Neurophysiology and Nerve Excitability

The rapid influx of sodium ions (Na+) into the nerve cell through voltage-gated sodium channels, causing the inside of the cell to become more positive. This is the key event that initiates the nerve impulse.

A process that moves molecules across a membrane against their concentration gradient, requiring energy. The sodium-potassium pump utilizes ATP to pump sodium out and potassium into the cell.

The most vulnerable nerve fibers to oxygen deprivation, due to their smaller size and slower conduction velocity. These fibers are responsible for transmitting pain, temperature, and autonomic functions.

An increase in the excitability of a nerve cell, making it more likely to fire an action potential. This can be achieved by increasing the membrane potential, making it closer to the threshold for firing.

Active transport is a process that moves molecules across a membrane against their concentration gradient, requiring energy. Its rate is limited by the number of available carriers.

Insulin administration leads to a decrease in extracellular potassium levels. Insulin promotes the uptake of potassium into cells, reducing its concentration in the blood.

Sympathetic nervous system stimulation causes bronchodilation, widening of the airways. This is important for increasing airflow during physical activity or stress.

Nicotinic action refers to the action of acetylcholine at nicotinic receptors. These receptors are found in autonomic ganglia, where they mediate the transmission of nerve impulses from preganglionic to postganglionic neurons.

The process of creating proteins from amino acids using instructions encoded in DNA.

The secretion of calcitonin is a function of the thyroid gland.

Cretinism is a developmental disorder caused by a lack of or deficiency in thyroxine.

Addison's disease is a disorder of the adrenal glands characterized by hyperpigmentation of the skin.

The Hering-Breuer reflex is a protective mechanism that prevents overinflation of the lungs.

A peripheral chemoreceptor responsible for detecting changes in blood oxygen levels.

Sympathetic preganglionic neurons originate in the thoracolumbar region of the spinal cord.

Arterioles are the smallest arteries and are responsible for regulating blood flow to individual organs.

Aldosterone, a hormone that regulates electrolyte balance, primarily acts on the distal tubule of the nephron, influencing sodium reabsorption and potassium excretion.

The stretch reflex, a monosynaptic reflex, involves a direct connection between a sensory neuron and a motor neuron, causing a rapid and involuntary muscle contraction in response to muscle stretching.

The Babinski sign, characterized by dorsiflexion of the big toe and fanning out of other toes, is a normal neurological finding in newborns during the first month due to the incomplete myelination of the corticospinal tract.

The primary motor area, located in Brodmann area 4, is responsible for initiating and controlling voluntary movements.

The fingers are represented by a large area on the motor cortex, highlighting the fine motor control needed for intricate finger movements.

The rubrospinal tract, a descending motor pathway, is often referred to as the lateral motor system, playing a role in fine motor control and coordination.

Intrinsic factor, a protein essential for vitamin B12 absorption, is secreted by parietal cells in the stomach. A gastrectomy, the removal of the stomach, would impair intrinsic factor production.

Blocking parasympathetic activity would lead to tachycardia, an increase in heart rate, as the parasympathetic nervous system normally slows down the heart rate.

The process of transmitting an action potential along myelinated nerve fibers. The signal jumps between the gaps in the myelin sheath, known as the nodes of Ranvier, making it faster than conduction in unmyelinated fibers.

The increase in the rate and depth of breathing is triggered by a rise in carbon dioxide (CO2) levels in the blood.

This type of hypoxia occurs when cells are unable to use oxygen efficiently, even though sufficient oxygen is available. This can be due to toxins or poisoning.

The maximum pressure exerted in the arteries during the contraction (systole) of the heart, when blood is ejected from the heart.

The movement of water from an area of low solute concentration (diluted) to an area of high solute concentration (concentrated) across a semi-permeable membrane.

This is a mechanism used by the body to conserve heat in cold weather. The blood vessels in the skin constrict, reducing blood flow to the surface.

During inspiration, the pressure inside the alveoli (air sacs in the lungs) becomes lower than the atmospheric pressure because of the movement of air into the lungs, creating a pressure gradient.

Extracellular fluid (ECF) is made up of two components: plasma, the fluid part of blood, and interstitial fluid, which is the fluid between cells.

An increase in the depth and rate of ventilation leads to an increase in the amount of carbon dioxide (CO2) in the body. This is because ventilation is the process of moving air in and out of the lungs, which helps to exchange oxygen and carbon dioxide between the body and the environment. When ventilation increases, more carbon dioxide is exhaled, reducing the amount of carbon dioxide in the blood.

Cardiac output refers to the amount of blood pumped by the heart per minute. It is calculated by multiplying the stroke volume (the amount of blood pumped with each heartbeat) by the heart rate (the number of heartbeats per minute).

Sympathetic stimulation increases cardiac output by increasing both heart rate and stroke volume. The sympathetic nervous system is part of the autonomic nervous system, which controls involuntary functions like heart rate and blood pressure. When the sympathetic nervous system is activated, it releases hormones that cause the heart to beat faster and stronger, increasing cardiac output.

Pulmonary ventilation refers to the total volume of air moved in and out of the lungs per minute. It is calculated by multiplying the tidal volume (the volume of air inhaled or exhaled in each breath) by the respiratory rate (the number of breaths per minute).

Expiration in normal resting conditions is achieved by the passive recoil of the lungs. The lungs have a tendency to naturally spring back to their resting position after inhalation. This recoil generates an outward force that pushes air out of the lungs.

Peripheral chemoreceptors are specialized sensory receptors located in the carotid arteries and aortic arch. They detect changes in the partial pressure of oxygen (PO2) in the blood and send signals to the brain to regulate breathing. A decrease in PO2 stimulates these receptors, leading to an increase in ventilation to restore normal oxygen levels.

Secondary active transport is a process that uses the energy stored in the concentration gradient of one molecule to move another molecule across a membrane. Glucose transport in the intestine and renal tubules is an example of secondary active transport, where the energy from the sodium gradient is used to transport glucose against its concentration gradient.

Atropine is a drug that blocks the action of acetylcholine, a neurotransmitter. Acetylcholine is involved in various physiological processes, including muscle contraction, glandular secretion, and heart rate regulation. Atropine's effect on the intestinal wall is to relax it by blocking the action of acetylcholine on the smooth muscle cells.

The intrinsic pathway of blood clotting is initiated by Factor 12, also known as Hageman factor. This pathway is triggered by exposure to certain negatively charged surfaces like collagen, which are present when blood vessels are damaged.

Sympathetic stimulation causes relaxation of the smooth muscles in the walls of the gastrointestinal (GI) tract, while simultaneously contracting the sphincter muscles. This allows for the redirection of blood flow away from the digestive system and towards skeletal muscles and other organs during times of stress.

Hypertonic solutions, like 3% saline, are used for cerebral edema because they draw water from the brain tissue into the bloodstream. By increasing the osmotic pressure of the blood, water moves out of the swollen brain cells, reducing the pressure and protecting brain tissue.

T-lymphocytes (T cells) are a type of white blood cell that plays a crucial role in immune response. They identify and attack foreign cells, including those from transplanted organs, leading to organ rejection.

The cardiac cycle is the duration of one complete heartbeat, encompassing the contraction and relaxation phases of the heart. It's calculated by dividing 60 by the heart rate, expressed in beats per minute.

Cardiac output represents the amount of blood pumped by the heart in one minute. It is calculated by multiplying the stroke volume (blood pumped with each beat) with the heart rate.

The aortic arch functions as a baroreceptor, a specialized sensor that monitors blood pressure. It detects changes in pressure and signals the nervous system to adjust heart rate and blood vessel constriction or dilation, effectively regulating blood pressure.

Chemoreceptors are sensitive to changes in blood chemistry, including oxygen levels. When arterial blood pressure falls below 80 mmHg, these chemoreceptors are stimulated, triggering a response to increase heart rate and blood pressure to maintain oxygen supply.

Potassium (K+) is the major cation (positively charged ion) found inside cells (intracellular fluid). This is because potassium plays a critical role in cellular processes such as nerve impulses and muscle contractions.

Glucose is a large molecule that cannot passively pass through cell membranes. Therefore, it utilizes facilitated diffusion, a process that uses membrane proteins as carriers to move glucose across the membrane following its concentration gradient from high to low.

The sympathetic nervous system is responsible for the 'fight-or-flight' response. It releases noradrenaline (also known as norepinephrine) as its primary neurotransmitter, which causes increased heart rate, dilated pupils, and other physiological changes associated with stress.

The parasympathetic nervous system is responsible for the 'rest-and-digest' functions. It originates in the brain stem and sacral region, and has short preganglionic fibers. Its main neurotransmitter is acetylcholine.

Total peripheral resistance (TPR) is the overall resistance to blood flow in the systemic circulation. It is mainly influenced by the radius of the arterioles. When arterioles constrict, TPR increases; when they dilate, TPR decreases.