week 1 - 1. principles of nervous system
TRANSCRIPT
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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)
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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
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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.)
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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
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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
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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
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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
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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
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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)
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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)
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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
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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
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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)
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An action potentialarrives and initiates
synaptic transmissionAfter synaptic transmis-sion,acetylcholine (Ach) and vesicles are received
Synaptic cleft
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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
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Types and subtypes of synapses
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I.Serial synapses
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PRESYNAPTIC
INHIBITION
(-)
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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
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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
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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
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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)
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12 pairs of cranial nerves (NI – NXII)
31 pairs of spinal nerves
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AUTONOMIC NS
SYMPATHETIC NS (blue)
(Centers: thoracolumbal:
T2-L3)
PARASYMPATHETIC
NS (red)
(Centers: craniosacral:
Pons, med.obl.,S2,3,4)
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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
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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.
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Axon
Collateral
Axon terminal
Cell body/soma NEURON
Dendrite
Direction of info. (orthodromic)
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Nissl’s bodies:
rERs (rough endoplasmic reticulum)
(Nissl’s stain: green)
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SYNAPSES (interneuronal contacts)
1. Axosomatic 2. Axodendritic
3. Axoaxonic 4. Dendrodendritic
Axon terminal
Postsynaptic neuron
Presynaptic neuron
NeurotransmitterSynaptic cleft
Electrochemical transmission
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TYPES OF NEURONS
1. UNIPOLAR/
PSEUDOUNIPOLAR (D)
2. BIPOLAR (E, F)
3. MULTIPOLAR (A, B, C)
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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)
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NEUROGLIA
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NEUROGLIA (GLIAL CELL)
1.Oligodendrocyte
2. Astrocyte
3. Microglia
4. Ependymal cell
1
2
3
4
NEUROGLIA
4
2
neuron
3
1
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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
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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)
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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)
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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
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• 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
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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
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Principal parts of the brain /encephalon (medial aspect):
1. Cerebrum (Cerebral hemispheres + Diencephalon); 2. Brain stem (truncus cerebri): Mesenc.+ Pons + Med. Obl.); 3. Cerebellum
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Cranial nerves(N I – N XII)
Originated in the brain stem,except N I & N II
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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
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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
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Cervical (8)
Thoracic (12)
Lumbar (5)
Sacral (5)
Coccygeal (1)
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SPINAL NERVE
(Spinal ganglion)
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Spinal cord in cross sectionWhite matter (substantia alba) collection of nerve fibersGrey matter (substantia grissea) collection of soma cells
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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
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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