Muscle and Nerve Experiments

Nerve and Muscle Experiments

• Experiments use the sciatic-gastrocnemius preparation.

Neuromuscular Transmission

• Arrival of action potential to presynaptic motor terminal triggers acetylcholine (ACh) release via exocytosis.
• ACh binds to nicotinic receptors on the motor end plate.
• Increased permeability to sodium (Na+) ions leads to the end-plate potential (EPP).
• Generation of an action potential (AP) in the adjacent areas of the muscle fiber.

Simple Muscle Twitch (SMT)

• Definition: A single contraction followed by relaxation due to a single stimulus.
• Stimulus: Single maximal stimulus applied indirectly (to the nerve).
• Principle: Stimulating the sciatic nerve with a single maximal stimulus causes a contraction followed by relaxation of the gastrocnemius muscle.

Phases of SMT

• Latent period (0.01 seconds): Events occur before contraction, including action potential propagation, synaptic delay and muscle fiber internal changes.
  • Propagation of action potential through the nerve fiber.
  • Synaptic delay at the neuromuscular junction.
  • Generation of action potential on sarcolemma.
  • Physical and chemical muscle changes (like actin and myosin sliding).
• Contraction phase (0.04 seconds): The muscle actively contracts
• Relaxation phase (0.05 seconds): The muscle passively relaxes after contraction.
• Total time of SMT = 0.1 seconds

Effect of Temperature on SMT

• Warming increases contraction speed and reduces the resistance to contraction. Warm muscles contract faster and relax quicker.
• Cooling slows the speed of contraction and increases resistance to contraction. Cold muscles contract more slowly and take longer to relax.
  • Increased viscosity during cooling means decreased resistance to contraction
  • Contraction/relaxation is faster with warmth

Effect of Fatigue on SMT

• Steps for the experiment
  • Record a Simple Muscle Twitch (SMT)
  • Apply 10 stimuli without recording; then record the next contraction
  • Repeat steps to gradually fatigue the muscle
  • Remove the electrodes from the nerve and stimulate the muscle directly
• Fatigue leads to a reduction of SMT amplitude (becoming weaker) and an increase in duration.

Effect of Several Successive Stimuli "Genesis of Tetanus"

• Steps to the experiment.
  • Set up the equipment like for a simple muscle twitch.
  • Stimulate muscle at a low frequency (e.g., 2/second) to get separate contractions.
  • Gradually increase the stimulation frequency (e.g., 5/second) to induce a staircasing contraction pattern called clonus.
  • Further increasing the stimulation frequency (e.g., 10/second) causes continuous contraction which is known as tetanus.

Observations on Tetanus

• Mechanical contractions can fuse to produce tetanus in the muscle, but the electrical response (action potentials) never fuses. Muscles typically contract by tetanic contractions which allow for sustainable work
• Tetanus is the more common method for muscle contraction in the body versus the SMT.

Staircase Phenomenon

• If skeletal muscle is stimulated rapidly and repeatedly as in a series of maximal stimuli(clonus, tetanus), during rest intervals to avoid fatigue each successive contraction usually increases in amplitude. This is due to increasing calcium (Ca2+) concentrations in the cytoplasm of the muscle fibers.

Effect of Temperature on Clonus and Tetanus

• Warming increases frequency of stimulation to achieve tetanus.
• Cooling increases frequency of stimulation to achieve clonus.

Compound Action Potential (CAP) and Nerve Conduction Velocity (NCV)

• Used to evaluate the conduction of electrical impulses through peripheral nerves.
• CAP represents the summed action potentials of many neurons in a nerve trunk.
• A CAP shows multiple peaks due to different types of nerve fibers having different conduction speeds.
• Nerve conduction velocity (NCV) is calculated by dividing the distance between stimulating and recording electrodes by the latency (time).
• NCV increases with larger nerve fiber diameter.
• NCV increases with myelination via saltatory conduction (jumping impulses from node to node along the axon).

Blood Composition

• Blood is made of plasma (55%) and cellular components (45%).
  • Plasma: liquid portion of blood, containing water, proteins, electrolytes, nutrients, and waste products.
  • Cellular components: Made up of red blood cells (erythrocytes, RBCs), white blood cells (leukocytes) and platelets.

Red Blood Corpuscles (RBCs)

• Non-nucleated biconcave discs.
• In adult males the number of RBCs is 5.4 million/mm3 , in females it is 4.8 million/mm3.

Hemoglobin (Hb)

• Red pigmented substance in RBCs that carries oxygen.
• Adult male Hb: 15-16 g/dL, females 13-14 g/dL. Newborns have 19 g/dL.

Hematocrit (PCV)

• Percentage of RBCs in blood
• Male: 46 +/- 6%, Female: 42 +/-6%.

Blood Indices

• Mean corpuscular volume (MCV): Average volume of a single RBC. Normal range: 80-95 μm³
• Mean corpuscular hemoglobin (MCH): Average amount of hemoglobin in a single RBC. Normal range: 25-32 pg.
• Mean corpuscular hemoglobin concentration (MCHC): Concentration of hemoglobin per unit volume of RBCs. Normal range: 32-38 g/dL.

Anemia

• Decrease in oxygen-carrying capacity of blood (due to RBC or hemoglobin deficiency).
• Symptoms: dizziness, headache, growth problems(children), shortness of breath, pale or yellow skin, cold extremities, tiredness, tachycardia (fast heart rate).

Classification and Causes of Anemia

• Normocytic normochromic anemia: Normal sized and coloured RBC, but decreased number.
• Microcytic hypochromic anemia: Smaller than normal and paler RBCs, due to iron deficiency.
• Macrocytic hyperchromic anemia: Larger than normal RBCs with more hemoglobin, usually due to vitamin B12 or folic acid deficiency.

Causes of Anemia

• Acute blood loss (hemorrhagic anemia).
• Bone marrow depression (aplastic anemia), such as that caused from exposure to radiation or certain medications.
• Excessive breakdown of RBCs (hemolytic anemia), such as from infections, chemicals, incompatible blood transfusions or snake venom.

Blood Grouping

• Importance: Prior to blood transfusion, blood grouping and cross matching is essential.

• Principle: Red blood cells (RBCs) have antigens (agglutinogens) attached to their membrane and the plasma contains antibodies (agglutinins) to recognize these antigens.

• The antibodies and antigen reaction determines the blood type (O, A, B or AB).

• Anti-A

• Anti-B

• Anti-D

Rh Factor

• An antigen on RBCs, presence of Rh antigens on cells designates a person as Rh-positive.
• Absence of Rh antigens on cells means a person is Rh-negative.
• Rh incompatibility can result from a Rh-negative mother carrying an Rh-positive fetus. This condition is called erythroblastosis foetalis where the mother's antibodies attack the fetal RBCs.

Blood Transfusion

• Indications: Restore whole blood lost in hemorrhage, replace a specific component (e.g., RBCs, platelets), or treat erythroblastosis foetalis.
• Precautions: Blood must be compatible between donor and recipient using cross matching. Recipient must be Rh-negative or receiving Rh- negative blood. Must be free from bloodborne diseases and contamination and good quality with sufficient hemoglobin (Hb).

Complications of Blood Transfusion

• Agglutination: Blocks capillaries producing backache, joint, and angina pain if coronary arteries occluded.
• Hemolysis: Rupture of RBCs causing hemoglobin increase resulting in blood viscosity increase which is then associated with heart failure, jaundice, renal failure and hypoxia. Other toxic substances such as histamine may also be released causing vasodilation, hypotension, and shock.
• Physical (overload): Excessive transfusion.
• Infective: Infectious hepatitis, AIDS, malaria, others.
• Mechanical: Air embolism.

Hemostasis

• Definition: Stoppage of bleeding from injured blood vessels. This involves the assessment of vascular spasm and platelet function in the first and second stages of hemostasis.
• Materials for the bleeding time experiment: Lancets, a stopwatch, cotton swabs, alcohol and filter paper.
• Normal bleeding time = 1 to 3 minutes. Prolonged bleeding time may indicate a coagulation disorder.
• Purpura: Purple colored spots appear on the skin or mucous membranes.

Coagulation Time

• Definition: Time needed for a blood clot to form, involving stages after vascular spasm and platelet function to the intrinsic coagulation pathways to form a fibrin clot.
• Materials: Used in this experiment are lancets, a stop watch, cotton swaps, alcohol wipes, and a non-heparinized capillary tube.
• Normal coagulation time = 3–9 minutes. Prolonged clotting time may indicate a deficiency of clotting factors like vitamin K or clotting factors VIII, IX, or XI.

This quiz focuses on the principles of neuromuscular transmission and muscle contraction, specifically through experiments with the sciatic-gastrocnemius preparation. It covers the process of action potentials, neurotransmitter release, and the phases of a simple muscle twitch. Test your understanding of these fundamental physiological concepts.