Ch. 13: The Peripheral Nervous System & Reflex Activity

What are the main components of the peripheral nervous system?

Sensory detectors, the communication lines extending from the central system, and the points where these lines activate muscles or glands.

What are afferent nerves?

Communication lines that carry signals towards the central nervous system.

What are efferent nerves?

Communication lines that carry signals away from the central nervous system.

What are motor endings?

The specialized points where nerve fibers connect with and activate muscles or glands.

What do sensory receptors respond to?

Changes in the surrounding environment.

What is the initial electrical event in a sensory receptor when stimulated?

A localized change in electrical potential.

What type of signal do sensory receptors ultimately trigger in afferent fibers?

Nerve impulses that travel to the central nervous system.

What type of stimulus do mechanoreceptors detect?

Physical forces like touch, pressure, and vibration.

What type of stimulus do thermoreceptors detect?

Changes in temperature.

What type of stimulus do photoreceptors detect?

Light energy.

What type of stimulus do chemoreceptors detect?

Dissolved molecules.

What type of stimulus do nociceptors detect?

Potentially harmful conditions that result in the sensation of pain.

Where are exteroceptors located and what do they respond to?

Near the body's surface, detecting stimuli from the external environment.

What types of sensations do exteroceptors include?

Touch, pressure, pain, temperature of the skin, limb position, and the special senses.

Where are interoceptors located and what do they respond to?

Within the body's internal organs and blood vessels, detecting internal stimuli.

What types of sensations do interoceptors include?

Stretch, pain, temperature, and chemical changes within the body.

Where are proprioceptors located and what do they respond to?

In skeletal muscles, tendons, joints, and ligaments, detecting internal stimuli related to body position and movement.

What is the function of proprioceptors?

To continuously inform the brain about body movements and position.

What are simple receptors?

Modified nerve endings of sensory neurons.

Where are simple receptors located and what type of information do they monitor?

Throughout the body, monitoring general sensations like touch, temperature, and chemical stimuli.

What are complex receptors?

Specialized structures involving multiple cell types, forming sensory organs.

What senses are associated with complex receptors?

Vision, hearing, balance, smell, and taste.

Describe the connective tissue wrapping around individual nerve fibers.

A layer surrounding each nerve fiber and its myelin sheath.

Describe the connective tissue wrapping around bundles of nerve fibers.

A layer enclosing groups of nerve fibers into fascicles.

Describe the connective tissue wrapping around an entire nerve.

The outermost layer enclosing multiple fascicles.

What other structures are typically found within a nerve alongside nerve fibers?

Blood vessels and lymphatic vessels.

What are mixed nerves?

Nerves containing both sensory and motor fibers.

What are sensory (afferent) nerves?

Nerves that primarily carry signals towards the central nervous system.

What are motor (efferent) nerves?

Nerves that primarily carry signals away from the central nervous system.

How else can nerves be classified based on the areas they serve?

By whether they carry sensory or motor information to or from somatic (body) or visceral (internal organ) structures.

How many pairs of cranial nerves are there and where do they primarily serve?

12 pairs, mostly serving the head and neck region.

Which cranial nerve is responsible for the sense of smell?

The first (I) cranial nerve.

Which cranial nerve is responsible for vision (light detection)?

The second (II) cranial nerve.

Which cranial nerve controls eye movement?

The third (III) cranial nerve.

Which cranial nerve also controls eye movement?

The fourth (IV) cranial nerve.

Which cranial nerve has both sensory and motor functions related to the face?

The fifth (V) cranial nerve.

What are the sensory functions of the fifth cranial (V) nerve?

Sensation from the skin and mucous membranes of the nose and mouth.

What is the motor function of the fifth (V) cranial nerve?

Muscles involved in chewing.

Which virus is clinically associated with the fifth (V) cranial nerve and what does it cause?

Herpes simplex virus type 1 (HBV-1), causing cold sores and fever blisters.

Where else can HSV-1 be found in relation to cranial nerves?

In the nerves responsible for facial sensation/movement and balance/hearing.

Which cranial nerve also controls eye movement (abduction)?

The sixth (VI) cranial nerve.

Which cranial nerve has both sensory and motor functions related to the face and taste?

The seventh (VII) cranial nerve.

What is the sensory function of the seventh (VII) cranial nerve?

The sense of taste.

What are the motor functions of the seventh (VII) cranial nerve?

Control of facial muscles (expression), tear production, and salivary glands.

Which condition is clinically associated with the seventh (VII) cranial nerve?

A sudden weakness or paralysis of facial muscles.

Which cranial nerve (VIII) is responsible for hearing and balance?

The eighth (VIII) cranial nerve.

Which cranial nerve has both sensory and motor functions related to taste and swallowing?

The ninth (IX) cranial nerve.

What is the sensory function of the ninth (IX) cranial nerve?

The sense of taste.

What are the motor functions of the ninth (IX) cranial nerve?

Control of muscles in the throat for swallowing and salivary glands.

Which cranial nerve extends from the brainstem to the throat, voice box, and internal organs?

The tenth (X) cranial nerve.

Which cranial nerve controls muscles of the neck and upper back?

The eleventh (XI) cranial nerve.

Which cranial nerve controls the muscles of the tongue?

The twelfth (XII) cranial nerve.

How many pairs of spinal nerves are there and where do they supply?

31 pairs, supplying all parts of the body except most of the head and some of the neck.

How are spinal nerves formed?

By the merging of sensory and motor roots from the spinal cord.

What does this formation make all spinal nerves?

Containing both sensory and motor fibers.

How are spinal nerves named?

According to the region of the vertebral column from which they emerge.

What do spinal nerves divide into shortly after leaving the spinal cord?

Branches that extend posteriorly and anteriorly.

What do dorsal rami of spinal nerves serve?

The skin and muscles of the back.

What do ventral rami of spinal nerves do (except in the thoracic region)?

Extend forward and merge with other ventral rami to form networks.

What is a plexus?

A network formed by the merging of ventral rami of spinal nerves.

What is the advantage of nerve plexuses?

Damage to a single spinal nerve segment is less likely to cause complete paralysis of a limb muscle.

What do intercostal nerves supply?

Muscles between the ribs, skin of the chest and abdomen.

What area does the cervical plexus primarily innervate?

Mostly the skin of the neck and shoulder.

Name an important nerve that arises from the cervical plexus and its function.

The phrenic nerve, which controls the diaphragm for breathing.

What can irritation of the phrenic nerve cause?

Involuntary spasms of the diaphragm, known as hiccups.

What happens if both phrenic nerves are severed?

Paralysis of the diaphragm and cessation of breathing.

What does the brachial plexus give rise to?

Nearly all the nerves that control the upper limb.

What can a "brachial block" achieve clinically?

Loss of sensation and movement in the arm.

Name some major nerves arising from the brachial plexus.

Axillary, radial, median, and ulnar nerves.

Which nerve is commonly compressed in carpal tunnel syndrome?

The median nerve.

What do the proximal branches of the lumbar plexus innervate?

Muscles of the abdominal wall.

What do the major branches of the lumbar plexus innervate distally?

The front and inner thigh.

Name a major nerve from the lumbar plexus and its innervation.

The femoral nerve, supplying the front thigh muscles and skin of the front thigh and inner leg.

What can lumbar nerve compression cause?

Gait problems and pain or numbness in the front of the thigh.

What areas do the branches of the sacral plexus serve?

The buttocks, lower limbs, pelvic region, and perineum.

Name the thickest and longest nerve in the body, arising from the sacral plexus.

The sciatic nerve.

What areas does the sciatic nerve innervate?

The back of the thigh and almost the entire lower leg.

What other functions are associated with branches of the sacral plexus?

Innervation of perineal muscles and skin, aiding in erection, and voluntary control of urination.

What can lower lumbar-sacral nerve compression or damage cause?

Pain, numbness, and impaired function of the lower limbs.

What is sciatica?

Pain radiating along the course of the sciatic nerve.

What are the consequences of severing the sciatic nerve?

Near uselessness of the leg, with hamstring paralysis and loss of foot and ankle movement.

What are dermatomes?

Areas of skin supplied by the sensory branches of individual spinal nerves.

How are dermatomes arranged on the body trunk?

In relatively uniform horizontal strips.

How are dermatomes arranged on the lower limbs?

In a more complex, spiraling pattern.

Which spinal nerves supply the anterior leg surfaces?

Lumbar nerves.

Which spinal nerves supply the posterior leg surfaces?

Sacral nerves.

How do efferent nerves in the PNS activate effectors?

By releasing chemical messengers.

What neurotransmitter is used by somatic nerves at voluntary skeletal muscles?

Acetylcholine (ACh).

What neurotransmitters are typically used by the autonomic nervous system?

Acetylcholine (ACh) or norepinephrine (NE).

Where do somatic nerves terminate on skeletal muscles?

At specialized junctions with a high concentration of neurotransmitters.

What is a characteristic of impulse transmission at the neuromuscular junction?

Very rapid signal transfer across the synapse.

How does the autonomic nervous system differ in its control of internal organs compared to somatic control of skeletal muscles?

It typically involves a two-neuron pathway.

What is the general role of the parasympathetic nervous system?

Promoting relaxation and slowing down organ activity during normal conditions.

What is the nature of parasympathetic responses?

Often localized to specific organs.

What is the general role of the sympathetic nervous system?

Preparing the body for activity, stress, or emergencies.

What is the nature of sympathetic responses?

Often involving widespread effects throughout the body.

How do motor endings differ on smooth muscle compared to skeletal muscle?

They are more spread out.

What is a characteristic of impulse transmission to smooth muscle?

Slower signal transfer.

What is the basic functional unit of the nervous system in terms of rapid, automatic responses?

A neural pathway involving sensory input, integration, and motor output.

What is the basic structural unit of the nervous system?

The individual nerve cell.