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THE NERVOUS
SYSTEM
Divisions of the nervous system
• Afferent
• Central Nervous
System
– Brain and spinal
cord
– Sensory
information from
receptors to CNS
• Efferent
• Peripheral
Nervous System
– Motor commands
to muscles and
glands
– Somatic division
– All neural tissue
outside CNS
• Voluntary
control over
skeletal muscle
– Autonomic division
• Involuntary
regulation of
smooth and
cardiac muscle,
glands
Neuronal Organization: CNS
• Two kinds of neural tissue found in both brain and spinal
cord:
• 1. Gray matter
• 2. White matter
Neuronal Organization: CNS
1. Gray matter =
unmyelinated neurons
+ neuroglia
-forms the outer layer of
the cerebrum = neural
or cerebral cortex
-also forms nuclei deep in
the brain = clusters of
neuronal cell bodies in
CNS
-collections of nuclei can
form a center (higher
brain function)
Neuronal Organization: CNS
• 2. White matter = myelinated
axons of neurons
• cell bodies are found in the
gray matter
• axons are bundled together to
form White matter tracts
• conduct nerve impulses from
gray region to gray region
• Brain – three types of tracts
(commisural, association,
projection)
• Spinal cord - two types:
sensory and motor tracts
(ascending and descending)
Major Regions of the Brain
Figure 15.1 Major Divisions of
the Brain
Cerebrum
• Cerebrum = largest portion of the brain
-left and right cerebral hemispheres divided by the longitudinal fissure
-hemispheres connected by the corpus callosum
– many gyri and sulci
have specific names
e.g. Central sulcus
•between the frontal
and parietal lobes
-cerebral cortex is folded into ridges and grooves
-grooves = sulci
-sulci divide the cerebrum into lobes
-ridges = gyri (gyrus)
-specific gyri are for the processing of sensation, area of voluntary
movement, speech, all thought processes -called motor and sensory
areas
Cerebrum
-cerebrum contains three categories of white matter tracts:
a. commissural – join areas between hemispheres
e.g. corpus callosum, anterior & posterior commissures
b. association – joins areas within a hemisphere
c. projection – joins cerebrum to brain stem
Gray Matter Nuclei: Basal Ganglia
•
•
modifies motor commands that
have originated from the cerebral
cortex
comprised of several nuclei
including the:
• 1. caudate nucleus: role in
•
•
•
posture and limb movement
2. putamen: precedes or
anticipates body movements
3. globus pallidus: regulates
muscle tone for movements
4. substantia nigra: role in eye
movements
–
high concentration of dopanergic
neurons
Diencephalon
• thalamus: 80% of the
diencephalon
• paired oval masses of gray
matter organized into nuclei,
interspersed with white matter
• major relay station for most
sensory impulses from the SC &
brain stem
• relays motor information from
cerebellum into the cerebrum
• relays nerve impulses to and
from different areas of the
cerebrum, the brain stem &
cerebellum
•hypothalamus
Diencephalon
1. control of the ANS – role
in regulating smooth &
cardiac muscle contraction
2. hormone production –
oxytocin and anti-diuretic
hormone (ADH)
3. regulates emotional and
behavioral patterns –
rage, aggression, pain and
pleasure + sexual arousal
4. regulates eating &
drinking
5. controls body temp
Diencephalon
•epithalamus – consists of the pineal gland and habenular nuclei
-pineal gland – part of the endocrine system
-secretes the hormone melatonin
-increased secretion in dark
-promote sleepiness and helps set the circadian
rhythms of the body (awake/sleep period)
•subthalamus – works with the cerebrum and cerebellum to control body
movements
BRAIN STEM
•comprised of three structures:
– midbrain
– pons
– medulla oblongata
Medulla Oblongata
– inferior most part of the brain stem
– made up of white matter tracts and
gray matter nuclei
– white matter - sensory/ascending and
motor/descending tracts
– nuclei regulate autonomic functions
– nuclei are known as reflex centers for
regulating heartbeat and BP
(cardiovascular center), respiration
(respiratory center), plus vomiting,
coughing, sneezing, hiccupping and
swallowing
-associated with 5 pairs of
cranial nerves
VIII
IX
X
XI
XII
Pons
• “bridge”
• connection from cerebrum to
cerebellum
– consists of multiple nuclei and
tracts
– nuclei control both somatic
(voluntary) and visceral
(involuntary) motor responses
MIDBRAIN
• relay station between the
cerebrum and the spinal cord,
and between the cerebrum and
cerebellum
– extends from the pons to the
diencephalon – as cerebral
peduncles
• white matter motor tracts through the
pons into the SC
• white matter sensory tracts up into
the thalamus
cerebral
peduncle
pons
medulla
oblongata
MIDBRAIN
• Posterior portion = tectum
-midbrain also connects the
cerebrum to cerebellum via
cerebellar peduncles
-white matter tracts (motor &
sensory)
-Corpora quadrigemina =
superior & inferior colliculi
-reflex centers for eye
movement, head and neck
movement (protection),
pupil size and eye
tracking
thalamus
pineal
gland
corpora
quadrigemina
median
eminence
medulla
oblongata
cerebellar
peduncle
Cerebellum
– divided into hemisphere with
lobes - like the cerebrum
• anterior and posterior lobes
– has a superficial layer of gray
matter called the cerebellar
cortex - like the brain
– deep to this gray matter are
tracts of white matter and gray
matter nuclei – like the
cerebrum
– evaluates and coordinates
involuntary and voluntary motor
activities initiated by the
cerebrum and corrects problems
by sending info back to the
cerebrum
– regulates posture & balance
– uses sensory data and stored
memories – “muscle memory”
• called the emotional brain
• involved in linking olfaction and memory
to basic emotional behaviors
• main components:
The Limbic
System
cingulate gyrus
hypothalmic nuclei
– 1. limbic lobe: includes the
anterior thalmic nuclei
hippocampus (within the
fornix
parahippocampal gyrus), the cingulate
gyrus, the insula and the dentate gyrus
corpus callosum
– 2. amygdala: integration center between
the limbic system, cerebrum and various
sensory systems
– 3. olfactory bulbs
– 4. mammillary bodies of the
olfactory tract
hypothalamus
mamillary body
amygdala
– 5. fornix - tract of white matter that
parahippocampal gyrus
connects the hippocampus to the
hippocampus
hypothalamus
• fibers end at the mammillary bodies
– 6. hypothalmic nuclei
– other areas
Protection: The Cranial Meninges
• Cranium is covered with protective membranes
= meninges
– Cranial meninges are continuous with
spinal meninges
– 3 layers: 1. outer, fibrous dura mater –
comprised of an outer endosteal layer and
and inner meningeal layer
– large spaces for the circulation of blood
can be found between these two layers =
sinuses
e.g. superior sagittal sinus
2. middle arachnoid mater
– the dura mater forms sheets
3. inner, thin pia mater
(falx) that separate the
cerebrum into hemispheres
and the cerebellum from the
cerebrum
Cranial Meninges
– there are spaces between these membranes
– A. subarachnoid space: between the arachnoid and pia maters
» large veins run through the subarachnoid space - e.g. cerebral veins
–
B. subdural space: between the arachnoid and the dura mater
» potential space in the cranial region
– C. epidural space – between the dura mater and the vertebral
canal in the spinal column
» potential space in the cranial region
Protection: CSF
• brain contains fluid-filled
chambers = Ventricles
– 2 lateral ventricles, 1 third
ventricle, 1 fourth
ventricle
– connects to the central
canal which runs into the
spinal canal
– These chambers contain
cerebrospinal fluid
– made by specialized cells in
the ventricles – choroid
plexus (ependymal cells)
Flow of CSF
•CSF continually circulates - ventricles and central canal to subarachnoid
space
•CSF is gradually reabsorbed into the blood through fingerlike projections into
the dural venous sinuses = arachnoid granulations (arachnoid villi)
The blood supply to the
brain
• Arterial blood reaches brain
via internal carotid and the
vertebral arteries
– both give rise to the Circle of
Willis
• made up of communicating
arteries and cerebral arteries
– the posterior communicating and
cerebral unite to form the basilar
artery
– the basilar the formed from the
union of the vertebral arteries
• Venous blood leaves via
internal jugular veins
Spinal Cord
• length in adults = 16 to 18 inches
• 31 segments – each with a pair of spinal
nerves
• Cervical and lumbar enlargements
– cervical = C4 to T1, nerves to and from
upper limbs
– lumbar = T9 to T12, nerves to and from
lower limbs
•Cervical
•and lumbar
enlargements
Spinal Cord
• Tapers to conus medullaris at
lumbar area
• fragments into a cauda equinae as
it runs through the sacral canal
– dorsal & ventral roots of lowest
spinal nerves
• filium terminale arises from the
conus medullaris
– extension of the pia mater that
anchors the SC to the coccyx
Histology of the Spinal Cord
• Central gray matter
– Contains cell bodies of
neurons and glial cells +
unmyelinated axons
– Gray matter projections are
horns
• Peripheral white matter
– Myelinated and
unmyelinated axons
– Organized as tracts or
columns
Histology of the Spinal Cord
• Organization of Gray Matter
• 1. Posterior gray horns
– sensory neurons entering the cord
• 2. Anterior gray horns
– somatic motor neuronal cell bodies
• 3. Lateral gray horns
– visceral motor neuronal cell bodies
• Gray commissures
– axons of interneurons crossing cord
• Organization of White matter
•
Anterior, lateral and posterior white
columns
– tracts of myelinated neuronal axons
– ascending = sensory information
– descending = motor information
White matter tracts