Chapter 14

Identify the number of spinal nerves in each region (cervical, thoracic, lumbar, sacral).

the number of spinal nerves for each segment of the spinal cord is equal to the number of vertebrae and the sole exception is the cervical segment of the spinal cord, which has 8 spinal nerves but only 7 vertebrae -the cervical segment has one "Extra" spinal nerve because CN 1 comes out on top of C 1 and CN 8 comes out on the bottom of C7 -12 thoracic spinal nerves -5 lumbar spinal nerves -5 sacral spinal nerves

sacral plexus

the sacral plexus is formed from the spinal nerves L4 through S4, and it supplies the legs, hamstrings, and buttocks. It is the smallest plexus in the body and its major nerve is the sciatic nerve, which is the largest nerve in the body. -the sciatic nerve consists of two nerves joined together by the tibial and common fibular nerves (this nerve splits into the deep fibular and superficial fibular nerve)

where do the soma of a motor nerve live?

the ventral horn of gray matter

Distinguish ventral from dorsal spinal roots, including the dorsal root ganglion.

ventral spinal roots carry only motor axons and dorsal spinal roots carry only sensory axons -you find sensory unipolar neurons in the dorsal root ganglion

CN VI

-Abducens -motor -innervates the lateral rectus on lateral aspect of the eyeball which abducts the eye (draws eyeball away from the midline)

organization of the PNS

PNS consists of nerves and ganglia -CNS and PNS are in constant communication with one another. Afferent, sensory information is transmitted from the PNS to the CNS, and efferent, motor information is transmitted from the CNS to the PNS.

cervical plexus

formed by spinal nerves C1 through C4. This network of axons runs deep in the neck, underneath the sternocleidomastoid muscle. The cervical plexus gives rise to the phrenic nerve, which innervates the diaphragm. Although the phrenic nerve is primarily a motor nerve, it has some sensory function as well. -Without a functional phrenic nerve, you cannot contract your diaphragm, so this is a very important plexus. This is why damage to the spinal cord at regions about C3 To C5 often causes fatal nerve damage that inhibits breathing.

brachial plexus

formed from spinal nerves C4 to T1. It is located in the neck and armpit region of the body and it innervates the arms and shoulders. -nerves it includes: 1. ulnar & median nerve innervate the anterior compartment of the antebrachium 2. radial nerve & axillary nerve run along the posterior aspect of the brachium and the posterior aspect of the antebrachium 3. musculocutaneous nerve innervates the anterior part of the brachium

lumbar plexus

formed from spinal nerves L1 to L4 -obturator nerve which innervates the medial compartment of the thigh (adductor muscles) -femoral nerve innervates the anterior aspect of the thigh (quadriceps)

CN I

-Olfactory -sensory; sense of smell -consists of several loosely associated bipolar axons that pass from inside the nasal cavity to the brain through olfactory foramina. These axons are part of bipolar neurons with cell bodies found in the epithelial tissue; they send their dendrites into the mucosa of the nasal cavity and the axons synapse inside the olfactory bulb, then the neurons send their axons back to the brain through the olfactory tract.

CN XI

-accessory -motor: innervates the sternocleidomastoid muscle and the trapezius muscle which both regulate the movement of the head and neck -different than other cranial nerves in that it does not originate from the brain, but originates from the ventral rootlets coming off of the cervical spinal cord and these rootlets come together to form a nerve

CN VII

-facial -mixed nerve -motor: make facial expressions -sensory: convey taste on the anterior 2/3 of the tongue

CN IX

-glossopharyngeal -both -motor: innervates skeletal muscles that allow for voluntary swallowing -sensory: facilitate taste for the posterior 1/3 of the tongue

CN XII

-hypoglossal -motor: innervates the tongue, allows for voluntary movement of the tongue, and it supplies constant innervation so that the tongue has some constant minimal level of torsion (so its not floppy) -aid tongue movements during feeding, swallowing, and speech

CN III

-oculomotor -motor -activates skeletal muscles that move the eyeball 1. medial rectus muscle 2. superior rectus muscle 3. inferior oblique muscle 4. inferior rectus muscle 5. levator palpebrae muscle, which is attached to the eyelid and causes the eyelid to open and close and damage here can cause someone to have a "droopy eyelid"

CN II

-optic -sensory -originates in the retina and involved in vision

Describe the somatic innervation of the back, trunk, and limbs.

-the back of the trunk is innervated in a segmented fashion by the dorsal rami. -segmented innervation is also observed by the thoracic region, where the ventral rami of the thoracic spinal nerves travel along the underside of each rib as intercostal nerves -areas of muscle innervated by each intercostal nerve overlap a little, so if you damage an intercostal nerve you won't completely lose feeling in any particular area

CN V

-trigeminal -largest -mixed -motor: mastication (chewing) -sensory: facial sensation, including touch, temperature, and pain (plucking chin hairs) -do not confuse with CN 7!!

CN IV

-trochlear -motor -innervates the superior oblique muscle (attached to the eyeball and responsible for involuntary movement of the eye and when you go for a ride in a car this muscle automatically corrects for bumps) -smallest -only cranial nerve originating from the dorsal aspect of the brai

CN X

-vagus -both -motor: swallowing and vocalization -sensory: visceral sensation and taste for the back of the throat, near the epiglottis (when you swallow something spicy, you can feel the burning at the back of your throat before you taste any real flavors) -provides a large amount of parasympathetic innervation to all of the organs of the thoracic and abdominal cavities (only cranial nerve that innervates anything below the clavicles, goes 2/3 of the way down your ventral body cavity)

CN VIII

-vestibulocochlear -sensory -balance & equilibrium and hearing

Distinguish spinal rootlets vs. spinal roots vs. spinal nerves vs. spinal rami. Classify the type of information carried in each (sensory, motor, mixed).

-when a dorsal and ventral root come together, they form a spinal nerve (which is a mixed nerve) -each of these spinal nerves bifurcates (splits in 2) forming dorsal and ventral rami (mixed nerves) -dorsal root only carries sensory axons -ventral root only carries motor axons -each of these roots is formed from a series of rootlets, which span the length of the spinal cord segment

Define dermatomes and relate this to spinal nerves.

A dermatome is an area of skin that is supplied by a single nerve. We can use this concept to create a sensory map of the body that describes which spinal nerves receive sensory input from various regions of the skin. -useful for two reasons: 1. localization of injuries- a physician with a patient who complains of a lack of sensation in an area of the body can use a dermatome to conclude which nerve may be damaged 2. nerve blocks- sometimes a surgeon gives a patient a nerve block before or after surgery to reduce or eliminate pain during or after surgery. Dermatomes help physicians determine which nerves to block.

Define nerve plexus

A plexus us a net of neurons (axons traveling in the PNS). The ventral rami of all spinal nerves (except T2-T12) branch and join one another forming an interlacing network of axons (No limbs hang off your thoracic region, so it makes sense that spinal nerves T2 through T12 use segmented innervation and do not form plexuses). These plexuses primarily serve the limbs. -the fact that multiple axons from various spinal nerves serve the same muscles means that damage to any individual nerve will not completely paralyze any muscle (functional redundancy). If you only had one nerve going directly to your biceps brachii and that nerve was damaged, you would lose all feeling in that muscle.

what neurotransmitter would be released by the hypoglossal nerve?

AcH because it innervates a skeletal muscle (motor)

cranial vs spinal nerves

cranial nerves are attached to or closely associated with the brain and there are 12 pairs, so 24 total -some of these are motor, some are sensory, and some are mixed spinal nerves are attached to the spinal cord and you have 31 pairs so 62 total -all of these are mixed

types if nerves

mixed: contain afferent and efferent axons traveling in the same sheath motor: only efferent axons sensory: only afferent axons