Peripheral Nervous System

What are the two main divisions of the nervous system?

The central nervous system (CNS) and the peripheral nervous system (PNS).

What does the central nervous system (CNS) consist of?

The brain and spinal cord.

What is the primary role of the CNS?

To integrate information.

What does the peripheral nervous system (PNS) consist of?

Cranial nerves, spinal nerves, peripheral ganglia, and sensory receptors.

What is the role of the PNS?

It serves as the communication network between the CNS and the rest of the body.

The autonomic nervous system (ANS) is part of which larger system?

It is a major component of the peripheral nervous system (PNS).

What does the autonomic nervous system (ANS) regulate?

Involuntary bodily functions such as heart rate, blood pressure, digestion, and breathing.

Does the ANS function with or without conscious thought?

Without conscious thought.

What are the three divisions of the autonomic nervous system (ANS)?

Sympathetic, parasympathetic, and enteric nervous systems.

What is the role of the sympathetic nervous system?

It controls the "fight-or-flight" response.

What is the role of the parasympathetic nervous system?

It controls the "rest-and-digest" response.

What is the role of the enteric nervous system?

It helps control the internal organs, especially the digestive system.

What is the overall function of the ANS divisions together?

To maintain homeostasis and regulate internal organs.

The peripheral nervous system (PNS) includes which type of receptors?

Somatic receptors in body tissues (e.g., skin and muscles) that monitor sensations such as temperature and pain.

What do somatic sensory nerves do?

They carry afferent sensory signals to the brain, where they are integrated into conscious experience.

What do voluntary efferent motor nerves do?

They transmit signals from the brain to skeletal muscles, causing them to contract on command.

Is the somatic nervous system voluntary or involuntary?

Voluntary — it operates under conscious control.

What type of signals does the somatic nervous system receive?

Signals from somatic receptors in tissues like skin and muscles.

What do autonomic sensory (afferent) nerves do?

They receive signals from visceral receptors monitoring internal conditions and send them to the CNS.

What do autonomic motor (efferent) nerves do?

They transmit signals from the CNS to smooth muscle, cardiac muscle, and glands, causing functional changes.

Autonomic motor signals can cause what two types of changes in target tissues?

Increased activity (excitation) or decreased activity (inhibition).

What tissues and organs are innervated by the autonomic division?

Cardiac muscle, smooth muscle, and secretory cells in the digestive tract.

How is the autonomic efferent division organized compared to the somatic division?

It uses two neurons: a preganglionic neuron and a postganglionic neuron.

Where is the cell body of the preganglionic neuron located?

In the CNS (axon exits through the ventral root).

Where does the preganglionic neuron synapse?

At an autonomic ganglion with a postganglionic cell.

Where do postganglionic neurons synapse?

With target cells such as smooth muscle, cardiac muscle, or glands.

What are the two main autonomic divisions?

Sympathetic and parasympathetic divisions.

What is dual innervation?

When a target receives input from both sympathetic and parasympathetic neurons, usually with opposite effects.

What is the main role of the sympathetic division?

To activate the “fight-or-flight” response during stress or emergencies.

What physiological changes are caused by the sympathetic division?

Increased heart rate, dilated pupils, redirected blood flow to muscles, and regulation of sweating, metabolism, and kidney activity.

Where are the cell bodies of sympathetic preganglionic neurons located?

In the lateral horn of the thoracic spinal cord.

Where are most sympathetic ganglia located?

In a chain of ganglia near the spinal cord (the sympathetic chain ganglia).

How are sympathetic neurons structured compared to parasympathetic?

They have long postganglionic neurons that release norepinephrine onto target tissues.

What is another name for the parasympathetic nervous system?

The "rest-and-digest" system.

When is the parasympathetic nervous system most active?

During states of relaxation and recovery, especially after eating.

What is the main role of the parasympathetic nervous system?

To conserve energy, promote digestion, and maintain homeostasis at rest.

Where do parasympathetic neurons primarily originate?

In the cervical spinal cord and the sacral areas (near the tailbone).

Which nerves often carry parasympathetic signals?

Several cranial nerves.

Where are parasympathetic ganglia (neuron meeting point) located?

Very close to or within the target tissues.

Why is the parasympathetic preganglionic neuron long and the postganglionic neuron short?

Because the ganglion is near the target organ — the first neuron travels far, but the second has a short distance to go.

What neurotransmitter do parasympathetic postganglionic neurons release onto target tissues?

Acetylcholine (ACh), which binds to muscarinic receptors on the target tissue.

What chemical (neurotransmitter) do preganglionic neurons release in both sympathetic and parasympathetic systems?

Acetylcholine (ACh) — it excites the next neuron using nicotinic receptors.

How do sympathetic postganglionic neurons differ?

They release norepinephrine (or epinephrine), which acts on alpha and beta adrenergic receptors.

Can acetylcholine have both excitatory and inhibitory effects?

Yes — it depends on the type of muscarinic receptor on the target cell.

Why are adrenergic and muscarinic receptors important in medicine?

They are G-protein coupled receptors (GPCRs) — many drugs target them to affect heart rate, digestion, and other automatic body functions.

What does the sympathetic nervous system do to the pupils?

It causes the pupils to dilate (get bigger) so more light enters the eye.

Where are the sympathetic preganglionic neurons that control pupil dilation located?

In the thoracic spinal cord.

What neurotransmitter do sympathetic postganglionic neurons release to dilate pupils?

Norepinephrine, which makes the radial muscles of the iris contract.

What does the parasympathetic nervous system do to the pupils?

It causes the pupils to constrict (get smaller).

Where are the parasympathetic preganglionic neurons for pupil constriction found?

In the midbrain nucleus.

Which nerve carries parasympathetic signals for pupil constriction?

The oculomotor nerve (cranial nerve III), which connects to the ciliary ganglion behind the eye.

What neurotransmitter causes pupil constriction?

Acetylcholine (ACh) — it activates the circular muscles of the iris.

What part of the nervous system controls involuntary urination actions (like bladder contraction)?

The autonomic nervous system.

What part of the nervous system controls voluntary urination actions (like external sphincter control)?

The somatic nervous system.

What happens when neurological disorders affect urination control?

They can cause incontinence — loss of normal control over urination.