Nervous System and Spinal Cord Essay

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CBIO Notes Test 5

Nervous System endocrine system- communicates by means of chemical messengers (hormones) secreted in the blood nervous system- employs electrical and chemical means to send messages quickly from cell to cell

3 Basic Nervous System steps
1. through sense organs and simple sensory nerve endings, it receives info about changes in the body and the external environment and transmits coded messages to the CNS
2. the CNS processes this info, relates it to past experience and determines what response is appropriate
3. the CNS issues commands primarily to muscle and gland cells to carry out the response

2 Major Anatomical Subdivisions
CNS
brain- protected and enclosed in the cranium spinal cord – protected and enclosed in the vertebral column
PNS
nerves- a bundle of nerve fibers (axon) wrapped in fibrous connective tissue ganglia- a knot like swelling in a nerve where the cell bodies of neurons are concentrated

Peripheral Nervous System
Sensory/Afferent Division- carries signals from receptors to the CNS
Somatic sensory- carries signals from receptors in the skin, muscles, bones, and joints
Visceral sensory- carries signals mainly from the viscera of the thoracic and abdominal cavities, such as the heart, lungs, stomach, and urinary bladder
Motor/Efferent Division- carries signals from the CNS to gland and muscle cells that carry out the body's responses
Somatic motor- carries signals to the skeletal muscles
Visceral motor (ANS)- carries signals to glands, cardiac muscle, and smooth muscle sympathetic – arouse the body parasympathetic – calming effect of the body

nerve cells= neurons
1. excitability/irritability- respond to environmental changes
2. conductivity- neurons respond to stimuli by producing electrical signals that are quickly conducted to other cells at distant locations
3. secretion- when the electrical signal reaches the end of a nerve fiber, the neuron secretes a chemical neurotransmitter that crosses the gap and stimulates the next cell

Functional Classes of Neurons:
Sensory afferent (meaning toward) neurons specialized to detect stimuli such as light, heat, pressure, and chemicals and transmit info to the CNS. Conduct signals from receptors to CNS
Interneurons (association) only in the CNS. Receive signals from other neurons and carry out the integrative function of the nervous system “they make decisions” 90% of neurons are these
Motor Efferent (meaning away from CNS) Neurons send signal predominantly to muscle and gland cells. Most of them lead to muscles

Structure of a Neuron

Soma/Neurosoma/Cell Body/Perikaryon = the control center single, centrally located nucleus cytoplasm contains mitochondria, lysosomes, golgi complex, and rough endoplasmic reticulum and cytoskeleton

Types of Neurons
Multiple neurons- one axon and multiple dendrites most common
Bipolar Neurons- one axon and one dendrite olfactory cells of the nasal cavity neurons of the retina and sensory neurons of the inner ear
Unipolar Neurons- only a single process leading away from the Soma
Anaxonic Neuron- multiple dendrites but no axon found in brain, retina, adrenal medulla

anterograde- movement away from the soma down the axon retrograde- movement up the axon toward the soma

Neurotransmitters
4 major categories
Acetylcholine
Amino Acids glycine aspartate glutamate GABA
Monoamines
epinephrine norepinephrine dopamine histamine serotonin
Neuropeptides

Synaptic Transmissions
Excitatory cholinergic synapse- employs acetylcholine as its neurotransmitter inhibitory GABA-ergic synapse- employs y-aminobutyric acid (GABA) as its neurotransmitter
Excitatory adrenergic synapse- employs norepinephrine, acts through 2nd messenger system, enzyme amplification

hyperpolarize- let out positively charged or let in negatively charged ion into the membrane

Postsynaptic Potentials
EPSP
glutamate aspartate IPSP

Temporal Summation
repeated
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