SPINAL CORD ANATOMY

Gross anatomy

1. Spinal cord – from foramen magnum to 1st or 2nd lumbar vertebra

2. Epidural space – between vertebrae and dural sheath; fat padding, veins

3. Spinal dural sheath – single layer of dura matter extend from brain

4. Arachnoid – extend to sacrum

5. Subarachnoid space – filled with cerebrospinal fluid

-a. Lumbar puncture – from this area; can’t hit spinal cord

6. Pia mater – clings to spinal cord

7. Deniculate ligaments – saw toothed shelves; pia matter; vertebral canal

8. Conus medularis – cone shaped end

9. Filum terminale – fibrous enxtension of pia mater; anchors to coccyx

10. Enlargements – cervical and lumbar; nerves serving upper and lower limbs

11. Cauda equina – collection of spinal roots extending inferiorly from spinal cord

Cross sectional anatomy

1. Anterior medial fissure – anterior

2. Posterior medial fissure – posterior

3. Central canal – extension of brain ventricles; cerebrospinal fluid

4. Gray matter – neuron cell bodies

-a. Gray commissure – encircles central canal; connect the lateral gray masses

-b. Posterior (dorsal) horn – interneurons

4. Gray matter – neuron cell bodies

-a. Gray commissure – encircles central canal; connect the lateral gray masses

-b. Posterior (dorsal) horn – interneurons

-c. Anterior (ventral) horn – motor neurons

-d. Lateral horns – thoracic and superior lumbar; sympathetic motor neurons

5. Dorsal root – afferent fibers; from peripheral sensory receptors

6. Dorsal root ganglion – enlarged region of dorsal root; sensory neurons

7. Ventral root – efferent motor fibers

8. Spinal nerve – dorsal and ventral roots fuse

9. White columns – fibers; communication; ascending, descending, transverse

-a. Funiculi – other name; anterior, posterior, and lateral

-b. Tracts – sensory (ascending); motor (descending)

SPINAL CORD PHYSIOLOGY: SENSORY AND MOTOR TRACTS

Ascending (sensory) pathways

1. Anterior spinothalmic tract – pain, temperature, crude touch

2. Lateral spinothalmic tract – same as anterior

3. Posterior columns – proprioception, discriminating touch

Descending (motor) pathways

1. Direct system – fast, fine voluntary movements; from cerebral cortex

2. Indirect system – from brain stem, other areas; automatic movement

SPINAL CORD PHYSIOLOGY: REFLEX ACTIVITY

General information

1. Reflex – rapid predictable motor response to a stimulus

2. Reflex arc – highly specific neural pathway through which a reflex occurs

3. Learned reflex – such as those used when driving a car

4. Override – higher brain areas can override reflex arcs

5. Somatic reflex – those which activate skeletal muscle

6. Spinal reflex – somatic reflexes which are mediated by spinal nerves

7. Autonomic reflex – those which activate autonomic (visceral) effectors

Reflex arc

1. Receptor – site of stimulus action

2. Sensory neuron – transmits afferent signal to the CNS

3. Integration center – always within the CNS; single neuron to more interneurons

4. Motor neuron – sends efferent signal to the effector from the integration center

5. Effector – muscle, gland that responds to efferent signal by contracting, secreting

Stretch reflex

1. Function – results in normal muscle tone; amount of stretch of a muscle

2. Postural reflex – all skeletal muscle which maintain body posture

3. Patellar (knee jerk) reflex – best example would be this

4. Monosynaptic – the main reflex does not involve any interneurons

5. Ipsilateral – motor activity on same side of body

6. Components – include

-a. Muscle spindle – noncontratile muscle fibers; ↑stretch ↑rate action potential

-b. Sensory neuron – cell body dorsal root ganglion, axon synapses motor neuron

-c. Motor neuron – excites the muscle associated with the stretch receptor.

7. Reciprocal inhibition – branches afferent fiber synapse with interneurons

-a. Antagonistic muscle – relaxed; motor neuron controlling it inhibit

Tendon reflex

1. Function – muscle relaxation and stretching in response to muscle contraction

2. Examples – quadriceps good example; Golgi tendon organ in patellar tendon

3. Polysynaptic – always involve interneurons in the CNS

4. Components – include

-a. Tendon organ – is activated due to stretching caused by muscle contraction

-b. Sensory neuron – sends impulse to CNS where it synapses with interneurons

-c. Interneurons – synapses with motor neuron

-d. Motor neuron – is inhibited, causing the muscle to relax

5. Reciprocal activation – other interneurons cause antagonistic muscles to contract

Flexor (withdraw) reflex

1. Function – withdrawal from painful stimulus

2. Withdraw reflex – other name

3. Examples – touch a hot plate; step on a piece of glass

4. Polysynaptic – is always going to involve a interneuron

5. Intersegmental – input from one sensory neuron to several segments

5. Components – include

-a. Nociceptor – usually a free nerve ending; could also be deep pressure receptor

-b. Sensory neuron – sends afferent to CNS

-c. Interneurons – relays stimulus to motor neuron

-d. Motor neuron – activates the muscles needed to pull away body part away

Crossed extensor reflex

1. Ipsilateral withdrawal reflex – pain on limb causes flexion

2. Contralateral extensor reflex – other limb extended

3. Polysynaptic – all parts of this require interneurons

4. Components – include

-a. Receptor – could include several

-b. Sensory neuron – sends impulse to CNS

-c. Interneurons – impulse to stimulated to flex; others to opposite to extend

-d. Motor neuron – carries out the impulses to the effector muscles

Superficial reflexes

1. Stimulation – brought about by gentle cutaneous stroking

2. Clinical uses – include

3. Plantar reflex – L4 to S2; blunt object pulled over lateral sole; toes flex downward

4. Babinski’s sign – big toe dorsiflexes other toes fan out; babies to 1; adults, damage

5. Abdominal reflexes – T8 - T12; stroking lateral abdomen; umbilicus to stimulus

NERVES

Nerve coverings

1. Endoneurium – delicate connective tissue; directly encloses nerve, myelin sheath

2. Perineurium – covers bundles of nerve fibers; made up of coarse connective tissue

-a. Fascicles – bundles of nerve fibers; covered by perineurium

3. Epineurium – tough fibrous connective tissue which covers the entire nerve

4. Associated structures – vessels, lymphatic; through connective tissue coverings

Nerves and associated ganglia: classification

1. Fiber type – include

-a. Sensory nerves – made up entirely of afferent fibers

-b. Motor nerves – made up entirely of efferent fibers

-c. Mixed nerves – the usual situation both

2. Origin – two types

-a. Cranial nerves – those which arise from the brain

-b. Spinal nerves – those which arise from the spinal cord

3. Ganglia – neuron cell bodies in PNS

-a. Dorsal root ganglia – sensory cells; covered last chapter

-b. Autonomic ganglia – associated with efferent motor fibers of the ANS

SPINAL NERVES

Spinal nerves: general

1. Distribution – named after the vertebrae

-a. Cervical – C1 through C8; C1 through C7 exit superiorly; C8 exits inferior to 7th

-b. Thoracic nerves – T1 through T12; inferior to vertebrae it is named after

-c. Lumbar nerves – L1 through L5; inferior to vertebrae it is named after

-d. Sacral nerves – S1 through S5; inferior to vertebrae it is named after

-e. Coccygeal nerves – C0; inferior to vertebrae it is named after

2. Roots – purely sensory or motor

-a. Dorsal root – sensory information enters

-b. Ventral root – motor impulses leave

3. Rootlets – from entire length of spinal cord segment; come together to form roots

4. Spinal nerve – dorsal and ventral root; mixed motor fibers; very short

5. Rami – each spinal nerve branches into three

-a. Ventral ramus – more anterior branch; longer

-b. Dorsal ramus – more posterior branch; shorter

-c. Meningeal branch – reenters spinal column; innervate meninges, blood vessels

6. Rami communicantes – at base of ventral rami in the thoracic region; autonomic

7. Nerve plexuses – interlacing network of nerves formed only by the ventral rami

-a. Advantage – damage to spinal nerve may not result in paralysis, loss of sensation

Posterior trunk: back

1. Dorsal rami – follow a neat segmental pattern

Anteriolateral thorax and the abdominal wall

1. Ventral rami – T1 through T12; form a simple segmental pattern

2. Intercostal nerves – most ventral rami deep to rib; supply

-a. Intercostal muscles – lying between the ribs

-b. Interiolateral thorax – the muscles and skin of the

-c. Abdominal wall – the muscles and skin of the

3. T1 – most of the fibers enter the bracial plexus

4. T12 – subcostal nerves, lies inferior to the 12th rib

Cervical plexus

1. Ventral rami – C1 through C4; but some contributions from C5

2. Cutaneous nerves – sensory from the skin of the neck, ear area, and the shoulder

3. Anterior neck muscles – also innervated by branches of the cervical plexus

4. Phrenic nerve – C3 and C4; motor fibers to diaphragm

Brachial plexus

1. Ventral rami – from C5 through C8 and T1; additional fibers from C4 and/or T2

2. Upper limb – innervated by the nerves from this plexus

3. Branching pattern – complex

-a. Roots – ventral rami converge to form trunks

-b. Trunks – upper, middle, and lower; each splits into a division

-c. Divisions – anterior and posterior; converge to form cords

-d. Cords – lateral, medial, and posterior; split, converge to form nerves

4. Axillary nerve – deltoid (and teres minor); skin and joint capsule of shoulder

5. Musculocutaneous nerve – flex the forearm; cutaneous sensation lateral forearm

6. Median nerve – pronate forearm, flex wrist, fingers; sensation anterior forearm

7. Ulnar nerve – involved in

-a. Motor – wrist, finger flexion; adduction, abduction medial fingers

-b. Sensory – cutaneous sensation of the medial aspect of the hand

-c. Funny bone – close to medial epicondyle of humerus

8. Radial nerve – involved in

-a. Motor – elbow, wrist, finger extension; forearm supination; abduction of thumb

-b. Sensory – cutaneous sensation of posterior of the arm; from posterior cord

Lumbosacral plexus

1. Lower limbs – innervated

2. Overlapping – many nerve fibers of lumbar plexus contribute to sacral plexus

Lumbar plexus

1. Innervates – anterior and medial thigh; some abdominal wall innervation

2. Ventral rami – from spinal nerves L1 through L4

3. Femoral nerve – involved in

-a. Motor – anterior thigh; thigh flexion and knee extension

-b. Sensory – cutaneous sensation anterior thigh; medial leg from knee to foot; foot

4. Obturator nerve – involved in

-a. Motor – thigh adductors

-b. Sensory – cutaneous sensation of medial thigh; hip and knee joints

Sacral and coccygeal plexuses

1. Innervates – buttocks, lower limb, pelvic structures, and perineum

2. Ventral rami – from spinal nerves L4 through S5

3. Sciatic nerve – largest; greater sciatic notch; tibial and common fibular

4. Tibial nerve – part of the sciatic nerve

-a. Motor – posterior compartment muscles leg; intrinsic muscles of foot

-b. Sensory – cutaneous sensation of posterior calf and sole of foot

5. Common fibular nerve – part of sciatic nerve

-a. Motor – extensors and dorsiflexion of the foot

-b. Sensory – cutaneous sensation of lateral calf and dorsum of the foot

-c. Common peroneal nerves – alternate name

6. Superior gluteal nerves – superior and inferior; gluteals and tensor fasciae latae

7. Pudental nerve – muscles and cutaneous sensation of perineum; genitalia

-a. Functions – urination, erection, sexual stimulation, external anal sphincter

Innervation of joints

1. Hilton’s law – nerve to muscle causing movement at a joint, innervates joint

Innervation of skin

1. Dermatomes – cutaneous branches of a single spinal nerve

2. Trunk – fairly uniform and horizontal on

3. Upper limbs – by ventral rami of C5 through T1 (or T2)

4. Anterior lower limb – ventral rami of lumbar nerves

5. Posterior lower limbs – ventral rami of the sacral nerves

HOMEOSTATIC IMBALANCES

Spinal cord

1. Trauma – include

-a. Paralysis – loss of motor function

-b. Paresthesias – sensory loss

-c. Flaccid paralysis – damage to ventral root or anterior horn; can not move

-d. Spastic paralysis – primary motor cortex damage; move by reflex

-e. Paraplegia – spinal cord transected between T1 and L1; legs affected

-f. Quadriplegia – transaction in cervical region

2. Poliomyelitis – anterior horn motor neurons; muscle pain, weakness, paralysis

3. Amyotorphic lateral sclerosis – Lou Gehrigs; anterior horn and pyramidal tract