Functional Organization of the Peripheral Nervous System

A collection of vocabulary words and their definitions related to the functional organization and structure of the Peripheral Nervous System.

Peripheral Nervous System (PNS)

Part of the nervous system that connects the central nervous system (CNS) to the limbs and organs.

What are the two main functional divisions of the PNS?

The Somatic Nervous System (SNS) and the Autonomic Nervous System (ANS).

What is the primary function of the PNS?

To transmit information between the CNS and sensory receptors, muscles, and glands throughout the body.

Sensory Neurons

Neurons that carry signals from sensory receptors to the central nervous system.

What is another term for sensory neurons?

Afferent neurons.

Where are the cell bodies of most sensory neurons located?

In ganglia, such as the dorsal root ganglia for spinal nerves.

Motor Neurons

Neurons that transmit impulses from the central nervous system to effectors like muscles and glands.

What is another term for motor neurons?

Efferent neurons.

To what effectors do motor neurons transmit impulses?

Muscles (skeletal, smooth, cardiac) and glands.

Interneurons

Neurons that connect sensory and motor neurons within the central nervous system.

Where are interneurons found?

Exclusively within the central nervous system (CNS).

What is the primary role of interneurons?

To connect sensory and motor neurons, and to integrate information within the CNS.

Dorsal Root Ganglion

Cluster of sensory neuron cell bodies located just outside the spinal cord.

What specific type of neuron cell bodies are clustered in the dorsal root ganglion?

Sensory neuron cell bodies.

Where is the dorsal root ganglion located?

Just outside the spinal cord, on the dorsal root of spinal nerves.

Proprioceptors

Specialized mechanoreceptors that provide information about body position and movement.

What information do proprioceptors provide to the CNS?

Information about body position, movement, and muscle stretch/tension.

Name two examples of proprioceptors.

Muscle spindles and Golgi tendon organs.

Mechanoreceptors

Receptors that respond to mechanical forces like pressure and vibration.

What types of stimuli do mechanoreceptors respond to?

Mechanical forces such as pressure, touch, vibration, and stretch.

Where are mechanoreceptors commonly found?

In the skin, muscles, joints, and inner ear.

Thermoreceptors

Receptors that detect temperature changes.

What specific changes do thermoreceptors detect?

Changes in temperature, differentiating between warmth and cold.

Where are thermoreceptors located in the body?

In the skin (peripheral) and the hypothalamus (central).

Chemoreceptors

Receptors that respond to chemical stimuli.

What types of chemical stimuli do chemoreceptors respond to?

Internal chemical changes (like O2, CO2, pH) and external chemical cues (taste, smell).

Name two locations where chemoreceptors are important for monitoring blood chemistry.

Carotid bodies and aortic bodies.

Photoreceptors

Receptors that respond to light, primarily located in the retina.

What are the two main types of photoreceptors in the retina?

Rods and Cones.

What is the primary function of rods and cones?

Rods detect dim light and motion; cones detect bright light and color.

Nociceptors

Receptors that respond to painful stimuli.

What types of stimuli activate nociceptors?

Painful stimuli, including extreme mechanical, thermal, or chemical changes.

Why are nociceptors essential for protective reflexes?

They alert the body to potential tissue damage, prompting withdrawal or avoidance.

Neuromuscular Junction

The synapse between a motor neuron and a skeletal muscle fiber.

What neurotransmitter is released at the neuromuscular junction?

Acetylcholine.

What is the effect of acetylcholine release at the neuromuscular junction?

It stimulates the skeletal muscle fiber to contract.

Acetylcholine

Neurotransmitter released at neuromuscular junctions that stimulates muscle contraction.

What is the primary role of acetylcholine at the neuromuscular junction?

To excite the muscle fiber and initiate muscle contraction.

What enzyme breaks down acetylcholine in the synaptic cleft?

Acetylcholinesterase (AChE).

Autonomic Nervous System (ANS)

Part of the PNS responsible for involuntary control over smooth muscles and glands.

What type of control does the ANS exert?

Involuntary control over smooth muscles, cardiac muscle, and glands.

What are the two main divisions of the ANS?

The Sympathetic and Parasympathetic divisions.

Sympathetic Division

Part of the ANS that mobilizes the body's resources under stress ('fight or flight').

What common response is associated with the sympathetic division?

The 'fight or flight' response.

Name one physiological effect of sympathetic activation.

Increased heart rate, dilated pupils, diverted blood flow to muscles, inhibited digestion.

Parasympathetic Division

Part of the ANS that conserves energy and oversees standard bodily functions ('rest and digest').

What common response is associated with the parasympathetic division?

The 'rest and digest' response.

Name one physiological effect of parasympathetic activation.

Decreased heart rate, constricted pupils, stimulated digestion, energy conservation.

Visceral Motor

Part of the peripheral nervous system that governs involuntary muscle activity.

What does visceral motor govern?

Involuntary muscle activity in smooth muscle, cardiac muscle, and glands.

Is visceral motor control part of the somatic or autonomic nervous system?

Autonomic nervous system.

Somatic Motor

Part of the peripheral nervous system that controls voluntary muscle activity.

What does somatic motor control?

A network of interweaving spinal nerves and their rami.

Is somatic motor control part of the voluntary or involuntary nervous system?

Voluntary.

Cranial Nerves

Twelve pairs of nerves that arise from the brain and brainstem.

How many pairs of cranial nerves are there?

Twelve pairs.

From where do cranial nerves arise?

From the brain and brainstem.

Are cranial nerves purely sensory, purely motor, or mixed?

They can be purely sensory, purely motor, or mixed, depending on the specific nerve.

Spinal Nerves

Thirty-one pairs of nerves that connect the spinal cord to the body.

How many pairs of spinal nerves are there?

Thirty-one pairs.

What is the general composition of spinal nerves?

They are typically mixed nerves, containing both sensory and motor fibers.

What are the major branches of a spinal nerve?

Dorsal (posterior) and ventral (anterior) rami.

Plexus

Network of nerves that innervates specific regions of the body.

What is a nerve plexus?

A network of interweaving spinal nerves and their rami.

Name the major nerve plexuses.

Cervical, Brachial, Lumbar, and Sacral Plexus.

Why are nerve plexuses important?

They ensure a region (e.g., limb) is innervated by multiple spinal nerve roots, preventing complete paralysis from a single nerve injury.

Dermatome

map showing the relationship between sensory receptors of the skin and the spinal nerves

What is the clinical use of dermatome maps?

To diagnose and localize the level of spinal nerve damage or irritation.

Paraplegia

Paralysis that affects the lower half of the body, including both legs, and sometimes parts of the trunk. It typically results from spinal cord injury at the thoracic or lumbar levels.

What parts of the body are affected by paraplegia?

Both legs and often the trunk, meaning the lower half of the body.

What spinal cord injury levels commonly lead to paraplegia?

Injuries to vertebrae between T1→L2

Quadriplegia (Tetraplegia)

Paralysis that affects all four limbs (both arms and both legs) and the trunk. It typically results from spinal cord injury at the cervical level.

What parts of the body are affected by quadriplegia?

All four limbs (arms and legs) and the trunk.

What spinal cord injury levels commonly lead to quadriplegia?

Injuries occur above T1

if damage above C4, impacts diaphragm→ cant breathe on their own

parasympathetic exits from

brainstem and sacral spinal nerves

sympathetic exits from

thoracic and lumbar regions

somatic motor neuron

one motor neuron runs between spinal cord and skeletal muscle

visceral motor neuron

two motor neurons run between spinal cord and target tissue (preganglionic and postganglionic)

• these two neurons synapse within an autonomic ganglion

what type of neurotransmitter is released from a somatic motor neuron at a synapse with a skeletal muscle fiber?

Acetylcholine (ACh) is released.

Length of preganglionic and postganglionic axons in the parasympathetic pathway

long preganglionic axons and short postganglionic axons.

Where are autonomic ganglia located in the parasympathetic pathway?

Autonomic ganglia are located within or very close to the target effector organs.

What neurotransmitter synapses within the autonomic ganglion in the parasympathetic pathway?

Acetylcholine (ACh) is released by the preganglionic neuron and binds to nicotinic receptors on the postganglionic neuron.

What neurotransmitter synapses between the postganglionic axon and target tissue in the parasympathetic pathway?

Acetylcholine (ACh) is released by the postganglionic neuron and binds to muscarinic receptors on the target effector organ.

Length of preganglionic and postganglionic axons in the sympathetic pathway

The sympathetic pathway has short preganglionic axons and long postganglionic axons.

Where are autonomic ganglia located in the sympathetic pathway?

Autonomic ganglia are located close to the spinal cord, primarily in the sympathetic trunk (paravertebral ganglia) or collateral ganglia (prevertebral ganglia).

What neurotransmitter synapses within the autonomic ganglion in the sympathetic pathway?

Acetylcholine (ACh) is released by the preganglionic neuron and binds to nicotinic receptors on the postganglionic neuron.

What neurotransmitter synapses between the postganglionic axon and target tissue in the sympathetic pathway?

Norepinephrine (NE) is typically released by the postganglionic neuron and binds to adrenergic receptors on the target effector organ (Note: Acetylcholine is released for sweat glands and some blood vessels).

Sympathetic Trunk Ganglion

Also known as paravertebral ganglia, these are a series of interconnected ganglia forming the sympathetic trunk along the vertebral column.

What is the primary role of sympathetic trunk ganglia?

They serve as a site for synapse between preganglionic and postganglionic sympathetic neurons, allowing for widespread sympathetic responses.

Sympathetic Trunk

A paired chain of ganglia and nerve fibers running vertically alongside the vertebral column from the neck to the pelvis.

What is the function of the sympathetic trunk?

It allows preganglionic sympathetic fibers to ascend, descend, or synapse at the same spinal level to innervate target organs throughout the body.

What is another name for the sympathetic trunk?

Paravertebral chain or ganglionic chain of the sympathetic nervous system.