Download Studying the concepts pg 344 1-7 Motor neurons are located in the

Studying the concepts pg 344 1-7
1.
Motor neurons are located in the central nervous system (CNS) they project their axons outside the CNS and directly
or indirectly control muscles. A typical neuron is divided into three parts: the soma or cell body, dendrites, and axon.
The soma is usually compact; the axon and dendrites are filaments that extrude from it. The dendrites of a neuron are
processes that send signals towards the cell body. The cell body is a part of a neuron that contains the nucleus and
other organelles. An axon conducts nerve impulses along its entire length. There are three classes of neurons: motor
neurons, sensory neurons and interneurons. In relation to the CNS a sensory neuron takes information to the CNS
while a motor neuron takes information away from the CNS. An interneuron conveys information between neurons in
the CNS.
2.
The sodium-potassium pump is an enzyme located in the plasma membrane in all animals. The pump helps
maintain resting potential, avail transport, and regulate cellular volume. In order to maintain the cell membrane
potential, cells must keep a low concentration of sodium ions and high levels of potassium ions within the cell thru
the sodium-potassium pump. When an axon is not conducting an impulse and the inside of the axon is negative
compared to the outside it is called resting potential.
3.
Action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls. It is
a rapid change in polarity across an axonmembrane as the nerve impulse occurs. The first part of action potential is
the sodium gates opening; this is when the gates of the sodium channels open and Na+ flows in the axon. This is
depolarization because the axon changes from negative to positive. The second part is the Potassium gates opening,
this is when the potassium channels open and K+ flows to the outside of the axon. This is repolarization because the
inside of the axon resumes a negative charge from positive.
4.
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. A
synapse is a region between two nerve cells, usually an axon and dendrite. Neurotransmitters are packaged
into synaptic vesicles clustered beneath the membrane on the presynaptic side (of a synapse, and are released into
the synaptic, where they bind to receptors in the membrane on the postsynaptic side of the synapse. Release of
neurotransmitters usually follows arrival of an action potential at the synapse. Neurotransmitters are
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either destroyed by specific Enzymes in the Synapse, diffuse out, or are reabsorbed by the Neuron. Two
well-known neurotransmitters are acetylcholine (Ach) and norepinephrine (NE).
The peripheral nervous system lies outside the central nervous system and contains nerves which are
bundles of axons. The PNS contains 3 types of nerves: sensory nerves, motor nerves and mixed nerves.
Mixed nerves contain motor and sensory fibres.
The Somatic Reflex: stimulus – sensory receptor (skin)generate nerve impulses – sensory nerve fibre pass
signals to many interneurons – spinal nerve – dorsal root ganglion – interneuron – motor transmission
carry impulses to effector – motor nerve fibre – effector (muscle) response to stimulus.
The autonomic system of the PNS regulates the activity of cardiac and smooth muscles and glands. Its two
major divisions are the sympathetic division and the parasympathetic division.
Sympathetic
Parasympathetic
-Arise from middle portion of spinal cord
-Arise from the sacral portion of spinal cord
-Terminated by ganglion immediately
-Craniosacral portion
-Preganglionic fibres are short
-Preganglionic fibres are long
-Postganglionic fires are long
-Postganglionic fires are short
-Emergency state “fights or flight”
-Relaxed state “housekeeper division
-Uses NE neurotransmitters
-Uses Ach neurotransmitters