Download Organization and Function of the Nervous System

Test 3 material Chapters 11,12
Organization and Function of the Nervous System
p. 334 - 416
Terms of the day
Otitis externa, otitis media, tinnitus, otoscope
Chondromalacia- Softening of any cartilage
Prebycusis – hearing loss due to age
Claudication – limping, usually intermittent
Myasthenia – muscular weakness
Ankylosis - fixation of a joint as the result of a disease process
Vertigo - dizziness
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3-4-99
Introduction
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stimulus - response system – designed to detect changes in the internal and external environment, and the
significance of the changes, and to respond to them if appropriate. The method of control function is based on the
stimulus.
Stimulus- something that causes a change in the systems homeostasis. Can be thermal, mechanical, chemical.
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Organization of the Nervous System - p. 334
Anatomic Divisions
• CNS - brain and spinal cord
• PNS - peripheral nervous system
– Cranial nerves - 12 pair
– Spinal nerves - 31 pair
Functional Divisions
• Autonomic Nervous System -( 25 questions on final on this)- a two neuron chain from the CNS to the
neuroeffector organ. Controls visceral organs, smooth muscle, cardiac muscle and glands. Exits in peripheral
nerve, will synapse in CNS, neuron out to visceral organs, smooth muscle, cardiac muscle and glands.
– Parasympathetic
– Sympathetic
• Somatic Nervous System - a one neuron chain from the CNS to the neuroeffector organ  skeletal muscle
Functions of the Nervous System p.334
• Perceive and respond to stimuli – receptors required
 Receptors are proteins on cell surface
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Coordination and control of body activities
Memory
Learning based on past experiences - deductive reasoning
Inductive reasoning ( required for test 3!) – to come up with creative new thought, go from the end point and find out
about the origin.
Instinctive behavior – very strong and powerful, even in humans, more than we think.
Terminology of the Nervous System Table 11.1, p. 335
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Sensory neuron – afferent – conducts stimulus  CNS by means of electrochemical impulse
Motor neuron – efferent – CNS out to effected tissue: visceral organs, smooth muscle, cardiac muscle and glands.
Nerve - a whitish ( due to myelinization) cord like structure composed of one or more bundles (fascicles) of
myelinated nerve fibers and connective tissue which transmit impulses to and from the CNS and the body.
Plexus - a network or entanglement of nerves
Ganglion - a collection of neuron cell bodies outside of the CNS – exception: basal ganglia
Nucleus - a collection of neuron cell bodies within the CNS
Tract - grouping of nerve fibers that interconnect regions of the CNS
Neuron – nerve cell , many neurons make up a nerve
Marie Paas
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Neurons and Neuroglia
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The Neuron - p. 338
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Basic structure and function
• cell body – soma (body), dendrite (afferent – receiving ), axon ( efferent – transmitting portion)
Neuroglia - Table 11.2, p. 341 – support and nourish neurons in the CNS and PNS
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Neurolemmocytes – Schwann cells, wrap around axons and dendrites. PNS  myelin
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Ependymal Cells – columnar cells, line the ventricles and central canal of the CNS, involved in formation of CSF.
Oligodendrocytes – “Schwann” cells of the CNS – form myelin in the CNS
Microglia – gitter cells, phagocytes
Astrocytes – form structural support between neurons and capillaries ( waste goes from neurons to cap.’s,
nutrients from cap.’s to neurons), foot process wraps around, blood-brain barrier.
Ganglionic Gliocytes – satellite cells, support cells in ganglia of the PNS
Myelination - formation of myelin sheath - p. 340 * van der Graff
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a process in which a neurolemmocyte (PNS) or an oligodendrocyte (CNS) surrounds a portion of an axon or
dendrite to provide support and aid in the conduction of nerve impulses, increases the speed of conduction.
myelin is a lipoproteinaceous material composed of regularly alternating membranes of lipid lamellae and protein
myelin gives the white matter of the brain and SC and peripheral nerves their whitish color
myelination of PNS neurons occurs as the neurolemmocytes grow and wrap around an axon or dendrite, the
outer surface is enclosed by a glycoprotein sheath called the neurolemmal sheath
each neurolemmocyte covers approximately 1 mm of space on the axon and their is a gap between each cell
called a Node of Ranvier or neurofibril node
Classification of neurons and nerves - p. 342
1. According to direction of impulse travel
– afferent versus efferent
2. According to Structure - figure 11.10, p. 346
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pseudounipolar - sensory neurons – cell body in dorsal root ganglion
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Type A fibers - large myelinated, rapid conducting – pain, touch, reflex arc ( even faster )
bipolar - special sensory neurons – vision, taste, smell
multipolar - motor neurons – found in ventral horn of SC, most common, lateral horn and peripheral autonomic
ganglia
3. Fiber diameter
Type B fibers - medium sized with less myelin – conduct more slowly, ANS, pre-ganglionic fibers
Type C fibers - small, less myelin, slow – autonomic post-ganglionic fibers
(Telephone story Emerson 83868)
4. According to specific type of tissue innervated – functional components p. 334
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( T= 7,9,10= taste )
GSA – general somatic afferent - somatic sensory, from skin, bones, joints, muscle, proprioception.
Pseudounipolar neurons
CN 5,T
GSE - motor to skeletal muscle, muscle is going to contract. Multipolar neurons
CN 3,4,6,11,12
GVA – general visceral afferent - sensory, pain & stretch from viscera & BV, general visceral, visceral organs,
smooth muscle, cardiac muscle and glands, bladder full, stomach growling
CN T
GVE - motor to smooth m., cardiac m. and glands – ANS: sympathetic & parasympathetic CN 3,T
SSA – sight & sound afferent - sensory from eye and ear – hearing, equilibrium, and eye
CN 2,8
SVA - sensory from taste & smell – stopped up nose no taste
CN 1,T
SVE – Special visceral efferent - somatic motor to SCM and trapezius, muscles of facial expression and
mastication, larynx, pharynx, derived from branchial arches
CN 5,T,11
Spinal nerves are mixed - contain all the “G’s”, contain no special components: GSA, GSE, GVA, GVE
Cranial nerves can have general, special or a mix of the two
Marie Paas
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Connective tissue covering of a nerve - p. 344, figure 11.11
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epineurium - surrounds entire nerve
perineurium - surrounds bundles( fascicles) of nerve fibers
endoneurium - surrounds individual nerve fiber, i.e. axon or dendrite
fasciculus - a bundle or group of nerve fibers
Transmission of Nerve Impulse
p. 346-348, Appendix #2
Nerve Impulse - p. 347, figures 11.13, 11.14
– the actual movement of sodium and potassium ions along the length of a nerve fiber which results in the creation
of a stimulus that excites another neuron or neuroeffector tissue
Irritability - ability of dendrites and cell bodies to respond to a stimulus and convert this stimulus into an
electrochemical impulse
Conductivity - the transmission of an impulse along an axon or dendrite of the neuron
Resting Membrane Potential - before a nerve fiber can respond to a stimulus it must be polarized, it must have a
charge inside ( - ) and outside (+).
Polarization - exists when there is an electrochemical gradient present between the inside of the cell and the
outside of the cell. A positive side and a negative side. This gradient exists because of the sodium/potassium
pump, semi-permeable membrane, presence of large negatively charged ions inside of the cell. Abundance of
sodium ions outside of the cell and potassium inside of the cell.
Depolarization - when a stimulus of sufficient strength reaches the receptors of the cell certain ions gates within the
cell membrane open and there is a rapid influx of sodium into the cell which causes a reversal of polarity called
depolarization. This wave of depolarization is conducted down the length of the nerve fiber.
Repolarization - sodium/potassium pump pumps sodium back out of the cell and potassium into the cell to reestablish the resting membrane potential.
Sodium-potassium pump
All or None Response - nerve impulses only travel in one direction and it is all or none meaning that when a
stimulus of sufficient strength triggers an action potential the nerve “fires” and the wave of depolarization will travel
the length of the neuron without a loss of voltage as it travels until it reaches the axon terminus.
Threshold - the internal voltage at which the cell will spontaneously depolarize. Enough Na has to come into the cell
and K out. You can make a neuron closer to threshold ( coffee) or further from threshold ( alcohol )
Synapse - p. 348, figure 11.15
– Definition - a functional connection between the axon terminal of the presynaptic neuron and the cell membrane
of the postsynaptic cell
– Presynaptic neuron
– Postsynaptic tissue
– Axon Terminal - synaptic bulb, knob - distal portion of the axon contains…
– Synaptic Vesicles - located in the axon terminal, contain neurotransmitter chemicals, quanta ( amount of NT in 1
vescicle )
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– Synaptic Cleft - gap between the pre and post synaptic cells
Neurotransmitters – is how a neuron makes a muscle contract or a gland secrete
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ACH - Choline + Acetyl Co A - myoneural junction, skeletal muscle
Acetylcholinesterase – neutralizes NT: ACH. Blocked by nerve gas.
Norepinephrine – in sympathetic NS, derived from Tyrosine  Dopa  Dopamine, opposite effect of ACH.
Nerve gas in the gulf war- Soman, Tupam. Same prinicple of Organophosphates, Dursban. Antidote is Atropine, stops
the effect on Heart, glands, and smooth muscle.
 IPSP - Inhibitory Post Synaptic Potential - Chloride ions, inside of the cell is negative, to make it more negative
means it requires a stimulus of greater magnitude to cause the cell to depolarize. GABA
11. EPSP - Excitatory Post Synaptic Potential - Sodium ions, inside of the cell is negative and if you add more positive
ions it brings the cell closer to threshold and therefore it requires a stimulus of lesser magnitude to cause the cell to
depolarize. Premature depolarization.
Terms for the day
3-9-99
Arthrodesis - artificial ankylosis; the stiffening of a joint by operative means
Exostosis – hyperostosis; a cartilage-capped bony projection arising from any bone that develops from cartilage
Marie Paas
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Spondylosyndesis - spinal fusion
Laminectomy - excision of a vertebral lamina; commonly used to denote removal of the posterior arch
Neuritis, atrophy, hyperkinesia, neuralgia, laminectomy, arthralgia, dystrophy
The Spinal Cord
p. 372 – 379
Basic Anatomy of the Spinal Cord
- Located in the vertebral canal
- Extends from the foramen magnum to L1 (L2), then spinal cord proper stops
- Conus medullaris – terminal cone
N 148
- Filum terminale – pia (tender) mater – a strand that connects the tip of the conus to coccyx, anchors cord down
- Cauda equina – distal - collection of spinal nerve roots
- Spinal segment is a cross section of the spinal cord that gives rise to a pair of spinal nerves
• spinal nerve
- Dural sac ends at L3
- Dorsal and ventral root come together at the IVFto form a spinal nerve
1. White matter – is white due to myelinated tracts
Anterior median sulcus – anterior indentation
Posterior median sulcus – posterior indentation
2. Gray matter of the spinal cord
Dorsal horn – entry – posterior horn – incoming info from pseudounipolar neurons, bring in sensory info
Ventral horn – exit – anterior horn – larger, multipolar motor neurons
Lateral horn – intermediolateral nucleus– multipolar neuron of the ANS ( T1-L2) GVE
Gray commissure – connects the two sides, transverse bar
Central canal – continuous with ventricles
Cervical enlargement – brachial plexus arises here – cord is bigger because more neurons come off here
Lumbar enlargement – lumbosacral plexus
Spinal Cord Tracts – in white matter, are bundles of fibers, ascending and descending
Funiculi - means cord or column
1. Anterior funiculi – 2, one on each side
2. Posterior funiculi – 2, one on each side
3. Lateral funiculi – 2, one on each side
Ascending tracts – sensory more superficial }
Descending tracts – motor – deeper
}  first you loose sensation, then you loose function!
N 151
1. Functions of the spinal cord
Impulse conduction
Reflex integration
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Spinal segment and formation of the spinal nerve - 31 pair of spinal nerves formed by the union of the ventral root
(motor) and the dorsal root (sensory) ( or 62 total spinal nerves )
Relationship of spinal segment to vertebral levels: in the cervical area there is a one to one relationship between
spinal segment, but below T1 that is lost
– Rootlets – coalesce into roots
2. Ventral Rootlet - motor
3. Dorsal Rootlet
Roots
1. Dorsal Root - GSA, GVA – sensory
Dorsal Root Ganglion - pseudounipolar neuron cell bodies
2. Ventral Root - GSE, GVE – motor
Bell-Magendie Law - dorsal root is sensory, ventral root is motor
The Spinal Nerve
p. 400 - 401
Dorsal Rami don’t form plexi
Marie Paas
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N 155
N 149
Anatomy Tri 1
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The Intervertebral Foramen - IVF
Naming of the Spinal Nerves
– Cervical - according to the vertebra they exit above
– All others - according to the vertebra they exit below – because of Spinal nerve C8 – it exits between C7 and T1
4 typical branches of a typical spinal nerve
1st branch: Recurrent meningeal = Sinuvertebral = meningeal ramus – reenters into the vertebral canal and
supplies the IVD, blood vessels of the spinal cord, meninges, and vertebral ligaments
2nd branch: Dorsal ramus – posterior primary ramus, supplies GSE, GSA, GVE, and GVA to skin and muscles
of the back from the midline to the lateral margin of the erector spinalis muscles.
Medial branch – C2 to T6 is sensory above T6, below T6 it is motor
Lateral branch is motor above T6, below T6 it is sensory
N 156
3rd branch: Rami communicantes
 Gray ramus – type C fibers – GVE – associated w/ all sensory spinal nerves
 White ramus – type B fibers – GVE, GVA , found on spinal nerves T1-L2
4th branch: Ventral ramus also called spinal nerve root, last branch off – motor, sensory, and sympathetic to
skin, and muscles of the anterior and lateral neck and trunk and all skin and muscles of the limbs,
including superficial back ( everything that is not supplied by the dorsal rami )
 Forms plexi: Cervical, brachial, lumbar, and sacral
 intercostal nerves
 spinal nerves T2-T12 do not form any plexus
The Cervical Plexus
p. 401, Table 12.3 ( 5-6 questions on test )
Look at Appendix 3,4,5,6: all test questions come from here!
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C1-C4 (mainly ventral rami of C2,3 and 4) – spinal nerve roots
Sensory branches – all exit SCM posterior border
• Lesser Occipital Nerve - C2,3 give contributions - skin posterior to the auricle and lateral portion of the
occipital region – easily seen on models ( lab practical 2)
• Greater Auricular Nerve- C2,3 - 2 branches
N 18, N 27
– anterior branch - skin over parotid salivary gland, located anterior to the ear lobe
– posterior branch - skin over the mastoid process and ear lobe
• Transverse Cervical Nerve - C2,3 - skin of anterior neck – bisects the SCM horizontally to exit
• Supraclavicular Nerves - C3,4. Consists of 3 branches:
– medial branch - skin from clavicle to the midline, little bit of the shoulder, anterior chest wall
– intermediate branch - skin of anterior chest wall
– lateral branch - skin over the shoulder
Motor branches
• Ansa cervicalis ( ansa=loop)- C1,2,3 - motor to omohyoid, sternohyoid, sternothyroid – can’t see
• Phrenic Nerve - C3,4,5 - motor to the diaphragm – between the anterior and middle scalene muscles, right
beside the heart
Other Cervical Nerves – not part of any plexus
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N 164, N 18
Suboccipital Nerve - dorsal ramus of C1 – all motor to the muscles of the SOT, no cutaneous sensory branch
Greater Occipital Nerve - dorsal ramus of C2 - sensory to the posterior scalp, motor to splenius m.
Third Occipital Nerve - dorsal ramus of C3 - the medial branch to sensory to a small area of the posterior scalp
3-11-99
Radiculitis – Inflammation of the intradural portion of a spinal nerve root
Hydranencephaly - a fluid-filled cavity; Congenital absence of cerebral hemispheres
Hyperesthesia - abnormal acuteness of sensitivity to touch, pain, or other sensory stimuli
Myelomalacia - softening of the spinal cord
Cephaligia, sciatica, hydrocephalus, tetraplegia, syncope, ataxia
The Brachial Plexus - C5,6,7,8,T1
p. 401 - 404, Table 12.4 (test)
Marie Paas
N 400
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Roots form trunks, which divides into divisions, which recombine to form cords, which divide into terminal branches
(RTDCB)
 Roots - ventral rami of C5 to T1
 Trunks - 3, formed by the convergence of roots
– Superior or upper trunk - ventral rami of C5 and C6
– Middle trunk - continuation of C7
– Inferior or lower trunk - ventral rami of C8 and T1
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Divisions - no branches off of the divisions
– anterior - innervate flexors
– posterior - innervate extensors
Cords - named in association with the axillary a.
– posterior cord - all 3 posterior divisions
– lateral cord - anterior divisions of upper and middle trunks, contains fibers for C5,6 and 7
– medial cord - continuation of the anterior divisions of the lower trunk, fibers from C8 and T1
 Terminal branches
4 Supraclavicular Branches of the Brachial plexus
1. Dorsal scapular nerve DSN - C5
N 401
– rhomboid mm. and levator scapulae m.
1. Long Thoracic nerve LTN - C5,6,7 – commonly damaged during radical mastectomy  winged scapula
– serratus anterior m.2. Nerve to the subclavius m. - C5,6 – superior trunk
– subclavius m.
3. Suprascapular nerve SSN - C5,6 – superior trunk
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supraspinatus m. and infraspinatus m.
Infraclavicular Branches of the Brachial Plexus
Lateral Cord - C5,6,7 – to the axillary artery
1. Lateral pectoral nerve LPN - C5,6,7
– pectoralis major m.
2. Musculocutaneous nerve MCN - C5,6,7
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biceps brachii m., coracobrachialis m., brachialis m.
lateral antebrachial cutaneous n. - sensory to skin of lateral forearm
3. Lateral root of the median nerve MN - C5,6,7 – 3/5th of the median nerve
Medial Cord - C8, T1
1. Medial pectoral nerve MPN - C8, T1
– pectoralis major and minor mm.
2. Medial Brachial Cutaneous nerve MBC - C8, T1
– skin of medial & posterior arm
3. Medial Antebrachial Cutaneous nerve MAC - C8, T1
– skin of medial & posterior aspect of forearm
4. Ulnar nerve UN - C8, T1 - van de Graff differs on this
– flexor carpi ulnaris m., flexor digitorum profundus m.- ulnar head, most of the muscles of the hand, skin of the
medial hand, little finger and medial half of ring finger
5. Medial Root of Median nerve - C8, T1
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median n. innervates flexors of the carpus and digits, except flexor carpi ulnaris m., lateral 2/3’s of the hand and
fingers, tips of thumb, index and middle fingers and lateral aspect of the tip of the ring finger, some muscles of the
hand (abductor pollicis brevis m., flexor pollicis brevis m., opponens pollicis m., and lateral lumbrical m.
Posterior Cord - C5,6,7,8,T1
1. Upper subscapular nerve - C5,6
– subscapularis m.
2. Thoracodorsal nerve - C6,7,8 – formerly called middle subscapular
Marie Paas
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– latissimus dorsi m.
3. Lower subscapular nerve - C5,6
– subscapularis and teres major m.
4. Axillary nerve - C5,6
– deltoid m. and teres minor m., sensory from skin over deltoid m.
5. Radial nerve - C5,6,7,8,T1
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innervates extensor muscles of the arm, forearm, carpus and digits; brachioradialis m., supinator m., and the
lateral portion of the brachialis m.
sensory to the skin of the posterior arm and forearm, lateral 2/3’s of the hand and fingers over the proximal and
middle phalanges
Lesions of the Brachial Plexus
Erb-Duchenne Palsy - C5,6
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Bulging of spinal nerve roots C5, 6
results from excessive displacement of the head to the opposite side and depression of the shoulder on the same
side.
Dorsal scapular n. - dropped shoulder and scapula falls laterally
Suprascapular n. - loss of lateral rotators
Axillary n. - humerus rotates medially due to loss of lateral rotators and unopposed pectoralis major m.
Musculocutaneous n. - paresis of muscles of the anterior arm and forearm pronates due to loss of biceps brachii
m.
“Waiter’s tip”
Klumpke’s Palsy
 Results from excessive traction or abduction of the arm as is seen in a fall when one grasps an object to try and
break the fall or when a mother jerks a child by one arm.
 Damage to T1
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inability to abduct the fingers (not the thumb), atrophy of the small muscles of the hand and loss of sensation
along medial aspect of arm
reversible depending on the amount of damage
Damage to long thoracic n. - C5,6,7
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“winged scapula” - seen in radical mastectomy or blows to the posterior triangle of the neck, serratius anterior
can’t hold on to vertebral border of scapula and it sticks out
Radial nerve damage
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“wrist drop” - seen in crutch injuries, “frogging”, and drunkard paralysis, church pew paralysis, damaged in
midhumeral spiral fracture
Median nerve damage
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indicated by numbness and pain in the lateral aspect of the palmar surface of the hand, inability to pronate the
forearm, weakness in the thumb and severe paresis in carpal flexion
primary in suicide attempts
Carpal tunnel syndrome
– carpal tunnel formed by the anterior surfaces of the carpal bones and the flexor retinaculum
– clinically see burning “pins and needle” sensation in the palmar aspect of the lateral 3 &1/2 fingers and paresis of
the thenar muscles. NO loss to sensation over the thenar eminence because no palmar branch involvement
Pronator teres syndrome
– median n. penetrates between the two heads of the pronator teres m. and can become entrapped there
– presents same as carpal tunnel EXCEPT there is loss of sensation over the thenar eminence because affects
entire length of median nerve
3/16/99
The Lumbar Plexus - L1,2,3,4
N 464
p. 404 - 405, Table 12.5
The lumbar plexus is embedded in the belly of the psoas major muscle ( only roots and divisions )
N 502/3
1. Femoral n. - L2,3,4
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motor to iliacus m. pectineus m., sartorius m., quadriceps
L2,3,4 – kick the door (extend the knee)
sensory - skin of anterior and medial thigh
Saphenous n. - off of femoral n. - skin of medial aspect of thigh and leg and foot
2. Obturator n. - L2,3,4
L2,3,4 – slam the door (adduct the thigh)
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motor - adductor longus m., adductor brevis m., gracilis m., obturator externus m., adductor magnus m.
sensory - skin of the medial thigh
3. Iliohypogastric n. - L1
N 462
Very first branch off!
– motor - muscles of the anterolateral abdominal wall, transverse abdominis and internal and external obliques
– sensory - skin of the lower abdomen and buttock
4. Ilioinguinal n. - L1 *
This nerve can be injured during inguinal hernia repair loss of sensation to skin of superior medial thigh (hands in
pocket)
– motor - part of the internal and external abdominal obliques mm.and transverse abdominis m.
– sensory - skin of upper medial aspect of the thigh, root of the penis and scrotum, labia majora and mons pubis
5. Genitofemoral n. - L1,2 - 2 branches *
a. motor - genital branch - cremaster m.
b. sensory - femoral branch - skin of middle anterior surface of thigh, scrotum - in male and labia majora in female
*There is some overlap between the ilioinguinal and the genitofemoral nerves.
6. Lateral Cutaneous Femoral n. - L2,3
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sensory - skin over the lateral and anterior thigh
7. Lumbosacral trunk - inferior portion of L4,5
The Sacral Plexus, L4,5, S1,2,3,4
N 465
p. 405 - 409, Table 12.6
1. Superior gluteal n. - L4,5,S1
 motor gluteus minimis and medius mm. And tensor fasciae latae m.
 no cutaneous sensory branch
2. Inferior Gluteal n. - L5,S1,2
N 504
 motor - gluteus maximus m.
 no cutaneous sensory branch
3. Sciatic n. - L4,5,S1,2,3
 The largest nerve in the body, actually 2 nerves in one neural sheath. It splits into its two respective divisions
just proximal to the knee. As the sciatic nerve it descends through the posterior thigh ( inferior border of
piriformis muscle ) sending branches to the hamstrings and adductor magnus m.
a. Tibial n. - L4,5,S1,2,3
 motor - semitendinosus and semimembranosus mm., long head of biceps femoris m., adductor magnus m.
gastrocnemius m., soleus m., plantaris m.;, popliteus m., tibialis posterior m., flexor digitorum longus m.,
flexor hallucis longus m.
 medial plantar n. - muscles of the foot and sensory to the skin over the medial 2/3’s of the plantar surface
of the foot
 lateral plantar n. - remaining muscles of the foot and the skin over the lateral 1/3 of the plantar surface of
the foot
 cutaneous sensory - skin of the posterior leg
b. Common Peroneal n. - L4,5,S1,2
 damaged in bike riders  causes foot drop
 motor - short head of biceps femoris m.
 The nerve then comes from the posterior side and crosses laterally over the head of the fibula where it them
divides into 2 branches:
• 1. superficial peroneal n. ( lateral crural compartment )
• motor - peroneus longus m., peroneus brevis m.
• sensory - skin over the distal 1/3 of the anterior aspect of the leg and dorsum of the foot
4. deep peroneal n. ( anterior crural compartment )
• motor - tibialis anterior m., extensor hallucis longus m., extensor digitorum m., peroneus tertius m.
• sensory - a small area of skin on the dorsum of the foot between the first and second toes
4. Pudendal n. (=ashamed)- S2,3,4
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motor - muscles of the perineum, levator ani m., external anal sphnicter m., external urethral sphnicter m.
sensory - skin of the penis and scrotum in male; clitoris, labia majora and minora and vagina in female
Coccygeal Plexus S(4), 5, Cy1
1. Branches
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N 469
Branch to the coccygeus m.
Branch to the skin over the coccyx ( above natal cleft )
2. Intercostal Nerves T2-T12 – the ventral rami do not form plexi
3. Dermatomes – areas of innervation by specific spinal nerves
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N 150
greater occipital nerve - C2
C3,4
upper and lower extremities
T4 - nipple
Reflex Arc and Reflexes
1. Simple Reflex Arc - Monosynaptic
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Components of a reflex arch
1. receptor –
2. sensory neuron –
3. association neuron – or connector neuron in spinal cord which connects it to 4.
4. motor neuron
5. effector organ
– Ipsilateral Reflexic Arc - knee jerk – monosynaptic – story of nail thru foot
2. Withdrawal Reflex - Disynaptic Reflex – First comes the withdrawal reflex then the pain.
No pain in traumatic injuries because there is sensory overload, the brain just shuts down, no pain is perceived until
later.
The End of the Nervous System
Have a nice day
Marie Paas
page 54
Anatomy Tri 1
05/06/17