Neurophysiology

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Neurophysiology

• Dean Arnaoutakis

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Organization

• Central Nervous System (CNS)
• Brain and spinal cord
• Neuron cell bodies form nuclei
• Neuron processes form tracts
• Peripheral Nervous System (PNS)
• Sensory System
• Sensory receptors, sensory nerves, and ganglia
  outside CNS
• Motor System
• Somatic Nervous System
• Autonomic Nervous System
• Neuron cell bodies form ganglia
• Neuron processes form nerves

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Neuron

• 1011 nerve cells in human brain
• 3 Regions
• Soma (cell body)
• Dendrites
• Extensions of the cell body that repeatedly
  divide
• Increase surface area for synaptic connections
• Axon
• Terminal end branches into numerous synaptic
  boutons
• Allows one neuron to make many contacts

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Neuron
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Supporting Cells of CNS

• Glial Cells
• Astrocytes
• Star-shaped cells
• Envelop capillaries forming the Blood-Brain
  Barrier
• Form scars after an injury
• Oligodendrocytes
• Produce myelin in CNS
• Microglia
• Become active due to inflammation or injury
• Phagocytose cellular debris

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Supporting Cells of PNS

• Schwann Cell
• Perform basic functions that are accomplished by
  3 types of glial cells in CNS

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CNS

• Spinal Cord
• Brain Stem
• Medulla, pons, and midbrain
• Cerebellum
• Diencephalon
• Thalamus and hypothalamus
• Cerebral Hemispheres
• Cerebral cortex, basal ganglia, hippocampus, and
  amygdala

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CNS
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CNS
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Spinal Cord

• Most caudal portion of CNS
• Extends from base of skull to first lumbar
  vertebra
• 31 pairs of spinal nerves
• Contain both sensory and motor nerves
• Ascending pathways
• Carry sensory info from periphery to higher
  levels of CNS
• Descending pathways
• Carry motor info from higher levels to motor
  nerves that innervate periphery

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Spinal Cord
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Brain Stem

• Medulla
• Rostral extension of spinal cord
• Regulates breathing and blood pressure
• Coordinates swallowing, coughing, and vomiting
• Pons
• Rostral to medulla
• Regulates breathing
• Relays messages from cerebral hemispheres to
  cerebellum
• Midbrain
• Rostral to pons
• Controls eye movements
• Relay center for auditory and visual systems

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Brain Stem
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Brain Stem
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Cerebellum

• Foliated structure attached to brain stem
• Lies dorsal to pons and medulla
• Coordinates and plans movement
• Maintains posture
• Coordinates head and eye movement

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Cerebellum
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Diencephalon

• Located between cerebral hemispheres and brain
  stem
• Thalamus
• Processes all sensory info going to cerebral
  cortex and most motor info coming from cortex to
  spinal cord
• Hypothalamus
• Ventral to thalamus
• Regulates body temperature, food intake, water
  balance
• Acts as endocrine glandsecretes hormones that
  regulate pituitary gland

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Diencephalon
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Cerebral Hemispheres

• Cerebral Cortex
• Convoluted surface
• Grooves sulci
• Ridges gyri
• 4 Lobes frontal, parietal, temporal, occipital
• Receives/processes sensory info and integrates
  motor functions

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Cerebral Hemispheres
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Cerebral Hemispheres

• 3 deep nuclei within hemispheres
• Basal Ganglia
• Receives input from cerebral cortex and project
  to frontal cortex
• Regulates movement
• Hippocampus
• Involved in memory
• Amygdala
• Involved with emotions

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Cerebral Hemispheres
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Sensory Systems

• Sensory (afferent) Neurons
• Brings info into nervous system using sensory
  receptors in periphery
• Visual, auditory, chemoreceptors, somatosensory
  (touch) receptors
• Afferent info ultimately is transmitted to
  cerebral cortex

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Somatic Nervous System

• Motor (Efferent) Neurons
• Carries info out of nervous system to periphery
• Controls skeletal muscle contraction and external
  sensory organs (skin)
• Voluntary because consciously control

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Autonomic Nervous System

• Set of efferent pathways from CNS that innervate
  smooth muscle, cardiac muscle, and glands
• 3 Major Divisions
• Sympathetic Nervous System
• Parasympathetic Nervous System
• Enteric Nervous System

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Autonomic Nervous System

• Composed of 2 neurons
• Preganglionic neuron
• Cell bodies in CNS and axons synapse in autonomic
  ganglia
• Postganglionic neuron
• Cell bodies in autonomic ganglia and synapse on
  effector organs (heart, blood vessels, glands)

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Autonomic Nervous System
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Parasympathetics

• Rest and Digest
• Preganglionic neurons are long so ganglia are
  in/near effector organ
• Both preganglionic and postganglionic neurons are
  cholinergic neurons
• Release Acetycholine (ACh) as neurotransmitter

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Sympathetics

• Fight or Flight
• Preganglionic neurons are short so ganglia are
  close to spinal cord
• Preganglionic neurons are cholinergic neurons
• Release ACh as neurotransmitter
• Postganglionic neurons are adrenergic neurons
• Release norepinephrine (NE) as neurotransmitter

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Parasympathetics vs Sympathetics
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Receptors in the ANS

• Cholinergic Receptors
• Nicotinic Receptors
• Located in autonomic ganglia (both sympathetic
  and parasympathetic) and neuromuscular junction
• Activated by ACh and produce excitation
• Muscarinic Receptors
• Located in heart, smooth muscle, and glands
• Activated by ACh
• Inhibitory in heart and excitatory in smooth
  muscle and glands (increase motility and
  secretions)

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Receptors in the ANS

• Adrenergic Receptors
• a1 Receptors
• Located in vascular smooth muscle of skin and
  splanchnic regions, GI/bladder
• Activated by NE and produce excitation
  (contraction/constriction)
• ß1 Receptors
• Located in SA node, AV node, and ventricular
  muscle
• Activated by Epi and NE and produce excitation (
  ? hr, ? contractility)
• ß2 Receptors
• Located in vascular smooth muscle of skeletal
  muscle, bronchial smooth muscle, and walls of
  GI/bladder
• Activated by Epi and NE and produce relaxation
  (dilate vessels, dilate bronchioles, relax
  bladder)

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Receptors in the ANS
 Branch  Type  Location Effect  Typical AgonistDrugs Typical Antagonist Drugs
 Sympathetic(adrenergic)  a1 Vascular arterioles of skin/GI,Sphincters of bladder/GI tract Constrict smooth muscle, Constrict sphincters NorepinephrineEpinephrine PhentolaminePrazosin
 Sympathetic(adrenergic)  ß1 Heart muscle Increase rate/contractility Norepinephrine Epinephrine Beta blockers Propranolol
 Sympathetic(adrenergic)  ß2 Bronchioles of lung, Arterioles of skeletal muscles Dilate smooth muscle EpinephrineIsoproteronolAlbuterol "Beta blockers"PropranololButoxamine
  Parasympathetic(cholinergic) Muscarinic Heart muscle,Sphincters of bladder/GI tract, Bronchioles of lung Decrease rate/contractility, Dilate sphincters, Constrict bronchioles AcetylcholineMuscarine Atropine
  Parasympathetic(cholinergic)   Nicotinic Neuromuscularjunctions,Autonomicganglia Depolarization AcetylcholineNicotine  Curare
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Meninges

• 3 connective tissue membranes that invest the
  brain and spinal cord
• Dura Mater
• Outermost tissue composed of 2 layers
• Periosteal layeradheres to inner surface of
  skull
• Meningeal layer
• Large venous sinuses form between these two
  layers
• Tough white fibrous connective tissue
• Arachnoid
• Located between dura and pia
• spidery layer where cerebrospinal fluid (CSF)
  percolates over brain
• Arachnoid granulations
• Pia Mater
• Closely covers surface of brain and spinal cord
• Delicate and highly vascular

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Meninges
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Meningeal Spaces

• Spinal Epidural Space
• Between vertebrae and dura
• Contain veins and lymphatics
• Can be injected with local anesthetic to produce
  paravertebral nerve block
• Cranial Epidural Space
• Potential space that contains arteries and veins

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Meningeal Spaces

• Subdural Space
• Potential space between dura and arachnoid
• Contains bridging veins
• Drain cerebral hemispheres en route to large
  venous sinuses (within two layers of dura)
• Subarachnoid Space
• CSF filled space
• Major arteries of brain travel within this space

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Meningeal Spaces
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Cerebrospinal Fluid

• Ventricles
• During development, 4 fluid-filled communicating
  cavities form within the brain
• Lined by ependymal cells and choroid plexus
• Produce CSF at a rate of 500 ml/day
• CSF exits 4th ventricle through a foramen to
  enter the subarachnoid space

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Cerebrospinal Fluid

• Clear, colorless, acellular fluid
• Functions
• Supports and cushions the CNS against concussive
  injury
• Removes waste products
• Circulation
• Flows from ventricles into subarachnoid space and
  enters dural venous sinuses via arachnoid
  granulations

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Cerebrospinal Fluid
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Blood-Brain Barrier

• Discovered by anatomists in 1800s when injected
  color dye into bloodstream
• All organs became stained except for the brain
• Endothelial cells forming most capillary walls
  are fenestrated
• Allows free passage of fluid and molecules
• In brain, capillary endothelial cells are linked
  by tight junctions forming BBB
• Protects brain from fluctuations in blood
  chemistry

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Blood-Brain Barrier
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Intracranial Mass Lesion

• Anything abnormal that occupies volume within the
  cranial vault
• Includes tumors, hemorrhage, edema, and other
  disorders
• Cause neurologic symptoms and signs due to
• Destruction of adjacent brain tissue
• Elevated intracranial pressure
• Displacement of brain structures into another
  compartment called herniation

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Elevated Intracranial Pressure

• Symptoms and signs
• Headache
• Altered mental status
• Nausea and vomiting
• Papilledemaengorgement of the optic disc
• Visual loss or Diplopia

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Brain Herniation Syndromes

• Transtentorial Herniation
• Herniate medial temporal lobe inferiorly through
  tentorial notch
• Ipsilateral Blown pupil (compress CN III),
  hemiplegia (compress descending motor tract), and
  coma (distort midbrain depresses consciousness)
• Tonsillar Herniation
• Cerebellar tonsils herniate downward through
  foramen magnum
• Respiratory arrest, blood pressure instability,
  and death (compress medulla)

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Brain Herniation Syndromes
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Intracranial Hemorrhage

• Epidural Hematoma (EDH)
• Rupture of middle meningeal artery due to
  fracture of temporal bone by trauma
• Rapidly expanding hemorrhage that can cause
  herniation
• Subdural Hematoma (SDH)
• Rupture of bridging veins due to shear injury
• Venous blood slowly collect
• Subarachnoid Hemorrhage (SAH)
• Rupture of arterial aneurysm causing worst
  headache of life
• Hypertension, smoking, alcohol are risk factors

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Neuro Case Chief Complaint

• At midnight, 51 year old man fell down stairs
  following a domestic altercation
• He was struck in the left temporal area and lost
  consciousness for 15 minutes
• When police and ambulance arrived, he was awake,
  smelled of alcohol, and was arrested
• Morning after spending the night in jail, he was
  unresponsive and thrashing incoherently
• He had vomited and defecated in the cell

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Neuro Case Test Results

• Unresponsive to commands and occasionally
  thrashed in stretcher
• Left pupil 5mm, fixed
• Right pupil 2mm, constricting to 1mm in response
  to light
• Right arm and right leg did not move
• CT scan was performed

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Neuro Case Test Results
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Neuro Case Diagnosis

• Patient suffered trauma to left temporal area
• Fracture of temporal bone can lacerate middle
  meningeal artery resulting in epidural hematoma
  causing left uncal herniation (transtentorial)
• Arterial bleed can cause rapid deterioration due
  to exapansion
• Impaired consciousness
• Lesion affecting midbrain
• Fixed, dilated left pupil
• Lesion involving left midbrain as CN III exits
  brainstem and travels to eye (affects
  parasympathetic fibers that cause pupillary
  constriction)
• Right-sided weakness
• Suggests motor neuron lesion on left side
  (descending pathway crosses to other side at
  junction of medulla and spinal cord)

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Neuro Case Treatment

• Immediately following CT scan, patient was taken
  to operating room
• En route, rapidly given mannitol and
  hyperventilated to reduce intracranial pressure
• In OR, craniotomy was performed, a large fresh
  clot of blood was evacuated, and middle meningeal
  artery was coagulated
• Patient gradually regained consciousness, ability
  to ambulate, and use of right hand