Peripheral Nervous System & Reflexes (BIO 105 Chapter 21)

Question and Answer flashcards covering spinal nerves, plexuses, dermatomes, cranial nerves, and reflexes based on Chapter 21 lecture notes.

How many pairs of spinal nerves exist in the human body?

31 pairs

Why are spinal nerves referred to as “mixed nerves”?

Because each spinal nerve carries both afferent (sensory) fibers toward the spinal cord and efferent (motor) fibers away from it.

Through which openings do spinal nerves exit the vertebral column?

The intervertebral foramina.

What are the numbers of cervical, thoracic, lumbar, sacral, and coccygeal spinal nerve pairs respectively?

Cervical 8, Thoracic 12, Lumbar 5, Sacral 5, Coccygeal 1.

Between which bones does the C1 spinal nerve exit?

Between the occipital bone and the atlas (C1 vertebra).

What is the collection of nerve roots that extends beyond the conus medullaris called?

The cauda equina.

At approximately which vertebral level does the spinal cord end (conus medullaris)?

Around the level of L2.

Which root of a spinal nerve contains motor fibers?

The ventral (anterior) root.

Which root of a spinal nerve contains sensory fibers and has a dorsal root ganglion?

The dorsal (posterior) root.

What type of fibers are found in the dorsal ramus of a spinal nerve?

Somatic motor and sensory fibers that supply the posterior head, neck, and trunk.

What three types of fibers are carried in the ventral ramus of a spinal nerve?

Somatic motor, somatic sensory, and autonomic (sympathetic) fibers.

What is a nerve plexus and its functional advantage?

A complex network formed by ventral rami that ensures damage to one spinal nerve does not completely paralyze a region.

Name the four major nerve plexuses.

Cervical, Brachial, Lumbar, and Sacral (with coccygeal).

Which spinal nerve roots form the cervical plexus?

Ventral rami of C1–C4 and a branch of C5.

Which nerve that “keeps the diaphragm alive” arises from the cervical plexus and what are its roots?

The phrenic nerve; roots C3, C4, and C5.

Which spinal nerve roots form the brachial plexus?

Ventral rami of C5–T1.

List the five terminal branches of the brachial plexus.

Axillary, Musculocutaneous, Radial, Median, and Ulnar nerves.

Which brachial plexus nerve innervates the deltoid and teres minor?

The axillary nerve (C5–C6).

Which nerve supplies motor fibers to biceps brachii, brachialis, and coracobrachialis?

The musculocutaneous nerve (C5–C7).

Which brachial plexus nerve provides motor supply to triceps brachii and extensor muscles of the forearm?

The radial nerve (C5–T1).

Which nerve supplies most forearm flexors and sensory fibers to the anterior hand?

The median nerve (C5–T1).

Which nerve innervates flexor carpi ulnaris and intrinsic hand muscles and supplies sensation to digits 4-5?

The ulnar nerve (C8–T1).

What dermatome corresponds to the deltoid region of the arm?

C5.

The anatomical snuff box on the dorsum of the hand is innervated by which dermatome?

C6.

Which dermatome includes the tip of the middle finger?

C7.

Digits 4 and 5 correspond to which dermatome?

C8.

Which dermatome covers the medial aspect of the forearm?

T1.

At what dermatome level is the nipple located?

T5.

The umbilicus lies in which dermatome?

T10.

Which dermatome supplies the medial ankle?

L4.

Which dermatome corresponds to the dorsum of the foot?

L5.

Which dermatome covers the posterior-lateral leg?

S1.

How many pairs of cranial nerves are there?

Twelve.

Give the mnemonic for remembering cranial nerve names.

“On Old Olympus’ Towering Tops A Friendly Viking Grows Vines And Hops.”

Give the mnemonic for remembering cranial nerve functions (sensory, motor, both).

“Some Say Marry Money But My Brother Says Big Business Matters More.”

Which cranial nerve (number and name) carries the sense of smell?

Cranial nerve I – Olfactory nerve (sensory).

Which cranial nerve is responsible for vision?

Cranial nerve II – Optic nerve (sensory).

Which cranial nerve controls most eye movements and pupil constriction?

Cranial nerve III – Oculomotor nerve (motor).

Which cranial nerve innervates the superior oblique muscle of the eye?

Cranial nerve IV – Trochlear nerve (motor).

Which cranial nerve provides facial sensation and innervates muscles of mastication?

Cranial nerve V – Trigeminal nerve (both).

Which cranial nerve abducts the eyeball via the lateral rectus?

Cranial nerve VI – Abducens nerve (motor).

Which cranial nerve controls facial expression muscles and conveys taste from the anterior two-thirds of the tongue?

Cranial nerve VII – Facial nerve (both).

Which cranial nerve is divided into vestibular and cochlear branches for balance and hearing?

Cranial nerve VIII – Vestibulocochlear (Acoustic) nerve (sensory).

Which cranial nerve supplies the tongue and pharynx and participates in blood pressure reflexes?

Cranial nerve IX – Glossopharyngeal nerve (both).

Which cranial nerve carries mostly parasympathetic fibers to thoracic and abdominal viscera?

Cranial nerve X – Vagus nerve (both).

Which cranial nerve innervates the trapezius and sternocleidomastoid for shoulder shrugging?

Cranial nerve XI – Accessory nerve (motor).

Which cranial nerve controls tongue movements and deviates toward the injured side when damaged?

Cranial nerve XII – Hypoglossal nerve (motor).

In the somatic nervous system, how many neurons connect the CNS to the effector muscle?

A single motor neuron.

Which neurotransmitter is released at somatic neuromuscular junctions?

Acetylcholine.

Define a reflex.

A predictable, automatic response to a stimulus mediated by a reflex arc.

What is the classification of the knee-jerk (patellar) reflex regarding location and laterality?

It is a spinal, segmental, ipsilateral, stretch (myotatic), extensor, deep reflex.

Which spinal cord segments mediate the ankle-jerk (Achilles) reflex?

First and second sacral segments (S1–S2).

What is the Babinski sign and what does its presence after 18 months indicate?

Upward fanning of toes during the plantar reflex; it suggests corticospinal tract damage.

Which nerves form the corneal reflex arc and what is the response?

Sensory via ophthalmic branch of CN V, motor via CN VII; response is blinking when the cornea is touched.

Absence of the abdominal reflex may indicate what type of lesion?

An upper motor neuron lesion (though it may also be absent normally or during pregnancy).