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Questions and Answers
What is the primary function of neuroglial cells?
What is the term for the part of the neuron that receives stimuli from other neurons?
Which type of neuron has one dendrite and one axon?
What is the function of sensory neurons?
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What is the name of the clusters of RER plus free polyribosomes found in the cytoplasm of the cell body?
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What is the term for the single process that soon divides into two in unipolar neurons?
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What is the function of motor neurons?
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What is the term for the trophic center of the neuron?
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What is the main function of the myelin sheath?
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Where are the nodes of Ranvier located?
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What is characteristic of unmyelinated nerve fibers?
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What is the main function of nerves?
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What is characteristic of dendrites in neurons?
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What type of nerve endings are responsible for temperature and pain sensation?
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What is characteristic of encapsulated nerve endings?
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What is the function of axon hillock?
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What is the primary function of the axolemma?
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What is the main difference between myelinated and unmyelinated nerve fibers?
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What is the term for the gaps in the myelin sheath between adjacent Schwann cells on an axon?
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What is the mechanism of transmission of nerve impulses in a chemical synapse?
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What is the purpose of synaptic vesicles in the presynaptic terminal?
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What is the width of the synaptic cleft?
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What is the function of receptors on the postsynaptic cell membrane?
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What occurs when the nerve impulse reaches the presynaptic terminal?
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What is the function of astrocytes in the CNS?
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What is the main function of oligodendrocytes?
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What is the function of microglia?
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Where are protoplasmic astrocytes typically found?
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Where are Tactile corpuscles (Meissner's corpuscle) primarily found?
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What is the function of Lamellar corpuscles (Pacinian corpuscles)?
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What is the function of ependymal cells?
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What is the function of Schwann cells?
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What is the structure of a Tactile corpuscle?
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What is the function of satellite cells?
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What is the function of Muscular spindles?
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What are peripheral nerves composed of?
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What is the structure of a Lamellar corpuscle?
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What is the function of a Motor neuron?
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What is the structure of a Motor neuron?
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What is the result of the action potential in the sarcolemma?
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Study Notes
Nervous Tissue Characteristics
- Made up of two types of cells: nerve cells (neurons) and neuroglial cells (glia)
- Neurons are the structural and functional units of nervous tissue, responsible for receiving, transmitting, and processing stimuli
- Neuroglial cells support, protect, and nourish neurons
Neuron Structure
- Most neurons consist of three parts: cell body, dendrite, and axon
- Cell body (perikaryon or soma): serves as the trophic center, variable in size and shape
- Dendrite: numerous elongated processes that receive stimuli from other neurons
- Axon: a single long process that generates and conducts nerve impulses to other cells
Neuron Classification
- Based on the number of processes:
- Anaxonic neurons: many dendrites but no true axon
- Bipolar neurons: one dendrite and one axon
- Unipolar or pseudounipolar neurons: single process that soon divides into two
- Multipolar neurons: two or more dendrites
- Based on functional roles:
- Sensory neurons (afferent): receive sensory stimuli
- Motor neurons (efferent): send impulses to effector organs
- Interneurons: establish relationships among other neurons
Neuron Components
- Perikaryon:
- Nucleus: large, spherical, and pale-staining, with a prominent nucleolus
- Cytoplasm: contains coarse or fine basophilic particles (Nissl body), microtubules, actin filaments, and intermediate filaments
- Dendrite:
- Dendritic spines: initial processing sites for synaptic signals
- Usually short and thick, devoid of Golgi complex
- Axon:
- Axon hillock: a conical region
- Axolemma and axoplasm
- Branches in axon: terminal arborization and collaterals
- Organelles in axon: very few, including polyribosomes or cisternae of RER
Nerve Impulse
- An electrochemical process initiated at the axon hillock
- A wave of membrane depolarization, involving voltage-gated Na+ and K+ channels
Synapses
- Sites where nerve impulses are transmitted from one neuron to another or from neurons to other effector cells
- Transmission is unidirectional
- Types of synapses:
- Chemical synapse: uses a chemical mediator (neurotransmitter) to transmit impulses
- Electrical synapse: permits direct flow of electrical current between two neurons (gap junction)
Synapse Structure
- Presynaptic axon terminal (terminal bouton):
- Contains mitochondria and numerous synaptic vesicles
- Releases neurotransmitter by exocytosis
- Synaptic cleft: extracellular space between pre- and postsynaptic membranes, about 20-30 nm wide
- Postsynaptic cell membrane: contains receptors for the neurotransmitter and ion channels or other mechanisms to initiate a new impulse
Neuroglial Cells
- Astrocytes:
- Most numerous glial cells
- Have a large number of long, radiating, branching processes
- Contain bundles of intermediate filaments made of glial fibrillary acid protein (GFAP)
- Have processes with expanded perivascular feet that cover capillary endothelial cells
- Oligodendrocytes:
- Fewer processes
- Myelinate and insulate CNS axons
- Microglia:
- Small cells with actively mobile processes
- Protect the CNS by engulfing infectious agents and other harmful substances
- Ependymal cells:
- Low columnar epithelial cells with cilia and processes
- Assist in the production and circulation of cerebrospinal fluid (CSF)
Peripheral Nervous System
- Schwann cells:
- Surround and insulate PNS axons
- Myelinate those having large diameters
- Satellite cells:
- Form a layer around cell bodies of neurons in the ganglia
- Electrically insulate PNS cell bodies and regulate nutrient and waste exchange
- Peripheral nerves:
- Bundles of nerve fibers (axons) individually surrounded by Schwann cells and connective tissue
- Establish communication between CNS and sense organs and effectors
Nerve Endings
- Terminal portion of dendrites and axons
- Classified into sensory and motor nerve endings
- Free nerve endings:
- Devoid of myelin sheath
- Distribute in skin, cornea, hair follicle, and connective tissue
- Responsible for temperature and pain
- Encapsulated nerve endings:
- A special connective tissue capsule surrounds the actual nerve endings
- Tactile corpuscles, lamellar corpuscles, and muscular spindles
Motor Nerve Endings
- Terminal structure of the axon of motor neuron
- Supply muscular tissue and gland
- Form effectors: somatic motor nerve endings and visceral motor nerve endings
- Somatic motor nerve ending:
- Motor end plate or neuromuscular junction
- A motor neuron innervates from one to more than a thousand muscle fibers
- Each branch of axon ends on a skeletal muscle fiber
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Description
This quiz covers the general characteristics of nervous tissue, including the types of cells, their functions, and how they work together to form neural networks. Test your knowledge of neurons, neuroglial cells, and nerve fibers.
