Nervous System (Flashcards)
What is the primary function of the nervous system?
To monitor internal and external changes, integrate information, and generate precise responses to maintain homeostasis
What are the two main types of cells in the nervous system?
Neurons and glial cells. Neurons transmit electrical signals, and glial cells support and protect neurons.
What creates the electrochemical gradients in cells?
Differences in the concentration of ions and molecules between intracellular and extracellular fluids
What is a nerve impulse?
An electrical signal that is generated and propagated along the axon of a neuron
List the important ions involved in establishing electrochemical gradients
K+, Na+, Cl-, Ca++, and large negatively charged organic ions (org-).
How is the resting membrane potential (RMP) established and maintained?
- Na+/K+-ATPase (sodium-potassium pump) maintains ion concentration gradients
- Non-gated K+ channels make the membrane more permeable to K+ at rest
- Large, negatively charged organic ions (org-) inside the cell.
Define graded potentials (GPs)
Small changes in the resting membrane potential, usually occurring on dendrites or the cell body, caused by the opening of gated ion channels
What are the different types of gated ion channels?
- Voltage-gated channels: open in response to membrane voltage changes.
- Chemically-gated channels: open in response to chemical binding (e.g., neurotransmitters).
- Temperature-gated channels: open in response to temperature changes.
- Mechanically-gated channels: open in response to mechanical deformation.
What is the approximate value of the resting membrane potential (RMP)?
Approximately -70 mV (inside of the cell is more negative).
What are the possible results of graded potentials?
- Depolarization:
- Membrane potential becomes more positive than RMP (e.g., -70 mV to -65 mV).
- Hyperpolarization:
- Membrane potential becomes more negative than RMP (e.g., -70 mV to -75 mV).
What is the relationship between graded potentials and action potentials?
If a graded potential causes sufficient depolarization to reach the threshold potential, it can trigger an action potential
Define action potential (AP)
A large, rapid change in membrane potential that propagates along the axon of a neuron
List the phases of an action potential
- Depolarization phase
- Repolarization phase
- After-hyperpolarization phase
What is the role of voltage-gated Na+ channels in the action potential?
They open in response to membrane potential changes, increasing Na+ permeability and causing depolarization
What is the role of voltage-gated K+ channels in the action potential?
They open during repolarization, increasing K+ permeability and allowing K+ to diffuse out of the cell, decreasing the membrane potential
What is the absolute refractory period?
A period during which no action potential can be generated, regardless of stimulus size, due to all Na+ channels being either open or inactivated
What is the relative refractory period?
A period during which an action potential can be generated, but only by a greater than normal stimulus, because Na+ channels are reactivated but K+ channels are still open.
What is synaptic transmission?
The process by which a presynaptic neuron communicates with a postsynaptic neuron via a synapse
How does myelination affect the rate of action potential propagation?
Myelinated fibers propagate action potentials faster due to saltatory conduction, where action potentials occur only at the nodes of Ranvier
State the all-or-none principle of action potentials
If the threshold is reached, an action potential is produced with the same maximum depolarization. Below the threshold, no action potential occurs
Compare Type A and Type C nerve fibers
- Type A:
- Large diameter, myelinated, fast propagation (~130 m/sec), found in sensory and motor neurons.
- Type C:
- Small diameter, unmyelinated, slow propagation (~0.5 m/sec), found in the autonomic nervous system and some pain fibers.
List the steps of synaptic transmission
- Action potential arrives at the axon terminal.
- Voltage-gated Ca++ channels open, and Ca++ enters the axon terminal.
- Increase in Ca++ triggers exocytosis of neurotransmitter (nt) containing vesicles.
- Neurotransmitter diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane.
- Gated ion channels open, causing a graded potential (postsynaptic potential).
What are the two types of postsynaptic potentials (PSPs)?
- Excitatory PSPs (EPSPs): cause depolarization.
- Inhibitory PSPs (IPSPs): cause hyperpolarization.
Describe synaptic transmission at the neuromuscular junction
- Neurotransmitter released is always acetylcholine (ACh).
- ACh binds to chemical gates on the muscle motor end plate, causing a graded potential (end plate potential, EPP).
- EPP triggers an action potential on the sarcolemma.
