Lange 7 Flashcards
what does the resting membrane potential close to?
Ek because K+ is the major determinant of the charge difference across a membrane
when are neurotransmitters released?
Ca++ dependent exocytosis
inhibitory neurotransmitters and actions
GABA and glycine: open Cl- channels causing inhibitory postsynaptic potential
what happens when NE binds B-adrenergic receptors?
activates adenylyl cyclase and stimulates the production of cAMP which activates the cAMP-dependent protein kinase that can phosphorylate voltage-gated calcium channels
what are the alpha1-adrenergic, muscarinic cholinergic, and metabotropic glutamate receptors coupled to?
phospholipase C which catalyzes the hydrolysis of the membrane lipid phosphatidylinositol-4,5 bisphosphate causing two second messengers: 1,2 diacylglycerol (activates enzymes in protein kinase C family) and inositol-1,4,5 triphosphate (binds intracellular receptor that is a calcium ionophore allowing release of calcium from intracellular stores into cytosol)
astrocytes functions
- regulate K and Ca concentrations within the interstitial space
- provide structural and trophic support for neurons through production of extracellular matrix molecules such as laminin and release of growth factors
- provide sites for release of cytokines and chemoattractants at blood vessels during CNS injury
- respond to brain injury by increasing and size and sometimes number
- important role in terminating neuronal responses to glutamate
- contain glutamine synthase (converts glutamate to glutamine) - detoxifies CNS of glutamate and ammonia
microglia
reside in CNS functioning as main immune effector cells - activated by brain injury, infection, or neuronal degeneration
damage to the lower motor neurons results in what?
loss of all voluntary and reflex movement (flaccid weakness) and muscle tone or resistance to passive movement is reduced
describe the path of motor neurons from brain to muscle
begin in principal motor area (precentral gyrus) which can also receive input from premotor area -> converge in corona radiata -> posterior limb of internal capsule -> cerebral peduncles -> central pons -> ventral medulla -> cross in pyramidal tract where most dessucate -> lateral corticospinal tract
what are the extrapyramidal neurons?
neurons in the caudate nucleus, putamen, globus pallidus, red nuclei, subthalamic nuclei, substantia nigra, reticular nuclei, neurons of the cerebellum. they are connected to the motor corticospinal and corticobulbar tracts but distinct from these cortical motor (pyramidal) neurons
what is the purpose of extrapyramidal neurons?
important for complex patterns of movement and for coordinating motor responses to sensory stimuli
motor unit
each alpha motor neuron axon contacts up to 200 muscle fibers
what do tendon reflexes and muscle tone depend on?
activity of alpha motor neurons, specialized sensory receptors known as muscle spindles and small gamma motor neurons whose axons innervate the spindles
lambert-eaton syndrome
antibodies to calcium channels inhibit calcium entry into nerve terminal and reduce neurotransmitter release - repetitive nerve stimulation facilitates accumulation of calcium and increases Ach release
what causes a similar syndrome to lambert-eaton syndrome?
aminoglycoside antibiotics
botulin toxin
cleaves specific presynaptic proteins preventing neurotransmitter release at both neuromuscular and parasympathetic cholinergic synapses
when do fibrillations occur?
in denervated muscles - receptors are not clustered and are spread across the muscle membrane
what are the upper motor neurons?
cortical motor neurons that converge in the corona radiata then descend in the posterior limb of internal capsule, cerebral peduncles, ventral pons, and medulla
neurons that innervate lower facial muscles are what?
primarily crossed fibers
motor neurons for the legs are found where?
medial surface of the hemisphere (face on ventral end of the central sulcus)
unilateral upper motor neuron lesions are characteristic how?
muscles innervated by lower motor neurons that receive bilateral cortical input such as eyes, jaw, upper face, pharynx, larynx, neck, thorax, abdomen are spared
upper motor neuron lesions appear how?
characteristic pattern of limb weakness and change in tone - antigravity muscles become more active, arms flex, pronated posture, legs become extended while muscles that move limbs out of this posture (extensors or arms and flexors of legs) are weakened
-tone is increased in antigravity muscles “clasp knife phenomenon”
what is clonus? when is it present?
series of involuntary muscle contractions in response to passive stretch - upper motor neuron lesions especially with spinal cord
how to tell if a lesion is above or below the pons
above the pons: impair movements of contralateral lower face, arm and leg
below the pons: spare the face