Organization of the Nervous System

What components constitute the central nervous system (CNS)?

The central nervous system (CNS) is made up of the brain and spinal cord, which together process and transmit information throughout the body.

What structures are included in the peripheral nervous system (PNS)?

The peripheral nervous system (PNS) consists of all the nervous system structures that lie outside the brain and spinal cord, including sensory and motor nerves.

How many pairs of spinal nerves are there and where do they arise from?

The spinal nerves consist of 31 pairs, arising from the spinal cord below the corresponding vertebra, except in the cervical region where there are additional pairs.

What type of impulses does the ventral root carry?

The ventral root carries motor impulses exclusively, directing signals from the CNS to muscles and glands.

What type of impulses does the dorsal root carry?

The dorsal root carries sensory impulses exclusively, conveying sensory information from the body to the CNS.

Where do cranial nerves arise from, and how many pairs are there?

Cranial nerves arise directly from the brain and consist of 12 pairs that serve various functions, including sensory and motor functions.

What functions do general somatic afferents (GSA) sense?

General somatic afferents (GSA) are responsible for sensing temperature, touch, pain, and pressure from the skin and musculoskeletal system.

Which fiber types conduct motor functions to skeletal muscle?

Motor functions to skeletal muscle are conducted by General somatic efferents (GSE), which transmit signals from the CNS to voluntary muscles.

What types of fibers are included in the visceral/autonomic division?

The visceral/autonomic division includes both afferent fibers, which carry sensory information from internal organs, and efferent fibers, which transmit motor signals to involuntary muscles and glands.

What do general visceral afferents (GVA) sense?

General visceral afferents (GVA) are responsible for sensing stretch within internal organs, as well as visceral pain and nausea.

What are the unique characteristics of neurons regarding longevity and division?

Neurons are characterized by extreme longevity, often living for many years, and are amitotic, meaning they generally do not divide or regenerate like other cell types.

What does the cell body of a typical neuron contain?

The cell body of a typical neuron contains the nucleus, which houses genetic material, the nucleolus, which is involved in ribosome production, and granular cytoplasm rich in organelles.

What is the direction of graded potentials transmitted by dendrites?

Dendrites transmit graded potentials toward the cell body of the neuron, where they can influence the overall electrical signal.

What is the axon hillock, and its significance in neuron function?

The axon hillock is the cone-shaped area of the soma (cell body) from which the axon arises; it is significant as the site where action potentials are initiated.

How does the myelin sheath affect the axon?

The myelin sheath wraps around the axon and serves to insulate it, which increases the speed of nerve impulse transmission along the nerve fiber.

What is the structural composition of multipolar neurons?

Multipolar neurons have one axon and many dendrites, facilitating connections with multiple other neurons and enabling complex signaling.

What characterizes bipolar neurons in terms of structure?

Bipolar neurons are characterized by having one axon and one dendrite, typically found in sensory pathways such as vision and olfaction.

Where do sensory (afferent) neurons relay impulses?

Sensory (afferent) neurons carry impulses from the skin and internal organs to the central nervous system (CNS) for processing.

What is the location and function of interneurons?

Interneurons are located within the CNS and are responsible for processing information, integration, and relaying signals between sensory and motor pathways.

What role do astrocytes play in the nervous system?

Astrocytes are the most abundant type of glial cell, crucial for supporting neurons by connecting them to blood vessels (capillaries) and maintaining the blood-brain barrier.

What function do microglia serve in the CNS?

Microglia act as specialized macrophages in the CNS, performing immune defense by cleaning up debris and responding to injury.

What is the role of Schwann cells in peripheral nerves?

Schwann cells are essential for the regeneration of peripheral nerves, aiding in repair and regrowth after injury.

What is the primary function of the myelin sheath in neurons?

The myelin sheath insulates the axon and increases the speed of nerve impulse transmission, allowing for rapid communication.

What are interneurons responsible for in the CNS?

Interneurons are responsible for transmitting impulses within the CNS, playing a critical role in reflexes and complex processing.

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

Astrocytes serve to connect neurons to blood vessels (capillaries) and help maintain the integrity of the blood-brain barrier.

How many pairs of cranial nerves exist in humans?

Humans have 12 pairs of cranial nerves, each with specific sensory, motor, or mixed functions.

Describe multipolar neurons and their structural characteristics.

Multipolar neurons are characterized by having one axon and multiple dendrites, allowing for integration of a wide range of inputs from other neurons.

In what part of the nervous system do sensory neurons typically carry impulses?

Sensory neurons typically carry impulses from the skin and internal organs to the central nervous system (CNS) for interpretation.

What initiates an action potential at the axon hillock of a neuron?

The axon hillock is where depolarization reaches a threshold level, initiating the action potential that travels down the axon.

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

In the peripheral nervous system, Schwann cells facilitate the regeneration of peripheral nerves after injury, supporting repair and regrowth.

What sensations are general visceral afferents responsible for?

General visceral afferents sense stretch, visceral pain, and nausea, providing feedback from internal organs to the CNS.

What is the role of the Na+/K+ pump in neurons?

The Na+/K+ pump maintains the resting membrane potential by expelling 3 sodium ions out and bringing 2 potassium ions in, thus establishing a concentration gradient essential for action potentials.

What causes depolarization in a neuron?

Depolarization occurs when sodium channels open, allowing Na+ ions to flow into the neuron, causing a shift towards a more positive internal charge.

What is hyperpolarization in neuronal activity?

Hyperpolarization is when the membrane potential becomes more negative than the resting potential, often due to the opening of potassium channels allowing K+ ions to exit.

What is a synapse, and what is its function?

A synapse is the junction between two neurons where neurotransmitters are released, allowing transmission of signals from one neuron to another.

What are neurotransmitters, and give an example?

Neurotransmitters are chemical messengers that transmit signals across the synapse to communicate between neurons; an example is serotonin.

What is the function of the blood-brain barrier?

The blood-brain barrier protects the brain from harmful substances while allowing essential nutrients and gases to pass through.

What are the main types of glial cells, and their general functions?

The main types of glial cells are astrocytes (support neurons), microglia (immune defense), oligodendrocytes (myelination in CNS), and Schwann cells (myelination in PNS).

What is the all-or-nothing principle in action potentials?

The all-or-nothing principle states that once an action potential is initiated, it will propagate along the axon without decreasing in amplitude.

What is the function of oligodendrocytes?

Oligodendrocytes provide support and insulation to axons in the central nervous system by forming myelin sheaths.

How do action potentials propagate along myelinated axons?

Action potentials propagate along myelinated axons via saltatory conduction, where they jump from one Node of Ranvier to the next, increasing speed.