Nervous System Overview

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Questions and Answers

What is the primary function of dendrites in a neuron?

Synthesize proteins

Transmit impulses away from the cell body

Receive signals from other neurons (correct)

Act as impulse generators

Which statement about axons is correct?

They contain chromatophilic bodies for protein synthesis

They typically have one axon per neuron (correct)

They transmit impulses toward the cell body

They can typically have multiple branches along their length

Where is the nerve impulse generated in a neuron?

In the dendrites

Along the branches of the axon

At the terminal boutons

At the initial segment of the axon (axon hillock) (correct)

What is the primary role of neurotransmitters at the synapse?

To facilitate communication between neurons Signup and view all the answers

What aids in the transport of substances in the axon?

Axonal transport involving neurofilaments and microtubules Signup and view all the answers

What occurs at the terminal boutons?

Synaptic vesicles release neurotransmitters Signup and view all the answers

Which neuron is responsible for conducting signals toward a synapse?

Presynaptic neuron Signup and view all the answers

What structural feature characterizes axon collaterals?

They are infrequently branching along the axon length Signup and view all the answers

What primary role do mitochondria serve in the terminal bouton?

They provide energy for neurotransmitter secretion. Signup and view all the answers

What is the structure that separates the plasma membranes of two neurons at the synapse?

Synaptic cleft Signup and view all the answers

What initiates the release of neurotransmitters from synaptic vesicles?

The arrival of an impulse along the presynaptic axon. Signup and view all the answers

What effect does binding of neurotransmitters on the postsynaptic membrane have?

It changes the membrane charge, influencing nerve impulse generation. Signup and view all the answers

Which type of neuron makes up well over 99% of neurons in the body?

Multipolar neurons Signup and view all the answers

What process enables the synaptic vesicles to release their neurotransmitter molecules?

Exocytosis Signup and view all the answers

Which of the following is NOT a function of the synapse?

Regenerating nerve impulses. Signup and view all the answers

Which of the following statements accurately describes synaptic vesicles?

They are found within the terminal bouton and release neurotransmitters into the synaptic cleft. Signup and view all the answers

What is the primary function of the sensory (afferent) division of the nervous system?

Conduct impulses from receptors to the CNS. Signup and view all the answers

Which type of muscle is controlled by the visceral motor division?

Both B and C. Signup and view all the answers

Which sensory division is involved in detecting stretch in tendons and muscles?

Somatic sensory. Signup and view all the answers

What characterizes neurons in the nervous system?

Neurons can live and function for a lifetime. Signup and view all the answers

The somatic motor division of the PNS controls which type of muscle movement?

Skeletal muscle contraction. Signup and view all the answers

Which system is also known as the involuntary nervous system?

Autonomic nervous system. Signup and view all the answers

Which division is responsible for the general visceral senses?

Visceral sensory division. Signup and view all the answers

What are neuroglial cells primarily responsible for?

Surrounding and supporting neurons. Signup and view all the answers

Which of the following is NOT a characteristic of neurons?

They can divide indefinitely. Signup and view all the answers

The sympathetic division of the autonomic nervous system is primarily responsible for what?

Mobilizing body systems during activity. Signup and view all the answers

Which term refers to the body’s sense of position and movement in space?

Proprioceptive senses. Signup and view all the answers

What feature do the chromatophilic substances in neurons primarily provide?

Renewal of membrane and proteins. Signup and view all the answers

What type of impulses does the motor division of the PNS conduct?

Impulses from the CNS to effectors. Signup and view all the answers

Which of the following is a special visceral sense?

Taste. Signup and view all the answers

What is the primary function of the integration process in the nervous system?

To process and interpret sensory input Signup and view all the answers

Which division of the nervous system is responsible for voluntary control of skeletal muscles?

Somatic motor division Signup and view all the answers

Which type of neuron relays information from sensory receptors to the central nervous system?

Sensory neuron Signup and view all the answers

What term describes the gap between two neurons at the site of synaptic transmission?

Synaptic cleft Signup and view all the answers

Which component is part of the central nervous system?

Brain Signup and view all the answers

What is the function of the myelin sheath?

To insulate axons and increase signal speed Signup and view all the answers

What distinguishes the visceral motor division from the somatic motor division?

Voluntary versus involuntary control Signup and view all the answers

What are Schwann cells primarily responsible for?

Myelination of peripheral nerves Signup and view all the answers

Which structural classification of neurons is primarily involved in sensory input?

Unipolar neuron Signup and view all the answers

What is the role of astrocytes in the nervous system?

Providing structural support and nutrient transfer Signup and view all the answers

Which part of the neuron is primarily responsible for receiving signals?

Dendrites Signup and view all the answers

What defines the term 'gray matter' in the context of the nervous system?

Cell bodies and unmyelinated fibers Signup and view all the answers

What is a reflex arc?

A direct neural pathway for involuntary responses Signup and view all the answers

Which of the following muscles is controlled by the autonomic nervous system?

Cardiac muscle Signup and view all the answers

What type of neuron primarily transmits impulses toward the CNS?

Sensory neurons Signup and view all the answers

What classification of neurons carries impulses away from the CNS?

Motor neurons Signup and view all the answers

Which glial cells are responsible for producing myelin sheaths in the CNS?

Oligodendrocytes Signup and view all the answers

What is the primary function of astrocytes in the CNS?

Regulate neurotransmitter levels Signup and view all the answers

Which structure is responsible for forming the myelin sheath in the PNS?

Schwann cells Signup and view all the answers

What type of reflex arc is characterized by having only one synapse?

Monosynaptic reflex arc Signup and view all the answers

Where are the cell bodies of motor neurons primarily located?

Within the CNS Signup and view all the answers

Which type of neuroglia serves as the macrophages of the CNS?

Microglia Signup and view all the answers

What makes up the gray matter in the CNS?

Cell bodies of neurons Signup and view all the answers

Which layer of connective tissue surrounds individual axons in nerves?

Endoneurium Signup and view all the answers

What is the role of ependymal cells in the CNS?

To circulate cerebrospinal fluid Signup and view all the answers

The primary functional role of satellite cells in the PNS is to:

Surround and support neuron cell bodies Signup and view all the answers

What is a characteristic feature of white matter in the CNS?

Composed of myelinated axons Signup and view all the answers

Study Notes

Functions of the Nervous System

The nervous system monitors changes in the internal and external environments.
The nervous system processes and interprets sensory input to make decisions regarding the appropriate response.
The nervous system activates effector organs (muscles and glands) to produce a response.

Basic Divisions of the Nervous System

The nervous system can be divided into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
The CNS consists of the brain and spinal cord.
As the integrating and command center, the CNS receives sensory signals, interprets them, and dictates motor responses based on prior experiences, reflexes, and current conditions.
The PNS includes nerves extending from the brain and spinal cord, including cranial nerves and spinal nerves.
The PNS acts as communication lines linking all body regions to the CNS.
Ganglia are collections of neuron cell bodies in the PNS.

Sensory and Motor Divisions of the PNS

The PNS has sensory (afferent) and motor (efferent) divisions:
- The sensory division carries impulses from the receptors to the CNS.
- The motor division carries impulses from the CNS to effectors (muscles and glands).
The sensory division further divides into somatic sensory (sensation from skin, body wall, and limbs) and visceral sensory (sensation from visceral organs).
The motor division consists of the somatic motor (voluntary, controls skeletal muscle innervation) and visceral motor (involuntary, controls smooth muscle, cardiac muscle, and glands) divisions.
The visceral motor division is also known as the autonomic nervous system.

Nervous Tissue

Nervous tissue is comprised of densely packed, intertwined cells.
The main cell types are neurons (transmitting electrical signals) and glial cells (non-excitable, supporting and surrounding neurons).
Neurons are excitable cells.

The Neuron

Neurons are the fundamental structural units of the nervous system.
They are specialized to conduct electrical impulses along the plasma membrane.
Neurons have specific characteristics:
- Longevity: They function for a lifetime.
- Inability to divide: Fetal neurons typically lose their ability to undergo mitosis, except for neural stem cells.
- High metabolic rate: They require significant oxygen and glucose.

Components of the Neuron

The cell body (soma) is the main part of the neuron, typically 5 to 140 microns in size.
The cell body houses typical cellular organelles and additional structures:
- Chromatophilic substance (Nissl bodies): Clusters of rough ER and free ribosomes responsible for renewing the neuron's membrane and cytosolic proteins.
- Neurofibrils: Bundles of intermediate filaments providing the cell with tensile strength.
Dendrites are extensively branching extensions from the cell body, transmitting electrical signals toward the cell body.
Axons are single extensions from the cell body, generating and conducting impulses away from the cell body.
Axonal transport is the movement of substances to and from the cell body along the axon.
Terminal arborization (telodendria) are multiple branches at the end of the axon, ending in knobs called terminal boutons (axon terminals).

Synapses

A synapse is the communication site between neurons.
Most communication occurs through chemical messengers (neurotransmitters).
Some communication is electrical, through gap junctions.
The presynaptic neuron conducts signals toward the synapse.
The postsynaptic neuron transmits electrical activity away from the synapse.

Structure of an Axodendritic Synapse

The terminal bouton of the presynaptic neuron contains synaptic vesicles, membrane-bound sacs filled with neurotransmitters.
Mitochondria are abundant in the terminal bouton due to the energy required for neurotransmitter secretion.
The plasma membranes of the two neurons are separated by a synaptic cleft.
When an impulse reaches the presynaptic neuron, synaptic vesicles fuse with the presynaptic membrane, releasing neurotransmitters via exocytosis.
Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane, changing its charge and influencing its ability to generate a nerve impulse.

Functional Classification of Neurons

Neurons are classified by the direction of the nerve impulse relative to the CNS.
Sensory neurons transmit impulses toward the CNS.
- Virtually all are unipolar neurons.
- Cell bodies are in ganglia outside the CNS.
- The central process terminates in the CNS.
- The peripheral process extends from sensory receptors.
Motor (efferent) neurons carry impulses away from the CNS to effector organs.
- Most motor neurons are multipolar.
- Cell bodies are within the CNS.
- Form junctions with effector cells.
Interneurons (association neurons) are mostly multipolar.
- Lie between motor and sensory neurons.
- Confined to the CNS.

Neuroglia

Six types of neuroglia: four in the CNS and two in the PNS.
CNS Neuroglia
- Astrocytes are the most abundant glial cell type.
  - Regulate neurotransmitter levels, signaling blood flow in active brain regions.
  - Produce molecules for neuron growth.
- Microglia are the smallest and least abundant glial cell type.
  - Act as phagocytes, engulfing microorganisms and dead neurons.
- Ependymal cells line the central cavity of the spinal cord and brain.
  - Possess cilia that help circulate cerebrospinal fluid.
- Oligodendrocytes have few branches and wrap their cell processes around axons in the CNS.
  - Produce myelin sheaths in the CNS.
PNS Neuroglia
- Satellite cells surround neuron cell bodies within ganglia.
- Schwann cells surround axons in the PNS.
  - Form myelin sheath around axons of the PNS.

Myelin Sheaths

Myelin sheaths are segmented structures composed of the lipoprotein myelin.
They surround thicker axons, providing insulation to prevent leakage of electrical current and increase the speed of impulse conduction.
In the PNS, myelin sheaths are formed by Schwann cells which wrap around the axon in concentric layers.
Myelin sheath gaps (nodes of Ranvier) are gaps along the axon that speed up nerve transmission.
In the CNS, myelin sheaths are formed by oligodendrocytes, which have multiple processes that coil around several axons.

Grey and White Matter of the CNS

Gray matter is gray-colored and surrounds hollow central cavities of the CNS.
- Forms a butterfly-shaped region in the spinal cord.
  - The dorsal half contains cell bodies of interneurons.
  - The ventral half contains cell bodies of motor neurons.
- Is the site where neuron cell bodies are clustered (ganglia).
- Is where synapses occur.
White matter lies external to the gray matter in the CNS.
- Is composed of myelinated axons.
- Consists of axons passing between specific regions of the CNS.
- Tracts are bundles of axons traveling to similar destinations.

Nerves

Nerves are cable-like organs in the PNS consisting of numerous axons wrapped in connective tissue.
Most nerves contain myelinated and nonmyelinated sensory and motor axons.
Endoneurium is a layer of delicate connective tissue surrounding the axon.
Perineurium is connective tissue wrapping surrounding a nerve fascicle, which is a group of axons bound into bundles.
Epineurium is the tough fibrous sheath surrounding the whole nerve.

Reflex Arcs

Reflex arcs are simple chains of neurons that explain reflex behaviors.
They determine the structural plan of the nervous system and are responsible for reflexes: rapid, autonomic motor responses.
Monosynaptic Reflex Arc:
- The simplest of all reflexes.
- Has just one synapse.
- Is the fastest of all reflexes.
- Example: knee-jerk reflex.
Polysynaptic Reflex Arc:
- The more common type of reflex.
- One or more interneurons are part of the pathway.
- Example: withdrawal reflexes.
- Interneurons signal the motor neuron to contract the muscle involved.

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Description

Explore the essential functions and basic divisions of the nervous system in this quiz. It covers the roles of the Central and Peripheral Nervous Systems, as well as sensory and motor divisions. Test your knowledge on how these systems monitor and respond to internal and external changes.