Color Atlas of Neurology

Hypoglossal n. (XII)

Lower trunk (C8/T1)

Great auricular n.

Lesser occipital n.

C 1

Transversus colli n.

C 2

Ansa cervicalis (from C1 to C3)

C 3

Supraclavicular nn.

C 3

C 4

Middle trunk (C7)

C 5

Upper trunk (C5/C6)

Dia-

C 4

C 6

Dorsal scapular n. (C3-C5)

phragm

C 7

Suprascapular n. (C4-C6)

Subclavian n. (C5/C6)

C 8

Musculocutaneous

T 1

n. (C5-C7)

Axillary n. (C5/C6)

Median n.

(C5-T1)

Medial

Axillary a.

pectoral n.

(C8/T1)

C 3/C 4

Radial n. (C5-T1)

Medial cord

Ribs 1 and 2

Ulnar n. (C7/8-T1)

(C8/T1)

Long thoracic

n. (C5-C7)

Medial cutaneous n. of forearm

Lateral cord

Phrenic n.

Medial cutaneous n. of arm

(C5-C7)

(C3/C4)

Posterior cord (C5-C8)

Cervicobrachial plexus

Deltoid m.

(C = cervical vertebra;

T = thoracic vertebra)

Biceps

Pectoralis

brachii m.

major m.

Flexor carpi ulnaris

Triceps

Pronator

m.

teres m.

brachii m.

Supraand

Abductor

infraspinatus

Extensor

digiti quinti m.

mm.

carpi radialis

m.

Interos-

Abductor

sei mm.

pollicis

Brachioradialis m.

brevis m.

Flexor carpi

Opponens

radialis m.

pollicis m.

Flexor policis

brevis m.

C 5

C 6

C 7

C 8

(Dermatome: blue)

(Dermatome: dark red)

(Dermatome: violet)

(Dermatome: light red)

Reflexes are involuntary and relatively stereo-

typed responses to specific stimuli. Afferent

nerve fibers conduct the impulses generated by

activated receptors to neurons in the central

nervous system, which fire impulses that are

then transmitted through efferent nerve fibers

to the cells, muscles, or organs that carry out the

reflex response. The pathway as a whole is

known as the reflex arc. Receptors are found at

the origin of all sensory pathways—in the skin,

mucous membranes, muscles, tendons, and pe-

riosteum, as well as in the retina, inner ear, ol-

factory mucosa, and taste buds. A reflex re-

sponse may involve the somatic musculature or

the internal organs. Most reflexes are relatively

Function

independent of the state of consciousness. An

interruption of the reflex arc at any point

weakens or abolishes the reflex. Intrinsic reflexes

are those whose receptors and effectors are lo-

Motor

cated in the same organ (e. g., the quadriceps re-

flex), while the receptors and effectors of extrin-

sic reflexes are in different organs (e. g., the

oculovestibular reflex). Reflexes are important

for normal function (e. g., for postural control

and goal-directed movement), and an impaired

reflex is an important objective finding in clini-

cal neurological examination.

Intrinsic Muscle Reflexes (Phasic Stretch

Reflexes, Tendon Reflexes)

Intrinsic muscle reflexes are triggered by stretch

receptors within the muscle (annulospiral nerve

endings of muscle spindles). The impulses

generated at the receptors are conveyed via af-

ferent fast-twitch Ia fibers to spinal alpha-motor

neurons, whose efferent α1 processes excite the

agonistic muscle of an opposing muscle pair.

The antagonistic muscle is simultaneously in-

hibited by spinal interneurons. The resulting

muscle contraction relaxes the muscle spindles,

thereby stopping impulse generation at the

stretch receptors. The spinal reflex arc is also

under the influence of higher motor centers.

Abnormal reflex responses imply an abnormal-

ity of the musculature, the reflex arc, or higher

motor centers. The most important reflexes in

clinical diagnosis are the biceps (C5–C6), bra-

Reflex response

Symbol

Absent, cannot be elicited

by maneuvers

0

Can only be elicited by maneuvers

+

(e.g., Jendrassik maneuver)

_

Diminished

1

Normal intensity

2

Heightened

3

Reflex response

Persistent clonus

4

(Proprioceptive muscle reflex)

Afferent (Ia) fiber

Extensor muscle

Efferent fiber (excitatory)

Efferent fiber (inhibitory)

Flexor muscle

Pseudounipolar nerve cells in

Supraspinal control

spinal ganglion

(inhibitory)

Afferent fiber

Efferent to

Proprioceptive

Annulospiral

extensors

(intrinsic) muscle

ending of

Extensor

reflex

muscle spindle

Efferent fibers to

Excitatory synapse

Interneuron

contralateral extensors

Flexor

and flexors

Inhibitory synapse

Efferent to flexors

Efferent fibers to

ipsilateral flexors

Afferent (Ia) fiber

and extensors

Free ending of

Supraspinal

afferent fiber (pain,

control

temperature)

(inhibitory)

Interneurons

Pressure receptor

(Vater-Pacini corpuscle)

Afferent fiber

Fibers to contralateral side of

commissural cell

Inhibitory synapse

Excitatory synapse