ZOO: DSM-351 Practical
Unit 2: Histology
Table of Contents
1. Recording of Simple Muscle Twitch
A simple muscle twitch is a rapid, jerky response of a muscle to a single threshold stimulus. It is studied through electrical stimulation.
Phases of a Muscle Twitch
- Latent Period: The time between the application of the stimulus and the beginning of the contraction.
- Contraction Phase: Period of shortening and tension development in the muscle.
- Relaxation Phase: Period when the muscle returns to its original length as calcium ions are pumped back.
2. Study of Unconditioned Reflex Action (Knee Jerk)
The knee jerk reflex is a classic example of an unconditioned (innate), monosynaptic reflex arc.
Mechanism
- Striking the patellar tendon stretches the quadriceps muscle.
- Stretch receptors (muscle spindles) send an impulse via sensory neurons to the spinal cord.
- In the spinal cord, the sensory neuron synapses directly with a motor neuron.
- The motor neuron sends an impulse back to the quadriceps, causing it to contract and the leg to kick forward.
3. Study of Permanent Slides of Mammalian Tissues
This section involves the microscopic identification of various organ tissues based on their characteristic structural features.
A. Integumentary and Connective Tissues
- Mammalian Skin: Identified by layers of stratified squamous epithelium (epidermis) and dense irregular connective tissue (dermis) containing sweat glands and hair follicles.
- Cartilage (Hyaline): Clear, glassy matrix with chondrocytes located in lacunae.
- Bone (TS): Characterized by the Haversian System (osteons), concentric lamellae, and a central Haversian canal.
B. Nervous System Tissues
- Spinal Cord (TS): Butterfly-shaped inner gray matter surrounded by outer white matter; contains a central canal.
- Brain Tissue (Cerebrum/Cerebellum): Cerebellum is identified by the highly branched Purkinje cell layer.
C. Endocrine and Reproductive Tissues
| Slide Name | Key Identification Features |
|---|---|
| Pituitary | Divided into Pars Distalis (acidophils/basophils) and Pars Nervosa (pituicytes/nerve fibers). |
| Pancreas | Presence of Islets of Langerhans (lighter staining clusters) amidst dark-staining acini. |
| Testis | Numerous circular seminiferous tubules containing germ cells in various stages of spermatogenesis. |
| Ovary | Presence of follicles at different stages (primordial, primary, and mature Graafian follicles). |
| Adrenal Gland | Outer cortex (3 zones: Glomerulosa, Fasciculata, Reticularis) and inner medulla. |
| Thyroid | Numerous thyroid follicles filled with pink-staining colloid (thyroglobulin). |
Exam Focus: Identification Keys and Viva Questions
Exam Tip: When identifying the Spinal Cord vs. Brain, remember: In the Spinal Cord, gray matter is internal (butterfly shape). In the Brain (Cerebrum), gray matter is external (cortex).
Common Mistake: Do not confuse Hyaline Cartilage with Bone. Cartilage lacks the circular Haversian canals and calcified lamellae seen in bone tissue.
Frequently Asked Questions (FAQs)
- Q: What is the "Haversian Canal"?
A: It is the central canal in a bone osteon that contains blood vessels and nerves. - Q: What does the "colloid" in thyroid follicles represent?
A: It is the stored precursor of thyroid hormones (T3 and T4). - Q: Why is the knee jerk called a "monosynaptic" reflex?
A: Because there is only one synapse in the central nervous system between the sensory neuron and the motor neuron.