Neurophysiology Introduction I

Questions and Answers

Which part of the nervous system is mainly responsible for processing sensory information?

Peripheral nervous system

Spinal cord

Brainstem

Central nervous system (correct)

What is the name of the substance that insulates many axons?

Neurotransmitter

Sarcoplasm

Myelin (correct)

Cytoplasm

Which part of a neuron is responsible for receiving incoming signals?

Nerve ending

Axon

Cell body

Dendrites (correct)

Which structure connects the axon to the cell body of a neuron?

Axon hillock Signup and view all the answers

Which division of the peripheral nervous system controls voluntary movements?

Somatic nervous system Signup and view all the answers

Which part of the brain is NOT included in the central nervous system?

Peripheral nerves Signup and view all the answers

What occurs at the presynaptic terminal of a neuron?

Release of neurotransmitters Signup and view all the answers

Which lobe of the brain is located at the back and is primarily involved in visual processing?

Occipital lobe Signup and view all the answers

What happens when a stimulus fails to reach the threshold level in a neuron?

No action potential is generated. Signup and view all the answers

What is the main reason conduction in myelinated axons is faster than in unmyelinated fibers?

Current flows only at the nodes of Ranvier. Signup and view all the answers

How does hyperkalemia affect the neuron's excitability?

Decreases the threshold for action potentials. Signup and view all the answers

What role do glial cells play in the nervous system?

Insulate neurons and supply them with nutrients. Signup and view all the answers

What is the impact of decreased extracellular Na+ on the action potential?

Has minimal impact on the action potential strength but affects resting potential. Signup and view all the answers

What is the primary function of myelin in the nervous system?

To act as an insulator and facilitate faster signal conduction. Signup and view all the answers

What effect does hypocalcemia have on neuronal membranes?

Increases membrane excitability. Signup and view all the answers

Which of the following is NOT a primary function of glial cells?

Generate electrical impulses in neurons. Signup and view all the answers

What is the primary characteristic of the action potential's propagation?

It follows the All-or-None law. Signup and view all the answers

What initiates the depolarizing phase of the action potential?

Open voltage-gated Na+ channels. Signup and view all the answers

Which ion primarily contributes to the repolarization phase of the action potential?

Potassium (K+) Signup and view all the answers

During which phase does the membrane potential become more negative than resting potential?

After-hyperpolarization Signup and view all the answers

What defines the absolute refractory period?

No stimulus can trigger an action potential. Signup and view all the answers

What does the strength-duration relationship indicate about weak stimuli?

They need a longer duration to trigger a response. Signup and view all the answers

What happens to Na+ channels at the peak of an action potential?

They inactivate quickly. Signup and view all the answers

The minimum strength of a stimulus needed to trigger an action potential is known as what?

Threshold intensity. Signup and view all the answers

What is the primary role of neurotrophins in the nervous system?

Promote the growth and function of neurons Signup and view all the answers

Which of the following accurately describes the effect of peripheral nerve damage?

Axonal sprouting is guided by Schwann cells Signup and view all the answers

What challenge does CNS axonal regeneration face after an injury?

Inhibition of axonal growth by CNS myelin Signup and view all the answers

What is a significant consequence of neural injury in the CNS compared to the PNS?

CNS neurons lack the chemicals necessary for regeneration Signup and view all the answers

Which of the following factors contributes to the unfavorable environment for regeneration following CNS injury?

Astrocytic proliferation and inflammation Signup and view all the answers

In what way does the peripheral nervous system (PNS) differ from the central nervous system (CNS) regarding axonal injury?

PNS axons typically sprout and grow towards their target Signup and view all the answers

What typically hinders the recovery process in nervous system injuries?

Activation of microglia and inflammation Signup and view all the answers

What is a likely outcome of incorrect connection during peripheral nerve regeneration?

Permanent impairment of fine motor skills Signup and view all the answers

What is the primary function of Schwann cells in the peripheral nervous system?

To wrap around the axon and form the myelin sheath Signup and view all the answers

At which part of the axon is the myelin sheath absent?

Nodes of Ranvier Signup and view all the answers

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

-70 mV Signup and view all the answers

What maintains the concentration gradient of Na+ and K+ ions across the neuronal membrane?

Na-K ATPase pump Signup and view all the answers

Which type of potential is primarily responsible for long-distance communication in the nervous system?

Action potentials Signup and view all the answers

What occurs when the threshold level of stimulus is reached in a neuron?

Creation of an action potential Signup and view all the answers

Which ion primarily determines the resting membrane potential due to its permeability?

K+ Signup and view all the answers

What happens to the membrane potential during the process of conduction in neurons?

It remains constant Signup and view all the answers

Study Notes

Nervous System Overview

The nervous system consists of two major divisions: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
CNS includes the brain (cerebrum, diencephalon, brainstem, cerebellum) and spinal cord.
PNS is divided into the somatic nervous system (sensory and motor) and the autonomic nervous system (sympathetic and parasympathetic).

Brain Anatomy

Cerebrum: Comprised of two hemispheres with the cerebral cortex (grey matter), white matter, basal ganglia, and lateral ventricles.
Diencephalon: Contains the epithalamus, thalamus, hypothalamus, and subthalamus, surrounding the 3rd ventricle.
Brainstem: Includes the midbrain (cerebral aqueduct), pons, and medulla oblongata.
Cerebellum: Located behind the brainstem, associated with motor control.

Neurons

Neurons are the functional units of the nervous system, with over 100 billion in the human brain.
Neurons exhibit varied specificity, size, and cell types, constituting distinct regions such as dendrites, axons, and nerve endings.

Functional Zones of Neurons

Dendrites: Receive incoming signals and transmit information to the soma (cell body).
Initial Segment: Where action potentials are initiated.
Axon: Long extension transmitting impulses.
Nerve Endings: Terminal regions releasing neurotransmitters upon action potential arrival.

Myelin and Its Role

Myelin, produced by Schwann cells in the PNS, insulates axons, enhancing conduction speed.
Action potentials "jump" between nodes of Ranvier through saltatory conduction, increasing transmission speed by up to 50 times compared to unmyelinated fibers.

Membrane Potential and Action Potentials

Resting Membrane Potential (RMP) in neurons is typically around -70 mV.
Unequal ion distribution (higher K+ inside, higher Na+ outside) is essential for maintaining membrane potential, managed by the Na+/K+ ATPase pump.
Action potentials are triggered by significant changes in membrane voltage, following the All-or-None principle.

Steps of Action Potential

Resting State: No ion movement across the membrane.
Depolarization: Voltage-gated Na+ channels open, increasing membrane potential.
Peak: Na+ channels inactivate, preventing further sodium entry.
Repolarization: K+ channels open, potassium exits the cell, restoring negative potential.
After-Hyperpolarization: Membrane becomes more negative before returning to RMP.

Refractory Periods

Absolute Refractory Period: No stimulus can generate an action potential.
Relative Refractory Period: A stronger-than-normal stimulus can trigger an action potential.

Ion Conductance and Channels

Neuronal membranes contain ligand-gated and voltage-gated ion channels.
Ion conductance is influenced by permeability and membrane resistance.

Regeneration and Repair Mechanisms

Peripheral Nerve Damage: Allows for some repair through axonal sprouting guided by Schwann cells.
CNS Axonal Injury: Characterized by limited regeneration due to lack of growth-promoting signals and formation of scar tissue.

Neurotrophins and Glial Cells

Glial cells support neuronal health and function, playing roles in nutrient supply and insulation.
Neurotrophins are crucial for neuronal growth, survival, and function, influencing both the CNS and PNS.

Clinical Correlates

Abnormal sodium and potassium levels can affect action potential generation.
CNS injuries lead to unfavorable healing environments due to inflammation and other factors, emphasizing the importance of rehabilitation.

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Description

This quiz covers the fundamental concepts of neurophysiology, focusing on the division of the nervous system into the central nervous system (CNS) and its components. Topics include the structure and function of the brain, including the cerebral cortex, diencephalon, and brainstem. Test your knowledge and understanding of these essential neurophysiological concepts.