Neurophysiology

1.Hearing

-Unlike other sensory systems, the central auditory pathways have bilateral representation of

sounds (sound from 1 ear reaches auditory cortex in both hemispheres).

-Pathway

-first neruons in spiral ganglion synapse in cochlear nucleus

-second neurons synapse bilaterally in superior olivary nuclei

-third neurons travel in the lateral lemniscus to synapse in the inferior colliculus

-fourth neurons then synapse in the medial geniculate nucleus

-the fibers then go to the transverse temporal gyrus of the cortex

-Conduction and nerve deafness

-Weber test (forehead)

-lateralizes to the affected ear with conduction deafness and to the unaffected

ear with nerve deafness

-Rinne test (mastoid process)

-distinguishes between better bone or air conduction of sound

2. Extraocular muscles

-Movements and innervation

-Medial Rectus – CN III – adduction (in)

-Superior Rectus – CN III – elevation (after abduction) (up)

-Inferior rectus – CN III – depression (after abduction) (down)

-Inferior oblique – CN III – elevation and adduction (up and in)

-Superior oblique – CN IV – depression and adduction (down and out)

-Lateral rectus – CN VI – abduction (out)

-Lesions

-CN III – eye turned down and out, ptosis, mydriasis

-CN IV – eye slightly up and in – diplopia going down stairs – tilting head away from the

affected side to correct the diplopia

-CN VI – eye deviates medially (abductor paralysis)

3. Chemical synapse, neurotransmitters, receptors, second messengers, effects

-Chemical synapse (BRS phys pg. 13-14)

-Presynaptic cell

-action potential – depolarization of presynaptic terminal – Ca2+ enters

presynaptic terminal – release of neurotransmitter into cleft

-Postsynaptic cell

-neurotransmitter binds to receptors causing a change in permeability to ion

-inhibitory neurotransmitters hyperpolarize – excitatory depolarize

-Receptor types (BRS phys pg.35-38)

-alpha 1 receptors – excitatory – epi and norepi – IP3 and increase intracellular Ca2+

-alpha 2 receptors – inhibatory – inhibit adenylate cyclase and decrease cAMP

-beta 1 receptors – excitatory – epi and norepi – activate adenylate cylcase – cAMP

-beta 2 receptors – relaxation – epi and norepi – activate adenylate cyclase – cAMP

4. Blood supply to brain

-Embolism – most frequently to middle cerebral artery leading to contralateral paralysis,

motor defects, sensory defects, aphasias

-Thrombosis – from atherosclerosis of carotids, vertebral and basilar aa., and middle cerebral aa.

-Hemorrhage – hypertension and coagulation disorders – most often in basal ganglia, pons,

frontal lobe, cerebellum

5. Basal Ganglia (globus pallidus, caudate, putamen)

-initiation of voluntary movements and control of postural adjustments

-Pathology of the basal ganglia

-Negative signs: akinesia, bradydinesia, abnormal postural adjustments

-Positive signs (dyskinesia at rest): hypertonicity (rigidity), tremors, chorea, athetosis,

ballismus

-Huntington disease – degeneration of striatal neurons (putamen and caudate)

-Parkinson disease – degeneration of the dopamine neurons in the substantia nigra

-Tardive dyskinesia – exposure to manganese and drugs – hypersensitivity to dopamine agonists

-Hemiballismus – lesions in contralateral subthalamic nucleus

6. Pituitary associations

-Optic chiasm sits on top of pituitary – bilateral hemianopsia

-Sits in the sella turcica - local pressure effects hypopatuitarism

7.Brain MRI and CT

-Abcess or cysticercosis CT and MRI – ring enhancing lesion

-Multiple sclerosis MRI – multiple focal areas of demyelination (plaques) in brain and spinal cord

-Huntington’s disease – atrophy of the caudate nucleus, putamen, and frontal cortex – looks like

ventricles have enlarged

8. Pupillary light reflex - doesn’t involve cortex

-Direct response – afferent pathway is optic nerve of eye tested – efferent pathway is CN III

to the eye tested

-Consensual response – afferent pathway is optic nerve of eye tested – efferent pathway is

CN III of opposite eye

-Accomodation – pupils constrict, eyes converge, lense more convex – depends on CN III

and visual association cortex

Category: Physiology Notes