krit.club logo

Human Physiology - Neural Control and Coordination (Neuron, CNS, PNS, Reflex Action, Sense Organs)

Grade 11ICSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

The Neuron: Comprises the cell body (CytonCyton), DendritesDendrites, and AxonAxon. Myelinated neurons have Nodes of RanvierNodes\ of\ Ranvier for saltatory conduction.

•

Nerve Impulse: Generation of action potential involves Na+Na^+ influx (depolarization) and K+K^+ efflux (repolarization).

•

Resting Potential: The membrane is polarized at approximately −70 mV-70\ mV due to the Na+/K+Na^+/K^+ pump and leaky channels.

•

Synaptic Transmission: Chemical transmission via neurotransmitters (e.g., AcetylcholineAcetylcholine) across the synaptic cleft from pre-synaptic to post-synaptic membranes.

•

Central Nervous System (CNS): Includes the Brain (Cerebrum for intelligence, Cerebellum for balance, Medulla for involuntary actions) and the Spinal Cord.

•

Peripheral Nervous System (PNS): Consists of Cranial nerves (12 pairs12\ pairs) and Spinal nerves (31 pairs31\ pairs). Divided into Somatic and Autonomic Nervous Systems.

•

Autonomic Nervous System (ANS): Comprises the Sympathetic (fight or flightfight\ or\ flight) and Parasympathetic (rest and digestrest\ and\ digest) systems.

•

Reflex Action: An involuntary response to a stimulus mediated by the reflex arc: Receptor→Receptor \rightarrow Sensory Neuron→Sensory\ Neuron \rightarrow Interneuron (Spinal Cord)→Interneuron\ (Spinal\ Cord) \rightarrow Motor Neuron→Motor\ Neuron \rightarrow EffectorEffector.

•

The Eye: Structure includes ScleraSclera, ChoroidChoroid, and RetinaRetina. The RetinaRetina contains photoreceptors: RodsRods (twilight vision/rhodopsin) and ConesCones (daylight/color vision/iodopsin).

•

The Ear: Outer ear collects sound, middle ear (ossicles: MalleusMalleus, IncusIncus, StapesStapes) amplifies it, and inner ear (CochleaCochlea) converts it to electrical signals. The Vestibular apparatusVestibular\ apparatus maintains body equilibrium.

📐Formulae

Vrest≈−70 mVV_{rest} \approx -70\ mV

Vthreshold≈−55 mVV_{threshold} \approx -55\ mV

3 Naout+:2 Kin+ (Sodium-Potassium Pump Ratio)3\ Na^+_{out} : 2\ K^+_{in} \text{ (Sodium-Potassium Pump Ratio)}

Action Potential Peak≈+30 mV to +40 mV\text{Action Potential Peak} \approx +30\ mV \text{ to } +40\ mV

💡Examples

Problem 1:

Calculate the net charge movement across the axonal membrane when the Na+/K+Na^+/K^+ pump completes 5 cycles.

Solution:

In one cycle, 3 Na+3\ Na^+ ions are pumped out and 2 K+2\ K^+ ions are pumped in. Net change per cycle = +1+1 charge outside. For 5 cycles: 5×(+1)=+55 \times (+1) = +5 net positive charges moved to the extracellular fluid (ECFECF).

Explanation:

The active transport mechanism maintains the resting potential by creating a concentration gradient where the exterior is more positive than the interior.

Problem 2:

A person accidentally steps on a sharp nail and immediately pulls their foot away. Trace the path of this reflex.

Solution:

Nociceptor (Pain receptor)→Nociceptor\ (Pain\ receptor) \rightarrow Sensory Neuron (Afferent)→Sensory\ Neuron\ (Afferent) \rightarrow Dorsal Root Ganglion→Dorsal\ Root\ Ganglion \rightarrow Spinal Cord (Grey matter)→Spinal\ Cord\ (Grey\ matter) \rightarrow Motor Neuron (Efferent)→Motor\ Neuron\ (Efferent) \rightarrow Skeletal Muscle (Effector)Skeletal\ Muscle\ (Effector).

Explanation:

This is a spinal reflex action that bypasses the conscious brain for an immediate response to prevent tissue damage.

Problem 3:

Explain why vision is sharpest at the Fovea centralisFovea\ centralis.

Solution:

The FoveaFovea is a thinned-out portion of the retina where only ConesCones are densely packed and the overlying layers of neurons are displaced.

Explanation:

Because each cone in the fovea often has a 1:11:1 ratio with bipolar and ganglion cells, visual acuity (resolution) is maximized at this point (Macula luteaMacula\ lutea).

Neural Control and Coordination (Neuron, CNS, PNS, Reflex Action, Sense Organs) Revision - Class…