nervous system Flashcards
what is a nerve net compared to cephalization?
in radially sym animals they have a net of nerves all over meanwhile bilat animals exhibit cephalization, the nervous system consists of a Central component (Brain and Spinal cord) and a peripheral component (nerves extending of either brain or spinal cord).
what are the meninges and the three layers?
The CNS in mammals is surrounded by either vertebrae or the skull and three thin membranes- meninges. The dura mater is the outer, thick and tough meninx that is adherent to the overlying skeleton (vertebrae or skull) and the pia mater is a thin meninx that lies tightly on the brain and spinal cord. A web-like arachnoid meninx connects the two. Many spaces are present in the arachnoid layer, which in life is filled with cerebral spinal fluid.
nervous system structure: how is it organized in CNS(central nervous system)
bundles of axons-tracts, aggregations of neuronal cell bodies form nuclei (singular = nucleus)
nervous system structure: how is it organized in PNS(periphery nervous system)
bundles of axons in the PNS are nerves, aggregations of neuronal cell bodies form ganglia (singular = ganglion)
nervous system structure-neurons: what are the three categories of neurons?
Sensory Neurons that carry information from receptors to the CNS, Motor Neurons that carry information from the CNS to an organ, such as gland or muscle, and Interneurons that link sensory and motor neurons in the CNS.
nervous system structure-neurons: how do these three neurons function in a simplex reflex arc?
a simple reflex arc will consist of the following: (1) receptor or sense organ, (2) sensory neuron, (3) interneuron in CNS, (4) motor neuron, and (5) effector organ, such as a muscle or gland. Consider a simple reflex, such as placing your hand on a hot stove. Your hand is removed immediately—even before you actually realize that you hand might be burning. How? Receptors in the hand are stimulated (might just be dendrites from the sensory neuron). The neuron is depolarized and sends information (electrical impulse) to the CNS –in our example, the spinal cord. The sensory neuron synapses with an interneuron, that synapses with a motor neuron, that carries information to muscles of your arm causing them to contract to remove your hand from the stove (remember the foot stepping on the nail example–interneurons can connect sensory and motor neurons on the same (ipsolateral side of the spinal cord) or to the opposite (contralateral) side . At the same time that the interneuron is synapsing with the motor neurons, it is also synapsing with neurons that carry information to the brain to let you “know” what is happening. This occurs through tracts in the white matter. Thus, the reaction to move the hand occurs at the same time you know that you might be burning.
nervous system structure-neurons: how is spine nerve formed?
is a mixed nerve (with both sensory and motor neurons), the dorsal root carries sensory information, and the ventral root carries motor information.
label your #1 flashcard
central canal, dorsal root, ventral root, spinal nerve, ganglion(bundle of sensory neurons), motor neurons, grey matter, white matter, inner neurons
cross sections of a spinal cord: why is there gray matter and white matter? (ie what makes them that color)
gray matter axons lack myelin, which is a fatty material and imparts a whitish coloration–the interneurons lack myelin and the middle section of the cord appears gray. The outer white matter consists of myelinated axons (which give the whitish coloration to the outer portion of the spinal cord)
cross sections of a spinal cord: why do we see swelling in the dorsal root?
The swelling is because of the cell bodies of the sensory neurons are large in diameter than the axons, which are bundled together as nerves. Because the cell bodies are aggregated together, they form a swelling.
cross sections of a spinal cord: what is the significance of the placement of sensory neurons?
all of the sensory neurons from your body are clustered in dorsal root ganglia, just inside your vertebrae. They are segmentally arranged. Consequently, if you severe a dorsal root on one side of your body, you would lose all sensory information from that body segment. You could burn that segment with a torch and feel no pain.
cross sections of a spinal cord: what is the significance of the placement of motor neurons?
Consider people who sever a foot during an automobile accident. Surgeons can reattach the foot. They reconnect the nerves, but remember what nerves are = bundles of axons—from motor neurons in our example. The cell bodies of the motor neurons are protected in the ventral horn of the gray matter, so the cells (neurons) survive the injury but the axons are severed—thousands of them associated with thousands of skeletal muscle fibers in the foot. The sections of the axons in the severed foot die, but axons regrow to the skeletal muscle fibers—but not necessarily to the same fiber. Thus, it takes the body a while to relearn how to move the foot.
cross sections of a spinal cord: why do we see swelling in the spinal cord?
Because the cell bodies of motor neurons are housed in the ventral horns(lower portion of the gray matter on each side), the more effector organs, such as skeletal muscle cells, associated with a body segment, the more motor neuron cell bodies and the larger the ventral horn. Spinal cords swell in the region of the cord associated with the limbs. The area of a spinal cord is thicker in the area of hind limbs compared to front limbs.
what are the two divisions of the peripheral nervous system?
sensory component and motor component
divisions of the peripheral nervous system: what is the sensory component?
brings messages from the sensory receptors to the CNS
divisions of the peripheral nervous system: what is the motor component? what are the two divisons?
carries information form the CNS to various organs. There are two major divisions of the Motor Component: (1) Somatic Nervous System and (2) Autonomic Nervous System.
divisions of the peripheral nervous system-motor divisions: what is the somatic nervous system?
under voluntary control—think of wiggling your finger and it wiggles. Although you have many neurons in parallel, a motor neuron originating in the ventral horn of gray matter will have a neuron that travels all the way to a skeletal muscle fiber.
divisions of the peripheral nervous system-motor divisions: what is the autonomic nervous system? what are the two components of the autonomic system?
under involuntary control. Motor neurons are sent from the ventral horn of the gray matter, but synapse outside of the CNS with other neurons that carry information to heart, guts, diaphragm, bladder, etc.—organs we cannot willfully control. Thus, two neurons in series (vs one neuron in the somatic NS). The Autonomic N.S. has 2 divisions: (a) Sympathetic Component and (B) Parasympathetic Component. (theyre antagonistic)
divisions of the peripheral nervous system-motor divisions-autonomic divisions: what is the sympathetic component? location? length? neurotransmitter?
sympathetic increases heart rate, Sympathetic decreases digestive activities, Sympathetic component is the fight or flight component that prepares the body in time of emergency. comes off the thorax and lumbar regions of the CNS (thoracolumbar), The first axon (preganlionic fiber(presynaptic)) is very short in the sympathetic NS, the second axon(postganlionic fiber(postsynaptic)) very long, Secretes epinephrine/norepinephrine
divisions of the peripheral nervous system-motor divisions-autonomic divisions: what is the parasympathetic component? location? length? neurotransmitter?
parasympathetic decreases heart rate, parasympathetic increases digestive activities, parasympathetic component is associated with vegetative process, such as eating or periods of relaxation. comes off the brain and sacral region (craniosacral), The first axon (preganlionic fiber(presynaptic)) is very long in the parasympathetic NS, the second axon(postganlionic fiber(postsynaptic)) very short, secretes acetylcholine onto the effector organ.
divisions of the peripheral nervous system-motor divisions-autonomic divisions: what are the regions each division effects?
para- top and bottom
sym- mid region
