Unit 6: ANS

Question 1

What structures in the body are controlled by the ANS?

Answer 1

The ANS (Autonomic Nervous System) controls involuntary structures such as:

-Smooth muscle (e.g., in the digestive tract, blood vessels, respiratory tract)

-Cardiac muscle (the heart)

-Glands (sweat, salivary, digestive, adrenal)

-Visceral organs (like the bladder, intestines, stomach)

Question 2

​Describe the components of a visceral reflex and be able to give a specific example.

Answer 2

Components of a visceral reflex arc:

1) Receptor – detects stimulus (e.g., stretch, chemical change)

2) Sensory neuron – sends info to the CNS

3) Integration center – often in the brainstem or spinal cord

4) Motor neurons – preganglionic and postganglionic neurons

5) Effector – smooth muscle, cardiac muscle, or gland

Example:
Baroreceptor reflex

-Baroreceptors in arteries detect high BP

-Sensory signals sent to brainstem

-Parasympathetic output slows heart rate

-BP lowers to normal

Question 3

Compare and contrast the parasympathetic division to the sympathetic division. Be sure
to discuss anatomy and physiology.

Answer 3

Question 4

Compare and contrast somatic pathways to autonomic pathways.

Answer 4

Question 5

​Describe the basic structure of a neural pathway in the ANS. How many neurons are in
each pathway? Where are ganglia? What are the possible effectors?

Answer 5

Two-neuron chain:

 -Preganglionic neuron (cell body in CNS) → releases ACh

 -Postganglionic neuron (cell body in ganglion) → releases ACh or NE

Ganglia are clusters of cell bodies located either near the spinal cord (sympathetic) or near/in target organs (parasympathetic).

Effectors include: smooth muscle, cardiac muscle, and glands.

Question 6

6.​Describe the enteric nervous system.

Answer 6

A semi-autonomous system in the GI tract

Regulates digestion (motility, secretion, blood flow)

Contains millions of neurons in two plexuses (myenteric and submucosal)

Can function independently but is modulated by the ANS

Question 7

What neurons in the ANS are cholinergic (release ACh) and which neurons are
adrenergic (release NE)?

Answer 7

Cholinergic neurons (release ACh):

 -All preganglionic neurons (sympathetic and parasympathetic)

 -All parasympathetic postganglionic neurons

 -Some sympathetic postganglionic neurons (e.g., sweat glands)

Adrenergic neurons (release NE):

 -Most sympathetic postganglionic neurons

Question 8

What two receptor types does ACh bind to? What is the response of the post-synaptic
neuron?

Answer 8

Nicotinic receptors → always excitatory, found on postganglionic neurons and adrenal medulla

Muscarinic receptors → can be excitatory or inhibitory, found on parasympathetic effectors

Question 8

​Be able to describe the various types of receptors found on neurons and effectors in the
ANS. What neurotransmitters do they respond to? What is the response? Where are
they located?

Answer 8

Question 9

Define dual innervation.

Answer 9

Most organs receive input from both sympathetic and parasympathetic divisions, allowing fine-tuned control.

Question 10

Give examples of how the parasympathetic and sympathetic divisions can be
antagonistic with each other.

Answer 10

Heart rate:

Sympathetic ↑ HR

Parasympathetic ↓ HR

Pupil size:

Sympathetic dilates (mydriasis)

Parasympathetic constricts (miosis)

GI activity:

Sympathetic inhibits

Parasympathetic stimulates

Question 11

Give examples of how the parasympathetic and sympathetic divisions can be
cooperative with each other.

Answer 11

While the sympathetic and parasympathetic divisions of the autonomic nervous system typically have opposing effects, they can also work cooperatively in certain physiological processes to produce a unified outcome. Here are key examples:

1. Sexual Function (Male Reproductive System)

• Erection (Parasympathetic): Parasympathetic activity promotes vasodilation in penile arteries, leading to an erection.
• Ejaculation (Sympathetic): Sympathetic activity triggers contraction of smooth muscle in the reproductive ducts and glands, causing ejaculation.

🔄 Cooperative Effect: Both divisions are necessary for normal male sexual function—parasympathetic for arousal and erection, sympathetic for orgasm and ejaculation.

2. Urination (Micturition)

• Bladder Contraction (Parasympathetic): The parasympathetic system contracts the detrusor muscle of the bladder.
• Relaxation of Internal Urethral Sphincter (Sympathetic withdrawal): Sympathetic tone typically keeps the internal sphincter contracted; its inhibition allows relaxation and urine flow.
• Somatic Component: Voluntary relaxation of the external urethral sphincter (via somatic motor pathways) completes the process.

🔄 Cooperative Effect: Coordinated activity of both divisions helps initiate and complete urination.

Question 12

Be able to discuss the effects of sympathetic and parasympathetic innervation for a
variety of visceral organs

Answer 12

The sympathetic and parasympathetic divisions of the autonomic nervous system (ANS) innervate many visceral organs, producing different—often opposing—effects to maintain homeostasis. Here’s a breakdown of their effects on several key organ systems:

🔵 Eye (Pupils & Lens)

• Sympathetic:
  • Pupil dilation (mydriasis) via contraction of radial muscles of the iris.
  • Flattens the lens for far vision by inhibiting ciliary muscle.
• Parasympathetic:
  • Pupil constriction (miosis) via contraction of circular muscles of the iris.
  • Rounds the lens for near vision via contraction of ciliary muscle.

🔵 Heart

• Sympathetic:
  • Increases heart rate (positive chronotropic effect).
  • Increases force of contraction (positive inotropic effect).
• Parasympathetic:
  • Decreases heart rate.
  • Minimal effect on contraction strength.

🔵 Lungs (Bronchi & Airways)

• Sympathetic:
  • Bronchodilation (relaxes bronchial smooth muscle for increased airflow).
• Parasympathetic:
  • Bronchoconstriction (constricts airways).
  • Increases mucus secretion.

🔵 Gastrointestinal (GI) Tract

• Sympathetic:
  • Decreases motility and secretion.
  • Contracts sphincters to inhibit digestion.
• Parasympathetic:
  • Increases motility and digestive secretions.
  • Relaxes sphincters to promote digestion.

🔵 Liver

• Sympathetic:
  • Stimulates glycogenolysis (breakdown of glycogen to glucose).
  • Increases blood glucose.
• Parasympathetic:
  • Slightly promotes glycogen synthesis and storage.

🔵 Urinary Bladder

• Sympathetic:
  • Relaxes detrusor muscle (prevents urination).
  • Contracts internal urethral sphincter.
• Parasympathetic:
  • Contracts detrusor muscle (promotes urination).
  • Relaxes internal sphincter.

🔵 Reproductive Organs (Male)

• Sympathetic:
  • Controls ejaculation via smooth muscle contraction.
• Parasympathetic:
  • Promotes erection through vasodilation (via nitric oxide release).

🔵 Adrenal Medulla (Sympathetic only)

• Stimulated by preganglionic sympathetic fibers to release epinephrine and norepinephrine into the bloodstream (systemic sympathetic response).

Question 13

Explain what transducers do.

Answer 13

In biological systems, particularly in the nervous system, sensory receptors act as transducers by:

Converting physical or chemical stimuli (like light, sound waves, pressure, or chemical concentration)

Into electrical signals (nerve impulses or graded potentials) that the nervous system can interpret.

🔹 Examples in the Human Body:
Photoreceptors in the eye convert light energy into electrical signals.

Mechanoreceptors in the skin convert mechanical pressure or stretch into nerve impulses.

Chemoreceptors in the nose and tongue convert chemical signals (odorants or tastants) into electrical activity.

Hair cells in the ear convert sound wave vibrations into electrical signals for hearing and balance.

In short:
👉 Transducers make sensory perception possible by translating external or internal stimuli into the “language” of the nervous system—electrical signals.

Question 13

Name the type of receptors that detect pain and explain how fast pain is different from
slow pain.

Answer 13

Pain is detected by nociceptors, which are free nerve endings found in the skin, muscles, joints, and some internal organs. These receptors respond to damaging or potentially damaging stimuli, including:

Mechanical (e.g., cuts, pressure, or stretching)

Thermal (extreme heat or cold)

Chemical (like histamine, bradykinin, or acidic environments)

Fast Pain vs. Slow Pain
🔹 Fast Pain
Carried by Aδ fibers, which are thin and myelinated.

These fibers transmit impulses quickly, at speeds of about 5–30 meters per second.

The pain sensation is sharp, well-localized, and immediate, like the pain from a needle prick or a small cut.

Fast pain is usually short-lived and serves as a quick warning of potential or actual injury.

🔹 Slow Pain
Carried by C fibers, which are unmyelinated and very thin.

These impulses travel more slowly—about 0.5–2 meters per second.

The pain is dull, aching, burning, or throbbing, and it develops more gradually after the initial injury.

It tends to be long-lasting and poorly localized, often associated with tissue inflammation or deeper internal damage.

Slow pain encourages protective behaviors and rest during healing.
Summary:
Fast pain alerts you immediately to potential injury (like touching a hot stove).

Slow pain persists and helps you protect the area during healing.

Question 14

Briefly describe the projection pathway for somesthetic/general senses.

Answer 14

The projection pathway for somesthetic (general) senses—such as touch, pressure, pain, temperature, and proprioception—involves three main neurons from the receptor to the cerebral cortex:

🔹 1. First-Order Neuron

• Begins at the sensory receptor (e.g., in the skin, muscles, or joints).
• The cell body is located in the dorsal root ganglion (or cranial nerve ganglion for the head).
• The axon enters the spinal cord or brainstem and synapses with the second-order neuron.

🔹 2. Second-Order Neuron

• Located in the spinal cord or medulla oblongata (depends on the sensory modality).
• The axon decussates (crosses over) to the opposite side of the CNS.
• It ascends to the thalamus, where it synapses with the third-order neuron.

🔹 3. Third-Order Neuron

• Located in the thalamus.
• The axon projects to the primary somatosensory cortex (postcentral gyrus of the parietal lobe), where conscious perception occurs.

Summary:

Receptor → Spinal cord/brainstem (1st order) → Thalamus (2nd order) → Somatosensory cortex (3rd order)

Question 14

Describe the various ways that receptors can be classified.

Answer 14

Receptors can be classified in several ways, depending on their structure, location, and the type of stimulus they detect. Here are the main classification methods:

🔹 1. By Stimulus Type (Modality)

This is based on what kind of energy or signal the receptor responds to:

• Mechanoreceptors – Respond to mechanical forces like pressure, stretch, or vibration (e.g., touch receptors, baroreceptors).
• Thermoreceptors – Detect changes in temperature (warm and cold receptors).
• Photoreceptors – Respond to light (e.g., rods and cones in the retina).
• Chemoreceptors – Detect chemical changes (e.g., taste buds, olfactory receptors, blood pH sensors).
• Nociceptors – Respond to tissue damage or potentially harmful stimuli (pain receptors).

🔹 2. By Location

This considers where the receptor is in relation to the stimulus source:

• Exteroceptors – Located at or near the body surface; detect external stimuli like touch, temperature, and pain.
• Interoceptors (Visceroceptors) – Located in internal organs; detect internal stimuli like blood pressure, stretch, or chemical changes.
• Proprioceptors – Found in muscles, tendons, and joints; detect body position and movement.

🔹 3. By Receptor Structure

This refers to the anatomical form of the receptor:

• Free nerve endings – Unencapsulated, simple structures (e.g., pain and temperature receptors).
• Encapsulated nerve endings – Nerve endings enclosed in connective tissue (e.g., Meissner’s corpuscles, Pacinian corpuscles).
• Specialized receptor cells – Separate from the sensory neuron, like hair cells in the ear or photoreceptors in the eye.

🔹 4. By Rate of Adaptation

This relates to how quickly a receptor stops responding to a constant stimulus:

• Phasic receptors – Rapidly adapt; respond strongly at first then stop firing (e.g., smell, pressure).
• Tonic receptors – Adapt slowly; maintain response as long as the stimulus is present (e.g., pain, proprioception).

Question 15

List the 5 primary taste sensations. What is the sensory transduction mechanism for
each (what is the specific stimulus for each taste and how does it affect the receptor)?

Answer 15

Here’s a breakdown of the 5 primary taste sensations along with their specific stimuli and sensory transduction mechanisms:

🔹 1. Sweet

• Stimulus: Sugars (e.g., glucose, sucrose), artificial sweeteners.
• Mechanism:
  • Sweet compounds bind to G-protein-coupled receptors (GPCRs) on the taste cell membrane (specifically T1R2 + T1R3 receptors).
  • This activates a second messenger cascade (via G-protein gustducin), leading to depolarization and release of neurotransmitters.

🔹 2. Sour

• Stimulus: Acids (hydrogen ions, H⁺).
• Mechanism:
  • H⁺ ions enter taste cells directly through proton channels or block K⁺ channels, leading to membrane depolarization.
  • The depolarization opens voltage-gated Ca²⁺ channels, causing neurotransmitter release.

🔹 3. Salty

• Stimulus: Sodium ions (Na⁺), typically from NaCl.
• Mechanism:
  • Na⁺ ions enter taste cells through epithelial sodium channels (ENaCs).
  • This causes direct depolarization of the taste cell membrane and initiates neurotransmitter release.

🔹 4. Bitter

• Stimulus: Various alkaloids and other bitter compounds (e.g., caffeine, quinine).
• Mechanism:
  • Bitter substances bind to GPCRs (mainly T2R receptors).
  • This triggers a G-protein (gustducin)-mediated cascade, leading to release of internal Ca²⁺ stores, depolarization, and neurotransmitter release.

🔹 5. Umami (savory)

• Stimulus: Amino acids, especially glutamate (e.g., MSG).
• Mechanism:
  • Glutamate binds to a GPCR (T1R1 + T1R3 receptors).
  • This activates a second messenger system, similar to sweet and bitter tastes, leading to depolarization and neurotransmitter release.

Summary of Transduction Types:

• Sweet, Bitter, Umami: Use G-protein-coupled receptors and second messenger pathways.
• Salty and Sour: Use ion channels for direct depolarization.

Question 16

Where in the cerebrum are taste sensations processed?

Answer 16

Taste sensations are ultimately processed in the cerebral cortex, specifically in the primary gustatory cortex, which is responsible for the conscious perception of taste.

🔹 Location of the Primary Gustatory Cortex:

• Found in the insula and the frontal operculum (a part of the frontal lobe near the lateral sulcus).
• Taste signals are also relayed to the somatosensory cortex (for texture and temperature) and the limbic system (for emotional and reward aspects of taste).

🔹 Pathway Summary:

1. Taste signals travel from taste buds via the facial (VII), glossopharyngeal (IX), and vagus (X) nerves.
2. They synapse in the solitary nucleus in the medulla.
3. Signals are then relayed to the thalamus.
4. From the thalamus, information is projected to the primary gustatory cortex in the insula and frontal operculum.

Question 17

What is found within the olfactory foramina of the cribriform plate? What bone is the
cribriform plate part of?

Answer 17

🔹 What is found within the olfactory foramina of the cribriform plate?

The olfactory foramina (tiny holes in the cribriform plate) contain the axons of olfactory receptor neurons. These axons:

• Pass from the olfactory epithelium in the nasal cavity,
• Through the foramina in the cribriform plate,
• Into the olfactory bulbs, where they synapse with second-order neurons.

🔹 What bone is the cribriform plate part of?

The cribriform plate is part of the ethmoid bone, a delicate bone located at the roof of the nasal cavity and forming part of the anterior cranial floor.

So, to summarize:

• Olfactory foramina contain olfactory nerve fibers (CN I).
• The cribriform plate belongs to the ethmoid bone.

Question 18

Do olfactory receptors adapt quickly or slowly? Explain.

Answer 18

Olfactory receptors adapt quickly. This means they become less sensitive to a continuous or repeated odor stimulus over time.

Why do olfactory receptors adapt quickly?
Receptor adaptation occurs as part of a neural process. When an odorant continuously stimulates the olfactory receptors, the olfactory receptor neurons become less responsive, and the signal sent to the brain weakens.

This phenomenon helps to prevent sensory overload and allows the brain to focus on new odors or changes in the environment. Essentially, it’s the body’s way of ignoring a constant, unchanging stimulus.

Mechanism:
After an odorant binds to the receptor, a second messenger system (often involving cAMP) is activated.

Over time, enzymes break down the cAMP, reducing receptor sensitivity.

Additionally, inhibition from the brain (through descending pathways) can modulate the sensitivity of the olfactory system, contributing to rapid adaptation.

Practical Example:
You may notice a strong perfume when you first enter a room, but after a few moments, the smell fades, even though it is still present. This is due to the rapid adaptation of your olfactory receptors.

Question 19

​What is the function of the pinna (auricle)?

Answer 19

The pinna (auricle) is the visible part of the ear, and it serves several important functions in the auditory system:

🔹 Functions of the Pinna:

1. Sound Collection and Amplification:
   • The pinna acts like a funnel, collecting sound waves from the environment and directing them into the external auditory canal (ear canal).
   • Its shape and structure help to amplify certain frequencies of sound, particularly those in the human speech range.
2. Localization of Sound (Sound Direction):
   • The unique shape of the pinna helps in localizing the direction from which a sound is coming. It helps determine whether the sound is coming from above, below, in front, or behind the listener.
   • The way sound waves are reflected and diffracted by the folds and contours of the pinna provides spatial information to the brain, which is essential for auditory localization.
3. Protection of the Ear Canal:
   • The pinna helps protect the external auditory canal by acting as a barrier to foreign objects, debris, and extreme temperatures.
4. Resonance:
   • The shape of the pinna also plays a role in the resonance of sound waves, especially for higher-frequency sounds. This resonance effect enhances the sensitivity to certain frequencies, particularly those that are important for speech perception.

In summary:

The pinna serves to collect, amplify, and localize sound, as well as protect the ear canal, helping to optimize hearing and spatial awareness of sounds.

Question 20

Describe and follow the sequence of events from a sound wave entering the pinna all
the way to the information being processed in the brain.

Question 21

What are the three regions of the ear and what structures are located within each
region and what is happening in each region?

Question 22

Explain the relationship between K+ gates and cochlear hair cells.

Question 22

Describe the location and function of the conjunctiva and the lacrimal apparatus.

Question 23

​Explain how the semicircular canals provide the brain with information about body position (equilibrium/balance)

Question 24

Name the three tunics/layers of the eye and briefly describe their functions. Be sure to include the location and function of the following parts of the eye: cornea, sclera, choroid, retina, optic disc, lens and iris as it relates to these three tunics.

Question 24

Describe the path of a photon of light and the subsequent nerve impulse through the parts of the eye and to the cerebral cortex.

Question 25

​Define emmetropia, hyperopia and myopia

Question 25

​Where are the two humors of the eye and what are their functions?

Question 26

Name and describe the optical components.

Question 27

How does your eye respond when looking at something close up versus something that is far away? In other words, describe the near response of the eye.

Question 28

Compare and contrast rods and cones. Where in the retina are they located? What is their function?

Question 29

Color blindness is a sex-linked trait – explain what this means.

Question 30

What two components make up the neural apparatus?

Question 31

24.​Review the eye lab notes. Be able to identify and spell each of the bolded structures on the lab notes.