Nervous System

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Questions and Answers

What is the primary function of neurons within the nervous system?

Produce neurotransmitters exclusively

Conduct action potentials and transmit signals (correct)

Transmit signals to external organs

Support other cells in the nervous system

Which part of the neuron is responsible for receiving information from other neurons?

Dendrite (correct)

Cell body

Axon

Axon hillock

What characterizes multipolar neurons?

Many dendrites and a single axon (correct)

One axon and one dendrite

Single process extending outwards

Two processes of equal length

In which location are bipolar neurons primarily found?

Retina of the eye and nasal cavity Signup and view all the answers

What is the function of pseudounipolar neurons?

Serve a sensory function with single process extensions Signup and view all the answers

What distinguishes the basic functionality of glial cells compared to neurons?

Neurons transmit signals, while glial cells provide support Signup and view all the answers

Which part of the neuron conducts signals away from the cell body?

Axon Signup and view all the answers

How do glial cells enhance neuronal function?

Through the production of myelin sheaths Signup and view all the answers

What primarily determines the speed of action potential conduction in axons?

The diameter of axon fibers Signup and view all the answers

How do neurotransmitters cross the synaptic cleft?

By exocytosis from the presynaptic terminal Signup and view all the answers

What is the role of Ca2+ ions in the process of neurotransmitter release?

They trigger exocytosis of neurotransmitters from the presynaptic terminal. Signup and view all the answers

Which ions are involved when neurotransmitters bind to postsynaptic receptors?

Na+, K+, and Cl− ions Signup and view all the answers

What is the conduction speed for large-diameter, heavily myelinated axons?

15 to 120 m/s Signup and view all the answers

What happens when the presynaptic terminal is reached by an action potential?

Voltage-gated Ca2+ channels open and allow Ca2+ to enter the cell. Signup and view all the answers

What type of synapse is formed between two neurons?

Neuroneuronal synapse Signup and view all the answers

Which factor does NOT influence the conduction speed of action potentials in axons?

The amount of neurotransmitters in the synaptic vesicles Signup and view all the answers

What occurs in a postsynaptic cell when Na+ channels open?

The cell becomes depolarized. Signup and view all the answers

What effect do K+ or Cl− channels have on the postsynaptic cell?

They create a hyperpolarized state. Signup and view all the answers

How are neurotransmitters typically removed from the synaptic cleft?

They are actively transported away. Signup and view all the answers

Which enzyme is responsible for breaking down acetylcholine in the synaptic cleft?

Acetylcholinesterase. Signup and view all the answers

What characterizes a converging neuronal pathway in the CNS?

It allows the integration of signals from multiple sources. Signup and view all the answers

What principle describes the all-or-none response of action potentials?

Action potentials are always initiated when threshold is reached. Signup and view all the answers

What is the significance of hyperpolarization in a postsynaptic cell?

It inhibits the generation of an action potential. Signup and view all the answers

How does norepinephrine typically return to the presynaptic terminal after its release?

Through active transport or enzymatic breakdown. Signup and view all the answers

Study Notes

Nervous System Overview

The nervous system is responsible for receiving sensory input, integrating information, controlling muscles and glands, maintaining homeostasis, and establishing and maintaining mental activity.
The nervous system is divided into two main components: the central nervous system (CNS) and the peripheral nervous system (PNS).
The CNS includes the brain and spinal cord.
The PNS includes all nervous tissue outside the CNS.
The PNS can be further divided into the sensory division and the motor division.
The sensory division carries signals from sensory receptors to the CNS.
The motor division carries signals from the CNS to effector organs (muscles and glands).
The divisions can further be divided into somatic nervous system and autonomic nervous system and enteric nervous system pathways.

Cells of the Nervous System

Neurons receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs.
Glial cells support neurons and maintain normal conditions in nervous tissue. The support cells are not responsible for action potentials unlike neurons.
Astrocytes are major supporting cells in the CNS and can stimulate or inhibit neural activity. They also create the blood-brain barrier.
Ependymal cells line cavities in the brain and spinal cord and hold cerebrospinal fluid.
Microglial cells act as the immune defense of the CNS by removing bacteria and cellular debris.
Oligodendrocytes and Schwann cells produce myelin for nerve axons within the CNS and PNS, respectively.

Neuron Structure

Neurons have a cell body containing a nucleus.
Dendrites extend from the cell body and receive information from other neurons and send it towards the cell body.
Axons extend from the axon hillock, carry sensory signals to the CNS and motor signals away from it. and can be myelinated.

Neuron Types

Multipolar neurons have many dendrites and a single axon. Most CNS and motor neurons are multipolar.
Bipolar neurons have one dendrite and one axon. They are found in some sensory organs like the retina.
Pseudo-unipolar neurons have one process that splits into two: one extending to the periphery and other to the CNS. They have sensory receptors at their periphery.

Myelin Sheath

Myelin sheaths are specialized layers around axons in some neurons (myelinated).
Myelin is produced by oligodendrocytes in the CNS and by Schwann cells in the PNS. Its insulation prevents most ion movement across the axon membrane.
Nodes of Ranvier are gaps in the myelin sheath where ion movement can occur and greatly enhances the speed of the impulses. Myelinated axons exhibit saltatory conduction.
Unmyelinated axons lack myelin and conduct action potentials in a continuous conduction manner, which is much slower than saltatory conduction.

Nervous Tissue Organization

Nervous tissue is gray or white matter depending on the abundance of myelinated axons.
Gray matter consists of neuron cell bodies and dendrites, with little myelin.
White matter consists of bundles of parallel axons with myelin sheaths, appearing whitish in color.

Resting Membrane Potential

All cells exhibit electrical properties at their membranes due to ion differences across it.
The cell membrane is not permeable to ions. It is permeable through ion channels.
Ions flow through leak channels or gated channels (voltage-gated and chemically gated), down their concentration gradient and along the electrical gradient.
In most resting neurons, more K+ are inside and more Na+ is outside the membrane, which creates a negative charge inside the membrane, and a positive charge outside.
The Sodium-Potassium pumps actively transport Na+ out and K+ in, which is responsible for maintaining the resting membrane potential.

Nerve Cell Communication

Nerve cells are excitable; their resting membrane potential can change in response to stimuli.
Changes in membrane potential are called action potentials, which allow cells to communicate.

Gated Membrane Channels

Stimuli activate gated channels, opening and closing in response to specific signals.
Changes in gated ion channel permeability affect membrane potential.

Action Potential

Action potentials are electrical signals traveling along the cell membrane.
Voltage-gated Na+ and K+ channels are involved in action potentials.
A stimulus opens Na+ channels for a brief period, allowing Na+ to rapidly enter the cell; this depolarizes it.
If the depolarization is strong enough (reaching threshold), more Na+ channels open, leading to a rapid depolarization.
Na+ channels close, and K+ channels open, allowing K+ to leave the cell, leading to repolarization.
Eventually, resting membrane potential is restored.

Action Potential Conduction

Action potentials may travel as continuous or saltatory conduction (in myelinated axons).

Synapse

Synapses are junctions where axons communicate with other neurons.
Presynaptic terminals release neurotransmitters across a synaptic cleft to postsynaptic neurons.
Ca2+ triggers the release of neurotransmitters via exocytosis.
Neurotransmitters bind to receptors on the postsynaptic membrane.
Resulting channel openings affect the postsynaptic neuron (depolarizing or hyperpolarizing it).
Neurotransmitters are removed from the synaptic cleft to prevent continuous stimulation.

Neuronal Pathways

Information transmission occurs in different pathways (converging and diverging pathways).
Converging pathways allow multiple inputs to converge onto a single target and are essential for processing various stimuli.
Diverging pathways allow a single input to be transmitted to multiple targets.

Summation

Summation is required for integration of multiple signals onto a target neuron.
Spatial summation involves signals from different locations on the postsynaptic cell.
Temporal summation involves signals arriving at the postsynaptic cell in rapid succession.

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Description

This quiz covers the key components and functions of the nervous system, including the central and peripheral nervous systems. It also delves into the roles of neurons and glial cells, and the divisions within the peripheral nervous system. Test your knowledge on this vital biological system and its processes.