Peripheral Nervous System: Videos & Practice Problems

The peripheral nervous system (PNS) transmits sensory (afferent) information to the central nervous system and motor (efferent) commands from it. The PNS divides into the somatic nervous system, controlling voluntary skeletal muscle movements, and the autonomic nervous system (ANS), regulating involuntary functions in smooth muscle, cardiac muscle, and glands. The ANS further splits into the sympathetic branch, which triggers the fight-or-flight response by increasing heart rate, dilating airways, and inhibiting digestion, and the parasympathetic branch, promoting rest-and-digest activities by decreasing heart rate, constricting airways, and stimulating digestion. This coordination maintains homeostasis and body function.

Introduction to PNS Concept 1

The peripheral nervous system (PNS) encompasses all nervous tissue located outside the central nervous system (CNS). Its primary function is to transmit information to the CNS and execute responses based on that information. Nerves within the PNS are bundles of axons that can be classified by the direction in which they carry signals. Specifically, afferent nerves transmit sensory information from the body to the CNS, while efferent nerves carry motor commands from the CNS to muscles and glands.

A useful mnemonic to differentiate these nerves is "Same Same," where "S" stands for sensory, linked to afferent nerves, and "M" stands for motor, linked to efferent nerves. For example, when you approach a hot flame, afferent nerves detect the heat and send this sensory input to the brain via the spinal cord. The brain processes this information and sends a motor response through efferent nerves, prompting you to withdraw your hand from the flame. This illustrates how the PNS facilitates communication between the body and the CNS to coordinate actions.

Understanding the roles of afferent and efferent nerves is essential for grasping how the peripheral nervous system functions to maintain bodily responses and interactions with the environment.

Introduction to PNS Example 1

Understanding the distinction between afferent and efferent nerves is essential in grasping how the nervous system processes sensory input and motor output. Afferent nerves, also known as sensory nerves, carry information from sensory receptors toward the central nervous system, allowing us to perceive stimuli such as temperature, taste, and touch. For example, when you feel cold stepping outside on a snowy day or identify food by taste without seeing it, afferent nerves transmit these sensory signals to the brain for interpretation.

In contrast, efferent nerves, or motor nerves, transmit signals away from the central nervous system to muscles or glands, initiating actions or responses. When you miss your bus and decide to start walking home, or when you message your dad to ask for a pickup, efferent nerves are responsible for sending the motor commands that enable these actions.

This differentiation highlights the fundamental roles of afferent and efferent nerves in the nervous system: afferent nerves facilitate sensory input, while efferent nerves control motor output. Recognizing these pathways helps in understanding how the body responds to internal and external stimuli, integrating sensory information, and producing coordinated movements or behaviors.

Subdivisions of the PNS Concept 2

The peripheral nervous system (PNS) is a crucial part of the overall nervous system, which is divided into the central nervous system (CNS) and the peripheral nervous system. The PNS itself is further subdivided into the somatic nervous system (SNS) and the autonomic nervous system (ANS), each serving distinct functions.

The somatic nervous system primarily controls voluntary movements by innervating skeletal muscles. For example, when performing an action like curling a dumbbell, the SNS activates the biceps during the lifting phase and the triceps during the extension phase. This system enables conscious control over muscle movements, allowing precise and intentional physical actions.

In contrast, the autonomic nervous system regulates involuntary functions by controlling smooth muscles, cardiac muscles, and glands. This includes processes such as digestion and heart rate, which operate without conscious effort. The smooth muscles in the digestive tract and the cardiac muscles of the heart are regulated by the ANS, ensuring vital bodily functions continue automatically. Since these activities are beyond voluntary control, they are classified as involuntary functions.

Understanding the distinction between the somatic and autonomic nervous systems highlights how the peripheral nervous system manages both voluntary and involuntary bodily functions, maintaining coordination between conscious actions and automatic physiological processes.

Subdivisions of the PNS Example 2

The nervous system is divided into two main components that control different types of bodily actions: the somatic nervous system and the autonomic nervous system. The somatic nervous system governs voluntary movements, meaning actions we consciously control, such as moving skeletal muscles. In contrast, the autonomic nervous system regulates involuntary functions, which occur without conscious control, like heart rate and hormone secretion.

For example, increasing your heart rate is controlled by the autonomic nervous system because it is an involuntary response that the body manages automatically. Similarly, the secretion of adrenaline, which triggers the body's "fight or flight" response, is also regulated by the autonomic nervous system since it happens without conscious effort.

On the other hand, activities like typing on a computer or throwing a ball involve deliberate control of skeletal muscles, making them functions of the somatic nervous system. These actions require conscious decision-making and motor coordination.

Feeling sleepy is another involuntary process controlled by the autonomic nervous system. Although one might try to stay awake, the sensation of sleepiness arises naturally and is not directly controlled. Likewise, reacting to a sudden jump scare is an involuntary reflex action. This rapid response bypasses conscious thought, illustrating how the autonomic nervous system manages quick, automatic reactions to stimuli.

Understanding the distinction between voluntary and involuntary actions helps clarify how the nervous system coordinates bodily functions. The somatic nervous system enables intentional movements, while the autonomic nervous system maintains essential involuntary processes that keep the body functioning smoothly without conscious input.

Branches of ANS Concept 3

The autonomic nervous system is divided into two main branches that have opposing effects on the body: the sympathetic and parasympathetic nervous systems. The sympathetic branch is activated during stressful or threatening situations, triggering the "fight or flight" response. This response prepares the body for immediate action by increasing heart rate, dilating airways to enhance lung capacity, raising blood pressure, and inhibiting digestion to prioritize energy for survival activities.

In contrast, the parasympathetic branch activates when the body is relaxed and at rest, promoting the "rest and digest" state. This branch decreases heart rate, constricts airways, lowers blood pressure, and stimulates digestion, allowing the body to conserve energy and focus on maintenance and recovery processes.

Understanding these two branches highlights how the autonomic nervous system regulates involuntary bodily functions to adapt to different environmental demands. The sympathetic nervous system mobilizes the body for rapid response to danger, while the parasympathetic nervous system supports restorative functions during calm periods. Together, they maintain homeostasis by balancing physiological states according to situational needs.

Branches of ANS Example 3

When the body is in a relaxed state, such as after eating a large meal and resting, the parasympathetic branch of the autonomic nervous system becomes active. This branch is responsible for the "rest and digest" response, which decreases heart rate and stimulates digestive processes to efficiently process the food. In contrast, when the body encounters a stressful or stimulating situation, like watching a horror movie, the sympathetic branch of the autonomic nervous system activates the "fight or flight" response. This leads to an increase in heart rate and activates sweat glands to prepare the body for rapid action.

Understanding the autonomic nervous system involves recognizing the opposing roles of its two branches: the sympathetic nervous system, which increases physiological arousal by raising heart rate and activating sweat glands, and the parasympathetic nervous system, which promotes relaxation by decreasing heart rate and enhancing digestion. These responses are crucial for maintaining homeostasis and adapting to different environmental demands.

Which of the following statements is true about the components of the PNS? 

• A. Efferent nerves take sensory information to CNS and afferent nerves bring motor information to skeletal muscles. 
• B. Somatic nervous system controls vital involuntary functions such as breathing and heart rate. 
• C. During physical activity sympathetic branch of ANS increases heart rate and speeds up digestion. 
• D. In a stressful situation, the parasympathetic branch of ANS prepares the body for fight-or-flight response. 
• E. Autonomic nervous system controls digestion including the release of digestive enzymes from glands.  

Answer: (E)

Here’s what students ask on this topic:

What is the peripheral nervous system and how does it function?

The peripheral nervous system (PNS) is the network of nerves located outside the central nervous system (CNS). Its primary function is to transmit information between the body and the CNS. The PNS consists of afferent nerves, which carry sensory information from the body to the CNS, and efferent nerves, which carry motor commands from the CNS to muscles and glands. For example, when you touch a hot object, afferent nerves send the sensory signal to the brain, which processes it and sends a response through efferent nerves to move your hand away. This system allows the body to respond to stimuli and perform actions, maintaining communication between the brain, spinal cord, and the rest of the body.

What are the subdivisions of the peripheral nervous system and their roles?

The peripheral nervous system is divided into two main subdivisions: the somatic nervous system (SNS) and the autonomic nervous system (ANS). The SNS controls voluntary movements by innervating skeletal muscles, such as when you consciously move your arm to lift a weight. In contrast, the ANS regulates involuntary functions by controlling smooth muscles, cardiac muscles, and glands. It manages processes like digestion, heart rate, and glandular secretions without conscious effort. Understanding these subdivisions helps explain how the body coordinates both voluntary actions and automatic physiological functions.

How does the autonomic nervous system regulate involuntary body functions?

The autonomic nervous system (ANS) controls involuntary body functions by regulating smooth muscle, cardiac muscle, and glands. It has two branches with opposing effects: the sympathetic and parasympathetic branches. The sympathetic branch activates the 'fight or flight' response during stress, increasing heart rate, dilating airways, raising blood pressure, and inhibiting digestion to prepare the body for action. Conversely, the parasympathetic branch promotes the 'rest and digest' state when the body is relaxed, decreasing heart rate, constricting airways, lowering blood pressure, and stimulating digestion. This balance maintains homeostasis and adapts bodily functions to different situations.

What are the differences between afferent and efferent nerves in the peripheral nervous system?

Afferent and efferent nerves are two types of nerves in the peripheral nervous system distinguished by the direction of information flow. Afferent nerves carry sensory information from receptors in the body to the central nervous system (CNS). For example, they transmit signals about temperature, pain, or touch. Efferent nerves carry motor commands from the CNS to muscles and glands, enabling actions like muscle contraction or gland secretion. A useful memory tool is 'SAME': Sensory = Afferent, Motor = Efferent. This distinction is crucial for understanding how the body senses stimuli and responds appropriately.

What happens in the body during the sympathetic 'fight or flight' response?

During the sympathetic 'fight or flight' response, the body prepares to face or escape a threat. This activation causes an increase in heart rate to pump more blood, dilation of airways to improve oxygen intake, and a rise in blood pressure to enhance circulation. Additionally, digestion is inhibited to conserve energy for immediate action. These physiological changes enable the body to respond quickly and effectively to stressful or dangerous situations. This response is part of the autonomic nervous system's sympathetic branch, which works in opposition to the parasympathetic branch that promotes relaxation.

How does the parasympathetic nervous system support the body's rest and digest functions?

The parasympathetic nervous system supports the body's 'rest and digest' functions by promoting relaxation and recovery. It decreases heart rate, constricts airways, lowers blood pressure, and stimulates digestion. These actions help conserve energy and facilitate processes like nutrient absorption and waste elimination. The parasympathetic branch acts when the body is at rest, counterbalancing the sympathetic 'fight or flight' response. This balance ensures that the body can maintain homeostasis by switching between states of activity and rest as needed.