8 - Nervous System Communication Flashcards
Which two extrinsic control systems are responsible for maintaining homeostasis?
- Nervous system
- Endocrine system
How is information encoded and transmitted in the nervous system?
Action potentials
- Changes in the plasma membrane polarization (from diff in cations and anions in ICF and ECF)
What ions are responsible for generating resting potential?
Na+ and K+ and anions (A-)
- Na+ greater conc. in ECF
- K+ greater conc. in ICF
(resting potential = when cells aren’t producing electrical signals)
What does the Na+ - K+ pump do?
The sodium/potassium pump actively transports Na+ out and K+ into the cell, to counteract leaking.
This keeps conc of Na high in ECF and conc of K high in the ICF
(Nae, Ki)
What does a downward deflection in membrane potential signify?
Increase in potential
What are the different types of ion-specific channels in the membrane?
- Leak channels
- Always open - Gated channels
- Voltage-gated
- Chemically-gated
- Mechanically-gated
- Thermally-gated
What is a graded potential? What determines the waveform?
- The change in membrane potential relative to resting potential
- Waveforms determined by membrane’s resistive and capacitive properties
Why are graded potentials more useful for communicating over short distances?
- Potential degrades with distance because of current leakage
How is an action potential generated? What is an action potential?
- If the depolarization stimulus reaches a threshold
- The AP is the key unit that the nervous system uses to encode/transmit info
Key properties:
- All-or-none phenomenon
- Stereotypical size/shape
- Doesn’t decrease in strength as it travels away from stimulation site
How does permeability and ion movement change during an action potential?
- Sodium channels open during depolarization by positive feedback
- When sodium channels become inactive, channels for potassium open. This repolarizes the membrane
How does an AP propagate in the membrane generally?
- AP develops at one point in membrane, it regenerates an identical AP at the next point
- AP travels along the plasma membrane undiminished, only in 1 direction
- A patch of membrane that has recently fired an AP cannot fire again for a few ms (refractory period)
What parts of the Neuron are involved in AP propagation?
- APs are propagated from the axon hillock to the axon terminals
- Basic parts of neuron (nerve cell):
1. Cell body
2. Dendrites - increase surface area available for receiving signals from other nerve cells, move the signal toward the cell body, (aka neuron’s input zone)
3. Axon - (Aka conducting zone) Nerve fibre, tubular extension that conducts APs away from cell body - Axon Hillock: First portion of the axon plus the region from which axon leaves (aka trigger zone)
- Axon Terminals: Release chemical messengers that influence other cells (output zone of neuron)
dendrites -> trigger zone -> conducting zone -> output zone
What are two types of nerve fibre propagation?
- Contiguous conduction:
- Conduction in unmyelinated fibres
- AP spreads along every portion of the membrane - Saltatory conduction:
- Rapid conduction in myelinated fibres
- Impulse jumps over sections of the fibre covered with insulating myelin
What is Myelin and how does it affect speed of conduction?
- Its composed of lipids and acts as an axon insulator
- Increases speed of impulses
- Produced by oligodendrocytes in the brain and spinal cord and by Schwann cells in the nerves running between the CNS and PNS
(*nodes of Ranvier lack myelin)
Does Saltatory conduction or contiguous conduction propagate AP faster?
- Saltatory, because AP doesn’t have to be regenerated at myelinated section
- Nerve impulses travel along myelinated axons about 50x faster than they do along unmyelinated axons.
What’s a synapse?
- Junction between two neurons (interaction site)
- Signal at synapse either excites or inhibits postsynaptic neuron
What are the two types of synapses?
- Excitatory synapses
- Inhibitory synapses
What are the two types of postsynaptic potential?
- Temporal summation
- Summation of several EPSPs occurring very close together in time because of successive firing of a single presynaptic neuron - Spatial summation
- Summation of EPSPs originating simultaneously from several diff presynaptic inputs
What’s the neuromuscular junction?
- Axon terminal of motor neuron forms neuromuscular junction with a single muscle cell
- Signals are passed between nerve terminal and muscle fibre by means of neurotransmitter ACh
(ACh binds to receptor sites on motor end plate of muscle cell membrane)
