Chapter 45 Flashcards
Where does the central motor systems receive input?
receives incoming signals mainly from dendrites, and a little from synapses on cell body.
Where are the outputs in the central motor systems?
travels via a single axon leaving the cell body, and then the axon has many separate branches to other parts of the CNS or PNS. A special feature of most synapses is that the signal passes in the forward direction only. The signal travels in the required direction for performing specific nervous functions.
What causes sensory stimulation?
sensory experience exciting sensory receptors, whether visual receptors in the eyes, auditory receptors in the ears, or tactile receptors on body surface. The input causes brain reaction or is stored as memory
After the peripheral nerves bring information to the CNS, where do the inputs go?
(1) Spinal cord
(2) Reticular substance of medulla, pons, and mesencephalon
(3) Cerebellum
(4) Thalamus
(5) Cerebral cx
What are the motor components of the nervous system?
i) Controls bodily movements/activities, by controlling contraction of skeletal muscle (body movement), smooth muscle (viscera), and secretion of chemical substances by exocrine and endocrine glands. The muscle and glands are called effectors b/c they perform the body function at the direction of nerve signals.
Is the main type of synapse in the CNS chemical or electrical?
chemical
WHat is a chemical synapse?
presynaptic neuron releases a NT which acts on the postsynaptic cell body, either exciting or inhibiting it (depending on NT and receptor)
Do chemical synapses travel in 1 direction or multiple?
only 1 direction
What are the main NT’s at chemical synapses?
epi, NE, histamine, GABA, glycine, serotonin, glutamate
What are electrical synapses?
i) Smooth muscle and cardiac muscle cells transmit potentials via electrical synapses using gap junctions. Gap junctions conduct electricity from one cell to another, this done by the gap junctions allowing ions to flow from one cell to another.
Do electrical synapses travel in 1 direction or multiple?
they allow bi-directional transmissions
What are the steps to NT release at the synapse?
a) AP depolarizes the presynaptic terminal which opens voltage gated Ca channels, allowing Ca to enter. The entry of Ca into the presynaptic terminal allows NT vesicles to fuse with the presynaptic membrane and empty NT into the cleft. The NT diffuses across the cleft to the postsynaptic terminal where it binds to the receptors on the postsynaptic membrane.
b) Ca causes NT vesicles to fuse with the presynaptic membrane b/c Ca binds to release sites w/in the presynaptic terminal. The more Ca that enters the presynaptic terminal, the more NT released
What is the ionosphore at the postynaptic membrane?
ionosphore can be a ion channel or second messanger
What is the difference between a cation channel and an anion channel?
i) Cation channel: allows passage of sodium. Lined with negative charge, which attracts Na and repels Cl, when the diameter is large enough Na will be attracted and will move through
ii) Anion channel: allows passage of chloride ions. This channel is not charged, it is just small enough to let Cl through but not anything else (Na and Ca)
What are second messengers?
when it binds NT it activates one or more substances inside the postsynaptic cell. Important for functions that require activation longer than a few milliseconds (memory), the activated second messenger can continue the response for a long time after the NT is gone
What is the most common type of 2nd messenger proteins?
i) G-proteins are the most common, they consist of alpha (activator), beta, and gamma. When the G-prot is activated the alpha component dissociates from the other subunits and is free to act w/in the cell and performs one or more of the tasks listed in the next objective
What are four changes which can be activated by a postsynaptic receptor?
i) Opening specific ion channels through the postsynaptic cell membrane, these usually stay open longer than directly activated ion channels
ii) Activation of cAMP or cGMP in the neuronal cell, which can cause long-term changes in cell structure itself, which in turn alters long-term excitability of the neuron.
iii) Activation of one or more intracellular enzymes, the enzymes can cause any one of many specific chemical functions in the cell.
iv) Activation of gene transcription. This is one of the most important effects of activation of the second messenger systems because gene transcription can cause formation of new proteins within the neuron, thereby changing its metabolic machinery or its structure.
What is an excitatory receptor?
a rec that allows positive ions (cations) to enter the postsynaptic cell, the positive charges of the Na will excite the neuron
WHat is an inhibitory receptor?
a rec that allows entry of anions which will hyperpolarize the cell and inhibiting it
What are small molecule NT’s?
are small and fast acting, causes most acute responses like transmission of sensory signals to the brain and of motor signals back to the muscles.
What are neuropeptides?
are larger and slow acting, cause more prolonged action such as long-term opening or closure of certain ion channels, or number/size of synapses
Where is the secretion of Ach?
secreted by neuron terminals of the large pyramidal cells from motor cx, different types of neurons in the basal ganglia, motor neurons that innervate the skeletal muscles, pregang neurons of the ANS, postgang neurons of parasympathetic nervous system, postgang neurons of the sympathetic nervous system
