Download Organization of the Nervous System

Organization of the
Nervous System
Joselito B. Diaz, MD, FPNA
College of Rehabilitation Sciences
Introduction
• The Nervous and Endocrine systems
together control and coordinate
functions of all body systems
– Coordinated as an interlocking system
termed the Neuroendocrine system
– Nervous system performs short term
crisis management
– Endocrine system regulates long term
ongoing metabolic activities
Nervous System
MEMORY
SENSORY
STIMULI
Afferent
CORRELATION
COORDINATION
Efferent
MUSCLES
GLANDS
Etc.
Overview of
Neural
Integration
Functional Organization of the Nervous System
Anatomical
Organization of the
Nervous System
Terminologies
Nervous Tissue
Specialized tissue for rapid conduction of electrical
impulses that convey information from one part of the
body to another
– 98% nervous tissue concentrated in brain and spinal cord
Nervous tissue contains two basic cell types
Neurons = functional units
transmit information in the form
of electrical current at their cell
membranes
Neuroglia = “nerve glue”
provide physical support for
neurons
represent 90% of a cells in brain
Nerve Cells and Astrocyte (SEM x2,250).
The neuron is the functional unit of the
nervous system
Dendrites receive
information from another
cell or receptor and
transmit the message to the
cell body
The cell body contains the
nucleus, mitochondria and
other organelles typical of
eukaryotic cells
The axon conducts
messages away from the
cell body
Central nervous system
• Consists of the brain located within the
skull and the spinal cord located within the
vertebral foramen
• Integration and command center of the
body
• Covered by meninges and surrounded by
cerebrospinal fluid
Central nervous system
BRAIN
• Forebrain
– Cerebrum
– Diencephalon
• Midbrain
• Hindbrain
– Pons
– Medulla
– Cerebellum
SPINAL CORD
• Cervical segments
• Thoracic segments
• Lumbar segments
• Sacral segments
• Coccygeal segments
Central nervous system
Meninges and CSF
• The meninges are 3 connective tissue
membranes that lie external to the brain
and the spinal cord
– Dura mater, arachnoid mater, pia mater
– Cover and protect the CNS
– Hold cerebrospinal fluid (CSF)
– Prevents harmful substances from entering
CSF
Meninges and CSF
• The CSF is the extracellular fluid found in
the ventricles of the brain and
subarachnoid space
– Surrounds the brain and spinal cord in the
subarachnoid space
– Cushions and protects the CNS from trauma
– Provides mechanical buoyancy and support
the brain
– Nourishes the CNS and removes metabolites
Meninges
Central nervous system - Brain
Brain
Fissures and gyri
The cerebral cortex
Surface contains gyri and sulci or fissures
• Longitudinal fissure separates two cerebral
hemispheres
• Central sulcus of Rolando separates the frontal
and parietal lobes
• Lateral Sylvian fissure separates the temporal
lobe from the frontal and parietal lobes
• Line drawn from the parieto-occipital sulcus
down to the preoccipital notch delineate the
occipital lobe from the temporal and parietal
lobes
Lobes of the cerebrum
The Cerebral Hemispheres
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White and gray matter
White Matter of the Cerebrum
• Association fibers
– connections from gyrus to gyrus
and from lobe to lobe in the same
hemisphere
– Superior longitudinal fasciculus
• Commissural fibers
– Connections occur between
homologous areas of the two
hemisperes
– Corpus callosum
• Projection fibers
– Connects the cerebral cortex to the
subcortical, brainstem and spinal
cord nuclei
Subcortical nuclei
Diencephalon
and Brainstem
Diencephalon
Composed of:
• Epithalamus
• Hypothalamus
• Subthalamus
• Thalamus
Thalamus
• Final relay point for
ascending sensory
information
• Coordinates the
activities of the
cerebral cortex,
basal nuclei and
cerebellum
Hypothalamus
• Controls somatic motor activities
at the subconscious level
• Controls autonomic function
• Coordinates activities of the
endocrine and nervous systems
• Secretes hormones
• Produces emotions and
behavioral drives
• Coordinates voluntary and
autonomic functions
• Regulates body temperature
• Coordinates circadian cycles of
activity
The Hypothalamus in Sagittal Section
Medulla
• Connects the brain with
the spinal cord
• Contains relay stations
reflex centers and cranial
nerve nuclei
– Olivary nuclei
– Cardiovascular and
respiratory rhythmicity
centers
• Reticular formation
begins in the medulla
oblongata and extends
into more superior
portions of the brainstem
Brainstem - Medulla
Pons
• Sensory and motor nuclei
for four cranial nerves
• Nuclei that help control
respiration
• Nuclei and tracts linking
the cerebellum with the
brain stem, cerebrum and
spinal cord
• Ascending, descending
and transverse tracts
Brainstem - Pons
Midbrain
• The tectum (roof)
contains the corpora
quadrigemina
– Superior and inferior
colliculi
• The mesencephalon
contains many nuclei
and tracts
–
–
–
–
Red nucleus
Substantia nigra
Cerebral peduncles
RAS headquarters
Brainstem - Midbrain
Cerebellum
• Adjusts postural muscles and tunes on-going
movements
• Cerebellar divisions
– Flocculonodular, anterior and posterior lobes
– Vermis and cerebellar hemispheres
• Superior, middle and inferior cerebellar
peduncles link cerebellum with brain stem,
diencephalon, cerebrum, and spinal cord
The Cerebellum
The Cerebellum
Cranial Nerves
• 12 pairs of cranial
nerves
– Each attaches to
the ventrolateral
surface of the
brainstem near the
associated sensory
or motor nuclei
Cranial Nerves
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Cranial Nerves
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Spinal cord
• The adult spinal cord ends between L1 and L2
• Locate the:
– Shallow posterior median sulcus
– Deep anterior median fissure
Spinal cord
• Enlargements are
composed of numerous
gray matter dealing
with sensory and motor
control of the limbs
• Cervical enlargement nerves to the shoulder
girdles and upper limbs
• Lumbar enlargement –
innervations to the
pelvis and lower limbs
• Conus medularis is the
end of the spinal cord
Spinal cord
• Spinal cord is divided into 31 segments
• Dorsal root ganglia – contain the cell bodies of
sensory neurons
• Dorsal root – composed of sensory axons which
bring sensory information into the spinal cord
• Ventral roots – axons of motor neurons; control
somatic and visceral effectors
• Sensory and motor roots are bound together into a
single spinal nerve (distal to the root ganglion)
• Spinal nerves are mixed nerves – contain both
afferent (sensory) and efferent (motor) fibers
Gross Anatomy of the Adult Spinal Cord
Spinal meninges
• Membranes surround and
protect the spinal cord
• Provide physical stability
and shock absorption
• Blood vessels branching
within these layers deliver
oxygen and nutrients to the
spinal cord
• Three layers:
– Dura mater
– Arachnoid
– Pia mater
The Spinal Cord and Spinal Meninges
Sectional anatomy of the spinal cord
• White matter is
composed of myelinated
and unmyelinated axons
• Gray matter dominated
by nerve cell bodies and
neuroglia
• Gray matter surrounds
the central canal
• Projections of gray
matter called horns
The Sectional Organization of the Spinal Cord
The Sectional Organization of the Spinal Cord
Sectional anatomy of the spinal cord
• Organization of Gray Matter
– Organized into function groups called nuclei
– Posterior horns are sensory
• Posterior gray horn contains somatic and visceral sensory
nuclei
– Anterior horns are motor
• Anterior gray horns deal with somatic motor control
• Lateral gray horns contain visceral motor neurons
– Gray commissures join the lateral sides together; axons
pass from one side of the spinal cord to the other
through the gray commissure
Sectional anatomy of the spinal cord
• Organization of White Matter
– Divided into six columns
(funiculi) containing tracts
– All axons within a tract relay the
same type of information
(sensory or motor) in the same
direction
– Ascending tracts relay
information from the spinal cord
to the brain
– Descending tracts carry
information from the brain to
the spinal cord
Ascending pathways
Descending pathways
Peripheral Nervous System
• The PNS consists of 12 pairs of cranial nerves
originate from the brain and 31 pairs of nerves are
attached to the spinal cord
• Sensory (afferent)
– all axons carry impulses from sensory receptors
via the PNS to the CNS
• Motor (efferent)
– all axons carry impulses via the PNS from CNS
• Mixed
– a mixture of sensory and motor neurons that
carry impulses via the PNS to and from CNS
– most common type of nerve in the body
Functional Organization of the Nervous System
Sensory Division of the PNS
Sensory division - made of afferent
neurons
• somatic
– sensory neurons send information from skin,
skeletal muscles, and joints
• visceral
– sensory neurons send information from
organs within the abdominal and thoracic
cavities
Motor Division of the PNS
Motor division
• made of efferent neurons
• control the action of muscles and glands
– somatic motor neurons send APs to voluntary
skeletal muscle
– visceral motor neurons send APs to involuntary
cardiac muscle, smooth muscle and glands
– a.k.a. the Autonomic Nervous System (ANS)
– 2 antagonistic (opposing) divisions
• Sympathetic
• Parasympathetic
– the two divisions control the same effectors
but create opposite responses in the
effectors
31 pairs of
spinal nerves
• Nerve sheath
consists of:
– Epineurium
– Perineurium
– Endoneurium
Spinal
nerves
• Dorsal ramus (sensory and motor innervation to the skin
and muscles of the back)
• Ventral ramus (supplying ventrolateral body surface, body
wall and limbs)
• Rami communicantes
– White ramus (myelinated axons)
– Gray ramus (unmyelinated axons that innervate glands and
smooth muscle)
• Each pair of nerves monitors one dermatome
Peripheral Distribution of Spinal Sensory Nerves
Peripheral Distribution of Spinal Motor Nerves
Dermatomes
Nerve plexus
• Complex interwoven network of nerves
• Four large plexuses
– Cervical plexus
– Brachial plexus
– Lumbar plexus
– Sacral plexus
The Cervical Plexus
The Brachial Plexus
The Brachial Plexus
The Lumbar and Sacral Plexuses
The Lumbar and Sacral Plexuses
Peripheral Nerves and Nerve Plexus
Autonomic Nervous System
• Coordinates cardiovascular, respiratory,
digestive, urinary and reproductive
functions
• Two divisions:
– Sympathetic division (thoracolumbar, “fight or
flight”)
• Preganglionic fibers leaving the thoracic and
lumbar segments
– Parasympathetic division (craniosacral, “rest
and repose”)
• Preganglionic fibers leaving the brain and sacral
segments
Sympathetic division anatomy
• Preganglionic neurons between segments
T1 and L2
• Ganglionic neurons in ganglia near
vertebral column
– Sympathetic chain ganglia (paravertebral
ganglia)
– Collateral ganglia (prevertebral ganglia)
• Specialized neurons in adrenal glands
Organization of the Sympathetic Division of the ANS
Organization of
the Sympathetic
Division
Parasympathetic division
• Preganglionic neurons in the brainstem
and sacral segments of spinal cord
– Preganglionic fibers leave the brain as cranial
nerves III, VII, IX, X
– Sacral neurons form the pelvic nerves
• Ganglionic neurons in peripheral ganglia
located within or near target organs
Organization of the Parasympathetic Division of the ANS
Organization of the
Parasympathetic
Division
Organization of the
Nervous System
Joselito B. Diaz, MD, FPNA
College of Rehabilitation Sciences