Week 4 Flashcards
What are the two main types of cells in nervous tissue?
Neurons (transmit electrical impulses) and Glial cells (provide support, insulation, and nutrients for neurons).
What are the key properties of neurons?
Excitability: Respond to stimuli and generate electrical signals.
Conductivity: Transmit electrical impulses over long distances.
Synaptic transmission: Communicate via synapses using neurotransmitters.
Plasticity: Adapt and form new connections in response to experiences.
What are the functions of glial cells (neuroglia)?
Support and protect neurons.
Provide electrical insulation (myelin sheath).
Increase impulse transmission speed.
Mitotic, meaning they have a higher generation capacity than neurons.
What are the main features of a neuron?
Dendrites: Receive signals and provide input to the cell body.
Cell body: Receives signals and processes information.
Axon: Transmits signals away from the cell body.
Myelin sheath: Insulates the axon to speed up signal transmission.
Axon terminals: Release neurotransmitters to communicate with other neurons.
What is the function of the myelin sheath?
It provides electrical insulation to the axon, increasing the speed of action potential conduction.
What are the three structural classifications of neurons?
Multipolar: Many dendrites and one axon (most common, 99%).
Bipolar: One fused dendrite and one axon (rare, found in retina and olfactory mucosa).
Unipolar: One process extends from the cell body and forms central and peripheral processes (found in PNS as sensory neurons).
What are the three functional classifications of neurons?
Sensory (afferent) neurons: Transmit impulses from sensory receptors to the CNS.
Motor (efferent) neurons: Transmit impulses from the CNS to muscles and glands.
Interneurons: Connect sensory and motor neurons, responsible for processing and integrating signals (99% of neurons).
What is the classification of neurons based on axon diameter?
Refer to table
Type Ia: Motor signals to skeletal muscles.
Type Ib: Touch and proprioception sensations.
Type II: Sharp, localized pain and temperature sensations.
Type III: Autonomic motor signals to regulate internal organs.
Type IV: Dull/aching pain and temperature sensations.
What is the resting membrane potential of neurons, and why is it negative?
Neurons have a resting membrane potential of around -70 mV. It is negative because the concentration of potassium (K+) is higher inside the cell and sodium (Na+) is higher outside the cell, creating an unequal distribution of charge
What are the two key factors that influence the negative resting membrane potential in neurons?
- High concentration of K+ inside the cell and high concentration of Na+ outside.
- The neuron membrane is selectively permeable, allowing K+ ions to move out more easily through leak channels.
What is the role of the sodium-potassium pump in maintaining the resting membrane potential?
The sodium-potassium pump moves 3 Na+ ions out of the cell and 2 K+ ions into the cell for each ATP molecule used. This helps establish and maintain the concentration gradient, crucial for the resting membrane potential.
How does the sodium-potassium pump work?
The sodium-potassium pump binds 3 Na+ ions inside the cell, which triggers ATP hydrolysis. The pump releases Na+ outside and binds 2 K+ ions from outside. The pump changes shape, releasing K+ inside the cell, and resets to bind Na+ again.
What is the function of leak channels in maintaining the resting membrane potential?
Leak channels allow ions, especially K+, to diffuse out of the cell, which contributes to the negative charge inside the cell. This selective permeability helps maintain the unequal distribution of ions necessary for the resting membrane potential.
What is an action potential and what is its amplitude?
An action potential is a brief reversal of the membrane potential, with an amplitude of about 100 mV, ranging from -70 mV to +30 mV.
What triggers the initiation of an action potential?
The action potential begins when the membrane reaches the threshold at the axon hillock, triggering voltage-gated sodium channels to open.
What happens during depolarization in an action potential?
During depolarization, sodium channels open, causing sodium ions (Na+) to flow into the cell. This creates a positive feedback loop, leading to the rising phase of the action potential.
What ends depolarisation and starts depolarisation in an action potential?
Depolarization ends when sodium channels become inactivated, and potassium channels open, leading to repolarization.
What is hyperpolarization during an action potential?
Hyperpolarization occurs when the membrane potential becomes more negative than the resting potential, often due to the continued efflux of potassium ions (K+).
What are the absolute and relative refractory periods during an action potential?
- Absolute refractory period: The neuron cannot generate a new action potential because sodium channels are inactive.
- Relative refractory period: The neuron can generate an action potential, but only with a stronger-than-normal stimulus because some sodium channels are reset, and potassium channels are still open.
How are all action potentials alike?
Once generated by a stimulus, all action potentials are identical in size and follow an all-or-none principle, meaning their amplitude is always the same.
How do sensory neurons encode stimulus intensity?
Sensory neurons encode stimulus intensity by the frequency of action potentials, not by their amplitude. A stronger stimulus results in a higher frequency of action potentials.
How do motor neurons control muscle contraction strength?
Motor neurons regulate muscle contraction strength by adjusting the frequency of action potentials. A higher frequency leads to a greater force of contraction.
How is ion flow different in myelinated axons?
In myelinated axons, ion flow occurs only at the nodes of Ranvier, where the myelin sheath is absent. This allows action potentials to jump from one node to the next.
Where are voltage-gated sodium channels concentrated in myelinated axons?
Voltage-gated sodium channels are concentrated at the nodes of Ranvier, where action potentials are generated.
