What is a Neuron?

Main Divisions of Nervous System

Neuron Characteristics

• Nerve cells
• Require oxygen and glucose
• Receive input, process input, produce a response

• Central Nervous System (CNS): brain and spinal cord
• Peripheral Nervous System (PNS): all neurons outside CNS

Functional Properties of Neurons

• Ependymal Cells
• Line the central hollow portions
• Ex: ventricles of the brain and central canal of spinal cord
• Cilia help circulate cerebrospinal fluid
• Oligodendrocytes Cells
• Forms the myelin sheath

In the PNS

More specific types of Neurons

• Synapse
• Where an axon attaches to a muscle, gland, organ, or other neuron
• Involved with release of neurotransmitters
• Ex. Neuromuscular junction

• Irritability: ability to respond to stimuli
• Conductivity: ability to transmit an impulse
• The plasma membrane at rest is polarized
• Fewer positive ions are inside the cell than outside the cell

• Schwann cells
• Produce myelin sheath
• Satellite Glia cells
• Line the smooth surface of neurons
• Regulating the environment
• Sensitive to inflammation and may exacerbate pathological pain

Neuron Structures

• Myelin Sheath
• Fatty, protective wrapping around axons - excellent insulator
• Nodes of Ranvier: gaps in myelin sheath where action potentials develop
• Saltatory conduction: jumping of action potentials
• Myelinated axons conduct action potentials more quickly (3-15 meters/sec) than unmyelinated due to Nodes of Ranvier.
• Multiple sclerosis: disease of myelin sheath that causes loss of muscle function

• Multipolar: many dendrites and a single axon
• Ex. CNS and most motor neurons
• Bipolar: one dendrite and one axon
• Ex. Eye and nasal cavity
• Pseudo-unipolar: one axon and no dendrites
• Ex. Sensory neurons

• Dendrite: receives stimulus from other neurons or sensory receptors
• Cell body:
• Processes stimulus
• Contains a nucleus
• Axon: transmits stimulus to a gland, muscle, organ, or other neuron

Types of Neurons

Neuroglia Types

• Sensory (afferent) neurons
• Carry impulses from the sensory receptors
• Cutaneous sense organs
• Proprioceptors – detect stretch or tension
• Motor (efferent) neurons
• Carry impulses from the central nervous system
• Interneurons (association neurons)
• Found in neural pathways in the central nervous system
• Connect sensory and motor neurons

• In the CNS
• Astrocytes
• Majority of glia cells in the brain and spinal cord
• Origin of all glia
• Process that extends between neurons and capillaries
• Provision of nutrients to the nervous tissue
• Maintains blood brain barrier and balance of extracellular ion balance
• Take up neurotransmitters
• Role in the plasticity of neural tissue and connections
• Role in repair and scarring process of the brain and spinal cord following traumatic injuries

Supporting Cells: Neuroglia

• Neuroglia Characteristics
• Supporting cells for neurons
• More numerous than neurons
• Can divide to produce more cells
• Five types

What is a Neuron?