NERVOUS SYSTEM

NERVOUS SYSTEM CONSISTS OF

1. CENTRAL NS (CNS):

BRAIN + SPINAL CORD

2. PERIPHERAL NS (PNS):

CRANIAL NERVES (12 prs)

SPINAL NERVES (31 prs)

A SERIES OF NERVOUS ORGANS WITH A SINGLE FUNCTION: INFORMATION COMMUNICATION (in electrochemical language:

fast travelling nerve impulses + releasing neurotransmitter)

COMPLICATED (ASTRONOMICAL) INTERCONNECTIONS

& INTERACTIONS

of neurons

(In the brain: - Neurons: 1011

- Synapses: 1015

1 Neuron 10,000 neurons

Convergence

Divergence

NERVOUS SYSTEMCharacterized by:

Complicated strutures & functions

NS FUNCTIONS:

INFORMATION COMMUNICATION

1. MONITORS

SOMATOSENSORY SOMATORECEPTOR EXTERNAL

CNS SENSORY ENVIRONMENT

VISCEROSENSORY VISCERORECEPTORINTERNAL2. COORDINATES (interneuron in CNS) APPROPRIATE RESPONSES

(PROCESSES, INTEGRATES)SOMATOMOTORIC SOMATOEFFECTOR

3. INSTRUCTS *: CNS MOTORIC (Skeletal muscles)

VISCEROMOTORIC VISCEROEFFECTOR

(Organ muscles: smooth m.,

cardiac m., vasa, glandular cell)* (1).Conscious (2). Unconscious

(info.)

(info.)

STIMULI

(MESSAGES)

ENVIRONMENT(INTERNAL,EXTERNAL)

CNS(brain &

spin. cord)

INTEGRATION(analyzedcombinedcompared

coordinated)

Muscles

(skeletal, smooth, cardiac,

vasa)

Glands

(endocrine, exocrine)

HOMEOSTASIS

HOMEOSTASIS (Lat. homois: same, stasis: standing still)

A state of inner balance and stability in the body, which remain relatively constant, despite external environmental changes

Aff.

Eff.

GENERAL FUNCTIONS OF THE NS

CNS(brain &

spin. cord)

PNS

(cran. nn. & spin. nn)

Afferent(sensory)Division

Visceral NS

Efferent(motor) Division(Autonomic NS)

Somatic NSAff. Div.

Eff. Div.

Sympathetic NS

ParasympathticNS

Complementeach other

Responds to stress & emergency situations

Conserves & restores body resources

Aff. Div.

Processes sensory input from visceral organs

Eff. Div.

Triggers responses in involuntary musc., glands

Stimulates voluntary muscles

Processes sensory input

from somatic structures

Aff

Eff

FUNCTIONAL UNITS OF THE NS

SOMATIC

AUTONOMIC

NERVOUS SYSTEM

1. CENTRAL NS

(1). BRAIN

(2). SPIN. CORD

(MED. SPIN.)

2. PERIPHERAL NS

(1). 12 CRANIAL NN.

(from the brain)

(2) 31 SPINAL NN.

(from the spin. cord)

a. SOMATIC

b. AUTONOMIC

(a). Sympathetic

(b) . Parasympathetic

NEURON:

STRUCTURAL & FUNCTIONAL UNIT OF THE NS

NEURON: - specialized in TRANSMIT IMPULSES from short to relatively long distances (from one part of the body or CNS to another).

- two important properties:

(1). EXCITABILITY (the ability to respond to stimuli)

(2). CONDUCTIVITY (the ability to conduct a signal/impulse)

(Nervous tissue: neuron + neuroglia)

The brain receives million bits of info.from the sensory organs

and integrates them into various responses

NEURON

The most important building block of the brain: nerve cell (neuron).

Neuron transmits info. in the form of electrical language (impulses).

The neurons are separated by tiny gaps (synapse clefts).

When an impulse moves through a neuron, the cell releases chemicals (neurotransmitters) into the synapses.

The neurotransmitters induce or inhibit impuses in connecting neurons

NERVOUS SYSTEM (NS)

PERIPHERAL NS CENTRAL NS

AUTONOMIC NS SOMATIC NS BRAIN

(ENCEPHALON)

SPINAL CORD

(MYELUM/medul- la spinalis)SYMPATHETIC NS PARASYMPATHETIC NS

FOREBRAIN

(PROSENCEPHALON)

MIDBRAIN

(MESENCEPHALON)

HINDBRAIN

RHOMBENCEPHALON

TELENC. DIENC. MESENC. METENC. MYELENC.

Cerebrum (cerebral cortex, Basal gangl.

Hippocampus Amygdala Medullary body

Thalamus Hypothalamus Tectum

Tegmentum

Pons

CerebellumMedulla

oblongata

(Medulla)

Parts of the brain

(embryologically)1. Prosencephalon

(1). Telencephalon (HC)

(2). Diencephalon (Thalamus, Hypothalamus)

2. Mesencephalon

3. Rhombencephalon

(1). Metencephalon (Pons, cerebellum)

(2). Myelencephalon

(Medulla oblongata)

NEURON : Fundamental unit (structural/functional) of NS100 billions of cells (stars in the Milkway Galaxy) in the brain

INFO. COMMUNICATION: electrochemical in nature (propagation of action potentials along the membrane of a neuron and transmission of neurotransmitters through the synapses)

SYNAPSE (1015): point of contact between neurons

Milkway Galaxy

Synapse

Transmission of chemical substances (neurotransmitters/NTs) from axon terminal to the next neuron (Ach, NE, DA, 5-HT etc.)

Types of synapse:

A. 1. Axosomatic;

2. Axodendritic;

3. Axoaxonic;

4. Dendrodendritic

B. 1. Electric;

2. Chemical (NT)

Point of contact among neurons

HOW NEURONS COMMUNICATE TO EACH OTHER ?

SYNAPSE CONSISTS OF:

-Presynaptic element (part of axon terminal)

-Synaptic cleft/space

-Postsynaptic region (receptor at the postsynaptic membrane of the innervated neuron or effector structure)

An action potentialarrives and initiates

synaptic transmissionAfter synaptic transmis-sion,acetylcholine (Ach) and vesicles are received

Synaptic cleft

TYPES OF SYNAPSES

1. Simple axodendritic or axosomatic

2. Dendritic spine synapse

3. Dendritic crest synapse

4. Simple synapse + axoaxonic

5. Combined axoaxonic and axodendritic synapse

6. Varicosities (“boutons en passant”)

7. Dendrodendritic synapse

8. Reciprocal synapse

9. Serial synapse

CONVERGENCE & DIVERGENCE

Types and subtypes of synapses

I.Serial synapses

PRESYNAPTIC

INHIBITION

(-)

I. SENSORY/AFFRENT SYSTEM(CNS RECEPTOR)

* COLLECTING* PROCESSING

EXTERNAL(somatosensory)RECEPTORS

INTERNAL(viscerosensory) RECEPTORS

(Info)

Tension, blood pressure, pressure, chemical composition of the blood(hormones, glucose, CO2, ions/electrolytes)

(events/stimuli)

CONTACT (pain, temp., touch, pressure)

DISTANT (sound, light, odours)

(INFO.)

(CNS) RECEPTOR

III

II. MOTOR/EFFERENT SYSTEM( CNS EFFECTOR)

MOTOR/MOTOR/AFFERENTAFFERENTSYSTEMSYSTEM

SOMATOMOTORIC Effector: SKELETAL MUSCLES

(INFO.)

VISCEROMOTORIC EFFECTOR: viscera, vasa

smooth muscle,

cardiac muscle,

glandular cell

(exocrine, endocrine)

II I

Three functional classes of neurons:

1. Afferent/sensory neuron: from receptor

2. Interneuron/association neuron (in the CNS: brain & spinal cord)

3. Efferent/motor neuron: to effector

DIVISIONS OF THE NERVOUS SYSTEM

BRAIN (Encephalon) (within the cranial cavity) CENTRAL (CNS)

SPINAL CORD (Medulla spinalis) (within the vertebral canal)CRANIAL NERVES (N I - XII)(from the brain)PERIPHERAL (PNS) SPINAL NERVES (31 pairs)(from the spinal cord) (functional)

AUTONOMIC (ANS)* (unconscious) SOMATIC (conscious)(to skeletal muscles)

SYMPATHETIC PARASYMPATHETIC(to smooth muscle, cardiac muscle and glands)(* ANS has its cranial component in the brain)

NERVOUSSYSTEM

(anatomical)

12 pairs of cranial nerves (NI – NXII)

31 pairs of spinal nerves

AUTONOMIC NS

SYMPATHETIC NS (blue)

(Centers: thoracolumbal:

T2-L3)

PARASYMPATHETIC

NS (red)

(Centers: craniosacral:

Pons, med.obl.,S2,3,4)

NEURON(NERVE CELL)

• STRUCTURAL AND FUNCTIONAL UNIT OF NS*

SOMA (celL body)(collective: gray matter/ sustantia grisea)

• COMPONENTDENDRITES

PROCESSESAXON (collective: white matter/ substantia alba)

TERMINAL SYNAPSE (contact with other neuron/

effector cells)

Fig. 1-2

*NEURON:

Specialized to receive info. Transmit electrical impulses

(action potentials) synapse: release of NT(into synaptic cleft) Influence other effector tissues (neuron, muscle (skeletal, smooth, cardiac), glands

NEURON

1. Soma cell (cell body)

(1). Membrane

(2). Cytoplasm

(3). Nucleus + nucleolus

2. Processes

(1). Dendrites

(2). Axon (one) Branches

Axon terminal (terminal boutton): contains vesicles with neurotransmitter (NT) granules

SYNAPSE: point of contact between neuronsNT: dopamin (DA), serotonin (5-HT),

epinphrine (E), norepinephrine (NE), GABA etc.

Axon

Collateral

Axon terminal

Cell body/soma NEURON

Dendrite

Direction of info. (orthodromic)

Nissl’s bodies:

rERs (rough endoplasmic reticulum)

(Nissl’s stain: green)

SYNAPSES (interneuronal contacts)

1. Axosomatic 2. Axodendritic

3. Axoaxonic 4. Dendrodendritic

Axon terminal

Postsynaptic neuron

Presynaptic neuron

NeurotransmitterSynaptic cleft

Electrochemical transmission

TYPES OF NEURONS

1. UNIPOLAR/

PSEUDOUNIPOLAR (D)

2. BIPOLAR (E, F)

3. MULTIPOLAR (A, B, C)

COMMUNICATION ACROSS THE SYNAPSE

ELECTRICAL IMPULSE (ACTION POTENTIAL) (in the membrane of presynaptic neuron)

RELEASE OF NEUROACTIVE SUBSTANCE (neurotransmitter /NT), neurmodulator, neuromediator) from the presynaptic element)

(NT is stored in synaptic vesicles in the terminal, and then is released into the synaptic cleft)

SYNAPTIC CLEFT (SPACE) (NT diffuse rapidly across the synaptic cleft)

BIND TO RECEPTOR SITES on the postsynaptic membrane

NEURON POSTSYNAPTIC MAY BE EXCITED/INHIBITED

(lead to the generation of action potential)

NEUROGLIA

NEUROGLIA (GLIAL CELL)

1.Oligodendrocyte

2. Astrocyte

3. Microglia

4. Ependymal cell

1

2

3

4

NEUROGLIA

4

2

neuron

3

1

GLIA (NEUROGLIA/GLIAL CELL)FUNCTIONS: • STRUCTURE SUPPORT• MAINTAIN APPROPRIATE MICROENVIRONMENT FOR NEURONAL FUNCTIONS• PHAGOCYTOSIS

CNS PNS

ASTROCYTE OLIGODENDROCYTE MICROGLIA EPENDYMAProtoplasmic Fibrous (Gray & white (Lining of cerebral(Gray matter) (White matter) matter) ventricles)

SCHWANN CELLSSATELLITE CELLS

TYPES OF GLIACentral glia Peripheral glia

GLIA

1. ASTROCYTES: - Framework for neuronal migration

(during development)- Frame certain cluster of neurons- Secrete growth factor- Secrete cytokines- Fill the space by breakdown of debris (astrocyte proliferate and/or hypertrophy)- Environment control (ionic/pH)- Metabolism (participate in neurotransmitter

metabolism)

FUNCTIONS: - Structural support

- Functional support

(maintains microenvironment of neuron)

2. OLIGODENDROCYTES

(occur in gray and whitematters)

Function: myelinisation

(the provision of electrochemically insulating sheath around some axons in the white matter: myelin

sheath

Myelin sheath:

-Increase speed of conduction of action potential (AP) along the axon saltatory conduction

- Not continuous NODE OF RANVIER

(between two segments/internodal segments/internodes)

3. MICROGLIA (1% of the CNS cell population)

Developed from blood cells (monocytic-macrophage)

Migrate to CNS

• Phagocytic scavengers (when activated)– Activates microglia– CNS suffers injury– Migrate to the site of damage– Proliferate – Phagocytose cell debris

• Produce cytokines (interleukins)• Antigen-presenting cells Participate in

autoimmune disease processes

• NEURONS --------- RECEIVE/PROCESS/SEND INFORMATION

• GLIA --------- * CONTROL ENVIRONMENT WITHIN THE CNS (MICRO- ENVIRONMENT)

• Shuttle nutritive molecules(blood neuron)

• Remove waste products of neurons• Maintain electrochemicals surroundings of neurons• Guiding developing neurons (migration)• Phagocytosis• Structural support for neurons

NERVOUS SYSTEM

STRUCTUREOF NEURON

CELL BODY (soma/perikaryon)DENDRITES Info

PROCESSESAXON TERMINALS (Info)

TERMINAL ARBORS

TERMINAL BOUTONS

SYNAPSES

EFFECTOR / TARGET CELLS

CELL BODY (soma cell)Contains: • Mitochondria (Power Plant)• Ribosomes• rER : stacks Nissl bodies• Golgi complex (Packing cell products)

UNIPOLAR/PSEUDOUNIPOLAR(sensory ganglia)

Peripheral/dendrite Branch ----

TYPES OF NEURON BIPOLAR Central/axon(see Tab. 2-1) (olfactory, auditory, vestibular)

MULTIPOLAR(many area of CNS)

Neuronal pole

Principal parts of the brain /encephalon (medial aspect):

1. Cerebrum (Cerebral hemispheres + Diencephalon); 2. Brain stem (truncus cerebri): Mesenc.+ Pons + Med. Obl.); 3. Cerebellum

Cranial nerves(N I – N XII)

Originated in the brain stem,except N I & N II

CENTRALNERVOUSSYSTEM(CNS)*

Spinal cord

Afferentdivision

Efferentdivision

Brain

PERIPHERALNERVOUS

SYSTEM (PNS)

Sensorystimuli

Visceralstimuli

Somaticnervoussystem

Autonomicnervoussystem

Sympatheticnervoussystem

Parasympatheticnervous system

Motorneurons

Skeletal muscle Smooth muscle Cardiac muscle

GlandsEFFECTOR ORGANS

(input to CNS from periphery) (output from CNS to periphery)

* FUNCTIONAL DIVISIONS OF THE NS

31 pairs of spinal nerves

12 pairs of cranial nerves

SPINAL CORD (MEDULLA SPINALIS)

• INSIDE THE VERTEBRAL COLUMN (in the vertebral canal)

• 31 SEGMENTS

31 PAIRS OF SPINAL NERVES CERVICAL (C) : 8THORACAL (T) : 12LUMBAR (L) : 5SACRAL (S) : 5COCCYGEAL (Co) : 1

• CONTAINS: - SENSORY FIBERS- MOTOR NEURONS- ASCENDING/DESCENDING FIBERS (PATHWAYS/TRACTS TO AND FROM THE BRAIN)

• REFLEX CENTER

Cervical (8)

Thoracic (12)

Lumbar (5)

Sacral (5)

Coccygeal (1)

SPINAL NERVE

(Spinal ganglion)

Spinal cord in cross sectionWhite matter (substantia alba) collection of nerve fibersGrey matter (substantia grissea) collection of soma cells

CLASSIFICATION& GROUPS OF NEURONS

GROUP OF CELL BODIES• NUCLEUS A cluster of functionally related nerve cell bodies

(pl. nuclei)• COLUMN (in cerebral cortex, spinal cord)• LAYER/STRATUM/LAMINA (in spinal cord)

BUNDLE OF AXONS• TRACT A bundle of axons of a specific

FASCICULUS populations of functionally related fibers(pl. fasciculi)

• LEMNISCUS FUNICULUS (pl. funiculi)/(pl. lemnisci) SYSTEM

CNSCNS

CELL BODIESGANGLION A collection of cell bodies(pl. ganglia)

SENSORY (dorsal root ganglion, cranial nerve ganglion)

MOTORIC (visceromotoric gangl., autonomic gangl.)

AXONSNERVES A bundle of axonsRAMUS(pl. rami)ROOT/RADIX

PNSPNS