The Neurological System: Anatomy and Physiology of the CNS

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The Neurological SystemAnatomy and Physiology
of the CNS

• NET 2420
• Lecture Handout
• S.Compton, RN, MSN

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Anatomy of Nervous System

• CNS-central nervous system
• Brain
• Spinal Cord
• PNS-peripheral nervous system
• Cranial nerves I XII
• Spinal nerves C1-S5
• ANS-autonomic nervous system
• Sympathetic
• Parasympathetic

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Cells of Nervous System

• Two cell types
• Neuroglia
• 5-10 times more numerous than neurons
• Provide support, nourishment, protection to
  neurons
• Mitotic CAN replicate if damaged
• Neurons
• Primary functional unit of the nervous system
• Nonmitotic cannot replicate

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Neuroglia (glial cells)

• Most primary tumors arise from _____ cells
• Several types ? different functions
• Oligodendroglia produce _______ sheath (CNS)
  (Schwann cells in PNS)
• Astrocytes found primarily in gray matter
• Help form blood brain barrier
• Help form scar tissue when CNS injured
• Ependymal cells line brain ventricles
• Formation of _______________ _____________

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Neurons Structure

• Cell body
• Dendrites short processes extending from cell
  body
• Receive conduct impulses FROM other neurons
  TOWARD cell body
• Axon projects from cell body in varying lengths
• Carries impulses TO other neurons or end organs

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Nerve Impulses

• Action potential initiated?Transmitted along
  axon? Reaches end of nerve fiber? transmitted
  across synapse (junction) to another neuron or
  receptor organ by means of neurotransmitters?
• Result excitation or inhibition of action
  potential
• Myelin white lipid substance insulator for
  conduction of impulses facilitates impulse
• Peripheral nerve axons gaps in myelin called
  Nodes of Ranvier
• Action potential hops from node to node FASTER

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Synapse Essential Components

• Pre-synaptic terminal
• End of axon
• Contains vesicles with chemical neurotransmitters
• Synaptic cleft
• Microscopic space between neuron and receptor
  cell
• Receptor site
• Post-synaptic cell

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Neurotransmitters

• Hundreds of synapses may occur on single neuron
• NET effect of neurotransmitters released will
  determine if impulse is excitatory or inhibitory
• Neurotransmitters continue to combine at receptor
  sites until they
• Are inactivated by ____________
• Are taken back up by pre-synaptic endings
• Diffuse away from synapse

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Common Neurotransmitters

• Major neurotransmitters Table 60-1 p 1822
• Acetylcholine
• Major transmitter of parasympathetic nervous
  system
• Destroyed by acetylcholine esterase
• Cholinergic receptors stimulated by
  acetylcholine
• Muscarinic
• Nicotinic
• Norepinephrine
• Major transmitter for sympathetic nervous system
• Destroyed by
• Catechol-O-methyl transferase (PNS)
• Monoamine oxidase (CNS)
• Adrenergic receptors (a-1, a-2, B-1, B-2)
  stimulated by norepinephrine, epinephrine, and
  other catecholamines

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Examples

• _________ seratonin reuptake inhibitors
• Barbiturates and benzodiazepines
• Potentiate GABA, enhance GABA, derivatives of
  GABA
• _________ MAO inhibitors
• MAO degrades dopamine, MAOIs allow dopamine to
  stay at receptor sites longer
• Dopaminergic drugs (______________ disease)
• Levodopa-increase brain levels of dopamine
• Anti-psychotic drugs (Haldol)
• Block dopamine receptors, do not allow dopamine
  to affect the limbic system? emotions

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CNS Level of Functioning

• Spinal Cord
• Lowest functioning level of CNS
• Automatic motor responses and reflexes
• Brain stem and subcortex (cerebellum and
  diencephalon)
• Second functional level
• Blood pressure, respirations, equilibrium, and
  primitive emotions
• Cortex
• Highest level
• Cognition, memory, thinking, abstraction

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Dominance of a Cerebral Hemisphere

• 90 have left hemispheric dominance? right handed
• Some left handed people are left dominant
• Each hemisphere receives sensory information from
  and controls skeletal muscles of
  __________________ side of body
• Hemispheres communicate with each other, but each
  hemisphere specializes in certain activities
• Left side
• language, analysis, problem solving, reading,
  writing, verbal communication
• Right side
• perception of environment, music, art, nonverbal
  communication and perception of spiritual
  environment

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Frontal Lobe

• Concentration, abstract thought
• Affect, personality, inhibitions
• Information storage, memory
• Motor function
• Voluntary motor control
• Betz cells/ pyramidal cells
• Specific arrangement to body parts
• Voluntary eye movement control
• Motor control of speech in dominant hemisphere?
  ____________ area
• Motor control of involuntary activities
• Respiration, BP, GI activity

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Parietal Lobe

• General sensation
• Primary sensory cortex arranged in correlation
  to motor strip
• Perception of touch, position, pressure,
  vibration
• Persons awareness of parts of body
  (_______________)
• Spatial perception and interrelationships
• Interprets sensory perceptions and sends
  information to thalamus and cortex

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Temporal Lobe Occipital Lobe

• Primary auditory receptive area
• ________________ area Auditory association
• Interpretive area At junction of temporal,
  parietal and frontal lobes
• Visual, auditory and olfactory perception and
  memory, learning, emotional affect

• Visual perception
• Visual association
• Some visual reflexes and involuntary eye
  movements (smooth tracking of objects)

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Basal Ganglia (basal nuclei)

• Several masses of subcortical nuclei located deep
  in cerebral hemispheres, just above thalamus
• Like brakes in a car? control of movement
• Controls and facilitates learned and automatic
  movements
• Fine motor control, particularly of hands and
  lower extremities

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Diencephalon Thalamus

• Egg shaped masses of gray matter lying ventro
  medially in hemispheres
• Major relay center for sensory and other afferent
  input to cortex
• Divided into groups of nuclei responsible for
  various functions
• Plays a role in conscious pain awareness,
  consciousness, focusing attention, emotions,
  among other vital functions
• Helps control primitive responses

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Diencephalon Hypothalamus

• Located below thalamus
• Regulates ____________ and autonomic functions
• Controls
• Temperature monitors blood temp and sends
  afferent impulses to sweat glands, muscles, etc
• Water metabolism (_____)
• Hypophyseal secretion
• Visceral and somatic activities BP, HR,
  peristalsis, etc
• Visible physical emotional expression (blushing,
  clammy hands)

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Internal Capsule

• Part of white matter of cerebrum
• The point at which fibers coming from various
  portions of the cortex converge at brain stem and
  enter thalamus-hypothalamus region
• Crucial anatomical area

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Limbic System

• Located lateral to hypothalamus
• forms border around brain stem
• Made up of several structures
• Hippocampus, fornix, mammillary body, amagdala
• Controls biological rhythms, sexual behavior,
  emotions of fear and rage
• Helps balance extremes in emotion
• Essential for normal memory (hippocampus)

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Reticular Formation

• Nuclei from brainstem and portions of
  diencephalon
• Motor and sensory neurons providing information
  about muscle activity
• Continuous input to support body against gravity
• Vasomotor and respiratory control

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Reticular Activating System RAS

• Nuclei in spinal cord, brain stem, thalamus and
  hypothalamus
• Control sleep-wakefulness cycle, consciousness,
  focused attention
• Stimulation of brain stem portion will cause
  wakefulness
• Stimulation of thalamic portion adds cognition
  and cerebral cortical activity

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Brainstem

• Midbrain nuclei for pupillary reflexes, eye
  movements auditory reflexes
• Pons Respiratory center, 4th ventricle,
  reticular formation, nuclei of several cranial
  nerves
• Medulla rate and strength of heartbeat rate and
  strength of respirations sneezing, sucking,
  coughing, gagging, swallowing, vomiting, blood
  vessel diameter

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Cerebellum

• Located in posterior cranial fossa
• Coordinates muscular activity so movements are
  fluid
• Position sense
• Coordinates agonist and antagonist muscles
• Maintains muscle tone and equilibrium
• Fine movement
• Balance

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Protective Structures

• Cranium portion of skull covering brain
• Composed of 8 bones
• Lobes named for bones they lie under
• Meninges
• Three layers of tissue
• Provide protection, support, and nourishment to
  brain and spinal cord

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Dura Mater (Hard mother)

• Outermost layer
• 2 layers of inelastic membrane? space between
  bone and dura is potential space called
• ______________________ SPACE
• Falx cerebri between the two hemispheres
• Tentorium cerebelli between cerebrum and
  cerebellum
• Falx cerebelli between lobes of cerebellum
• Diaphragm sella over the sella tursica
  (pituitary)

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Arachnoid Mater

• Thin, delicate, elastic layer, covers entire
  brain
• Houses blood vessels of different sizes
• Space between dura and arachnoid called
  ________________ SPACE
• Pia Mater
• __________________________________________________
  __________________________________________________
  __________________________________________________
  ________
• Covers entire surface of brain, follows surface
  folds
• Space that separates arachnoid and pia called
  _____________________ SPACE ? CSF flow

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Ventricular System

• 4 fluid filled cavities within brain connect
  with each other and cord
• 2 lateral ventricles
• Cerebral hemispheres
• Third ventricle
• Walls made up of thalamus and hypothalamus
• Fourth ventricle
• Lies between cerebellum and
• medulla and pons

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Cerebrospinal Fluid (CSF)

• Clear, colorless fluid found within brain
• Surrounds brain and spinal cord
• Functions
• Cushions brain
• Allows fluid shifts from cranial cavity to spinal
  cavity
• Carries nutrients
• Produced by choroid plexus specialized structure
  in ventricles
• Approximately 400 500 ml/day
• Reabsorbed at same rate by arachnoid villi
• Approximately 150 ml in ventricular /
  subarachnoid system
• Provides valuable diagnostic information

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Flow of CSF

• Low pressure system 9-14 mmHG
• Choroid plexus? lateral ventricles? Foramen of
  Monro? Third Ventricle? Aqueduct of Sylvius?
  Fourth Ventricle? several foramen? subarachnoid
  space ? circulates around brain and spinal cord?
  reabsorbed into venous circulation through the
  arachnoid villi? protrusions of arachnoid
  primarily in the sagittal sinus

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Cerebral Blood Flow

• Anteriorly internal carotid arteries
• Divide into anterior and middle cerebral arteries
• Anterior 3/5 cerebrum
• Posteriorly vertebral arteries? join to form
  BASILAR artery
• Divides at midbrain to form posterior cerebral
  arteries
• Posterior 2/5 of cerebrum cerebellum and
  brainstem

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Cerebral Arteries

• Anterior Cerebral Artery
• Supplies anterior portion of brain frontal lobes
• Areas affected control thought, personality,
  motor movement especially of leg
• Middle Cerebral Artery
• Largest branch off internal carotid
• Areas affected sensory and motor for face,
  throat, hand and arm
• Dominant hemisphere motor speech receptive
  speech
• Most often occluded in stroke!!

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Circle of Willis

• Internal carotids branch
• 2 anterior cerebral arteries joined to each other
  by anterior communicating artery
• 2 posterior communicating arteries
• 2 posterior cerebral arteries

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Cerebral Venous Drainage

• Does NOT parallel its arterial supply
• Cerebellar and brain stem venous drainage DOES
  parallel
• Cerebral veins drain into dural sinuses formed
  between dural layers? (superior sagittal sinus
  transverse sinus) drain into internal jugular
  veins
• Decreased venous outflow can _____________
  intracranial pressure

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Blood Brain Barrier

• Structure of CNS capillaries different
• Junctions between endothelial cells very tight
• Solutes and water must pass through endothelial
  cells, NOT junctions
• Astrocytes form transport system
• Oxygen, glucose, other nutrients allowed to
  enter, waste products removed
• Excludes water soluble and ionized large
  molecules (most antibiotics)
• Allows _________ soluble substances
• Affects penetration of pharmaceutical substances
• Altered by trauma, cerebral edema, cerebral
  hypoxemia

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Vertebral Column and Spinal Cord

• 33 vertebrae (bones)
• 7 cervical
• 12 thoracic (each corresponds to a rib)
• 5 lumbar
• 5 sacral fused into one bone? sacrum
• 4 coccygeal fused into one bone? coccyx

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Spinal Cord

• Extension of the brain
• Contains white matter (nerve tracts) and grey
  matter (cell bodies)
• Covered with meninges bathed with CSF
• Carries sensory information TO and motor
  information FROM brain
• Cord actually extends from vertebral C1 to L1
• End of cord termed conus medullaris
• Thoracic nerves begin to elongate
• Lumbar and sacral nerves with very long roots
  which bundle together to form CAUDA EQUINA
  (horses tail)

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Spinal Cord

• Central H-shaped gray matter
• Dorsal (posterior) horns
• Sensory cell bodies and neuroglia
• Ventral (anterior) horns
• Motor neurons and neuroglia
• White matter- myelinated axons of sensory and
  motor nerves

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Sensory PathwaysAfferent UP Spine to Brain

• ANTERO-LATERAL SPINOTHALAMIC TRACT
• Pain and temperature
• Neuron 1 enters DORSAL HORN and synapses with 2
• IMMEDIATELY decussates to opposite side travel up
  to
• THALAMUS? synapses with 3? postcentral gyrus
• POSTERIOR COLUMNS
• Tactile, pressure, vibration, proprioception
• Neuron 1 sensory neuron enters dorsal root
  ganglia
• Axon travels length of cord to MEDULLA where they
  
• Synapse with Neuron 2? decussates
• Enter THALAMUS? synapses with neuron 3 processed
  to cortex

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Motor Pathways Voluntary

• Pyramidal (voluntary) or Extra-pyramidal
  (involuntary) tracts
• Older terms delineated motor tracts by how fibers
  passed through pyramids of medulla
• PYRAMIDAL (VOLUNTARY)
• Corticospinal, corticobulbar ? brain to cord
• Consists of two groups of neurons
• Upper motor neuron (UMN)
• Located in the motor cortex, cerebellum, brain
  stem (CNS)
• Lower motor neurons (LMN)
• Located in CNS and PNS

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Voluntary Motor Neurons

• UMN ? Impulses travel from MOTOR CORTEX, through
  the INTERNAL CAPSULE? MEDULLA? DECUSSATION?SPINAL
  CORD? ANTERIOR HORNS? synapse with LMN (lower
  motor neuron)?SPINAL NERVES? peripheral muscle
• Smeltzer Bare p 1832
• Table 60-4
• Comparison of UMN and LMN lesions

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Motor Pathways Involuntary

• EXTRA-PYRAMIDAL (INVOLUNTARY)
• Vestibulospinal, Reticulospinal, Rubrospinal
• Originate in midbrain, pons, medulla
• Impulses travel from UMN in pre-motor area? PONS?
  DECUSSATION? down SPINAL CORD?ANTERIOR HORNS?
  LMN? muscle
• Autonomic nervous system activity smooth muscle
  and glands
• Integration of movements to maintain posture

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REFLEX Response

• Ability of nervous system to respond to stimuli
  from environment without brain involvement
• Simple reflex arc requires
• Stimulus? sensory neuron? dorsal root ganglion?
  anterior horn? synapse with motor neuron? exits
  spine by ventral root? effector muscle

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Reflex Response
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Reflex Responses

• Usual effect on the reflexes by UMN from the
  cortex are INHIBITORY (overall effect)
• If UMN are diseased, will see hyperactive
  reflexes spasticity
• If cord damage, may see hyperactive reflexes
  below level of injury
• Decreased or absent reflexes indicate a disorder
  of the LMN or anterior horn of the spinal cord at
  level of reflex

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Spinal Nerves

• Mixed Have an afferent (dorsal sensory) root and
  an efferent (ventral motor) root
• 31 pairs
• 8 cervical (C1-C8)
• 12 thoracic
• 5 lumbar, 5 sacral, 1 coccygeal
• Lumbosacral nerves ? very long roots travel down
  vertebral column to exit at appropriate formina
• Actual cord level stops at L1

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Spinal Nerves

• 8 cervical
• C1 exits above C1 vertebra
• C2 exits below C1 vertebra
• C3 exits below C2 vertebra or ABOVE C3
• C4 exits ABOVE C4
• C8 exits ABOVE T1
• Exit below the corresponding vertebrae
• 12 thoracic
• T1 Exits below T1
• 5 lumbar
• 5 sacral

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Nerve Plexus

• Spinal nerves split into anterior rami and
  posterior rami
• Anterior rami form plexi networks of nerve
  fibers that branch into peripheral nerves
• Brachial Plexus C5-C8, T1
• Arms, wrists, hands
• Lumbar plexus L2-L4
• Anterior lower body
• Sacral Plexus L5-S5
• Posterior lower body

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Dermatomes Specific areas of skin innervation
at various spinal cord segments
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Cranial Nerves

• 12 pairs (CN I XII)
• Transmit MOTOR or SENSORY or BOTH between brain
  or brainstem and head and neck
• ALL cranial nerves except for CN I and CN II exit
  from the mid-brain, pons, or medulla
• Table 60-2 p 1828

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Autonomic Nervous System

• Efferent System
• Ennervates all internal organs, smooth muscle,
  glands
• Carries messages from endocrine system and brain
  stem
• Two Major Divisions
• Sympathetic exit between T1 to L2 ?thoracolumbar
• Parasympathetic exit with cranial nerves from
  mid-brain and medulla and with nerves from S2-S4
  ? craniosacral

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Pre-ganglionic and Post-ganglionic Neurons

• Neurons in the ANS synapse OUTSIDE of CNS in a
  ganglion
• Pre-ganglionic neuron leaves brainstem or spinal
  cord area? myelinated axon travels to ganglia
  where it synapses and releases acetylcholine
• Postganglionic neuron cell body in ganglion?
  UNMYELINATED axon leaves ganglion and travels to
  effector tissue
• Location of ganglion and neurotransmitter
  released at effector tissue depends on whether it
  is parasympathetic or sympathetic

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Sympathetic Nervous System

• Sympathetic ganglion near cord
• Sympathetic chain contain
• postganglionic neurons
• Some pre-ganglionic axons terminate at adrenal
  medulla? epinephrine released
• Physiologic effects FIGHT OR FLIGHT
• Increased BP, increased blood flow to skeletal
  muscles, increased heart rate, increased
  respiratory rate, bronchiolar dilatation,
  pupillary dilatation
• Primary neurotransmitter of POST-GANGLIONIC
  neurons norepinephrine

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Parasympathetic Nervous System

• Physiologic effect Maintenance of body function
• Reduces HR, reduces contractility and
  conductivity
• Decreased RR, increased bronchiolar constriction
• Increased GI tone with sphincter relaxation
• Vasodilation of external genitalia
• Pupil constriction
• Table 60-3 p 1830
• Main neurotransmitter at both pre-ganglionic and
  post-ganglionic synapses ACETYLCHOLINE