spinal nerves, plexus, reflexes

spinal nerve

where motor axons originate

ventral roots

forms from ventral rootlets

-cell bodies found in ventral and lateral horns

sensory axons

enter spinal cord through dorsal aspect (afferent pathway)

dorsal root

contain short central axons of sensory neurons

-dorsal root ganglion houses cell bodies

rami

convergence of dorsal and ventral roots

-distal to spinal nerve and formed by branches of spinal nerves

dorsal ramus

innervate deep muscles and skin of back (dorsal side)

ventral ramus

splits into multiple branches

-gives rise to nerves most familiar with

-trunk and upper lower limbs

form nerve plexuses

rami comunicans

autonomic nervous system

-extends between spinal nerve and sympathetic ganglions

topographical regionalization

spinal nerves organized based on what they innervate

-upper limbs enter and exit at inferior cervical region (cervical enlargement)

-lower limbs enter and exit at inferior thoracic and superior lumbar region (lumbar enlargement)

dermatome

area of skin supplied with sensory info by pair of spinal nerves (sensory activity)

myotome

muscles that particular spinal nerve innervates (motor activity)

plexus

interweaving of ventral rami of spinal nerves

-combine several nerves that innervate same part of body into one larger nerve

-allows axons to travel various paths/branches to reach destination

-info sent down multiple tracts

-damage to single spinal nerve does not result in complete loss

intercostal nerves

thoracic nerves don't form plexuses (except T1)

T2 (underarm)

T3-T6

T7-T12

cervical plexus (C1-4)

back of neck (C1-C4)

-innervate superficial nerve structures

-muscles of hyoid bone, surface of neck, lower head

cutaneous and motor branches

cutaneous branches

Innervate for sensory input:

-occipital nerve (scalp)

-auricular nerve (skin of ear and meatus)

-cervical nerve (skin of anterior neck)

-supraclavicular (shoulder region)

motor branches

-ansa cervicalis (muscles of throat)

-phrenic nerve (diaphragm)

brachial plexus

Rami• Continuation of the anterior rami of spinalnerves C5 - T1• Trunks• Unification of the rami• Superior: Formed by C5 & C6• Middle: Formed by C7• Inferior: Formed by C8 & T1• Divisions• Fibers of the trunks diverge to travel to anterioror posterior portions of the upper arm• Two divisions called anterior and posterior• Found deep to the clavicleDivisions

cords of brachial plexus

Convergence of anterior and posterior divisions• Named for their position relative to the axillary artery• Posterior• Formed by the posterior divisions of all 3 trunks• Contains portions of C5 - T1• Medial• Formed by the anterior division of the inferior trunk• Contains portions of C8 - T1• Lateral• Formed by the anterior division of superior andmiddle trunks• Contains portions of C5 - C7• Terminal Branches arise from the cords• Five major branches• Contains all the nerves of the upper limb

major terminal branches of brachial plexus

axillary nerve

-posterior cord

-innervates deltoid

-receives sensory info superolateral of arm

musculocutaneous nerve

-lateral cord

-innervates anterior arm muscles

-sensory info from lateral arm

radial nerve

-posterior cord

-innervates posterior nerve and forearm muscles

-receives sensory from posterior and forearm and lateral 3 digits

median nerve

-medial and lateral cords

-innervates most of anterior forearm lateral hand

-sensory from lateral palmar and dorsal tips of lateral 3 fingers

Ulnar nerve

-medial cord

-Innervates anteromedial forearm and intrinsic hand muscles

-Receives sensory from medial 1½ digits (anterior and posteriorly)

lumbar plexus

frontal medial portion of body (anterior pelvis)

-formed by ventral rami L1-L4

-less complex than brachial but has anterior and posterior divisions

-has nerves innervating anterior aspect of lower limbs and abdomen, pelvis and buttock

femoral nerve

main nerve of posterior

-flexion and extension of knee

Obturator nerve

-Main nerve of the anterior division

-Innervates the medial thigh

-Receives sensory from the superomedial thigh

sacral plexus

• Located in the posterior pelvis (inferior tothe lumbar pelvis)• Overlaps with lumbar plexus• Formed by the anterior rami of spinal nervesL4 - S4• Organized into anterior and posteriordivisions• Anterior division tend to innervate muscles thatflex• Posterior division tend to innervate muscles thatextend• Contains nerves innervating the posterioraspect of the lower limbs as well as theabdomen, pelvis and buttock

-sciatic/ischiatic nerve

-tibial nerve

-common fibular nerve

sciatic/ischiatic nerve

Longest and largest nerve in the body• Formed from portions of both anterior and posterior divisions ofthe sacral plexus• Has two divisions wrapped in a common sheath, tibial divisionand common fibular division that give rise to the tibial andcommon fibular nerve

tibial nerve

-anterior division of sciatic nerve

-Innervates posterior thigh and leg and plantar foot muscles

-Hip extension, thigh adduction, knee and foot flexion, and toe flexion• Plantar nerves cause flexion and adduction of the toes• Receives sensory input from the plantar region of the foot (viasural nerve)

common fibular nerve

-posterior division of sciatic nerve

-Innervates a knee muscle, anterior and lateral leg muscles

-Receives sensory input from the anteroinferior region of the foot(via its branches) and the dorsal interspace between the 1st and 2nd toe

reflexes

rapid, pre-programmed, involuntary reaction of muscles or glands to stimulus

-spinal cord responsible for integration of basic reflexes

-basic or conditioned

reflex arc

-basic unit of nervous system

-smallest, simple circuit receives stimulus and produces response

-action potential never travels to brain for processing

neural pathways

-ipsilateral

-contralateral