Chapter 45 - Guyton Flashcards
How many neurons are found in the central nervous system?
more than 100 billion
Information from the somatic portion of the nervous system receives sensory information from peripheral nerves and conducts it to where?
spinal cord (all levels), reticular substance of the pons, medulla, and mesencephalon of the brain, cerebellum, thalamus, cerebral cortex
What are the motor functions of the nervous system?
1) contraction of skeletal muscle 2) contraction of smooth muscle in organs 3) secretion of active chemical substances by exocrine and endocrine glands
In the motor functions of the nervous system, what are the effectors?
muscles and glands (anatomical structures that perform the functions dictated by the nerve signals)
What levels of the CNS can control skeletal muscles?
spinal cord, reticular substance of the pons, medulla, and mesencephalon, basal ganglia, cerebellum, motor cortex
What is the primary difference between higher and lower region control of skeletal muscle?
higher regions - deliberate, complex muscle movements controlled by thought process of brain; lower regions - primarily automatic, instantaneous muscle responses to sensory stimuli
What is meant by the term “integrative function” in regards to the nervous system?
processing information so that appropriate mental and/or motor responses will occur, important info is immediately channeled into proper regions to elicit response (99% of all sensory is discarded as irrelevant and unimportant..we shall now call wednesday from 1-6 pm “integrative function” class)
What are some selective actions performed by synapses?
blocking weak signals and allowing strong to pass, selecting and amplifying certain weak signals, channeling signals in many directions rather than just one
Where is most memory stored?
cerebral cortex (small amount in basal regions of brain and spinal cord)
Signals generated within the brain itself can
cause transmission of impulses through the same
sequences of synapses, even when the sensory input is not excited. This gives the person a perception of experiencing the original sensations, although the perceptions are only memories of the sensations. What does this describe?
facilitation (useful after injury)
What are the three major levels of the CNS?
spinal cord, subcortical, cortical
Specific functional characteristics of the spinal cord.
conduit for signals from the periphery of the body to the brain, or vice versa
What functions might still occur after an injury to the spinal cord in the high neck region?
walking movements, reflexes that withdraw a body portion from pain, stiffen the legs to support body against gravity, control local blood vessels, GI movements, urinary excretion
Specific functional characteristics of the subcortical level (lower brain).
most subconscious activities of the body (arterial pressure, respiration, salivation, equilibrium, licking of lips, emotional patterns)
Specific functional characteristics of the cortical level (higher brain).
essential for most of our thought processes but cannot function by itself, without cerebral cortex functions of lower brain centers are imprecise
What areas are included in the subcortical level?
medulla, pons, mesencephalon, hypothalamus, thalamus, cerebellum, basal ganglia
Almost all the synapses used for signal transmission in the central nervous system of the human being are:
chemical synapses
Two types of synapses:
chemical and electrical
Most important neurotransmitters:
acetylcholine, norepinephrine, epinephrine, histamine, gamma-aminobutyric acid (GABA), glycine, serotonin, and glutamate
Two examples of gap junctions that transmit signals via electrical synapses:
APs are transmitted from one smooth muscle fiber to the next in visceral smooth muscle and from one cardiac muscle cell to the next
Which synapses can only conduct information one way?
chemical synapses
Gap junctions allowing ion movement are characteristic of which type of synapse?
electrical
Do more of the presynaptic terminals lie on the soma or the dendrites of the anterior motor neuron?
80-95% on the dendrites
Neurons in other parts of the cord and brain differ from the anterior motor horn in:
1) size of body 2) length, size, number of dendrites 3) length and size of axon 4) number of presynaptic terminals
Two important internal structures of the presynaptic terminal.
transmitter vesicles and mitochondria
What causes the vesicles to empty into the synaptic cleft?
AP spreads over presynaptic terminal and depolarizes the membrane
Role of the calcium ons in the spread of action potential.
voltage-gated calcium ion channels in the presynaptic membrane allow calcium into the terminal when the membrane depolarizes; calcium ions bind to release sites and allow transmitter vesicles to release transmitter into the cleft
Two important components of receptor proteins.
binding component that protrudes out into the synaptic cleft and ionophore component that passes through the postsynaptic membrane
Two types of ionophore component (receptor protein).
ion channel or second messenger