lecture 2

• Neurons are the structural and functional units of the nervous system.
• Neurons respond to chemical and physical stimuli.
• Neurons conduct electrochemical impulses.
• Neurons release chemical regulators.
• Neurons enable perception of sensory stimuli, learning, memory, and control of muscles and glands.
• Most neurons cannot divide, but can repair.
• The general structure of neurons includes a cell body (soma) that contains the nucleus, Nissl bodies, and other organelles.
• In the Central Nervous System (CNS), a cluster of cell bodies is referred to as nuclei.
• In the Peripheral Nervous System (PNS), a cluster of cell bodies is referred to as ganglia.
• Dendrites receive impulses and conduct a graded impulse toward the cell body.
• Axons conduct action potentials away from the cell body.
• Anterograde transport is from the cell body to dendrites and axon, and uses kinesin molecular motors.
• Retrograde transport is from dendrites and axon to the cell body, and uses dynein molecular motors.
• Needed for the formation of synapses in the CNS.
• A regeneration tube is formed by Schwann cells.
• Regulate neurogenesis in regions of the adult brain.
• When an axon in the PNS is cut or damaged, the severed part degenerates and is phagocytosed by Schwann cells.
• Death receptors form that promote apoptosis of oligodendrocytes.
• CNS axons are not able to regenerate.
• Inhibitory proteins in the myelin sheath prevent regeneration.
• Form the blood-brain barrier.
• Release transmitter molecules (gliotransmitters) that can stimulate or inhibit neurons; includes glutamate, ATP, adenosine, D-serine.
• Growth factors are released that stimulate growth of axon sprouts within the tube.
• Glial scars from astrocytes form that also prevent regeneration.
• Can store glycogen and produce lactate for neurons to use.
• A new axon eventually connects to the undamaged axon or the effector.
• Astrocytes take up K+ from the extracellular environment to maintain ionic environment for neurons.
• Chemicals are recycled by astrocytes.
• Myelinated axons in the CNS lack neurilemma.
• Myelinated axons in the PNS and CNS conduct impulses more rapidly.
• Gray matter is composed of cell bodies and dendrites which lack myelin sheaths.
• Astrocytes end-feet around capillaries take up glucose from blood for use by neurons to make ATP, which is converted first to lactic acid.
• Sympathetic motor neurons are active in emergency situations, also known as "fight or flight".
• Somatic motor neurons are responsible for reflexes and voluntary control of skeletal muscles.
• Motor (efferent) neurons conduct impulses from the CNS to target organs (muscles or glands).
• Myelin gives these tissues (axons) a white color, which is referred to as white matter.
• Neuroglia (glial cells) are found in four types in the CNS: Oligodendrocytes, Microglia, Astrocytes, and Ependymal cells.
• Astrocytes take up extra neurotransmitter released from axon terminals, particularly glutamate.
• Parasympathetic motor neurons are active in normal functions, also known as "rest and digest".
• Neuroglia (glial cells) are found in two types in the PNS: Schwann cells (neurolemmocytes) and satellite cells (ganglionic gliocytes).