BIOL 3103: Exam 2 Study Guide

Dual Innervation

An organ receives input from both sympathetic and parasympathetic systems. They usually have opposite effects.

Somatic Nervous system

Skeletal muscle control

Autonomic Nervous System

Innervation of most visceral organs. Parasympathetic and sympathetic nervous systems.

Parasympathetic Nervous System

“Rest and digest”, maintains homeostasis, and has acetylcholine

Sympathetic Nervous System

“Fight or flight”, may disrupt homeostasis, and has acetylcholine and norepinephrine

Dual Innervations examples

Eye, heart, lungs, pancreas, and digestive tract.

Parasympathetic dominance: Eye

Constriction of pupil for near vision

Parasympathetic dominance: Heart

Decreased rate and force

Parasympathetic dominance: Lungs

Constriction of bronchioles (smaller airway)

Parasympathetic dominance: Pancreas

Insulin and glucagon release (as determined by blood sugar level)

Parasympathetic dominance: Digestive tract

Increased motility (most of blood needs to go here)

Sympathetic dominance: Eye

Dilation of pupil for far vision

Sympathetic dominance: Heart

Increased rate and force

Sympathetic dominance: Lungs

Dilation of bronchioles (larger airway)

Sympathetic dominance: Pancreas

Glucagon release (discharge stored glucose)

Sympathetic dominance: Digestive tract

Decreased motility

Sympathetic dominance state

Active state

Parasympathetic dominance state

Resting state

Dual innervations exceptions

Salivary glans, sweat glans, and most veins and arterioles

Sympathetic Salivary glands

Stimulatory

Parasympathetic Salivary glands

Stimulatory

Sympathetic Sweat glands

none

Parasympathetic Sweat glands

Stimulatory

Parasympathetic most Veins and Arterioles

not much change

Sympathetic most Veins and Arterioles

Construction determined by action potential firing rate

Location of nicotinic receptors in the autonomic nervous system

Neuromuscular junctions, ganglionic neurons, and adrenal medulla

Location of muscarinic receptors in the autonomic nervous system

Gut, heart, bronchioles (lung), sweat glands, and blood vessels of skeletal muscle

Vertebrate stress response

The body’s response to a stressor that activates both the sympathetic nervous system and the endocrine system.

Physiology of hormonal stress

Slower but longer-lasting stress response involving the hypothalamus, pituitary gland, adrenal cortex, and glucocorticoids.

Physiology of neutral stress

A fast, short-lasting (transient) stress response triggered by activation of the sympathetic nervous system.

How does hypothalamus mediate responses to stressors?

Activation of the sympathetic nervous system and secretion of corticotropin releasing hormones.

Glucocorticoids

Stress hormones such as cortisol and corticosterone released during the hormonal stress response.

Stress response effects on the heart

Stress causes increased heart rate and increased force of contraction.

Stress response effects on the lungs

Stress causes bronchodilation, meaning the bronchioles become larger.

Stress response effects on the liver

Stress causes the liver to make/release more glucose so energy is available.

Stress response effects on the pancreas

Sympathetic stimulation causes glucagon release, helping make stored glucose available.

Chronic stress leftover effects

Immunosuppression, hypertension, muscle loss, and inhibition of growth

Peripheral nervous system

The part of the nervous system that connects the CNS to the rest of the body through sensory input and motor output. Contains afferent and efferent pathways.

Afferent sensory tracts

Sensory information traveling towards the CNS

Efferent motor tracts

Motor information traveling away from the CNS toward muscles/organs.

Decussation

A neural pathway crossing from one side to the other, as shown in the pathway diagram.

Nerve

A bundle of axons in the peripheral nervous system.

Ganglion

A relay point in the PNS where neurons communicate; in the ANS it lies between the preganglionic and postganglionic neuron.

Collateral (corollary)

Shown as part of a sympathetic pathway

How does the peripheral nervous system and central nervous system interact with each other?

The PNS carries sensory information into the CNS and carries motor commands out of the CNS.

Dorsal root/ horn

Carries/contains afferent sensory information

Ventral root/horn

Carries/contains efferent motor information

Reflex

A rapid response that can be integrated at the spinal cord, allowing a faster response without waiting for higher brain processing.

Withdrawal reflex

A spinal reflex that causes a limb to pull away from a painful stimulus.

Crossed extensor reflex

A spinal reflex where one limb withdraws from pain while the opposite limb extends to support the body.

Enteric nervous system (ENS)

The nervous system associated with the digestive tract, controlling digestive muscle activity and secretion. “Brain in your gut”.

Submucosal plexus

Contains sensory cells that communicate with the myenteric plexus and motor fibers that stimulate fluid secretion into the lumen.

Myenteric plexus

Contains neurons that regulate the enzyme output of adjacent organs.

Lumen

Nerves do not enter this area and digestion occurs here.

Mesentery

Attaches the bowel to the body wall and contains major arteries, veins, lymphatic system, and external nerves.

Enteric nervous system complexity

Highly complex system containing about 100 million neurons and using 30+ neurotransmitters

Enteric nervous system neurotransmitters

Uses many of these to control digestive activity

Varicosities

Swollen regions along autonomic neurons.

Why are varicosities useful to the enteric nervous system?

Help spread the neural message widely across smooth muscle.

When is sympathetic dominant?

during an active/stressed state → “fight or flight”

When is parasympathetic dominant?

during the resting state → “rest and digest”

Where does the sympathetic system emerge from in the central nervous system?

Thoracic and lumbar regions

Where does the parasympathetic system emerge from in the central nervous system?

Cranial and sacral regions

Parasympathetic fiber lengths

Long preganglionic and short postganglionic

Sympathetic fiber lengths

Short preganglionic and long postganglionic

Sympathetic preganglionic neurotransmitters

acetylcholine (ACh)

Parasympathetic preganglionic neurotransmitters

acetylcholine (ACh)

Parasympathetic postganglionic neurotransmitters

acetylcholine (ACh)

Sympathetic postganglionic neurotransmitters

norepinephrine (NE)

Major types of cholinergic receptors

Nicotinic and muscarinic receptors

Nicotinic receptor

A cholinergic receptor that causes excitation through ion influx.

Muscarinic receptor

A cholinergic receptor that is G-protein coupled and is found on target tissues.

Nicotinic receptor agonists

ACh, nicotine, and carbachol

Muscarinic receptor agonists

ACh, muscarine, and carbachol

Nicotinic receptor cellular response

Binding causes excitation through ion influx.

Muscarinic receptor cellular response

Muscarinic receptors are G-protein coupled, and the response depends on the target tissue.

First step of muscle contraction:

Action potential arrives at a terminal button (of the neuromuscular junction), it then simulates the release of ACh, which then moves across the cleft, and then triggers action potential in the muscle fiber.

Second step of muscle contraction:

Third step of muscle contraction:

Second step of muscle contraction:

Fourth step of muscle contraction:

Fifth step of muscle contraction:

Sixth step of muscle contraction:

Seventh step of muscle contraction:

Eighth step of muscle contraction:

Sliding filament hypothesis

Myosin pulls actin toward the sarcomere's center. The filaments don't shorten; they slide past each other (which is how muscles shorten).

Calcium role in sliding filament

Binds troponin and initiates contraction

Troponin role in sliding filament

Changes shape when calcium binds

Tropomyosin role in sliding filament

Blocks binding sites on actin when muscle is relaxed

Actin role in sliding filament

Thin filaments pulled by myosin

Myosin role in sliding filament

Thick filament; its heads form cross-bridges and produce power strokes

Sarcoplasmic reticulum role in sliding filament

Stores and releases calcium

Transverse tubules role in sliding filament

Conduct action potentials into muscle fibers

Ryanodine receptors role in sliding filament

Release Ca²⁺ from the sarcoplasmic reticulum

Dihydropyradine receptors role in sliding filament

Triggers adjacent ryanodine receptors

SERCA2 role in sliding filament

Uses ATP to move calcium back into the sarcoplasmic reticulum

ATP binding role in sliding filament

Causes myosin to detach from actin

ATP hydrolysis role in sliding filament

Energizes the myosin head

Phosphorylation role in sliding filament

Activates myosin in smooth muscle by adding phosphate to myosin light chains, allowing actin–myosin interaction and contraction.

Dephosphorylation role in sliding filament

Removes phosphate from myosin light chains, reducing cross-bridge cycling and promoting smooth muscle relaxation.

Release in the myosin power stroke role in sliding filament

Release of Pi and ADP during the cycle which allows myosin to pull actin toward the center of the sarcomere, producing muscle contraction.