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Questions and Answers

What type of receptor is activated by the physical deformation of its membrane?

Thermoreceptor

Chemoreceptor

Mechanoreceptor (correct)

Photoreceptor

Which neurotransmitter's reuptake is increased by serotonin reuptake inhibitors in the treatment of irritable bowel syndrome?

Serotonin (correct)

Dopamine

Norepinephrine

Epinephrine

What is the process called that transforms environmental stimuli into electrical stimuli?

Sensory adaptation

Sensory integration

Sensory transduction (correct)

Sensory perception

Which type of receptor is primarily responsible for detecting temperature changes?

Thermoreceptor Signup and view all the answers

How do chemoreceptors respond to stimuli?

By binding a ligand that opens ion channels Signup and view all the answers

What aspect of sensation allows us to be consciously aware of stimuli?

Perception Signup and view all the answers

Which pathway conveys information from the brain to muscles or endocrine glands?

Efferent neural pathways Signup and view all the answers

What type of stimuli do nociceptors specifically respond to?

Painful stimuli Signup and view all the answers

What determines the intensity of a stimulus?

The frequency of action potentials from receptors in an area Signup and view all the answers

How is stimulus location primarily determined?

By the specific afferent pathways used to transmit the information Signup and view all the answers

What effect does overlapping receptive fields have on stimulus localization?

It enhances the ability to determine the exact location of a stimulus Signup and view all the answers

What happens to the perception of stimuli when receptive fields are large?

It becomes difficult to differentiate between two stimuli Signup and view all the answers

Which factor contributes to higher acuity in sensory perception?

Smaller receptive fields Signup and view all the answers

What is the result of stimulating all nerve endings in response to a strong stimulus?

Heightened graded potential and more frequent action potentials Signup and view all the answers

Which of the following is true regarding convergence in sensory pathways?

Less convergence is associated with better acuity Signup and view all the answers

Which of the following explains the 'seeing stars' phenomenon when rubbing your eyes?

Pressure-induced activation of both visual and pressure receptors Signup and view all the answers

What is a characteristic of sensory cells that are modality-specific?

They are only responsive to their designated type of stimulus. Signup and view all the answers

What is the primary role of corticotropin-releasing hormone (CRH)?

To trigger the anterior pituitary to release ACTH Signup and view all the answers

How does cortisol affect the immune system during stress?

It partially suppresses the immune system. Signup and view all the answers

What physiological function is regulated by cortisol?

Maintaining glucose levels Signup and view all the answers

What characterizes Cushing's disease?

Abdominal obesity and immunosuppression Signup and view all the answers

What is the consequence of cortisol hyposecretion?

Symptoms of Addison’s disease Signup and view all the answers

What triggers the release of cortisol in response to stress?

Hypothalamus releasing CRH Signup and view all the answers

Which symptom is associated with hyperthyroidism?

Increased appetite Signup and view all the answers

What causes a goiter?

Iodine deficiency and TSH hypersecretion Signup and view all the answers

What is the effect of T3 on metabolism?

Increase in body heat production Signup and view all the answers

Which of the following is NOT a long-term effect of cortisol release?

Enhancements of cognitive function Signup and view all the answers

How do the hair cells near the oval window respond to sound frequencies compared to those near the helicotrema?

They respond to higher frequencies. Signup and view all the answers

What is the primary function of the vestibular system?

To control eye movement and maintain balance. Signup and view all the answers

Which component of the vestibular system specifically detects horizontal acceleration?

Utricle. Signup and view all the answers

What role do otoliths play in the function of the utricle and saccule?

They help detect linear acceleration. Signup and view all the answers

How do hair cells in the semicircular canals transmit sensory information during head movements?

By opening mechanically-gated ion channels when stereocilia bend. Signup and view all the answers

Which type of receptors is primarily involved in detecting head rotation?

Mechanoreceptors. Signup and view all the answers

What initiates the release of neurotransmitters from hair cells in the taste buds?

Binding of specific ligands. Signup and view all the answers

What is the main pathway of olfactory transduction?

Ion channels open leading to receptor depolarization. Signup and view all the answers

What type of ions primarily cause depolarization in taste receptor cells when sweet substances are present?

Monosaccharides and disaccharides. Signup and view all the answers

What happens to the stereocilia of hair cells in the utricle when a person experiences forward acceleration?

They are displaced toward their tallest point. Signup and view all the answers

What is the effect of moving the head in the opposite direction on the mechanically-gated ion channels in the semicircular canals?

They close and result in hyperpolarization. Signup and view all the answers

What happens during taste transduction when sour substances are detected?

H+ ions result in cell depolarization. Signup and view all the answers

What type of transduction occurs when olfactory receptor neurons are activated?

G protein-coupled receptor activation. Signup and view all the answers

What mechanism do water-soluble hormones primarily use to produce a response in target cells?

They bind to cell surface receptors. Signup and view all the answers

Which of the following statements about steroid hormones is incorrect?

They bind to receptors on the surface of target cells. Signup and view all the answers

What is the function of tropic hormones released by the anterior pituitary gland?

They stimulate other endocrine glands to release hormones. Signup and view all the answers

How does the endocrine system primarily regulate hormone secretion?

One hormone controlling the synthesis of another hormone. Signup and view all the answers

What is the primary cause of hyperresponsiveness in target cells?

Excessive receptor production leading to increased sensitivity. Signup and view all the answers

In what way do peptide and protein hormones differ from steroid hormones?

Peptide hormones are synthesized from amino acids. Signup and view all the answers

What is the primary effect of oxytocin when released from the posterior pituitary gland?

Promotion of social bonding and milk production. Signup and view all the answers

Which statement about the half-life of hormones is true?

Epinephrine has a half-life of approximately one minute. Signup and view all the answers

Which scenario best describes the role of the adrenal medulla?

Synthesis of catecholamines like epinephrine. Signup and view all the answers

Which of the following is a characteristic of amino acid derivative hormones?

They are mostly not lipid soluble and bind to cell surface receptors. Signup and view all the answers

What type of feedback mechanism predominantly regulates hormone levels in the body?

Negative feedback primarily. Signup and view all the answers

Which of the following hormones is produced by the adrenal cortex?

Cortisol. Signup and view all the answers

Which of the following best explains hyposecretion?

The body does not produce enough hormones. Signup and view all the answers

What role do carrier proteins play in the transport of steroid hormones?

They help dissolve these hormones in blood, aiding their transport. Signup and view all the answers

Study Notes

Endocrine Glands

Exocrine glands release substances into ducts or tubes.
Examples include sweat glands and the gallbladder
Endocrine glands secrete substances directly into the bloodstream.
Examples include the pineal gland secreting melatonin.
Some organs, like the pancreas, perform both endocrine and exocrine functions.

Hormone Mechanisms of Action

Water-soluble hormones bind to cell surface receptors.
They alter the activity of existing proteins, resulting in faster responses compared to lipid-soluble hormones.
Water-soluble hormones can also influence the synthesis of new proteins, impacting gene expression.
Fat-soluble hormones bind to intracellular receptors.
They increase or decrease the synthesis of new proteins, affecting gene expression.
Fat-soluble hormones require carrier proteins for transport in the bloodstream.
Because they require new hormone synthesis, transcription, and translation, their response time is longer.

Chemical Classes of Hormones

Amino acid derivatives:
- Most are not lipid soluble.
- Bind to receptors on the surface of target cells.
- Examples: epinephrine, tyrosine.
Polypeptide hormones:
- They are not lipid soluble.
- Bind to receptors on the surface of target cells.
- Example: secretin.
Steroid hormones:
- They are lipid soluble.
- Often bind to receptors inside target cells.
- Examples: cholesterol, cortisol.
Amine Hormones:
- Made from the tyrosine amino acid.
- Two types:
  - Catecholamines:
    - Made by modifying side groups of tyrosine.
    - They are polar and bind to cell surface receptors.
    - Produced in the adrenal medulla (of the adrenal gland).
    - Examples: epinephrine & norepinephrine.
  - Thyroid hormones:
    - Made from two tyrosines and iodine atoms.
    - Slightly polar and bind to intracellular receptors.
    - Produced by the thyroid gland.
    - Examples: T3 & T4.
- Different glands have different enzymes, enabling them to synthesize specific hormones. For example, the adrenal gland produces epinephrine, but not T3, due to its specific enzyme profile.
Peptide & Protein Hormones:
- Represent most hormone types.
- Examples: insulin, ACTH, TSH.
- They are large and generally polar, binding to cell surface receptors.
- Synthesized through transcription and translation, encoded by a gene.
- Many are initially made as longer proteins, and later cleaved into smaller, biologically active peptides.
- Secreted through exocytosis.
Steroid Hormones:
- Made from cholesterol.
- They are nonpolar and bind to intracellular receptors.
- Produced in the adrenal cortex and gonads.
- Synthesized when another hormone binds to an endocrine cell's GPCR, activating steroid synthesis enzymes.
- Secreted via diffusion due to their small, nonpolar nature.
- Hormone Synthesis:
  - By the adrenal gland:
    - Adrenal cortex (outer):
      - Corticosteroids (steroid hormones):
        
        Aldosterone: regulates blood osmolarity.
        
        Cortisol: involved in stress response and metabolism.
    - Adrenal medulla (inner):
      - Catecholamines (amine hormones):
        
        Epinephrine
        
        Norepinephrine
      - Different parts of the adrenal gland produce different hormones because they express different enzymes for each synthesis.
  - By gonads:
    - Androgens: testosterone.
    - Estrogens: estradiol.
    - Both sex hormones are produced in men and women, but in different ratios.
    - Ovaries produce more aromatase, converting more testosterone to estradiol.
Transport:
- Carrier proteins:
  - Albumin, binding globulins:
    - Examples: corticosteroid-binding globulin, thyroxine-binding globulin (binds T4).
    - Steroids are nonpolar, making them insoluble in blood.
    - Hormones detach from the carrier when entering the target cell.

Endocrine System Regulation Outline

Regulating factors:
- Hormone synthesis/secretion:
  - Three main inputs:
    - Ions/Nutrients: Changes in concentration stimulate hormone production or secretion.
      - Examples:
        
        Glucose and insulin/glucagon:
        
        High glucose levels lead to insulin release.
        
        Low glucose levels lead to glucagon release.
        
        Calcium and parathyroid hormone:
        
        Low calcium levels lead to parathyroid hormone release.
    - Neurons: Activating or inhibiting hormone synthesis or release from glands.
      - Example: the sympathetic nervous system and the adrenal medulla.
    - Other hormones: Tropic hormones from the hypothalamus and pituitary stimulate the synthesis or release of hormones from other glands.
      - Examples:
        
        CRH triggers the pituitary gland to release ACTH, which in turn triggers the adrenal cortex to release cortisol.
        
        TRH stimulates the pituitary gland to release TSH, which binds to receptors on the thyroid gland, causing the release of thyroid hormone.
- Hormone metabolism & excretion:
  - Not all hormones circulating in the blood reach target cells.
  - Some are metabolized (activated or inactivated).
    - Activated hormones go to target cells.
  - Some are excreted in urine or feces.
  - Some reach the target cell directly.
  - Half-life: Time it takes for half of the hormone to be cleared from the bloodstream, indicating how long a hormone persists.
    - Examples:
      - Cortisol half-life is about one hour.
      - Epinephrine half-life is about one minute.
- Regulation of Hormone Receptors:
  - A cell's ability to respond to a hormone depends on the presence of specific receptors for that hormone.
  - Up-regulation: Increasing the cell's sensitivity to a hormone by synthesizing more receptors.
    - Example: Exocytosis of cell-surface receptors increases the number of receptors on the cell surface.
  - Down-regulation: Decreasing the cell's sensitivity to a hormone by degrading existing receptors or decreasing their synthesis.
    - Example: Endocytosis of vesicles containing receptors removes them from the cell surface.
  - Endocytosed receptors can be recycled and re-exocytosed.

Endocrine Disorders

Hyposecretion: Not enough hormone production.
- Examples:
  - Type I diabetes
  - Dwarfism - hyposecretion of growth hormone (GH).
Hyporesponsiveness: Enough hormone production, but the body doesn't respond to it.
- Example: Type II diabetes.
Hypersecretion: Too much hormone production.
- Examples:
  - Hyperthyroidism.
  - Gigantism - hypersecretion of GH.
Hyperresponsiveness: Cells respond excessively to a normal amount of hormone.
- Cause: Target cells produce too many receptors.

Pharmacological Effects of Hormones

Birth control: Increases estrogen and progesterone levels, mimicking a pregnant state.
Corticosteroids: Used for allergies and inflammation. Synthetic versions of cortisol.
Hormone replacement: Used for menopause to manage the sharp decline in estrogen levels.
Anabolic steroids: Used in bodybuilding to stimulate protein synthesis and muscle growth.
Thyroid hormone: Used for people with hypothyroidism.

Hypothalamus and Pituitary Gland Regulating Hormone Production

Hypothalamus (hypophysis):
- Contains neurosecretory cells, neurons that produce hormones.
- Connected to the pituitary gland by the infundibulum, containing axons and blood vessels.
- Releases hormones into:
  - The posterior pituitary.
  - Blood vessels, which transport them to the anterior pituitary.
Posterior Pituitary Gland:
- Contains axon terminals of hypothalamic neurons.
- Hormones are synthesized in the hypothalamus (specifically in the cell bodies of hypothalamic neurons).
- Hormones are released from the posterior pituitary (specifically from the axon terminals of hypothalamic neurons).
  - The posterior pituitary is not a site of synthesis; it only releases hormones into the blood and cannot produce its own hormones.
- Hormones:
  - Oxytocin: Regulates reproduction and social behavior, promoting milk production and reinforcing social bonding.
  - Antidiuretic hormone (ADH): Regulates blood osmolarity, primarily affecting cells in the kidney where ADH receptors are found.
Anterior Pituitary Gland:
- Produces its own hormones.
- Releases hormones only in response to hypophysiotropic hormones from the hypothalamus.
- Synthesizes tropic hormones that regulate the function of other endocrine glands.
  - Examples: TSH, ACTH.

Hypothalamic-Pituitary-Adrenal Axis (HPA Axis)

A series of events triggered by stress:
1. Stress triggers the hypothalamus.
2. Hypothalamus releases corticotropin-releasing hormone (CRH).
3. CRH binds to receptors on the anterior pituitary.
4. Anterior pituitary releases adrenocorticotropic hormone (ACTH).
5. ACTH binds to receptors on the adrenal cortex.
6. Adrenal cortex releases cortisol.
7. Negative feedback: Cortisol binds to receptors in the anterior pituitary and hypothalamus, inhibiting ACTH & CRH production.

Physiological Functions of Cortisol

Regulates metabolism and maintains glucose levels.
- Stimulates gluconeogenesis (production of glucose from non-carbohydrate sources).
- Stimulates catabolism of fats and proteins.
Regulates the immune system.
- Suppresses inflammation.
- Prevents autoimmunity.
  - Excessive cortisol can suppress the immune system, explaining why people become susceptible to illness during periods of stress.
Maintains blood pressure.
Regulates the sleep-wake cycle.
- Lower cortisol levels around bedtime.
- Higher cortisol levels when awake.
Essential for development.
Increases during stress.

Two Systems Respond to Stress: Sympathetic NS and HPA axis

Short-term stress response and adrenal medulla (sympathetic nervous system):
- Epinephrine and norepinephrine release:
  - Glycogenolysis: Breakdown of glycogen to glucose, increasing blood glucose levels.
  - Increased blood pressure.
  - Increased breathing rate.
  - Increased metabolic rate.
  - Changes in blood flow patterns: Prioritizes blood flow to tissues needing oxygen and nutrients, enhancing fight-or-flight response and leading to alertness. This also reduces activity in the digestive, excretory, and reproductive systems.
Long-term stress response and the adrenal cortex (HPA axis):
- Release of cortisol: Part of glucocorticoids.
- Effects of glucocorticoids:
  - Proteins and fats are broken down and converted to glucose, increasing blood glucose levels.
  - Partial suppression of the immune system: The immune system is energy-demanding. Suppressing it conserves energy.
  - Glycogen is quickly used up in the short-term stress response. Cortisol prolongs the response to stress by ensuring a sustained supply of glucose.

Diseases Affecting Cortisol Levels

Cortisol hyposecretion:
- Causes:
  - Infections or cancers that destroy adrenal cortex cells.
  - Hyposecretion of ACTH by the anterior pituitary.
- Example: Addison's disease.
  - Symptoms: Weakness, weight loss, autoimmune disease.
Cortisol hypersecretion:
- Causes:
  - Tumor in the adrenal cortex, oversecreting cortisol.
  - Hypersecretion of ACTH by the anterior pituitary.
- Example: Cushing's disease.
  - Symptoms: Hyperglycemia, abdominal obesity, immunosuppression.

Hypothalamic-Pituitary-Thyroid Axis (HPT Axis)

T4 conversion to T3:
- T4 (thyroxine) is converted to T3 (triiodothyronine) by deiodinase.
- T3 binds to intracellular receptors.
Effects of T3: Increases metabolism and body heat.
- Increases carbohydrate absorption.
- Increases lipid catabolism.
- Increases mitochondria.
- Stimulates Na+/K+ pumps.
Developmental Deficiencies:
- Deficiencies during development impair growth and nervous system development.

Diseases Affecting Thyroid Levels

Hypothyroidism:
- Symptoms: Cold intolerance, weight gain, fatigue, depression.
- Treatment: Synthetic thyroid hormones.
Hyperthyroidism:
- Symptoms: Heat intolerance, weight loss, increased appetite, anxiety.
- Treatment: Thyroid gland removal, inhibitors of T4 synthesis enzymes, radioactive iodine.
Goiter:
- Overgrowth of the thyroid gland.
- Caused by TSH hypersecretion or iodine deficiency.

Endocrine Control of Ca2+ Homeostasis

Maintaining extracellular calcium levels is crucial for:
- Bone health: Calcium is a structural component of bones and teeth.
- Muscle function: Calcium is essential for muscle contraction.
- Nerve function: Calcium is involved in nerve impulse transmission.

Sensory System

Two components:
- Sensory receptors: Specialized cells that receive stimuli from the external or internal environment.
- Afferent neural pathways: Chains of neurons that conduct information from receptors to the CNS.
  - Sensory (afferent) vs. Motor (efferent) - Afferent pathways convey information from the body TO the CNS (brain & spinal cord). Motor pathways convey information FROM the CNS to the body (muscles, glands).
Not All Stimuli are Perceived:
- Sensation: Sensory information that reaches the conscious level (cerebral cortex).
- Perception: Awareness of a sensation or understanding its meaning.
  - Example: Pain is a sensation, while awareness that a tooth hurts is a perception.

Sensory Receptors

Specialized Sensory Cells: Respond to sensory stimuli.
Types of Receptors:
- Mechanoreceptors: For touch, hearing, and balance.
  - Utilize mechanically-gated ion channels to produce graded potentials.
- Thermoreceptors: For temperature.
  - Found in the skin.
- Photoreceptors: For light (vision).
  - Receive light for vision.
- Chemoreceptors: For chemicals (taste, smell).
  - Use ligand-gated ion channels.
- Nociceptors: For pain.
Stimulus: Energy (light, sound, etc.) or a chemical that activates a receptor.
Sensory transduction: Transformation of environmental stimuli into electrical signals (neural responses).

Sensory Transduction

Stimulus: Triggers the opening or closing of ion channels in sensory receptors, producing a graded potential (receptor potential).
- Chemoreceptors: Stimulus binds to the receptor structure, opening ion channels and allowing ions to flow in or out of the cell.
- Mechanoreceptors: Physical deformation of the membrane (stretching) opens ion channels.
- Photoreceptors: Specialized proteins inside photoreceptors respond to light, which triggers the opening or closing of ion channels.

Sensory Receptors

Receptors are specialized for one modality, but can overlap when stimulus is extremely strong.
Example: Sensory cells in the eye respond to light, not sound.
Strong stimuli can trigger multiple receptors.
- Example: Rubbing eyes with knuckles can cause seeing "stars" because of pressure and light.
- Example: Extreme heat can induce pain.

Stimulus Intensity

Receptors distinguish a strong stimulus from a weak one by:
- Increased frequency of action potentials from a single receptor in an area.
  - Weak stimulus causes fewer mechanically gated ion channels to open, resulting in lower frequency of action potential.
  - Strong stimulus causes more mechanically gated ion channels to open, resulting in larger graded potential and higher frequency of action potential.
- Increased number of receptors stimulated. Stronger stimuli affect a larger area of the body.

Stimulus Location

Specific afferent pathways and locations in the CNS are associated with specific modalities, helping the brain determine the location of a stimulus.
Acuity refers to the precision with which we distinguish multiple stimuli.
- Depends on:
  - Size of the receptive field: Smaller receptive field = higher acuity.
  - Amount of convergence of afferent pathways:
    - Less convergence = better acuity.

Improving Acuity: Size of Receptive Fields

Large receptive field: A stimulus applied at two points within the same receptive field cannot be distinguished as two separate stimuli because both points are sensed by the same neuron.
Small receptive field: A stimulus applied at two points hitting different receptive fields will be perceived as two separate points.
- Better distinction of stimuli.
- More receptors can be packed in a smaller area.
- Used in sensitive areas like the retina.

Improving Acuity: Overlapping Receptive Fields

Overlapping receptive fields help localize the exact location of a stimulus because multiple neurons are activated by the same stimulus, providing more precise location information to the brain.

Ascending Sensory Pathways

Afferent sensory pathways ascend the spinal cord to the brain.
They carry specific sensory information, helping the brain interpret the type and location of a stimulus.

Hearing

Sound vibrations travel through the air and are collected by the outer ear.
Sound vibrations are converted into mechanical vibrations by the middle ear.
In the inner ear, the vibration of the stapes against the oval window creates pressure waves in the fluid filled cochlea.
The cochlea's basilar membrane, which has varying stiffness, vibrates at different locations depending on the frequency of the sound wave:
- Higher frequency vibrates near the oval window.
- Lower frequency vibrates near the helicotrema.
Hair cells on the basilar membrane are stimulated and send signals to the auditory cortex via afferent pathways.

Vestibular System

The vestibular system is responsible for balance, spatial orientation, and coordination of eye movements.
It consists of three semicircular canals, utricle, and saccule.
It uses mechanoreceptors (hair cells) to detect head movement and acceleration.

Semicircular Canals

Detect head rotation along three axes: "yes," "no," and ear-to-shoulder.
Hair cells are located in the ampulla, embedded in a gelatinous substance called the cupula.
Head movement causes fluid inside the canal to move, pushing on the cupula and bending the stereocilia.
Bending towards the tallest stereocilia opens ion channels, causing hair cell depolarization.
Bending towards the shortest stereocilia closes ion channels, causing hair cell hyperpolarization.
Afferent pathways carry information to the vestibular cortex.

Hair Cells of the Semicircular Canals

Bending in one direction opens mechanically gated ion channels, depolarizing sensory neurons and increasing the frequency of action potentials.
Bending in the opposite direction closes ion channels, hyperpolarizing the sensory neurons and decreasing the frequency of action potentials.
This change in action potential frequency signals the direction of head movement.

Utricle & Saccule

Detect linear acceleration (head movement up and down/back and forth).
Hair cells are covered with a layer of gel and calcium carbonate crystals called otoliths.
Utricle: Responds to horizontal acceleration.
Saccule: Responds to vertical acceleration.
Acceleration causes the otoliths and gel to move, bending hair cells and generating signals transmitted to the vestibular cortex via afferent pathways.
At rest or constant motion, hair cells depolarize slightly, releasing some neurotransmitters, resulting in low frequency of action potentials.
Forward acceleration bends stereocilia, increasing the frequency of action potentials.
Backward acceleration bends stereocilia away from the tallest stereocilia, closing ion channels and decreasing the frequency of action potentials.

Taste (Gustation)

Taste buds are found in the walls of lingual papillae.
Basic tastes:
- Sweet
- Sour
- Salty
- Bitter
- Savory (umami)

Gustatory Transduction

Ligands:
- Sweet: Monosaccharides and disaccharides
- Salty: Na+
- Sour: H+
- Umami: Glutamate
- Bitter: Plant alkaloids
Ligand binding to receptors triggers changes in ion channel opening or closing, leading to depolarization, calcium channel opening, neurotransmitter release, and action potential generation in afferent neurons.
Afferent pathways end at the gustatory cortex.

Smell (Olfaction)

Olfactory receptor neurons are located in the olfactory epithelium in the upper part of the nasal cavity.
Odorants dissolve in mucus and bind to G protein-coupled receptors on olfactory receptor neuron cilia.
Binding triggers a cascade of events leading to the opening of Na+ channels.

Olfactory Transduction

Na+ channel opening causes depolarization and neurotransmitter release, which in turn triggers action potentials in afferent neurons.
Afferent pathways end at the olfactory cortex.

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