central nervous system dr. anderson gcit. animal body plans
TRANSCRIPT
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Central Nervous System
Dr. AndersonGCIT
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Animal Body Plans
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Cephalization
• Organisms that have a proper and distinct “head end”
• Why is this important?
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Cephalization
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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)
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Brain Divisions - Anatomical
• Cerebrum (Cerebral Hemispheres)• Diencephalon• Brain Stem (Pons, midbrain, medulla)• Cerebellum
Each of these divisions can be divided further, into anatomical AND functional divisions
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Brain Ventricles
• “Spaces” in the brain that are left over from embryonic brain development
• Spaces are filled with cerebro-spinal fluid
• Why?
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Hydrocephaly
• “Water on the brain”
• Pressure inside the brain inceases due to too much cerebro-spinal fluid (CSF) being produced or drainage is blocked
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Functional Anatomy
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Major Brain Divisions
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Cerebrum
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Cerebrum
• Divided into hemispheres bilaterally
• Each half of the cerebrum is further divided into regions by:– Gyri “Twisters”– Sulci “shallow grooves”– Fissures “Deeper grooves”
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Major Fissures
Longitudinal Fissure Transverse cerebral fissure
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Major Sulci and Gyri
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Brain and SkullFrontal 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
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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)
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Stroke
• People that have motor areas affected on only one side of their brain
• Opposite part of the body may be paralyzed
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Cortex – Thin Shell of Grey Matter
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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
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Motor and Sensory Areas
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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!
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Premotor Cortex
• Anterior to precentral gyrus
• Provides a ‘memory bank’ for skilled motor activities
• Also controls motor activity that rely on sensory feedback
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Outline the Primary and Premotor Cortices
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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)?
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Outline Broca’s Areas
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Frontal Eye Field
• Lies anterior (and within) premotor cortex
• Controls voluntary movements of the eyes
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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)
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Somatosensory Association Cortex
• Integrates sensory inputs to produce an understanding of what is being felt
• DEMO
• What would damage to this area do?
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Label the Primary and Association Somatosensory Cortices
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Primary Visual Cortex
• Receives input from the cells in the retina of the eye
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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.)
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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
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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
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Auditory and Olfactory Cortices
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Insula
• Part of the cerebral cortex that is just deep to the temporal and frontal lobes
• Seen when temporal lobe is retracted
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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
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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
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Motor Homonculus (cortical)
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Somatosensory Homonculus
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Anterior Association Area
• In frontal lobe
• Center for– Intellect– Personality– Judgement– Planning– Abstract Ideas
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Posterior Association Area• Temporal, parietal,
occipital lobes
• Allows to recognize:– Patterns and faces– Localizing yourself in
space– Self-awareness
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Limbic Association Area• Includes the singulate gyrus, hippocampus– Provides emotional impact that is tied to certain
situations
– Example?
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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
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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
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Grey and White Matter Distribution
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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)
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Diencephalon
• Forms the core of the forebrain (surrounded by cerebral hemispheres)
• 3 major divisions– Thalamus– Hypothalamus– Epithalamus
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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
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Hypothalamus
• Located inferior to the thalamus
• The main visceral control center of the body, maintains homeostasis
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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,
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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
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Epithalamus
• Most dorsal portion of the diencephalon
• Most notably contains the pineal gland, which secretes the hormone melatonin– Helps regulate the
sleep-wake cycle
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Brain Stem
• Directly inferior to diencephalon
• Three major areas– Midbrain– Pons– Medulla Oblongata
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Midbrain• Function– Fight-or-flight response– Visual reflex centers (visual
tracking)– Startle reflex
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Pons
• Helps to maintain the normal rhythm of breathing
• Serves as a bridge between the motor cortex and the cerebellum
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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
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Cerebellum• Bilaterally
symmetrical organ that occurs inferiorly to the occipital lobe
• Times our efferent motor impulses, resulting in smooth coordinated movements
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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
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The Limbic System• Our “emotional” brain
• Composed of organs that surround the upper brain stem– Rhinencephalon– Cingulate gyrus– Amygdala – Hypothalamus– Fornix
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Emotional Brain• Amygdala– Recognizes fearful facial
expressions– Core of the fear
response
• Cingulate gyrus– Helps to express
emotions as gestures– Resolves mental
conflicts
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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??
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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
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Levels of Consciousness
Alert Drowsy/Lethargic Stupor Coma
What causes us to shift along this continuum?
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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)
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Protection of the Brain• Meninges (Physical protection)
• Cerebrospinal Fluid (Physical Protection)
• Blood-Brain Barrier (Chemical Protection and Immune Function)
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Meninges• Sheets of fibrous
connective tissue that surrounds the brain– Dura Mater
• Continues inferiorly as the spinal dura mater
– Arachnoid membrane– Pia mater
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Dura Mater
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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
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Spinal Tap• CSF may need to be sampled to check for
infection/injury– No blood/bacteria should be isolated from CSF in
healthy individuals
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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?
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Concussion• Generally due to a violent jarring or twisting of
the brain inside the cranium
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Progressive Brain Diseases
• What types of diseases are responsible for slow, progressive loss of mental function?
• Name of disease• Symptoms• Mode of pathology• Prognosis• Treatment
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Spinal Cord - Anatomy
• Enclosed by the neural arches of the vertebrae
• Extends from the base of the skull to the 1st-2nd lumbar vertebrae
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Spinal Cord - Function
• Provides afferent and efferent nerve pathways to and from the brain and peripheral nerves
• Major reflex center
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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
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Spinal Meninges
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Epidurals
• Anesthetic is placed in epidural space using a fine needle (catheter)
• Often used during labor, surgery or diagnostic procedures
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Spinal Cord Terminus
• Spinal cord ends at the conus medullaris at 1st-2nd 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
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Cauda Equina
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Spinal Cord Cross-Sectional Anatomy