Anatomy and physiology - Essay Example

Reflex Action On the Basis of Auditory and Visual Stimuli: Explanation of the Case Study The system worked on the principle that both the stimuli combined (summation of stimuli) produced the response. The auditory stimuli were transmitted by stimulating the basilar membrane of the internal ear which provoked response in the inner hair cells which produced glutamate as the neurotransmitter which acted on the dendrites of the bipolar auditory nerve (1st order neurons). There are glutamate receptors which causes opening of sodium channels causing depolarization and setting of action potential in the auditory nerve .

The action potential was carried from the auditory nerve to the vestibular nerve and vestibulocochlear nerves (2nd order neurons) to the cochlear nuclei. From here lateral lemniscuses column (3rd order neurons) go to the inferior colliculi and superior colliculi that also receives visual impulse and acts as an integration center to carry impulse to the primary auditory cortex of the CNS in the temporal lobe at Brodmann area 41 and 42. The visual pathway was carried from the eyes to the optic nerve to the visual cortex.

The afferent auditory neurons from the organ of corti (inner ear) and auditory cortex involves many synapses which are in the brain stem and medial geniculate body of thalamus. The brain stem causes the input for arousal and alertness. The thalamus sorts and relays signals upwards to generate the action in the individual (Purvez, 2012) (Janmey2007).To elicit the visual response signal transduction occurred in the rod cells to convert rhopodpsin into metarhodopsin which activated trasducin. Transducin blocked the sodium ions entry into the rods causing hyperpolarization which caused liberation of inhibitory neurotransmitter release from rods.

Thus the inhibition on the bipolar cells was lifted and they got stimulated to release glutamate. Glutamate acted on the ganglion cells and stimulated them that lead to activity in the optic nerve (1st order neurons). The optic nerve is the IInd Cranial nerve and criss -cross at the optic chiasm and reaches the lateral geniculate nucleus from where impulse go to the primary visual cortex which is the Brodmann Area 17, 18 and 19 through the optic radiations( 2nd order neurons) Further as the individual was under stress the hypothalamic locus ceruleus system got activated to release nor epinephrine that was responsible for flight or fight response (getting into action) (Purvez, 2012) (Janmey2007).

The reaction starts in the amygdala which stimulates hypothalamus, which cause release of ACTH from pituitary on one hand and stimulates sympathetic nervous system which releases acetylcholine from preganglionic neurons and acts on Ach receptors on adrenal medulla (chromaffin cells, which are actually considered the post ganglionic neurons)to release adrenaline. The liberate adrenaline cause disinhibition of spinal reflexes for movement and liberates metabolic energy for muscle contraction.Actually all the three systems acted as a polysynaptic reflex arc where all the three stimuli caused generation of neurotransmitter release and this stimulated an impulse (action potential or wave of depolarization and repolarization) in the efferent motor nerve innervating the muscles.

In case of shutting off the alarm it perhaps was carried to the carpal and metacarpal muscles of the right hand( as he shut off the alarm in that hand) while during getting up the efferent impulse was relayed to the hamstrings and gastrocnemius muscles of the left limb ( as he put that foot forward while getting up). The neurophysiological basis of the action of the muscles was because the nerve impulse in the motor nerve caused liberation of acetylcholine which got bound to the Ach receptors in muscles that caused opening of sodium channels in the muscle.

The muscle got depolarized and elicited Calcium ions to be released from sarcoplasmic reticulum. The released calcium ions caused actin –myosin cross bridge formation that resulted in muscle contraction (Purvez, 2012) (Janmey2007). Coupled with multimodal stimulation of efferent motor neuron innervating muscles and decreasing the inhibition of spinal reflexes such activity was possible in the case study.ReferencesJanmey, Paul A.; McCulloch, Christopher A. (2007). "Cell Mechanics: Integrating Cell Responses to Mechanical Stimuli".

Annual Review of Biomedical Engineering 9: 1–34.Purves, Dale (2012). Neuroscience (5th ed.). Sunderland, MA: Sinauer