phys 2


Nervous System & Endocrine Study Guide




CHAPTER 7 – Neurons & Signaling




Nervous System Divisions



CNS (Central Nervous System)


  • Brain

  • Spinal cord



PNS (Peripheral Nervous System)


  • All nerves outside CNS



Sensory (Afferent) pathway


  • Carries signals TO CNS



Motor (Efferent) pathway


  • Carries signals FROM CNS



Autonomic nervous system


  • Involuntary

  • We do not consciously control it






Neuron Structure



Axon hillock


  • Contains many voltage-gated ion channels

  • Site where action potentials start

  • Summation of inputs occurs here






Myelination



Myelin


  • Lipid insulation around axons

  • Speeds up action potentials



PNS myelination


  • Schwann cells



CNS myelination


  • Oligodendrocytes






Glial Cells



Microglia


  • Phagocytosis

  • Immune defense



Ependymal cells


  • Produce cerebrospinal fluid (CSF)






Membrane Potentials



Resting membrane potential (RMP)


  • ~ -70 mV




Depolarization



  • Membrane becomes less negative




Repolarization



  • Membrane returns to resting potential




Hyperpolarization



  • Membrane becomes more negative than -70






Ion Channels




Ligand-gated channels



  • Open when neurotransmitter binds

  • Example: Na⁺ channels




Mechanical-gated channels



  • Respond to physical stimulus

  • Example: bug crawling on arm




Leak channels



  • Always open

  • Not gated




Voltage-gated channels



Open when membrane potential changes


  • Na⁺ channels → depolarization

  • K⁺ channels → repolarization



Threshold ≈ -55 mV





Graded Potentials



Characteristics


  • Can be depolarizing or hyperpolarizing

  • Lose strength over distance

  • Do not produce action potentials directly



But:

All action potentials begin from graded potentials





Action Potentials



All-or-nothing


Steps:


  1. Depolarization

    • Voltage-gated Na⁺ channels open

    • Sodium rushes into cell


  3. Peak

  4. Repolarization

    • K⁺ channels open

    • Potassium leaves cell


  6. Hyperpolarization

  7. Return to RMP

    • Na⁺/K⁺ pump restores gradients







Refractory Period



Absolute refractory period


  • During depolarization

  • No new AP possible



Relative refractory period


  • During hyperpolarization

  • Requires stronger stimulus






Saltatory Conduction



Occurs in myelinated axons


Action potentials jump between nodes of Ranvier


Result:


  • Much faster conduction






Synapse



Synapse


  • Junction between neurons



Steps:


  1. Action potential arrives

  2. Ca²⁺ enters presynaptic neuron

  3. Neurotransmitter released by exocytosis

  4. Neurotransmitter binds receptors on postsynaptic cell






Neurotransmitters




Excitatory



Cause depolarization


Examples:


  • Glutamate

  • Acetylcholine (ACh)




Inhibitory



Cause hyperpolarization


Examples:


  • GABA






Summation



Occurs at axon hillock



Temporal summation



  • Rapid signals from one neuron




Spatial summation



  • Signals from multiple neurons






CHAPTER 8 – Brain




Brain Structure



Gyri


  • Bumps/folds on brain surface



Corpus callosum


  • Connects left and right hemispheres



Gray matter


  • Neuron cell bodies

  • Superficial



White matter


  • Myelinated axons

  • Deeper






Lobes of Brain



Frontal lobe


  • Decision making

  • Precentral gyrus → motor cortex



Parietal lobe


  • Sensory processing

  • Postcentral gyrus → somatosensory cortex



Temporal lobe


  • Hearing



Occipital lobe


  • Vision



Insula


  • Sensory processing of visceral organs






Language Areas



Broca’s area


  • Motor speech production



Damage:


  • Can’t form words



Wernicke’s area


  • Speech comprehension



Damage:


  • Can’t understand language






Diencephalon



Thalamus


  • Sensory relay station



Hypothalamus


  • Homeostasis

  • Controls pituitary gland






Brain Stem



Parts:


  • Midbrain

  • Pons

  • Medulla oblongata



Controls vegetative functions


Examples:


  • Heart rate

  • Breathing

  • Blood vessel diameter






Reticular Activating System (RAS)



Promotes wakefulness and alertness





Sleep



Two main states:


REM sleep


  • Dreaming



NREM sleep


  • Stages 1–4



Controlled partly by circadian rhythm





Cerebellum



Second largest brain structure


Function:


  • Coordination

  • Balance



Damage causes:


  • Ataxia (uncoordinated movement)






Spinal Cord



Functions:


Ascending tracts


  • Sensory signals to brain



Descending tracts


  • Motor signals from brain






Spinal Nerves



Contain both sensory and motor fibers


Dorsal root


  • Sensory input



Ventral root


  • Motor output






Reflex Arc



Example: Withdrawal reflex


Steps:


  1. Pain receptor activated

  2. Signal goes to spinal cord

  3. Flexor muscles activated

  4. Extensors inhibited



Spinal cord responds before brain





Autonomic Nervous System




Sympathetic



Fight or flight


  • Short preganglionic

  • Long postganglionic



Neurotransmitters:


  • ACh → ganglion

  • Norepinephrine → target






Parasympathetic



Rest and digest


  • Long preganglionic

  • Short postganglionic



Neurotransmitter:


  • Acetylcholine






Important Drugs



Beta blockers


  • Block sympathetic effects



Albuterol


  • Beta agonist

  • Opens airways



Atropine


  • Blocks muscarinic receptors

  • Causes pupil dilation






CHAPTER 10 – Sensory Systems




Sensation vs Perception



Sensation


  • Detecting stimulus



Perception


  • Interpreting stimulus






Steps of Perception



  1. Stimulus

  2. Transduction

  3. Conduction

  4. Perception in brain






Receptors



Chemoreceptors


  • Smell, taste



Nociceptors


  • Pain



Proprioceptors


  • Body position






Receptor Types



Tonic receptors


  • Do not adapt

  • Example: pain



Phasic receptors


  • Adapt quickly

  • Example: clothing






Taste (Gustation)



Taste receptors detect:


  • Salty → Na⁺

  • Sour → H⁺

  • Sweet → sugars

  • Bitter → toxins

  • Umami → proteins



Taste buds last ~10 days


Primary taste cortex:


  • Insula






Smell (Olfaction)



Odor molecules must be:


  • Water soluble

  • Present in sufficient concentration



Smell strongly influences:


  • Taste

  • Memory

  • Behavior






Vestibular System (Balance)



Located in temporal bone


Semicircular canals


  • Detect head rotation



Hair cells


  • Mechanoreceptors



Endolymph


  • Fluid inside canals






Hearing



Sound waves cause:


  1. Tympanic membrane vibration

  2. Movement of bones:

    • Malleus

    • Incus

    • Stapes


  4. Fluid movement in cochlea

  5. Hair cells bend → nerve signal



Frequency = pitch


Amplitude = loudness





Vision




Eye Structures



Cornea


  • Bends most incoming light



Lens


  • Adjusts focus (accommodation)



Iris


  • Controls pupil size






Retina



Three layers:


  1. Photoreceptors

  2. Bipolar cells

  3. Ganglion cells






Photoreceptors



Rods


  • Night vision

  • Light sensitive

  • Black/white



Cones


  • Color vision

  • High acuity



Colors:


  • Red

  • Green

  • Blue






Dark vs Light Adaptation



Dark adaptation


  • Regeneration of rod pigments



Light adaptation


  • Breakdown of cone pigments






CHAPTER 11 – Endocrine System




Hormone Interactions



Additive


  • Two hormones produce same effect



Complementary


  • Different hormones contribute to same outcome



Permissive


  • One hormone increases sensitivity to another



Antagonistic


  • Opposite effects



Example:


  • Insulin vs Glucagon






Hypothalamus & Pituitary



Hypothalamus controls pituitary through releasing hormones


Examples:


  • GnRH

  • TRH

  • CRH

  • GHRH






Anterior Pituitary Hormones



  • FSH

  • LH

  • TSH

  • ACTH

  • Growth Hormone

  • Prolactin






Posterior Pituitary



Releases hormones made in hypothalamus:


  • ADH

  • Oxytocin






Adrenal Gland




Adrenal Cortex



Produces steroid hormones:


Mineralocorticoids


  • Aldosterone

  • Na⁺ and K⁺ balance



Glucocorticoids


  • Cortisol

  • Glucose metabolism



Androgens


  • Sex hormones






Adrenal Medulla



Releases:


  • Epinephrine

  • Norepinephrine



Part of sympathetic nervous system





Thyroid



Hormones:


  • T3

  • T4



Functions:


  • Increase metabolism

  • Increase sensitivity to catecholamines



Requires iodine





Thyroid Disorders



Hypothyroidism


  • Low metabolism

  • Can cause goiter



Hyperthyroidism


  • Graves disease

  • Bulging eyes






Parathyroid



PTH


  • Increases blood calcium



Mechanism:


  • Breaks down bone



Calcitonin


  • Opposite effect

  • Builds bone






Pancreas



Alpha cells


  • Glucagon

  • Raises blood glucose



Beta cells


  • Insulin

  • Lowers blood glucose



Insulin:


  • Moves glucose into cells

  • Stimulates glycogen storage






Pineal Gland



Secretes:


  • Melatonin



Controls:


  • Sleep cycle