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46 Cards in this Set
- Front
- Back
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how is information transmitted between circuits? how are these circuits produced? what happens to unused circuits?
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info transmitted via action potentials.
most are produced from GENETIC instructions during embryonic and fetal development. unused circuits are dismantled unless maintained by activity dependent processes. (neurotrophic factors) |
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what are 'reflexes'? what are they composed of? what does an abnormal reflex indicate?
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reflexes are elementary units of fxn of the nervous system.
involve sensory neuron, motor neuron and one or more interneurons. abnormal indicates pathology along the circuit. |
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how are reflexes characterizied?
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somatic v. autonomic
visceral superficial v deep normal v pathologic cord/brain stem connection |
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what does a somatic reflex involve? autonomic? visceral?
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somatic: skeletal mm.
autonomic: rarely skeletal mm (smooth m or glands) visceral: BOTH. usually under some degree of conscious control. |
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how are superficial reflexes stimulated? what are deep reflexes?
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superficial: stimulate mucus membranes or skin (corneal, snout, rooting, suckling, abdominal, plantar, cremasteric and sphincter)
deep are stretch reflexes. |
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what occurs during development with regard to reflexes?
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the cerebral cortex begins to exert inhibition on various circuits in the brain stem and cord resulting in disappearance of reflexes in these areas.
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what is babinski's reflex an indication of?
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it's an infantile reflex which may indicate that damage exists to the cortical control mechanism.
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what type of reflex is the stretch reflex?
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it's segmental, meaning it activates AT it's spinal cord level.
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what type of reflex is 'intersegmental'?
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intersegmental means the action goes either above or below the cord level from where it was initiated.
it's a FLEXION WITHDRAWL action. |
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which cord level reflex has part of it's circuitry in the brain stem? what does it control?
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suprasegmental.
swallowing. |
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what do graded responses reflect?
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the intensity of the stimulus
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what is the local sign?
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it's a relationship between the site of stimulation and the particular muscles that contract.
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what are fixed action patterns?
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unlearned reflexive responses to complex environmental stimuli (smiling, grimaces, speech sounds, etc)
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what is the first level in a hierarchy of motor response?
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the SPINAL REFLEX. (huhgling jackson)
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describe the myotatic reflex. what types of mm does it occur in?
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myotatic probably operates to maintain mm tone and occurs when the mm is STRETCHED. (charles sherrington)
occurs in both flexors and extensors but esp anti-gravity mm. |
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which muscle spindle is involved in the myotatic reflex?
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muscle spindle 1A excites homonymous muscle and synergists monosynaptically.
a single 1A fiber may synapse on ALL ALPHA MOTOR NEURONS innervating the muscle (300) |
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how many inhibitory synaptic interactions may be involved in a myotatic reflex? describe them.
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two:
1.reciprocal inhibition: through excitation of an interneuron connected to antagonist mm. 2.recurrent inhibition: via RENSHAW cell excited by alpha motor neuron which in turn INHIBITS it. this DAMPENS the intensity and duration of the reflex. |
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what is the inverse myotatic reflex also known as? when does it occur?
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the 'clasp-knife' reflex. it occurs when 1B fibers from golgi tendon organs are stimulated.
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what is the fxn of the inverse myotatic reflex? describe it's action, requirements for elicitation and any additional components.
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it functions to dampen excessive tension by exciting antagonists and inhibiting homonymous mm.
it's action is via glycinergic interneurons. elicitation requires MORE TENSION than myotatic. has a crossed extensor component. |
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explain the hierarchical organization of a motor fxn.
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if two reflex pathways are simultaneously stimulated, one will take precendence over the other.
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how are flexor withdrawl reflexes mediated? what sort of movement is elicited?
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by skin and pain receptors.
ipsilateral flexion and contralateral extension. it functions to remove limb from potentially harmful stimulus and maintain balance. |
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what does the flexor withdrawl reflex resemble? why?
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resembles fixed action patter b/c a full blown response requires a certain threshold. it's a NON-LINEAR input-output relationship.
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which part of the body exhibits an opposite flexor withdrawl reflex?
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light touch to the foot pads may cause reflex EXTENSION (positive supporting reaction)
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how is local sign related to flexor withdrawl response?
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the final limb position is a function of the site of stimulus.
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why are withdrawl reflexes considered 'pre-potent'?
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they preempt spinal pathways from any other reflex activity taking place.
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where are somatic reflexes, coughing, sneezing and gagging located?
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they are integrated in the medulla.
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what nerves are induced to activity via irritation of nasal, tracheal, bronchial or esophageal mucosa? what can be said about their efferent fibers?
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glossopharyngeal and vagus. efferent fibers are mostly somatic.
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describe visceral reflexes?
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fibers from autonomic and somatic nervous system. usually under some degree of conscious control.
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describe the formation and circulation of CSF?
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it's secreted by the cell walls of the ventricles and by the choroid plexus (in ventricles).
lateral ventricles interventricular foramen 3rd ventricle cerebral aqueduct 4th ventricle medial and lateral apertures OUT to subarachnoid space crosses arachnoid villi into blood stream/lymphatics |
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what is a cistern?
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large areas of subarachnoid space
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how do the ventricles develop, ontogenically?
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the nueral tube is the original site of ventricles and central canal
neuraxis bends: bulges = reservoirs stenosis = passageways |
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where does the choroid plexus originate from?
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mesodermal cells growing down into neural fold and join ependymal cells from inner neural tube
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why are the lateral ventricles c-shaped?
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early growth of the lateral cerebral hemispheres in rostro-caudal direction.
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how does CSF differ from blood composition?
what is their relationship? |
there are 145 ccs of CSF. has elevated Mg++ and Cl-
lower K+, HCO3, Ca++, glucose lower protein and v.few blood cells blood and CSF are in osmotic equilibrium |
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what is the relationship between intracranial pressure and CSF?
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normal changes in blood brain volume are accompanied by surges in CSF movement from ventricles to subarachnoid space.
increased icp causes papilloedema and increased CSF in lumbar cistern. |
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when should you NOT do a lumbar puncture?
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increased ICP. could cause herniation of the cerebellum thru the formaen magnum. measure CSF via lumbar puncture using manometer.
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how is cranial perfusion pressure measured?
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ICP-MAP= CPP
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what causes brain edema and hydrocephalus?
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defects in CSF production, movement or removal (eg papilloma of choroid plexus secrete excess CSF).
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what causes communicating hydrocephalus?
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impaired excretion of CSF thru arachnoid villi
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what causes non-communicating hydrocephalus?
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stenosis of cerebral aqueduct or blockage of medial/lateral foramina.
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what causes vasogenic edema?
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increase in brain capillary endothelial cell permeability causing increase in extracellular fluid volume.
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what causes cytotoxic edema?
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cytotoxic edema is increased INTRA cellular volume due to failure of mechanisms removing Na+ from cells (ie inactive Na+ pump by hypoxia)
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what clinical info can be gained from CSF?
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more RBC: dz in brain or meninges
increased IgG: MS Myelin basic protein: demyelinating dz |
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what is cushing's reflex?
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with increased ICP, get increased BP (compressed blood vv in brainstem). not as much O2 is getting to sensors, that causes increase in BP.
bradycardia accompanies via baroreceptors detecting increased BP. |
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when will CSF composition approach that of blood plasma?
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BBB interruption via:
tumors in brain meningitis brief period of 'hyperosmolarity' to unzip the tight junctions of BBB (infuse inert carbs) |
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how is intracranial pressure measured?
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via sensors. intraventricular catheter inserted to frontal lobe into lateral ventricle.
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