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
Capillary
Neuron
(b) Microglial cell
(a) Astrocyte
Nerve fibers
Myelin sheath
Fluid-filled cavity
Process of
oligodendrocyte
(c) Ependymal cells
Schwann cells
(forming myelin sheath)
Brain or spinal cord tissue
Cell body
of neuron
Satellite cells
(d) Oligodendrocyte
Nerve fiber
(e) Sensory neuron with Schwann cells and satellite cells
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
Dendrites
(receptive
regions)
Cell body
(biosynthetic center
and receptive region)
Neuron cell body
Nucleus
Dendritic
spine
(a)
Axon
(impulse generating
and conducting
region)
Nucleolus
Nissl bodies
Axon hillock
(b)
Neurilemma
(sheath of
Schwann)
Impulse
direction
Node of Ranvier
Schwann cell
(one internode)
Terminal branches
(telodendria)
Axon terminals
(secretory
component)
Structure of a synapse
Ca2+
1
Neurotransmitter
Axon terminal of
presynaptic neuron
Postsynaptic
membrane
Mitochondrion
Axon of
presynaptic
neuron
Na+
Receptor
Postsynaptic
membrane
Ion channel open
Synaptic vesicles
containing
neurotransmitter
molecules
5
Degraded
neurotransmitter
2
Synaptic
cleft
Ion channel
(closed)
3
4
Ion channel closed
Ion channel (open)
Na+
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
Schwann cell
cytoplasm
Axon
Schwann
cell plasma
membrane
Schwann cell
nucleus
Myelin sheath
(a)
Schwann cell
cytoplasm
Neurilemma
(b)
(d)
Neurilemma
Myelin
sheath
(c)
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
Interneurons
+
+
–
Afferent
fiber
+
+
–
Efferent
fibers
Efferent
fibers
Extensor
inhibited
Arm movements
Flexor
stimulated
Key:
+ Excitatory synapse
– Inhibitory synapse
Right arm
(site of stimulus)
Left arm (site of
reciprocal activation)
Flexor
inhibited
Extensor
stimulated
Structure of a nerve
Axon
Blood vessels
Perineurium
Myelin sheath
Endoneurium
Perineurium
Epineurium
Fascicle
Fascicle
Blood
vessels
(a)
Endoneurium
Nerve fibers
(b)
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
Plasma
membrane
Ground electrode
outside cell
Microelectrode
inside cell
Axon
Neuron
The basis of the resting membrane potential
Cell interior
Na+
15 mM
Cell
exterior
Na+
+
Na+ Na
K+
Na+–K+
pump
150 mM
Cl–
10 mM
Na+
Na+
A–
Na+
100 mM
150 mM
A–
0.2 mM
Cell exterior
K+
5 mM
K+
Cl–
120 mM
Cell
interior
Plasma
membrane
Na+
K+
K+
K+
Membrane potential (mV)
Changes in membrane potential produced by a depolarizing graded potential
Active area
(site of initial
depolarization)
–70
Resting potential
Distance (a few mm)
Refractory periods in an AP
Absolute refractory
period
Membrane potential (mV)
+30
Relative refractory
period
Depolarization
(Na+ enters)
0
Repolarization
(K+ leaves)
After-hyperpolarization
–70
Stimulus
0
1
2
Time (ms)
3
4
5
Membrane potential (mV))
Propagation of an action potential (AP)
Voltage
at 2 ms
+30
Voltage
at 0 ms
Voltage
at 4 ms
–70
(a) Time = 0 ms
Resting potential
Peak of action potential
Hyperpolarization
(b) Time = 2 ms
(c) Time = 4 ms
Voltage
Membrane potential (mV)
Relationship between stimulus strength and action potential frequency
Action
potentials
+30
–70
Threshold
Stimulus
amplitude
0
Time (ms)
Saltatory conduction in a myelinated axon
Node of Ranvier
Cell body
Myelin
sheath
Distal
axon
Central nervous system
The nervous system’s functions
Sensory input
Integration
Motor output
Levels of organization in the nervous system
Key:
Central nervous system (CNS)
Brain and spinal cord
Integrative and
control centers
Key:
Brain
= Sensory (afferent)
division of PNS
= Motor (efferent)
division of PNS
= Structure
= Function
Visceral
sensory fiber
Peripheral nervous system (PNS)
Cranial nerves and spinal
nerves
Communication lines
between the CNS and the
rest of the body
Parasympathetic
motor fiber of ANS
Visceral organ
Sympathetic
motor fiber of ANS
Skin
Sensory (afferent) division
Somatic and visceral
sensory nerve fibers
Conducts impulses from
receptors to the CNS
Sympathetic division
Mobilizes body systems
during activity
Parasympathetic division
Conserves energy
Promotes housekeeping
functions during rest
(a)
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
Somatic sensory
fiber
Motor fiber of
somatic nervous
system
Skeletal
muscle
Somatic nervous
System
Somatic motor
(voluntary)
Conducts impulses
from the CNS to
skeletal muscles
Peripheral nervous system
(PNS)
(b)
Central
nervous
system
(CNS)
Spinal
cord
Gross Anatomy of the Brain and
Cranial Nerves
1. Human Brain (activity 1,2)
A.
B.
C.
D.
Cerebral Hemispheres of the cerebrum
Diencephalon
Brain Stem
Cerebellum
2. Meninges
A. Cerebrospinal Fluid
– Choroid processes (ependymal cells + capillaries)
3. Cranial Nerves (activity 3)
4. Spinal cord
5. 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
Central
cavity
Migratory
pattern of
neurons
Cortex of
gray matter
Inner gray
matter
Outer white
matter
Gray matter
Cerebrum
Cerebellum
Region of cerebellum
Central
cavity
Inner gray
matter
Outer white
matter
Gray matter
Brain stem
Central
cavity
Spinal cord
Outer white
matter
Inner gray
matter
Lobes and fissures of the cerebral hemispheres
Central sulcus
Precentral gyrus
Postcentral gyrus
Parietal lobe
Frontal lobe
Parieto-occipital sulcus
(on medial surface
of hemisphere)
Lateral sulcus
Frontal lobe
Occipital lobe
Temporal lobe
Transverse
cerebral fissure
Cerebellum
Pons
Medulla oblongata
(a)
Spinal cord
Gyri of insula
Gyrus
Cortex
(gray matter)
Sulcus
White matter
Fissure
(a deep sulcus)
Temporal lobe
(pulled down)
(b)
Central sulcus
Lobes and fissures of the cerebral hemispheres
Anterior
Longitudinal
fissure
Frontal lobe
Cerebral veins
and arteries
covered by
arachnoid
Parietal lobe
Right
Cerebral
hemisphere
Occipital
lobe
Left cerebral
hemisphere
Posterior
(c)
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
Central sulcus
Primary
somatosensory
cortex
Somatosensory
association area
Primary motor area
3 1
Premotor cortex
4
6
Frontal
eye field
5
Gustatory cortex
(in insula)
45
43
44
22
41 42
Broca's area
(outlined by dashes)
Prefrontal cortex
(a)
Taste
Wernicke's area
(outlined by dashes)
Executive area for
task management
Solving complex,
multitask problems
Somatic
sensation
7
8
Working memory
for spatial tasks
Working memory for
object-recall tasks
2
19 18
11
47
22
17
Primary
visual
cortex
Visual
association
area
Auditory
association
area
Primary
auditory
cortex
Vision
Hearing
Functional and structural areas of the cerebral cortex
Premotor
cortex
Corpus
callosum
Cingulate
gyrus
Primary
motor area
4
6
Central sulcus
Primary somatosensory
cortex
8
6
4
Frontal eye field
8
1-3
5
Parietal lobe
Prefrontal
cortex
Somatosensory
association area
7
19
Parieto-occipital
sulcus
Occipital
lobe
Processes emotions
related to personal
and social interactions
18
18
17
34
Orbitofrontal
cortex
28
Olfactory bulb
Olfactory tract
(b)
Fornix
Temporal lobe
Uncus
Primary olfactory
cortex
Calcarine
sulcus
Visual
association
area
Primary
visual cortex
Parahippocampal
gyrus
Motor and sensory areas of the cerebral cortex (homuculus)
Sensory
Leg
Motor
Toes
Face
Genitals
Lips
Jaw
Tongue
Swallowing
Motor cortex
(precentral gyrus)
Intraabdominal
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
Fibers of
corona radiata
Corpus
striatum
Caudate
nucleus
Thalamus
Lentiform
nucleus
Tail of caudate
nucleus
Internal capsule
(projection fibers
run deep to
lentiform nucleus)
(a)
Basal nuclei
Anterior
Cerebral cortex
Cerebral white matter
Corpus callosum
Anterior horn
of lateral ventricle
Caudate nucleus
Third ventricle
Putamen
Lentiform
Globus pallidus nucleus
Thalamus
Inferior horn
of lateral ventricle
(b)
Posterior
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 of
cerebral hemisphere
Corpus callosum
Fornix
Septum pellucidum
Interthalamic
adhesion
(intermediate
mass of thalamus)
Choroid plexus
Occipital lobe of
cerebral hemisphere
Thalamus
(encloses third ventricle)
Posterior commissure
Pineal body/gland
(part of epithalamus)
Corpora
quadrigemina
Midbrain
Cerebral
aqueduct
Frontal lobe
of cerebral
hemisphere
Interventricular
foramen
Anterior
commissure
Hypothalamus
Optic chiasma
Pituitary gland
Temporal lobe of
cerebral hemisphere
Arbor vitae
Fourth ventricle
Mammillary body
Pons
Medulla oblongata
Spinal cord
Choroid plexus
Cerebellum
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 point
of 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
Skin of scalp
Periosteum
Bone of skull
Periosteal
Meningeal
Superior
sagittal sinus
Subdural
space
Subarachnoid
space
(a)
Dura
mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood
vessel
Falx cerebri
(in longitudinal
fissure only)
Meninges
Skull
Scalp
Superior
sagittal sinus
Occipital lobe
Tentorium
cerebelli
Cerebellum
Arachnoid mater
over medulla
oblongata
(b)
Dura mater
Tranverse
sinus
Temporal
bone
Partitioning folds of dura mater in the cranial cavity
Falx cerebri
Superior
sagittal sinus
Straight
sinus
Tentorium
cerebelli
Crista galli of the
ethmoid bone
Cavernous
sinus
Internal carotid
artery
Falx cerebelli
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 CSF
Superior
sagittal sinus
Superior
cerebral vein
Arachnoid
villus
Choroid plexus
Cerebrum covered
with pia mater
Subarachnoid space
Arachnoid mater
Meningeal dura mater
Periosteal dura mater
Great cerebral vein
Septum
pellucidum
Corpus
callosum
Interventricular
foramen
Tentorium cerebelli
Straight sinus
Confluence of sinuses
Third ventricle
Pituitary gland
Cerebellum
Choroid plexus
Cerebral vessels
that supply
choroid plexus
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Central canal
of spinal cord
Spinal dura mater
Inferior end of
spinal cord
Filum terminale
(inferior end
of pia mater)
(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 anatomy
Cervical plexus
Brachial plexus
Cervical
nerves
C1– C8
Cervical
enlargement
Intercostal
nerves
Thoracic
nerves
T1– T12
Lumbar
enlargement
Lumbar plexus
Sacral plexus
Cauda equina
Conus medullaris
Lumbar
nerves
L1– L5
Sacral
nerves
S1– S5
Coccygeal
nerve
C0
Filum terminale
Structure of the Spinal Cord
Ventral root
Dorsal root
Dorsal root
ganglion
Dorsal ramus
of spinal nerve
Ventral ramus
of spinal nerve
Spinal nerve
Rami communicantes
Sympathetic trunk
(chain) ganglion
(a)
White matter
Gray matter
Dorsal and ventral
rootlets of spinal
nerve
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
Dorsal root
(sensory)
Dorsal horn (interneurons)
Dorsal root
ganglion
SS
VS
Somatic sensory neuron
VM
Visceral sensory
neuron
SM
Visceral motor
neuron
Somatic motor neuron
Spinal nerve
Ventral root (motor)
Ventral horn
(motor neurons)
Transversal section of the Spinal Cord
Funiculus: fiber
tracts with the
same origin,
terminus and
function
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
Frontal lobe
Filaments of
olfactory
nerve (I)
Olfactory bulb
Olfactory tract
Temporal lobe
Optic nerve (II)
Optic chiasma
Optic tract
Infundibulum
Facial
nerve (VII)
Vestibulocochlear
nerve (VIII)
Oculomotor
nerve (III)
Trochlear
nerve (IV)
Trigeminal
nerve (V)
Glossopharyngeal nerve (IX)
Vagus nerve (X)
Abducens
nerve (VI)
Accessory nerve (XI)
Cerebellum
Hypoglossal nerve (XII)
Medulla
(a)
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
Optic nerve
Optic chiasma
Thalamus
Optic tract
Floor of
hypothalamus
Infundibulum
(pituitary removed)
Mammillary
body
Oculomotor nerve (III)
Crus cerebri of
cerebral peduncles
(midbrain)
Trochlear
nerve (IV)
Pons
Trigeminal nerve (V)
Middle
cerebellar
peduncle
Abducens nerve (VI)
Hypoglossal
nerve (XII)
Pyramid
Decussation of
pyramids
Spinal
cord
(a) Ventral view
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory
nerve (XI)
Ventral root
of first cervical
nerve
Relationship of the brain stem and the diencephalon
Thalamus
Optic tract
Crus cerebri of
cerebral peduncles
(midbrain)
Superior colliculus
Infundibulum
Pituitary gland
Trigeminal nerve (V)
Inferior colliculus
Trochlear nerve (IV)
Superior cerebellar
peduncle
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Pons
Abducens
nerve (VI)
Glossopharyngeal
nerve (IX)
Middle cerebellar
peduncle
Inferior cerebellar
peduncle
Vagus nerve (X)
Olive
Fasciculus gracilis
Hypoglossal
nerve (XII)
Fasciculus cuneatus
Accessory
nerve (XI)
(b) Left lateral view
Relationship of the brain stem and the diencephalon
Third ventricle
Thalamus
Pineal gland
Lateral geniculate
nucleus
Medial geniculate
nucleus
Superior
colliculus
Inferior
colliculus
Corpora
quadrigemina
of tectum
Midbrain
Trochlear (IV) nerve
Superior cerebellar peduncle
Middle cerebellar peduncle
Anterior wall of
fourth ventricle
Pons
Inferior cerebellar peduncle
Facial (VII) nerve
Vestibulocochlear (VIII) nerve
Medulla
Choroid plexus
(fourth venticle)
Glossopharyngeal (IX) nerve
Posterior median sulcus
Vagus (X) nerve
Fasciculus cuneatus
Accessory (XI) nerve
Fasciculus gracilis
Posterior (dorsal) root
of first cervical nerve
(c) Dorsal view