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Chapter 12
The Central Nervous System:
The Brain and Spinal Cord
J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D..
The Brain

General
 100 billion neurons

about 1.6 kg in males/1.45 kg in females
 proportional to body size

divided into hemispheres and lobes

its size is not representative of intelligence

complexity dictates processing power
Major Subdivisions of the Brain

Cerebral hemispheres

Diencephalon




Brain stem




thalamus
hypothalamus
epithalamus
midbrain
pons
medulla oblongata
Cerebellum
Distribution of Gray and White Matter


Gray matter: mostly
unmyelinated processes
and neuron cell bodies
White matter:
myelinated fiber tracts

cerebrum & cerebellum



brain stem


gray matter mostly
superficial (cortex)
white matter deep
variable
spinal cord


white matter superficial
gray matter deep
Brain Ventricles

Fluid filled spaces in brain

2 lateral ventricles



3rd ventricle




C-shaped chambers located deep in
cerebral hemispheres
connected to 3rd ventricle
a slit between and inferior to the right
and left halves of thalamus
connects to lateral ventricles
connects to 4th ventricle
4th ventricle


lies between brain stem and
cerebellum
connects to central canal of spinal
cord
Cerebral Hemispheres of Brain


~80% of the brain’s mass
During development, gray
matter grows faster than
white matter





gyrus - elevated ridges
sulcus - shallow grooves
fissure - deep grooves that
separate major regions
Longitudinal fissure separates R and L
hemispheres
Transverse fissure separates cortex from
cerebellum
Cerebral Lobes (5/hemisphere)

Frontal, parietal, temporal,
occipital lobes

Central sulcus separates
frontal from parietal lobe





precentral gyrus
postcentral gyrus
Lateral sulcus separates
frontal from temporal lobe
Parieto-occipital sulcus
separates parietal from
occipital lobe
Insula: deep to portions of
the temporal, parietal, and
frontal lobes
Cerebral Cortex






~40% of brain’s mass
Only 2-4 mm thick
Center of consciousness
Contains neuron cell
bodies, dendrites,
unmyelinated axons,
glial cells
Folds greatly increase
its surface area
A rich capillary blood
supply is nearby
Cortex: General Functional Organization

Three types of activity (areas)



motor
sensory
association
Each hemisphere primarily
controls the opposite side of
the body
 Although roughly equal in
structure, the hemispheres are
not equal in function
 No functional area of the brain
works alone
 Consciousness involves all
areas of the brain

Motor Areas of the Cerebral Cortex

Primary motor cortex (4*)
[* Brodmann areas]
precentral gyrus of frontal lobe
 primarily involved in voluntary motor control with more
area devoted to skilled muscles (e.g., controls fingers, face)

Map of the Primary Motor Cortex




Motor homunculus – shows
the locations on the precentral
gyrus which control the skeletal
muscles of each body region
The “size” of the illustrated body
part indicates the number of
neurons dedicated to that region
Control is contralateral
Note: areas of specialization for
communication (large size of
tongue, face) and manipulation
(hands)
Motor Areas of the Cerebral Cortex

Premotor cortex



Anterior to the
primary motor cortex
Involved in learned
repetitious or
patterned
movements, e.g.,
playing a piano,
typing
Also important in
planning movements
Homeostatic Imbalance of Motor Cortex

Damage to the primary motor cortex effects
the opposite side of body, e.g., stroke, trauma



only voluntary control of skeletal muscle is lost
reflexes remain -- controlled by the spinal cord
Damage to the premotor cortex


loss of programmed motor skills
muscle strength and the ability to perform tasks
remain



one can still make finger movements to type, etc.
not automatic
need to re-learn fine motor control
Motor Areas of the Cerebral Cortex

Language areas (Broca's area, 44, 45)




only found in one hemisphere - left?
a motor center for speech, controlling the muscles of the tongue,
throat, and lips
also involved in planning some voluntary motor activities
Frontal eye field (8) - voluntary movements of eyes
Broca's area
Sensory Areas of the Cerebral Cortex

Primary somatosensory area


Receives inputs directly from peripheral somatic sensory
receptors
Localizes points of the body where sensations originate
Note:
primary areas are directly wired to
the peripheral sensory receptors or
motor effectors
secondary areas receive input from
primary areas

Sensory Areas of the Cerebral Cortex

Primary somatosensory area


distribution of input areas for cutaneous sensations
spatial discrimination - identifies the areas of the body
being stimulated
Motor
Compare motor
and sensory
homunculi:
Sensory
Sensory Areas of the Cerebral Cortex

Somatosensory association area



Gets input from primary somatosensory association area
Integrates and analyzes information relative to size,
texture for identification of objects
Uses memories and experiences for object identification
without visual input
Posterior to the primary
somatosensory area
Sensory Areas of the Cerebral Cortex

Visual area


Medial surface of occipital lobe
Impulses from the eyes are routed through the thalamus
Sensory Areas: Visual Cortex

Sensory fibers cross over to
the opposite side -75%/25% at the optic
chiasm


lateral geniculate nucleus
(visual area) of the thalamus
occipital lobe



primary sensory area
association areas
Processing



different areas for different
functions
monocular vs binocular
color, form, movement
Motion Aftereffect
Pinwheel
Stare directly into the center of the pinwheel for 60
seconds. Then immediately look away from the
screen and at the back of your hand. Try looking at
other things in the immediately vicinity as well!
Color Afterimage
Stare directly at the center of the next screen for 60 seconds.
+
+
What did you see?
Let’s repeat it.
+
green
red
+
yellow
blue
Reviews of Neural Processing

Different levels

Neuron to neuron communication



Specific hardwired pathways route information
in predictable directions to specific locations
Association areas permit integration and
interpretation of different types of sensory
information
Motor areas issue appropriate commands to
effector organs
Sensory Cortex: Auditory Area

Superior part of the temporal lobe

Primary auditory cortex (anterior arrow) for pitch, rhythm,
loudness

Auditory association area (posterior arrow)
identifies/perceives sounds using memories as references
Sensory Cortex: Olfactory Cortex


Located above the orbits and in the medial portion of
the temporal lobes
Conscious awareness of different smells
Multimodal Association Areas

Anterior association area (prefrontal cortex)


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
anterior frontal lobe
intellect, complex learning, recall and personality
judgement, & planning
matures slowly – influenced by environment
Frontal Lobotomy
 1500’s
1950’s 

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sever the frontal lobes from the rest of the brain
stops all strong emotional reactions
once a popular medical/psychiatric procedure with a
long history
obsolete: patients had problems with planning and
performing socially appropriate behaviors despite
seeming to know what those behaviors would be
films: Frances and One Flew Over the Cuckoo’s Nest
Multimodal Association Areas

Posterior association area

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Temporal, parietal and occipital lobes
Pattern recognition, localizing position
Receives input from motor and other sensory association areas and
interprets it


dropping an acid bottle (sound, sight, touch, smell, memory, learning)
many sensory inputs, but the dominant feeling is of danger
Multimodal Association Areas

Limbic association area


Cingulate and parahippocampal gyri, & hippocampus
Provides emotional impact and sense of danger
Association: Language Areas

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Wernicke’s area - involved in pronouncing and interpreting
words
Broca’s area - speech production
lateral prefrontal cortex - language comprehension, word
analysis
lateral, ventral temporal lobe - auditory, visual aspects
(naming objects, reading)
the right side is more
involved in body
language
Brain Lateralization

both hemispheres participate in every activity, but
one hemisphere is dominant for most activities

e.g.: the left hemisphere is dominant for language
skills in most people (90%)

the left is also dominant for math abilities and logic

the right hemisphere is usually dominant for
“creative” skills:

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visual-spatial skills
intuition
emotion
appreciation of art and music
most left-hemisphere-dominant people are righthanded
Brain Lateralization (or Not)



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Hemispheric dominance is reversed or lacking in
10% of people
Most right-hemisphere-dominant people are lefthanded and male
Equal hemispheric function may result in
ambidexterity and/or dyslexia
Beware of the many “pop psychology”
interpretations of the significance and meaning of
hemispheric dominance
Cerebral White Matter

Myelinated fibers provide
3 types of connections
within the CNS:

commissural fibers




connect the hemispheres
(right   left)
ex: corpus callosum
association fibers – connect
neurons within one
hemisphere
projection fibers


connect cerebral hemispheres
to other parts of the CNS
ex: internal capsule
Deep Cerebral Gray Matter: Basal Nuclei



Diffuse masses of gray
matter deep within the
cerebral hemispheres
Involved in regulating slow,
sustained motor movements
– ex: arm swinging
Also inhibit unnecessary
movements (stabilize and
smooth primary
movements)


this area is affected in
Parkinson’s disease
results in tremors and slow,
unsteady movements
Brain Regions: Diencephalon



Composed of the
thalamus,
hypothalamus, and
epithalamus
Surrounded by the
cerebral hemispheres
Encloses the third
ventricle
Thalamus (“Gateway” to the Cortex)

An egg shaped collection of
nuclei serving as major
“switching station” as
impulses transfer from one
neuron to the next

Forms the lateral walls of
the third ventricle

Receives input from:



all ascending pathways
afferent impulses from all
senses except smell
Processes sensory
information

crude recognition of
sensation (cerebral
processing required for
precise localization and
conscious awareness)
Hypothalamus (below Thalamus)

Forms the bottom of
the third ventricle

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
many nuclei
infundibulum – the
stalk connecting the
hypothalamus and
pituitary gland
Pituitary gland


endocrine gland – “the
master gland”
releases its several
hormones in response to
chemical regulation
factors from the
hypothalamus
Functions of the Hypothalamus
1. Autonomic Nervous System (visceral) control
center – important in homeostasis
a center for emotional responses and
behaviors
body temperature regulation
regulation of food intake
regulation of water balance and thirst
regulation of sleep-wake cycles
controls many endocrine system functions
2.
3.
4.
5.
6.
7.

neuroendocrine feedback control
Epithalamus (upon the Thalamus)


Dorsal portion of
the diencephalon
Pineal gland (body)

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
melatonin
involved in sleepwake cycles
Location of one of
the choroid plexus
sites for production
of cerebrospinal
fluid (CSF)
Brain Regions: Brain Stem



Composed of the
midbrain, pons and
medulla
Involved in automatic,
unconscious behaviors
needed for survival
Provides pathways
(fiber tracts) for
neurons which are
communicating up or
down
midbrain
pons
medulla
Brain Stem: Midbrain



Pons to the lower
portion of the
diencephalon with the
cerebral aqueduct
passing through it
Main connecting routes
for all parts of the brain
and spinal cord
Connections between
the cerebellum and the
brainstem (cerebellar
peduncles)
Brain Stem: Pons




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above the medulla and anterior
to the cerebellum
contains both gray matter
nuclei and white fibers tracts
primarily conduction pathways
site of origin for several cranial
nerves
cerebral peduncles
Brain Stem: Medulla Oblongata


most inferior part of the
brain; merges into the
spinal cord inferiorly
involved in maintaining
internal homeostasis

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
cardiovascular center
respiratory center
other centers for:

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vomiting
hiccuping
swallowing
coughing
sneezing
Brain Regions: Cerebellum



Second-largest brain
region (cerebellum =
“small brain”)
Separated from the
cerebrum by the
transverse fissure
Its surface is the
cerebellar cortex (gray
matter) with folds (folia);
its white matter fiber
tracts are located in the
interior (arbor vitae =
“tree of life”)
Cerebellar Structure and Function

Shaped like a butterfly


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central vermis (“worm”)
cerebellar hemispheres
Functions to compare an
intended movement
(directed from the cortex)
with what movement is
actually happening
Constantly receiving sensory
input from muscle, tendon,
and joint proprioceptors,
and visual and equilibrium
receptors
Homunculi: maps of the
functional areas
arbor vitae
Cerebellar Structure and Function

Purkinje neurons play a major role in control over
the refinement of motor activities initiated by the
frontal motor cortex
Functional Systems of the Brain

Limbic System



encircles the brain stem
the “emotional” center
different regions of gray matter, including part of
the hypothalamus and the olfactory bulbs
Limbic System (cont.)


Functions in emotional aspects of behavior related to
survival
Also functions with the cerebrum in memory

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olfactory centers are near the limbic system
individuals, objects and experiences which initiate strong
emotional responses or are associated with smells are
committed to memory more easily
Memory impairment results from damage to the
limbic system
Also associated with pleasure and pain


electrical stimulation elicits different responses
includes defensive posturing (rage); others inspire timidity
Brain Systems: Reticular Formation



Gray matter (nuclei)
distributed within the
medulla, pons, and
midbrain
Axonal connections to
many other areas of
the brain
Structural and
functional areas


sensory, integrative
and motor functions
receives input from
higher centers for
skeletal muscle actions
Reticular Formation

Reticular Activating System


functions to alert the cerebral
cortex to important incoming
signals
filters signal “noise” = repetitive
stimuli (LSD interferes with this)


maintenance of consciousness and
waking from sleep (sudden stimuli)



e.g., studying in a noisy room
sends a constant stream of
information to the cortex,
maintaining arousal
the RAS is inhibited by sleep
centers in the hypothalamus
the RAS is depressed by alcohol,
sleep-inducing drugs (hypnotics)
and anti-anxiety drugs
LSD
Protection of the Brain


Soft tissue which needs to be protected
Several different protective mechanisms



scalp hair to prevent sunstroke?
bones – the cranium (“brain case”) of the skull
meninges


cerebrospinal fluid (CSF)


three connective tissue membranes wrapping the CNS
a fluid “shock absorber” which cushions and nourishes
the brain
blood-brain barrier

the physical and physiological separation of the CNS
from the bloodstream
Functions of the Meninges




Covers and protects brain
and spinal cord
Protect blood vessels and
enclose venous sinuses
Confine the cerebrospinal
fluid in the subarachnoid
space
Form major connective
tissue partitions for brain
regions within skull

falx cerebri, falx cerebelli,
tentorium cerebelli
Meninges: Dura Mater



Outermost layer
Dense, irregular fibrous connective tissue
Strong, protective wall around the brain and
spinal cord (dura mater = “tough/hard
mother”)
Meninges: Arachnoid Membrane


Loose connective tissue layer deep to the dura mater
Subdural space



Arachnoid villi extend into the subdural space


separates the arachnoid from the dura
contains interstitial fluid
CSF is reabsorbed back into the blood here
Subarachnoid space


separates arachnoid from pia mater
contains CSF
CSF
Meninges: Pia mater




Deepest layer
A thin, tight transparent fibrous connective tissue
supporting a network of many tiny blood vessels
Pia mater extends into the sulci and follows the large
blood vessels into the brain
Pia mater = “gentle/little mother”
Protection of the Brain: Cerebrospinal Fluid





CSF protects against chemical & physical injury; it
serves as a second circulatory system and nourishes
the CNS
Found in the four ventricles and subarachnoid space
80-150 ml of CSF is normal for an adult
CSF composition differs slightly from plasma
Clear, colorless plasma filtrate containing:





H2O, glucose, other nutrients, proteins, lactic acid, urea
cations (Na+, K+, Ca2+, Mg2+)
anions (Cl-, HCO3-)
some lymphocytes (white blood cells)
Formed by the choroid plexuses; reabsorbed by the
arachnoid villi and returned to the plasma
Functions of Cerebrospinal Fluid

Mechanical protection



Chemical protection

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

shock absorbing fluid
the brain “floats” in this fluid
provides a constant chemical environment
the pH of the CSF is important in the control of
breathing
CSF composition is important for regulating
cerebral blood flow
Circulation for the exchange of nutrients and
waste products between the blood and
nervous tissue
Cerebrospinal Fluid: Choroid Plexuses



Special capillary networks
in certain places in the
ventricular walls
Ependymal cells
Fluid from plasma passes
through the ependymal
cells at choroid plexuses




cells have ion pumps
modify CSF
regulate and maintain the
blood-brain barrier
Protect the brain from
harmful substances in the
blood
Blood-Brain Barrier

Penetration of molecules from the blood into
the brain is regulated by:




tight junctions between capillary cells
thick basal lamina (connective tissue layer)
astrocytes pressed against capillaries
The barrier is a selective membrane



some substances, particularly if lipid-soluble, pass
easily from blood to the brain (water, glucose, O2,
CO2, alcohol, caffeine, nicotine, heroin, most
anesthetics)
most charged ions do not pass easily
proteins and most antibiotics do not pass at all
Blood-Brain Barrier

Permeability is variable depending on the site



choroid plexus – CSF production
vomiting center in brain stem - monitors the blood
for toxic molecules and poisons
hypothalamus


has no blood-brain barrier
monitors blood composition for water balance,
temperature, pH, osmolarity and many other
homeostatic metabolic functions
Homeostatic Imbalances of the Brain

Traumatic Brain Injuries

concussion

a blow to head





possibly, there is no visible external damage
a variety of cognitive problems follow
contusion



the skull stops, but the brain keeps moving
the brain bounces off the inside of the skull
breaks in small vessels, some bleeding, visible bruising
effect depends on the location
laceration


tearing of the brain
knife and gunshot wounds, other major traumas
Homeostatic Imbalances of the Brain

Traumatic Brain Injuries (cont.)

epidural or subdural or subarachnoid hemorrhage





bleeding from ruptured vessels into that space
a person is normal immediately after the injury, but deteriorates as
the bleeding continues
hemorrhage increases intracranial pressure
effects vary with the location of the hematoma
surgical intervention



drill holes
remove clots
install drainage tubes
subarachnoid hemorrhage
Homeostatic Imbalances of the Brain

Cerebrovascular Accidents (CVA’s)

Stroke






third leading cause of death in the United States
ischemia anemia caused by reduced or blocked blood flow)
hemorrhages and blood clots increase intracranial pressure
brain tissue dies (infarct)
risk factors: high blood pressure, high cholesterol, heart
disease, narrowed carotid arteries, diabetes, smoking,
obesity, excessive alcohol intake
Transient ischemic attack (TIA/ministroke)



may last minutes
flow is reduced and brain tissue suffers temporarily
blood flow is re-established
Homeostatic Imbalances of the Brain

Degenerative brain diseases

Alzheimer’s disease




about 11% of population over age 65, 4 million people
suffer, 100,000 die annually; hereditary component
widespread cognitive deficits - (short term) memory
loss, shortened attention span and disorientation, loss
of language skills
death from secondary causes, e.g., due to being
bedridden
diagnosis is difficult since there is no definitive test;
only after death can it be confirmed by autopsy:




significant loss of neurons in specific regions
abnormal proteins are deposited in brain tissue
tangled nerve masses
generally, the damage is limited to the cerebral cortex
Alzheimer’s
Disease
Homeostatic Imbalances of Brain

Degenerative brain diseases (cont.)

Parkinson’s disease






progressive disorder of the CNS which typically affects
victims at age 60 or so
cause(s) unknown; hereditary component sometimes
characterized by degeneration of dopamine-releasing
neurons
characterized by tremor (shaking) and rigidity
(continuous contraction)
motor performance impaired by bradykinesia (slow
motion) and hypokinesia (reduced range of motion)
treatments try to increase dopamine and decrease ACh
with therapeutic drugs or by experimental implantation
of fetal brain cells
Homeostatic Imbalances of Brain

Traumatic brain diseases

Cerebral Palsy





damage to motor areas of brain during fetal life, at
birth, or during infancy, usually transient O2 deprivation
poor control and coordination of voluntary muscle
activities but usually little impact on intellect
irreversible, but not progressive
70% of victims appear to be mentally retarded



often due to their inability to hear or speak well
generally, they are more aware and understanding of their
situation and surroundings than they appear
Concussion, Contusion, Sudural or Subarachnoid
Hemorrhage, Cerebral Edema, CVAs
Not Everybody is an Einstein!
The Spinal Cord


Spinal cord is located within the vertebral column
Passes through the vertebral foramina
Anatomy and Protection of Spinal Cord



Bone of vertebral arch
CSF
Spinal meninges



dura mater, arachnoid,
pia mater
meninges cover spinal
cord and spinal nerves
epidural space



space between the dura
mater and wall of the
vertebral canal
filled with adipose and
loose connective tissue
nerves exit through
intervertebral foramina
External Spinal Cord Anatomy




Roughly cylindrical but slightly
flattened dorsi-ventrally
From foramen magnum to
second lumbar vertebra (L2)
About 2 cm wide and 42-45 cm
long
Cervical enlargement and lumbar
enlargement are conspicuous


cervical enlargement - nerves for
upper extremities
lumbar enlargement - nerves for
lower extremities
External Anatomy (cont.)




Spinal cord tapers, ends in the
conus medullaris between L1 and
L2
Filum terminale (pia mater)
extends from the conus to attach
the spinal cord to the coccyx
Some nerves exit the vertebral
column below the level of their
exit from the spinal cord
Cauda equina – “horse's tail” at
end of the cord are the last few
pairs of spinal nerves
Cross-Sectional Anatomy of the Spinal Cord
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

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
“H” shaped gray matter –
“butterfly” surrounded by
white matter
Anterior median fissure
Posterior medial sulcus
Gray commissure forms
the cross bar of the 'H'
Central canal




small space in middle of gray
commissure
extends length of spinal cord
at superior end continuous
with the 4th ventricle
contains CSF
Cross-Sectional Anatomy of the Spinal Cord


Anterior to the gray
commissure is the anterior
white commissure
The gray matter of the spinal
cord is divided into horns



closer to front are the anterior
(ventral) gray horns
closer to back are the posterior
(dorsal) gray horns
lateral gray horns



between anterior and posterior
horns
present only in thoracic, upper
lumbar, and sacral segments
gray matter also has some named
nuclei
dorsal
lateral
ventral
Gray Matter




Anterior horn – visceral & somatic motor neurons
Ventral root - efferent (motor) nerves to skeletal
muscles and to the visceral organs (effectors)
Posterior horn – somatic & visceral sensory neurons
Dorsal root - afferent nerves from skin, skeletal
muscles, connective tissues, visceral organs
Gray matter



In Chapter 13 we will examine the basic connections
in the spinal cord, such as the reflex arc
The simplest connection is a two cell reflex
connecting a sensory neuron directly to a motor
neuron
More complicated reflexes have one or more
intervening interneurons
White Matter of the Spinal Cord


Conduction tracts in the spinal cord
Named by


where each is coming from
where each is going to
White Matter of the Spinal Cord



Fasciculi cuneatus and gracilis - fine touch and pressure
Lateral and anterior spinothalamic tracts - pain, temperature,
deep pressure and coarse touch
Two paths for similar functions
The Spinal Cord
In Chapter 13 we will examine the routes
and means by which the Central Nervous
Connection interacts with and controls
the rest of the body.
Those routes form the Peripheral Nervous
System.
End Chapter 12
Some slides of specific spinal cord tracts appear
after this slide. You are not responsible for those
specific tracts for the exam.
Specific and Posterior Spinocerebellar
Tracts
• Specific ascending
pathways within the
fasciculus gracilis and
fasciculus cuneatus
tracts, and their
continuation in the
medial lemniscal
tracts
• The posterior
spinocerebellar tract
Nonspecific Ascending Pathway

Nonspecific
pathway for pain,
temperature, and
crude touch
within the lateral
spinothalamic
tract
The Direct (Pyramidal) System





Direct pathways originate with
the pyramidal neurons in the
precentral gyri
Impulses are sent through the
corticospinal tracts and synapse
in the anterior horn
Stimulation of anterior horn
neurons activates skeletal
muscles
Parts of the direct pathway,
called corticobulbar tracts,
innervate cranial nerve nuclei
The direct pathway regulates
fast and fine (skilled)
movements
Indirect (Extrapyramidal) System



Includes the brain stem, motor
nuclei, and all motor pathways not
part of the pyramidal system
This system includes the
rubrospinal, vestibulospinal,
reticulospinal, and tectospinal tracts
These motor pathways are complex
and multisynaptic, and regulate:



Axial muscles that maintain
balance and posture
Muscles controlling coarse
movements of the proximal
portions of limbs
Head, neck, and eye movement
Extrapyramidal (Multineuronal)
Pathways

Reticulospinal tracts – maintain balance

Rubrospinal tracts – control flexor muscles

Superior colliculi and tectospinal tracts
mediate head movements
End Chapter 12