Spinal Cord, Spinal Nerves and Spinal Reflexes Flashcards
reflexes
quick autimatic, nerve responses triggered by specific stimuli
spinal reflexes
-controlled by the spinal cord alone without input from the brain
-Example is dropping a hot pan. reflex causes release of the pan before the information reaches the brain
spinal cord
-housed within meninges and vertebral column
-carries sensory and motor information berween brain and most other parts of the body
-give rise to spinal nerves
gross anatomy of the spinal cord
-18 inches long
-half inch wide
-from brain to L1 and L2
-4 regions
-bilateral symettery (pairs of nerves)
-31 segments giver ise to spinal nerves
-central canal contains CSF
grooves that divide spinal cord into left and right
-posterior median sulcus
-anterior median fissure
gross anatomy of spinal cord photo
enlargements of the spinal cord
-areas of the spinal cord that supply the limbs, have more gray ,atter and are visibly wider
-cervical enlargement: supplies shoulder and upper limb
-lumbosacral enlargement: supplies pelvis and lower limbs
distal end of the spinal cord important components
-conus medullaris:tapered conical end of cord below lumbar enlargement
-cauda equina: nerve roots extending below conus medullaris
-filum terminale: thread of fibrous tissue at end of conus, attaches to coccygeal ligament
spinal roots
-anterior root - axons of motor nuerons
-posterior root - axons of sensory nuerons
-spinal nerve roots divide into rootlets before entering or leaving the spinal cord
spinal ganglia
-contain cell bodies of sensory nuerons that form the posterior root
-located between pedicles of adjacent vertebrae
spinal nerves
-formed by union of posterior and anterior roots
-pairs
-each has a white ramus communicans and gray ramus communicans that innervate glands and smooth muscle
-mixed - containing both afferent and efferent motor fibres
-each spinal nerve quickly divides into rami
spinal nerve rami
-posterior ramus - supplies skin and muscles of the back
-anterior ramus - supplies most of body wall skin and limbs
naming the spinal nerves
-designed by vertebral region and number
-C1 runs above first cervical vertebrae
-C8 below 7th cervical vertebrae
-all other names for vertebrae above
the spinal meninges
-dura mater - outermost layer
-arachnoid mater - middle layer
-pia mater - innermost layer
-function to protect spinal cord and cushion with CSF, carry blood supplu
-continous with cranial meninges
meningitis
-viral or bacterial infection of the meninges
the dura mater
-outermozt meningeal layer
-tough with dense collagen fibers
-continous with cranial dura mater and fuses with periosteum of occipital bone
-distal end joins with coccygeal ligament
epidural space
-between vertebrae and dura mater
-contains loose connective and adipose tissue
subdural space
-potential space deep to dura mater
denticulate ligament photo
arachnoid mater
-middle meningeal layer
-two components: arachnoid membrane and arachnoid trabeculae
subarachnoid space
-space wither arachnoid trabeculae
-between arachnoid mater and pia mater
-filled with CSF
-lumbar puncture or spinal tap withdraws CSF from subarachnoid space
pia mater
-innermost meningeal layer
-mesh of collagen and elastic fibers
-firmly attaches to underlying nueral strcutres it surrounds
-blood vessels for SC are on surface of pia mater within the subarachnoid space
-paired denticulate ligaments anchor pia mater to dura mater and prevent lateral movement of spinal cord
functional organization of gray matter
-masses of gray matter within cNS are called nuceli and are organized into regions called horns
-posterior horns (sensory nuclei)
-anterior horns (motor nuceli)
-lateral horns (visceral motor nuclei)
-sensory or motor nucleus location within gray matter determines which body part it controls
gray commisures
-organised gray matter
-narrow bands of gray matter around central canal
-axons cross here to the other side of spinal cord
tract
-bundle of axons in CNS
-ascending tracts (toward brain)
-descending tracts (down the spinal cord)
structural organization of white matter
-three columns
-posterior white column
-anterior white column
-lateral white colimn
three connective tissue layers surrounding the spinal. nerves
-epineurium
-perinerium
-endonuerium
spinal nerves
pair of spinal nerves emerhes laterallu from each spinal cord segment
-form by junction of anterior and posterior roots
-all spinal nerves are mixed nerves
peripheral nerves
-form from branching and re-sorting spinal nerves
-all are mized nerves
-same connective tissue layers as spinal nerves
dermatomes
-specifical bilateral region of skin supplied by a single pair of spinal nerves
peripheral nueropathies
-regional losses of neural function that affect dermatomes often nerve trauma, compression and various illnesses
shingles
-rash/symptoms occur along dermatomes
sensory information picture
motor commands photo
nerve plexuses
-complex interwoven networks of nerve fibers
-formed from blended fibers of anterior rami of adjacent spinal nerves
-allows multiple spinal nerves to supply the same structures
four major nerve plexuses
–cervical plexus
-brachial plexus
-lumbar plexus
-sacral plexus
cervical plexus
-includes anterior rami of spinal nerves
-innervated scalp behind ear neck and diaphragm
-phrenic nerve controlling diaphragm
-lesser occipital nerve
-greater auricular nerve
-transverse cervical nerve
-supraclavicular nerve
brachial plexus
-innervates pectoral girdle, upper back and upper lumb
-anterior rami of C5-T1
-rami first form 3 trunks then trunks form cords
-cords are named by their positions relative to axillary artery
-most nerves of brachial plexus come off the cords
major brachial pleux nerves
-musculocutanerous nerve
-median nerve
-ulnar nerve
-axillary nerve
-radial nerve
carpal tunnel syndrome
-compression of median nerve usually when adjacent tendons are swollen
-median nerve passes through the small carpal tunnel on the anterior wrist
the hand is innervated by
-ulnar median and radial nerves
the lubar plexus
-includes anterior rami of spinal nervez T12-L4
-includes: iliohypgastrix nerve, ilio-inguinal nerve, femoral nerve, obturator nerve, genitofemoral nerve, lateral femoral cutaneous nerve
sacral plexus
-includes anterior rami of spinal nerves L4-S4
-sciatic nerve, superior and inferior gluteal nerves, pudendal nerve
-two branches of sciatic nerve: fibular nerve, tibial nerve
sensory innervation of the foot
branches from these peripheral nerves supply the foot anjle
-saphenous nerve, sural nerve, fubular nerve, tibial nerve
-mapping touch/pain perception and checking muscle function can determine damage to specific peripheral nerves
functional organization of nuerons
-sensory:10 million, bring info to CNS
-motor: 0.5 million, send commands from CNS out to peripheral effectors
-internuerons - 20 billion located withint he CNS, interpret plan and coordinate signals coming in and out
neuronal pools
-internuerons organized into functional groups of interconnected neuerons
-each has limited input sources and output destinations
-may stimulate or depress parts of brain or spinal cord
five patterns of nueral circuits in nueronal pools
-divergence
-convergence
-serial processing
-parallel processing
-reverebration
divergence
-spreads information from one nueron or nueronal pool to many
-especially common in sensory pathways
convergence
-several nuerons synapse on a single nueron
-example is subconcious and conscious control of the diaphragm in breathing - two nueronal pools synapse with same motor nuerons
serial processing
-information moves along a single path, sequentially from one nueron or nueronal pool to the next
-example: pain signals pass sequentially through two nueronal pools to reach conscious brain
paralell processing
-several nuerons and nueronal pools process the same information at the same time
-eaxmple step on a bee, signals spread through several nueronal pools so you can shfit your weight lift your foot and yell in pain at about the same time
reverberation
-xollateral branches of neurons extend back and continue stimulating presynaptic nuerons
-forms positive feedback loop continues until synaptic fatigure or inhibition occurs
-examples: may maintain consciousness, breathing and muscle coordination
nueral reflexes
-rapid, autonomic responses to specific stimuli
-basic building blocks of nueral function
-a specific reflex produces the same motor response each time
5 components of a reflex arc
-sensory receptor
-sensory nueron
-information processing in CNS
-motor nueron
-effector
events in a spinal reflex arc
-atimulus activates receptor
-with enough stimulation action potential is generated in sensory nueron, axon enters SC via posterior root
-information processing in spinal cord usually occurs at one or more internuerons
-internuerons stimulate action potenitlas in motor nueron, its axon leabes bia anterior root
-motor nueron stimulated effecto
events in reflex arc photo
four types of calssification of reflexes
-developmental
-motor response
-complex of nueral circuit
-site of information processing
developmental reflexes
-innate -chewing, visual tracking, withdrawl
-acquired - reptition enhances them, braking car in emergency
motor repsonse
-soamtic relfex - control skeletal muscle contracting, immediat eimportant emergencies
-visceral reflexes - control other effectors - smooth muscle ,cardiac muscle or glands
complexity of nueral circuit relfexes
-monosynaptic relfelx - single synapse, fast, sensory nueron synapses directly with motor nueron
-polysynaptic relfex - atleast one internueron-slower response,
intersegmental relfex arch
polysynaptic reflex
-many spinal cord segments interact
-produce variable response
sites of information processing
spinal relxes - processing occurs in spinal cord
-cranial reflexes - processing happens in brain
monosynaptic relfexes
-stretch relfex
-regulated skeletal muscle length throughout body
-very rapid (large myelinated fibers)
-patellar reflex
steps in a stretch reflex
-stimulus - muscle stretching
-distortion of receptors sends action potential through sensory nueron
-sensory nueron synapses with motor nuerons in spinal cord
-motor nuerons send sigma;s to motor untis, triggers reflexiative contraction of stretched muscle
muscle spindle strcutre
-receptors in stetch reflexes
-made of bundles of small specialized intrafusal muscle fibers
-innervated by sensory and motor nuerons
-muscles spindle is surrounded by extrafusal muscle fibers which maintain muscle tone and contract muscle
posterual reflexes
-include both stretch reflexes and polysynaptic
-maintain upright posture
-often involve many muscle grousp
-maintain firm muscle tone
-extremely sensitive receptors allow constant adjustments to be made as needed
can internuerons control mutliple muscle groups
yes
examples of polysynaptic reflex
-tendon reflex
-withdrawl relfex
-crossed extensor relfext
tendon reflex
-prevents skeletal muscles from developing to much tension or tearing or breaking tendons
withdrawl reflexes
-move body part away from stimulus
-flexor reflex
-strength and extent of response depends on intesnity and location of stimulus
reciporical inhibition
-for flexor reflex to work stretch reflex of antagonistic muscles must be inhibited
-when flexors contract, extenors relax
-when extensorys contract, reflexors relax
ipsilateral reflex arc
-occur on same side of body as stimulus
-stretch tendon and withdrawl reflexes
crossed extensor reflexors involve contralateral relx arcs
-occur on side opposite stimulus
-ciirdubated with flexor reflex
-strwp on something sharp before flexor can lift injured foot, crossed extesnorreflex straightnes opposite limb to recieve body wight
-maintained by reverberating cricuits
five general characteristics of polysynaptic reflexes
-inolve pools of nuerons
-involve more than one spinal segment
-involve reciperoical inhibition
-have reverterbating ciruicts
-several reflexes may cooperate
integration and control of spinal reflexes
-reflex behaviours are automatic but processing ceenters in the brain can facilitate or inhibit spinal reflex motor patterns
voluntary movements and reflex motor patterns
-spinal reflexes produe characteructis response for a given stimulus
-brain can also activate these same motor patterns through descending pathways (inhibit or fine tune)
einforcement or spinal relfelxes
-higher centers can adjust sensitivity o reflexes by stimulating excitatory or inhibitory internuerons in brainstem or spinal cord
-when excitatory synapses are chronically stimulated post synaptic nuerons can be in general facilitation
-this reinforcement enhances spianl relfexes
inhibtion of spinal relfexes
-higher centers inhibit spinal relces by
-stimulating inhibitory nuerons
-creating IPSPs at reflex motor nuerons
-suppressing postsynaptic nuerons thus inhbiting the reflex
plantar reflex
normal in adults
-strol lateral sole causes reflexive toe curling
babinski reflex
normal in infants may indicate damage in adults
