💪 Muscular and Nervous Tissues
Muscular tissue and nervous tissue are called excitable tissues because they respond to stimuli.
- Muscular tissue responds by contracting (shortening) → produces force and movement.
- Nervous tissue responds by generating and conducting nerve impulses → control and coordination.
✅ Key Idea: Muscle = movement, Nerve = message/impulse.
🦾 1️⃣ Muscular Tissue
Muscular tissue is made of elongated cells called muscle fibres (myocytes). These fibres contain myofibrils made of two main contractile proteins:
- Actin (thin filaments)
- Myosin (thick filaments)
⭐ Key properties
- Excitability (irritability): responds to stimulus
- Contractility: shortens to produce force
- Extensibility: can be stretched
- Elasticity: returns to original length
✅ Types of muscular tissue
We classify muscles based on three factors: Structure (Striations), Control (Voluntary/Involuntary), and Location.
| Feature | Skeletal Muscle | Smooth Muscle | Cardiac Muscle |
|---|---|---|---|
| Appearance | Striated (Striped light & dark bands). Cylindrical, long, unbranched. | Non-striated (Smooth). Spindle-shaped (tapered ends). | Striated. Cylindrical but branched. |
| Nucleus | Multinucleated (Syncytium). Nuclei are peripheral. | Uninucleated (Single nucleus). Central nucleus. | Uninucleated. Central nucleus. |
| Control | Voluntary (You control them). | Involuntary (Automatic). | Involuntary (Automatic). |
| Location | Attached to skeleton (Biceps, Triceps). | Walls of hollow internal organs (Stomach, Intestine, Blood vessels). | Wall of the Heart only. |
| Function | Locomotion, body posture. | Moving food (peristalsis), regulating blood flow. | Pumping blood rhythmically. |
| Special Feature | Fatigue easily. | Do not fatigue easily. | Intercalated Discs (Communication junctions). Never fatigues. |
🧩 Why cardiac muscle works as a unit
Cardiac muscle cells are connected by intercalated discs. These contain:
- Desmosomes → strong mechanical attachment (cells don’t separate)
- Gap junctions → electrical coupling (impulse spreads fast)
So the heart behaves like a functional syncytium (works like one unit).
⚡ 2️⃣ Nervous Tissue
Nervous tissue is specialized for communication and control. It has two main cell types:
- Neurons → excitable cells that generate and conduct impulses
- Neuroglia (glial cells) → supporting cells (nutrition, protection, insulation, repair support)
👉 Neuroglia are more numerous than neurons and form a large part of neural tissue.
✅ Structure of a neuron
A neuron typically has:
- Cell body (Cyton): contains nucleus and cytoplasm
- Nissl bodies (RER) are present here → protein synthesis
- Dendrites: short, branched → receive signals towards cell body
- Axon: single long process → carries impulse away from cell body
- Myelin sheath (in many neurons) insulates axon and increases speed
- Nodes of Ranvier (gaps in myelin) help rapid conduction (saltatory conduction)
👉 Nissl bodies are absent in the axon.
🔌 Synapse (connection between neurons)
A synapse is the functional junction between:
- axon terminal of one neuron and dendrite/cell body of another neuron (or a muscle/gland)
In most synapses, impulse is transmitted using neurotransmitters (chemical synapse).
🧠 Comparison (Quick Revision)
| Feature | Muscular Tissue | Nervous Tissue |
|---|---|---|
| Main job | Movement | Control & communication |
| Functional unit | Muscle fibre | Neuron |
| Response to stimulus | Contraction | Nerve impulse conduction |
| Key proteins/structures | Actin, myosin | Nissl bodies, axon, synapse |
👉 Exam Tip: If question mentions intercalated discs → Cardiac muscle. If mentions Nissl bodies → Neuron (cyton/dendrites).
💡 Questions and Answers
Q1. What are intercalated discs and why are they important?
A1.
Intercalated discs are special junctions between cardiac muscle cells. They keep cells tightly attached and also allow electrical signals to pass quickly from one cell to another. Because of this, the heart muscles contract in a coordinated and rhythmic manner.
Q2. Which muscle is voluntary and multinucleated? Give a reason.
A2.
Skeletal (striated) muscle is voluntary and multinucleated. It is voluntary because it works under our control (like moving arms/legs). It is multinucleated because each muscle fibre is formed by fusion of many cells during development.
Q3. What are Nissl bodies? Where are they present and absent?
A3.
Nissl bodies are granular structures made of rough endoplasmic reticulum (RER). They help in protein synthesis needed for neuron function and repair. They are present in the cell body (cyton) and dendrites, but absent in the axon.
Q4. Differentiate between dendrites and axon (any three points).
A4.
- Dendrites are short, branched and usually many; axon is usually single and long.
- Dendrites carry impulses towards the cell body; axon carries impulses away from the cell body.
- Dendrites commonly have Nissl bodies; axon does not.
Q5. Why do smooth muscles work slowly but for a long time (like in intestine)?
A5.
Smooth muscles contract slowly and steadily and are controlled involuntarily. This is perfect for organs like the intestine and blood vessels because they need continuous movements (like peristalsis) without getting tired quickly.