Exam 3 Study Guide: Reflexes, Muscles, Cardiovascular and Respiratory Physiology

Reflexes

Monosynaptic vs. Polysynaptic Reflexes

Reflexes are rapid, involuntary responses to stimuli. They are classified based on the number of synapses between sensory and motor neurons.

• Monosynaptic Reflex: Involves a single synapse between a sensory neuron and a motor neuron. Example: The patellar (knee-jerk) reflex.

• Polysynaptic Reflex: Involves one or more interneurons and multiple synapses. Example: Withdrawal reflex.

• Example: The stretch reflex is monosynaptic, while the flexor withdrawal reflex is polysynaptic.

Names and Operation of Reflexes

• Patellar Reflex: Monosynaptic; causes leg extension when the patellar tendon is tapped.

• Withdrawal Reflex: Polysynaptic; causes withdrawal from painful stimuli.

• Crossed Extensor Reflex: Polysynaptic; supports body weight when the opposite limb withdraws.

Muscle Physiology

Muscle Relaxation

Muscle relaxation occurs when calcium ions are pumped back into the sarcoplasmic reticulum, stopping contraction.

• Key Point: ATP is required for both contraction and relaxation.

• Key Point: Removal of acetylcholine from the synaptic cleft ends stimulation.

Cardiovascular Anatomy & Physiology

Anatomy of the Heart

The heart is a muscular organ with four chambers: two atria and two ventricles.

• Key Point: The heart is located in the thoracic cavity, specifically the mediastinum.

• Key Point: Major structures include the atria, ventricles, septa, and valves.

Heart Valves and Their Function

• Atrioventricular Valves: Tricuspid (right) and bicuspid/mitral (left); prevent backflow into atria.

• Semilunar Valves: Pulmonary and aortic; prevent backflow into ventricles.

Propagation of Action Potentials in the Heart

Action potentials originate in the sinoatrial (SA) node and spread through the atria, then to the atrioventricular (AV) node, bundle of His, bundle branches, and Purkinje fibers.

• Key Point: This sequence ensures coordinated contraction.

Poiseuille’s Law of Resistance

Describes resistance to blood flow in vessels:

• Formula:

$R = \frac{8 \eta L}{\pi r^4}$

• Variables: $R$ = resistance, $\eta$ = viscosity, $L$ = length, $r$ = radius.

• Key Point: Small changes in vessel radius greatly affect resistance.

Heartbeat Sounds

• First Sound ("lub"): Closure of AV valves.

• Second Sound ("dub"): Closure of semilunar valves.

Response Loop

The response loop is a feedback mechanism involving stimulus, sensor, input signal, integrating center, output signal, target, and response.

Blood Flow Through Arterioles

• Key Point: Vasoconstriction decreases blood flow; vasodilation increases blood flow.

• Mechanisms: Controlled by smooth muscle contraction and relaxation.

Mechanoreceptors Detecting Blood Pressure

• Baroreceptors: Located in the carotid sinus and aortic arch; detect changes in blood pressure.

Vessels with Slowest Blood Flow

• Capillaries: Have the slowest flow rate due to their large total cross-sectional area, allowing for efficient exchange.

Colloid Pressure

Colloid osmotic pressure is the pressure exerted by plasma proteins, mainly albumin, that draws water into the blood vessels.

• Importance: Maintains fluid balance between blood and tissues.

Blood Cells and Hematology

Blood Cells: Names, Functions, and Origin

Cell Type	Function	Origin
Red Blood Cells (Erythrocytes)	Transport oxygen and carbon dioxide	Bone marrow
White Blood Cells (Leukocytes)	Immune defense	Bone marrow
Platelets (Thrombocytes)	Blood clotting	Bone marrow

Hemoglobin and Iron Source

• Key Point: Iron for hemoglobin is obtained from dietary sources and recycled from old red blood cells.

Hemophilia

• Definition: Genetic disorder affecting blood clotting.

• Inheritance: Usually X-linked recessive.

Respiratory Anatomy & Physiology

Anatomy and Location of the Lungs

• Key Point: Lungs are located in the thoracic cavity, flanking the heart.

• Structure: Each lung has lobes, bronchi, bronchioles, and alveoli.

Muscles Associated with the Lungs

• Primary Muscle: Diaphragm

• Accessory Muscles: Intercostal muscles, sternocleidomastoid, scalenes

Bronchi Dilation and Constriction

• Dilation: Increases airflow and oxygen delivery.

• Constriction: Decreases airflow, can cause conditions like asthma.

Partial Pressures and Gas Exchange

Gas exchange depends on differences in partial pressures across membranes.

• Key Point: Oxygen diffuses from high partial pressure in alveoli to low in blood; CO2 diffuses from high in blood to low in alveoli.

• Formula:

$\text{Gas moves from high to low partial pressure}$

• Example: Proper gas exchange requires maintained gradients.

CO2 Transport in Blood

• Dissolved in plasma

• Bound to hemoglobin

• As bicarbonate ion: $\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3 \rightarrow \text{H}^+ + \text{HCO}_3^-$

Source of CO2 in the Body

• Key Point: CO2 is produced as a byproduct of cellular metabolism, especially during aerobic respiration.

Control of Rhythmic Breathing

• Medulla Oblongata: Main control center for rhythmic breathing.

• Pons: Modulates breathing patterns.

Hypoxia vs. Hypercapnia

• Hypoxia: Low oxygen levels in tissues.

• Hypercapnia: Elevated carbon dioxide levels in blood.

Types of Hypoxia

• Hypoxic Hypoxia: Low arterial PO2

• Anemic Hypoxia: Low O2 carrying capacity

• Ischemic Hypoxia: Reduced blood flow

• Histotoxic Hypoxia: Cells unable to use O2

Receptors for Partial Pressure Detection

• Peripheral Chemoreceptors: Located in carotid and aortic bodies; detect changes in PO2, PCO2, and pH.

• Central Chemoreceptors: Located in the medulla; primarily detect changes in PCO2 and pH.