Central Nervous System
Dr. Anderson
GCIT
Animal Body Plans
Cephalization
• Organisms that have a proper and distinct
“head end”
• Why is this important?
Cephalization
Major Divisions
• Brain
– Processes information coming in from afferent
nerves
– Sends signals (motor) out to body via spinal cord
and cranial nerves
• Spinal Cord
– Connects brain to peripheral nerves
– May also initiate motor responses (reflexes)
Brain Divisions - Anatomical
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•
•
•
Cerebrum (Cerebral Hemispheres)
Diencephalon
Brain Stem (Pons, midbrain, medulla)
Cerebellum
Each of these divisions can be divided further,
into anatomical AND functional divisions
Brain Ventricles
• “Spaces” in the brain
that are left over from
embryonic brain
development
• Spaces are filled with
cerebro-spinal fluid
• Why?
Hydrocephaly
• “Water on the brain”
• Pressure inside the
brain inceases due to
too much cerebrospinal fluid (CSF)
being produced or
drainage is blocked
Functional Anatomy
Major Brain Divisions
Cerebrum
Cerebrum
• Divided into hemispheres bilaterally
• Each half of the cerebrum is further divided
into regions by:
– Gyri “Twisters”
– Sulci “shallow grooves”
– Fissures “Deeper grooves”
Major Fissures
Longitudinal Fissure
Transverse cerebral fissure
Major Sulci and Gyri
Brain and Skull
Frontal lobes lie within the
anterior cranial fossa
The anterior parts of the
temporal lobes lie within the
middle cranial fossa
The posterior cranial fossa
houses the brain stem and
cerebellum
Cerebral Cortex
• Only 2-4 mm thick, but 40% of brain mass
• Contains BILLIONS of neurons (convolutions
increase surface area)
• Functional areas can be identified, but all areas of
the cortex are interconnected
• Each hemisphere is associated with the opposite
side of the body (laterally)
Stroke
• People that have
motor areas affected
on only one side of
their brain
• Opposite part of the
body may be
paralyzed
Cortex – Thin Shell of Grey Matter
Functional Cortex Areas
• Motor – initiates movement in areas of the
body
• Sensory – Sensations from the body come
here to be processed
• Association Areas – where incoming
information from the body is processed
Motor and Sensory Areas
Primary Motor Cortex
• Located in the pre-central gyrus
• Pyramidal cells – allow conscious control and
coordination of voluntary movements
– Connect to spinal cord (pyramidal tracts)
• Motor areas are not simply discrete, but
interconnected!
Premotor Cortex
• Anterior to precentral gyrus
• Provides a ‘memory bank’ for skilled motor
activities
• Also controls motor activity that rely on
sensory feedback
Outline the Primary and Premotor
Cortices
Broca’s Areas
• Control the muscles that are responsible for
speech
• Also active during “planning” of motor
activities
• Would you expect this area to be smaller or
larger in chimps (our closest animal relative)?
Outline Broca’s Areas
Frontal Eye Field
• Lies anterior (and
within) premotor
cortex
• Controls voluntary
movements of the
eyes
Sensory Areas – Primary
Somatosensory cortex
• Post-central gyrus of the parietal lobe
• Neural input from the skin and
proprioreceptors (from muscles and joints) is
decoded and the stimulated body part is
identified (spatial discrimination)
Somatosensory Association Cortex
• Integrates sensory inputs to produce an
understanding of what is being felt
• DEMO
• What would damage to this area do?
Label the Primary and Association
Somatosensory Cortices
Primary Visual Cortex
• Receives input from the cells in the retina of
the eye
Visual Association Cortex
• Uses past visual stimuli
“visual memories” to
determine what is
being seen
• Uses different aspects
of the visual data
(shape, contrast, depth
perception, etc.)
Primary Auditory Cortex
• Superior margin of temporal lobe
• Gathers data on pitch, loudness and location
(by the difference in impulses received by
each ear)
• Auditory Association Area – interprets sound
by relating to past auditory memories
Olfactory Cortex
• On medial aspect of temporal lobe
• Part of the old “rhinencephalon” (nose brain)
that still exists
– Most of the rest of our ancestral rhinencephalon
has evolved to process “higher” emotions – the
limbic system
Auditory and Olfactory Cortices
Insula
• Part of the cerebral
cortex that is just
deep to the
temporal and
frontal lobes
• Seen when
temporal lobe is
retracted
Other Cortices
• Gustatory Cortex - Perceives taste stimuli
– Just deep to temporal lobe (on the insula)
• Visceral Cortex – Perceives information from the
gut
– Just posterior to gustatory cortex
• Vestibular Cortex – provides information about
the position of the head in space
– Posterior of insula
Multimodal Association Areas
• Generally receives information after being
processed by the association cortices for each
sense
• Receives input from multiple stimuli, and
–
–
–
–
–
Give meaning to it
Devote it to memory
Act upon it
Relate it to previous experience
Senses related to conciousness
Motor Homonculus (cortical)
Somatosensory Homonculus
Anterior Association Area
• In frontal lobe
• Center for
– Intellect
– Personality
– Judgement
– Planning
– Abstract Ideas
Posterior Association Area
• Temporal, parietal,
occipital lobes
• Allows to recognize:
– Patterns and faces
– Localizing yourself in
space
– Self-awareness
Limbic Association Area
• Includes the singulate gyrus, hippocampus
– Provides emotional impact that is tied to certain
situations
– Example?
Lateralization
• Each hemisphere of the brain is functionally
identical
• However, each hemisphere is considered to be
functionally different (slightly) in higher brain
functions, but research continues
– “Left-brain” – math, logic, language
– “Right-brain”- art, music, creativity
Cerebral White Matter
• Deep to the cortex
• Connects “grey matter” cortices to each other
and to the lower CNS (spinal cord)
• White color is due to the myelination of the
fibers composing the tissue
Grey and White Matter Distribution
White Matter Fibers
• Commissures – Connect corresponding grey
matter of the two brain hemispheres
– Allows them to act together
• Association Fibers – Connect different parts of
the same hemisphere
• Projection Fibers – connect the brain to the
rest of the nervous system (spinal cord)
Diencephalon
• Forms the core of the forebrain (surrounded
by cerebral hemispheres)
• 3 major divisions
– Thalamus
– Hypothalamus
– Epithalamus
Thalamus
• Consists of 2 bilateral
egg-shaped “nuclei”
• Serves as a relay station
for all impulses
entering the brain
– All afferent impulses are
directed to the relevant
areas of the brain
– All efferent impulses are
directed to the relevant
areas of the body
Hypothalamus
• Located inferior
to the thalamus
• The main visceral
control center of
the body,
maintains
homeostasis
Hypothalamus Functions
• Autonomic control center
– Heart rate, blood pressure, digestive tract
movements, etc.
• Emotional Responses
– Pleasure, fear, rage, sex drive
• Body Temperature
– Fever, sweating, shivering,
Hypothalamus Functions (con’d)
• Food intake
– Monitors glucose levels in the blood
• Water balance and thirst
– Monitors levels of solute concentrations in the
blood
• Sleep-wake cycles
• Major controller of the endocrine system
Epithalamus
• Most dorsal portion of
the diencephalon
• Most notably contains
the pineal gland,
which secretes the
hormone melatonin
– Helps regulate the
sleep-wake cycle
Brain Stem
• Directly inferior to
diencephalon
• Three major areas
– Midbrain
– Pons
– Medulla Oblongata
Midbrain
• Function
– Fight-or-flight response
– Visual reflex centers (visual
tracking)
– Startle reflex
Pons
• Helps to maintain the normal rhythm of
breathing
• Serves as a bridge between the motor cortex
and the cerebellum
Medulla Oblongata
• Located just in the opening of the foramen
magnum (top of spinal cord)
• Regulates many homeostatic functions
– Cardiovascular regulation
– Respiratory rhythm
– Hiccuping, coughing, vomiting, swallowing,
sneezing
Cerebellum
• Bilaterally
symmetrical organ
that occurs inferiorly
to the occipital lobe
• Times our efferent
motor impulses,
resulting in smooth
coordinated
movements
Cerebellar Processing
1. Cerebral motor areas relay their intent to start
voluntary muscle contraction
2. Afferent impulses from proprioreceptors send
information about body position and momentum
3. Cerebellar cortex calculates the amount and direction
of muscle contraction needed to complete the action
4. The “plan” of motion is sent back to the motor areas
of the cerebrum, where impulses are sent for the
action to be executed
The Limbic System
• Our “emotional” brain
• Composed of organs that surround the upper
brain stem
– Rhinencephalon
– Cingulate gyrus
– Amygdala
– Hypothalamus
– Fornix
Emotional Brain
• Amygdala
– Recognizes fearful facial
expressions
– Core of the fear
response
• Cingulate gyrus
– Helps to express
emotions as gestures
– Resolves mental
conflicts
Crossed Communication
• Even Numbers
• The limbic system communicates directly with the
frontal lobe via white matter.
• Odd Numbers
• Most limbic system actions are regulates by the
hypothalamus
• What issues might these connections
cause??
The Reticular Activating System
• The reticular neural formation extends from
the brain stem into many major areas of the
brain
– Makes this system ideal for arousing the brain as a
whole
• The RAS filters out “typical” stimuli, but
arouses the brain when something unusual or
significant happens
Levels of Consciousness
Alert
Drowsy/Lethargic
Stupor
Coma
What causes us to shift along this continuum?
Memory
• The storage and retrieval of information
• Memories are stored in parts of the brain that
need them (e.g. visual association cortex for
memories of shapes)
• What affects the vividness and length of
memories?
– Emotional State
– Repetition
– Association (mnemonic devices)
Protection of the Brain
• Meninges (Physical protection)
• Cerebrospinal Fluid (Physical Protection)
• Blood-Brain Barrier (Chemical Protection and
Immune Function)
Meninges
• Sheets of fibrous
connective tissue
that surrounds the
brain
– Dura Mater
• Continues inferiorly
as the spinal dura
mater
– Arachnoid
membrane
– Pia mater
Dura Mater
Cerebrospinal Fluid
• Fills the spaces in and around the brain and
spinal cord
– Ventricles
– Meninges
• Absorbs shock, provides buoyancy and
delivers materials (electrolytes, etc.) to the
brain
Spinal Tap
• CSF may need to be sampled to check for
infection/injury
– No blood/bacteria should be isolated from CSF in
healthy individuals
Blood-Brain Barrier
• Brain needs to be protected from
– Pathogens
– Wild swings in chemistry
• Capillaries serving the brain are only
permeable to the smallest molecules essential
for brain function
– Tight junctions in blood vessel epithelia
– Astrocytes – limit what comes in and out of brain
tissue
Always a good thing?
Concussion
• Generally due to a violent jarring or twisting of
the brain inside the cranium
Progressive Brain Diseases
• What types of diseases are responsible for
slow, progressive loss of mental function?
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•
•
•
•
Name of disease
Symptoms
Mode of pathology
Prognosis
Treatment
Spinal Cord - Anatomy
• Enclosed by the
neural arches of the
vertebrae
• Extends from the
base of the skull to
the 1st-2nd lumbar
vertebrae
Spinal Cord - Function
• Provides afferent and efferent nerve pathways
to and from the brain and peripheral nerves
• Major reflex center
Spinal Cord – Protection
• Resides within the spinal canal (vertebrae)
• Also surrounded by meninges
– Spinal Dura Mater
– Arachnoid Membrane
– Pia Mater
• CSF between arachnoid membrane and pia
mater
Spinal Meninges
Epidurals
• Anesthetic is placed in
epidural space using a
fine needle (catheter)
• Often used during
labor, surgery or
diagnostic procedures
Spinal Cord Terminus
• Spinal cord ends at the conus medullaris at 1st2nd Lumbar vertebra
• Filum terminale anchors the spinal cord to the
coccyx
• Nerve roots for lumbar and sacral region
extend through the vertebral canal and exit
through their respective vertebrae
Cauda Equina
Spinal Cord Cross-Sectional Anatomy