16.1 Nervous and Endocrine Systems
3 min read•august 7, 2024
The nervous and endocrine systems work together to control and coordinate bodily functions. Neurons transmit electrical signals, while act as chemical messengers. These systems maintain homeostasis and regulate processes like growth, metabolism, and reproduction.
The nervous system's quick responses complement the endocrine system's longer-lasting effects. Understanding how these systems interact is crucial for grasping human physiology and the body's ability to adapt to various stimuli and maintain balance.
Nervous System Components
Structure and Function of Neurons
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- Neurons are the basic functional units of the nervous system that transmit electrical and chemical signals
- Consist of a cell body, dendrites (receive signals from other neurons), and an (transmits signals to other neurons or effector cells)
- Action potentials are electrical impulses that travel along the axon to the axon terminals where neurotransmitters are released
- , produced by Schwann cells, insulates the axon and increases the speed of propagation (multiple sclerosis)
Communication Between Neurons
- Synapses are the junctions between neurons where information is transmitted from one neuron to another
- Neurotransmitters are chemical messengers released from the presynaptic neuron that bind to receptors on the postsynaptic neuron
- Common neurotransmitters include acetylcholine (muscle contraction), dopamine (reward and motivation), and serotonin (mood regulation)
- Excitatory neurotransmitters (glutamate) increase the likelihood of an action potential in the postsynaptic neuron while inhibitory neurotransmitters (GABA) decrease it
Organization of the Nervous System
- (CNS) consists of the brain and spinal cord and integrates and processes information
- (PNS) consists of nerves that connect the CNS to the rest of the body and includes (carry information to the CNS) and (carry information from the CNS to effectors)
- Somatic nervous system is part of the PNS that controls voluntary movements (skeletal muscles) while the autonomic nervous system controls involuntary functions (heart rate, digestion)
- Sympathetic division of the autonomic nervous system prepares the body for "fight or flight" responses while the parasympathetic division promotes "rest and digest" functions
Endocrine System Components
Hormones and Their Functions
- Hormones are chemical messengers secreted by endocrine glands that travel through the bloodstream to target cells
- (testosterone, estrogen) are lipid-soluble and can pass through cell membranes to bind to intracellular receptors
- (, ) are water-soluble and bind to receptors on the cell surface to initiate signaling cascades
- Hormones regulate many physiological processes including growth and development, metabolism, and reproduction (menstrual cycle)
Major Endocrine Glands and Their Hormones
- is a region of the brain that produces releasing and inhibiting hormones that control the secretion of hormones from the
- Pituitary gland is the "master gland" that secretes hormones that regulate other endocrine glands (, , gonads)
- Thyroid gland produces thyroid hormones (T3 and T4) that regulate metabolism and calcitonin that regulates blood calcium levels
- Adrenal glands produce hormones such as (stress response) and (blood pressure regulation)
- Pancreas secretes insulin (lowers blood glucose) and (raises blood glucose) to maintain glucose homeostasis ()
Regulation of Hormone Secretion
- is a regulatory mechanism that maintains homeostasis by reducing the output of a system when it exceeds a set point
- In the hypothalamic-pituitary-thyroid axis, high levels of thyroid hormones inhibit the secretion of TRH from the hypothalamus and TSH from the pituitary gland
- is less common but occurs during childbirth when oxytocin stimulates uterine contractions, which in turn stimulate more oxytocin release
- Endocrine disorders can result from hyposecretion (hypothyroidism) or hypersecretion (hyperthyroidism) of hormones
Key Terms to Review (30)
Action Potential: An action potential is a rapid, temporary change in the electrical charge across a neuron's membrane that occurs when a neuron is activated. This process is crucial for transmitting signals along neurons and plays a vital role in the nervous system's communication, enabling the transfer of information through nerve impulses.
Adrenal glands: Adrenal glands are small, triangular-shaped glands located on top of each kidney, playing a crucial role in producing hormones that help regulate metabolism, immune response, blood pressure, and stress. These glands consist of two main parts: the outer adrenal cortex, which produces steroid hormones, and the inner adrenal medulla, which produces catecholamines such as adrenaline and noradrenaline. Their function is vital for maintaining homeostasis and responding to physiological stressors.
Aldosterone: Aldosterone is a steroid hormone produced by the adrenal glands that plays a crucial role in regulating blood pressure and electrolyte balance in the body. It primarily acts on the kidneys to promote sodium retention, potassium excretion, and water reabsorption, thereby influencing fluid balance and blood volume. This hormone is part of the renin-angiotensin-aldosterone system (RAAS), which is vital for maintaining homeostasis in response to changes in blood pressure and volume.
Axon: An axon is a long, slender projection of a neuron that conducts electrical impulses away from the neuron's cell body. It plays a crucial role in transmitting information throughout the nervous system, allowing communication between neurons and other target cells such as muscles or glands. The axon is often insulated by a myelin sheath, which enhances the speed of signal transmission.
Central nervous system: The central nervous system (CNS) is a critical part of the nervous system that comprises the brain and spinal cord, serving as the primary control center for processing information and coordinating actions throughout the body. It is responsible for integrating sensory information, generating responses, and regulating bodily functions. The CNS works closely with the peripheral nervous system to maintain homeostasis and facilitate communication between different parts of the body.
Cortisol: Cortisol is a steroid hormone produced by the adrenal glands, playing a crucial role in the body’s response to stress. It helps regulate various functions such as metabolism, immune response, and blood pressure. Often referred to as the 'stress hormone,' cortisol is released in higher amounts during stressful situations, influencing both physical and psychological responses.
Diabetes mellitus: Diabetes mellitus is a chronic metabolic disorder characterized by elevated blood glucose levels due to insufficient insulin production or the body's cells becoming resistant to insulin. This condition disrupts the body's ability to use glucose for energy, leading to various health complications over time. Diabetes mellitus encompasses two primary types: Type 1, where the pancreas produces little to no insulin, and Type 2, where the body cannot effectively use insulin, often linked to lifestyle factors.
Excitatory neurotransmitter: An excitatory neurotransmitter is a type of chemical messenger that promotes the generation of an electrical signal in a neuron, leading to the transmission of a nerve impulse. These neurotransmitters bind to receptors on the postsynaptic neuron, resulting in depolarization and making it more likely for that neuron to fire an action potential. This process is crucial for communication between neurons and plays a significant role in various physiological functions, including muscle contraction and cognitive processes.
Feedback loop: A feedback loop is a biological mechanism that helps maintain homeostasis by using information from the output of a process to regulate its own activity. In both the nervous and endocrine systems, feedback loops can be either negative, which counteracts a change, or positive, which enhances a change. This self-regulating system plays a crucial role in controlling various physiological processes.
Glucagon: Glucagon is a peptide hormone produced by the alpha cells of the pancreas that plays a crucial role in glucose metabolism. It works primarily to increase blood glucose levels by promoting glycogenolysis, the breakdown of glycogen to glucose in the liver, and gluconeogenesis, the formation of glucose from non-carbohydrate sources. This hormone acts as a counter-regulatory agent to insulin, maintaining energy homeostasis and ensuring that the body has a continuous supply of glucose during periods of fasting or low carbohydrate intake.
Growth hormone: Growth hormone, also known as somatotropin, is a peptide hormone produced by the anterior pituitary gland that plays a critical role in growth, metabolism, and overall body composition. It stimulates growth and cell reproduction in various tissues, promoting an increase in height during childhood and regulating body composition, muscle, and bone mass in adults. The function of growth hormone is closely tied to the endocrine system and has significant implications for health and development.
Hormones: Hormones are chemical messengers produced by glands in the endocrine system that regulate various physiological processes in the body, such as growth, metabolism, and mood. They travel through the bloodstream to target organs or cells, where they bind to specific receptors and initiate changes in cellular activity. Hormones play a crucial role in maintaining homeostasis and coordinating complex bodily functions.
Hypothalamus: The hypothalamus is a small but vital region of the brain located below the thalamus, playing a crucial role in maintaining homeostasis by regulating various autonomic functions. It connects the nervous and endocrine systems, controlling the release of hormones from the pituitary gland and influencing essential bodily processes like temperature regulation, hunger, thirst, and sleep cycles.
Inhibitory neurotransmitter: An inhibitory neurotransmitter is a chemical messenger that decreases the likelihood of a neuron firing an action potential by making the postsynaptic membrane more negatively charged. This process helps to regulate and balance excitatory signals within the nervous system, ensuring that neural communication remains coordinated and controlled.
Insulin: Insulin is a hormone produced by the pancreas that plays a crucial role in regulating blood glucose levels. It facilitates the uptake of glucose by cells, promoting its use as energy and storage as glycogen. This hormone is essential for maintaining metabolic homeostasis and is intricately linked to both active transport processes and the endocrine system's function.
Motor neurons: Motor neurons are specialized nerve cells that transmit signals from the central nervous system to muscles, facilitating movement and coordination. They play a crucial role in the functioning of both voluntary movements, like walking, and involuntary actions, such as reflexes. These neurons are essential for connecting the brain and spinal cord to muscles, allowing for the execution of motor functions throughout the body.
Myelin sheath: The myelin sheath is a protective covering made of lipid-rich substance that surrounds the axons of many neurons, facilitating faster transmission of electrical signals along the nerve fibers. This structure plays a critical role in enhancing the speed and efficiency of nerve impulse conduction by insulating the axon and allowing for saltatory conduction, where impulses jump between gaps known as nodes of Ranvier.
Negative feedback: Negative feedback is a process in biological systems that helps maintain homeostasis by counteracting changes in a controlled variable, leading to a decrease in the output of a system. This mechanism is crucial for regulating various physiological processes, ensuring that conditions remain stable despite external or internal fluctuations. By detecting changes and initiating responses that counteract those changes, negative feedback plays a key role in systems such as temperature regulation, hormonal balance, and ecological interactions.
Neuroplasticity: Neuroplasticity refers to the brain's ability to reorganize itself by forming new neural connections throughout life. This adaptability allows the brain to modify its structure and function in response to learning, experience, or injury. Neuroplasticity is a key mechanism underlying recovery from brain damage, skill acquisition, and even the development of habits, showcasing the dynamic nature of the nervous system.
Neurotransmitter: A neurotransmitter is a chemical messenger that transmits signals across synapses from one neuron to another or to other types of cells. These molecules play a critical role in communication within the nervous system, influencing a range of functions from muscle contraction to mood regulation.
Parkinson's Disease: Parkinson's disease is a progressive neurodegenerative disorder that primarily affects movement control due to the loss of dopamine-producing neurons in the brain. The condition leads to a range of motor symptoms, such as tremors, stiffness, and difficulty with balance and coordination. This disease highlights the intricate relationship between the nervous system and how neurodegeneration can significantly impact overall bodily functions.
Peptide hormones: Peptide hormones are short chains of amino acids that act as signaling molecules in the body, primarily regulating physiological processes such as growth, metabolism, and reproduction. They are synthesized in the endocrine glands and are released into the bloodstream to reach target organs, where they bind to specific receptors and initiate a response. These hormones play a crucial role in the communication between the nervous and endocrine systems, demonstrating how these two systems work together to maintain homeostasis.
Peripheral Nervous System: The peripheral nervous system (PNS) is a network of nerves that connects the central nervous system (CNS) to the rest of the body, allowing for communication between the brain, spinal cord, and peripheral organs. It plays a crucial role in transmitting sensory information to the CNS and relaying motor commands from the CNS to muscles and glands, facilitating bodily functions and responses to external stimuli.
Pituitary Gland: The pituitary gland is a small, pea-sized endocrine gland located at the base of the brain that plays a crucial role in regulating various bodily functions by secreting hormones. Often referred to as the 'master gland,' it influences other glands in the endocrine system, thus affecting growth, metabolism, and reproductive processes. The pituitary gland is divided into two main parts: the anterior pituitary and the posterior pituitary, each releasing different hormones that regulate distinct physiological activities.
Positive Feedback: Positive feedback is a process in which a change in a system causes further changes that amplify the original effect. This mechanism often leads to a rapid increase in output or activity, and it can be beneficial or detrimental depending on the context. It is important to understand how positive feedback loops can lead to significant changes within various biological and environmental systems.
Reflex Arc: A reflex arc is the neural pathway that mediates a reflex action, consisting of a sensory neuron, an interneuron (in some cases), and a motor neuron. This pathway allows for rapid responses to stimuli without requiring conscious thought, enabling quick reactions that are crucial for survival. Reflex arcs play an essential role in the nervous system by facilitating communication between the sensory input and motor output, often bypassing the brain for immediate action.
Sensory neurons: Sensory neurons are specialized nerve cells that transmit sensory information from sensory receptors to the central nervous system. They play a crucial role in how organisms perceive their environment, converting stimuli such as light, sound, and touch into electrical signals that the brain can interpret. These neurons help in processing external stimuli, allowing organisms to react and adapt to their surroundings.
Steroid hormones: Steroid hormones are a class of hormones derived from cholesterol that play critical roles in regulating various physiological processes in the body. These hormones are lipophilic, meaning they can easily pass through cell membranes to bind with specific receptors inside target cells, leading to changes in gene expression and cellular function. Common steroid hormones include cortisol, testosterone, and estrogen, which influence metabolism, immune response, and reproductive functions.
Synapse: A synapse is the junction between two neurons where communication occurs, allowing for the transmission of signals through chemical or electrical means. This critical connection is essential for the functioning of the nervous system, as it facilitates the propagation of nerve impulses and enables the coordination of bodily functions and responses to stimuli.
Thyroid gland: The thyroid gland is a butterfly-shaped endocrine gland located in the front of the neck that produces hormones essential for regulating metabolism, growth, and development. It plays a crucial role in maintaining the body's energy levels and is intricately linked to both the nervous and endocrine systems, affecting various bodily functions through hormone secretion.