SciOly flashcards

Nervous System: 

Neurons are specialized cells that transmit electrical signals rapidly throughout the body. Dendrites receive incoming signals from other neurons or sensory receptors, and the cell body contains the nucleus and integrates all incoming information. The axon carries electrical impulses away from the cell body toward other cells, and axon terminals release neurotransmitters into synapses to communicate with other neurons or effectors. Myelin sheaths insulate axons and increase conduction speed, with Schwann cells forming myelin in the PNS and oligodendrocytes forming myelin in the CNS. Nodes of Ranvier are gaps in myelin where action potentials are regenerated, and saltatory conduction allows impulses to jump from node to node, greatly increasing speed. Synapses are junctions where neurons communicate with other cells. Chemical synapses use neurotransmitters to transmit signals across a synaptic cleft. An action potential arriving at the terminal opens voltagegated calcium channels, and calcium entry triggers vesicles to release neurotransmitter into the synaptic cleft. Neurotransmitters bind to receptors on the postsynaptic cell and open ion channels. Excitatory neurotransmitters depolarize the postsynaptic cell, while inhibitory neurotransmitters hyperpolarize it. Neurotransmitters are removed by reuptake, enzymatic breakdown, or diffusion. Important neurotransmitters include acetylcholine, glutamate, GABA, glycine, dopamine, serotonin, and norepinephrine. Acetylcholine is used at neuromuscular junctions and in autonomic pathways. Glutamate is the main excitatory neurotransmitter in the CNS, while GABA is the main inhibitory neurotransmitter. Dopamine is involved in movement and reward, serotonin regulates mood, sleep, and appetite, and norepinephrine is involved in arousal and attention. Glial cells support and protect neurons. Astrocytes maintain the bloodbrain barrier and regulate extracellular ions. Oligodendrocytes form CNS myelin, microglia act as immune cells and remove debris, and ependymal cells line ventricles and help circulate cerebrospinal fluid. Schwann cells form PNS myelin, and satellite cells surround neuron cell bodies in PNS ganglia. The resting membrane potential is about negative seventy millivolts. It is created by unequal ion distributions and selective permeability. Potassium leak channels allow potassium to leave the cell more easily than sodium enters, and the sodiumpotassium pump maintains gradients by pumping three sodium ions out and two potassium ions in. The GoldmanHodgkinKatz equation describes membrane potential as a weighted average of ion equilibrium potentials based on permeability. At rest, the membrane is most permeable to potassium, so the resting potential is close to the potassium equilibrium potential. An action potential is an allornone electrical signal. When threshold is reached, voltagegated sodium channels open and sodium enters the cell, causing depolarization. Sodium channels then inactivate and voltagegated potassium channels open, allowing potassium to leave and repolarize the membrane. Potassium channels stay open briefly, causing hyperpolarization. The absolute refractory period prevents another action potential, while the relative refractory period requires a stronger stimulus. Unmyelinated axons conduct impulses continuously, while myelinated axons conduct impulses by saltatory conduction between nodes of Ranvier. The cerebrum controls cognition, sensation, voluntary movement, memory, and language. The frontal lobe controls planning, decision making, personality, and voluntary motor control. The parietal lobe processes touch, pressure, pain, temperature, and spatial awareness. The temporal lobe handles hearing, language comprehension, and memory, while the occipital lobe processes vision. The basal nuclei help initiate and smooth movements, and the limbic system regulates emotion and memory. The cerebellum coordinates voluntary movements, balance, and posture, and damage to the cerebellum causes uncoordinated movements and balance problems. The brainstem includes the midbrain, pons, and medulla and controls breathing, heart rate, blood pressure, and reflexes such as coughing and swallowing. The spinal cord contains central gray matter surrounded by white matter. Dorsal horns process sensory information, and ventral horns contain motor neuron cell bodies. Dorsal roots carry sensory fibers into the spinal cord and contain dorsal root ganglia, while ventral roots carry motor fibers out of the spinal cord. Dorsal and ventral roots merge to form mixed spinal nerves. EEG waveforms include delta waves in deep sleep, theta waves in drowsiness, alpha waves when awake and relaxed, and beta waves during alert mental activity. The peripheral nervous system includes sensory neurons that carry information to the CNS and motor neurons that carry commands from the CNS. Somatic motor neurons control voluntary skeletal muscle, while the autonomic nervous system controls involuntary functions. The sympathetic division prepares the body for fight or flight, increasing heart rate, blood pressure, and energy availability. The parasympathetic division promotes rest and digestion, slowing heart rate and increasing digestive activity. Sympathetic pathways have short preganglionic and long postganglionic fibers, while parasympathetic pathways have long preganglionic and short postganglionic fibers. A reflex arc includes a receptor, sensory neuron, integration center, motor neuron, and effector, and reflexes are rapid, automatic responses that protect the body and maintain posture. Epilepsy involves abnormal electrical activity in the brain that causes seizures. Alzheimer’s disease involves memory loss and cognitive decline due to plaques, tangles, and neuron loss. Multiple sclerosis is an autoimmune disease that destroys CNS myelin. Parkinson’s disease involves loss of dopamineproducing neurons and causes tremors and slow movement. Cerebral palsy results from early brain injury and causes movement and posture problems. Stroke occurs when blood flow to the brain is interrupted. ALS involves degeneration of motor neurons and leads to muscle weakness and paralysis. Alcohol enhances GABA signaling and suppresses glutamate signaling, causing slowed reactions and impaired coordination. Caffeine blocks adenosine receptors and increases alertness. Nicotine stimulates nicotinic acetylcholine receptors and increases dopamine release. Marijuana’s THC activates cannabinoid receptors and alters perception, memory, and coordination. Tetrodotoxin blocks voltagegated sodium channels and prevents action potentials. Curare blocks nicotinic acetylcholine receptors and prevents muscle contraction. Botulinum toxin prevents acetylcholine release and causes flaccid paralysis. Anatoxina overstimulates nicotinic receptors and causes depolarization block. Tetanus toxin blocks inhibitory neurotransmitter release and causes uncontrolled muscle contraction. 

Special Senses: 

The cornea is the clear, curved front surface of the eye that allows light to enter and begins bending light toward the retina. The lens is a flexible, transparent structure that changes shape to focus light on the retina. The iris is the colored part of the eye that controls the size of the pupil and regulates how much light enters. The pupil is the opening in the center of the iris that changes size depending on light levels. The retina is the inner layer of the eye containing rods and cones that convert light into electrical signals. The optic nerve carries visual information from the retina to the brain. Light enters through the cornea, passes through the aqueous humor, pupil, lens, and vitreous humor, and is focused on the retina. The lens changes shape through accommodation to focus on near or distant objects. Rods detect dim light and provide night and peripheral vision. Cones detect bright light and color and provide sharp visual detail, especially in the fovea. The outer ear includes the pinna and ear canal, which collect and direct sound waves inward. The middle ear contains the eardrum and ossicles, where the eardrum vibrates and the ossicles amplify and transmit vibrations. The inner ear contains the cochlea and semicircular canals. The cochlea is a fluidfilled structure containing hair cells that detect sound vibrations. Hair cells bend when cochlear fluid moves, converting mechanical vibrations into electrical signals. Different regions of the cochlea detect different frequencies, and greater amplitude produces louder sound. The semicircular canals detect rotational head movements, while the vestibular system detects balance and spatial orientation. Movement of fluid in the semicircular canals bends hair cells, signaling head rotation, and the vestibule detects linear acceleration and head position relative to gravity. The nasal cavity contains the olfactory epithelium, which houses olfactory receptor cells. Olfactory receptor cells have cilia that bind odor molecules. When odor molecules bind, they trigger electrical signals that travel through the olfactory nerve to the olfactory bulb. The olfactory bulb processes smell information and sends it to the brain. The tongue contains taste buds located on papillae. Taste buds contain taste receptor cells that detect chemicals dissolved in saliva. Taste receptor cells send signals through gustatory nerves to the brain. The major taste sensations include sweet, sour, salty, bitter, and umami. Myopia is nearsightedness, caused by an eye that is too long or a cornea that is too curved. Hyperopia is farsightedness, caused by an eye that is too short or a cornea that is too flat. Presbyopia is agerelated loss of lens flexibility, making near focus difficult. Nyctalopia is night blindness, caused by poor rod function. Astigmatism is blurred vision, caused by an irregular cornea or lens. Conjunctivitis is inflammation of the conjunctiva, causing redness and irritation. Color blindness results from defective cone photopigments. Otitis externa is infection of the outer ear canal, while otitis media is infection of the middle ear. Conductive deafness occurs when sound cannot reach the inner ear, while sensorineural deafness occurs when hair cells or the auditory nerve are damaged. Anosmia is loss of smell, dysosmia is distorted smell, and dysgeusia is altered taste perception. 

Endocrine System: 

Steroid hormones are lipidsoluble hormones derived from cholesterol. They include cortisol, aldosterone, estrogen, progesterone, and testosterone. Steroid hormones pass through the cell membrane and bind to intracellular receptors. Steroid hormone receptor complexes enter the nucleus and directly alter gene transcription, producing slower but longerlasting effects. Peptide hormones are watersoluble chains of amino acids. They include insulin, glucagon, growth hormone, ADH, oxytocin, and many pituitary hormones. Peptide hormones cannot cross the cell membrane and bind to surface receptors. They activate second messenger systems and act quickly but briefly. Amine hormones are derived from amino acids such as tyrosine or tryptophan. They include epinephrine, norepinephrine, dopamine, melatonin, and thyroid hormones. Thyroid hormones behave like steroid hormones, entering the nucleus, while catecholamines act like peptide hormones on surface receptors. Nuclear hormone action occurs when lipidsoluble hormones enter the cell and bind to receptors in the cytoplasm or nucleus, directly regulating gene expression. Cytoplasmic or membrane hormone action occurs when watersoluble hormones bind to surface receptors, activating second messengers such as cAMP, IP3, or calcium. Hypersecretion occurs when too much hormone is produced, causing exaggerated effects. Hyposecretion occurs when too little hormone is produced, causing deficiency symptoms. Hypersensitivity occurs when target cells overrespond, while hyposensitivity occurs when target cells underrespond to normal hormone levels. The hypothalamus produces releasing and inhibiting hormones that control the pituitary gland. It also produces ADH and oxytocin, stored in the posterior pituitary. The pituitary gland secretes growth hormone, TSH, ACTH, LH, FSH, prolactin, ADH, and oxytocin. Growth hormone stimulates bone and muscle growth. TSH stimulates thyroid hormone release. ACTH stimulates cortisol release. LH and FSH regulate reproduction. Prolactin stimulates milk production. ADH increases kidney water reabsorption. Oxytocin stimulates uterine contractions and milk ejection. The pineal gland secretes melatonin, regulating sleep cycles. The thyroid gland secretes T3 and T4, increasing metabolic rate, and calcitonin, lowering blood calcium. The parathyroid glands secrete PTH, raising blood calcium. The thymus secretes thymosin, aiding Tcell development. The adrenal cortex secretes cortisol, aldosterone, and androgens. Cortisol increases blood glucose and stress response. Aldosterone increases sodium retention and blood pressure. The adrenal medulla secretes epinephrine and norepinephrine for fightorflight responses. The pancreas secretes insulin, lowering blood glucose, and glucagon, raising blood glucose. The gonads secrete sex hormones: estrogen and progesterone in ovaries, testosterone in testes. Diabetes mellitus occurs when insulin is insufficient or ineffective, causing high blood glucose. Type 1 diabetes is autoimmune destruction of beta cells, while Type 2 diabetes is insulin resistance. Central diabetes insipidus occurs when ADH is deficient, causing excessive urination and thirst. Hypoglycemia occurs when blood glucose is too low, often from excess insulin. Hyperparathyroidism occurs when too much PTH is secreted, causing high blood calcium and bone loss. Hypoparathyroidism occurs when too little PTH is secreted, causing low blood calcium and muscle spasms. Hyperthyroidism occurs when the thyroid produces too much T3 and T4, and Graves’ disease is an autoimmune form with symptoms such as weight loss, heat intolerance, and bulging eyes. Hypothyroidism occurs when the thyroid produces too little T3 and T4, and Hashimoto’s disease is an autoimmune form. Goiter is an enlarged thyroid, often due to iodine deficiency or abnormal TSH stimulation. Congenital iodine deficiency syndrome occurs when a fetus lacks thyroid hormone, causing developmental delays. Primary hyperaldosteronism occurs when too much aldosterone is produced, causing high blood pressure and low potassium. Polycystic ovary syndrome involves hormonal imbalance, excess androgens, irregular cycles, and ovarian cysts.