Q1: Explain the mechanism of generation of a nerve impulse (Action Potential).

Answer:

In a resting neuron, the outer side of the membrane is positively charged and the inner side is negatively charged. This happens because there is more Na+Na^+ outside and more K+K^+ inside, and the sodium-potassium pump keeps moving 3 Na+Na^+ out and 2 K+K^+ in.

When a proper stimulus is applied, the membrane at that point becomes highly permeable to Na+Na^+. Sodium ions quickly rush inside the neuron. Because of this, the polarity gets reversed and the inside becomes positive. This temporary reversal of charge is called the action potential or nerve impulse.

After this, the sodium channels close and the membrane becomes more permeable to K+K^+. Potassium ions move out of the cell, and the membrane returns to its original resting condition. This is called repolarization.

Key points:

  • Resting state = outside positive, inside negative
  • 3 Na+Na^+ out, 2 K+K^+ in by pump
  • Na+Na^+ influx causes depolarization
  • K+K^+ efflux causes repolarization.

Q2: Describe the transmission of an impulse across a chemical synapse.

Answer: When an electrical signal needs to jump from one neuron to the next, it uses a chemical bridge.

  1. Arrival: The electrical signal reaches the end of the first neuron (axon terminal).
  2. Release: This makes tiny bags called synaptic vesicles move to the edge, burst open, and dump chemicals called neurotransmitters into the gap (synaptic cleft).
  3. Binding: These chemicals float across the gap and lock into specific receptors on the next neuron's membrane.
  4. New Signal: This locking action opens up ion channels in the second neuron, sparking a brand new electrical signal to keep the message moving.

Q3: Differentiate between Myelinated and Non-myelinated nerve fibres.

Answer:

Feature Myelinated Fibre Non-myelinated Fibre
Insulation Wrapped in a thick myelin sheath made by Schwann cells. Also has Schwann cells wrapped around, but they do not produce a myelin sheath.
Nodes of Ranvier Present (these are the bare gaps between myelin). Absent (because there is no myelin to have gaps in).
Speed Very fast because the signal jumps from node to node (Saltatory Conduction). Slower because the signal has to travel continuously along the whole fibre.
Found in Cranial and Spinal nerves. Autonomic and Somatic neural systems.

Q4: What are the functions of the Hypothalamus?

Answer: The Hypothalamus is a tiny part at the base of the brain that acts as our ultimate survival control center. Its main jobs are:

  • Acting as the body's thermostat to regulate body temperature.
  • Giving us the urge to eat and drink (it contains our hunger and thirst centers).
  • Controlling the endocrine system by releasing neurosecretory hormones.
  • Working with the limbic system to regulate emotions (like pleasure or rage) and sexual behavior.

Q5: Distinguish between the Blind Spot and the Fovea.

Answer:

  • Blind Spot: This is the "exit door" at the back of the eye where the optic nerve leaves. It has absolutely no photoreceptors (zero rods or cones), meaning we can't see any image that lands there.
  • Fovea: This is a tiny pit right in the center of the yellowish macula lutea. It is packed exclusively with cones. It is the absolute "sweet spot" of the eye, giving us our sharpest and highest-resolution vision.

Q6: Explain the mechanism of hearing.

Answer:

  1. Sound waves enter the ear and make the Tympanic Membrane (eardrum) vibrate.
  2. The three little ear bones (Ossicles) amplify these vibrations and push them against the Oval Window of the inner ear.
  3. This pushing creates fluid waves inside the Cochlea (traveling through the perilymph and endolymph).
  4. The fluid waves cause the Basilar Membrane to ripple up and down.
  5. This rippling pushes the Hair Cells (our auditory receptors) up against a flap called the Tectorial Membrane, bending their tiny hairs.
  6. The bending triggers an electrical nerve impulse that travels via the auditory nerve to the brain, which translates it into the sound we hear.

Q7: What is Saltatory Conduction?

Answer: Saltatory conduction is the super-fast way nerve impulses travel down myelinated axons. Because the fatty myelin sheath acts like electrical insulation (blocking ions from moving in and out), the electrical signal can't travel smoothly along the whole wire. Instead, it literally "jumps" from one bare gap (Node of Ranvier) to the next. This skipping makes the signal travel much faster and saves the neuron a lot of energy.

Q8: List the components of the Brain Stem and their general function.

Answer: The Brain Stem is the stalk that connects the upper brain to the spinal cord.It consists of three parts:

  1. Midbrain
  2. Pons
  3. Medulla Oblongata Function: It is the autopilot of the body. It controls vital, involuntary, life-sustaining functions like our breathing rate, heart rate, blood pressure, and digestion.

Q9: Describe the structure and function of the Organ of Corti.

Answer: The Organ of Corti is our actual "hearing machine" located inside the cochlea.

  • Structure: It sits on top of the Basilar Membrane. It contains highly specialized Hair Cells that have tiny bristles (stereocilia) on top. Just above these hairs hangs a thin, elastic flap called the Tectorial Membrane.
  • Function: It acts as a transducer. When sound waves ripple the fluid and the basilar membrane, the hair cells are pushed against the tectorial membrane. The bending of the hairs converts physical sound vibrations into electrical nerve impulses.

Q10: What is the Limbic System and what is its role?

Answer: The Limbic System is often called the "emotional brain." It is a complex set of structures deep inside the inner parts of the cerebral hemispheres, including the Amygdala and Hippocampus. Role: Working very closely with the hypothalamus, it completely regulates our emotional reactions (like excitement, intense fear, pleasure, and rage), our motivation, and our sexual behavior.

Q11: Differentiate between Rods and Cones.

Answer:

Feature Rods Cones
Best for Seeing in the dark or dim light (Scotopic vision). Seeing clearly in bright daylight (Photopic vision).
Color Vision Cannot see colors (black and white only). Can see colors (Red, Green, Blue types).
Pigment Contain Rhodopsin (visual purple, made from Vitamin A). Contain Iodopsin (visual violet).
Location Spread out across the retina. Densely packed in the center, especially at the Fovea.

Q12: How is the Resting Membrane Potential maintained?

Answer: When a neuron is resting, it keeps its inside negatively charged compared to the outside. It does this in two main ways:

  1. The Pump: The Sodium-Potassium (Na+Na^+-K+K^+) pump uses energy to constantly throw 3 positive Sodium ions out for every 2 positive Potassium ions it brings in. This means a net loss of positive charge from the inside.
  2. Leaky Gates: The resting membrane is naturally much more permeable (leaky) to Potassium than Sodium. So, positively charged K+K^+ leaks out of the cell easily, leaving behind large negatively charged proteins inside.

Q13: What constitutes the Inner Ear (Labyrinth)?

Answer: The inner ear, or labyrinth, is a fluid-filled system made of two parts:

  • Bony Labyrinth: The hard, hollowed-out outer shell carved into the skull, filled with a fluid called Perilymph.
  • Membranous Labyrinth: A soft, continuous sac floating inside the perilymph, filled with its own fluid called Endolymph. Functionally, it is split into the Cochlea (the coiled part for hearing) and the Vestibular Apparatus (the semicircular canals and otolith organ, for maintaining body balance).

Q14: What are Meninges? Name the layers.

Answer: Meninges are the three protective, connective-tissue membranes that wrap around and cushion the brain and spinal cord. From the outside (closest to the skull) going in, the layers are:

  1. Dura Mater: The thick, tough, and durable outer layer.
  2. Arachnoid: The delicate, spider-web-like middle layer.
  3. Pia Mater: The thin, highly vascular inner layer that directly touches and hugs the grooves of the brain tissue.