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