W1 L1 peripheral nervous system

What is the peripheral nervous system (PNS)?

The PNS is the extensive network of nerves that extends from the central nervous system (CNS) throughout the body, comprising sensory neurons that carry information from sensory receptors to the brain and motor neurons that transmit commands from the brain to various muscles and glands. It connects the CNS with limbs and organs.

What are the two main divisions of the nervous system?

The nervous system is divided into two main parts: the central nervous system (CNS), which includes the brain and spinal cord, serving as the control center for processing and transmitting information, and the peripheral nervous system (PNS), which consists of all the neural pathways that branch out from the CNS and connect it to every part of the body.

What is the function of afferent neurons?

Afferent neurons, also known as sensory neurons, are responsible for transmitting sensory impulses from sensory receptors located throughout the body to the central nervous system, where this information is processed and interpreted, allowing for responses to environmental stimuli.

How do efferent neurons function in the nervous system?

Efferent neurons, or motor neurons, are specialized for carrying motor commands from the central nervous system to the muscles and glands in the body, facilitating movement and physiological activities by instructing these effectors to contract or secrete.

Define a sensory receptor field.

A sensory receptor field is the specific area of skin or body surface that is monitored by a single sensory nerve fiber or neuron. The size and characteristics of these fields can affect sensory perception and localization, with smaller fields allowing for finer discrimination between stimuli.

What are mechanoreceptors responsible for?

Mechanoreceptors are specialized sensory receptors that detect mechanical forces such as touch, pressure, vibration, and stretching. They play a crucial role in providing the brain with information about tactile sensations and the physical state of the body, contributing significantly to our sense of touch.

What distinguishes chemoreceptors from mechanoreceptors?

Chemoreceptors are specialized sensory receptors that respond to chemical stimuli, detecting molecules such as odors, tastes, and changes in blood chemistry, while mechanoreceptors respond to physical stimuli and mechanical forces. This distinction highlights the different ways our sensory systems gather information about the environment.

What is the role of Schwann cells in the PNS?

Schwann cells are glial cells in the peripheral nervous system that play a vital role in the formation of the myelin sheath, an insulating layer that surrounds axons. This myelination enhances the speed and efficiency of electrical impulse conduction along the nerve fibers, facilitating rapid communication within the nervous system.

What is Wallerian degeneration?

Wallerian degeneration is a biological process that occurs following a nerve injury, particularly when an axon is severed. It involves the degeneration of the distal portion of the axon, leading to cell death and the subsequent removal of cellular debris. This process is crucial for the regeneration of the nerve, as it sets the stage for new axonal growth.

How does the speed of conduction relate to myelin?

Myelinated fibers conduct action potentials significantly faster than unmyelinated fibers due to the presence of the myelin sheath, which allows the electrical impulse to jump between nodes of Ranvier, a process known as saltatory conduction. Increased myelination directly correlates with higher conduction velocities, ensuring efficient neural communication.

What is a dorsal root ganglion?

A dorsal root ganglion is a cluster of nerve cell bodies located just outside the spinal cord, part of the peripheral nervous system. It contains the cell bodies of afferent neurons, which transmit sensory information from the body to the central nervous system, playing a crucial role in sensory signal processing.

What is the relationship between spinal nerves and dermatomes?

Spinal nerves are responsible for transmitting sensory information from specific regions of the body to the central nervous system and controlling motor functions in those same regions. Dermatomes are anatomical areas of skin that correspond to specific spinal nerves, providing a map for sensory innervation and functional assessment in clinical settings.

Why are receptive fields important for sensory discrimination?

Receptive fields are crucial for sensory discrimination because smaller receptive fields enhance the ability to accurately localize and differentiate between different sensory stimuli. This means that the more precisely we can pinpoint the area where a stimulus is acting, the better our brain can interpret and respond to that stimulus.

What are the types of spinal nerves?

The spinal nerves are categorized into five primary types based on their positions in the vertebral column: cervical (8 pairs), thoracic (12 pairs), lumbar (5 pairs), sacral (5 pairs), and coccygeal (1 pair), each serving distinct regions of the body and providing essential sensory and motor functions.

What are the potential consequences of peripheral nerve injury?

Peripheral nerve injuries can lead to a variety of symptoms, including pain (neuropathic pain), numbness, tingling sensations, and loss of motor function. The specific effects depend on the location and extent of the injury, which can significantly impact mobility and quality of life.

Explain the process of myelination.

Myelination is a developmental process in which glial cells, particularly Schwann cells in the PNS and oligodendrocytes in the CNS, wrap around the axons of neurons, creating a myelin sheath. This insulation not only protects axons but also increases the speed and efficiency of electrical signal transmission through nerve fibers.

What happens to action potentials when the myelin sheath is damaged?

When the myelin sheath is damaged, the conduction of action potentials is impaired, leading to slower signal transmission or complete blockages. This can result in neurological symptoms such as weakness, loss of coordination, and sensory disturbances, as seen in conditions like multiple sclerosis.

What is an action potential?

An action potential is a rapid, all-or-nothing electrical impulse generated by the depolarization of the neuron's membrane, allowing for the transmission of signals along the axon. It is crucial for neuron-to-neuron communication and for the propagation of signals throughout the nervous system.

Describe the role of free nerve endings in sensory detection.

Free nerve endings are the most basic type of sensory receptor found in the skin and other tissues. They detect a variety of stimuli, including temperature changes, pain (nociception), and mechanical stimuli, providing essential information about external and internal environments to the central nervous system.

What does a neural spike train encode?

A neural spike train encodes information about the frequency and timing of action potentials generated by neurons in response to stimuli, providing the central nervous system with data regarding the intensity, duration, and location of tactile or sensory input.

How does the regeneration of peripheral nerves occur after injury?

After peripheral nerve injury, regeneration occurs through the meticulous efforts of Schwann cells, which align along the endoneurial sheath to facilitate axonal regrowth. They create a supportive environment that promotes healing, allowing the injured axon to reconnect with its target tissues and possibly restore lost functionality.