science olympiad

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Central Nervous System

Brain & spinal cord

Peripheral Nervous System

Everything else outside CNS

Role of the CNS

Integration, processing, decision‑making; sends commands to the PNS

Components of the PNS

Cranial nerves (12 pairs), spinal nerves (31 pairs), ganglia, and sensory & motor pathways

Functional subdivisions of the PNS

Afferent (sensory) division and Efferent (motor) division

Afferent (sensory) division

Carries information from receptors toward the CNS

Efferent (motor) division

Carries commands from CNS to effectors (muscles, glands)

Subdivisions of the efferent division

Somatic nervous system (to skeletal muscles) and autonomic nervous system (to smooth muscle, heart, glands)

Branches of the autonomic nervous system

Sympathetic (fight or flight) and Parasympathetic (rest & digest)

Enteric nervous system

The intrinsic nervous system of the gastrointestinal tract; part of ANS control over digestion

Neuron

The basic functional cell of the nervous system; it transmits impulses

Types of neurons by function

Sensory (afferent), Motor (efferent), Interneurons (association)

Sensory neuron

A neuron that brings messages to the CNS from receptors

Motor neuron

A neuron that carries messages from the CNS to effectors (muscles or glands)

Interneuron

A neuron that connects sensory and motor neurons within the CNS

Dendrite

A branch‑like extension of the neuron that receives stimuli and carries impulses toward the cell body

Cell body (soma)

Contains the nucleus and most of the cytoplasm; integrates incoming signals

Axon

A fiber that carries impulses away from the cell body to other neurons or effectors

Schwann cells

Glial cells in the PNS that produce the myelin sheath around axons

Myelin sheath

A lipid (fat) insulating layer around the axon that speeds conduction of impulses

Nodes of Ranvier

Gaps in the myelin sheath where the axon is exposed; important in saltatory conduction

Path of an impulse in a neuron

Dendrite → cell body (soma) → axon → axon terminal

Self‑propagating impulse

Once initiated, the action potential continues along the axon without weakening

Na⁺/K⁺ pump

Essential in restoring membrane potential after an action potential

Synapse

The junction between two neurons (or a neuron and effector) where communication occurs

Synaptic cleft

The gap between neurons at a synapse where they do not physically touch

Role of neurotransmitters

Chemical messengers released from the presynaptic neuron that cross the cleft and bind to receptors on the postsynaptic neuron to initiate (or inhibit) a new impulse

Reflex arc

A neural pathway that mediates a reflex (rapid, involuntary reaction)

Receptor

sensory neuron → integration center (CNS, often interneurons) → motor neuron → effector

Monosynaptic reflex

A reflex with only one synapse between sensory and motor neuron (no interneuron) — e.g. the knee-jerk reflex

Polysynaptic reflex

A reflex with one or more interneurons between sensory and motor neurons — e.g. withdrawal reflex

Major parts of the brain

Brainstem (medulla, pons, midbrain), diencephalon (thalamus, hypothalamus), cerebellum, cerebrum

Lobes of the cerebrum

Frontal, parietal, temporal, occipital

Broca's area and Wernicke's area

Regions associated with language: Broca's = speech production; Wernicke's = comprehension

Limbic system

A network of brain structures involved in emotion, memory, and motivation

Sense receptors

Receive stimuli, generate receptor potentials, and (if stimulus strong enough) cause action potentials in neurons

Types of sensory receptors

Mechanoreceptors — pressure, touch, movement, balance; Thermoreceptors — temperature; Pain (nociceptors) — damage, chemical, lack of oxygen; Chemoreceptors — chemical changes (e.g. O₂, CO₂, pH, taste/smell); Photoreceptors — light

Special senses vs general senses

Special senses are mediated by organs in the head (vision, hearing, smell, taste, equilibrium), while general senses are widely distributed (touch, pressure, temperature, pain, proprioception)

Receptor types for each sense

Smell & taste → chemoreceptors; Sight → photoreceptors; Hearing & equilibrium → mechanoreceptors; Touch/pressure → mechanoreceptors; Temperature → thermoreceptors; Pain → nociceptors (a kind of mechanoreceptor detecting damage)

Proprioceptors

Receptors in muscles, tendons, ligaments, and joints that detect stretch and position to help maintain muscle tone and coordinate movement

Referred pain

When pain from an internal organ (visceral) is perceived as coming from a somatic area because their afferent pathways converge (e.g. heart pain felt in left arm)

Disorders of the nervous system

Epilepsy, seizures, Alzheimer's disease, multiple sclerosis, Parkinson's disease, shingles, cerebral palsy, glaucoma, conjunctivitis ("pink eye")

Effects of drugs on the nervous system

By altering neurotransmitter release, receptor binding, or reuptake; examples include alcohol, caffeine, nicotine, marijuana

Nervous system vs endocrine system

Nervous: uses neurotransmitters, acts via synapses, fast & short‑lasting effects, controls muscles & glands; Endocrine: uses hormones, acts through bloodstream to distant targets, slower onset but longer lasting effects

Major endocrine organs

Hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, adrenal glands, pancreas, ovaries, testes

Exocrine glands vs endocrine glands

Exocrine glands: secrete through ducts to a surface or cavity; Endocrine glands: secrete hormones directly into bloodstream

Homeostasis

The maintenance of stable internal conditions

Feedback mechanism

Negative feedback in endocrine control

The most common mechanism: rising hormone levels inhibit further release upstream (e.g. T3/T4 inhibit TRH/TSH)

Positive feedback example

Oxytocin during childbirth: uterine contractions stimulate more oxytocin release, increasing contractions until delivery

Hormones

Chemical messengers secreted by endocrine glands that act on target cells

Protein/peptide hormones

Hydrophilic hormones that bind to cell membrane receptors and use second messengers (cAMP, IP3)

Steroid hormones

Lipophilic hormones that diffuse through membranes, bind to intracellular receptors, and affect gene transcription

Example of a peptide hormone

Insulin binds to a membrane receptor → activates G proteins, triggers second messenger (e.g. cAMP) → cellular response

Example of a steroid hormone

Estradiol diffuses into cell, binds intracellular receptor, hormone-receptor complex binds DNA to regulate gene transcription

Hypothalamus and pituitary gland relationship

The hypothalamus controls pituitary secretions (via releasing/inhibiting hormones for anterior lobe, and direct neural connection to posterior lobe)

Neurosecretory cells

Specialized neurons in the hypothalamus that synthesize hormones and send them to the posterior pituitary for release

Releasing & inhibiting hormones of the hypothalamus

TRH, GHRH, somatostatin (GHIH), PIH (prolactin inhibiting hormone), releasing/inhibiting factors

Hormones produced by the anterior pituitary

TSH → stimulates thyroid; GH (growth hormone) → growth of tissues; ACTH → stimulates adrenal cortex; Prolactin → milk production; FSH & LH → regulate gonads

Hormones released by the posterior pituitary

Oxytocin (labor, milk ejection) and ADH (antidiuretic hormone, water reabsorption in kidneys)

Pineal gland function

Secretes melatonin, which helps regulate sleep-wake cycles and circadian rhythms

Thyroid gland secretion

Produces T3 & T4 (thyroid hormones) that regulate metabolic rate; requires iodine

Function of the parathyroid glands

Secrete parathyroid hormone (PTH), which regulates blood calcium levels and bone calcium metabolism

Thymus gland function

Secretes thymosin, which stimulates T‑cell development (important in the immune system)

Hormones secreted by the adrenal gland

Adrenal medulla: epinephrine (adrenaline) and norepinephrine (for fight/flight); Adrenal cortex: cortisol (metabolism), aldosterone (electrolyte balance), and androgens

Endocrine functions of the pancreas

Secretes insulin (lowers blood glucose) and glucagon (raises blood glucose)

Hormones secreted by ovaries and testes

Ovaries: estrogen and progesterone (female reproductive hormones); Testes: testosterone (male reproductive hormone)

Hypersecretion disorders

Too much hormone is produced; can lead to overactivity of target organ

Hyposecretion

Too little hormone is produced; target organs underperform

Target cell insensitivity

When target tissues don't respond properly to a hormone, producing effects similar to hyposecretion

Examples of endocrine system disorders

Diabetes, hypoglycemia, Graves' disease (overactive thyroid), goiter (thyroid enlargement)