ga 1 spinal cord

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Gross Anatomy Lecture 1: Spinal Cord and Nerves

I. Basic TerminologyA. Neuron

1. Cell body processes called neuritisa. Dendrites receive informationb. Axon carries away information from cell body

2. Nucleus collection of nerve cell bodies that perform a common function withinbrain or spinal cord

3. Ganglion a collection of nerve cell bodies outside brain and spinal cord4. Afferents nerve fibers that carry information or signals to a ganglion or nucleus5. Efferents nerve fibers that carry info away from cell body6. Types of Neurons:

a. Sensory neuron (Dorsal root ganglia)b. Motor neuron (spinal cord)

B. Central Nervous System (CNS)1. Neurons whose cell bodies and neuritis are contained within brain and SC

C. Peripheral Nervous System (PNS) carry motor, sensory and/or autonomic signalsbetween CNS and body (composed of cranial, spinal, splanchnic nerves)

1. Somatic Nervous System innervates skeletal muscles of the body wall or limbs andmaintain voluntary control over body movement

-Somatic nerves that innervate skeletal muscles at SC levels are SPINAL

nerves; at brain or brainstem level are CRANIAL nerves

a. Motor Somatomotor: voluntary and reflex contraction of skeletal muscleb. Sensory somatosensory: sensory innervation of skin, muscles, and joints

2. Visceral Nervous System innervates internal organs, smooth/cardiac muscle, andsweat glands. Controls most of unconscious homeostatic mechanisms of the body

and innervate smooth muscle of BV, cardiac muscle of heart, glands in skin and

various organs or viscera in body cavity

-Splanchnic nerves innervate visceral nervous system

a. Motor - Visceromotor (Autonomic Nervous System): involuntary contractionof smooth muscle, cardiac muscle and glands

i. Divided into sympathetic and parasympathetic divisionsb. Sensory Viscerosensory: modulates blood pressure and chemistry,

respiration, etc.

II. Spinal CordA. General morphology

1. Extends from foramen magnum and ends in cone shaped structured (conusmedularis between L1 and L2 of vertebral column

a. Filum terminale ligament attaches SC to vertebral column caudally2. Cauda equine collection of dorsal and ventral roots exiting and entering SC below

L1 or L2 (continue below level of conus medularis)3. Lumbar cistern: space between conus medularis and end of vertebral canala. Lumbar punctures are performed in patients to assess the content of the CSF

and are done at the level of the cauda equina in order to prevent damage to

the spinal cord

b. Needle inserted in midline between spinous processes of L3 and L4 (or L4and L5) vertebrate

4. 2 enlargements towards cranial and caudal endsa. Cervical enlargement area of cord where additional motor neurons are

located that innervate upper limb

b. Lumbar enlargement contains neurons that innervate lower limb


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5. Spinal nerves exit vertebral canal between individual vertebrae throughintervertebral foramen to innervate muscles from neck to feet

a. 31 pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1coccygeal)

6. Relationship between spinal cord level and vertebral level in adulta. Vertebral level position of an individual vertebrate along vertebral columnb. Spinal cord level location of an individual spinal cord segment along the SC

i. Spinal cord segment region of spinal cord that contains all theneurons and nerve roots that make up individual spinal nerve

c. In adults SC and vertebral elves not equivalent because vertebral columnelongates at faster rate than the SC

i. SC shorter than vertebral column ends at L1 (cauda equina extend toend of vertebral column)

ii. 31 pairs of spinal nerves and only 30 vertebrated. Position of spinal nerve as it exist vertebral column changes in relation to the

vertebrate it exists adjacent to

i. Between C1-C7, spinal nerve exists above the vertebrate with sameanatomical name

ii. SN C8 exits between C7 and T1 vertebrateiii. Caudal to T1 all spinal nerves exit column below vertebrae with the

same name

e. In cervical region, SC segment and vertebral level closely linkedf. In lumbar region, they are far apart

B. Gray and white matter1. Gray matter: Central parts of cord contain the cell bodies

a. Shape of gray matter has H or butterfly appearance 3 partsi. Dorsal (posterior) horn: specialized for receipt of sensory information

from peripheral nerve

ii. Ventral (anterior) horn: contains motor neurons whose axons exit thespinal cord and innervate skeletal muscle

iii. Intermediate (lateral) horn at levels T1-L2: contains neurons that arepart of the ANS and exit spinal cord to modulate autonomic activity in

the periphery

2. White matter area surrounding gray matter that contains myelinated axons thattravel up and down the cord

3. Grey/White Matter Characteristics of spinal cord grey/white matter ratio differs indifferent parts of SC

a. Cervical SCi. Large ventral horns for innervation of upper limbii. Large amount of dorsal white matter for transmission of sensory

information from all parts of bodyb. Thoracic spinal cordi. Special area of gray matter (lateral horn) that houses cell bodies for

sympathetic (preganglionic) neurons)

III. Spinal NervesA. Nerve roots

1. Dorsal root carries sensory information from periphery into dorsal horn of spinalcord

a. Composed of sensory axons whose cell bodies are located in dorsal rootganglion (somatosensory and viscerosensory axons)


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b. Dorsal root ganglion contains somatosensory and viscerosensory cellbodies

2. Ventral root carries motor information form spinal cord to peripherya. Somatomotor axons in ventral root derived from motor neurons in ventral

horn

b. Ventral roots of thoracic and lumbar spinal nerves carry visceromotor(autonomic sympathetic preganglionic) axons from cell bodies in

intermediate horn of spinal cord

3. Spinal nerve anatomical definition small part of nerve where roots and ramicome together and sensory and motor fibers cross

a. At intervertebral foramen, two nerve roots join to form spinal nerve whichdivides into two primary rami

B. Rami1. Dorsal primary ramus- first branch of spinal nerve that courses dorsally

(somatosensory, Somatomotor, post-ganglionic sympathetics)

a. Supplies fibers (sensory and motor) to synovial joints of vertebral column,deep muscles of the back and the skin that overlays the deep back

musculature

b. Posterior cutaneous nerve: begin at surface of erector spinae muscle andcontinue to the skin, passing though superficial back muscles without

innervating them

2. Ventral primary ramus carries both sensory and motor fibers to and from rest ofthe body including anterior and lateral muscles of trunk and limbs

a. Lateral or anterior cutaneous nerve: part of ventral ramus that innervatesskin on the lateral and anterior surface of the trunk

3. Cutaneous nerve: nerve that innervates the skin and contains somatosensory andvisceromotor (ANS) axons

C. Components of spinal nerve have two targets (skeletal muscles and skin)1. Innervates muscles all three components

a. Somatomotor, somatosensory, visceromotor2. Innervates skin

a. Contains somatosensory and visceromotor ANS axonsD. Dermatome - area of skin innervated by sensory fibers of single spinal nerve or spinal cord

segment

1. Sensory or cutaneous fibers of primary rami that innervate skin remainedsegregated and have segmented distribution on skin surface

2. Sensory fibers from dorsal and ventral rami of each SC segment come together toform a continuous band of sensory input from a localized area of body wall

IV. Processing of sensory informationA. Sensory motor circuit

1.

Sensory info conveyed to CNS by sensory fibers located in spinal and cranial nerves2. Sensory limb (afferent) gives info to brain/SC which gives info to motor limb(efferent)

3. Sensory motor circuit integrates information between peripheral and central NSB. Two pathways to respond of sensory stimulus

1. Voluntary sensory info can be evaluated at higher centers such as cortex toformulate conscious (voluntary) motor plan to guide desired response

a. Ex picking up glass of waterb. Sensory limb spinal cordcortex spinal cordmotor limb

2. Reflex - rapid involuntary movement in response to sensory stimulus that does notrequire conscious thought


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a. Somatic reflex contraction of skeletal muscle and occur naturally to preventinjury from harmful stimulus (stepping on tack or touching hot pot)

i. Integrity of somatic reflex tested clinically using stretch reflexKnee jerk reflex tests L2, l3, L4Ankle jerk reflex tests S1, S2

ii. Decreased reflex response indicates peripheral nerve injuryiii. Exaggerated reflex indicates injury to the CNS

b. Cranial nerve reflex -involve components of either or both visceral andsomatic nervous system as well s our special senses

i. Pupillary light reflex regulates size of pupil based on intensity oflight

ii. Accommodation reflex adjusts thickness of lens to maintain focus ofobjects both near and far

iii. Corneal reflex eyes blink to lubricate eye to remove foreign objectiv. Gag reflex prevent something from entering throat except as part of

normal swallowing, also evoked by strong negative taste

ga 1 spinal cord

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