Group 8/26/19 Flashcards
Learning issues
Propogation of nerve impulses at the neuronal synapse [(Guyton parts of ch. 46) (Boron part of Chapter 8)]
Propogation of nerve impulses at the neuromuscular junction [(Guyton Ch. 7 finished) (Boron part of chapter 8)]
Physiology of somatic sensation of pain (receptors, types, supression)
Plan: Read Guyton-Hall ch 7 and ch 46
what are skeletal muscle fibers innervated by, and where do they come from in the spinal cord?
skeletal muscle fibers are innervated by large, myelinated nerve fibers that come from motoneurons in the anterior horns of the spinal cord
each nerve ending makes a ? with the muscle fibers near its midpoint
neuromuscular junction
motor end plate
the nerve fiber forms a complex of branching nerve terminals that invaginate into the surface of the muscle fiber but lie outside the plasma membrane, and this entire structure is the motor end plate
synaptic cleft
space between the terminal and the fiber membrane
what is acetylcholine and where is it located in the neuromuscular junction?
an excitatory transmitter that excites the muscle fiber membrane. Synthesized in cytoplasm of terminal, then absorbed into synaptic vesciles
how is acetylcholine released from its vesicles?
- voltage gated calcium channels release calcium when there is an action potential
- calcium ions activated Ca-calmodulin dependent protein kinase, phosphorylates synapsin proteins so that they release ACh vesicles
- ACh vesicles move to the active zone
- they release ACh into synaptic space via exocytosis
how is the end plate potential formed?
- there are ACh receptors in the muscle fiber membrane, which are ACh-gated ion channels
- channels opens when two ACh bind to alpha subunit proteins
- positive ions like Na, K, and Ca move through opening
- creates local positive potential in muscle fiber membrane, the end plate potential
how is acetylcholine destroyed, why is this important?
- destroyed by acetylcholinesterase, located in synaptic space, or diffuses out of synaptic space
- prevents muscle re-excitation
high safety factor
each impulse that arrives at the neuromuscular junction causes 3x as much end plate potential that was required to stimulate the muscle fiber
myasthenia gravis
a disorder that causes muscle weakness. The neuromuscular junction is unable to transmit enough signals from the nerve fibers to the muscle fibers. Autoimmune disease where the patient’s antibodies destroy their own ACh receptors. End plate potentials are too weak for depolarization.
what are some differences in muscle action potential as compared to regular action potential?
- same resting potential, -80 -90mV
- longer duration of action potential
- slower velocity of transmission
what is the importance of the transverse tubules?
- they carry action potentials and span from the outside of the cell membrane to deep in the muscle fiber.
- They run transverse to the myofibrils, and connect with the exterior of the muscle fiber.
excitatory “pulse”
when the t tubules and SR become fully excited, the calcium concentration will increase greatly, for a short period of time called a “pulse,” then the calcium pumps bring the concentration back down again.
Muscle contraction happens during the pulse
where do signals come into the neuron?
mostly dendrites, but also cell body
where do signals exit the neuron?
signals exit through one signal axon leaving the neuron, which may have branches to other parts
sensory information coming from the sensory receptors in the body goes to sensory areas in which brain structures?
spinal cord, reticular substance of medulla, pons, and mesencephalon, cerebellum, thalamus, and areas of the cerebral cortex
effectors
the muscle and glands involved in various bodily activities. Actual anatomical structures that perform functions dictated by the nerve signals.
what are the brain structures that play a role in skeletal muscle function, what does each section do?
- spinal cord, reticular substance of medulla, pons, and mesencephalon, basal ganglia, cerebellum, motor cortex
- lower regions control automatic, instantaneous muscle responses to sensory stimuli
- higher regions have deliberate complex muscle movements
integrative function of the nervous system
we receive a lot of sensory stimulation, but the processes it and channels only important sensory information to the integrative and motor regions for us to respond.
what is the role of synapses in processing information?
- determine directions that nervous signals spread
- filter passage of signals
- can amplify signals
facilitation of synapses
- each time sensory information passes through the synapse, the synapses become more capable of transmitting the same information.
- Brain will be able to generate its own signal without sensory input to trigger the same pathway as a memory, and compare new to old sensory information
functions of the spinal cord level of the CNS
- contains neuronal circuits responsible for walking and reflexes such as withdrawing from pain, standing, and bodily processes
- sends signals to control areas so that they perform their functions
structures in the lower brain/subcortical level of the CNS and their functions
- includes medulla, pons, mesencephalon, hypothalamus, thalamus, cerebellum, basal ganglia
- controls subconscious body activities, like breathing, equilibrium, eating, emotions
functions of the higher brain/cortical level of the CNS
- memory, thought processes
- works together with other areas to help them carry out their functions and its own functions
what are some differences between chemical and electrical synpases?
- chemical synapses are more common in CNS
- chemical synapse involves a neuron that secretes neurotransmitter to act on receptor proteins on membrane of next neuron
- electrical synapses involve adjacent cytoplasm of cells, connected by clusters of ion channels called gap junctions
principle of one-way conduction
chemical synapses always transmit the signal in one direction. Presynaptic neuron secretes neurotransmitter, and this goes to the postsynaptic neuron.
soma
main body of the neuron
how does the presynaptic cleft release neurotransmitters?
- presynaptic cleft contains transmitter vesicles and mitochondria
- action potential depolarized presynaptic membrane, voltage gated calcium channels open, calcium released into terminal
- calcium binds to release sites on presynaptic membrane, causes neurotransmitter to be released into cleft
what are the parts of the postsynaptic neuron membrane?
- postsynaptic neuron membrane contains receptor proteins
- receptors have a binding component (contacts synaptic cleft, binds with incoming neurotransmitter), and intracellular component (passes into postsynaptic neuron)
