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The Nervous System is split into 2 parts, what are they?
- Central Nervous System (CNS)
- Peripheral Nervous System (PNS)
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What body parts are included in the Central Nervous System (CNS)?
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What is the input and the output of the Peripheral Nervous System (PNS) called?
- Input - Afferent Information
- Output - Efferent Information
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What senses are part of afferent information?
- Somatic senses
- Special senses
- Visceral senses
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What are the 2 types of efferent information?
- Somatic - voluntary
- Autonomic - involuntary
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What are the 2 categories of the autonomic PNS?
- Sympathetic
- Para-sympathetic
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Whatpart of the PNS is responsible for Fight or Flight?
Sympathetic
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What are the cells of the Nervous System?
- Neurons (10%)
- Glial Cells (90%)
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What is the role of Neurons?
- Excitable cells
- Functional units of CNS
- Transmit electrical impulses/signals
Electrical Signals = Action Potentials
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What are the components of Neurons?
Soma - nucleus, organelles
Dendrites - receive info from other neurons
- Axon - transmit action potentials
- - Axon Hillock - axon origin, where action potentials initiated
- - Axon Terminal - releases neurotransmitters
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Define Synapse
Site of communication between two neurons or between a neuron and an effector organ
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What are the properties of leak channels in neurons?
- Always open
- Ion movement based on the concentration gradient
- Throughout the neuron
- Maintain resting membrane potential
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What are the properties of ligand-gated channels in neurons?
- Open or closed in response to ligand binding
- Ion movement down concentration gradient
- Located on dendrites and cell body
- Synaptic potentials
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What are the properties of voltage-gate channels?
Open/close in response to change in Vm
- 2 types:
- Na+/K+ channels
- Calcium channels
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Where are Na+/K+ channels located and what do they maintain?
- Throughout, more in axon (hillock)
- Action Potentials
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Where are calcium channels located and what do they maintain?
- Axon terminal
- Release of neurotransmitter
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What are the structural classes of neurons?
- Bipolar
- Pseudo-unipolar
- Multipolar
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What are the functional classes of neurons?
- Afferent neurons
- Efferent neurons
- Interneurons
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What is the structural organization of neurons? Lowest level to highest level.
Nuclei < Pathways and tracts < Commissures < Ganglia < Nerves
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What are the different types of glial cells?
- Astrocytes (star-shaped cells)
- Ependymal Cells
- Microglia
- Oligodendrocytes
- Schwann Cells
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What are properties of Oligodendrocytes?
- CNS
- 1 oligodendrocyte forms several myelin sheaths which myelinate sections of several axons
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What are properties of Schwann Cells?
- PNS
- 1 Schwann Cell forms one myelin sheath which myelinates one section of an axon
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What is the resting membrane potential (in mV) and why does it exist?
- ~ -70 mV
- More negative charges inside cell and more positive charges outside cell
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What 2 factors are critical in determining resting membrane potential?
- Ion concentration gradients
- Membrane permeability to these ions - ion channels
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What percent of the RMP is directly due to the Na/K-ATPase and why? ...indirectly?
20% - 3 Na+ out, 2 K+ in: net 1+ out
80% - Produces concentration gradient: Na high outside, K high inside
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How is K+ equilibrium potential reached?
- K+ diffuses out of the cell (chemical force out)
- Inside of cell becomes more negative
- K+ is pulled back into the cell (electrical force in)
- Elec/Chem forces eventually equal eachother at -94 mV
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How is Na+ equilibrium potential reached?
- Na+ diffuses into the cell (chemical force in)
- Inside of cell becomes less negative
- Na+ is pushed out of cell (electrical force out)
- Elec/Chem forces eventually equal eachother at +60 mV
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What is the difference in K+ and Na+ permeability in a typical neuron?
Membrane is 25x more permeable to K+
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How are the ions distributed inside/outside a neuron cell?
- Inside: K+, organic anions
- Outside: Na+, Cl-
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Describe the process of establishing a resting membrane potential.
- Chemical driving forces - K+ out, Na+ in
- Membrane more permeable to K+
- More K+ leave cell than Na+ enters
- Inside of cell becomes more negative
- Electrical forces develop - Na+ in, K+ in
- K+ outflow slows, Na+ inflow speeds
- Steady state develops - Na+ inflow = K+ outflow
- RMP of a neuron = -70 mV
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What maintains the RMP?
Sodium pump
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How do Na+ and K+ move in/out of a neuron at rest?
- Small Na+ leak (high force, low permeability)
- Small K+ leak (low force, high permeability)
- Sodium pump returns Na+ & K+ to maintain gradients
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