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Lecture

15. Nervous System.pdf

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Department
Anatomy & Cell Biology
Course
ANAT 261
Professor
Craig Mandato
Semester
Fall

Description
Naveen Sooknanan McGill Fall 2011 Nervous System: The nervous system is made up of cells called neurons. Working together, neurons are responsible for all of your thought and consciousness  Structurally speaking, neurons are made of the same components as other cells, but their complex connections and active nature give us a sense of self A very famous Canadian neurosurgeon names Walter Graves Penfield is actually responsible for the mapping the brain using a technique now called the “Montreal procedure”  He was an American born Canadian neurosurgeon  He was responsible for figuring out how epileptic seizures worked  The patient was given a local anasthetic in the head, and the skull was cut open, exposing the brain o The brain was probed in different areas while the patient was awake  This is possible because the brain itself contains no pain receptors o The patient said he smelled burnt toast before his/her seizure, which allowed Dr. Penfield to examine and locate the region of the brain causing the seizures The adult brain is comprised of around 10 billion neurons (a 21 year old). The number begins to diminish as you age and these cells do NOT regenerate (i.e. you’re born with a certain amount and that’s it). Nerve tissue is distributes throughout the body in an integrated communication network  Classification of nervous tissue: o Anatomically:  CNS: brain, cerebellum, spinal cord  Either grey (cell bodies) or white matter (axons)  PNS: Nerve fiber, nerve ganglia o Histologically:  Neurons (nerve cells)  Neuroglial  Glial cells are the brain’s equivalent of CT; involved in support, neuron protection, defence and nutrition  Glial cells also define the blood brain barrier o Gray matter  Cell bodies of neurons, neuroglia o White matter:  Neuronal processes (axons) and neuroglia  White matter gets it color from an axon coating made of myelin (which is white) The function of nerve tissue is to:  Detect, analyze, integrate and transmit information generated by sensory stimuli (heat, light, etc.) and by chemical and mechanical changes in the external of internal milieu o E.g. you touch a hot stove, you realize it hurts o Done by afferent neurons coming into the CNS from the sensory inputs 1Synapses of Inhibitory or ory N oligodendrocytes -7 Schwann Cells The axon ends in terminal arborizations and end bulbs called terminal boutons which are part L of synapses o skeletal muscle Perikary (soma, body) Nucleus Axon Hillock Gray Matter CNS My White matter Nodes and PNS Neuroglia Terminal Bouton (Mot end Plate) Synapses of Inhibitory or ory N oligodendrocytes -7 Schwann Cells The axon ends in terminal arborizations and end bulbs called terminal boutons which are part L of synapses o skeletal muscle Perikary (soma, body) Nucleus Axon Hillock Gray Matter CNS My White matter Nodes and PNS Neuroglia Terminal Bouton (Mot end Plate)Naveen Sooknanan McGill Fall 2011  To organize and coordinate, directly or indirectly, most functions of the body, especially the motor, visceral, endocrine and mental activities o Done by efferent neurons sent out of the CNS Neurons are capable of responding to stimuli by altering electrical potential differences between their inner and outer surfaces  The same properties can be found in muscle and glandular cells Neurons react promptly to stimuli; modification of electrical signals may be restricted to the place that it received the stimulus or may be propagated as a nerve impulse (action potential) to transmit to other neurons or to muscle/glands  E.g. the neuromuscular end plate located on the center of every striated muscle fiber o This marks the connection (synapse) between a muscle fiber and the axon of a nerve (motor neuron) The nervous system can be divided into the central nervous system and the peripheral nervous system  The peripheral nervous system (PNS) brings in afferent neurons coming from receptors all over the body (skin, eyes, taste buds, nose, ears, muscle joints) o They form synapses in the spinal cord where they enter the central nervous system (CNS)  The central nervous system includes the brain and spinal cord, which are the major information processing units o This is where thinking and conscious actions, as well as subconscious actions, manifest themselves o The CNS sends out afferents neurons which outputs corresponding to the inputs from the PNS o These outputs travel to where they came from and give the body instructions on how to respond to stimuli  They innervate mainly muscle cells (smooth and striated) as well as glands All neurons have 2 processes: a number of dendrites and a single axon  The perikaryon is the cell body of the neuron, located within the CNS, where the nucleus is o This part of the neuron resembles a typical cell, containing organelles such as the ER and the mitochondria 2NU AH Ultrasincture of Neurons Axo-dendri Axo-somatic PrSM Axo-axonic SV Synap Lipofuscin PoSM Nissl Bodies (RER, free ribosomes) Neurotransmitters (released in synaptic clefts): Acetyl Choline, Norepinephrine, es Golgi GABA (gamma-amino butyric acid). Gl Extend throughout dendrites but not into Acid. Dop Serotonun the axon hillok Neuropeptides (not released in synaptic clefts): Endorphin. Intermedi Filaments Enkephalin. Neurofilaments) NU AH Ultrasincture of Neurons Axo-dendri Axo-somatic PrSM Axo-axonic SV Synap Lipofuscin PoSM Nissl Bodies (RER, free ribosomes) Neurotransmitters (released in synaptic clefts): Acetyl Choline, Norepinephrine, es Golgi GABA (gamma-amino butyric acid). Gl Extend throughout dendrites but not into Acid. Dop Serotonun the axon hillok Neuropeptides (not released in synaptic clefts): Endorphin. Intermedi Filaments Enkephalin. Neurofilaments)Naveen Sooknanan McGill Fall 2011 o The cytoplasm is filled with Nissl bodies, which are bundles of RER  Dendrites are input processes of the neuron and also contain Nissl bodies o Dendrites can branch out to form synapses with the axons of other neurons; these synapses can either be excitatory of inhibitory  The axon hillock is the beginning of the axon. There are NO MORE Nissl bodies here, which is how you can tell it apart from a dendrite  The axon is a single process which comes out of the neuron through the axon hillock o These axons are sometimes wrapped with myelin, making them look white o In the CNS, myelin is produced by oligodendrocytes, and in the PNS, it is produced by Schwann cells o Axons end in terminal arborisations called terminal boutons, which are part of synapses  For example, here the terminal boutons are motor end plates on striated skeletal muscle  Therefore, the CNS contains both dark matter and white matter: o Dark matter are cell bodies and neuroglia o White matter are myelinated axons and neuroglia  The PNS only contains white matter, which are myelinated axons and neuroglia (but no oligodendrocytes)  The autonomic nervous system is a branch of the peripheral nervous system which innervated various organs The ultrastructure of the neuron cell body is not unlike a “typical cell”  The nucleus is round and central  Nissl bodies are located throughout the cytoplasm everywhere but the axon and axon hillock o They are bundles of RER  Lysosomes are present in the neuron cell body and are responsible
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