HSSLIVE Plus One Zoology Chapter 11: Chemical Coordination and Integration Notes

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

1. Central Nervous System (CNS): Brain and spinal cord
2. 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

1. Structural Classification:
   • Multipolar: Multiple dendrites, one axon (most common)
   • Bipolar: One dendrite, one axon
   • Unipolar: Single process that divides into central and peripheral branches
2. 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

1. Electrical Synapses: Direct physical connection through gap junctions
2. 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

1. Action potential reaches presynaptic terminal
2. Voltage-gated calcium channels open, Ca²⁺ enters
3. Ca²⁺ causes synaptic vesicles to fuse with membrane
4. Neurotransmitters are released into synaptic cleft
5. Neurotransmitters bind to receptors on postsynaptic membrane
6. Postsynaptic membrane changes permeability (excitatory or inhibitory)
7. 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

1. 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
2. Midbrain:
   • Connects forebrain and hindbrain
   • Controls eye and head movements
   • Corpora Quadrigemina: Four rounded masses for visual and auditory reflexes
3. 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

Chapter 11: Chemical Coordination and Integration (550+ words)

Introduction to Endocrine System

The endocrine system consists of ductless glands that secrete hormones directly into the bloodstream. Hormones are chemical messengers that regulate physiological processes in the body.

Difference Between Nervous and Endocrine System

• Nervous System: Electrical signals, rapid action, short-term effects
• Endocrine System: Chemical signals, slower action, long-term effects

Hormones

• Definition: Chemical messengers produced by endocrine glands
• Chemical Nature:
  • Protein/Peptide Hormones: Water-soluble (insulin, growth hormone)
  • Steroid Hormones: Lipid-soluble (sex hormones, cortisol)
  • Amino Acid Derivatives: Modified amino acids (thyroxine, adrenaline)
• Mechanism of Action:
  • Protein Hormones: Bind to membrane receptors, activate second messengers
  • Steroid Hormones: Enter cells, bind to nuclear receptors, affect gene expression

Major Endocrine Glands and their Hormones

1. Hypothalamus

• Located in the brain, connects nervous and endocrine systems
• Hormones:
  • Releasing Hormones: Stimulate pituitary to release hormones
  • Inhibiting Hormones: Inhibit pituitary hormone release
  • Oxytocin: Uterine contraction, milk ejection
  • ADH (Vasopressin): Water reabsorption in kidneys

2. Pituitary Gland (Hypophysis)

• Small pea-sized gland located below hypothalamus
• “Master gland” as it controls many other endocrine glands
• Two lobes: Anterior (adenohypophysis) and Posterior (neurohypophysis)

Anterior Pituitary Hormones:

• Growth Hormone (GH): Stimulates growth of bones and muscles
• Prolactin (PRL): Stimulates milk production
• Thyroid-Stimulating Hormone (TSH): Stimulates thyroid gland
• Adrenocorticotropic Hormone (ACTH): Stimulates adrenal cortex
• Follicle-Stimulating Hormone (FSH): Stimulates gamete production
• Luteinizing Hormone (LH): Stimulates ovulation, testosterone production

Posterior Pituitary Hormones:

• Oxytocin: Produced in hypothalamus, released from posterior pituitary
• Antidiuretic Hormone (ADH/Vasopressin): Produced in hypothalamus, released from posterior pituitary

3. Pineal Gland

• Small gland in the brain
• Melatonin: Regulates sleep-wake cycle, influences reproductive functions

4. Thyroid Gland

• Butterfly-shaped gland in the neck
• Hormones:
  • Thyroxine (T₄) and Triiodothyronine (T₃): Regulate metabolism, growth, development
  • Calcitonin: Reduces blood calcium levels

5. Parathyroid Glands

• Four small glands embedded in thyroid
• Parathyroid Hormone (PTH): Increases blood calcium levels

6. Thymus Gland

• Located behind sternum
• Thymosin: Promotes T-lymphocyte development and immunity
• Largest in childhood, gradually reduces in size after puberty

7. Adrenal Glands

• Located on top of kidneys
• Two regions: Outer cortex and inner medulla

Adrenal Cortex Hormones:

• Glucocorticoids (Cortisol): Regulate metabolism, stress response
• Mineralocorticoids (Aldosterone): Regulate electrolyte balance
• Small amounts of Sex Hormones: Androgens, estrogens

Adrenal Medulla Hormones:

• Adrenaline (Epinephrine): “Fight or flight” hormone
• Noradrenaline (Norepinephrine): Similar to adrenaline, affects blood pressure

8. Pancreas

• Both endocrine and exocrine gland
• Endocrine part consists of Islets of Langerhans

Pancreatic Hormones:

• Insulin (β cells): Decreases blood glucose levels
• Glucagon (α cells): Increases blood glucose levels
• Somatostatin (δ cells): Inhibits insulin and glucagon release

9. Gonads (Sex Glands)

Testes (Male):

• Testosterone: Development of male secondary sexual characteristics, spermatogenesis

Ovaries (Female):

• Estrogen: Development of female secondary sexual characteristics, menstrual cycle
• Progesterone: Prepares uterus for implantation, maintains pregnancy

Mechanism of Hormone Action

Hormones with Cell Surface Receptors

1. Hormone binds to receptor on cell membrane
2. Activates second messenger system (e.g., cAMP)
3. Second messenger activates enzymes
4. Enzymes cause cellular response

Hormones with Intracellular Receptors

1. Hormone enters cell
2. Binds to receptor in cytoplasm or nucleus
3. Hormone-receptor complex binds to DNA
4. Affects gene expression, protein synthesis

Feedback Mechanisms

Feedback mechanisms regulate hormone secretion to maintain homeostasis.

Negative Feedback

• Most common type
• Increase in hormone effect leads to decrease in hormone production
• Example: Thyroid hormone regulation
  1. Low thyroid hormone levels stimulate hypothalamus to release TRH
  2. TRH stimulates pituitary to release TSH
  3. TSH stimulates thyroid to release thyroid hormones
  4. High thyroid hormone levels inhibit hypothalamus and pituitary

Positive Feedback

• Increase in hormone effect leads to further increase in hormone production
• Example: Oxytocin during childbirth
  1. Fetal pressure stimulates oxytocin release
  2. Oxytocin causes uterine contractions
  3. Contractions increase fetal pressure
  4. More oxytocin is released

Disorders of Endocrine System

1. Diabetes Mellitus

• Inadequate insulin action
• Types:
  • Type 1: Autoimmune destruction of β cells
  • Type 2: Insulin resistance or insufficient insulin
• Symptoms: Polyuria, polydipsia, polyphagia, hyperglycemia

2. Thyroid Disorders

• Hypothyroidism: Insufficient thyroid hormone
  • In infants: Cretinism (stunted growth, mental retardation)
  • In adults: Myxedema (lethargy, weight gain, cold intolerance)
• Hyperthyroidism: Excess thyroid hormone
  • Graves’ disease: Weight loss, nervous excitability, protruding eyes

3. Disorders of Adrenal Gland

• Addison’s Disease: Underproduction of adrenal hormones
• Cushing’s Syndrome: Overproduction of glucocorticoids

4. Growth Disorders

• Dwarfism: Insufficient growth hormone in childhood
• Gigantism: Excess growth hormone in childhood
• Acromegaly: Excess growth hormone in adulthood

Hormone Supplements and Therapy

• Insulin Therapy: For diabetes
• Hormone Replacement Therapy (HRT): For menopausal symptoms
• Growth Hormone Therapy: For growth hormone deficiency
• Thyroid Hormone Supplements: For hypothyroidism