Neuro Pathophysiology
What is the flexor reflex?
Autonomic withdrawal of a body part from a painful stimuli
What are the two types of synapses?
Chemical (use a neurotransmitter, MC, excitatory/inhibitory capabilities) Electrical (current passes through gap junctions)
What is hyperpolarization? Hypopolarization? What will hyperkalemia cause?
-Further decrease in resting potential (decreased likelihood of action potential) -Increase in resting potential (increased likelihood of action potential) -Hypopolarization (resulting in muscle weakness and impaired cardiac contractility
What is a motor unit? What are lower motor neurons?
-Group of muscle fibers that is innervated by one nerve and all fibers fire at once if stimulated -Nerve cells that control the motor unit exit the spinal cord through the ventral horn
What are free nerve endings? Meissner corpuscles? Pacinian corpuscles? Hair follicle end organs? Ruffini end organs?
-Detect touch and pressure -Nonhairy skin, light touch -Immediately beneath the skin and deep tissue, stimulated by rapid movements of tissues -detect movement on the body surface -skin and deep structures including joints (heavy continuous touch and pressure)
What is acuity? Tactile sensation? Where are tactile sensations located?
-How well the nerves can tell the difference between stimuli -Skin and tissues beneath the skin and pressure from deformation in deeper tissues
What are the types of stimulation of nociceptors? What are the two types of pain? What are the two types of fibers in nociceptors?
-Mechanical, thermal, chemical -Nociceptive (stimuli that cause or are close to causing injury), neuropathic (pain caused by disorder in neurologic system) -A and C
Where do 90% of the axons in the corticospinal tract cross? Where do 10% of uncrossed fibers descend down the ventral column cross?
-Midline at the junction of the medulla and spinal cord -Cervical spine
What is saltatory conduction? How well will a nerve fire if there is a large fiber diameter compared to a small? Types of nerve fiber classifications?
-Myelin sheath acts as insulation, AP has to jump from one node of ranvier to the next (propagate much faster with myelin) -Faster -A (large diameter in sensory and skeletal muscle functions), B and C (medium and small diameter in the ANS)
What are the two tracts that pain travels up? Where to?
-Neospinothalamic (faster conducting, sharp-fast pain) -Paleospinothalamic (slower conducting, diffuse/dull/aching unpleasant sensations, travel to limbic system (emotional aspect) and arousal to painful response (increased HR, BP))
What is ACh? Clinical relevance?
-Nicotinic (excitatory, direct action)/muscarinic (excitatory or inhibitory with indirect action via 2nd messengers) receptors -ACh esterase blocked by nerve gas and organophosphate insecticides (tetanic muscle spasms), release inhibited by botulinum toxin, inhibited by atropine
What are the excitatory postsynaptic potentials? Inhibitory?
-Occurs when a release of a neurotransmitter causes depolarization of the post synaptic membrane -Occurs when a release of a neurotransmitter causes hyperpolarization of the post synaptic membrane
What are the neuroglial cells? What do they do?
-Oligodendrocytes (form myelin), astrocytes (most abundant, maintain structural interactions), microglia (small phagocytes), ependymal cells (form lining of ventricular system) -Provide neuron support/protection, regulate blood flow, segregate neurons into compartments
What are the three components of the synapse?
-Presynaptic terminal (secrete neurotransmitters in response to an AP) -Synaptic cleft (secreted neurotransmitters into synaptic cleft, where neurotransmitters are broken down by enzymes) -Postsynaptic membranes (membrane bound receptors respond to neurotransmitter)
What are the three ways sensory info can interact with ascending neural pathways? What is used for discriminative pathways? How many neurons for transmission? What is the discriminate pathway responsible for?
-Reflex arc, discriminative pathway, anterolateral pathway -Rapid transmission of sensory information -3 (Primary dorsal root ganglion, dorsal column neuron, thalamic neuron) -Two point discrimination, sterognosis, spatial orientation
Tell me about the anterolateral pathway (spinothalamic pathway)
-Slow conducting** -Transmission of pain, thermal, crude touch, pressure that doesn't require discrete localization or fine discrimination -Fibers cross in anterior commissure within a few segments of origin of opposite anterolateral pathway -Nerve fibers give off numerous projection to the thalamus and reticular activating system (increase wakefulness, generalized startle rxn)
How are reflexes categorized? What are the components of a reflex arc?
-Somatic (activates skeletal muscles), autonomic (visceral) -1. receptor, sensory neuron, integration center, motor neuron, effector
What is pain?
-unpleasant sensory and emotional experience associated with actual or potential tissue damage
What rules out peripheral nerve dz, disorders of the dorsal root ganglion, dz of the neuromuscular junction and severe muscle dz?
Normal response to sharp sensation applied to the sole of the foot (withdrawal reflex)
What are the spinal reflexes?
Stretch reflex, Tendon reflex, Flexor withdrawal reflex, Crossed extensor reflex, Muscle tone
What are the three neurotransmitters involved in the pain response in the spinal cord?
Substance P (released by C fibers in dorsal horn) Glutamate NE
What does the somatosensory component of the nervous system provide an awareness of?
Touch Temperature Proprioception (body position) Pain * receptors located in skin, muscle, tendons, joints
Where are flexor and crossed-extensor reflex are coupled?
Weight bearing extremities
How much of the cardiac output does the NS receive? O2? What is the major fuel source? What occurs almost immediately after cardiac arrest?
-15-20% -20% -Glucose -Unconsciousness
How many pairs of spinal nerves are there? Breakdown of each section of spine?
-31 -8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccyxgeal
What is glutamate? Clinical significance?
-Amino acid, excitatory with direct action) -Important in learning and memory, stroke neurotransmitter (>80X higher in strokes), neuronal death, alcohol inhibits glutamate excitation)
What is GABA? Clinical significance?
-Amino acid, generally an inhibitory compound, direct/indirect actions) -Presynaptic inhibition at axon synapses, augmented by ETOH, benzos, barbituates, if blocked, can induce convulsions)
What is dopamine? Clinical relevance?
-Biogenic amine, excitatory or inhibitory with 2nd messenger -Feel good, enhanced by L-dopa and amphetamines, reuptake blocked by cocaine, deficient in parkinson's, neurotransmission increased in schizophrenia
What is histamine? Clinical relevance?
-Biogenic amine, excitatory or inhibitory with 2nd messenger -Involved in wakefulness, appetite control, learning/memory, first gen antihistamines cross BBB, can cause impaired school performance, and have anti-ACh effects
What is serotonin? Clinical relevance?
-Biogenic amine, mainly inhibitory and action via 2nd messenger -Role in sleep, appetite, nausea, migraine, mood, drugs that block uptake relieve anxiety/depression (SSRIs), LSD blocks serotonin, enhanced by ecstasy
What is NE? Clinical relevance?
-Biologic amine, excitatory or inhibitory with indirect action via second messenger -feel good neurotransmitter (enhanced by amphetamines), removal from synapse inhibited by TCAs and cocaine, brain levels reduced by reserpine (HTN drug, causes depression), shock management
What are the 3 receptor types with regards to thermal sensation? 2 proprioceptive receptors? What does the info for proprioception travel on?
-Cold (50-104), warm (90-118), pain (>118 or <50) -Muscle spindle receptors, golgi tendon organs -Discriminative pathway
What are the four major types of sensation? What is a sensory unit? Are the three types of nerve fibers myelinated or unmyelinated and fast or slow conduction?
-Stimulus discrimination, tactile sensation, thermal sensation, position sensation -Cell body located her, peripheral branch innervate small branches in the periphery, central axon projects to CNS -A (myelinated, fast, touch/temp/pain/mech), B (myelinated, fast, convey cutaneous/subQ mechanoreceptors), C (unmyelinated, slow, warm-hot sensation, pain)
What happens when stretch is applied to a muscle? What happens when there is tension on the tendon?
-Stretch reflex (prevent further stretching) -Tendon reflex (reflexive relaxation of muscle and contraction of antagonistic muscle) **prevent legs from buckling when standing and maintaining muscle tone
At what point does sensory info begin to enter consciousness? What transmits info from the thalamus to the somatosensory cortex?
-Thalamus -Third-order neurons
What needs to be reached in order for depolarization to occur? What is repolarization? What are the two parts of refractory periods?
-Threshold (opens Na+ voltage gated channels allowing Na+ into the cell) -Na+ channels close, K+ channels open (K+ exits cell) -Absolute (cannot fire at this moment) -Relative (requires stronger than normal stimulus to fire)
What channels regulate the ion channels? What are the three phases of action potentials? What is the resting state voltage? What is more abundant outside of the cell?
-Voltage and ligand gated channels -Resting, depolarization, repolarization - -70 mV -Na+ and Cl-
What are pathologic upper motor neuron findings? Pathologic lower motor neuron findings?
-Weakness with slowness, hyperreflexia, atrophy (over time), tone increased (spasticity), no fasciculations -Weakness, hyporeflexia, atrophy, tone decreased, fasciculations
What are schwann cells? Satellite cells?
-Wrap around axon and have gaps between form fluid gaps called nodes of ranvier -Secrete basement membrane that protects cell body of neurons in the PNS
What are the four parts of the brain that are part of the organization of movement?
Motor cortex (highest level of motor function) Cerebellum and basal ganglia (smooth movement and posture) Brain stem (medial pathway (basic postural control) and lateral pathway (goal-directed movements) Spinal cord (neuronal circuits for reflex)
