KIN 336 Exam 1

neuron

• basic component of nervous system

• 4-100 microns

• receive, integrate, and send information throughout the entire nervous sytem

cell body

• contains nucleus (regulars cellular homeostasis)

• gray matter

dendrites

• extensions from cell body (0 to 1000+ per neuron)

• receive information from other neurons

axons

• only one per neuron

• most have many branches (collaterals)

• white matter (myelin)

terminal

end of axons that allow chemical signals (neurotransmitters) to be passed between neurons

synapse

gap between axon and dendrites 

multipolar neuron (most common)

bipolar neuron

(pseudo)unipolar neuron (rare)

sensory (afferent) neurons

• primary in PNS

• transmit signals from sensory receptors to CNS

interneurons (connector neurons)

between neurons within CNS

motor (efferent) neurons

transmits signals from CNS to muscles

anterograde transport

• from soma to axon

• proteins, neurotransmitters, organelles

retrograde transport

• from axon to soma

• old mitochondria, pinocytotic vesicles from axon terminal (e.g., rabies virus)

pinocytosis

non-specific intake of liquids

phagocytosis

engulfing large particles (phagosomes, need trigger)

Amytrophic Lateral Sclerosis (ALS)

• Motor neuron degeneration

• progressive degeneration of upper & lower motor neurons

• disrupted axonal transport, glutamate excitotoxicity, oxidative stress

• muscle weakness, atrophy, and eventual paralysis

properties of glial cells

• maintain environment

• no electric current passes through

• more numerous than neurons

central nervous system (CNS) glial cells

• astrocytes

• oligodendrocytes

• microglia

peripheral nervous system (PNS) glial cells

• satellite cells

• Schwann cells

• macrophages 

astrocytes

• In CNS

• provide structural support

• secretes growth factors to support neurons

• act as intermediary between other cells

• can modulate synaptic activity by releasing glutamate and D-serine

• buffer pH and ionic environment in extracellular space

• removes extracellular K+ from action potentials and transports it to perivascular spaces

• absorbs nutrients from blood supply and passes it to neuron

microglial cells

• In CNS

• immune cells of brain

• phagocytic scavengers (like macrophages in PNS)

  • secretes neurotoxic substances (e.g, cytokines)

oligodendrocytes

• In CNS

• Cover CNS cell axons in myelin

• myelin: raises conduction speed of neural transmission

• loss of oligodendroytes → demyelinating diseases (e.g., multiple sclerosis) 

Selma Blair Multiple Sclerosis (MS) diagnosis

• Demyelination of CNS axons

• loss of oligodendrocytes → impaired myelin sheath formation

• slowed or blocked action potential conduction

• leads to muscle weakness, fatigue, impaired coordination, impaired speech

satellite cells (PNS)

surround neuronal cell bodies in ganglia; regulate microenvironment

Schwann cells (PNS)

myelinate one axon per cell; critical for PNS axon regeneration

macrophages (PNS)

immune cells that clear debris and aid recovery after injury

Oligodendrocytes vs Schwann Cells

• Oligodendrocytes

  • wrapping: cell body projections

  • only in CNS

• Schwann cells

  • wrapping: pancake

  • only in PNS

general neuropathic pain

• maladaptive glial & synaptic activity

• overactive microglia release proinflammatory cytokines

• enhanced excitatory transmission, reduced inhibition in spinal circuits

• leads to chronic pain syndromes

Excitable cell membrane

• electrical potential changes in response to a stimulus

• each neuron receives stimuli from many neurons at dendrites

excitatory potential

• increases electrical potential of cell membrane (+)

• brings neuron closer to threshold

inhibitory potential

• decreases electrical potential of cell membrane (-)

• takes neuron father from threshold

If net effect of all + and - stimuli on a neuron maintains membrane potential below threshold level,

Neuron does not generate an action potential (AP)

If net effect of all + and - stimuli on a neuron increases membrane potential above threshold level,

• Neuron depolarizes and AP is generated

  • propagates down axon to terminal endings to stimulate

    • sensory neuron: other dendrites

    • motor neuron: muscle fibers