PSYC314 Chapter Notes - Chapter 2 : Myasthenia Gravis, Peripheral Nervous System, Axon Terminal
27 Apr 2018
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Chapter 2 structure and functions of cells of the nervous system
• All we are capable of doing is made possible by the integrated activity of the
nervous system – how we perceive, think, learn, remember, act
• Myasthenia gravis – grave muscle weakness- autoimmune disease when the
immune system breaks down proteins in the nervous system that allow cells
to receive messages
• Nervous system consists of 2 basic divisions- the central nervous system CNS
and the peripheral nervous system PNS
• The central nervous system consists of the parts surrounded by the bones of
the skull and the spinal column – the brain and spinal cord
➢ The CNS communicates through nerves to the rest of the body – the
nerves that are attached to the brain and spinal cord
• The peripheral nervous system is found outside those bones and consists of
the nerves and most of the sensory organs
• Nerves – bundles of thousands of individual neurons all wrapped in a tough
protective membrane
➢ Nerve fibers transmit messages through the nerve from a sense organ
to the brain or from the brain to a muscle of gland
• Sensory neurons – the PNS specialized cells gather light, sound waves, odors,
tastes, contact with objects
➢ Motor neurons- movements are accomplished by the contraction of
muscles in the PNS
➢ Interneurons- in between sensory and motor, they are the neurons
that lie entirely within the CNS there are local interneurons and relay
interneurons
• Neurons – information processing and information transmitting element of
the nervous system
➢ Have a high rate of metabolism but have no means of storing nutrients
– they have to be supplied constantly with nutrients and oxygen or
they will quickly die
➢ 4 structures of neurons –
➢ 1. Cell body or soma – cell body contains nucleus and much of the
machinery that provides for the life processes of the cell
➢ 2. Dendrites – serve as receivers of messages between communicating
neurons – receive neural messages that are transmitted across the
synapse (a small space between terminal buttons) of the sending cell
and a portion of the somatic/dendritic membrane of the receiving cell
– communication at a synapse proceeds in one direction from the
terminal button to the membrane of the other cell
➢ 3. Axon – the long slender tube often covered by myelin sheath – the
outer surface of the axon carries information from the cell body to the
terminal buttons and functions like an electrical cord carrying
electrical message from an outlet to an appliance – the basic message
the axon carries is called an action potential
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❖ action potential is a brief electrical even that starts at the end
of the axon next to the cell body and travels toward the
terminal buttons – like a brief pulse and is always the same
size and duration – it splits but does not diminish in size
❖ like dendrites axons and their branches come in different
shapes
➢ 4. Terminal buttons – at the ends of the branches there are knobs
called terminal buttons – their function is when an action potential
traveling down the axon reaches them they secrete a chemical called a
neurotransmitter – this chemical either excites or inhibits the
receiving cell and helps to determine whether an action potential
occurs in its axon – they release chemicals into the synapse
❖ an individual neuron receives information from the terminal
buttons of axons of other neurons and the terminal buttons of
its axons form synapses with other neurons
❖ can form synapses on the membrane of the dendrites or the
soma (cell body)
❖ axoplasmic transport is an active process that propels
substances along microtubule tracks that run inside the
length of the axon- movement from the soma to the terminal
buttons is called anterograde axoplasmic transport and this
type of transport is accomplished by molecules of a protein
called kinesin
❖ kinesin molecules resembles legs and feet and attach to the
item being transported down the axon it then walks down a
microtubule carrying the cargo to its destination
❖ dynein- a protein that carries substance from the terminal
buttons to the soma a process called retrograde axoplasmic
transport
❖ retrograde axoplasmic transport is about half as fast as
anterograde transport
• cell membrane – defines the boundary of the neuron, consists of a double
layer of lipid fatlike molecules – embedded in the membrane are protein
molecules some that detect substances outside of the cell such as hormones
and pass information about the presence of these substances to the interior
of the cell – others control access to the interior of the cell and others act as
transporters actively carrying certain molecules into or out od the cell
➢ interior of the neuron – contains a matrix of strands of protein called
cytoskeleton which gives the neuron its shape – made of 3 kinds of
protein strands linked to each other and forming a cohesive mass
❖ microtubules are the thickest of the strands and are bundles of
13 protein filaments arranged around a hollow core
❖ cytoplasm – a jellylike, semiliquid substance that fills the space
outlined by the membrane – contains small structures called
organelle
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❖ the nucleus – is a round or oval structure found in the soma the
cell body – it is enclosed by the nuclear membrane – the
nucleolus and the chromosomes reside inside the nucleus
❖ the nucleolus is responsible for the production of ribosomes,
small structures that are involved in protein synthesis
❖ the chromosomes which consist of DNA contain the organisms
genetic information
❖ when they are active chromosomes which are genes cause
production of another complex molecule messenger
ribonucleic acid mRNA which receives a copy of information
stored in that location – the mRNA leaves the nuclear
membrane and attaches to ribosomes
❖ proteins are produced through a 2 step process – the first step
transcription = information from DNA is transcribed into a
portable form mRNA which then takes this information to the
ribosomes for the 2nd step translation – during translation the
ribosomes use information from the mRNA and create proteins
❖ proteins provide structure and serve as enzymes which direct
the chemical process o f a cell by controlling chemical reactions
– enzymes are special protein molecules that act as catalysts
causing chemical reactions to take place without becoming a
part of the final product themselves
• endomembrane system (a network od internal membranes) – comprised of:
❖ endoplasmic reticulum = appears in two forms rough which contains
ribosomes and smooth which provides channels for the segregation of
molecules involved in various cellular processes – lipid fatlike
molecules are also produced here
❖ Golgi apparatus- special form of smooth endoplasmic reticulum –
some complex molecules made up of simpler molecules are assembled
here – also serves as a wrapping or packaging agent such as with
secretory cells that release hormones would wrap their product in
this
- when the cell secretes its product it uses a process called exocytosis
in which the membrane wrapped product migrates to the inside of the
outer membrane of the cell, fuses with the membrane and bursts
spilling its content into the fluid surrounding the cell – neurons
communicate by secreting chemicals in this way
❖ lysosomes – small sacs that contain enzymes that break down
substances no longer needed by the cell – these products are then
recycled or excreted from the cell
• mitochondria – shaped like oval beads and are formed from a double
membrane – the power plant of neurons
➢ the inner membrane is wrinkled creating shelves (cristae) that fill the
inside of the bead
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Document Summary
Motor neurons- movements are accomplished by the contraction of. They have to be supplied constantly with nutrients and oxygen or. Cell body or soma cell body contains nucleus and much of the. Dendrites serve as receivers of messages between communicating neurons receive neural messages that are transmitted across the. Communication at a synapse proceeds in one direction from the. Action potential is a brief electrical even that starts at the end. Like dendrites axons and their branches come in different terminal buttons like a brief pulse and is always the same size and duration it splits but does not diminish in size. Can form synapses on the membrane of the dendrites or the. Axoplasmic transport is an active process that propels shapes soma (cell body) Kinesin molecules resembles legs and feet and attach to the item being transported down the axon it then walks down a microtubule carrying the cargo to its destination.
