ZOO: DSM-351 Practical
Unit 2: Histology
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.
[Image of the knee jerk reflex arc diagram]
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
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.