nervous regulation of functions . excitation and inhibition in cns

Nervous regulation of functions.Excitation and inhibition in CNS

Lecture 2

Questions:

• General principles of function regulation.• Functional systems. Positive and negative

feedback.• Nervous regulation of functions. Neuron as

the structural and functional unit.• Nervous centers and their properties.• Reflex, reflex arch, its structure.• Principles of reflex coordination

Regulationprocess of the maintenance of

homeostasisHomeostasis – maintenance of static (or constant) conditions in the internal environmentInternal environment – liquid environment of human body (blood, lymph, extracellular fluid etc.)

Regulation is realized by control systems

• There are thousands control systems• Example: respiratory system together with

nervous system regulates concentration of carbon dioxide

Biological regulation• Levels:

cellular (local regulation)organ (local into organ)system and organism (central)

Regulation of body functionsis provided by regulatory systems

• Nervous system• Hormonal system

Central regulation

• Realizes by means:central nervous systemendocrine system

Functional system

• Functional association some structures activity of which aimed to regulation some homeostatic parameters

Regulatory apparatus (feed-back mechanism) includes:

• Positive and negative feedback loops.

• Positive: the more parameter the more functional activity of organ

• Negative: the more parameter the lesser functional activity of organ

Role of feedback

mechanism

• When a homeostatic constant of

internal environment deviates

significantly from normal range,

through feedback mechanism the

deviation is corrected to

maintain homeostasis

Importance

• Autoregulation is possible • negative feedback loop is typical for healthy

human body

Nervous regulation of functions

• NS provides the control of functions of the body: the rapid activities of the body (muscular contractions, rapidly changing visceral events and the rates of secretion of some endocrine glands).

NS•Central nervous system (CNS) - brain and spinal cord

•Peripheral nervous system (PNS) – cranial nerves (I-XII), spinal nerves, ganglia, enteric plexuses

Functions

• Sensory• Integrative• Motor

Neuron

• is a basic structural and functional unit of the nervous system. As well as the NS in whole a neuron receives information from the different sensory organs and integrates it producing body’s response.

Structure of neuron

• Has dendrites (reception of information), cell body (processing and analysis of information) and trigger zone – axon hillock (AP initiated – efferent command)

Functions of neuron:

• Receptive • Analysis and synthesis of information

(integrative function)• Motor function (generation of AP)

Classification of neurons:

is based on functions (a), number of processes (b), neurotransmitters (c),

shape and size.(a) sensory (afferent), contact

(intraneuron), motor (efferent);(b)unipolar, bipolar, multipolar;

Cholinergic, adrenergic

Neuroglia

• Astrocytes • Oligodendrocytes• Microglia• Ependymal cells (only in CNS)• Schwann cells and sattelite cells in PNS

Functions of neuroglia

• Trophic: provides nutrients to neurons• Homeostatic (helps to maintain appropriate

chemical environment);• Supporting function (network around CNS

neurons);• Protective (from microbe diseases) etc.

Nervous center

• Is a association (group) of neurons which together regulate a definite function (respiratory center, hemodynamic center etc).

Properties• Summation of excitation • Occlusion• One-way conduction• Delayed conduction• Prolongation (post-action)• Transformation• Divergence• Convergence

Summation

• Generation of AP in response to subthreshold impulses when they come to the center one after another at short interval along one nerve fiber

• Or• when they come to the center

simultaneously from different fibers

Types of summation

• Temporal (consecutive) summation• Spatial summation

Occlusion

• Decreased reaction response (effect) on simultaneous stimulation

This phenomenon can be explained as two nervous centers can have some common neurons that belong on both centers

One-way conduction

• In CNS the impulses can be conducted only in one direction (from afferent neuron to efferent neuron)

Delayed conduction

• The impulses pass through the nervous center more slowly than along nerve because the chemical processes in the synapses take some time – synaptic delay

Prolongation

• Reflex can continue after end of stimulation.

Transformation

• Change of the rhythm of excitation

Divergence (or irradiation)

• Excitation can spread increasingly and involving more and more neurons

Convergence

• Excitation spreads from multiple neurons to single neuron

Neurons circuits (chains)

• Diverging• Converging• Reverberating• Parallel after-discharge etc

Neurons circuits

Reflectory principle

• Reflex is response of organism on external stimulation (R.Decart, 17th century)

For CNS: “Reflexes of brain” M.Sechenov (1869)

Links of reflex arc

• Afferent (receptor, afferent fiber, afferent neuron) – Receptive field : group of receptors which send sensory information to one afferent neuron

• Central (contact (inter-) neurons)• Efferent (efferent neuron, efferent fiber,

effector organ)

Classification of reflexes (based on localization of chains of reflex

arcs)• Exteroceptive• Interoceptive (visceral)• Proprioceptive

Central chains

• Spinal• Bulbar• Mesencephalic (mid-brain)• Diencephalic (interbrain)• Cortical

Efferent chain

• Motor (muscles)• Secretory (glands)

Structure of reflex arc

• Monosynaptic• Bisynaptic • Polysynaptic

• Reflex time depends on number of synapses in reflex arc

Other classifications

• Physiological: cardiovascular, respiratory, digestive, excretory, locomotor, stato-kinetic

• Biological: nutritive, defensive, sexual• Somatic, autonomic• Conditioned, unconditioned

Principles of coordination

Coordination

• Interaction of neurons and neuron processes (reflexes)

Principles of reflex coordination

• Reciprocal innervation• Common final path• Dominant

Principle of common final path (by CH.S. Sherrington)

Domimant (by Ukhtomsky)

• In definite conditions one nervous center always is the most active (higher tonus) than other centers. And even more, this center inhibits other centers. It is important because iy permits to focus brain only on one action, realization of which is the most important in concrete situation.

Excitation end inhibition in CNS. Central synapses

Inhibition

• Is the nervous process, opposite excitation• It archives by means hyperpolarization on

the postsynaptic membrane (postsynaptic inhibition) or as result of inhibition of mediator secretion in the synaptic cleft from presynaptic membrane (presynaptic inhibition).

Central synapses

• Excitatory neurotransmitters (acetylcholine, amino acids, biogenic amines, ATP and other purines, nitric oxide)

• Inhibitory neurotransmitters (glycine, gamma aminobutyric acid - GABA).

• About 100 chemical substances

Bioginic amines:

• Norepinehrine – in the brain a smaller number of neurons use - awakening from deep sleep, dreaming and regulating mood;

• Dopamine – emotional responses, addictive behaviors and pleasurable experiences, tonus of skeletal muscles (Parkinson desease, one form of schizophrenia)

Biogenic amines:

• Serotonin – sensory perception, temperature regulation, control of mood, appetite, induction of sleep

ATP and other purines

• Excitatory NT in CNS and PNS act with NE

Neuropeptides

• Enkephalins analgetic action stronger than morphin

• Opioid peptids (endorphyns) – analgesia (loss of pain sensation, improving of memory and lesrning, feelings of plesure or euphoria, sexual drive etc. and depression and schizophrenia.

• Substance P – pain sensations

Nitric oxide

• Has widespread effects throughout the body.

• Main effects – vasodilatation, m.b.memory and learning (Viagra).

Inhibitory neurotransmitters

• Inhibitory NS cause IPSP by opening Cl ions. Antianxiety drugs such as diazepam (Valium) enhance the action of GABA.

• GABA is found only in CNS. In spinal cord about half of inhibitory synapses use amino acid glycine and half use CABA

Iontropic receptors

Metobotropic receptors

Serotoninergic synapse

AcH transmission

Questions 1. Spinal cord in regulation of the motor

function2. Brain stem. Role of the Reticular

Formation in control of motor function3. Function of Cerebellum in controlling of

movements4. The Basal Ganglia and motor control5. Motor functions of the Cerebral Cortex

Functions of the Spinal cord

¾ reflectory (motor, autonomous)¾conductive

Bell-Magendie law

• Posterior roots contain centripetal, afferent fibers

• anterior roots contain centrifugal, efferent fibers

Neuronal organization of s.c.

• Dorsal horns: afferent centers• Lateral horns: vegetative centers• Ventral horns: motor centers

• Sensory• Integrative• Motor

Sensory f.

• 12 laminas (1-YI – in dorsal horns; 2-3 –substantia gelatinosa) - reception of information from mechanoreceptors (Aβ,Aδ, C), nociceptors (Aδ,C), cold receptors(Aδ), thermoreceptors ©.

Integrative function

• Interneurons are present in all areas of the cord gray matter

• Renshaw cells –inhibitory cells – transmit inhibitory signal to the nearby motor neuron

Motor function

• 2 types of motor neurons:• Α-motoneurons regulate the extrafusal

muscle fibers (contraction of muscle)• γ-motoneurons provide dynamic and static

reactions in response on information from intrafusal muscle fibers

Receptors

• Muscle spindle reacts to changes of a muscle length

• Golgi Tendon Organ – to changes of tension

Control of Gamma Efferent Discharge (gamma-loop)

• Length of muscle spindles regulates a length of this muscle

Gamma coactivation(during voluntary movements)

Spinal motor reflexes

• Stretch (myotatic, tendon) reflexes regulate muscular tone and posture – fast stretch of muscle

• Phasic reflexes - skin reflexes (exteroceptive reflexes)

Myotatic (muscle stretch) reflex (Fast change of posture)

Inverse stretch reflex (active muscle contraction)

• Receptors – Goldgi tendon organ (unlike the spindles) are stimulated by both passive and active contraction of the muscle.

• Stretch stimulates the spindle – Ia fibers -motor neurons

• It stimulates also Golgi tendon organ, Ib fibers activate the interneuron to release inhibitory mediator glycine

• Strong stretch stops discharging

Phasic reflexes (withdrawal reflex, skin reflexes)

Clinical reflexes

• flexion-extension reflexes (biceps reflex, triceps reflex, Achilles reflex)

• Knee-jerk reflex• Abdominal reflexes

Mechanisms of coordination

• Convergence• Divergence• Reciprocal inhibition• Inverse (recurrent) inhibition

Convergence

• The motor neurons in the spinal cord constitute the common final path – the root, by which all central activity influences motor neurons

Convergence

Divergence

• Spreading of impulses from 1 neuron to some neurons

Divergence

Reciprocal inhibition

• Collateral branches of type Ia axons inhibit the motor neurons of antagonist muscles

Reciprocal inhibition

Recurrent inhibition

• Stimulation of one neuron causes the inhibition of surrounding motor neurons

Autonomous reflexes

• Vessels• Smooth muscles of visceral organs (act of

urination, defecation, erection etc)

Ascending tracts9spinocerebellar9spinotalalamic 9fasciculus gracilus and fasciclus cuneatus

Descending tracts9corticospinal9rubber-spinal 9tecto-spinal 9reticular-spinal9vestibulo-spinal

• Proprioceptors of the muscles, tendons –spinal ganglia - medulla oblongata –thalamus – cerebral cortex

Fasciculus gracilus and fasciclus cuneatus (Goll’s and Burdach’s)

spinotalalamic

• Pain and temperature receptors – lateral spinotalamic tract – thalamus- cortex

• Tactile receptors of the skin – ventral spinothalamus tract – cerebral cortex

spinocerebellar(Gowers’ and Flechsig’s)

• Proprioceptors - cerebellum

Descending tracts

• corticospinalrubber-spinal tecto-spinal reticular-spinalvestibulo-spinal

Spinal shock

• Transsection of s.c. in the upper neck causes depression all reflexes.

• After a few hours to a few weeks (months) the reflexes recover

Brain stem

• Medulla• Pons • mesenchephallon

Hind brain and cerebellum

Diencephalons

• Thalamus• Hypothalamus

Functions

• 1. sensory and motor functions of face and head regions which are provided by cranial nerves (afferent and efferent as in spinal cord)

• 2. many special control functions by means own nuclei:

Nuclei which provide

• Respiration• The cardio-vascular system• The gastrointestinal system• Many stereotyped movements of the body• Control of equilibrium• Control of eye movement

Medulla oblongata

• XII –n.hypoglossus (motor)• XI – n.accessorius (motor)• X –n.vagus (sensory and motor)• IX – n.glossopharingeus (sensory and

motor)• YIII – n.vestibulo-cohlearis (sensory and

motor)

Pons

• YII – n.facialis (sensory and motor)

• YI – n.olfactoris (sensory and motor)

• Y – n.trigeminus (sensory and motor)

Mesencephalon

• III – n.oculomotoris• IY – n. trochlearis

Cranial nerves

Sensory and motor nuclei

Vital and other centers in medulla and pons

• Inspiratory, expiratory, pneumotaxic centres - (vital centers of the respiratory system and centers of the coughing and sneezing)

• Hemodynamic center – vital center of the cardiovascular system (pressor and depressor)

• Centers of the chewing, sucking, swallowing, vomiting – the digestive system

• Vestibular n. (Deiter’s n. in pons)• Reticular n.• Olivar n.• Fasciculus gracilus and fasciclus cuneatus (Goll’s and

Burdach’s tracts)

Functions of hind brain

• Sensory (from receptors along aff.cranial nerves)• Vegetative (autonomous regulation of the vital

centers)• Motor function: a)participation in the regulation of

the static and stato-kinetic reflexes together with midbrain; b) reticular (regulation of the spinal centers tone) and vestibular (regulation of the tonic reflexes of the position of the body) nuclei

• Conductive function (Goll’s and Burdach’s tracts etc.)

Nuclei in the Midbrain• N. lamina (tecti) quadrigemina: superior

(anterior)quadrigeminal bodies– primary optic centers; inferior – acustic center

• S.nigra – regulation of tone, delicate movements of fingers requiring great accuracy, coordination of the complex acts of deglutition and mastication

• N.ruber – regulation of muscular tone

Motor functions of the brain stem

• the static reflexes : regulation of the posture and equilibrium

• statokynetic reflexes: regulation of the pose and equilibrium during movement

Static reflexes

• Support of the body against gravity are provided by reticular and vestibular nuclei.

• Reticular nuclei include: the pontine reticular n. and medullary reticular n. (reciprocal relations)

• Descending Reticular spinal tract (medial and lateral) - regulation of the tone of the axial muscles (vertebral column and the extensor muscles of the limbs), which support the body against gravity

Vestibular n.

• Afferent information - from vestibular apparatus

• vestibular nuclei (Deiter’s n. activates the tone of extensor muscles)

• Efferent signals maintain equilibrium by means descending vestibular-spinalis tract

Decerabrate rigidity

• Exclusion influence of the red n. on hind brain (Deiter’s n. ) causes to increasing of extensor muscles tone

•

Static reflexes

- of position – regulation of pose (redistribution of muscle tone) in response on:impulsation from neck proprioceptors – neck

tonic reflexes from vestibular apparatus –

labyrinth tonic reflexes- of righting – recover of pose after its change

Stato-kinetic reflexes

• Arise during change of a movement velocity

labyrinth reflexes

•Lift reflexes

Nystagmus of the eye(during stato-kynetic reflexes)

• During rotation the eyes turns slowly as far as possible to the side opposite to the direction of rotation, then is reversed by a quick motion to a normal position in relation to the trunk

Postural reflexes

• Maintain equilibrium and posture in response on sudden changes in the orientation of an animal in space

Orientation reflexes

• turning of the head and body towards a new or strong or sudden sound or light stimulation

Reticular formation

• Diffuse aggregations of cells of various types and sizes, which are thickly interlaced by numerous fibers passing in different directions

• Function: regulation the excitability and tone of all divisions of the CNS (activation influence on the cerebral cortex - Megoun, Morutzi; activation and inhibition of the spinal centers (Sechenov)

Ascending activating influence of the reticular formation

Thalamus

Functions

• Collect all sensory information: specific, non-specific, associative, relay nuclei

Controlling stereotyped movements

• Flexion, extension, rotation, turning movements of the entire body by nuclei of mesencephalic and lower diencephalic region

Connections of the thalamus

Specific n.

• Connect with specific sensory areas of neocortex.

• It provides a fast analysis of sensory information and fast reaction on it

Nonspecific n.

• Connect with associative areas of neocortex.

• It provides slow but detailed analysis of the information

Associative n.

• Provide interaction of the thalamic neurons• It is reputed that analysis of the sensory

information on thalamic level causes formation unconscious sensations

The Cerebellum

Nucleus emboliformisNucleus dentatusNucleus globosusNucleus fastigii

3 layers of cortex

Functions of Cerebellum

9 Posture - paleocerebellum (aff.pathways from vestibular analizer)

9Control of rapid muscular activities, such as running, typing, sequence the motor activities, monitors and makes corrective adjustments in the motor activities elicited by other parts of the brain -acheocerebellum (from spinal cord)

9 Fast movements in accordance with “command” from brain cortex and basal ganglia (from neocortex)

Inretaction of cerebellum with cortex

Symptoms9Disequilibria – lack of balance9Asthenia – quick tiredness9Ataxia – disturbance of walking9Atonia – lack of muscular tonus9Adiadohokines – inability to perform some

simultaneous movement9Dismetria – wrong of measurement

Hypothalamus

Basal ganglia

• caudate nucleus• Putamen• Globus pallidus• But• Functiomally subthalamic nuclei and s.nigra

belong on basal ganglia

Functions

• Aff.from sensory and associative areas of cortex,s.nigra - striatum-pallidum, s.nigra –thalamus – motor zone, nuclei of brain stem/

• Through pyramidal tract (cortico-spinalis) the basal ganglia tonic influence on alfa-motoneurons of flexor muscles

• Through the reticular formation - influence on tone flexor and extensor muscles

Functions

• Together with s.nigra – inhibition of the spinal motor reflexes (alfa- and gama-motoneurons

• Disturbance a connection between s.nigra and basal ganglia (lack of DOFA) –Parkinson’s des.

• Together with cerebellum – memorization of motor program

Clinical syndromes resulting from damage to the basal ganglia

Caudate nucleus and putamen9Hyperkinesia9Hypotonus

Globus pallidus

9Hypokinesia9Hypertonus

Motor zone of neocortex

• Associative zones– plan of the future movement

• Precentral gyrus – program of the future movement

The primary somatic area is located in the postcentral gyrus.

Both (somatic and motor) areas have the detail topography (homunculus), a hand and a face take the most place on surface of these areas.

Different parts of body are representedin different groups of neurons