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Prescribed Learning Outcome
The Nervous System
Neuron to Reflex Arc
Dendrite: part of a nerve cell which conducts signals toward the cell body
Cell body: part of a nerve cell which contains the nucleus
Axon: part of a nerve cell which conducts impulses away from the cell body
Sensory neuron (afferent neuron): type of neuron which takes a message from a sense organ to the CNS
Motor neuron (efferent neuron): type of neuron which takes a message away from the CNS to an effector (muscle or gland), it has short dendrites and a long axon
Interneuron (association): type of neuron found completely within CNS which conveys messages between parts of the system; has short dendrites and long/short axon
Schwann cells (neurolemmocytes) are neuroglial cells which encircle a fiber, leaving gaps called the nodes of Ranvier (neurofibril nodes). Schwann cells wrap themselves around the axon many times, and in this way lay down several layers of plasma membrane containing myelin, which forms a myelin sheath. Impulses travel through a fiber by jumping from node to node. This is called saltatory conduction. It allows rapid conduction (200m/sec).
Axon bulb is the small swelling on an axon branch, lying very close to the dendrite/cell body of another nuron.
Presynaptic membrane is the membrane of the first neuron (the axon).
Postsynaptic membrane is the membrane of the next neuron (the dendrite).
Synaptic cleft is the small gap between the presynaptic and postsynaptic membrane.
Neurotransmitters are chemicals stored at then ends of axons in vesicles that is responsible for transmission across a synapse, by causing excitation (causes Na+ channels to open; neuron transmits a nerve impulse) or inhibition. Two neurotransmitters are acetylcholine (ACh) are norepinephine (NE).
The postsynaptic membrane contains enzymes that rapidly inactivate the neurotransmitter. For example, acetycholinesterase (AChE) breaks down acetylcholine. Sometimes, the synaptic ending rapidly reabsorbs the neurotransmitter, possibly for repackaging in a synaptic vesicle or for chemical breakdown.
Reflex arc is an automatic, involuntary response to changes occurring inside or outside the body. It involves the spinal chord and a spinal nerve.
Divisions and the Brain
CNS consists of the spinal cord and the brain where nerve impulses are received, coordinated, and interpreted. Contains cell bodies.
PNS located outside the midline of the body; contains nerves. Contains cranial nerves, spinal nerves, therefore sensory fibers, and motor fibers. The motor fibers are involved in the somatic and autonomic system. The somatic system involves nerves sending sensory impulses from receptors to the CNS and send motor impulses from the CNS to the skeletal muscles. In the autonomic system, consisting of the sympathetic and parasympathetic systems, motor impulses travel to smooth muscle, cardiac muscle, and the glands.
Sympathetic system is associated with "fight or flight" emergency responses. It accelerates the heartbeat, dilates the bronchi, and inhibits the digestive tract.
Parasympathetic system is the "housekeeper system" in that it promotes all the internal responses associated with a relaxed state. It causes the pupil of the eye to contract, promotes digestion of food, and retards heartbeat.
Source gland: adrenal medulla.
-Increase blood glucose level, increases metabolic rate
-Bronchioles dilate and breathing rate increases
-Blood vessels to the digestive tract and skin constrict; those to skeletal muscles dilate
-Cardiac muscle contracts more forcefully and heart rate increases
There are neurons in the hypothalamus that are called neurosecretory cells because they respond to neurotransmitters and also produce hormones. They pass through axons that run between the hypothalamus and the posterior pituitary. These hormones are stored in axon endings. For example, neurosecretory cells in the hypothalamus produce and release the hormones ADH and oxytocin, which are stored in the posterior pituitary.
The hypothalamus controls the anterior pituitary by producing hypothalamic-releasing and release-inhibiting hormones. Each type of hypothalamic hormone either stimulates or inhibits production and secretion of a specific anterior pituitary hormone. The anterior pituitary secretes these different types of hormones into the blood stream.