Cell Structure and Function - Neural Tissue

Axon Hillock (Definition)

A negative stained portion of the cell body that contains mostly neurotubules, where the axon of the neuron originates.

Free Nerve Ending (Definition)

Dendrites which end freely in tissue and responds to stimuli.

Axon Collaterals (Definition)

A branch originating on an axon, at an angle of approximately 90 degrees. These branches may occur anywhere in unmylenated axons, but are restricted to nodes of Ranvier in mylenated axons.

Ganglia (Definition)

A collection of nerve cell bodies in the PNS.

Axon (Definition)

A long and thin appendage of a neuron.

Dendrites (Definition)

A short tapering process which do not contain nuclei or golgi that merges with the cell body.

Axosomatic Synapse (Definition)

A synapse between axons and cell bodies.

Axodendritic Synapse (Definition)

A synapse between axons and dendrites.

Axoaxonic Synapse (Definition)

A synapse between axons and other axons.

Cell Body (Definition)

Also called soma, these structures can be star shaped, round or pyramidal, with large nuclei and prominent nucleoli.

Supporting Cells of the CNS (4)

Astrocytes, Oligodendrocytes, Microglia, Ependymal Cells

Types of Synapses (3)

Axodendritic, axosomatic, axoaxonic.

Axon (Function)

Conduct nerve impulses away from the cell body.

Layers of Peripheral Nerve Coverings

Endoneurium, Perinerium, Epinerium

Types of Sensory Receptors (2)

Free and encapsulated

Schwann Cells (Definition)

Glial cells of the PNS which insulate peripheral axons.

Schwan Cells (Function)

Glial cells which ensheath between 2 and 20 PNS axons less than 1μm in diameter, but leave them exposed to the extracellular fluid. Also mylenate axons greater than 1μm in diameter.

Encapsulated Nerve Ending (Definition)

Have a dendrite at the core of connective tissue which responds to stimuli.

Oligodendrocytes (Definition)

Have fewer processes than astrocytes and are the second most abundant glial cell in the CNS.

Microglia (Function)

In areas of injury in the CNS, these glial cells proliferate, enlarge and become phagocytotic, cleaning up cellular debris and ingesting damaged myelin.

Dendrites (Function)

Increases the surface area of the neuron and recieves input from surrounding axons and conducts the signal toward the cell body.

Endoneurium

Innermost sheath of a peripheral nerve made of loose connective tissue. Also contains fibroblasts, macrophages,, and capillaries.

Nissl Bodies (Definition)

Large aggregation of RER and free polysomes arranged in alternating layers. These are the only subcellular structures visible in light micrographs of neurons.

Neurotubules (Definition)

Microtubules found in neuronal cells.

Synaptic Cleft (Definition)

Narrow intercellular space between the pre- and post synaptic membranes.

Neuronal Organelles Visible in Light Micrographs

Nissl bodies and Lipofuscin Pigment

Presynaptic Membrane (Definition)

Part of an axon terminal that delivers an action potential to the synapse.

Postsynaptic Membrane (Definition)

Part of another neuron, gland or muscle that responds to the action potential from the presynaptic membrane.

Perineurium

The middle layer of cells in a peripheral nerve bundle which transport nutrients and wastes via transcytosis. Work with external laminae to prevent the passage of large molecules, viruses and bacteria into the endoneurium.

Supporting Cells of the PNS (2)

Schwann Cells, Satellite Cells

Types of Ganglia in the PNS (2)

Sensory and Autonomic (motor)

Nissl Bodies (Function)

Synthesize proteins needed by the neuron.

Astrocyte (Function)

The expanded tips of their processes attach to neurons or capillaries and support neurons by regulating ionic concentrations, metabolites and wastes.

Synapse (Definition)

The functional connection between the axon terminus of one neuron and part of another neuron, muscle or gland.

Astrocytes (Definition)

The most abundant glial cell in the CNS, which are star shaped and have many cytoplasmic processes. They form the blood/brain barrier.

Multipolar Neuron (Definition)

The most common type of neuron in the CNS, which has two or more dendrites and one axon radiatiing from the soma. The dendrites conduct impulses toward the cell body, through the cell body, and onto the axon away from the body.

Epineurium

The outermost wrapping of a nerve bundle, which is composed of dense connective tissue. This layer protects the nerve from direct physical injury.

Initial Segment (Definition)

The segment of a mylenated axon just proximal to the point where mylenation begins.

Chemical Synapse (Definition)

The type of synapse which employs the use of neurotransmitters to transmit nerve impulses. Can be excitatory and inhibitory.

Electrical Synapse (Definition)

The type of synapse which transmits nerve impulses through gap junctions which permit ions to pass directly from the presynaptic cytoplasm to the postsynaptic cytoplasm. Always excitatory.

Types of Neurons (3)

Unipolar, Bipolar, Multipolar

Neurotubules (Function)

These act like conveyor belts to transport numerous substances along an axon between the soma and the axon terminal.

Satellite Cells (Definition)

These cells form a continuous layer with Schwann cells in the PNS.

Microglia (Definition)

These cells have scant cytoplasm, dense oval nuclei and short tortuous processes. They are the macrophages of the CNS.

Oligodendrocytes (Function)

These cells mylenate short portions of many neurons by wrapping their plasmalemmas around axons greater than 1μm in diameter.

Ependymal Cells (Function)

These cells produce the cerebrospinal fluid or CSF.

Satellite Cells (Function)

These cells surround nerve cell bodies and dendrites in the PNS, and serve as a buffer.

Ependymal Cells (Definition)

These glial cells line the ventricles of the brain and the central canal of the spinal cord by forming a simple epithelium with cilia that varies from cuboidal to columnar.

Unipolar Neuron (Definition)

These neurons have a dendrite situated at the end of a mylenated axon, which conducts the impulse past the cell body through the same axon, and onto other cells.

Bipolar Neuron (Definition)

These neurons have one dendrite and one axon, with the cell body in the middle. Mostly involved in sight and olfaction. Most are not mylenated.

White Matter

This portion of the CNS contains axons, supporting cells, and capillaries and has a pale color due to myelin sheaths of the axons.

Gray Matter

This portion of the CNS contains cell bodies, axons, dendrites, axon terminals, astrocytes, oligodendrocytes, microglia, and capillaries, and takes on a relatively dark hue.

Retrograde Transport (Definition)

Transport of cellular vesicles from the axon terminal toward the cell body. Always fast transport.

Anterograde Transport (Defnition)

Transport of cellular vesicles from the cell body toward the axon terminal. Can be fast or slow.