Neurophysiology Flashcards
What is the central nervous system composed of?
Brain and Spinal Cord
What is the peripheral nervous system composed of?
Spinal Nerves and Cranial Nerves (except cranial nerve II)
What is the tract that connects the hemispheres of the brain?
Corpus callosum; principle means of communication between two hemishpheres
What are the three components of the brain stem?
Midbrain, Pons, Medulla oblongota
What are the 3 layers of the meninges in the brain?
- Dura mater- thick, tough collagenous. Venous sinuses filled with venous blood from the cerebral veins are located between the dura layers
- Arachnoid layer- thin and semi-transparent, web-like. Strands of collagenous connective tissue stretch from arachnoid to pia mater =subarachnoid space
- Pia Mater- thin. Attached to brain and follows every sulcus and gyrus
What are the 3 layers of the spinal meninges?
(end at 2nd sacral vertebra)
- Spinal dura (1 layer)
- Spinal arachnoid- CSF filled subarachnoid space between arachnoid layer and pial lining
- Spinal Pia- much tougher/thicker than cerebral pia. Connects the cauda equina at the level of L1 and L2 to the caudal end of the spinal dural sheath where it is tethered to the end of the vertebral column (filum terminale)
Where does the spinal cord extend to?
1st and 2nd lumbar vertebra; the conus medullaris = large subarachnoid cistern (lumbar cistern). Where CSF samples usually obtained from
What is white matter?
The tracts of the brain and spinal cord made up of myelinated axons. Appear white d/t the lipid makeup of myelin
What is gray matter?
Contains the cell bodies, dendrites and axon terminals of neurons in the brain and spinal cord
What is the organization of white and gray matter in the brain?
White matter tracts are on the inside and gray matter cell bodies are on the outside (cerebral cortex).
What is the organization of gray and white matter in the spinal cord?
White matter tracts are on the outside and gray matter cell bodies are on the inside
What are the protective structures of the CNS?
- Cranium
- Vertebra
- Meninges
- CSF
- BBB
What is CSF made by?
The choroid plexus located in the lateral and third ventricles
How is CSF reabsorbed?
- 150-175mls in circulation at a time
- Rest reabsorbed by arachnoid villi into the venous system via one way valves.
- Fluid in the venous sinus CANNOT flow into the subarachnoid space
How does hydrocephalus occur?
CSF production is independent of BP and intraventricular pressure. CSF will continue to be produced even when path of circulation or absorption is blocked.
What two arteries supply blood to the brain?
- Internal carotid arteries (anterior circulation)
2. Vertebral arteries (posterior circulation)
What is the ring of vessels that unites the anterior and posterior circulation at the base of the brain known as?
Circle of Willis
What are the large vascular channels, formed by folds in the dura, that cerebral veins drain into?
Sinuses
How does blood return to the heart from the brain?
From the sinuses, venous blood returns to the heart by way of the jugular veins
What is the BBB?
- Specialized tight junctions between the cells that line the CSF spaces and between the endothelial cells of brain capillaries prevent leakage of molecules through the spaces between the cells.
- Substances must move through these barrier cells to access the CNS
- Lipid soluble molecules move through more easily than water soluble (ions, nutrients, drugs, proteins, and other charged or polar substances are highly restricted.
The integrity of the BBB is maintained in part by CNS cells called:
Astrocytes
What is the CSF-brain barrier?
- Similar to BBB
- Ependymal cells that line the ventricles are tightly joined and regulate the movement of water soluble elements between the CSF and neurons
- These cells also remove unwanted substances from the CNS and secrete them into the CSF for removal by the venous system
Specialized function of the Occipital Lobe
Visual cortex and association areas
Specialized function of the Parietal Lobe
Somatosensory cortex and association areas
Specialized function of the Temporal Lobe
Hearing and equilibrium, emotion, and memory
Specialized function of the Frontal Lobe
Motor cortex and association areas, prefrontal cortex involved in complex thought, ethical behavior, and morality
Specialized function of Limbic Structures
Emotions, short-term memory, olfaction
Specialized function of the basal ganglia (large masses of gray matter that lie deep within the cerebral hemispheres)
Initiation and planning of learned motor activities
Specialized function of Broca (frontal lobe) and Wernicke (temporal lobe) areas
Interpretation and expression of language
Major lobes of the cerebrum (4)
- Frontal
- Parietal
- Occipital
- Temporal
What is the diencephalon?
Lies deep within the brain and forms connecting structures between the upper brainstem (midbrain) and the cerebral hemispheres.
Principle structures of the diencephalon (5):
- Thalamus
- Hypothalmus
- Pineal gland
- Epithalmus
- Ventral thalamus
The thalamus is:
- Principle receiving site and relay center for impulses traveling to the cerebral cortex from the spinal cord, cerebellum, and basal ganglia.
- Involved in executing motor activties
- Propagates the constant background electrical activity of brain (EEG)
- Necessary to maintain connection with brainstem reticular activating system to maintain conciousness
- Necessary to maintain limbic connection to express emotion, language, creativity, and complex thought.
The hypothalmus is:
- Located just beneath the thalamus on the floor of diencephalon
- Extends downward to form pituitary gland
- Posterior pituitary is an extension of the neuronal tissue of the hypothalmus
- Anterior pituitary is derived from glandular tissue
- Responsible for life-sustaining functions (CV, resp)
- Important regulatory center for ANS (sleep cycle, etc)
The epithalamus:
-contains the pineal gland; important to regulating circadian rhythms in response to light-dark cycles
The ventral thalamus:
-Contains the basal ganglia structure called the subthalmic nucleus
Where is the cerebellum located?
In the posterior fossa behind the pons, separated from the cerebrum by the tentorium cerebelli
What are main roles of the cerebellum?
- Coordinate and smooth movements and to maintain posture and balance.
- Receives info from proprioceptors in muscles and joints and from the vestibular apparatus in the inner ear about the position of the head in space.
- Some of the fastest-conducting neurons in the nervous system are involved in relaying this information
Where is the brain stem located?
Between the upper spinal cord and diencephalon
What does the brain stem do?
- Transmits impulses between the brain and spinal cord.
- Vital centers for regulating resp and CV function are located in the medulla and the pons
- 10 of the 12 cranial nerves originate from the nuclei in the brainstem
What is the general organization of the PNS?
Two Divisions:
- Sensory (afferent)
a. somatic sensory
b. visceral sensory - Motor (efferent)
a. Somatic Nervous System
b. Autonomic Nervous System (Parasympathetic and Sympathetic)
Sympathetic NS Innervation:
- ‘Fight or Flight’
- Neurons arise in thoracic, lumbar regions
- SHORT pre-ganglionic, LONG post-ganglionic neurons
- Neurotransmitters: Acetylcholine (cholinergic)- pre and post-ganglionic sweat glands; NE (adrenergic)
- Receptors: Adrenergic (a1, a2, B1, B2, D1, D2); Muscarinic (sweat); Nicotinic
Neurotransmitter of pre-ganglionic neurons and receptor of the Sympathetic NS:
Acetylcholine (at nicotinic receptors)
Neurotransmitter released by post-ganglionic neurons and receptor of the Sympathetic NS:
Norepinephrine (at alpha and beta adrenergic receptors)
Parasympathetic NS Innervation:
- ‘Rest and Digest’
- Neurons arise in cranial, sacral regions
- LONG pre-ganglionic and SHORT post ganglionic neurons
- Neurotransmitters: Acetylcholine (cholinergic)-pre and post ganglionic
- Receptors: Nicotinic (pre) and Muscarinic (post)
Neurotransmitter of pre-ganglionic neurons and their receptors of the Parasympathetic NS:
Acetylcholine (at nicotinic receptors)
Neurotransmitter of post-ganglionic neurons and their receptors of the Parasympathetic NS:
Acetylcholine (at muscarinic receptors)
Describe descending or efferent motor pathways:
Motor pathways that are initiated in the brain to the spinal cord and terminate in muscled, glands, etc.
Describe ascending or afferent sensory pathways:
Sensory pathways that begin in the periphery and terminate in the brain (thalamus)
Basic structure of a neuron:
- Cell body with nucleus
- Dendrites (receive signals and conduct them to cell body)
- Axon (generates and conducts action potentials)
Describe the flow of information from one neuron to another or from one neuron to a structural target:
- Reception
- Transmission
- Integration
- Conduction
- > Neuron, muscle, gland, adipose tissue, glia (structural target)
Structural classes of Neurons(3):
- Multipolar- large number of dendrites extending from cell body and one axon; most common
- Bipolar- only on dendrite and one axon extending from cell body
- Unipolar- Single process from cell body that splits to form a dendrite and an axon
Functional classes of Neurons (3):
- Efferent/motor neurons (multipolar)
- Interneuron (bipolar; CNS/sp cord)
- Afferent/ sensory neurons (unipolar; spinal cord)
What does the Nernst Equation calculate?
It quantifies the membrane potential by calculating the equilibrium potential for an ion based on the charge of the ion and its concentration gradient across the membrane.
What happens when a cell reaches it’s membrane potential?
Voltage gated channels open and the Na+ ions move into the cell, making it more positive (depolarization)
What happens during repolarization of a cell?
Na+ gates close and K+ voltage gates open causing K+ to move out of the cell making it more negative
What happens during hyperpolarization of a cell?
The cell becomes too negative because the K+ channels releasing positive ions into the extracellular fluid are slow to close. Once K+ channels close the cell settles at its resting membrane potential.
What are the steps of an Action Potential?
- Initiation
- Summation
- Conduction
- Transmission
What channels are involved in the steps of an action potential?
- Leak channels: K and Na
- Na/K ATPase
- Voltage gated channels (VGKC, VGNaC)
What area of the neuron must reach -55 in order for summation of the action potential to start?
The axon hillock
To optimize speed of conduction (2):
- Lower resistance (widen diameter of axon)
2. Insulation (more myelin=increased speed of conduction)
Where in myelinated neurons are action potential generated?
nodes of Ranvier (allow impulse to hop from node to node down axon=saltatory conduction)
What is the neuronal synapse?
The point at which the axon from one neuron touches the next neuron. The point of transmission.
Explain the chemical subtype of message transfer at the synapse.
Most common. An action potential coming down the axon as an electrical signal and is converted to a chemical signal via synaptic vesicles. These vesicles dump chemicals into the synaptic cleft and signal is translated into electrical signal in post synapse.
Explain the electrical subtype of message transfer at the synapse
An action potential moves through the channels to the post synapse as electrical signal. Some of signal is lost causing a smaller potential; needs summation to continue on.
When are neurotransmitters released from vesicles docked on membrane of pre synaptic neuron?
When Ca increases enough neurotransmitters are released and target specific receptors on the post synapse
What are the 4 major classes of neurotransmitters?
- Acetylcholine
- Amino Acids (3G’s, fast acting)
- Monamines (emotions; amines+epi and norepi)
- Peptides
What are the primary modes of neurotransmitter elimination at the synapse? (3)
- Diffusion
- Enzymatic degradation
- Reuptake
Regeneration of nerves occurs primarily in the _____.
PNS; limited to myelin fibers
Ex. Nerve regeneration following Guillian-Barre but NOT MS (affects secondary to CNS damage therefore cannot regenerate)
Which spinal cord pathways go UP?
Afferent (sensory) pathways go up to the brain
Which spinal cord pathways go DOWN?
Efferent (motor) pathways go down to the periphery
Where does each spinal cord pathway cross over?
At the level of the medulla
How many neurons are involved in each pathway?
2 motor
3 sensory
Describe the 3 Ascending/Sensory Tracts and their functions:
- Spinothalmic- temperature, pressure, pain, light tough
- Dorsal Column- proprioception, deep pressure, vibration
- Spinocerebellar- proprioception
Describe the 2 Descending/Motor Tracts and their functions:
- Pyramidal/corticospinal- skeletal muscle tone, voluntary muscle movement
- Extrapyramidal- skeletal muscle activity (balance and posture), autonomic and gross movement
What are some adult risk factors for stroke?
- HTN
- Cigarette smoking
- DM/insulin resistance
- Impaired cardiac function
- Afib
- Polycythemia and thrombocytopenia
- Elevated blood lipoprotein
- Hyperhomocysteinemia
- Chlamydia pneumoniae
What are some pediatric risk factors for stroke?
- Congenital cardiac disease
- Sickle cell
- Arterial dissection
- Prothrombotic d/s
- MoyaMoya disease
- Head and neck trauma
CVA/stroke classifications:
- Ischemic
a. Thrombotic
b. Embolic
c. Lacunar - Global hypoperfusion
- Hemorrhagic
What primarily regulates blood flow to the brain?
CO2
How do CNS tumors differ from other tumors?
-Do not metastasize as readily as tumors in other organs BUT 25% of patients with other cancers develop mets to the brain
CNS tumors in pediatrics:
- 2nd most common group of tumor
- 70% are located infratentorially (cerebellum)
CNS tumors in adults:
- 70-75% located supratentorially (cerebrum)
- Incidence decreased after age 70
What are the cardinal signs of a CNS infection?
Fever, head or spine pain, and generalized neurologic dysfunction.
Types of Meningitis (4):
Infection of the meninges (coating of brain/spinal cord)
- **Bacterial
- Aseptic (viral, nonpurulent lymphocytic)
- Fungal
- Tubercular
S/s of meningitis:
- Inflammation and irritation
- Local tissue dysfunction
- Mass effect
- Vascular compromise
What is encephalitis and what most commonly causes it?
Acute febrile illness, usually of viral origin with nervous system involvement
Most commonly caused by arthropodborne viruses (transmitted by arthropod bite; ie-Lyme disease) and herpes simplex virus.
Which demographic is most at risk for bacterial meningitis?
-Sickle cell population, day care populations, college age students
Why are viral and bacterial meningitis treated the same?
Viral meningitis is treat with antibiotics until proved otherwise because bacterial meningitis is life-threatening.
Common organisms that cause bacterial meningitis in birth to 3mos
Group B Strep
Gram neg enteric bacilli
Listeria monocytogenes
Common organisms that cause bacterial meningitis in 3mos to 2yrs
Step pneumoniae
Neisseria meningitides
H. influeza type B
Common organisms that cause bacterial meningitis in 2 to 18yrs
Neisseria meningitudes
Strep pneumoniae
When does the posterior fontanel close?
3months
When does fibrous union occur?
6months
When does the anterior fontanel close?
12-24months
When does complete ossification happen?
8yrs
When are all cranial sutures completely fused?
12yrs
What two cranial deformities can limited brain development in the infant?
Microcephaly and craniostenosis
What is spinal shock and when does it occur?
- Occurs in complete or incomplete injuries of the spine
- Complete loss of function below the level of injury
- Can last from a few hours to weeks
S/s of spinal shock include:
Symptoms occurring below the level of injury
- Flaccid paralysis of all skeletal muscles
- Loss of all spinal reflexes
- Loss of pain, proprioception, and other sensations
- Bowel and bladder dysfunction w/paralytic ileus
- Loss of thermoregulation
What patients are at risk for developing autonomic dysreflexia?
- Chronic, ongoing complication of spinal cord injuries occurring at or above the T6 vertebra
- Potentially life-threatening and can occur any time after spinal shock as resolved.
What are the s/s of autonomic dysreflexia?
- HTN
- HA
- Bradycardia
- Upper-body flushing and lower body vasoconstriction
- Goosebumps (piloerection)
- Sweating
What is the stimulus that causes autonomic dysreflexia?
Activation of visceral or cutaneous pain receptors below the level of injury (ex- full bladder or constipation)
What is the pathophysiology of autonomic dysrelexia?
Stimulation of afferent pain receptors causes activation of sympathetic efferents in the cord and reflex vasoconstriction. Sustained activation of sympathetic neurons below the level of cord injury increased blood pressure significantly. The HTN initiates baroreceptor response, mediating inhibition of heart rate and vasodilation of vessels above the level of injury (upper body flushing). Descending signals from the brain cannot pass the cord injury so inhibition of sympathetic neurons below injury does not occur. BP can be dangerously high.
What are the initial clinical manifestations noted immediately after spinal cord injury
Loss of deep tendon reflexes and flaccid paralysis.
The _____ is a large network of neurons within the brainstem that is essential for maintaining wakefulness.
Reticular activating system
Mostly commonly motor paralysis and sensory impairment is _________ to the side of the brain in which the stroke occurs.
Contralateral
Ischemic stroke according to location of arterial blockage: Anterior cerebral.
Territory of Perfusion: Medial aspect of the frontal lobes
S/S: Contralateral hemiparesis, contralateral sensory loss, impaired cognition and decision making, aphasia(left-sided stroke), incontinence
Ischemic stroke according to location of arterial blockage: Middle cerebral
Territory of Perfusion: Most of lateral cerebral hemisphere, internal capsule, basal ganglia
S/S: Contralateral hemiplegia, contralateral sensory loss, aphasia (left sided stroke), homonymous hemianopsia, altered consciousness, neglect syndrome
Ischemic stroke according to location of arterial blockage: Posterior cerebral
Territory of Perfusion: Occipital lobe and medial aspect of temporal lobe.
S/S: Visual defects including homonymous central blindness and color blindness, memory impairment
Ischemic stroke according to location of arterial blockage: Basilar and vertebral
Territory of Perfusion: Thalamus, cerebellum, and brainstem
S/S: Sensory loss, mild hemiparesis, disturbances of gait, speech, swallowing, and vision
What demographic is most at risk for spinal injury from minor trauma?
Older adults/elderly
Pupillary changes related to stroke and injury are located on _______ to the site of injury
Ipsilateral (same side).
Alzheimer’s Disease:
- Cortical
- Altered breakdown and clearance (late onset) or altered processing and overproduction (early onset) of beta amyloid
- Extracellular beta amyloid plaques
- Hypophosphorylation of tau protein = intraceullular neurofibrillary tangles
**Inside brain:
The cortex, particularly the hippocampus-key to memory shrinks
Ventricles enlarge
Amyloid plagues cluster between neurons
Tangles (twisted proteins) found within neurons
Alzheimer’s s/s:
Cognitive: Memory loss and deterioration in thinking and planning functions
Physical: In mid-stage disease could include slowness, rigidity, and tremors
Parkinson’s Disease:
- Subcortical
- Degeneration of subcortical structures (basal ganglia and midbrain- substantia nigra’s pigmented dopamine neurons)
**Inside the brain: Cells shrink in the substantia nigra, where dopamine is produced Lewy bodies (clusters of alpha-synuclein protein) accumulate inside neurons
What is the leading cause of death in children 1-15yrs?
Brain tumors (infratentorial- medullablastomas, cerebellar astrocytomas, and brainstem gliomas)
What are 2 common Embryonal Tumors?
- Neuroblastoma=Aggressive; originating in neural crest cells that normally give rise to the sympathetic nervous system. Abdomen/lung. Diagnosis young (<5yrs)
- Retinoblastoma= Rare, congenital eye tumor. Unilateral. Acquired or autosomal dominant (RB1 TSG mutation). Prognosis excellent but may increase risk for other cancers
The physiologic mechanisms involved in pain phenomenon are_________ .
Nociception
What are the four stages of nociception?
- Transduction
- Transmission
- Perception
- Modulation
What happens during Transduction of pain?
** Nociceptor activation
Nociceptors transduce noxious stimuli into neuronal action potentials that progress centrally to the spinal card and the brain
What happens during Transmission of pain signal?
**Transfer of signals generated by nociceptors
Stimulated nociceptors transmit impulses to the CHS by means of specialized sensory fibers.
Explain the pathway which transmits a pain signal to the brain.
Nociceptors generate impulses along 1st order neurons-> dorsal horn of the spinal cord-> synapse with 2nd order neurons-> cross over to the contralateral side of spinal cord-> ascend lateral spinothalmic tract->synapse with 3rd order neurons at the thalamus-> somatosensory cortex
What type of stimuli can activate nociceptors?
Mechanical, chemical, thermal
What are the primary sensory fibers fibers involved in transmission of pain impulses?
A delta
C fibers
What type of pain do the large, mylenated A delta fibers transmit?
Acute pain: Sharp, well localized (fast)
What type of pain do the smaller, unmyelinated C fibers transmit?
Chronic pain: dull, aching pain, diffuse (slow)
What is a dermatome?
An area of skin in which sensory nerves derive from a single spinal nerve root
What are the four theories of pain modulation?
- Specificity
- Intensity
- Pattern
- Gate control
What is specificity theory?
There are specific nociceptors and pathways that when activated lead to specific pain
What is intensity theory?
Sensory receptors that when activated at low levels interpret innoculous stimuli (no pain) as impulse magnitude increased pain is increased
What is pattern theory?
A pattern of impulses that enter the CNS will determine whether stimulation is epicritic or noxious
What is gate control theory?
The capacity for interneurons in the spinal cord to modify the transmission of nociceptor impulses. Impulses can ‘close the gate’ on nociceptors impulses so that pain signals can be blocked in the spinal cord and not progress to the brain
What is the neuromatrix theory of pain?
Pain is an inter-related, multidisciplinary area and can be affected by: Social Culture Genetics Molecular Cellular Physiologic Body (organ) Psychosocial
What is referred pain?
Pain arising in one area being perceived in another area
-Areas of the spinal cord that innervated by visceral and somatic nociceptor tracts (particularly dermatomes) are inappropriately activated causing referred pain
Describe the response to treatment in patients with acute, chronic, and neuropathic pain?
acute- usually easily relieved
chronic- often unresponsive
neuropathic- often unresponsive
What are the most common locations for spinal cord injury and why?
C1-2, 4-7, and T1-L2. These are the most mobile parts of the spine.
