open ion channels that depolarize the postsynaptic membrane. As more action potentials come to the pre-synaptic terminal then more neurotransmitter will be released which then will cause more ion channels to open creating a larger depolarization. The goal for an action potential is to reach threshold and so several EPSP can be added over time to create a total EPSP enough to continue the signal as an action potential.
IPSP-Inhibitory postsynaptic potentials
do the opposite of EPSP. It uses neurotransmitters to hyperploralize. They also can be added together to further hyperpolarization. They can also be added to cancel the EPSP neurotransmiiter release.
is where many EPSP are added together in time before the 1st fades away. They are added (summated) together so that there is enough to give rise to an action potential that will pass threshold.
is similar because the end result is the same but the process of getting there is different. In spatial summation presynaptic axons converge on the same postsynaptic membrane at the same time to be sufficient to reach threshold
Draw a simple Golgi tendon organ reflex arc and explain the actions.
Golgi tendon reflex
is located on the tendon and as the muscle contracts it sends afferent signal to the cerebellum to asses the amount of muscle tension. The cerebellum can then send efferent motor signal back to the muscle to stop or continue contraction. In this way the reflex can protect the tendon if its being stretched too much. For example, if the tension on a tendon is greater than anticipated like lifting an unexpectedly heavy wight, the GTO’s fire and inhibit the alpha motor neurons. The GTO also has an inhibitory interneuron between the Ib afferent and the alpha motorneuron efferent. In this way the tension can inhibit voluntary muscle contractions. This is useful in rapid flextion and extension changes in m like running
Draw a simple knee-jerk reflex arc and explain the action.
the tendon is stretched by a reflex hammer which stretches the spindle which creates a large generator potential. The sensory nerve carries action potentials to the synaps in the spinal cord and the alpha motoneuron fires with out ever being transmitted in the brain. the muscle than contracts and the stretches is relieved-creating the knee jerking action. This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the brain will receive sensory input while the reflex action occurs
What information can a doctor obtain from knee-jerk reflex testing?
the absence of the knee jerk is called hypotonia. any break in the reflex arc will cause the loss of stretch reflexes. the problem may be at the spindle, afferent neuron, synapse, alpha motor neuron, neuromuscular junction, or the m itself. This an issue with the Lower Motor neuron lesion because it involves the dorsal roots, spinal gray matter, ventral roots, spinal nerves or peripheral nerves. Polio or ALS are LMN diseases An overactive or excessive jerk is called hyperreflexia. It is caused by a lack of inhibition from the CNS on jerk reflexes. normally the CNS dampens the jerk from being too high so when places like lobes in the cerebrum, cerebellum or basal ganglia are damaged the reflex jerks unchecked and therefore excessive. This is an upper motor neuron lesion and examples include Parkinson's disease which cause degeneration of brain regions
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