon Unipolar - 1 process off of soma Bipolar- rare - retina Multipolar - most abundant

The ____________ is the only functional class of neuron entirely restricted to the ____________ nervous system.

Association neuron; central

Types of Glial cells in CNS:

Astrocytes Ependymal Cells Microglia Oligodendrocytes

In terms of nerve impulse conduction, unmyelinated is to ____________ as myelinated is to ____________.

Continuous; saltatory

Axon regeneration in the CNS is restricted by which of the following factors?

- Oligodendrocytes do not release a nerve growth factor -Crowded axons in the brain and spinal cord complicate regrowth -Astrocytes and connective tissue coverings may form obstructive scar tissue

Special characteristics of neurons:

-Electrical conductivity - move ions and generate action potential -Extreme longevity - last entire lifetime -Do not divide -High metabolic rate- aerobic conditions --> O2 and nutrients

Glial cells in the PNS:

-Satellite cells - dorsal root ganglia, make sure unipolar cells survive -Neurolemmocytes (Schwann cells) - form myelin sheath

3 major functions of the nervous system:

1. Sensory input - collecting info 2. Integration - processing and evaluating info 3. Motor Output - responding to info

Nerves:

A bundle of many parallel axons organized in three layers: Endoneurium: around single axon Perineurium: around a fascicle Epineurium: around all of the fascicles

The cell body of a mature neuron does not contain:

A centriole

The epineurium is:

A thick, dense irregular connective tissue layer enclosing the nerve

A multipolar neuron that synapses on a gland cell is functionally classified as:

A visceral motor neuron

Which nervous system divions or components contain NO afferent neurons?

ANS and SNS

Sensory Neurons

Afferent Neurons - information from body into CNS - detect changes in environment Unipolar, some bipolar

With regard to control of effectors, ____________ is to involuntary as ____________ is to voluntary.

Autonomic; somatic

The phrase "terminally differentiated," as applied to mature neurons, means that they:

Cannot divide mitotically to produce daughter cells

A nerve impulse involves ____ across a neuron's plasma membrane:

Changes in voltage AND movement of ions

Motor Neurons

Efferent Neurons - transmit nerve impulses from the CNS to muscles or glands Multipolar

The glial cells that help produce CSF in the CNS are:

Ependymal cells

Although classified as glial cells, ____________ are also ____________ that line the cavities in the brain and spinal cord and help form the choroid plexus.

Ependymal cells; epithelial cells

A myelinated axon conducts impulses ____ than an unmyelinated axon, and the larger the diameter of the axon the _____ the rate of conduction.

Faster; faster

Oligodendrocytes:

Forms Myelin in the CNA and insulates CNS axons - increases rate of conduction

Interneuron:

Found ONLY in CNS; facilitates communication between motor and sensory neurons Multipolar

At an electrical synapse, presynaptic and postsynaptic membranes interface through:

Gap junctions

Ganglion

Group of nerve cells bodies in the PNS

Sensory neurons in which of the following locations receive and transmit only visceral input? (1) skin (2) joints (3) heart (4) fascia (5) stomach

Heart and stomach

Layers of connective tissue in nerves:

Individual axons in the PNS are surrounded by neurolemmocytes and then wrapped in a delicate layer of loose connective tissue called the endoneurium. Groups of axons are wrapped into bundles, called nerve fascicles, by a cellular dense irregular connective tissue layer called the perineurium. All of the fascicles are bundled together by a superficial dense irregular connective tissue covering termed the epineurium.

Channels:

Interneurons are organized into neuronal pools, which are groups of interconnected neurons with a specific functions

Which neurons are located ONLY within the CNS?

Internuerons

Astrocyte:

Large cell with numerous cell processes; in contact with neurons and capillaries, most common type of glial cell. - Helps form blood-brain barrier -Control electrolyte concentration in brain -Nurse cell - replaces damaged neurons

Microglial cell:

Least common type of glial cell - Removes debris -Phagocytizes wastes -Defends against pathogens

Bundles of neurofilaments extending into dendrites and axons to provide structural support are called:

Neurofibrils

Which of the following is NOT a part of the CNS? brain, microglial cell, spinal cord, neurolemmocyte

Neurolemmocyte

Which glial cells participate in the repair of damaged nerves?

Neurolemmocytes

In PNS, an axon may be enveloped by ___ without being ____.

Neurolemmocytes; myelinated

Which of these cells transmits, transfers and processes a nerve impulse? -Neurolemmocyte -Astrocyte -Neuron -Oligodendrocyte

Neuron

Neurofibril nodes

Nodes of Ranvier - Non-myelinated spaces between Schwann Cells

Differences between oligodendrocytes and neurolemmocytes:

Oligodendrocytes form the myelin sheath in the CNS; neurolemmocytes form it in the PNS. Each oligodendrocyte can myelinate several small portions of different axons in the CNS, however each neurolemmocyte can only myelinate a small portion of one axon in the PNS.

The methods are different, but ___ in the CNS and ____ in the PNS perform similar functions:

Oligodendrocytes; neurolemmocytes

Synapses are categorized on the basis of

Point of contact and mode of impulse transmission

A structure or cell the collects sensory information is a:

Receptor

At a chemical synapse, ____________ are found only in the plasma membrane of the ____________ cell.

Receptor proteins; postsynaptic

Microglial cells:

Respond to CNS infection

Functional divisions of the nervous system include:

SNS and PNS

Functional Classification of Neurons:

Sensory Neurons Motor Neurons Interneurons

Ependymal cell:

Simple cuboidal epithelial cell lining cavities in brain and spinal cord; cilia on apical surface. -Choroid Plexus! - Lines ventricles of brain and central canal of spinal cord - Assists in production and circulation of CSF

Effector:

Skeletal muscle fiber

Glial cells:

Smaller cells, capable of mitosis, occur within both CNS and PNS. Do NOT transmit nerve impulses, but do assist neurons with their functions. Collectively, physically protect and help neurons, and provide organized, supporting framework for all nervous tissue.

Which structural classes of neurons are always sensory in function?

Unipolar and bipolar