Neurons

What are neuroglia, or glial cells?

Cells that support and protect neurons. Their name means “nerve glue.”

What are the four types of glial cells in the CNS?

Astrocytes, oligodendrocytes, microglial cells, and ependymal cells.

What are the two types of glial cells in the PNS?

Schwann cells, also called neurolemmocytes, and satellite cells.

What do microglial cells do?

Act as phagocytes, engulfing debris and harmful material in the CNS.

What do oligodendrocytes do?

Form myelin sheaths around axons to insulate them and speed up nerve impulses in the CNS

What do ependymal cells do?

Line fluid-filled spaces in the CNS and help produce and circulate cerebrospinal fluid

What do satellite cells do?

Support neuron cell bodies and control their chemical environment in PNS ganglia.

What do Schwann cells do?

Form myelin around axons in the PNS and help repair damaged nerve fibres.

What do astrocytes do?

Support neurons, control their chemical environment, and help maintain the blood-brain barrier in the CNS.

How do glial cells differ from neurons in transmitting messages?

Glial cells do not generate and transmit nerve impulses the way neurons do.

What are neurons?

The basic functional units of nervous tissue, specialized to transmit messages throughout the body.

What is the neuron’s cell body?

The part containing the nucleus and most organelles, from which the neuron’s processes extend.

What are nuclei in the nervous system?

Clusters of neuron cell bodies in the CNS.

What are ganglia?

Clusters of neuron cell bodies in the PNS.

What are neurofibrils?

Cytoskeletal structures that help support the neuron.

What is chromatophilic substance?

Clusters of rough endoplasmic reticulum involved in protein synthesis, also called Nissl substance.

What are the two types of neuron processes?

Dendrites and axons.

What do dendrites do?

Receive signals through receptors that respond to neurotransmitters released by other neurons.

What does an axon do?

Conducts nerve impulses toward other neurons, muscles, or glands.

How many dendrites and axons can a typical neuron have?

Many dendrites, but only one axon.

What mainly makes up white matter?

Bundles of myelinated axons.

What are axon collaterals?

Branches of an axon.

What is the axon hillock?

The region of the cell body where the axon begins.

What are axon terminals?

Small endings of an axon that form synapses with other neurons or effector cells.

Where are neurotransmitters stored in axon terminals?

In synaptic vesicles.

What is a synapse?

A junction where a neuron communicates with another cell.

What is the synaptic cleft?

The tiny gap between an axon terminal and the receiving cell.

What is myelin?

A fatty material that insulates axons and helps nerve impulses travel faster.

What is a myelinated nerve fibre?

An axon surrounded by a myelin sheath.

How do Schwann cells form myelin?

They wrap tightly around an axon in layers, like a jelly roll.

How is the myelin sheath formed along a PNS axon?

Many individual Schwann cells each wrap around a different segment of the axon.

What are nodes of Ranvier?

Gaps between neighbouring segments of the myelin sheath.

Why are there gaps in the myelin sheath?

The sheath is made of separate myelin segments rather than one continuous covering.

What are the three structural types of neurons?

Unipolar or pseudounipolar, bipolar, and multipolar.

What is a pseudounipolar neuron?

A neuron with one short process extending from the cell body that divides into peripheral and central branches.

What does the peripheral branch of a pseudounipolar neuron do?

Carries sensory signals from the periphery toward the cell body region.

What does the central branch of a pseudounipolar neuron do?

Carries sensory signals into the CNS.

Which structural type are most sensory neurons?

Pseudounipolar.

What is a bipolar neuron?

A neuron with two processes attached to its cell body: one dendrite and one axon.

Where are bipolar neurons found?

In special sensory structures associated with the eye, ear, and olfactory mucosa.

What is a multipolar neuron?

A neuron with many dendrites and one axon.

Which structural type are most motor neurons?

Multipolar.

What are the three functional types of neurons?

Sensory neurons, motor neurons, and interneurons.

What is another name for a sensory neuron?

An afferent neuron.

What do sensory neurons do?

Carry impulses from sensory receptors toward the CNS.

Where can sensory neurons receive information from?

Internal organs, skin, skeletal muscles, joints, and special sensory organs.

Where are most sensory neuron cell bodies located?

In ganglia outside the CNS.

What is another name for a motor neuron?

An efferent neuron.

What do motor neurons do?

Carry impulses away from the CNS to muscles and glands.

Where are most motor neuron cell bodies located?

In the CNS.

What do interneurons do?

Connect neurons within the CNS, including pathways between sensory and motor neurons.

Where are interneurons located?

Entirely within the CNS.

What structural type are most interneurons?

Multipolar.

How can you remember afferent versus efferent?

Afferent signals arrive at the CNS. Efferent signals exit the CNS.

What is a tract?

A bundle of axons in the CNS.

What is a nerve?

A bundle of axons in the PNS.

What does a sensory nerve carry?

Sensory impulses toward the CNS.

What does a motor nerve carry?

Motor impulses away from the CNS.

What do the ventral roots of spinal nerves carry?

Motor fibres carrying impulses away from the spinal cord.

What is a mixed nerve?

A nerve containing both sensory and motor fibres.

Are spinal nerves sensory, motor, or mixed?

All spinal nerves are mixed nerves.

What is the endoneurium?

A delicate connective tissue layer surrounding each individual nerve fibre.

Is the endoneurium the same as the myelin sheath?

No. The endoneurium is connective tissue outside the nerve fibre’s covering. Myelin is an insulating layer around the axon.

What is a fascicle?

A bundle of nerve fibres within a nerve.

What is the perineurium?

The connective tissue layer surrounding a fascicle.

What is the epineurium?

The tough, fibrous connective tissue layer surrounding the whole nerve.

What are the nerve’s connective tissue layers, from innermost to outermost?

Endoneurium → perineurium → epineurium.

What else travels within a nerve besides nerve fibres?

Blood vessels and lymphatic vessels.