The nervous system

Question 1

Central nervous system consists of nerves in:

Answer 1

• brain

- spinal cord

Question 2

Peripheral nervous system consists of nerves:

Answer 2

• everywhere else (nerves peripheral to brain + spinal cord)
  Terms:
• ganglia (cell bodies)
• plexus (networks of nerves)

Question 3

spinal segment

Answer 3

• a section of the spinal cord with its associated pair of (left and right) nerve roots

Question 4

spinal segment from medial to lateral

Answer 4

• spinal cord
• off spinal cord splits into two nerve roots
• a ventral root (contains motor nerves), a dorsal root (contains sensory nerves)
• they combine to form the spinal (mixed) nerve (contains sensory and motor nerves)
• these then split off into the dorsal ramus (contains sensory + motor nerves, supplies muscles of the back (motor) and overlying skin (sensory))
  and the ventral ramus (contains sensory + motor nerves, supplies muscles of anterior trunk and limbs (motor) and overlying skin (sensory))

Question 5

Features of the brachial plexus (ACRONYM)

Answer 5

Read
The
Damn
Cadaver
Book

Rami/Roots
Trunks
Divisions
Cords
Branches

Question 6

Musculocutaneous nerve

Answer 6

Course: 
- pierces coracobrachialis 
Root value:
- C5, 6, 7
Motor distribution: 
- muscles in anterior compartment of arm (corachobrachialis, biceps brachii, brachialis)
Sensory distribution:
- skin over lateral forearm, shoulder and elbow joints
Vulnerable: 
- pierces coracobrachialis

Question 7

Median nerve

Answer 7

Course:
- Lower half of arm: passes medial to brachial artery, passes b/w two heads of pronator teres, then deep to FDS, then passes b/w FDS + FCR, under the flexor retinaculum (i.e. in the carpal tunnel) to enter the hand
Root value:
C5, 6, 7, 8, T1
Motor distribution:
- Supplies all forearm flexors except 1 ½ muscles (FCU + medial ½ of FDP)
as well as thenar muscles + lateral 2 lumbricals
Sensory distribution:
- Anterior surface of palm and lateral 3 ½ digits, extending posteriorly to the distal IP joint line
Vulnerable:
- b/w heads of pronator teres, carpal tunnel

Question 8

Ulnar nerve

Answer 8

Course: 
- Passes medial to brachial artery, passes posteriorly over medial head of triceps to lie b/w the medial epicondyle + olecranon (the nerve at the “funny bone”), enters forearm by passing between two heads of FCU to lie on FDP, passes anterior to flexor retinaculum and around medial side of hook of hamate to enter the hand
Root value:
C8, T1
Motor distribution: 
- FCU + medial ½ of FDP
- all intrinsic muscles of the hand besides lateral 2 lumbricals + thenar eminence
Sensory distribution:
Anterior and posterior palm and medial 1 ½ digits
Elbow and wrist joints
Vulnerable: 
Medial epicondyle
Hook of hamate

Question 9

RADIAL NERVE

Answer 9

Course:
- passes in radial groove of shaft of humerus to divide long and lateral heads of triceps. passes b/w brachialis + brachioradialis just above elbow, crosses elbow anteriorly and divides into superficial (radial) and deep (posterior interosseus) branches,
superficial branch: runs deep to brachioradialis, surfaces posteriorly near its tendon
Deep branch: Winds around neck of radius to posterior forearm, passes b/w two heads of supinator, runs along posterior surface of interosseus membrane
Root value:
C5, 6, 7, 8, T1
Motor distribution:
- All muscles in posterior compartment of arm + forearm
- Abductor pollicis longus
Sensory distribution:
- Skin over posterior arm, forearm and hand
Vulnerable:
- Spiral groove along the humerus
- B/w heads of supinator

Question 10

Axillary nerve

Answer 10

Course: 
- Inferior shoulder joint, surgical neck of humerus
Root value:
- C5, 6
Motor distribution: 
- Deltoid and teres minor 
Sensory distribution:
- Skin over upper arm, shoulder joint 
Vulnerable: 
- Surgical neck of humerus

Question 11

other branches off brachial plexus (OFF THE C5 NERVE ROOT + UPPER TRUNK)

Answer 11

C5 NERVE ROOT
- Dorsal scapula nerve: supplies rhomboids + levator scapulae
- long thoracic nerve: supplies serratus anterior
UPPER TRUNK
- nerve to subclavius 
- suprascapula nerve 
Course: 
- Passes through suprascauplar notch into supraspinous fossa
Root value:
- C5, 6
Motor distribution: 
- Supra + infraspinatus 
Sensory distribution:
- Shoulder + A/C joints 
Vulnerable: 
- Suprascapular notch

Question 12

other branches off brachial plexus (OFF THE POSTERIOR BRANCH)

Answer 12

Upper and lower subscapular nerve: supply subscapularis (+ teres major by lower subscapular n.). shoulder joint
- thoracodorsal nerve: supplies latissimus dorsi

Question 13

other branches off brachial plexus (OFF THE LATERAL CORD + LOWER TRUNK)

Answer 13

LATERAL CORD:

- lateral pectoral nerve: supplies pectoralis major, shoulder joint

Question 14

other branches off brachial plexus (OFF THE MEDIAL CORD)

Answer 14

• Medial cutaneous nerve of arm and forearm

- medial pec nerve

Question 15

Nerve supply to joints (shoulder, elbow, wrist)

Answer 15

Shoulder: axillary, suprascapular, subscapular, lateral pectoral, musculocutaneous
Elbow: musculocutaneous, median, radial, ulnar
Wrist: median, radial, ulnar

• As a general rule, a nerve that supplies a joint also tends to supply the muscles that move the joint and the skin over the distal attachments of the muscles (Hilton’s Law)