How many vertebrae are in the spinal cord? How many are there of each type?

31 segments:

8 cervical

12 thoracic

5 lumbar

5 sacral

1 coccygeal

What are the enlargements and plexuses of the spinal cord?

cervical enlargement -> brachial plexus

lumbar enlargement -> lumbosacral plexus

Where does the spinal cord begin?

at the foramen magnum

Where does the spinal cord terminate?

at the conus medullaris (L1/L2)

What is the organization of gray and white matter in the spinal cord?

white matter is on the outside (external) while gray matter is internal

What are the 3 funiculi of the spinal cord?

1. posterior (dorsal)

2. anterior (ventral)

3. lateral

What is a funiculus?

groups of spinal cord white matter that contain ascending and descending tracts

Which funiculus is solely concerned with ascending tracts?

posterior (dorsal) funiculi

Wht is the function of the ascending tracts?

To convey sensory information from the periphery to the brain

How many neurons are involved in relaying an impulse in an ascending tract?

3

What happens to the fibers in an ascending tract on their way to the brain?

They all become crossed to the contralateral side of the cord; either at the same level or one or two levels up

What is the function of the descending tracts?

to convey impulses from the brain to lower motor neurons

What are the 2 main groups of descending tracts?

1. pyramidal

2. extrapyramidal

How are non-segmental nerves arranged and when do they form a plexus?

Non-segmental nerves split and combine with other nerves to form a network of nerves called a plexus. A plexus of nerves is then capable of sending fibers from multiple spinal cord levels to specific areas of the body

Which part of the spinal nerve contributes to the plexus?

the ventral primary rami

What happens to the dorsal rami of a non-segmental spinal nerve?

the same thing that happens to the dorsal ramus in typical nerves: it is distributed to the dorsal body wall for sensory and motor innervation

From what vertebral levels do the 3 plexuses arise?

brachial plexus: C5-T1

lumbosacral plexus: L1-S4

What is each plexus responsible for innervating?

brachial plexus = upper limb

lumbosacral plexus = lower limb

What is meant by the term "typical" spinal nerve?

the typical spinal nerve distributes to the periphery without ramifying with any other nerves to form a plexus

What vertebral levels exhibit typical spinal nerves?

T2-T11 are great examples of typical spinal nerves

What does a typical spinal nerve supply?

a typical body segment; a dermatome with sensory and motor innervation

CN I

Olfactory nerve

special sense of smell

CN II

Optic nerve

Special sense of sight

CN III

Oculomotor nerve

Motor to selected extraocular muscles;

Parasympathetic to ciliary & sphincter pupillae muscles via the ciliary ganglion

CN IV

Trochlear nerve

Motor to superior oblique extraocular muscle

CN V

Trigeminal nerve

Ophthalmic division (V1) – sensory to orbit & forehead

Maxillary division (V2) – sensory to upper jaw & region

Mandibular division (V3) – sensory to lower jaw & region, 

                                           motor to muscles of mastication

CN VI

Abducens nerve

Motor to lateral rectus extraocular muscle

CN VII

Facial nerve

Motor to muscles of facial expression;

Carries special sense of taste to anterior 2/3 of tongue;

Parasympathetic to sublingual to submandibular salivary glands via the submandibular region;

Parasympathetic to lacrimal gland via pterygopalatine ganglion

CN VIII

Vestibulocochlear nerve

Special senses of hearing, balance, & acceleration

CN IX

Glossopharyngeal nerve

Sensory to pharyngeal wall & tongue;

Parasympathetic to parotid gland via otic ganglion

CN X

Vagus nerve

Parasympathetic to organs in thoracic & abdominal regions via local ganglion

CN XI

Accessory nerve

Motor to sternocleidomastoid & trapezius

CN XII

Hypoglossal nerve

Motor to muscles of tongue

What are the purely sensory cranial nerves?

Olfactory (CN I)

Optic (CN II)

Vestibulocochlear (CN VIII)

2 divisions of trigeminal (CN V):

    --ophthalmic division (V₁ )

   --maxillary division (V₂)

What are the purely motor cranial nerves?

Trochlear (CN IV)

Abducens (CN VI)

Accessory (CN XI)

Hypoglossal (CN XII)

What are the motor & sensory (mixed) cranial nerves?

1 division of trigeminal (CN V):

--mandibular division (V₃)

What is the motor & parasympathetic cranial nerve?

Oculomotor (CN III)