# Peripheral Nervous System

Psychology I · Behavioral Biology · https://tryals.app/learn/psychology-i/peripheral-nervous-system

## The Peripheral Network

The **Peripheral Nervous System (PNS)** links the central nervous system to the rest of the body. It splits into two major functional divisions.

The **somatic nervous system** handles voluntary control. **Afferent (sensory)** nerves carry information inward from skin, muscles, and joints, while **efferent (motor)** nerves carry commands outward to skeletal muscles.

The **autonomic nervous system (ANS)** governs involuntary functions like heart rate, digestion, and glandular secretion.

## Sympathetic vs Parasympathetic

The ANS splits into two opposing branches:

| Branch | Nickname | Typical Effects |
| --- | --- | --- |
| Sympathetic | Fight-or-flight | Heart rate up, pupils dilate, digestion inhibited |
| Parasympathetic | Rest-and-digest | Heart rate down, pupils constrict, digestion stimulated |

The **adrenal medulla** amplifies sympathetic stress signals via adrenaline. The **vagus nerve** dominates parasympathetic restoration.

**Common pitfall:** Treating these as good/bad switches. Both are constantly active, and organ state reflects the **balance** between them. Chronic stress damages health.

## Practice questions

5 of this lesson's 12 practice questions, with answers. The full set is in the app.

### 1. Atropine blocks acetylcholine receptors on the heart. Given to a resting patient it raises the heart rate substantially, although it does nothing whatever to the sympathetic system. Why does blocking a receptor speed the heart up?

A. Because acetylcholine is also the sympathetic transmitter.
B. Because blocking a receptor produces the opposite effect.
C. Because the resting heart is under constant drive from both branches.
D. Because the drug stimulates the sympathetic ganglia.

**Answer:** C. Because the resting heart is under constant drive from both branches.

**Why:** The word doing the work is 'resting'. A resting heart is not idling free of input, it is being held down by continuous vagal brake, and atropine takes the foot off it. Blocking a receptor removes a signal rather than generating its opposite, the speeding was there all along, unopposed.

Page: https://tryals.app/practice/psychology-i/peripheral-nervous-system/atropine-blocks-acetylcholine-receptors-on-the-heart-given-to-a

### 2. A large meal makes you sleepy and a fright kills your appetite instantly. Why do digestion and alertness trade against each other so directly?

A. Because the parasympathetic branch directly suppresses consciousness
B. Because the two branches bundle incompatible whole-body states
C. Because the stomach physically presses on the diaphragm, reducing oxygen to the brain
D. Because digestion consumes glucose that the brain then lacks

**Answer:** B. Because the two branches bundle incompatible whole-body states

**Why:** The branches sell whole postures, not organ-by-organ settings: rest-and-digest commits blood to the gut, fight-or-flight yanks it to muscle. You cannot buy half of each, which is why a heavy lunch and a sharpened mind are in genuine competition.

Page: https://tryals.app/practice/psychology-i/peripheral-nervous-system/a-large-meal-makes-you-sleepy-and-a-fright-kills-your-appetite

### 3. Order the sympathetic 'fight-or-flight' response, from threat to recovery.

**Answer:**

1. A threat is perceived and the sympathetic branch activates.
2. Heart rate rises, pupils dilate, and digestion is inhibited.
3. The adrenal medulla releases adrenaline into the bloodstream.
4. Adrenaline amplifies and prolongs the body's aroused state.
5. Once the threat passes, the parasympathetic branch restores rest-and-digest.

**Why:** Sympathetic activation drives the immediate changes, then the adrenal medulla's adrenaline amplifies and prolongs them, and finally the parasympathetic branch restores calm. The hormonal amplification comes after the fast neural response, and recovery is an active parasympathetic step.

Page: https://tryals.app/practice/psychology-i/peripheral-nervous-system/order-the-sympathetic-fight-or-flight-response-from-threat-to

### 4. Sort each scenario by which autonomic branch is driving it.

**Answer:**

- Sympathetic activation: Your heart pounds and your pupils widen as a car swerves at you, Adrenaline floods your bloodstream from the adrenal medulla, Digestion is put on hold to free up resources
- Parasympathetic activation: After a big meal, blood flows to the gut and digestion ramps up, Saliva flows and your heart rate settles as you relax

**Why:** Sympathetic activation mobilizes the body (pounding heart, dilated pupils, adrenaline, digestion halted); parasympathetic activation restores and conserves (digestion up, saliva, calming heart). Digestion is the giveaway - it goes up under parasympathetic, down under sympathetic.

Page: https://tryals.app/practice/psychology-i/peripheral-nervous-system/sort-each-scenario-by-which-autonomic-branch-is-driving-it

### 5. Select every statement that is TRUE about the PNS.

A. Once the sympathetic branch activates, the parasympathetic branch switches fully off.
B. The somatic nervous system carries commands to skeletal muscle.
C. The parasympathetic branch prepares the body for fight-or-flight.
D. Chronic, unrelieved sympathetic dominance is what damages health over time.
E. The sympathetic and parasympathetic branches usually oppose each other on the same organ.

**Answer:** B. The somatic nervous system carries commands to skeletal muscle.; D. Chronic, unrelieved sympathetic dominance is what damages health over time.; E. The sympathetic and parasympathetic branches usually oppose each other on the same organ.

**Why:** Somatic-to-muscle, opposing branches, and chronic-dominance harm are all true. The branches are not a full on/off switch (organ state is their balance), and fight-or-flight is sympathetic, not parasympathetic - so those two are false.

Page: https://tryals.app/practice/psychology-i/peripheral-nervous-system/select-every-statement-that-is-true-about-the-pns