Nervous System Overview
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Nervous System Overview

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Questions and Answers

What are the two major divisions of the nervous system?

The two major divisions of the nervous system are the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

Name the four lobes of the cerebral hemisphere.

The four lobes of the cerebral hemisphere are the frontal, parietal, temporal, and occipital lobes.

What is the functional unit of the nervous system?

The functional unit of the nervous system is the neuron.

What role do dendrites play in a neuron?

<p>Dendrites extend from the cell body to receive incoming signals and process them before sending information to the soma.</p> Signup and view all the answers

Where are action potentials typically generated in a neuron?

<p>Action potentials are typically generated at the initial segment of the axon.</p> Signup and view all the answers

What is the function of the myelin sheath?

<p>The myelin sheath insulates the axon, increasing the speed of impulse transmission.</p> Signup and view all the answers

What are the two components of the autonomic nervous system?

<p>The two components of the autonomic nervous system are the sympathetic and parasympathetic nervous systems.</p> Signup and view all the answers

What structures are included in the brainstem?

<p>The brainstem includes the midbrain, pons, and medulla oblongata.</p> Signup and view all the answers

What role do Schwann cells play in the peripheral nervous system?

<p>Schwann cells wrap around the axon to form the myelin sheath, which insulates the axon.</p> Signup and view all the answers

Describe what happens at the nodes of Ranvier during the conduction of action potentials.

<p>At the nodes of Ranvier, the axon is unmyelinated, allowing action potentials to 'jump' between these nodes for faster conduction.</p> Signup and view all the answers

What are the two types of potentials generated by neurons?

<p>Neurons generate local (non-propagated) potentials and propagated action potentials.</p> Signup and view all the answers

How does the Na+/K+ ATPase pump contribute to maintaining membrane potential in neurons?

<p>The Na+/K+ ATPase pump actively moves Na+ out of the cell and K+ into the cell, maintaining the concentration gradients necessary for membrane potential.</p> Signup and view all the answers

What is the typical resting membrane potential (RMP) of neurons?

<p>The resting membrane potential of neurons is typically around -70 mV.</p> Signup and view all the answers

What is an action potential and what conditions must be met for it to occur?

<p>An action potential is an electrochemical signal that transmits impulses, occurring when there's a change in voltage across the membrane and a threshold level of stimulus is reached.</p> Signup and view all the answers

Explain the significance of the unequal ion distribution in maintaining resting membrane potential.

<p>The unequal distribution of ions, particularly higher K+ concentration inside the cell and higher Na+ concentration outside, is crucial for establishing the resting membrane potential.</p> Signup and view all the answers

What causes potassium ions (K+) to move out of the neuron at rest?

<p>K+ moves out of the neuron when K+ channels are open due to the concentration gradient driven by the higher K+ concentration inside the cell.</p> Signup and view all the answers

What is the All-or-None law in relation to action potentials?

<p>The All-or-None law states that an action potential either occurs fully or not at all.</p> Signup and view all the answers

Describe the role of voltage-gated Na+ channels during the depolarization phase of an action potential.

<p>During depolarization, voltage-gated Na+ channels open, allowing Na+ ions to rush into the cell, causing further depolarization.</p> Signup and view all the answers

Explain the difference between the absolute and relative refractory periods.

<p>The absolute refractory period occurs from the start of the action potential until part of repolarization, where no stimulus can trigger another action; during the relative refractory period, a stronger than normal stimulus can initiate a response.</p> Signup and view all the answers

What happens during the repolarization phase of an action potential?

<p>During repolarization, voltage-gated K+ channels open, allowing K+ ions to exit the cell, which causes the membrane potential to decrease.</p> Signup and view all the answers

How does the strength-duration relationship influence action potential generation?

<p>Weak stimuli require a longer duration to trigger an action potential, while strong stimuli can evoke a response with a shorter duration.</p> Signup and view all the answers

What is hyperpolarization, and when does it occur during action potentials?

<p>Hyperpolarization is when the membrane potential becomes more negative than resting level, occurring after the K+ channels close.</p> Signup and view all the answers

What is the significance of the threshold intensity in action potential generation?

<p>Threshold intensity is the minimum strength of a stimulus needed to trigger an action potential, determining whether a neuron fires.</p> Signup and view all the answers

Explain the process that leads to the inactivation of Na+ channels during an action potential.

<p>Na+ channels inactivate after the membrane potential approaches +60 mV, preventing further influx of Na+ and contributing to the repolarization phase.</p> Signup and view all the answers

What happens when a stimulus fails to reach the threshold level in relation to action potentials?

<p>An action potential will not be generated if the stimulus is subthreshold.</p> Signup and view all the answers

Explain how sodium concentration outside the cell affects action potentials.

<p>Decreased Na+ outside the cell lowers the strength of the action potential but minimally impacts the resting membrane potential.</p> Signup and view all the answers

Describe the process of saltatory conduction in myelinated axons.

<p>Saltatory conduction involves depolarization jumping from one node of Ranvier to the next, facilitated by the insulating effect of myelin.</p> Signup and view all the answers

How does increased potassium (K+) outside the cell affect neurons?

<p>Hyperkalemia lowers the threshold for action potential, making neurons more excitable.</p> Signup and view all the answers

What are the primary functions of glial cells in the nervous system?

<p>Glial cells support neurons by holding them in place, supplying nutrients, insulating them, and removing pathogens.</p> Signup and view all the answers

What is the effect of hypokalemia on the neuron's membrane potential?

<p>Hypokalemia hyperpolarizes the membrane, making it more negative and reducing the likelihood of an action potential.</p> Signup and view all the answers

How does calcium concentration affect neuronal excitability?

<p>Decreased Ca2+ increases membrane excitability, while increased Ca2+ decreases it.</p> Signup and view all the answers

What role do nodes of Ranvier play in nerve signal conduction?

<p>Nodes of Ranvier allow for the circular current flow necessary for saltatory conduction in myelinated axons.</p> Signup and view all the answers

What is the primary function of the Blood Brain Barrier (BBB)?

<p>The BBB primarily separates the central nervous system from peripheral blood circulation.</p> Signup and view all the answers

How do neurotrophins support neurons in the nervous system?

<p>Neurotrophins support the growth, survival, and function of neurons.</p> Signup and view all the answers

What role do Schwann cells play in peripheral nerve regeneration?

<p>Schwann cells release growth-promoting factors that guide axonal sprouting towards the distal stump.</p> Signup and view all the answers

Why is peripheral nerve regeneration more successful than CNS regeneration?

<p>Peripheral nerve regeneration is more successful due to the presence of growth-promoting factors and viable connective tissues.</p> Signup and view all the answers

What happens to axons in the CNS after an injury?

<p>Axons in the CNS form short sprouts, but rarely recover or form new synapses.</p> Signup and view all the answers

Identify two factors that create an unfavorable environment for CNS axonal regeneration.

<p>Astrocytic proliferation and scar formation are two such factors.</p> Signup and view all the answers

What is the significance of neurotrophins in the context of axonal injury?

<p>Neurotrophins produced by the distal stump promote axonal growth during regeneration.</p> Signup and view all the answers

Explain how inflammatory responses affect CNS axonal regeneration.

<p>Inflammatory responses lead to immune cell invasion and create a hostile environment for regeneration.</p> Signup and view all the answers

Study Notes

Nervous System Overview

  • The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
  • The CNS includes the brain and spinal cord.
  • The PNS consists of all the nerves that connect the CNS to the rest of the body.

Brain Structure

  • The brain is divided into four major parts: the cerebrum, diencephalon, brainstem, and cerebellum.
  • The cerebrum is the largest part of the brain and is responsible for higher-level functions like thinking, language, and memory.
  • The diencephalon is located below the cerebrum and serves as a relay center for sensory information.
  • The brainstem connects the cerebrum and cerebellum to the spinal cord.
  • The cerebellum is responsible for coordinating movement and balance.

Neuron Structure

  • Neurons are the basic functional units of the nervous system.
  • The primary structure of a neuron includes the dendrites, initial segment, axon, and nerve endings.
  • Dendrites receive signals from other neurons and transmit them to the cell body.
  • The initial segment is where action potentials are generated.
  • The axon transmits signals to other neurons or target cells where action potentials arrive at nerve endings.
  • Nerve endings (presynaptic terminals) release neurotransmitters that communicate with other neurons.
  • Many axons are covered by myelinated sheaths, formed by Schwann cells (PNS) or oligodendrocytes (CNS).

Neuron Excitation & Conduction

  • Neurons generate two types of potentials: local (non-propagated) and action potentials.
  • Local potentials are graded responses, whereas action potentials are all-or-none responses.
  • Action potentials are generated by the opening and closing of voltage-gated ion channels, typically Na+ and K+ channels.
  • Ion conductance depends on permeability and resistance of the membrane.

Action Potential Process

  • Resting state: Neuron is at rest with no ion movement across the membrane.
  • Depolarizing stimulus: Stimulus causes Na+ channels to open, allowing Na+ to enter the cell, leading to threshold potential.
  • Rapid depolarization: More Na+ channels open, causing a rapid rise in membrane potential (upstroke).
  • Na+ channels inactivate: Membrane potential moves towards +60 mV (Na+ equilibrium potential), but Na+ channels inactivate.
  • Repolarization: Voltage-gated K+ channels open, allowing K+ to exit the cell, causing repolarization.
  • After-hyperpolarization: Slow closure of K+ channels causes a brief period of hyperpolarization.
  • Return to resting state: Membrane potential returns to its resting level after K+ channels close.

Action Potential Properties

  • Threshold intensity: The minimum stimulus strength needed to trigger an action potential.
  • Strength-duration relationship: Stronger stimuli have shorter durations to reach threshold, whereas weaker stimuli have longer durations.
  • Refractory periods: Absolute refractory period (no response during depolarization) and relative refractory period (needs a stronger stimulus to elicit a response).
  • All-or-none principle: An action potential will only occur if the threshold level is reached. If subthreshold, no action potential occurs. The size remains constant once threshold is reached.
  • Conduction: Action potential propagates as positive charges flow into the region of depolarization, triggering local responses.

Myelinated Axons and Saltatory Conduction

  • In myelinated axons, current flows only at the nodes of Ranvier, the gaps between myelin, due to the insulating effect of myelin.
  • Depolarization jumps from one node to the next, called saltatory conduction, making signal transmission significantly faster.

Ion Concentration Effects on Excitability

  • Decreased Na+ outside: Reduces AP strength but minimal impact on resting potential.
  • Increased K+ outside: Lowers AP threshold, making neurons more excitable.
  • Decreased K+ outside: Hyperpolarizes the membrane, reducing AP likelihood.
  • Decreased Ca2+: Increases membrane excitability.
  • Increased Ca2+: Decreases membrane excitability.

Glial Cells - Supporting Role

  • Glial cells are non-neuronal cells in the CNS and PNS that support neuron function.
  • Types of glial cells: oligodendrocytes, astrocytes, ependymal cells, microglia (CNS); Schwann cells and satellite cells (PNS).
  • Functions: surround and hold neurons, supply nutrients and oxygen, insulate neurons from each other, destroy pathogens and remove dead neurons.

Blood-Brain Barrier (BBB)

  • BBB is a specialized barrier between the blood and CNS, regulating what substances can enter the brain.
  • it protects the brain from harmful substances in the blood.

Neurotrophins - Growth and Development

  • Neurotrophins are a family of proteins that regulate the growth, survival, and function of neurons.
  • They play essential roles in the development and maintenance of the nervous system.

Axonal Injury and Regeneration

  • Peripheral nerve damage can often be repaired. The axon degenerates beyond the injury, but the distal stump survives.
  • Axons regenerate from the proximal stump, guided by Schwann cells and neurotrophins from the distal stump.
  • CNS axonal injury is more difficult to repair, as CNS neurons lack the growth-promoting chemicals and myelin inhibits axonal growth.
  • CNS damage treatments focus on rehabilitation rather than repairing the damaged nerves.

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Description

This quiz covers the fundamental aspects of the nervous system, including its division into the central and peripheral nervous systems. You'll explore the major parts of the brain and the structure of neurons. Test your understanding of how these components function and their roles within the body!

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