Comprehensive Nervous System and Neuron Function Review

What are the main components of the nervous system?

The brain, spinal cord, and receptors in complex sense organs such as the eye and ear.

What is the primary function of the nervous system?

To receive information from external and internal stimuli, process that information, and send signals to initiate responses.

What are the three divisions of the nervous system?

The central nervous system (CNS), peripheral nervous system (PNS), and enteric nervous system (ENS).

What does the central nervous system (CNS) consist of?

The brain and spinal cord.

What is the role of the central nervous system (CNS)?

To integrate, process, and coordinate sensory data and motor commands.

What does the peripheral nervous system (PNS) include?

All nervous tissue outside the CNS and ENS.

What are the two subdivisions of the peripheral nervous system (PNS)?

The somatic nervous system and the autonomic nervous system.

What is the function of the afferent division of the PNS?

To bring sensory information to the CNS from receptors in peripheral tissues and organs.

What are effectors in the context of the nervous system?

Target organs that respond to motor commands from the CNS.

What does the efferent division of the PNS do?

Carries motor commands from the CNS to muscles, glands, and adipose tissue.

What is the somatic nervous system responsible for?

Controlling skeletal muscle contractions, both voluntary and involuntary.

What is the autonomic nervous system (ANS) responsible for?

Automatically regulating smooth muscle, cardiac muscle, glandular secretions, and adipose tissue.

What are the two divisions of the autonomic nervous system (ANS)?

The sympathetic division and the parasympathetic division.

What is the enteric nervous system (ENS)?

An extensive network of neurons and nerve networks in the walls of the digestive tract.

How does the enteric nervous system (ENS) function in relation to the CNS?

It initiates and coordinates many complex visceral reflexes locally without instructions from the CNS.

What are neurons?

Nerve cells specialized for intercellular communication.

What are some characteristics of neurons?

They are generally long-lived, have a high metabolic rate, and possess an excitable plasma membrane.

What is the role of mitochondria in neurons?

To generate the energy needed by an active neuron.

What is the significance of action potentials in neurons?

They place a substantial demand on a neuron's energy resources.

What is the role of sensory receptors?

To detect changes in the environment or respond to specific stimuli.

What is the difference between cranial nerves and spinal nerves?

Cranial nerves are connected to the brain, while spinal nerves are attached to the spinal cord.

What are nerve fibers?

Bundles of axons that carry sensory information and motor commands in the PNS.

What do most neurons lack that is important for cell division?

Centrioles.

Why can't typical CNS neurons divide?

Most neurons lack centrioles, which are important for organizing the cytoskeleton and moving chromosomes during mitosis.

What happens to neurons lost to injury or disease?

They cannot be replaced because typical CNS neurons cannot divide.

Where do neural stem cells persist in the adult nervous system?

They are typically inactive except in the nose and the hippocampus.

What are the four general regions of a neuron?

1. Large cell body (soma) 2. Several short, branched dendrites 3. A single long axon 4. Terminal branches of the axon (telodendria).

What is contained within the cell body (soma) of a neuron?

A large, round nucleus with a prominent nucleolus and cytoplasm called the perikaryon.

What is the cytoskeleton of the perikaryon composed of?

Neurofilaments and neurotubules, similar to intermediate filaments and microtubules of other cells.

What are neurofibrils?

Bundles of neurofilaments that extend into dendrites and axons, providing internal support.

What organelles are found in the perikaryon?

Mitochondria, free and fixed ribosomes, and membranes of rough endoplasmic reticulum (RER).

What is the function of mitochondria in neurons?

They generate ATP to meet neuronal energy demands.

What are Nissl bodies?

Clusters of rough endoplasmic reticulum and free ribosomes in the perikaryon that stain darkly with cresyl violet.

What color do Nissl bodies give to areas containing neuron cell bodies?

Gray, contributing to the gray matter seen in the brain and spinal cord.

What are the two types of neuron processes?

Dendrites and axons.

How do dendrites function in neurons?

They convey incoming messages toward the cell body and provide a large surface area for receiving signals.

What are dendritic spines?

Bristled appendages on finer dendrites that represent points of synaptic contact with other neurons.

What is the role of the axon in a neuron?

It is the conducting region that generates and transmits nerve impulses away from the cell body.

What is the axon hillock?

The cone-shaped area of the cell body where the axon begins.

What is a nerve fiber?

Any long axon, which can extend a meter or more in some neurons.

What occurs at the junction of the axon hillock and axon?

The nerve impulse is generated at the trigger zone.

What happens when a nerve impulse reaches the axon terminals?

It causes neurotransmitters to be released into the extracellular space.

What is the primary function of neurotransmitters?

They are signaling chemicals that facilitate communication between neurons.

What is the typical length of axons in motor neurons controlling skeletal muscles?

They can extend a meter or more from the lumbar region of the spine to the foot.

What is the significance of the axolemma?

It is the plasma membrane of the axon through which nerve impulses are transmitted.

What role do neurotransmitters play in neuron communication?

They either excite or inhibit neurons and effector cells such as muscles or glands.

How do neurons interact with each other?

Each neuron receives signals from and sends signals to multiple other neurons, engaging in 'conversations' simultaneously.

What organelles are absent in axons compared to dendrites and cell bodies?

Axons lack rough endoplasmic reticulum and a Golgi apparatus.

What are the two main dependencies of axons for nutrient distribution?

(1) They depend on the cell body to renew necessary proteins and membrane components. (2) They rely on efficient transport mechanisms to distribute these components.

What is axonal transport?

It is a cellular process that facilitates the movement of organelles, proteins, and vesicles along the axon of a neuron.

What are the two types of movement in axonal transport?

Anterograde movement (away from the cell body) and retrograde movement (toward the cell body).

What substances are transported in the anterograde direction?

Mitochondria, cytoskeletal elements, membrane components for the axon plasma membrane, and enzymes for neurotransmitter synthesis.

What is the purpose of retrograde transport?

It allows organelles to return to the cell body for degradation or recycling and facilitates intracellular communication.

What type of proteins are involved in axonal transport?

ATP-dependent motor proteins such as kinesin (for anterograde transport) and dynein (for retrograde transport).

How fast can substances travel along the axon via axonal transport?

Up to 40 cm (15 inches) per day.

What are the four structural classifications of neurons?

Anaxonic, bipolar, unipolar, and multipolar.

What are the characteristics of anaxonic neurons?

They have numerous dendrites but no obvious axons and are located in the brain and special sense organs.

What defines bipolar neurons?

They have two distinct processes: one dendrite and one axon, with the cell body between them, and are rare, occurring in special sense organs.

What is unique about unipolar neurons?

The dendrites and axon are continuous, with the cell body located off to one side, and they are commonly found in sensory neurons of the peripheral nervous system.

What are multipolar neurons?

Neurons with two or more dendrites and a single axon, which are the most common type in the CNS.

What types of neurons are classified by function?

(1) Sensory neurons, (2) Motor neurons, (3) Interneurons.

What is the role of sensory neurons?

They form the afferent division of the peripheral nervous system (PNS) and carry signals from sensory receptors to the central nervous system.

What are the primary functions of motor neurons?

They transmit signals from the central nervous system to effector cells, such as muscles and glands.

What is the function of interneurons?

They connect sensory and motor neurons within the central nervous system and are involved in reflexes and complex processing.

Where are the longest axons of unipolar neurons found?

They carry sensations from the tips of the toes to the spinal cord.

What type of neurons control skeletal muscles?

Multipolar neurons.

What is the significance of the axon in neuron structure?

It is responsible for transmitting action potentials and communicating signals to other neurons or effector cells.

How do axons depend on their cell bodies?

Axons rely on their cell bodies to renew necessary proteins and membrane components for their function.

What are sensory neurons also known as?

Afferent neurons.

Where are the cell bodies of sensory neurons located?

In peripheral sensory ganglia.

What type of neurons are sensory neurons classified as?

Unipolar neurons.

What do sensory neurons do?

They deliver information from sensory receptors to the spinal cord or brain.

How many sensory neurons does the human body have approximately?

About 10 million.

What do somatic sensory neurons monitor?

The outside world and our position within it.

What do visceral sensory neurons monitor?

Internal conditions and the status of other organ systems.

What is the primary function of motor neurons?

To carry impulses away from the CNS to effector organs.

What type of neurons are motor neurons?

Multipolar neurons.

Where are the cell bodies of motor neurons located?

In the CNS, except for some neurons of the autonomic nervous system.

What role do interneurons play in the nervous system?

They shuttle signals between motor and sensory neurons in neural pathways.

What percentage of neurons in the body are interneurons?

Over 99%.

What type of neurons are most interneurons classified as?

Multipolar.

What are neuroglia?

Supportive cells that separate and protect neurons.

What is one of the main functions of neuroglia?

To provide a supportive framework for nervous tissue.

How do neuroglia help maintain the nervous system?

They regulate the composition of the interstitial fluid.

How many types of neuroglia are there in the CNS and PNS?

Six types—four in the CNS and two in the PNS.

Name the four types of neuroglia found in the CNS.

Astrocytes, microglial cells, ependymal cells, oligodendrocytes.

What are astrocytes known for?

Being the largest and most numerous neuroglia in the CNS.

What is one key function of astrocytes?

They help determine capillary permeability and guide neuron migration.

How do astrocytes maintain the chemical environment around neurons?

By mopping up leaked potassium ions and recycling neurotransmitters.

What protective role do microglial cells serve in the CNS?

They act as phagocytes, consuming microorganisms and neuronal debris.

What happens to microglial cells when they sense injured neurons?

They migrate toward the injured neurons and transform into macrophages.

What is the role of ependymal cells in the central nervous system (CNS)?

Ependymal cells line the central canal and ventricles, assist in producing and monitoring cerebrospinal fluid (CSF), and help circulate CSF with their cilia.

What are the enlarged chambers in the brain formed by the fluid-filled central passageway called?

Ventricles.

What is the function of oligodendrocytes in the CNS?

Oligodendrocytes form a myelin sheath along the length of axons, myelinating segments of several axons.

What are the segments of an axon that are wrapped in myelin called?

Internodes.

What are the small gaps between adjacent internodes on a myelinated axon called?

Nodes of Ranvier.

What distinguishes white matter from gray matter in the CNS?

White matter consists of myelinated axons, while gray matter contains neuron cell bodies, dendrites, and unmyelinated axons.

What are the two types of neuroglia found in the peripheral nervous system (PNS)?

Satellite cells and Schwann cells.

What is the function of satellite cells in the PNS?

Satellite cells surround neuron cell bodies and have functions similar to astrocytes in the CNS.

What is the role of Schwann cells in the PNS?

Schwann cells surround all nerve fibers and form myelin sheaths around thicker nerve fibers, aiding in regeneration of damaged peripheral nerve fibers.