Nervous System

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Nervous System
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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.

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Neuroglia
Capillary
Neuron
(b) Microglial cell
(a) Astrocyte
Nerve fibers
Myelin sheath
Fluid-filled cavity
Process of oligodendrocyte
(c) Ependymal cells
Brain or spinal cord tissue
Cell body of neuron
(d) Oligodendrocyte
Satellite cells
Schwann cells (forming myelin sheath)
Nerve fiber
(e) Sensory neuron with Schwann cells and
satellite cells
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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)

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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)
Impulse direction
Nucleolus
Node of Ranvier
Nissl bodies
Axon terminals (secretory component)
Axon hillock
Schwann cell (one inter- node)
Neurilemma (sheath of Schwann)
Terminal branches (telodendria)
(b)
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Structure of a synapse
Neurotransmitter
Na
Ca2
Axon terminal of presynaptic neuron
Receptor
Action Potential
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Postsynaptic membrane
Mitochondrion
Postsynaptic membrane
Axon of presynaptic neuron
Ion channel open
Synaptic vesicles containing neurotransmitter
molecules
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Degraded neurotransmitter
Na
2
Synaptic cleft
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4
Ion channel closed
Ion channel (closed)
Ion channel (open)
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Myelinated fibers

• Made by
• Oligodendrocytes in CNS
• Schwann cells in PNS
• Structures
• Myelin sheath
• Neurilemma sheath of Schwann cells.
• Nodes of Ranvier

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Myelination of axons in the PNS by Schwann cells
Schwann cell cytoplasm
Schwann cell plasma membrane
Axon
Myelin sheath
Schwann cell nucleus
(a)
Schwann cell cytoplasm
Axon
Neurilemma
(b)
(d)
Neurilemma
Myelin sheath
(c)
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Activity 1

• Identify the parts of a neuron in a slide.
• Identify the parts of a neuron in a model

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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.

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Neuron classification by their structure
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Neuron Classification

• Classification by function
• Sensory
• Afferent
• Association

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Classification of neurons by function
Interneurons






Efferent fibers
Afferent fiber
Efferent fibers
Extensor inhibited
Flexor inhibited
Arm movements
Flexes
Flexor stimulated
Extensor stimulated
Extends
Key Excitatory synapse Inhibitory synapse
Right arm (site of stimulus)
Left arm (site of reciprocal activation)

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Structure of a nerve
Axon
Perineurium
Blood vessels
Myelin sheath
Endoneurium
Perineurium
Epineurium
Fascicle
Fascicle
Blood vessels
Endoneurium
Nerve fibers
(a)
(b)
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Neurophysiology

• How action potentials trigger nervous impulses.
• Resting potential
• Action potential
• Depolarization of the membrane.
• Refractory period
• Repolarization of the membrane
• Stimuli transmission

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Measuring membrane potential in neurons
Voltmeter
Plasma membrane
Ground electrode outside cell
Microelectrode inside cell
Axon
Neuron
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The basis of the resting membrane potential
Cell exterior
Na
Na 15 mM
Cell interior
Na
Na
K 150 mM
ion
NaK pump
Diffusion
us
Diff
Cl 10 mM
Na
-70 mV
Na
A 100 mM
Na 150 mM
K
Na
Plasma membrane
Na
A 0.2 mM
K
K 5 mM
Cl 120 mM
K
Cell interior
Cell exterior
K
K
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Changes in membrane potential produced by a
depolarizing graded potential
Active area (site of initial depolarization)
Membrane potential (mV)

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Resting potential
Distance (a few mm)
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Refractory periods in an AP
Absolute refractory period
Relative refractory period
Depolarization (Na enters)
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0
Repolarization (K leaves)
Membrane potential (mV)
After-hyperpolarization
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Stimulus
0
1
2
3
4
5
Time (ms)
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Propagation of an action potential (AP)
Voltage at 2 ms
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Membrane potential (mV))
Voltage at 0 ms
Voltage at 4 ms
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(a) Time 0 ms
(b) Time 2 ms
(c) Time 4 ms
Resting potential
Peak of action potential
Hyperpolarization
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Relationship between stimulus strength and action
potential frequency
Action potentials
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Membrane potential (mV)

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Stimulus amplitude
Threshold
Voltage
0
Time (ms)
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Saltatory conduction in a myelinated axon
Node of Ranvier
Cell body
Myelin sheath
Distal axon
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Central nervous system
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The nervous systems functions
Sensory input
Integration
Motor output
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Levels of organization in the nervous system
Key
Brain
Central nervous system (CNS) Brain and spinal
cord Integrative and control centers
Sensory (afferent) division of PNS Motor
(efferent) division of PNS
Key
Structure Function
Visceral sensory fiber
Central nervous system (CNS)
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
Sympathetic motor fiber of ANS
Visceral organ
Spinal cord
Skin
Somatic sensory fiber
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)
Motor fiber of somatic nervous system
Skeletal muscle
Sympathetic division Mobilizes body systems
during activity
Autonomic nervous system (ANS) Visceral motor
(involuntary) Conducts impulses from the
CNS to cardiac muscles, smooth muscles,
and glands
Somatic nervous System Somatic motor
(voluntary) Conducts impulses from the CNS
to skeletal muscles
Peripheral nervous system (PNS)
Parasympathetic division Conserves energy
Promotes housekeeping functions during rest
(b)
(a)
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Gross Anatomy of the Brain and Cranial Nerves

• Human Brain (activity 1,2)
• Cerebral Hemispheres of the cerebrum
• Diencephalon
• Brain Stem
• Cerebellum
• Meninges
• Cerebrospinal Fluid
• Choroid processes (ependymal cells capillaries)
• Cranial Nerves (activity 3)
• Spinal cord
• Brain dissection

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CerebrumCerebral 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)

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Arrangement of gray and white matter in the CNS
Central cavity
Cortex of gray matter
Migratory pattern of neurons
Inner gray matter
Cerebrum
Outer white matter
Cerebellum
Gray matter
Region of cerebellum
Central cavity
Inner gray matter
Outer white matter
Gray matter
Brain stem
Central cavity
Outer white matter
Inner gray matter
Spinal cord
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Lobes and fissures of the cerebral hemispheres
Central sulcus
Postcentral gyrus
Precentral gyrus
Parietal lobe
Frontal lobe
Parieto-occipital sulcus (on medial surface of
hemisphere)
Central sulcus
Frontal lobe
Lateral sulcus
Occipital lobe
Temporal lobe
Transverse cerebral fissure
Cerebellum
Pons
(a)
Medulla oblongata
Spinal cord
Gyri of insula
Gyrus
Temporal lobe (pulled down)
Cortex (gray matter)
Sulcus
(b)
White matter
Fissure (a deep sulcus)
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Lobes and fissures of the cerebral hemispheres
Anterior
Longitudinal fissure
Frontal lobe
Cerebral veins and arteries covered by arachnoid
Parietal lobe
Right Cerebral hemisphere
Left cerebral hemisphere
Occipital lobe
Posterior
(c)
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Functional and structural areas of the cerebral
cortex

• Primary somatosensory cortex post central gyrus
• Somatosensory association area immediate after
  PSC
• Primary motor area
• Brocas area speech
• Prefontral area intellect, personality

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Functional and structural areas of the cerebral
cortex
Central sulcus
Primary somatosensory cortex
Primary motor area
Somatic sensation
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Premotor cortex
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2
Somatosensory association area
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Frontal eye field
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Gustatory cortex (in insula)
Taste
Working memory for spatial tasks
Wernicke's area (outlined by dashes)
Executive area for task management
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Broca's area (outlined by dashes)
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Primary visual cortex
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Working memory for object-recall tasks
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Vision
Visual association area
Solving complex, multitask problems
Auditory association area
Prefrontal cortex
Hearing
Primary auditory cortex
(a)
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Functional and structural areas of the cerebral
cortex
Premotor cortex
Cingulate gyrus
Primary motor area
Corpus callosum
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Central sulcus
Primary somatosensory cortex
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6
1-3
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Frontal eye field
5
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Parietal lobe
Somatosensory association area
Prefrontal cortex
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Parieto-occipital sulcus
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Occipital lobe
Processes emotions related to personal and social
interactions
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Visual association area
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Orbitofrontal cortex
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Calcarine sulcus
Olfactory bulb
Primary visual cortex
Uncus
Temporal lobe
Olfactory tract
(b)
Fornix
Parahippocampal gyrus
Primary olfactory cortex
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Motor and sensory areas of the cerebral cortex
(homuculus)
Motor
Sensory
Shoulder
Trunk
Trunk
Knee
Neck
Head
Leg
Hip
Hip
Arm
Arm
Elbow
Elbow
Forearm
Wrist
Hand
Hand
Fingers
Fingers
Thumb
Thumb
Eye
Neck
Nose
Brow
Face
Eye
Lips
Genitals
Toes
Face
Teeth
Gums
Lips
Jaw
Tongue
Jaw
Tongue
Pharynx
Swallowing
Motor cortex (precentral gyrus)
Intra- abdominal
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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.

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Basal nuclei
Fibers of corona radiata
Caudate nucleus
Thalamus
Corpus striatum
Lentiform nucleus
Tail of caudate nucleus
Internal capsule (projection fibers run deep to
lentiform nucleus)
(a)
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Basal nuclei
Anterior
Cerebral cortex
Cerebral white matter
Corpus callosum
Anterior horn of lateral ventricle
Caudate nucleus
Third ventricle
Putamen
Lentiform nucleus
Globus pallidus
Thalamus
Inferior horn of lateral ventricle
(b)
Posterior
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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).

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Midsagittal section of the brain illustrating the
diencephalon and brain stem,
Parietal lobe of cerebral hemisphere
Septum pellucidum
Corpus callosum
Interthalamic adhesion (intermediate mass of
thalamus)
Fornix
Choroid plexus
Occipital lobe of cerebral hemisphere
Frontal lobe of cerebral hemisphere
Thalamus (encloses third ventricle)
Posterior commissure
Interventricular foramen
Pineal body/gland (part of epithalamus)
Anterior commissure
Corpora quadrigemina
Midbrain
Hypothalamus
Cerebral aqueduct
Optic chiasma
Pituitary gland
Arbor vitae
Temporal lobe of cerebral hemisphere
Fourth ventricle
Mammillary body
Choroid plexus
Pons
Cerebellum
Medulla oblongata
Spinal cord
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D. Brain Stem

• Major structures
• Cerebral peduncles
• Pons
• Medulla oblongata
• Decussation of pyramids

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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
Midbrain
Mammillary body
Pons
Temporal lobe
Medulla
Cerebellum
Spinal cord
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E. Cerebellum

• Features
• Center midline vermis
• Arbor vitae tree of life
• Function
• Balance and equilibrium

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Anterior view
Posterior view
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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.

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Meninges
Skin of scalp
Periosteum
Bone of skull
Periosteal
Dura mater
Meningeal
Superior sagittal sinus
Arachnoid mater
Pia mater
Subdural space
Arachnoid villus
Blood vessel
Subarachnoid space
Falx cerebri (in longitudinal fissure only)
(a)
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Meninges
Skull
Scalp
Superior sagittal sinus
Dura mater
Occipital lobe
Tentorium cerebelli
Tranverse sinus
Cerebellum
Temporal bone
Arachnoid mater over medulla oblongata
(b)
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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
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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.

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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
Septum pellucidum
Periosteal dura mater
Great cerebral vein
Corpus callosum
Tentorium cerebelli
Interventricular foramen
Straight sinus
Confluence of sinuses
Third ventricle
Cerebellum
Pituitary gland
Choroid plexus
Cerebral aqueduct
Cerebral vessels that supply choroid plexus
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)
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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.

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Spinal cord external anatomy
Cervical plexus
Cervical nerves C1 C8
Brachial plexus
Cervical
enlargement
Thoracic nerves T1 T12
Intercostal
nerves

Lumbar
enlargement
Conus medullaris
Lumbar nerves L1 L5
Lumbar plexus

Sacral plexus
Sacral nerves S1 S5
Filum terminale
Cauda equina
Coccygeal nerve C0
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Structure of the Spinal Cord
White matter
Ventral root
Gray matter
Dorsal root
Dorsal root ganglion
Dorsal and ventral rootlets of spinal nerve
Dorsal ramus of spinal nerve
Ventral ramus of spinal nerve
Spinal nerve
Rami communicantes
Sympathetic trunk (chain) ganglion
(a)
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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

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Organization of the gray matter of the spinal cord
Dorsal horn (interneurons)
Dorsal root (sensory)
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)
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Transversal section of the Spinal Cord
Funiculus fiber tracts with the same origin,
terminus and function
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Transversal sections of the spinal cord
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3. Cranial Nerves

• Part of the PNS
• Mnemonic On ocassion, our trusty truck acts
  funny-very good vehicle anyhow.

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Location and function of cranial nerves
Filaments of olfactory nerve (I)
Frontal lobe
Olfactory bulb
Olfactory tract
Optic nerve (II)
Temporal lobe
Optic chiasma
Optic tract
Infundibulum
Oculomotor nerve (III)
Facial nerve (VII)
Trochlear nerve (IV)
Vestibulo- cochlear nerve (VIII)
Trigeminal nerve (V)
Glosso- pharyngeal nerve (IX)
Abducens nerve (VI)
Vagus nerve (X)
Cerebellum
Accessory nerve (XI)
Medulla
Hypoglossal nerve (XII)
(a)
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Sheep brain dissection

• Identify the following structures
• Ventral
• Olfactory bulb
• Optic nerve
• Mammilary body
• Cerebral peduncle
• Cranial nerves
• Medulla oblongata
• Dorsal
• Cererbum
• Cerebellum

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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

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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

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Relationship of the brain stem and the
diencephalon
Optic nerve
Thalamus
Optic chiasma
Optic tract
Floor of hypothalamus
Infundibulum (pituitary removed)
Oculomotor nerve (III)
Mammillary body
Crus cerebri of cerebral peduncles (midbrain)
Trochlear nerve (IV)
Pons
Trigeminal nerve (V)
Abducens nerve (VI)
Middle cerebellar peduncle
Facial nerve (VII)
Vestibulocochlear nerve (VIII)
Hypoglossal nerve (XII)
Glossopharyngeal nerve (IX)
Pyramid
Vagus nerve (X)
Decussation of pyramids
Accessory nerve (XI)
Spinal cord
Ventral root of first cervical nerve
(a)
Ventral view
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Relationship of the brain stem and the
diencephalon
Thalamus
Optic tract
Crus cerebri of cerebral peduncles (midbrain)
Superior colliculus
Infundibulum
Inferior colliculus
Pituitary gland
Trochlear nerve (IV)
Trigeminal nerve (V)
Superior cerebellar peduncle
Facial nerve (VII)
Pons
Vestibulocochlear nerve (VIII)
Middle cerebellar peduncle
Abducens nerve (VI)
Glossopharyngeal nerve (IX)
Inferior cerebellar peduncle
Vagus nerve (X)
Olive
Fasciculus gracilis
Hypoglossal nerve (XII)
Fasciculus cuneatus
Accessory nerve (XI)
(b)
Left lateral view
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Relationship of the brain stem and the
diencephalon
Third ventricle
Thalamus
Superior colliculus
Corpora quadrigemina of tectum
Pineal gland
Inferior colliculus
Lateral geniculate nucleus
Midbrain
Medial geniculate nucleus
Trochlear (IV) nerve
Superior cerebellar peduncle
Middle cerebellar peduncle
Pons
Inferior cerebellar peduncle
Anterior wall of fourth ventricle
Facial (VII) nerve
Vestibulocochlear (VIII) nerve
Medulla
Choroid plexus (fourth venticle)
Glossopharyngeal (IX) nerve
Vagus (X) nerve
Posterior median sulcus
Accessory (XI) nerve
Fasciculus cuneatus
Fasciculus gracilis
Posterior (dorsal) root of first cervical nerve
(c)
Dorsal view