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
Is the same neurotransmitter always released at the same synapse?
Yes. As long as the NT is bound to receptor sites, the alteration in membrane permeability responsible for the changes in the postsynaptic cell continues
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)
