nervous system. histology of the nervous system types of cells in the nervous tissue. –neurons...
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Nervous System
Histology of the Nervous System
• Types of cells in the nervous tissue.– Neurons– Glial cells or neuroglias support cells.
• CNS: astrocyte (control chemical enviroment), oligodendrocyte (myelination), microglia (phagocyte), ependimal cells (production of CSF)
• PNS: Shwann cells (myelination) and satellite cells.
Neuroglia
(a) Astrocyte
(d) Oligodendrocyte
(e) Sensory neuron with Schwann cells and satellite cells
(b) Microglial cell
(c) Ependymal cells
Schwann cells(forming myelin sheath)
Cell bodyof neuron
Satellite cells
Nerve fiber
Capillary
Neuron
Nerve fibers
Myelin sheath
Process ofoligodendrocyte
Fluid-filled cavity
Brain or spinal cord tissue
Neuron Anatomy
• Major parts:– Cell body (grey matter) or Soma
• Central Nervous System (CNS): clusters = nuclei; in Peripheral Nervous system (PNS) = ganglia
– Neuron processes (axons): • CNS: tracts• PNS: nerves
– Neurofibrils: cytoskeleton– Nissle bodies: RER that is chomatophilic– Dendrites: processes that carry impulses towards the cell body.– Axons: processes that carry impulses away from the cell body.– Axon Hillock– Axon terminals– Synaptic cleft– Myelin fibers (not all the axons)
Structures of a motor neuron
(b)
(a)
Dendrites(receptiveregions)
Cell body(biosynthetic centerand receptive region)
Nucleolus
Nucleus
Terminal branches(telodendria)
Nissl bodies
Axon(impulse generatingand conductingregion)
Axon terminals(secretorycomponent)
Axon hillock
Neurilemma(sheath ofSchwann)
Node of Ranvier
Impulsedirection
Schwann cell(one inter-node)
Neuron cell body
Dendriticspine
Structure of a synapse
Synaptic vesiclescontaining neurotransmitter molecules
Axon of presynapticneuron
Synapticcleft
Ion channel(closed)
Ion channel (open)
Axon terminal of presynaptic neuron
PostsynapticmembraneMitochondrion
Ion channel closed
Ion channel open
Neurotransmitter
Receptor
Postsynapticmembrane
Degradedneurotransmitter
Na+
Na+
Ca2+
Action Potential
1
2
34
5
Myelinated fibers
– Made by:• Oligodendrocytes in CNS• Schwann cells in PNS
– Structures:• Myelin sheath• Neurilemma: sheath of Schwann cells.• Nodes of Ranvier
Myelination of axons in the PNS by Schwann cells
(a)
(b)
(c)
(d)
Schwann cellcytoplasm
Axon
NeurilemmaMyelinsheath
Schwann cellnucleus
Schwanncell plasmamembrane
Myelin sheath
Schwann cellcytoplasm
Neurilemma
Axon
Activity 1
• Identify the parts of a neuron in a slide.
• Identify the parts of a neuron in a model
Neuron Classification
• By structure– Unipolar neurons: 1 process
• Sensory neurons, impulse CNS
– Bipolar neurons: 2 processes• Part of receptor system: eye, ear, olfactory
– Multipolar neurons: several processes.• Impulse CNS
– Activity 2: identify different neurons in the slide.
Neuron classification by their structure
Neuron Classification
• Classification by function– Sensory– Afferent– Association
Classification of neurons by function
Afferentfiber
Efferentfibers
Extensorinhibited
Flexorstimulated
Right arm(site of stimulus)
Left arm (site ofreciprocal activation)
Arm movements
Interneurons
Key:+ Excitatory synapse– Inhibitory synapse
Efferentfibers
Flexorinhibited
Extensorstimulated
+
–+
–
+
+
Flexes
Extends
Structure of a nerve
(a)
(b)
Fascicle
Perineurium Blood vessels
Endoneurium Nerve fibers
Axon
Endoneurium
Perineurium
Epineurium
Myelin sheath
Bloodvessels
Fascicle
Neurophysiology
• How action potentials trigger nervous impulses.– Resting potential– Action potential
• Depolarization of the membrane.
– Refractory period– Repolarization of the membrane– Stimuli transmission
Measuring membrane potential in neurons
Voltmeter
Microelectrodeinside cell
Plasmamembrane
Ground electrodeoutside cell
Neuron
Axon
The basis of the resting membrane potential
Na+ Na+
K+
K+
K+
K+
Na+
Na+
Na+
Na+
Cell interiorNa+
15 mMK+
150 mMCl–
10 mM A–
100 mMNa+
150 mMA–
0.2 mM
Cell exterior
K+
5 mM Cl–
120 mM
Cellexterior
Cellinterior
Plasmamembrane
Na+–K+
pumpDif
fusi
on
K+ N
a+ D
iffus
ion
-70 mV
Changes in membrane potential produced by a depolarizing graded potential
Distance (a few mm)
–70Resting potential
Active area(site of initialdepolarization)
Mem
bra
ne
po
ten
tial
(m
V)
Refractory periods in an AP
Stimulus
Mem
bra
ne
po
ten
tial
(m
V)
Time (ms)
–70
0
+30
0 1 2 3 4 5
Absolute refractoryperiod
Relative refractoryperiod
Depolarization(Na+ enters)
Repolarization(K+ leaves)
After-hyperpolarization
Propagation of an action potential (AP)
–70
+30
(a) Time = 0 ms (b) Time = 2 ms (c) Time = 4 ms
Voltageat 2 ms
Voltageat 4 ms
Voltageat 0 ms
Resting potential
Peak of action potential
Hyperpolarization
Me
mb
ran
e p
ote
nti
al
(mV
))
Relationship between stimulus strength and action potential frequency
Time (ms)
Vo
ltag
eM
emb
ran
e p
ote
nti
al (
mV
)
–70
0
+30
Threshold
Actionpotentials
Stimulusamplitude
Saltatory conduction in a myelinated axon
Node of Ranvier
Cell bodyMyelinsheath
Distalaxon
Central nervous system
The nervous system’s functions
Sensory input
Motor output
Integration
Levels of organization in the nervous systemCentral nervous system (CNS) Brain and spinal cord Integrative and control centers
Sensory (afferent) division Somatic and visceral sensory nerve fibers Conducts impulses from receptors to the CNS
Motor (efferent) division Motor nerve fibers Conducts impulses from the CNS to effectors (muscles and glands)
Autonomic nervous system (ANS) Visceral motor (involuntary) Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands
Sympathetic division Mobilizes body systems during activity
Parasympathetic division Conserves energy Promotes housekeeping functions during rest
Peripheral nervous system (PNS) Cranial nerves and spinal nerves Communication lines between the CNS and the rest of the body
Somatic nervous System Somatic motor (voluntary) Conducts impulses from the CNS to skeletal muscles
= Structure= Function
Key:
Centralnervoussystem(CNS)
= Sensory (afferent)division of PNS= Motor (efferent)division of PNS
Key: Brain
SpinalcordSkin
Visceral organ
Skeletalmuscle
Peripheral nervous system(PNS)
Motor fiber ofsomatic nervoussystem
Somatic sensoryfiber
Sympatheticmotor fiber of ANS
Parasympatheticmotor fiber of ANS
Visceralsensory fiber
(a)
(b)
Gross Anatomy of the Brain and Cranial Nerves
1. Human Brain (activity 1,2)A. Cerebral Hemispheres of the cerebrumB. DiencephalonC. Brain StemD. Cerebellum
2. MeningesA. Cerebrospinal Fluid– Choroid processes (ependymal cells + capillaries)
3. Cranial Nerves (activity 3)4. Spinal cord5. Brain dissection
A. Cerebrum:Cerebral Hemispheres
• Mainly grey matter (soma of neurons)• 5 lobes
– Frontal: anterior to the Central sulcus– Parietal: posterior to the central sulcus, superior to the
lateral sulcus, superior to the parietal-occipital sulcus– Temporal: inferior to the lateral sulcus, – Occipital: inferior to the parietal-occipital sulcus– Insula (within the lateral sulcus, covered by the
temporal and parietal lobes)
Arrangement of gray and white matter in the CNS
CerebrumCerebellum
Migratorypattern ofneurons
Cortex ofgray matter
Inner graymatter
Gray matter
Outer whitematter
Centralcavity
Central cavity
Inner graymatter
Gray matter
Outer whitematter
Central cavity
Inner graymatter
Outer whitematter
Region of cerebellum
Brain stem
Spinal cord
Lobes and fissures of the cerebral hemispheres
(a)
(b)
Postcentral gyrus
Central sulcus
Precentral gyrus
Frontal lobe Parietal lobe
Parieto-occipital sulcus (on medial surfaceof hemisphere)
Lateral sulcus
Transversecerebral fissure
Occipital lobe
Temporal lobe
Cerebellum
Medulla oblongata
Spinal cord
Cortex(gray matter)
Fissure(a deep sulcus)
Gyrus
Sulcus
White matter
Central sulcusFrontal lobe
Temporal lobe(pulled down)
Gyri of insula
Pons
Lobes and fissures of the cerebral hemispheres
(c)
Parietal lobe
Frontal lobe
RightCerebralhemisphere Occipitallobe
Left cerebralhemisphere
Cerebral veinsand arteriescovered byarachnoid
Longitudinalfissure
Posterior
Anterior
Functional and structural areas of the cerebral cortex
• Primary somatosensory cortex: post central gyrus
• Somatosensory association area: immediate after PSC
• Primary motor area– Broca’s area: speech– Prefontral area: intellect, personality
Functional and structural areas of the cerebral cortex
(a)
Primary motor area
Premotor cortex
Frontaleye field
Working memoryfor spatial tasks
Executive area fortask management
Working memory for object-recall tasks
Broca's area(outlined by dashes)
Solving complex,multitask problems
Prefrontal cortex
Central sulcus
Primary somatosensorycortex
Somatosensoryassociation area
Somatic sensation
Gustatory cortex(in insula)
Taste
Wernicke's area(outlined by dashes)
Primary visualcortex
Visualassociation area
Vision
Auditoryassociation area
Primary auditory cortex
Hearing
1147
4544
8
6 43 1 2
5
43
7
19 1817
224241
22
(b)
Frontal eye field
Prefrontalcortex
Processes emotionsrelated to personaland social interactions
Olfactory bulb
Orbitofrontalcortex
Olfactory tract
Fornix
Temporal lobe
Corpuscallosum
Premotorcortex Primary
motor areaCingulategyrus
Central sulcus
Primary somatosensorycortex
Parietal lobe
Parieto-occipitalsulcus
Somatosensoryassociation area
Occipitallobe
Visual associationarea
Calcarine sulcus
Parahippocampalgyrus
Uncus
Primary olfactorycortex
Primaryvisual cortex
Functional and structural areas of the cerebral cortex
8
1-36
8
6 4
45
7
19
18
181734
28
Thumb
Motor and sensory areas of the cerebral cortex (homuculus)
GenitalsToes
Swallowing
Tongue
Jaw
Motor cortex(precentral gyrus)
Motor Sensory
Le
gLips
Face
NeckBrowEye
FingersH
andW
ristE
lbo
w
Arm
Sh
ou
lder
Tru
nk
Hip
Kn
ee
Hip
Tru
nk
Ne
ck
Hea
d
Arm
Elb
owFo
rear
mH
and
Fing
ers
Thum
b
Eye
Nose
Face
Lips
Teeth
Gums
Jaw
Tongue
Pharynx
Intra-abdominal
B. Basal ganglia (nuclei)
• Islands of grey matter within the white matter.• Flank lateral and third ventricle.• Function: Subcortical motor nuclei
(extrapyramidal system), regulates voluntary motor control.
• Caudate nucleus (memory, love?), lentiform nucleus, putamen (learning reinforcement), globus pallidus.
• Corona radiata: projection of fibers.
Basal nuclei
(a)
Fibers ofcorona radiata
Corpusstriatum
Internal capsule(projection fibersrun deep to lentiform nucleus)
Caudatenucleus
Lentiformnucleus
Thalamus
Tail of caudatenucleus
Basal nuclei
(b)
Corpus callosumAnterior hornof lateral ventricleCaudate nucleus
Third ventriclePutamen Lentiform
nucleusGlobus pallidus
Thalamus
Cerebral cortex
Cerebral white matter
Anterior
Posterior
Inferior hornof lateral ventricle
C. Diencephalon
• Embryologically, part of the forebrain• Major structures:
– Thalamus– Hypothalamus/Pituitary gland– Epithalamus
• Trigunium habenulae• Pineal body• Posterior commussire
– Pretectum (pupilary light relfex)
• Externally– Olfactory, optic tracts, optic nerves, optic chiasma, pituitary
gland, mammilary bodies (part of the limbic system; emotions, long term memory, etc).
Midsagittal section of the brain illustrating the diencephalon and brain stem,
Parietal lobe ofcerebral hemisphere
Corpus callosum
Choroid plexusOccipital lobe ofcerebral hemisphereThalamus(encloses third ventricle)
Pineal body/gland(part of epithalamus)
Posterior commissure
Corporaquadrigemina
Cerebralaqueduct
Arbor vitae
Fourth ventricle
Choroid plexus
Cerebellum
Septum pellucidum
Interthalamicadhesion(intermediatemass of thalamus)
Frontal lobeof cerebralhemisphere
Interventricularforamen
Anteriorcommissure
Hypothalamus
Optic chiasma
Pituitary gland
Temporal lobe ofcerebral hemisphere
Mammillary body
Pons
Medulla oblongata
Spinal cord
Midbrain
Fornix
D. Brain Stem
• Major structures:– Cerebral peduncles– Pons– Medulla oblongata– Decussation of pyramids
Ventral aspect of the human brain, showing the three regions of the brain stem
Frontal lobe
Olfactory bulb(synapse pointof cranial nerve I)
Optic chiasma
Optic nerve (II)
Optic tract
Mammillary body
Pons
Temporal lobe
Medulla
Cerebellum
Spinal cord
Midbrain
E. Cerebellum
• Features:– Center midline: vermis– Arbor vitae “tree of life”
• Function:– Balance and equilibrium
Anterior view
Posterior view
2. Meninges
• Three connective tissue membranes that protect the brain and the medulla from mechanical stress.
• Inflammation of this tissue membrane is called meningitis. If infected, it produces encephalitis.
Meninges
(a)
Superiorsagittal sinus
Skin of scalp
Periosteum
Falx cerebri(in longitudinalfissure only)
Bloodvessel
Arachnoid villus
Pia materArachnoid mater
Duramater
MeningealPeriosteal
Subduralspace
Subarachnoidspace
Bone of skull
Meninges
(b)
Occipital lobe
Superiorsagittal sinus
Dura mater
Tranversesinus
Temporalbone
Scalp
Skull
Tentoriumcerebelli
Cerebellum
Arachnoid materover medullaoblongata
Falx cerebri
Tentorium cerebelli
Superiorsagittal sinus
Straightsinus
Crista galli of theethmoid bone
Cavernoussinus
Internal carotidartery
Falx cerebelli
Partitioning folds of dura mater in the cranial cavity
A. Cerebrospinal fluid
• Fluid, similar in composition to blood plasma, is circulated through the ventricles (cisternas).
• Function: mechanical stress protection of the brain and medulla, acting as a cushion.
• Produced in the choroid plexuses.– Capillary knots in the surface of the ventricles.
Formation, location, and circulation of CSFSuperiorsagittal sinus
Arachnoidvillus
Subarachnoid spaceArachnoid materMeningeal dura materPeriosteal dura materGreat cerebral vein
Tentorium cerebelliStraight sinusConfluence of sinuses
Cerebellum
Choroid plexusCerebral vesselsthat supplychoroid plexus
Central canalof spinal cordSpinal dura mater
Inferior end ofspinal cord
Filum terminale(inferior endof pia mater)
Superiorcerebral vein
Choroid plexusCerebrum coveredwith pia mater
Septumpellucidum
Corpuscallosum
Interventricularforamen
Third ventriclePituitary gland
Cerebral aqueduct
Lateral aperture
Fourth ventricleMedian aperture
(b)
4. Spinal cord
• Location: from C1-C2 (continuation of the brain stem) to the conus medullaris (L1-L2).
• Characteristics: – Protected by the meninges (S1-S2 to the filum
terminale).– Attaches to the vertebras by the denticulate ligaments
of the pia mater and the filum termiale (coccygeal canal)
• Function: association and communication center. Central point of the reflex arc.
Spinal cord external anatomyCervicalnervesC1– C8
ThoracicnervesT1– T12
LumbarnervesL1– L5
SacralnervesS1– S5
Coccygealnerve
C0
Cervical plexus
Intercostalnerves
Cervicalenlargement
Lumbarenlargement
Cauda equina
Brachial plexus
Lumbar plexus
Sacral plexus
Conus medullaris
Filum terminale
Structure of the Spinal Cord
(a)
Dorsal rootganglion
Gray matter
White matterVentral root
Dorsal root
Dorsal and ventralrootlets of spinal nerveDorsal ramus
of spinal nerve
Ventral ramusof spinal nerve
Sympathetic trunk(chain) ganglion
Spinal nerve
Rami communicantes
Histology of the Spinal cord
• Grey matter: H form– Ventral (anterior) horns
• Ventral root (motor)
– Dorsal (posterior) horns• Dorsal roots (sensory)• Dorsal ganglions
– Lateral horn (thoraxic and lumbar region)
• White matter
Organization of the gray matter of the spinal cord
Somatic sensory neuron
Dorsal root(sensory)
Dorsal rootganglion
Visceral sensoryneuron
Somatic motor neuron
Spinal nerve Ventral root (motor) Ventral horn(motor neurons)
Dorsal horn (interneurons)
Visceral motorneuron
SSVS
VM
SM
Funiculus: fiber tracts with the same origin, terminus and function
Transversal section of the Spinal Cord
Transversal sections of the spinal cord
3. Cranial Nerves
• Part of the PNS
• Mnemonic: On ocassion, our trusty truck acts funny-very good vehicle anyhow.
Location and function of cranial nerves
(a)
Frontal lobe
Temporal lobe
Infundibulum
Facialnerve (VII)Vestibulo-cochlearnerve (VIII)
Glosso-pharyngeal nerve (IX)Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Filaments ofolfactory nerve (I)Olfactory bulb
Olfactory tract
Optic nerve (II)
Optic chiasma
Optic tract
Oculomotornerve (III)Trochlearnerve (IV)Trigeminalnerve (V)
Abducensnerve (VI)
Cerebellum
Medulla
Sheep brain dissection
• Identify the following structures– Ventral:
• Olfactory bulb• Optic nerve• Mammilary body• Cerebral peduncle• Cranial nerves• Medulla oblongata
– Dorsal• Cererbum• Cerebellum
Sheep brain dissection– Sagital section
• Cerebral hemisphere• Corpus callosum• Frontal lobe of the cerebellum• Intermedate mass of the cerebellum• Cerebral peduncle• Optical quiasma• Parietal lobe• Cerebellum• Pineal body• Arbor Vitae• Corpora quadrigema• Fourth ventricle• Medulla oblongata• Pons
Sheep brain dissection
– Frontal section of the brain• Fornix• Corpus triatum• Amygdaloid nucleus• Third ventricle• Lateral ventricle• Intermediate mass of the thalamus• Thalamic nuclei• hypothalamus
Relationship of the brain stem and the diencephalon
(a)
Optic chiasma
Floor of hypothalamus
Mammillary body
Trochlear nerve (IV)
Pons
Middle cerebellar peduncle
Hypoglossal nerve (XII)
Pyramid
Decussation ofpyramids
Spinalcord
Optic nerve
Thalamus
Optic tract
Infundibulum(pituitary removed)
Oculomotor nerve (III)Crus cerebri of cerebral peduncles (midbrain)
Trigeminal nerve (V)
Abducens nerve (VI)
Facial nerve (VII)
Vestibulocochlear nerve (VIII)
Glossopharyngeal nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Ventral rootof first cervicalnerveVentral view
Relationship of the brain stem and the diencephalon
(b)
Thalamus
Optic tract
Crus cerebri of cerebral peduncles (midbrain)
Trigeminal nerve (V)
Abducens nerve (VI)
Facial nerve (VII)
Vestibulocochlear nerve (VIII)
Glossopharyngeal nerve (IX)
Vagus nerve (X)
Infundibulum
Pituitary gland
Pons
Olive
Hypoglossalnerve (XII)
Accessory nerve (XI)
Superior colliculus
Inferior colliculus
Trochlear nerve (IV)
Superior cerebellar peduncle
Middle cerebellarpeduncle
Inferior cerebellarpeduncle
Fasciculus gracilis
Fasciculus cuneatus
Left lateral view
Relationship of the brain stem and the diencephalon
(c)
Posterior median sulcus
Choroid plexus(fourth venticle)
Pineal gland
Lateral geniculatenucleusMedial geniculatenucleus
Anterior wall offourth ventricle
Fasciculus cuneatus
Fasciculus gracilis
Third ventricle
Thalamus
Superiorcolliculus
Midbrain
Inferiorcolliculus
Trochlear (IV) nerve
Superior cerebellar peduncle
Middle cerebellar peduncle Pons
Inferior cerebellar peduncle
Facial (VII) nerve
Vestibulocochlear (VIII) nerve
Glossopharyngeal (IX) nerve
Vagus (X) nerve
Accessory (XI) nerve
Posterior (dorsal) rootof first cervical nerve
Medulla
Corporaquadrigeminaof tectum
Dorsal view