Physiology of thePhysiology of thecentral nervous systemcentral nervous system

ReflexReflex

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

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

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

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)

Spinal cord white matter nerve fibres

(afferent , efferent ) grey matter cell bodies

- dorsal root sensory fibres- ventral root motor fibres

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

Knee jerk the patellar reflex

- tap on the tendon of m. quadriceps femoris- the leg makes a kick (extension in knee joint occurs)

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

DrawDraw a sa spinalpinal reflex arcreflex arc

integration centre

sensory neuron = afferent pathway

motor neuron=efferent pathway

sensory neurons body

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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)

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

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

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

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

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

MonosynapticMonosynaptic reflex reflex arcarc

Autonomic reflex arc Autonomic reflex arc (efferent pathway (efferent pathway 2 neurons 2 neurons connected in ganglia)connected in ganglia)

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)

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

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

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)

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

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