7.3 Spinal nerves

Question 1

how many spinal nerves are there

Answer 1

31 pairs of mixed nerves

Question 2

what is dermatome

Answer 2

• area of skin innervated by cutaneous branches of a single spinal nerve

*all spinal nerves except C₁ innervate skin

• most dermatomes overlap
• way of determining site of spinal cord damage (see what they feel above and below site)

Question 3

Describe spinal nerve innervation of joints

Answer 3

hiltons law

• any nerve serving a nuslce that produces movement at a joint also innervates the joint and the skin over the joint

(also provides sensroy)

Question 4

describe roots of the spinal nerve

Answer 4

Spinal chord -> Rootlets -> root -> spinal nerve -> rami

• doral and ventral rootlets: come together to foem a root
• dorsal root and ventral root

*roots/rootlets and only be motor or sensory

Question 5

Describe the rami of spinal nervess

Answer 5

each spinal nerve branches into 4 mixed rami:

1. meningeal branch: to spinal meninges & blood vessels
2. dorsal ramus: to posterior bdoy trunk (deep muscles of back)
3. ventral ramus: form plexuses (except T2-T12: act as itnercostal nerves -> muscles of ribs, anterolateral thorax & abdonimal wall

*intercostal nerves that run beteen ribs

4. rami communicantes: autonomic pathways (join to ventral remi in thoacic region)

Question 6

Why do we have a plexus of ventral rami

Answer 6

*looks like mesh

• fibers from various ventral rami crisscross & become redistributed so:
• > each resulting branch has fibers from several spinal nerves
• > fibers from each ventral ramus travel to target via seveeral routes

result: each muscle in limb receives nerve suply from more than one spinal nerve

benefit: demaging one spinal segment/root will not completely paralyze any limb muscle

*plexus gives lots of back up

Question 7

Describe the cervial plexus

Answer 7

ventral rami: C1-C5

• innervates skin & muscles of neck, ear, back of head and shoulders

*C345 keeps diaphragm alive -> forms Phrenic nerve that innervates diaphragm

Question 8

describe brachial plexus

Answer 8

• formed by ventral rami of C5-C8, and T1
• gives rise to nerves that innervate upper limb & pectoral girdle (motor and sensory)

Question 9

what are the major branches of the brachial plexus

Answer 9

Rugby Teams Drink Cold Beer

• Roots (ventral rami)
  
  • C5, C6, C7, C8, T1
• Trunks
  
  • upper, middle, lower
• Divisions
  
  • Anterior or posteriro
• Chords
  
  • Lateral, medial, posterior
• Bracnches (major termial branches -> peripheral nerves)
  
  • musculocutaneous, medial, ulnar, radial and axillary

Question 10

How to draw brachial plexus

Answer 10

Question 11

General function of brachial plexus:

Radial nerve

Answer 11

Motor: most posterior muscles of limb

Sensory: posterior skin of limb

*goes down posterior aspect of upper limb (extensors)

*allows to extend wrist against gravity

*C5-8 and T1

Question 12

brachial plexus: General functions

Axillary nerve

Answer 12

*arm pit

Motor: deltoid, teres minor (shoulder abduction)

sensory: skin & joint capsule of shoulder

*innercation from C5&6

Question 13

General function of brachial plexus:

musculocutaneous

Answer 13

elbow flex and bicep flex

• Motor: anterior arm muscles (musculo)
  sensory: skin of lateral forarm (cutaneous)

*innervation from C5,6 and 7

Question 14

General function of brachial plexus:

nedian nerve

Answer 14

*nothing in arm, just forarm and hand

motor: lateral flexors & pronators in forarm + some lateral intrinsic muscles of hand
sensory: skin of lateral aspect of hand

*innervation from C5,6,7,8 and T1

Question 15

General function of brachial plexus:

Ulnar nerve

Answer 15

*forarem -> ulnar bone is medial so this does the medial forarm msucles

Motor: anterior medial forearm msucles + most medial intrinsic muscles of hand

Sensory: skin of medial aspect of hand

*innerved by nerves C8 and T1

Question 16

what would happen if lateral chord of the left brachial plexus was completely severed

Answer 16

Question 17

describe lumbar plexus, what nerves are part of it

Answer 17

• innervate thigh, abdominal wall and psoas muscles
• obturator nerve: passes through obturator foramen to innervate adductor muscles

*into medial thigh

femorla nerve: innervates anterior thigh muscles of skin of anteiror/medial tigh and medial leg (goes in front)

Question 18

Describe Sacral plexus and assocaited nerves

Answer 18

*comes off sacral aspect of spinal chord

• serves buttock, lower limb, pelvic structures and perineum
• Pudendal nerve: skin/muscles of perineum

-Sciatic nerve: longest/thickest nerve of body

• > runs posteriorly
• > innervates hamstrings, adductor magnus and most muslces in leg and foot
• > composed of tibial and common fibular nerves

Question 19

a tight ____ can impact siactic muscle

Answer 19

piri formis

Question 20

where to give gluteal nijection

Answer 20

*DONT WANT TO HIT SCIATIC

• aim for superior lateral quad