Chapter 7: Intro to Nervous System: Neurons/Synapses Flashcards
List the divisions of the nervous system and the structures that include.
- Central Nervous System (CNS)
- Brain and Spinal cord
- Peripheral Nervous System (PNS)
- Cranial and Spinal nerves
- (Also the autonomic nervous system - ANS)
List the two types of cells in the nervous system.
- Neurons
- Supporting cells/Glial cells
(Supporting cells = PNS)
(Glial cells = CNS)
Define a neuron.
Neurons are the functional units of the nervous system.
Discuss the functional classifications of neurons. (3)
- Sensory/Afferent: neurons send messages to the CNS; posterior root (incoming info)
- Motor/Efferent: neurons carry messages out of the CNS; anterior root (info going out)
- Asssociation/Interneurons: only in CNS and integrate functions of the nervous system
Note: Pre- and Post- synaptic neurons are different lengths depending on system
What do neurolemmocytes (Schwann Cells) do?
Myelinate the axons of the neurons in the PNS.
Name the 4 glial/supporting cells found in the CNS and their functions.
- Astrocytes: Regulate the area around the neurons; Blood Brain Barrier!
- Oligodendrocytes: Produce myelin sheath that surrounds several axons (myelin gives tissues white color = white matter)
- Ependymal Cells: Make CSF
- Microglia: Phagocytes; eat foreign and degenerated material
Discuss the node of Ranvier.
- It’s the uninsulated gap of axon between Schwann cells
- They increase the speed of transmission
Discuss neuron regeneration differences between CNS and PNS.
CNS:
- Astrocytes form glial scar physically blocking regeneration
- Oligodendrocytes produce inhibitory proteins
PNS
- Schwann cells + macrophages phagocytize cellular debris
- Schwann cells form regeneration tube and release chemicals to attract the growing tip of the axon
- Regeneration tube ensures that the axon grows back/reconnects to the correct location
Discuss Resting Membrane Potential (RMP)
- At rest, cells have a negative internal charge (-70mV); considered “polarized”
- Na+/K+ Pump (3Na+ out for every 2K+ in)
- At rest Na+ conc. high outside cell and K+ conc. high inside the cell
- Cell is more permeable to K+
Discuss the (3) changes to membrane potential.
- Depolarization: pos charges flow into the cell reducing the charge difference across the membrane; (Na+ flows in)
- excitatory
- Hyperpolarization: caused by neg charges flowing into the cell or positive charges flowing out of the cell; cell becomes more neg
- inhibitory
- Repolarization: membrane potential returns to resting membrane potential (-70mV)
Discuss an Action Potential. How do they work?
- it’s a wave of membrane potential change that sweeps along the axon; a nerve impulse
- occurs by rapid depolarization of membrane - Na+ influx; followed by rapid repolarization by K+ efflux
- voltage-gated channels are opened by depolarization
- Do NOT need ATP; Na+ and K+ follow their concentration gradients
- Action potentials do NOT summate; all-or-none event;
- Once they reach -55 mV the action potential goes!
Recap or charge changes:
Start: -70 mV (Resting Membrane Potential)
Increase to +30 mV (Deporlarization)
Decrease to -85 mV (Hyperpolarization)
Increase to -70 mV (Repolarization to Resting)
What is the difference between absolute refractory period and relative refractory period?
Absolute Refractory Period: Membrane “absolutely” cannot produce another action potential
Relative Refractory Period: Membrane can depolarize but it requires a stronger stimulus
for it to reach threshold (because you’res starting more negative than -70… so you have to go further to get to -55)
Discuss conduction of the UNMYELINATED axon.
- Axon Hillock reaches threshold and fires action potential
- Na+ influx depoarizes adjacent regions of membrane
- Generates a new action potential and the process repeats down the axon
- Conduction is SLOW
Discuss conduction of the MYELINATED axon.
- Ions can’t flow across myelinated membrane because lack voltage gated channels
- Nodes of Ranvier contain many voltage gated Na+ channels
- Saltatory Conduction
Discuss saltatory conduction.
- Action potential only occurs at nodes of Ranvier in myelinated axons
- Current from action potential at one node can depolarize the next node
- Fast because action potentials can skip from node to node
Discuss speed of action potentials.
Speed depends on diameter of the axon and myelination
- Myelinated and large = very FAST
- Unmyelinated and small = SLOW
Discuss a synapse.
- Functional connection between a neuron (presynaptic) and another cell or neuron (post synaptic)
- There are chemical and electrical synapses
- Synaptic transmission at chemical synapse occurs via neurotransmitters
- Electric synapses are RARE in the nervous system
Discuss chemical synapses.
- Synaptic cleft separates terminal bouton of presynaptic from postsynaptic cel
- Neurotransmitters are in synaptic vesicles and release from bouton by exocytosis
- Amt of neurotransmitter released depends on frequency of action potentials
Discuss Ca+ and the synaptic vesicles.
- Action potential reaches axon terminals.
- Voltage gated Ca+ channels open.
- Ca+ binds to sensor protein in cytoplasm.
- Ca+ protein complex stimulates fusion and exocytosis of neurotransmitters
Then: neurotransmitter (ligand) bind to receptor proteins on post-synaptic membrane which opens ligand gated ion channels (chemically regulated into channels)
Ion channels that depolarize cause EPSPs (excitatory)
Ion channels that hyper polarize cause IPSPs (inhibitory)
Discuss graded potential.
- Ligand gated ion channels open and the membrane potential changes depending on which ion channel is open
- Opening Na+ or Ca2+ channels = graded depolarization = EPSP
(More of this one? Then YES, SEND action potential) - Opening K+ and Cl- channels = graded hyper polarization = IPSP
(More of this one? Then NO, do NOT SEND action potential)
Discuss EPSP and IPSPs
- EPSPs summate and that determines whether an action potential occurs or not
- These use neurotransmitters
- EPSP (excitatory) move membrane potential closer to threshold; may require EPSPs from several neurons to produce action potential
- Graded in magnitude
- Have no threshold
- Cause depolarization
- Capable of summation
- No refractory period
- Can be initiated by neurotransmitters
- IPSP (inhibitory) more membrane potential farther from threshold; can counter EPSPs from other neurons
Discuss Acetylcholine (ACh).
- Most widely used neurotransmitter
- Excitatory or Inhibitory depending on ion channels that are open
- Has 2 receptor subtypes:
1. Nicotinic: Always excitatory; produces EPSPs when ACh binds to it
- Muscarinic: Excitatory or Inhibitory; uses G-proteins to open some and close other K+ channels
What does Acetylcholinesterase (AChE) do?
Inactivates ACh, terminating its action
What are “cholinergic” neurons?
Neurons that use ACh as a neurotransmitter
