HSSLIVE Plus One Zoology Chapter 10: Neural Control and Coordination Notes – Hsslive | Hsslive.co.in | Hss Live

The nervous system enables rapid coordination of body functions through electrical signaling. This chapter investigates the structure and function of neurons, the transmission of nerve impulses, and the organization of the human nervous system into central and peripheral components. It explores the processing of sensory information, integration in the brain and spinal cord, and motor responses. The chapter also examines specialized sense organs and how they convert different types of stimuli into neural signals that the brain can interpret.

Chapter 10: Neural Control and Coordination

Introduction to Neural System

The neural system is responsible for detecting, processing, and responding to stimuli. It coordinates various body functions through electrical signals (nerve impulses). Along with the endocrine system, it maintains homeostasis in the body.

Classification of Neural System

Central Nervous System (CNS): Brain and spinal cord
Peripheral Nervous System (PNS):
- Somatic Nervous System: Controls voluntary actions
- Autonomic Nervous System: Controls involuntary actions
  - Sympathetic Division: “Fight or flight” responses
  - Parasympathetic Division: “Rest and digest” responses

Neuron – Structural and Functional Unit

A neuron is a specialized cell designed to transmit information as electrical impulses.

Structure of a Neuron

Cell Body (Soma): Contains nucleus and cytoplasm with organelles
Dendrites: Short, branched projections that receive signals
Axon: Long projection that conducts impulses away from cell body
Myelin Sheath: Insulating layer around axon (formed by Schwann cells)
Nodes of Ranvier: Gaps in myelin sheath
Axon Terminals: End branches that release neurotransmitters

Types of Neurons

Structural Classification:
- Multipolar: Multiple dendrites, one axon (most common)
- Bipolar: One dendrite, one axon
- Unipolar: Single process that divides into central and peripheral branches
Functional Classification:
- Sensory/Afferent Neurons: Carry impulses from receptors to CNS
- Motor/Efferent Neurons: Carry impulses from CNS to effectors
- Interneurons/Association Neurons: Connect sensory and motor neurons

Nerve Impulse

A nerve impulse is an electrochemical signal that travels along the neuron.

Resting Membrane Potential

When a neuron is not transmitting signals, it maintains a resting potential
Inside of cell is negatively charged (-70 mV) compared to outside
Maintained by sodium-potassium pump (Na⁺-K⁺ pump)
Na⁺ concentration higher outside, K⁺ concentration higher inside

Action Potential

Stimulus causes sodium channels to open
Na⁺ rushes in, causing depolarization (inside becomes positive)
If threshold potential is reached (-55 mV), action potential is generated
After depolarization, K⁺ channels open, K⁺ moves out (repolarization)
Brief hyperpolarization occurs before returning to resting potential
All-or-none principle: Either full action potential or none at all

Conduction of Nerve Impulse

Continuous Conduction: In unmyelinated axons, impulse travels continuously
Saltatory Conduction: In myelinated axons, impulse jumps from one node of Ranvier to next
- Faster and more energy-efficient

Synapse

A synapse is a junction between two neurons where information is transmitted.

Types of Synapses

Electrical Synapses: Direct physical connection through gap junctions
Chemical Synapses: Communication via neurotransmitters (most common)

Structure of Chemical Synapse

Presynaptic Terminal: Contains synaptic vesicles with neurotransmitters
Synaptic Cleft: Gap between neurons
Postsynaptic Membrane: Contains receptors for neurotransmitters

Synaptic Transmission

Action potential reaches presynaptic terminal
Voltage-gated calcium channels open, Ca²⁺ enters
Ca²⁺ causes synaptic vesicles to fuse with membrane
Neurotransmitters are released into synaptic cleft
Neurotransmitters bind to receptors on postsynaptic membrane
Postsynaptic membrane changes permeability (excitatory or inhibitory)
Neurotransmitters are removed by:
- Enzymatic degradation
- Reuptake by presynaptic neuron
- Diffusion

Common Neurotransmitters

Acetylcholine: Muscle contraction, attention, arousal
Norepinephrine: Alertness, vigilance
Dopamine: Reward, pleasure, motor control
Serotonin: Mood, appetite, sleep
GABA (Gamma-Aminobutyric Acid): Inhibitory, reduces excitability
Glutamate: Excitatory, learning, memory

Human Brain

The brain is the control center of the body, weighing about 1.3-1.4 kg in adults.

Protection of Brain

Cranium: Bony covering
Meninges: Three membrane layers
- Dura mater: Outermost, tough layer
- Arachnoid: Middle layer with web-like structure
- Pia mater: Innermost, delicate layer
Cerebrospinal Fluid (CSF): Cushions brain, supplies nutrients, removes waste

Major Parts of Brain

Forebrain:
- Cerebrum: Largest part (70%)
  - Cerebral cortex (outer gray matter)
  - Inner white matter
  - Left and right hemispheres connected by corpus callosum
  - Lobes: Frontal, parietal, temporal, occipital
  - Functions: Voluntary actions, thought, memory, intelligence, language
- Diencephalon:
  - Thalamus: Relay center for sensory impulses
  - Hypothalamus: Regulates homeostasis, controls pituitary
  - Limbic System: Emotions, behavior, memory
Midbrain:
- Connects forebrain and hindbrain
- Controls eye and head movements
- Corpora Quadrigemina: Four rounded masses for visual and auditory reflexes
Hindbrain:
- Cerebellum: Coordinates muscular activities, maintains posture and balance
- Pons: Connects cerebellum with other brain regions, regulates breathing
- Medulla Oblongata: Controls involuntary functions (heart rate, breathing, blood pressure)

Spinal Cord

Long, cylindrical structure extending from medulla oblongata to lumbar region
Protected by vertebral column and meninges
Structure:
- H-shaped inner gray matter (cell bodies)
- Outer white matter (myelinated axons)
- Central canal filled with CSF

Reflex Action and Reflex Arc

Reflex Action: Automatic, involuntary response to stimulus
Reflex Arc: Neural pathway for reflex action
- Components:
  1. Receptor
  2. Sensory neuron
  3. Interneuron (in spinal cord)
  4. Motor neuron
  5. Effector (muscle or gland)
- Example: Knee-jerk reflex, withdrawal from painful stimulus

Sensory Reception and Processing

Eye (Vision)

Structure:
- Sclera: Protective outer layer
- Cornea: Transparent anterior portion
- Choroid: Middle vascular layer
- Retina: Inner layer with photoreceptors (rods and cones)
- Lens: Biconvex structure for focusing
- Iris: Colored portion that regulates light entry
- Pupil: Opening in iris
- Aqueous Humor: Fluid in anterior chamber
- Vitreous Humor: Gel-like substance in posterior chamber
Vision Process:
1. Light enters through cornea
2. Passes through pupil
3. Focused by lens onto retina
4. Photoreceptors convert light to nerve impulses
5. Optic nerve carries impulses to brain
6. Brain interprets image

Ear (Hearing and Balance)

Structure:
- External Ear: Pinna, auditory canal
- Middle Ear: Eardrum, ossicles (malleus, incus, stapes)
- Inner Ear: Cochlea (hearing), vestibule and semicircular canals (balance)
Hearing Process:
1. Sound waves collected by pinna
2. Waves vibrate eardrum
3. Ossicles amplify and transmit vibrations
4. Vibrations reach fluid in cochlea
5. Hair cells in organ of Corti convert vibrations to nerve impulses
6. Auditory nerve carries impulses to brain

Disorders of Nervous System

Alzheimer’s Disease: Progressive brain disorder affecting memory and thinking
Parkinson’s Disease: Degeneration of dopamine-producing neurons
Epilepsy: Recurrent seizures
Depression: Mood disorder with persistent sadness
Meningitis: Inflammation of meninges
Multiple Sclerosis: Autoimmune disease affecting myelin sheaths

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