BIO 202 ch 10

What is the difference between the somatic and autonomic motor pathways?

The somatic nervous system controls voluntary movement using a single motor neuron that innervates skeletal muscle. The autonomic nervous system controls involuntary functions using a two-neuron pathway (preganglionic and postganglionic neurons) that innervates smooth muscle, cardiac muscle, and glands.

What is voluntary control?

Voluntary control is conscious control over skeletal muscle through the somatic nervous system.

What is involuntary control?

Involuntary control is automatic regulation of smooth muscle, cardiac muscle, and glands through the autonomic nervous system.

What tissues are targeted by the somatic nervous system?

Skeletal muscle.

What tissues are targeted by the autonomic nervous system?

Smooth muscle, cardiac muscle, and glands.

Describe the organization of the somatic motor pathway.

A single motor neuron extends from the CNS directly to skeletal muscle without synapsing in a ganglion.

How many neurons are in the somatic motor pathway?

One motor neuron.

What is the effector organ of the somatic nervous system?

Skeletal muscle.

What is the neuromuscular junction (NMJ)?

The specialized synapse where a somatic motor neuron communicates with a skeletal muscle fiber.

What structures make up the neuromuscular junction?

Axon terminal, synaptic cleft, motor end plate, and nicotinic acetylcholine receptors.

What neurotransmitter is released at the neuromuscular junction?

Acetylcholine (ACh).

Describe the events at the neuromuscular junction.

Action potential arrives → calcium enters axon terminal → ACh released → ACh binds nicotinic receptors → sodium enters muscle fiber → muscle action potential generated → contraction begins.

How is the signal terminated at the neuromuscular junction?

Acetylcholinesterase breaks down acetylcholine into acetate and choline, ending stimulation.

What does botulinum toxin do?

Blocks acetylcholine release, preventing muscle contraction and causing flaccid paralysis.

What does curare do?

Blocks nicotinic acetylcholine receptors so ACh cannot bind, preventing muscle contraction.

What do organophosphates do?

Inhibit acetylcholinesterase, causing excessive acetylcholine accumulation and continuous muscle stimulation (spastic paralysis).

What is the autonomic nervous system (ANS)?

The division of the nervous system that regulates involuntary functions of smooth muscle, cardiac muscle, and glands.

What are the functions of the autonomic nervous system?

It regulates heart rate, blood pressure, digestion, gland secretion, respiration, and many other homeostatic processes.

What are visceral effectors?

Smooth muscle, cardiac muscle, and glands controlled by the autonomic nervous system.

What is dual innervation?

Most organs receive both sympathetic and parasympathetic nerve fibers that usually produce opposite effects.

Describe the autonomic motor pathway.

A preganglionic neuron leaves the CNS and synapses in an autonomic ganglion with a postganglionic neuron, which then innervates the target organ.

What is a preganglionic neuron?

The first neuron in the autonomic pathway; its cell body is in the CNS and it releases acetylcholine.

What is a postganglionic neuron?

The second neuron in the autonomic pathway that extends from an autonomic ganglion to the effector organ.

What is an autonomic ganglion?

A cluster of neuron cell bodies outside the CNS where preganglionic neurons synapse with postganglionic neurons.

Describe the autonomic motor pathway to the adrenal medulla.

Preganglionic sympathetic neurons synapse directly with chromaffin cells of the adrenal medulla, which release epinephrine and norepinephrine into the bloodstream.

What are the three divisions of the autonomic nervous system?

Sympathetic, parasympathetic, and enteric divisions.

What is the sympathetic division?

The fight-or-flight division that prepares the body for stress and emergencies.

What is the parasympathetic division?

The rest-and-digest division that conserves energy and promotes digestion and maintenance.

What is the enteric nervous system?

A network of neurons within the gastrointestinal tract that controls digestive function.

What is thoracolumbar outflow?

The sympathetic division originates from spinal cord segments T1-L2.

What are sympathetic chain ganglia?

Ganglia located alongside the vertebral column that distribute sympathetic signals throughout the body.

What are collateral ganglia?

Sympathetic ganglia located anterior to the vertebral column that supply abdominal and pelvic organs.

What is craniosacral outflow?

The parasympathetic division originates from the brainstem and sacral spinal cord (S2-S4).

What are terminal ganglia?

Parasympathetic ganglia located near or within target organs.

What is the neuroeffector junction?

The site where autonomic postganglionic neurons communicate with smooth muscle, cardiac muscle, or glands.

What are varicosities?

Swollen regions along autonomic axons that release neurotransmitters over a broad area of target tissue.

Describe signal transmission at the neuroeffector junction.

Action potential reaches varicosities → calcium enters → neurotransmitter released → neurotransmitter binds receptors on the effector → target tissue responds.

What are cholinergic neurotransmitters?

Neurotransmitters that use acetylcholine.

Where is acetylcholine used in the autonomic nervous system?

Released by all preganglionic neurons and by parasympathetic postganglionic neurons.

What are adrenergic neurotransmitters?

Neurotransmitters that use norepinephrine or epinephrine.

Where is norepinephrine released?

By most sympathetic postganglionic neurons.

Where is epinephrine released?

By chromaffin cells of the adrenal medulla into the bloodstream.

What are nicotinic receptors?

Cholinergic receptors found on autonomic ganglia and skeletal muscle at the neuromuscular junction.

What are muscarinic receptors?

Cholinergic receptors located on parasympathetic target organs.

What are alpha adrenergic receptors?

Adrenergic receptors that usually stimulate smooth muscle contraction such as vasoconstriction.

What are beta adrenergic receptors?

Adrenergic receptors that often increase heart activity or relax smooth muscle such as bronchodilation.

What is autonomic tone?

The continuous baseline activity of both sympathetic and parasympathetic divisions that allows rapid adjustments in organ function.

What regulates autonomic tone?

The hypothalamus.

How do the sympathetic and parasympathetic divisions regulate organs?

They work reciprocally, with one division increasing activity while the other decreases activity.

What are the parasympathetic functions?

Conserve energy, slow heart rate, stimulate digestion, increase gland secretion, and promote waste elimination.

What does SLUDD stand for?

Salivation, Lacrimation, Urination, Digestion, and Defecation.

What are the sympathetic functions?

Increase heart rate, blood pressure, blood glucose, respiration, and blood flow to skeletal muscles while inhibiting digestion.

Why are sympathetic effects diffuse and long-lasting?

Because many organs are activated simultaneously and epinephrine released into the bloodstream prolongs the response.

What role does the sympathetic nervous system play during exercise and stress?

It increases ATP production, oxygen delivery, heart rate, blood pressure, and blood flow to skeletal muscles.

What are autonomic reflexes?

Automatic involuntary responses that help maintain homeostasis, such as regulating blood pressure and digestion.

Where are autonomic control centers located?

In the hypothalamus, brainstem, and spinal cord.

What cardiovascular control centers regulate?

Heart rate and blood pressure.

What respiratory control centers regulate?

Breathing rate and depth.

Compare the structure and function of the somatic and autonomic motor pathways.

The somatic pathway uses one neuron to control skeletal muscle voluntarily and is always excitatory. The autonomic pathway uses two neurons to control smooth muscle, cardiac muscle, and glands involuntarily and may excite or inhibit its targets.

How does the autonomic nervous system integrate with the endocrine system?

The hypothalamus regulates autonomic activity and stimulates the adrenal medulla to release epinephrine and norepinephrine into the bloodstream.

How does the autonomic nervous system integrate with the cardiovascular system?

It continuously adjusts heart rate, blood vessel diameter, and blood pressure to maintain homeostasis.

What are examples of autonomic dysfunction?

Orthostatic hypotension, autonomic neuropathy, hypertension, botulism, organophosphate poisoning, and myasthenia gravis.

Compare sympathetic and parasympathetic divisions.

Sympathetic = fight or flight, thoracolumbar outflow, short preganglionic and long postganglionic neurons, norepinephrine at most target organs. Parasympathetic = rest and digest, craniosacral outflow, long preganglionic and short postganglionic neurons, acetylcholine at target organs.

Where is acetylcholine used versus norepinephrine?

Acetylcholine is released by all preganglionic neurons, parasympathetic postganglionic neurons, and somatic motor neurons. Norepinephrine is released by most sympathetic postganglionic neurons.

Distinguish nicotinic, muscarinic, alpha, and beta receptors.

Nicotinic receptors bind acetylcholine in autonomic ganglia and skeletal muscle. Muscarinic receptors bind acetylcholine on parasympathetic target organs. Alpha and beta receptors bind norepinephrine and epinephrine on sympathetic target organs.

Describe the steps of signal transmission at the neuromuscular junction.

Action potential reaches axon terminal → calcium enters → acetylcholine released → acetylcholine binds nicotinic receptors → sodium enters muscle fiber → muscle action potential generated → acetylcholinesterase breaks down acetylcholine to terminate the signal.