Neuroscience Chapter: Nerves and Glial Cells

Questions and Answers

What is the difference between nerves and tracts?

Nerves are in the CNS and tracts are in the PNS.

Nerves carry only one type of information, tracts carry multiple.

Tracts can consist of multiple types of information. (correct)

What are ganglia and where are they located? What is the counterpart to ganglia?

Ganglia are clusters of cell bodies of nerves located in the PNS; the counterpart is nuclei found in the CNS.

Astrocytes form the __________ barrier.

blood-brain

What is the resting membrane potential and how is it maintained? How many ions are exchanged in this maintenance?

-70mV, maintained by Na+/K+ ATPase which pumps 3 Na+ out and 2 K+ in. Signup and view all the answers

Describe the activity of the channels in a neuron during an action potential and how is the nerve impulse propagated unidirectionally?

Potassium channels open at the peak of the action potential; propagation is unidirectional due to the refractory period in the preceding axon segment. Signup and view all the answers

What occurs after the action potential reaches the nerve terminal?

Neurotransmitters are released into the synaptic cleft. Signup and view all the answers

What types of receptors are on the postsynaptic membrane?

Ligand-gated ion channels or G protein-coupled receptors. Signup and view all the answers

What are the three ways neurotransmitters are cleared from the postsynaptic receptors, and what does clearing them accomplish?

<ol> <li>Enzymatically broken down; 2) absorbed back into presynaptic neuron by reuptake channels; 3) diffused out of synaptic cleft.</li> </ol> Signup and view all the answers

What neurons ascend to the CNS and what neurons exit?

Afferent (sensory) neurons ascend to the CNS; Efferent (motor) neurons exit the CNS. Signup and view all the answers

What is a reflex arc and what are the 2 types?

A reflex arc is the nerve pathway involved in a reflex action. The two types are monosynaptic and polysynaptic. Signup and view all the answers

What is white and gray matter, and where is each located in the brain and spinal cord?

White matter consists of myelinated axons, and gray matter consists of unmyelinated cell bodies and dendrites; in the brain, white matter is deeper, while in the spinal cord, gray matter is deeper. Signup and view all the answers

Study Notes

Nerves vs. Tracts

Nerves are bundles of neurons in the peripheral nervous system (PNS) that transmit various information types (sensory, motor, or both).
Tracts are bundles of neurons in the central nervous system (CNS) that carry a single type of information.

Ganglia and Nuclei

Ganglia are clusters of cell bodies of the same type of neuron located in the PNS.
Nuclei refer to the equivalent clusters of cell bodies found in the CNS.

Functions of Glial Cells

Astrocytes contribute to the formation of the blood-brain barrier, regulating substance passage into the brain.
Ependymal cells line brain ventricles and produce cerebrospinal fluid, providing cushioning and shock absorption for the brain.
Microglia act as phagocytic immune cells, defending the CNS against pathogens and debris.
Oligodendrocytes produce myelin sheaths in the CNS, enhancing signal transmission.
Schwann cells generate myelin sheaths in the PNS.

Resting Membrane Potential

The resting membrane potential of a neuron is approximately -70 mV.
This potential is maintained by the Na+/K+ ATPase pump, which moves 3 sodium ions (Na+) out of the cell and 2 potassium ions (K+) into the cell.

Action Potential and Propagation

During an action potential, potassium channels open at the peak, leading to repolarization.
The refractory period following an action potential prevents reverse propagation, allowing the impulse to travel unidirectionally along the axon.

Post-Action Potential at Nerve Terminal

After reaching the nerve terminal, action potentials trigger the release of neurotransmitters from synaptic vesicles into the synaptic cleft.

Postsynaptic Receptors

The postsynaptic membrane contains ligand-gated ion channels or G protein-coupled receptors that respond to neurotransmitters.

Neurotransmitter Clearance

Neurotransmitters are cleared from postsynaptic receptors through:
- Enzymatic breakdown.
- Reuptake by presynaptic neurons via reuptake channels.
- Diffusion out of the synaptic cleft.
Clearing neurotransmitters ceases signal propagation, ensuring precise control of neuronal communication.

Neuron Types in CNS

Afferent (sensory) neurons ascend towards the CNS.
Efferent (motor) neurons descend from the CNS.
Interneurons are the most abundant neuron type, facilitating communication within the CNS.

Reflex Arc

A reflex arc is the nerve pathway for reflex actions, consisting of at least a sensory neuron and a motor neuron connected by a synapse.
Monosynaptic arcs involve a single synapse between an afferent sensory neuron and an efferent motor neuron.
Polysynaptic arcs include one or more interneurons between sensory and motor neurons, allowing for complex reflex responses.

White Matter vs. Gray Matter

White matter consists of myelinated axons that facilitate rapid communication between brain regions.
Gray matter contains unmyelinated portions (cell bodies and dendrites) involved in processing and integrating information.
In the brain, white matter is located deeper than gray matter, while in the spinal cord, gray matter is situated deeper than white matter.

Description

Test your knowledge on the differences between nerves and tracts, as well as the roles of glial cells in the nervous system. This quiz covers essential concepts in neuroscience, including functions of neurons and cells that support them. Dive into the structure and function of the PNS and CNS.