Download The Nervous System: Neural Tissue

The Nervous System:
Neural Tissue
• Master controlling /communicating system
of the body.
• 3 overlapping functions: (1) Sensory input;
(2) Integration; (3) Motor output.
• Neuron
Organization of the Nervous
System
• CNS-integrating/command center of
nervous system.
• PNS-spinal,cranial nerves;functional
subdivisions----afferent(sensory),
efferent(motor)
• Fibers-somatic(SA,SE)visceral(VA,VE)
Organization of Nervous System
(cont’d)
• The motor division has 2 main parts:(1)
Somatic nervous system
(voluntary/involuntary);(2) Autonomic
nervous system (visceral motor)—
functional subdivisions are sympathetic/
parasympathetic (opposite effects on
viscera-stimulaton/inhibition)
Histology of Nervous Tissue
• Neuron-excitable nerve cells that transmit
electrical signals
• Supporting cells-surround and wrap
neurons;both cell types
(neurons/supportive) are bases for
CNS/PNS
Histology of Nervous Tissue
(Neuroglia)
• Nonnervous supporting cells
• Six types-4 in CNS, 2 in PNS, each has
unique function
• Scaffold neurons
• Chemical production guides young neurons
to proper connections; promote
health/growth.
CNS Supportive Cells
• Astrocytes- most numerous & versatile, radiating
processes anchor neurons to capillaries (form
BBB); chemical control (K, recycle neurotrans.)
• Microglia- Ovoid cells, monitor neuron health,
macrophage.
• Ependymal cells- range in shape from squamous
to columnar, line central cavities of CNS, circulate
CSF.
• Oligodendrocytes- producers of myelin sheaths.
PNS Supportive Cells
• Satellite cells (amphicytes)-surround neuron soma
within ganglia;regulate nutrient/waste product
exchange between soma and ECF.
• Schwann cells (neurolemmocytes)-surround and
form myelin sheaths (functionally similar to
oligodendrocytes);vital to peripheral nerve fiber
regeneration.
Neurons
• Structural unit of nervous system
• Have extreme longevity
• Amitotic; exceptions are olfactory &
hippocampal.
• High metabolic rate, require ample supply
of glucose & oxygen.
Neurons (cont’d)
• Large, complex cells
• Soma, processes
• 3 functional components: input region,
conducting component, & secretory
component.
Neurons (cont’d)
Cell Body
• Soma or perikaryon; transparent, spherical
nucleus (biosynthetic center) with
conspicuous nucleolus; lack centrioles.
• Free ribosomes, RER (Nissl bodies), Golgi
apparatus arcs around nucleus;
mitochondria, neurotubules, neurofibrils;
CNS soma (nuclei), PNS soma (ganglia).
Neurons (cont’d)
Processes
• CNS contain soma and processes, PNS
contain mostly processes;bundles of
processes in CNS called tracts, nerves in
PNS.
• Dendrites-short, tapering branching
extensions; receptive regions;dendritic spine
point of synapse.
Neurons (cont’d)
Processes
• Axon arises from hillock; long axon is a
nerve fiber; each neuron possesses 1 axon;
collaterals, telodendria (terminal branches);
motor neuron impulse triggered at hillock,
terminal represents secretory component;
axolemma
• Axoplasmic transport is anterograde and
retrograde
Neurons (cont’d)
Myelin sheath and Neurilemma
• Myelin protects and electrically insulates
fibers and hastens impulses(myelinated 150
m/s vs. unmyelinated ≤ 1m/s );Schwann
cells; neurilemma;nodes of Ranvier
(collaterals arise);white matter (myelinated
fibers), gray matter(soma & unmyelinated
fibers)
Classification of Neurons
Structural
• Bipolar-single dendrite & unmyelinated
axon; rare;special senses.
• Unipolar-continuous dendritic/axonal
processes; PNS sensory neurons/myelinated
neurons.
• Multipolar-Most common (99%); all
skeletal muscle motor neurons; myelinated
axons.
Classification of Neurons
Functional
• Sensory(afferent)-Unipolar, soma located in
sensory ganglia outside CNS; only most distal
parts act as impulse receptor sites.
• Motor (efferent)-Carry impulses away from CNS
to effector organs (muscles/glands); multipolar,
soma located in CNS.
• Interneurons-Lie between motor and sensory
neurons;confined within CNS; comprise 99% of
neurons of body.
Membrane Potentials
• Depolarization-inside becomes less neg.
• Hyperpolarization-inside becomes more
neg.
• Action potentials
Generation of AP
• (1) Resting stage: voltage-gated channels
closed
• (2) Depolarizing phase: Na+ permeability
increases
• (3) Repolarizing phase:K+permeability
increases
• (4) Undershoot-K+ permeability persists
The Synapse
• Electrical-very rapid; less common; gap
junctions;embryonic nerve tissue; jerky eye
movements; eventually replaced by
chemical
• Chemical-presynaptic terminals; vesicles;
cleft;postsynaptic membrane (receptors)
Neurotransmitters
• Acetylcholine-excitatory to skeletal
muscles
• Biogenic Amines-norepinephrine (E or I),
dopamine (E or I), Serotonin (I);emotional
behavior & biological clock
• Amino acids-GABA (E), Glutamate (E),
Glycine (I)
Classification of Neurons(cont’d)
Receptors
• Exteroceptors- External environment information;
touch, temperature, pressure; complex special
senses (somatic sensory neurons)
• Proprioceptors- Gauge somatic movement
(somatic sensory neurons)
• Interoceptors- Gauge digestive, respiratory,
cardiovascular systems; deep pressure sensations
(visceral sensory neurons).
Brain Organization
• Telencephalon-cerebral hemispheres
• Diencephalon-thalamus, hypothalamus,
epithalamus
• Mesencephalon-midbrain
• Metencephalon-pons, cerebellum
• Myelencephalon-medulla oblongata
Cranial Meninges & CSF
• Dura mater- Falx cerebri, tentorium
cerebelli, falx cerebelli
• Arachnoid
• Pia mater
• Choroid plexus-combination of ependymal
cells & permeable capillaries
Brain Ventricles
•
•
•
•
•
Lateral ventricles
Interventricular foramen
Third ventricle
Cerebral aqueduct
Fourth ventricle
Cerebral hemispheres
•
•
•
•
80% of total brain mass
Gyri,sulci
Fissures (longitudinal, transverse)
Lobes: Frontal, Temporal, Parietal,
Occipital, and Insula
Cerebral Cortex Motor &
Sensory Areas
• Precentral gyrus-primary motor cortex
(pyramidal cells)
• Postcentral gyrus-primary sensory cortex
• Occipital lobe-visual cortex
• Temporal lobe-auditory/olfactory cortex
• Insula/portions of frontal lobe –gustatory
cortex
The Cerebral (Basal)Nuclei
• Amygdaloid nucleus-Limbic system
component
• Corpus striatum(lentiform nucleus,
caudate nucleus)-Subconscious
adjustment/modification of voluntary motor
commands
Limbic System
• Hippocampus-involved in learning/long
term memory
• Amygdala
• Cingulate gyrus
• Fornix
The Thalamus
• Makes up 80% of diencephalon; bilateral
masses adhered by intermediate mass
• Anterior nuclei-hypothalamus
• Pulvinar,lateral dorsal &posterior nucleiProject visual/auditory information to
visual/auditory cortices.
• Mediates sensation, motor activities.
The Hypothalamus
•
•
•
•
•
•
•
•
Mammillary bodies
Infundibulum
Functions
Controls autonomic functions
Sets appetite & thirst drives
Homeostasis
Emotional response
Sleep-wake cycles
The Epithalamus
• Pineal gland-melotonin
• Choroid plexus
Mesencephalon (Midbrain)
• Cerebral peduncles
• Cerebral aqueduct
• Corpora quadrigemina-sensory nuclei
Superior collicus-visual input
Inferior colliculus-auditory input
• Red nucleus, substantia nigra
The Pons
• Brain stem region wedged between
midbrain & medulla
• Cerebellar peduncles
The Cerebellum
•
•
•
•
•
•
•
Accounts for 10 % of total brain mass
Cerebellar hemispheres
Vermis
Folia
Primary fissure (anterior,posterior lobes)
Cortex contains Purkinje cells
Arbor vitae-internal white matter
Medulla Oblongata
• Pyramids
• Decusssation point
• Visceral motor nuclei for: cardiovascular,
respiratory rhythmicity & others (hiccuping,
swallowing, etc,)
The Cranial Nerves
• Components of PNS
• 12 pairs
• Positioned along longitudinal axis
Olfactory (I)-Special sensory (smell)
Optic (II)-Special sensory (vision)
Oculomotor (III)-Motor, eye movements
Trochlear (IV)-Motor, eye movements
Cranial Nerves (cont’d)
• Trigeminal (V)-Mixed, maxillary/mandibular
branches
• Abducens (VI)-Motor, eye movements
• Facial (VII)-Mixed
• Vestibulocochlear (VIII)-Special sensory, hearing
• Glossopharyngeal (IX)-Mixed
• Vagus (X)-Mixed
• Accessory (XI)-Motor
• Hypoglossal (XII)-Motor, tongue movements
The Spinal Cord and Spinal
Nerves
• Spinal cord extends from foramen magnum
to level of first or second lumbar vertebra (
42 cm long, 1.8 cm thick)
• Major reflex center, ascending &
descending tracts.
Gross Anatomy of Spinal Cord
•
•
•
•
•
•
•
Posterior, anterior median sulci
Cervical, lumbar enlargements
Conus medullaris
Filum terminale
Dorsal,ventral root ganglia
Spinal nerve (31 pairs)
Cauda equina
Spinal Meninges
• Three layers: Dura mater, arachnoid, pia
mater
• Continuous with cranial meninges
• Cerebrospinal fluid
• Epidural space
Spinal meninges (cont’d)
The dura mater
• Outermost covering of spinal cord and brain
• Fuse at margins of foramen magnum
• Coccygeal ligament merges with
components of filum terminale
Spinal meninges (cont’d)
Arachnoid
• Subdural space
• Arachnoid-middle meningeal layer, simple
squamous epithelium
• Subarachnoid space-arachnoid trabeculae
(collagen, elastin fibers)
Spinal Meninges (cont’d)
The pia mater
• Innermost layer
• Anterior, posterior spinal arteries
• Spinal cord surface consist of astrocytes
that reinforce pia mater in place
• Denticulate ligament
• Filum terminale
Cross-Sectional Anatomy of the Spinal Cord
Gray Matter & Spinal Roots
• Posterior (dorsal) gray horn-somatic & visceral
sensory neurons (interneurons)
• Anterior(ventral)gray horn-somatic motor control
• Lateral gray horn- located in thoracic/superior
lumbar segments; contain visceral motor nuclei.
• Ventral root
• Dorsal root
• Gray commissures
Cross Sectional Anatomy of the Spinal Cord
White Matter
• Anterior, posterior white columns (funiculi)
• Anterior white commissure
• Lateral white columns
• Columns contain ascending, descending tracts
Spinal Nerves
• 31 pairs (cervicals precede adjacent vertebra); 1st
cervical spinal nerve is between the skull & the
atlas;C1-C8; thoracics procede adjacent vertebra
• Epineurium-collagen fibrous sheath;continuous
with dura at intervertebral foramina
• Perineurium-surround fascicles
• Endoneurium-surround individual axons
Peripheral Distribution of Spinal
Nerves
• Spinal nerves are formed by fusion of
ventral & dorsal roots.
• White ramus
• Gray ramus
• Dorsal ramus
• Ventral ramus
• Dermatomes
Nerve Plexuses
• Convergence of ventral rami of adjacent
spinal nerves producing a series of
compound nerve trunks.
• Major plexuses: Cervical, brachial, lumbar,
sacral.
Cervical Plexus
C1-C5
• Buried deep under sternocleidomastoid;
formed by ventral rami of 1st four cervical
nerves.
• Innervate neck muscles; phrenic is major
nerve; cutaneal branches (superficial);
motor branches (deep).
Brachial Plexus
C5-T1
• Larger,more complex than cervical, situated
partly in the neck & axilla; gives rise to
nerves that innervate upper limb;
organizational sequence: roots,trunks,
divisions, cords.
• Nerves: axillary, radial,
musculocutaneous, median, ulnar.
Lumbar Plexus
T12-L4
• Arises from 1st four lumbar spinal nerves
and lies within psoas major muscle
• Nerves: Femoral, obturator, iliohypogastric,
ilioinguinal, genitofemoral.
Sacral Plexus
L4-S4
• Nerves: Gluteal, Sciatic (tibialis, peroneal),
Pudendal