Download - CNS Reflex 1112
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Physiology of thePhysiology of thecentral nervous systemcentral nervous system
ReflexReflex
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General function of the nervous system (NS)Nervous system-communication network of neurons that allows the organism to interact with the environment (external, internal)
main function: regulation of body functions purpose: adaptation to changes - maintenance of homeostasis and survival
http://www.alz.org/braintour/images/neuron_forest.jpg
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Components of the nervous system (NS)Components of the nervous system (NS)
1. Peripheral NS2. Central nervous system
A/ sensory part:- detection and transmission of stimuli
B/ information processing perception integration (combining several signals) thinking, learning memory storage and retrieval of data planning and implementation of motor
commands emotions
C/ motor part: determination of response and its transmission to effectors
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Spinal cord - conducts sensory information to the brain - conducts motor information to the effector organs - serves as a simple regulatory centre (reflexes)- damage of the spinal cord breaks down the connection between
periphery and higher centres serious consequences
Brain - subcortical level - control of involuntary and
subconscious functions, emotions
- cortical level- control of voluntary functions- control of lower levels of CNS- brain - site of cognitive (higher) functions:
memory, learning, thinking
Levels of the CNS
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Peripheral nervous system (PNS)- transmits information from periphery to the centralnervous system and vice versaIncludes
- cranial nerves originate in brain (I XII)- spinal nerves - originate in spinal cord (C1, C2...Th,..L, S..)
ComponentsA. afferent (sensory) nervous system (incoming to CNS)B. efferent (motor) nervous system (outgoing from CNS)
a. somatic nervous system (transmit impulses to skeletal muscle)b. autonomic nervous system (transmit impulses to smooth muscles,
cardiac muscle and glands)
I. sympathetic division (fight or flight)II. parasympathetic division (rest and repair)
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Spinal cord white matter nerve fibres
(afferent , efferent ) grey matter cell bodies
- dorsal root sensory fibres- ventral root motor fibres
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Neurons of the spinal grey matter motor neurons- their axons leave via ventral roots (and cranial nerves) and terminate in muscles
(on the motor end-plate)- discharge of a -motor neurons causes a skeletal muscle contraction- synapse with sensory neurons, interneurons, neurons descending from brain
(pyramidal pathway)
motor neurons- innervate muscle fibres of the muscle spindles (intrafusal muscle fibres)- control of muscle tone- synapse with neurons
of extrapyramidal pathways
interneurons
propriospinal neurons- short fibres, - synapse within the spinal cord- vertical connections
ventral
dorsal
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Knee jerk the patellar reflex
- tap on the tendon of m. quadriceps femoris- the leg makes a kick (extension in knee joint occurs)
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ReflexReflex one type of function of the NS definition: predictable, quick, stereotyped and involuntary response to stimulus action that results from passing a nerve impulse over a reflex arc
Reflex arc the basic circuit that underlies a reflex:1. sensory receptor gathers stimuli2. afferent nervous fibre signal transduction into CNS3. reflex (integration) centre processes information4. efferent nerve fibre transduction of response5. effector (muscle, gland) performance, response to the stimulus
Spinal reflex arc
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DrawDraw a sa spinalpinal reflex arcreflex arc
integration centre
sensory neuron = afferent pathway
motor neuron=efferent pathway
sensory neurons body
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Classification of reflexes Classification of reflexes with respect to:with respect to:A/ Count of synapses:
1. Monosynaptic= 1 synapse in reflex arc
2. Polysynaptic= 2 or more synapses in reflex arc
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Classification of reflexes Classification of reflexes with respect to:with respect to:B/ Type of sensory receptor
Exteroceptive receptor in the reflex arc is an exteroceptor (gathers stimuli from external environment)Proprioceptive receptor in the reflex arc is an proprioceptor (gathers stimuli about position of the body)Interoceptive receptor in the reflex arc is an proprioceptor (gather stimuli from internal environment)
C/ Centre Cranial (brain)Spinal (spinal cord)Extracentral (ganglia)
D/ EffectorSomatic effector: skeletal muscleAutonomic (visceral) effector: cardiac muscle, smooth muscle, gland
E/ OriginInborn related to locomotion, defence, food intake, sexual behaviourAcquired develop during life
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involved in movement, muscle tone and posture regulation
motor control in part conscious to major extent - subconscious reflex action spinal reflexes
coordination of movement depends on: discharges in the appropriate muscles (contraction) absence of discharges in inappropriate muscles (relaxation)
types of sensory receptors involved in spinal reflexes: muscle spindles Golgi tendon organs
Monosynaptic reflexes Monosynaptic reflexes Muscle stretch reflexes (Muscle stretch reflexes (myotaticmyotatic)) spinal reflexes centre in spinal cord example: knee jerk
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The muscle spindleThe muscle spindle
a stretch receptor in a musclea bundle of modified muscle fibres encased in a capsule = intrafusal fibres
intrafusal fibres paralell with all muscle fibres (extrafusal) fixed to connective tissue of the muscle terminal parts elastic, centre non-elasticsensory nerve wrapped around the centre ofthe intrafusal fibres
adequate stimulus for a muscle spindle: muscle stretching
passive stretching with a reflex hammer= stimulus that elicits a reflex
response contraction of extrafusalmuscle fibres of the same muscle
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Operation of the muscle spindleOperation of the muscle spindle
resting state resting frequency of potentials
if the muscle spindle is passively prolonged the spacing between the coils of the
sensory nerve become more apart larger discharge rate trnasmitted to the -
motoneuron result: muscle contraction
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tapping on the muscle spindle (of differentmuscles) passive prolongation = stimulation(1)
action potential is transmitted by afferent fibre (2) afferent fibre enters spinal cord through posterior
roots
afferent fibre synapses with efferent fibre ( motoneuron)
synapse = integration centre (3) (information is processed)
action potential is transmitted by efferent fibre ( motoneuron) into muscles (via neuromuscular endplate) (4)
muscle contraction occurs (5-response) this is seen as movement (flexion)
afferent fibre
efferent fibre
dorsal roots
ventral roots
Spinal reflexSpinal reflexeses
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Spinal cord
segmental organization
segments (levels) of the spinal cord contain regulatory circuits involved in control of the
movements of a particular region of the body
Muscles in axial parts of the body limbs( motoneurons medial part) ( motoneurons -lateral part)= somatotopic organization
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Examination of reflexes in a humanExamination of reflexes in a human
basic examination in neurology indicates the function of reflex arc (and all its components) reflex - stereotypic reaction = predicted response normoreflexia normal reflex response on a stimulus
abnormal response indicates disorder in a part of reflex arc
Abnormal results: hyperreflexia (or clonus) hyperactive reflex hyporeflexia diminished reflex areflexia absence of response abnormal reflex the response on the stimulation is abnormal
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Principle sensory receptors are stimulated the reflex response on stimulation is observed and evaluated
Procedure the patient is in sitting or lying position (depends on the reflex)
sensory receptors are stimulated by a reflex hammer, cotton, light, needle (depends on the reflex that we want to examine)
examine following reflexes (see next slides)
Task: Examination of reflexes in a humanTask: Examination of reflexes in a human
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Proprioceptive (deep tendon) reflexes- sensory receptor in muscle, tendon
Masseter reflex (n V)S: tap on a spatula put on the
lower jaw(mouth is moderately open)
R: closing the mouth
Naso-palpebral reflex (n V,VII)S: tap on the nasal baseR: closing of eyelids
Biceps reflex (C5)S: tap on lacerus fibrosus m. bic. brachiiR: flexion of the forearm
Triceps reflex (C7)S: tap on olecranon ulnaeR: extension of the forearm
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Styloradial reflex (C7)S: tap on proc. styloideus radiiR: flexion of forearm
Patellar reflex (knee jerk, L 2-4)S: tap on the tendon of m. quadriceps
femorisR: extension in knee joint- the patient is sitting, and the examined
limb is put over the knee of the other- if no response occurs, do the
Jendrassik manoeuver (abduce one hand from another)
Achilles tendon reflex (ankle jerk, L5-S2)
S: tap on Achilles tendonR: extension of the foot- the patient may lie or kneel
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Achilles tendon reflex measurementAchilles tendon reflex measurement
Principle:- thyroid hormones (thyroxin, triiodthyronine) influence the activity of
the central nervous system- examination of Achilles tendon reflex is an indirect indicator of thyroid
activity (Ankle jerk)- reflex time (stimulation response) depends directly on the level of
thyroid hormones
- normal reflex response euthyrosis- weak response hypothyrosis- excessive response hyperthyrosis
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Exteroceptive reflexes- sensory receptors in skin or mucosa
Corneal reflex (n V, VII)S: touching the cornea with a piece of cottonR: blinking(used in surgery-depth of anaesthesia)
Abdominal reflexes (Th 5 Th 11) epigastric mesogastric hypogastric
S: drawing of the abdominal wall with a needle
R: muscle contraction (lying position)
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Plantar reflex (L5-S2)S: stimulation of external side of planta pedis with a needle (from heel to little
finger and other fingers)R: plantar flexion or the toe (or all fingers)
- if pyramidal pathway is impaired the response in plantar reflex is abnormal (this is called Babinski phenomenon)
R: extension of the toe- normal in babies up to 6-8 months, later a sign of disorder- indicates abnormalities in pyramidal tract
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Autonomic (vegetative) reflexesAutonomic (vegetative) reflexes- response transmitted by autonomic fibres
Pupilary reflexS: illumination of an eye (use battery)R: miosis diameter of the pupil becomes narrow
- consensual reaction if one eye is illuminated, miosis occur bilaterally
Oculocardial reflexS: moderate pressure on the eyeballR: decrease in pulse frequency (by 5-10 per minute) Orthostatic reflexS: sudden change position from lying to sittingR: increase in pulse frequency Clinostatic reflexS: sudden change of position from sitting to lyingR: decrease in pulse frequency
all reflexes- measure heart rate only 15, then multiply by 4 (rate per min)
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AlphaAlpha--ggammaamma co co -- activationactivation
gamma motor neurons adjust the sensitivity of the muscle spindle
gamma fibres terminate in the polar parts of muscle spindle
the stimulation by gamma fibres causes contraction of muscle fibres in the polar region (periphery) of the muscle spindle
the fibres in the centre (equatorial region) become prolonged= stimulus that elicits a muscle stretch reflexthat results in contraction of the muscle
response - muscle contraction In this way the muscle tone is regulated
Gamma - fibre
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1.Stretch reflex (myotatic) monosynaptic- receptor: muscle spindle (stimulus: passive prolongation)- signal transmitted via afferent fibre - synapse in spinal cord to:- efferent fibre: alpha motoneuron (it gets stimulated)- response: skeletal muscle contraction (the same muscle where the receptor is
located)
2. Inverse myotatic reflex polysynaptic- receptor: Golgi tendon organ (can be stimulated by very strong contraction or
stretching)- signal transmitted via afferent nerve fibre and by interneurons in spinal cord to- efferent fibre: alpha motoneuron it gets inhibited !!!- response: muscle relaxation (the same muscle where the receptor is located)
- function: protection against rupture of the muscle
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a proprioceptive sensory receptor organ
located at the insertion of skeletal muscle fibers into the tendons of skeletal muscle
made up of strands of collagen connected at one end to the muscle and at the otherwith the tendon
when the muscle contracts, the collagenfibrils are pulled tight, and this activates theGolgi tendon organ afferent
it detects tension of the muscle
synapses with interneurons that inhibit a motoneurons
response: relaxation of the muscle(prevents rupture)
GolgiGolgi tendontendon organorgan
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3. Flexion reflex polysynaptic
-stimulus causes response in both flexors and extensors of the same side:
1. activation of alpha motoneurons of the ipsilateral flexor muscles,
2. at the same time inhibits alpha motoneurons that supply antagonistic
extensor muscles
- example: when touching a hot object contraction of flexors and relaxation of extensors causes removing the hand
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4. Crossed extension reflex polysynaptic
a stimulus causes response on both sides in bots extensors and flexors:
1.activation of alpha motoneurons of the ipsilateral flexor muscles
2.inhibits alpha motoneurons that supply antagonistic extensor muscles
- the opposite pattern occurs on contralateralside
3.flexors are inhibited4.extensors are stimulated
- example: when a person steps on a nail, the leg that is stepping on the nail pulls away, while the other leg takes the weight of the whole body- reflex enhances postural support
- example: locomotor pattern generator
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MonosynapticMonosynaptic reflex reflex arcarc
Autonomic reflex arc Autonomic reflex arc (efferent pathway (efferent pathway 2 neurons 2 neurons connected in ganglia)connected in ganglia)
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Task: Measurement of the reaction timeTask: Measurement of the reaction time
Reaction time - time between onset of the stimulus and the onset of a conscious reaction-important for some professions: pilot, surgeon, sportsman, etc.
Reflex time- time between onset of a stimulus and reflex response (involuntary)
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Components the of reaction time
1. time for transfer of the information into the
primary cortex
2. time for cortical processing completed by
excitation of projection motor neurons in gyrus praecentralis
3. time for transfer of impulse from the
projection motoneurons via medullar motoneurons into reacting muscles
4. time of spreading of action potential in the
muscle and muscle contraction
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Factors that influence the reaction time
type of stimulus
- visual (0,195 s)- acoustic (0,15 s), etc.
functional characteristics of the anatomic structures that are involved
attention (decrease duration) practice/skills (decrease duration) distractors/tiredness (prolongs reaction time) age (increasing age/increasing reaction time) alcohol (prolong reaction time) drugs
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Principle of the task- computer generates visual and/or acoustic stimulus- the examined person responds by pressing any key
Procedure- select a test (1-5)- start with test 1(the easiest)- then complete the tests 2-3-4-5
- each of the following tests is more complicated than the previous one - requires more attention- this should be reflected in reaction time(more complicated test longer duration of the reaction time)
- select the count of stimuli per test (recommended is 10)
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Tests
1. visual static- a bright spot occurs on screen, it disappears after
measurement- next spot occurs on the same place
2. visual dynamic- a bright spot occurs on screen, it disappears after
measurement- next spot occurs in another place
3. visual additive- a bright spot occurs on screen, it does not disappears after
measurement
4. acoustic- the computer beeps
5. combined visual/acoustic- stimulicome in random order
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How to respond? when you see/hear the stimulus, press any key
Results and conclusion for each stimulus - record the average reaction time compare the reaction times of all tests do the results correspond with the
level of the test? look at the bar chart and describe how the reaction time has changed during
the course of each testing (measurement 1 10) try to explain your observation