Nervous System Flashcards
Most of the synapses used for signal transmission in the central nervous system of the human being are chemical synapses. In these synapses, the first neuron secretes at its nerve ending synapse a chemical substance called a neurotransmitter (often called a transmitter substance ), and this transmitter in turn acts on receptor proteins in the membrane of the next neuron to excite the neuron, inhibit it, or modify its sensitivity in some other way
More than 50 important neurotransmitters have been discovered thus far. Some of the best known are acetylcholine, norepinephrine, epinephrine, histamine, gamma-aminobutyric acid (GABA), glycine, serotonin, and glutamate.
In electrical synapses , the cytoplasms of adjacent cells are directly connected by clusters of ion channels called gap junctions that allow free movement of ions from the interior of one cell to the interior of the next cell
is by way of gap junctions and other similar junctions that action potentials are transmitted from one smooth muscle fiber to the next in visceral smooth muscle
Although most synapses in the brain are _______________, electrical and chemical synapses may coexist and interact in the central nervous system. T
Chemical
The ion channels are not suitable for causing prolonged postsynaptic neuronal changes because these channels close within milliseconds after the transmitter substance is no longer present. However, in many cases, prolonged postsynaptic neuronal excitation or inhibition is achieved by activating a ______________ chemical system inside the postsynaptic neuronal cell, and then it is the ______________ that causes the prolonged effect.
Second messanger
Inactivation of the G protein occurs when the GTP bound to the α subunit is hydrolyzed to _______ This action causes the α subunit to release from its target protein, thereby inactivating the second messenger systems, and then to combine again with the β and γ subunits, returning the G protein complex to its inactive state.
GDP
___________ are synthesized as integral parts of large-protein molecules by ribosomes in the neuronal cell body.
Neuropeptides
An example of co-release of two small molecule transmitters is found in the raphe nucleus, located in the brain stem. These neurons provide innervation to several brain regions, they can co-release serotonin and glutamate, and they play an important role in the cycle of sleeping and wakefulness
Nernst potential
EMF(mV)=±61×log(ConcentrationinsideConcentrationoutside)
Three states of a neuron. A, Resting neuron , with a normal intraneuronal potential of −65 mV. B, Neuron in an excited state, with a less negative intraneuronal potential (−45 mV) caused by sodium influx. C, Neuron in an inhibited state , with a more negative intraneuronal membrane potential (−70 mV) caused by potassium ion efflux, chloride ion influx, or both.
Presynaptic inhibition is caused by release of an inhibitory substance onto the outsides of the presynaptic nerve fibrils before their own endings terminate on the postsynaptic neuron. In most cases, the inhibitory transmitter substance is __________, which opens anion channels, allowing large numbers of chloride ions to diffuse into the terminal fibril. The negative charges of these ions inhibit synaptic transmission because they cancel much of the excitatory effect of the positively charged sodium ions that also enter the terminal fibrils when an action potential arrives.
GABA
The autonomic nervous system is activated mainly by centers located in the ________, ____________ and _______
Spinal cord, brain stem and hypothalmus
The efferent autonomic signals are transmitted to the various organs of the body through two major subdivisions called the ____________ and the ______________, the characteristics and functions of which are described in the following sections.
sympathetic nervous system and the parasympathetic nervous system,
Sympathetic nervous system. The black lines represent postganglionic fibers, and the red lines show preganglionic fibers.
Central nervous system (CNS)
Central nervous system (CNS)
● begins to form in the third week of embryonic development as the neural plate. The neural plate becomes the neural tube, which gives rise to the brain and spinal cord.
Peripheral nervous system (PNS)
Peripheral nervous system (PNS)
● consists of spinal, cranial, and visceral nerves and spinal, cranial, and autonomic ganglia.
● derived from three sources:
1. Neuralcrestcells
● give rise to peripheral ganglia, Schwann cells, and afferent nerve fibers. 2. Neuraltube
● gives rise to all preganglionic autonomic fibers and all fibers that innervate skeletal muscles. 3. Mesoderm
● gives rise to the dura mater and to connective tissue investments of peripheral nerve fibers (endoneurium, perineurium, and epineurium).
FIGURE 4.1. Diagrams illustrating the dorsal aspect of the human embryo. (A) Late presomite and early neural plate stage. (B) Early somite stage and neural groove stage. (C) Eight-somite stage and early neural tube stage. The anterior and posterior neuropores provide transitory communication between the neural canal and the amniotic cavity. (Modified from Carpenter MB, Sutin J. Human Neuroanatomy. 8th ed. Baltimore, MD: Williams & Wilkins; 1983:63.)
FIGURE 4.2. Schematic diagrams of trans- verse sections of embryos at various stages. (A) Neural plate stage. (B) Early neural groove stage. (C) Late neural groove stage. (D) Early neural tube and neural crest stage. (E) Neural tube and spinal ganglion stage. (Modified from Truex RC, Carpenter MB. Human Neuro- anatomy.
In which of the following would we find the unmyelinated postganglionic axons of the sympathetic nervous system?
Gray ramus. This is the correct answer. The gray ramus communicans exits the sympathetic chain ganglion carrying unmyelinated axons of the postganglionic cells to the spinal nerve, and on to the effector.
TAKEAWAY: All preganglionic nerves of the ANS that exit the spinal cord, both sympathetic and parasympathetic, originate in the intermediolateral cell column in the lateral horn and send their axons out through the ventral horn and ventral root. Sympathetic preganglionic nerves quickly veer off into the white (lightly myelinated) ramus communicans into the sympathetic chain ganglia, where they synapse on postganglionic sympathetic nerves, which then project axons out via the gray (unmyelinated) ramus communicans back to the spinal nerves, and then off to the effectors.
The ventral root carries the axons of both somatic motor neurons and preganglionic ANS neurons.
Ventral root
Intermediolateral cell column. The IML contains the cell bodies of the preganglionic ANS neurons.
Intermediolateral cell column
The sympathetic chain ganglia house the cell bodies of the postganglionic sympathetic neurons onto which the preganglionic sympathetic neurons synapse.
The sympathetic chain ganglia
The white ramus communicans is a byway from the spinal nerve into which preganglionic sympathetic nerves turn and enter to synapse on the postganglionic sympathetic nerves in the sympathetic chain. The white refers to the myelination of these axons.
The white ramus communicans
The cell bodies for preganglionic autonomic nervous system (ANS) neurons in the spinal cord are found in which of the following?
Lateral horn. This is the correct answer. The cell bodies of spinal cord preganglionic nerves of the autonomic nervous system are found in the intermediolateral cell column of the lateral horn.
TAKEAWAY: In the spinal cord, the autonomic preganglionic nerves for both the sympathetic and parasympathetic nervous systems have the cell bodies located in the intermediolateral cell column in the region called the lateral horn, roughly midway between the dorsal (posterior) and ventral (anterior) horns.
The dorsal (posterior) root carries the axons of __________
sensory afferents.
The dorsal (posterior) horn is the arrival station for sensory afferents. They either synapse there onto secondary neurons, or move to a fasciculus and begin their ascent in the spinal cord
The dorsal (posterior) horn
The ventral (anterior) horn houses the cell bodies of motor neurons, and also axons of both motor neurons and autonomic preganglionic neurons.
The ventral (anterior) horn
The ventral (anterior) root carries the axons of both motor neurons and autonomic preganglionic neurons.
The ventral (anterior) root
A graduate student is studying the postganglionic autonomic neurons and its spinal root pathways. As he dissects a cadaver the student discovers the sympathetic chain ganglion. Which spinal nerve rami contain unmyelinated postganglionic sympathetic fibers?
Gray ramus communicans -This is the correct answer - The gray ramus communicans contain postganglionic nerve fibers of the sympathetic nervous system and are composed of largely unmyelinated neurons. This is in contrast to the white rami communicans, in which heavily myelinated neurons give the rami their white appearance.
TAKEAWAY: Each spinal nerve receives a branch called a gray ramus communicans from the adjacent paravertebral ganglion of the sympathetic trunk. Gray rami communicantes carry postsynaptic sympathetic fibers from the sympathetic trunk to all spinal nerves.
The meningeal ramus innervates the meninges and vertebral column.
The meningeal ramus
The meningeal ramus innervates the meninges and vertebral column.
The meningeal ramus
The posterior primary ramus innervates the skin and muscles of the back. Dorsal primary rami: Posterior part of the spinal nerve. Branch from spinal nerve after leaving the intervertebral foramen. Innervate: The skin of the back and dorsal neck, deep muscles of the back (e.g., erector spinae), the posterior vertebrae and facet joints, and the superficial ligamenta flava. Mixed nerves (relay both sensory and motor information).
The posterior primary ramus
The anterior primary ramus innervates the anterolateral muscles and skin of the trunk, extremities, and visceral.
The anterior primary ramus
The white rami communicans contain both myelinated and unmyelinated preganglionic sympathetic fibers, (GVE and GVA). The white ramus appears white because there are more myelinated than unmyelinated fibers unlike the gray rami.
The white rami
