Nervous and Endocrine Systems

Nervous System: Structure and Function

  • Major functions
    • high-level control and integration of body systems
    • response to external influences
    • sensory input
      • sensory = afferent
      • nerve impulses conveyed to the CNS.
    • motor output
      • motor = efferent
      • nerve impulses from the CNS to effector organs.
    • integrative and cognitive abilities
  • Organization of vertebrate nervous system
    nervous system organization
    • CNS = Central Nervous System = Brain and spinal cord
      • Brain
      • Spinal Cord
    • PNS = Peripheral Nervous System = Everything else
      • Sensory = Afferent = Nerves carrying signal toward CNS.
      • Motor = Efferent = Nerves carry signal toward effector organs.
        • Somatic Nervous System = Voluntary = Controls skeletal muscles.
        • Autonomic Nervous System = Involuntary = Effects visceral organs.
          • Sympathetic division = fight or flight response.
          • Parasympathetic division = Rest.
  • Sensor and effector neurons
    • Sensor = senses, carries sensory signals from the body to the CNS.
    • Effector = causes an effect = carries motor signals from the CNS to the body.
  • Sympathetic and parasympathetic nervous systems (functions, antagonistic control)
    • Sympathetic = prepares body for activity = fight or flight response.
      • Increase heart rate, blood pressure
      • More blood flow to muscles, less to digestive system.
      • Pupil dilation.
      • Break down glycogen to release glucose into blood.
    • Parasympathetic = prepares body to rest
      • Decrease heart rate, blood pressure.
      • Less blood to muscles, more to digestive system.
      • Pupil constriction.
      • Synthesizes glycogen for storage from glucose.
  • Reflexes
    • feedback loop, reflex arc, effects on flexor and extensor muscles
      • Feedback loop = positive feedback (reinforce initial event), negative feedback (counteracts initial event), or reflex arc (usually a type of negative feedback).
        • positive feedback = uterine contraction lead to oxytocin release, which causes more uterine contraction.
        • positive feedback = blood clotting platelets activated at wound site attract more platelet activation and clumping.
        • negative feedback = drop in blood pressure causes ADH release, which increases it. Conversely increase in blood pressure causes a drop in ADH.
        • Reflex arc = withdrawal from a painful stimulus = negative feedback.
        • Reflex arc = knee jerk = tapping the knee tendon causes sudden stretching of the muscle, which lead to contraction of that muscle that creates the knee jerk = negative feedback.
      • Reflex arc = receptor → sensory neuron → integration center → motor neuron → effector
        • receptor = site of stimulus
        • sensory neuron = carries impulse from receptor to integration center
        • integration center = connects sensory to motor neuron via synapse inside the CNS
          • monosynaptic = no interneuron, direct synapse of sensory to motor.
          • polysynaptic = interneuron(s) present.
        • motor neuron = carries impulse toward effector.
        • effector = site of response to the stimulus
      • Examples of reflexes: knee-jerk, withdrawal from pain
      • Effects on flexor and extensor muscles
        • During the knee-jerk, in addition to contracting the extensor, the reflex relaxes the flexor.
        • Golgi tendon reflex: sudden contraction of the quads (extensor), causes a negative feedback that relaxes the quads and contracts the hamstrings (flexor).
    • role of spinal cord, brain
      • Spinal cord provides the synapse (or synapses if it's polysynaptic) for the reflex arc.
      • Even though the reflex arc bypasses the brain, the brain is still aware of it happening.
    • efferent control
      • Brain can override spinal reflexes (eg. you don't jerk away from getting a vaccine shot)

Nervous System: Sensory Reception and Processing

  • Skin, proprioceptive, and somatic sensors
    • Skin: touch, heat and pain receptors close to the surface (dermis-epidermis boundary), pressure receptors deeper in the dermis.
    • proprioceptor: senses the position of a body part, located in muscle and connective tissue.
    • somatic sensors:
      • mechanoreceptors - touch, pressure
      • thermoreceptor - temperature change (a warm object will feel warm if your hand is cool, but won't feel warm if your hand is already warm)
      • photoreceptor - light
      • chemoreceptor - taste, smell
      • nocioreptors - pain (extreme heat, cold, pressure, chemicals)
  • Olfaction, taste
    • Olfaction:
      1. Chemicals enter the nose via nostrils.
      2. Gets into the nasal cavity.
      3. Trapped in the mucus on top of the nasal cavity.
      4. Picked up by the membrane receptors on cilia (non-mobile, but they increase the surface area) of the olfactory receptor cell.
      5. Causes cell depolarization, and subsequent transduction of signal to the brain.
    • Taste:
      1. Chemicals dissolve in saliva.
      2. Carried inside taste bud
      3. Hair-like microvilli of taste cells inside taste bud picks up chemicals.
      4. Releases neurotransmitters to send signal to brain.
  • Hearing
    • ear structure
      • Ear canal = auditory canal.
      • Tympanic membrane = eardrum.
      • Ear bones = malleus (hammer) → incus (anvil) → stapes (stirrup).
      • Vestibule = contacts the oval window (where stirrup vibrates), is continuous with semicircular canals and cochlea.
      • Cochlea = spiral = houses hair cells.
      • Semicircular canals = 3 of them perpendicular to one another = senses position and movement of the head, help you balance.
    • mechanism of hearing
      1. Sound enters ear.
      2. Hits ear drum (tympanic membrane)
      3. Malleus (hammer) → Incus (anvil) → Stapes (stirrup)
      4. Vibrates fluid in Cochlea.
      5. Transmits to fluid in Cochlea.
      6. Cochlear hair cells excited by vibrations, and sends signal to brain.
  • Vision
    • light receptors
      • Photoreceptor cells located on the back of the retina.
      • Rods = senses light and dark (no color), more sensitive.
      • Cones = senses color, less sensitive.
      • Rhodopsin = chemical responsible for light reception = Retinal (chemical) + Opsin (transmembrane protein)
      • Light converts cis-retinal → trans-retinal.
      • trans-retinal then causes hyperpolarization of photoreceptor cell, which prompts the chain of events that sends signal to the brain.
      • Sends signal to brain via a bundle of nerves on the back of the retina (where the blind spot is)
    • eye structure
      1. Light first travels through the cornea
      2. Through the pupil (hole in the iris muscle)
      3. Lens = focuses light on retina.
      4. Vitreous humor = fluid.
      5. Retina = screen on the back of the eye = contains photoreceptors.
    • visual image processing
      • The lens of the eye, just like a convex lens in physics, forms a real image on the retina.
      • Real images are inverted.
      • The brain processes this inverted image to make it seem upright in your mind.
      • The brain combines the two images from each eye to make a 3D image, from which you can judge distance.
      • Another reason for combining the two images from both eyes is that it gets rid of the blind spot in each eye.

Endocrine system: Hormones

  • Function of endocrine system (specific chemical control at cell, tissue, and organ level)
    • Endocrine system = make hormones = specific control of all target cells of that hormone.
  • Definition of endocrine gland, hormone
    • endo = within, crine = to secrete
    • endocrine glands secreting hormones into surrounding tissue fluids.
    • endocrine vs. exocrine, autocrine, paracrine
      • endocrine: hormone, no duct, acts long distances
      • exocrine: non-hormone secretions into ducts.
      • autocrine: local chemicals, act short distances on themselves
      • paracrine: local chemicals, act short distances on other cells
    • hormone = chemicals that regulate metabolism and function of cells.
  • Major endocrine glands (names, locations, products)
    endocrine system
    • Hypothalamus: Releasing hormones for the pituitary, ADH and oxytocin.
      • Releasing hormones/factors stimulates pituitary to release its hormone.
      • GnRH = Gonadotropin Releasing Hormone = stimulates pituitary to release FSH and LH.
      • CRF = Corticotropin Releasing Factor.
      • TRH = Thyroid Releasing Hormone.
      • Dopamine = inhibits prolactin release.
      • GHRH = Growth Hormone Releasing Hormone.
      • ADH = Antidiuretic Hormone = Vasopressin = increase water reabsorption in kidney = conserve water, increase blood pressure.
      • Oxytocin = stimulates uterine contractions during labor, also milk secretion during suckling.
    • Pituitary: makes FLAT PEG, stores ADH and oxytocin.
      • FSH = Follicle Stimulating Hormone = Stimulate ovary follicles to mature, testis to produce sperm.
      • LH = Luteinizing Hormone = LH surge triggers ovulation, stimulates testis to produce testosterone.
      • ACTH = AdrenoCorticoTropic Hormone = Stimulates adrenal cortex to release glucocorticoids and mineralocorticoids.
      • TSH = Thyroid Stimulation Hormone = Stimulate thyroid to release thyroid hormones.
      • PRL = Prolactin = Stimulates breast to produce milk.
      • E = Endorphins.
      • GH = Growth Hormone = Stimulates growth of muscle, bone, burns fat.
    • Pineal: makes melatonin, which makes you sleepy at night.
    • Thyroid
      • Thyroid hormones: increase metabolism, requires iodine.
      • Calcitonin: turns blood Ca2+ into bone. Lowers blood Ca2+.
    • Parathyroid: makes Parathyroid Hormone (PTH), which increases blood Ca2+ by bone resorption, dietary calcium absorption, and calcium reabsorption in kidneys.
    • Thymus: Thymus hormones (thymo-, thymic), stimulates T cells to develop.
    • Adrenal
      • Epinephrine and norepinephrine = fight or flight response
      • Mineralocorticoids = aldosterone = increase Na+ and water retention, raises blood pressure.
      • Glucocorticoids = cortisol = stress hormone = increase blood sugar.
      • Androgens = testosterone.
    • Pancreas
      • Glucagon = increases blood sugar (break down glycogen, stimulate gluconeogenesis).
      • Insulin = lower blood sugar (stimulates glucose uptake by cells).
    • Ovary: make estrogen (and a small amount of testosterone).
    • testis: make testosterone.
  • Endocrine diseases
    • Diabetes
      • no insulin made, or no insulin receptors
      • glucose can't enter cells
      • high blood sugar
      • cell starved of sugar, leading to fatty acid metabolism, which leads to production of ketone bodies, which lead to ketoacidosis (more acidic blood).
      • sugar in urine, leading to more water in urine due to osmosis.
    • Hypothyroidism
      • Decreased thyroid hormone.
      • Low metabolism.
      • If cause of disease is lack of iodine in diet, then goiter develops from an accumulation of thyroid hormone precursor lacking iodine.
    • Hyperthyroidism
      • Too much thyroid hormone.
      • High metabolism.
    • Gigantism = too much Growth Hormone during growing age = well-proportioned giants.
    • Acromegaly = too much Growth Hormone later on in life = disproportioned growth of certain areas of the body (the parts that still respond to growth hormone).
  • Major types of hormones
    • amino acid based = amino acid derivatives = most hormones are this type.
    • steroids = cholesterol derivatives = testosterone, estrogen, adrenocortical hormones.

Endocrine system: Mechanisms of hormone action

  • Cellular mechanisms of hormone action
    • water soluble hormones
      • Can't cross the plasma membrane.
      • Bind to membrane receptors on the outside of cells.
      • Secondary messengers then relay the signal inside the cell.
    • lipid-soluble hormones
      • Able to cross the plasma membrane.
      • Directly activate genes.
    • cAMP pathway:
      1. Amino acid hormone binds membrane receptor.
      2. G protein activated.
      3. Adenylate cyclase activated.
      4. cAMP made.
      5. Protein kinase cascade.
    • Phospholipid pathway:
      1. Amino acid hormone binds membrane receptor.
      2. G protein activated.
      3. Phospholipase C activated.
      4. Membrane phospholipid split into DAG and IP3.
      5. DAG triggers protein kinase cascade.
      6. IP3 releases Ca2+ from the ER.
    • Steroid pathway:
      1. Steroid hormone (and thyroid hormone even though it's amino acid based) goes inside the cell.
      2. Hormone binds receptor inside the cell (cytoplasm or nucleus).
      3. Hormone-receptor complex (transcription factor) turns certain genes on inside the nucleus.
  • Transport of hormones (bloodstream): hormones travel long distances via blood and lymph.
  • Specificity of hormones (target tissue)
    • Specificity depends on the target cells having the receptors for the hormone, and non-target cells lacking receptors for the hormone.
    • Cells can either upregulate or downregulate the receptors they express.
  • Integration with nervous system (feedback control)
    • The nervous system can modulate and override normal control of hormones based on the status of the body. For example, the body's blood "normal" glucose level is set higher when you're under stress.
    • Hormones can modulate the nervous system. For example, low estrogen levels during menses give you a bad mood.
    • Normal control of hormones
      • Humoral: glands directly respond to chemical levels in the blood (parathyroid respond to low blood calcium).
      • Neural: glands release hormones when stimulated by nerves (fight or flight response).
      • Hormonal: glands release hormones when stimulated by other hormones (tropic hormones).