conduction
up and down moventment of electrical impluses within the spinal cord.
locomotion
simple repetive central pattern generators
somatic reflexes
quick, involuntary, stereotypic responses to stimuli
may or may not involve brain, they are unlearnt skeletal muscle reflex, testing these help diagnose diseases
plexus
combination of interlaced parts, a network especially of nerve, blood vessels or lymphatics
spinal cord
cylinder of nervous tissue that aries from the brainstem at the foramen magnum of the skull
segement
part of spinal crod supplied by each pair of spinal nerve
features of spinal cord
- it passes through the vertebral canal
-ends at L1 or little beyound in adults
- gives rise to 31 pairs of spinal nerve
- ave 1.8 cm thick and 45cm long
anterior median fissure
posterior median sulcus
grooves on anterior side
grooves on posterior side
division of spinal nerve
cervical, thoracic,lumbar and sacral
caudia equina
bundle of nerve root that occupy the vertebral canal from L2 to S5
formed from roots that arise from L2-Coccyx
cervical and lumbar enlargement
two ares of the cord thicker than elsewhere, cervical: nerve to upper limbs and lumbar: lower in thoracic that supply nerves to pelvis region and lower limbs.
meninges of the spinal cord
three layers of fibrous connective tissue membranes
- enclose the brain and spinal cord
- separate soft tissue of central nervous system from bones
of cranium and vertebral canal
dura mater arachnoid mater - pia marer (DAP)
from superficial to deep vertebral bone - epidural space
gray matter
central area shaped like butterfly or H in the spinal cord, surrounded by white matter,
- neuron cell bodies have little myelin
- information processing, site of most synpases
- carries signal from one part to another of CNS
Parts of Gray Matter
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white matter
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Spinal tracts
ascending: carry sensory info up spianl cord
descending: carry motor info down sipnal cord
decussation:as fibers pass through the brainstem they cross over
contralatteral: opposite side of body
ipsilateral: same side of body
nerve
cordlike organ composed of numerous nerve fibers (axon) bound by connective tissue
composed of thousands of fibers carrying currents
sipnal nerve function
allow spinal cord communication with rest of body
Schwann cells
nerves of the peripheral nervous system are ensheathed in these
Endoneurium
external to myelin sheath,each fiber surround by this
Fascicles
nerve fiber gathered in bundles wrapped in perineurium
Epineurum
bundles numerous fascicles that make up whole nerve, consist of dens irregular connective tissue fiber ( conituous with dura meter
protects nerve from streching and injury
blood vessels function in nerves
they penetrate connective tissue coverings to supply the plentiful need by the high metabolic rates of nerve
classification of nerve
afferent fiber, efferent fiber, somatic fiber, visceral fiber, general fiber, special fiber
sensory (afferent )nerve
carry signals from sensory receptors to CNS
motor (efferent) nerve
carry signals from CNS to muscles and glands
mixed nerve
consit of both afferent and efferent fibers
conduct signals in two directions
somatic fibers
innervate skin, skeletal muscles, bones and joints
visceral fiber
innervates blood vessels, glands and viscera
general fibers
innervate wide sperad organs eg. muscles,skin,glands,visceras, blood vessels
specail fibers
innervate more localized organs in the head eg. eyes, ears, olfactory, taste, muscles for chewing, swallowing and facial movements
ganglion
cluster of neuron cell bodies outside CNS,surrounded by epineurium, continuous with tract of nerve and dura mater
dorsal root ganglion
contians cell bodies of afferent neurons
Spinal Plexses location
Cervical plexses(C1-C5,8 pairs of nerve); Brachial plexses(C5-T1);Intercostal/thoracic nerve (12 pairsof nerve, T1-T12)
Lumbar plexses(L1-L5, 5 pairsof nerves); Sacral plexes(5 pairs of nerves); Sacral plexses(L4-S4,5 pairs of nerve)Coccygeal plexes (S4-Co1, i co nerve)
spinal nerve proper
merging of dorsal and ventral roots
dorsal root proximal anatomy
sensory input to spinal cord, six to eight rootlets that enter posterior horn
ventral root proximal anatomy
motor output of spinal cord,six to eight rootlets that converge to form anterior root
anterior ramus
innervates the anterior and lateral boby
posterior ramus
innervates the back
communicating rami
T1-L2 these additional braches pair form sympathetic (chain) ganglion outside nertebrae
somatosensory function
carry sensory signals from bones, joints, muscles and skin
proprioception
brian receives info about body position and movements fron nerve endings in muscle, tendons and joints
motor function
primarily to stimulate muscle contraction
dermatome
-specific area of the skin that recieves sensory input fr pair of spinal nerve, they overlap their edges as mcuh as 50 times,
-severing or anesthetize three successive spinal nerve cause loss of sensation in one dermatome
dermatome map
a diagram of the cutaneous regions innervated by each spinal nerve
reflexes
reactions of glands and muscles to stimulation, they are quick, involuntary and stereotyped, can incldue glandular secretions of contraction of any three muscle types
four properties of reflexes
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pathway of reflex arch (1-5)
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interfusal fiber
muscle fiber within spindle
muscle spindle
-stretch receptor embedded in myelin sheath
-enable control of coordinated movmment, muscle tone and pressure
-serve as proprioceptors to onitor position and movement of body(muscle ;ength and change in length
3 types of nerve fiber in muscle spindle
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tendon reflex
reflexive contraction of a muscle when its tendon is tapped,
-knee-jerk(patellar) reflex is monosynaptic reflex, no interneuron
strech reflex
-stretch muscle 'figth back' and contract which maintains increased tonus thus muscle is stiffer than unstretch muscle
-maintain posture and equilibrium, stablilize joint by balacning tension in extensors and flexors smoothing muscles actions
path of patellar tendon reflex arc
1. extensor muscle stretched 2. muscle spindle stimulated 3.primary afferent neuron excietd 4. primary afferent neuron stimulates alpha motor neuron to extensor muscle 5.alpha motor neuron stimulates extensor muscle to contract 6.primary afferent neuron stimulates inhibitory interneuron 7.interneuron inhibits alpha motor neruon to flexor muscle
path of flexor (withdrawal) reflexes
1. stimulation of sensory receptors 2.sensory neuron activi-ates multiple iterneurons 3.ipsilateral motor neuron to flexor excited.4.ipsilateral flexor contracts 5.contrlateral motor neurons to extensor excited 6. contralateral extensor contracts
flexor reflexor
quickcontraction of flexor muscles resulting in the withdrawal of limb fr an injurious stimulus
-requires contractionof flexor and relaxation of extensors in limb.
reciprocal inhibition
prevent muscles fr wking against each oyher by inhibiting tha antagonist.
polysynaptic reflex arc
pathway in which signals travels over the many synapses on their way back to muscle
ipsilateral reflex arc
sensory input and motor output are on the same sides of spinal cord
crossed extension reflex
contraction of extensor muscles in limb of one that is withdrawn
contralateral reflex arc
one in which input and output are on opposite side.
goli tendon organ
proprioceptors in a tendon near its junction with a muslce.
tendon reflex
in response to excessive tension on the tendon
-reduces muscle contraction b4 it tears a tendon or pulls it loose fr the muscle of bone.
complete transection
complete severance of spinal cord
-immediate loss of motor control below level of injury
-above C4 threat to respiratory failure (phrenic nerve) and spinal shock, paralysis
paraplegia
paralysis of both lower limbs
quadriplegia
paralysis of all four limbs
hemiplegia
paralysis on one side of body due to BRAIN INJURY not spinal cord.
sciatic nerve injury
sharp pain travels fr gluteal region along posterior side of thigh and leg to ankle
-90% result fr herniated intervertebral disc or osteoporosis
sciatic nerve
longest nerve in body, fron lower spine all dwn to ankles
spina bifida
congenital defect where one or more vertebrae fail to form a complete vertebral arch. 1:1000 born with it folic acid reduce risks
poliomyelitis
caused by polio virus, spread by fecal contaminated water
-destroy motro neuron in brian and anterior horn of spinal cord, muslce pain, weakness, loss of some reflexes, muscular atrophy
amyotrophic lateral sclerosis
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chicken pox
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shingles(herpes zoster)
localized disease caused by virus traveling dwn sensory nerves when immune system is compromised
-over 50 yo,pain, itching,chest and waist of body it shows
-chicken pox vaccine reduce risk