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The Nervous System - Micro


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Visual this or perish!
Slide 8 in Nervous System PowerPoint!
Overview of physiology/function-What are the NS’s three main functions:
1) Sensory (sensations coming in) 2) Integrative (associates/processes/“thinks”) 3) Motor (directs movement)
Histology
Study of Cells
What are the two principal cell types inside the nervous system?
1) Neurons 2) Neuroglia (glial cells)
Sensory Function
Sensory Going In 1) Wires for every sense we have 2) each individual wire carries a different signal 3) heat perceived by a receptor (light/deep touch/cold/pain) all carried separately 4) Wires all go to different parts of the brain 5) Required because the brain cannot interact with the environment directly
Integrative Function
1) Input integration-Brain must decide what to do with sensory input 1) Asks- what does it mean?/Is it a threat?/Is it good?/Do I want to eat it?/Is it something I want to mate with? 3) All of the senses-auditory cues/visual cues/olfactory
What do neurons do?
1) Run electrical signals down wires (Excitable cells that transmit electrical signals) 2) Their cell membrane is designed to carry electrical signals. This is how we get a signal from our brain to ou
Motor Function
1) Motor output goes to the muscles2) Brain must decide what to do about it – Am I going to tell my adrenal glands to pump out some adrenalin to get me ready for fight/flight reaction? Am I going to move my hand? Am I going to start digesting my food? 3) Upper part of brain (higher cortex) deciding what to do (make an effect) with stimulus at hand.
What do neuroglia (glial cells) do?
Supporting cells – “Glue cells” which help the NS function 1) (CNS) Astrocytes/Microglia/Ependymal cells/Oligodendrocytes 2) (PNS) Satellite cells/Schwann cells Astrocytes
Microglia
1) Immune system (defensive ) component of the CNS - Phagocytize microorganisms and neuronal debris. Migrate toward injured neurons (take broken cells
Sensory Input - Review
1) Information gathered by sensory receptors about internal and external changes 2) Sensory input=ascending fibers going up-sensory input coming from bottom/up along the ascending fibers along the sides of the spinal cord until it gets to the higher parts of the brain
Integration - Review
Interpretation of sensory input
Oligodendrocytes
Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers (Not in the PNS). 1) Processes wrap CNS nerve fibers
Motor Output Review
1) Activation of effector organs (muscles and glands) produces a response 2) Descending fibers leaving the brain via synapsing neurons (chemical communication as the brain tells something else what to do
Satellite Cells and Schwann Cells
Satellite cells and Schwann cells (which form myelin) surround neurons in the PNS. 1) Satellite cells - Surround neuron cell bodies in the PNS 2) Schwann cells (neurolemmocytes) - Surround peripheral nerve fibers and form myelin sheaths 3) Vital to regeneration of damaged peripheral nerve fibers
What are the two parts of the Nervous System?
1) Central Nervous System (CNS) 2) Peripheral Nervous System (PNS) 3) They are both anatomically and physiologically different
Ependymal Cells
1) Brain/Blood Barrier. Separate the CNS interstitial fluid from the cerebrospinal fluid in the cavities (creates an air-tight/water-tight barrier around the brain) 2) Line the central cavities of the brain and/or spinal column - Maintains concussive events/cushions the brain (keeps us alive after high velocity accidents 3) Separates blood supply from the brain making it more difficult for infections to occur. 4) Range in shape from squamous to columnar – very cellular tightly packed 5) May be ciliated
Neurons
Nerve Cells
Central Nervous System (CNS)
1) Brain and Spinal Cord 2) Integration and command center
Are neurons long or short-lived?
Long-lived (100 + years)
Peripheral Nervous System (PNS)
1) All the nerves connected outside the spinal cord 2) Paired spinal and cranial nerves carry messages to and from the CNS
What is amitosis?
Relating to or denoting the division of a cell nucleus into two parts by constriction without the involvement of a mitotic apparatus. (Mitosis is cloning)
How or Why do we die when we are hanged?
1) We paralyze the nerve that goes to the diaphragm which is located inside the CNS 2) We do not die from the breaking of the neck 3) Nerves located in CNS are mostly impossible to fix-brain damage and spinal cord damage are permanent
Is brain damage permanent?
Yes! Brain damage is permanent. Brain can change but cannot heal.
What happens to nerves that are damaged outside the CNS?
1) Nerves located in the PNS will rewire 2) At a growth rate of one mm per day
Do we make new nerve cells?
No! We are born with all we will every have (what about regeneration?) But we do have billions of neurons.
What are the functional divisions of the PNS?
1) Sensory Division2) Motor Division
What does the Sensory division do?
1) It carries sensation (sensorium) 2) Afferent (sensory) division (Up-toward the brain)
Are neurons highly metabolic?
Yes! They carry a huge amount of oxygen and glucose demand.
Sensory fibers
1) Somatic (coming from the body) afferent (sensory going towards the brain) fibers (made out of nerve cells) —convey impulses from skin/skeletal muscles/joints 2)Visceral (coming from the organs) afferent fibers—convey impulses from visceral organs (literally means guts but used for organs in general)
Why does the brain need so much oxygen and glucose?
Because it is always doing something - always breathing/thinking/regulating/processing information/balancing muscles against gravity/keeping you awake.
What does the Motor Division do?
1) Transmits impulses from the CNS to effector organs 2) Efferent division (Descending-away from the brain - toward the organs or skeletal muscles)
What happens if you cut off oxygen to the brain?
Central Nervous System problems. Even after a few minutes you will have cell death. Brain death happens very quickly.
Hypoxia
Deficiency in oxygen to tissues
What are the two Motor Divisions of PNS?
1) Somatic (voluntary) nervous system 2) Autonomic (involuntary) nervous system (ANS)
Somatic (voluntary) nervous system
Conscious control of skeletal muscles
Metabolism
The chemical processes that occur within a living organism in order to maintain life.
Autonomic (involuntary) nervous system (ANS)
1) Visceral motor nerve fibers 2) Regulates smooth muscle/cardiac muscle/and glands 3) Two functional subdivisions: a) Sympathetic and b) Parasympathetic
Cell Membrane
Phospholipid bilayer adapted to run an electrical signal
Can you see a neuron?
No! Neurons are microscopic
What is an axon?
It is the part of the neuron that stretches to the periphery
What about the length of neurons?
Axons Yet can be very long → 3 or 4 feet long (10s of 1000’s neurons long) But you still can’t see it!
Which cell can you see with the naked eye?
Ovum – female egg
What is the center of the neuron cell body called?
Soma Body(perikaryone)
Soma contents?
1) Has a nucleus 2) Well developed Golgi Apparatus 3) Neurofilaments 4) Rough ER What are neurotransmitters made out of?
Inside the Cell Body (Perikaryon or Soma)
1) Network of neurofibrils (neurofilaments) 2) Axon hillock—cone-shaped area from which axon arises 3) Clusters of cell bodies are called nuclei in the CNS
Axon
Wire going away from the neuron-propagating a signal away from the neuron-outgoing information to muscle/another neuron/gland/etc
Where do the cell bodies all hang out in the larger parts of brain and spinal cord?
Ganglia or nuclei within the CNS. Cell bodies that all correspond to one place in the spinal cord.
Recognize subcomponents of a neuron
Slide 25
What do the dendrites do?
1) Dendrites are little wires that go towards the cell body 2) Typically bringing a signal in towards the nucleus 3) Incoming information
What do axons do?
Axons – propagate a signal out/away to somewhere else where that axon is wired to→muscle/another neuron/gland/etc.
Saltatory conduction
Signal jumping from one node of Ranvier to the other
Nodes of Ranvier
1) Gaps between the Schwann cells where there is no insulation
Saltatory conduction - Pathway of Electrical Signal
1) Electrical signal goes down the wire over the axon from the neuron sending/initiating at the axon hillock 3) the wire has signals going down the wire protected in this case by the Schwann cell 4) Electrical signal sent the same exact time 5) two separate signals coming down 6) signals jumping across the parts
Terminal branches
1) Where an axon ends or terminates 2) plural because there are multiple branches making multiple endings 3) If it were a bicept endings would intercept at 10-15 parts of muscle to initiate a muscle contraction
Neuromuscular junction
Where the signal changes from electrical signal to a chemical signal.
Wiring of Process Bundles (Pathways)
1) Nerves have to run in the same direction
Where are pathways (tracts) located?
CNS
Where are pathways (nerves) located?
PNS
Where is the nerve?
The nerve is not where the cell body is it is were the axons and dendrites are?
Dendrites – Review
1) Short/tapering/diffusely branched 2) Receptive (input) region of a neuron (coming into the cell body) 3) Convey electrical signals toward the cell body as graded potentials
Axon – Review
1) One axon per cell arising from the axon hillock 2) Long axons (nerve fibers) 3) Occasional branches (axon collaterals)
More about the End of the Axon
1) Numerous terminal branches (telodendria) 2) Knob-like axon terminals (synaptic knobs or boutons) a) Secretory region of neuron b) Release neurotransmitters to excite or inhibit other cells (accelerate or decelerate activity)
Where is the chemical part of the signal?
The chemistry at the neuron end → neuromuscular junction
Axon Function
1) The wire leading away 2) Conducting region of a neuron 3) Generates and transmits nerve impulses (action potentials) away from the cell body Axon Function Directions
Anterograde Transmission Examples:
mitochondria/membrane components/enzymes
Retrograde Transmission Examples:
organelles to be degraded/signal molecules/viruses/bacterial toxins
Myelin Sheath
1) Fatty tissue surrounding the axon to protect the tissue 2) Phosopholipid membrane protects the axon
What does the myelin sheath protect?
1) The electrical signal of the axon by keeping it insulated 2) The more fat the more efficient the Schwann Cells or Oligodentricytes wrap around the axon → faster the speed of the neuron
What does rubbing the arm do?
Overload the brain with faster coated nerve signals. Process: Hit your funny bone → Pain stimulus → rub the area → stimulates other nerve cells in the area → brain feels friction/vibration/touch → fee
Why is pain perception so slow?
Because pain fibers are unmyelinated the pain signal is relatively slow in getting to the brain
Myelin Sheath in the PNS
Concentric layers of Schwann cell membrane
What is the Neurilemma in PNS
peripheral bulge of Schwann cell cytoplasm
What are the Nodes of Ranvier?
1) Myelin sheath gaps between adjacent Schwann cells (PNS) 2) Sites where axon collaterals can emerge
Unmyelinated Axons in PNS
1) Thin nerve fibers are unmyelinated 2) One Schwann cell may incompletely enclose 15 or more unmyelinated axons
Myelin Sheaths in the CNS
1) Formed by processes of oligodendrocytes
Why are Omega-3’s good and where do they come from?
1) High fatty acids good for the brain. 2) Come from fish 3) Omega-3 much more stable and protective than other omegas.
What is the brain made out of?
Brain matter is created out of fat.
What is White matter?
Dense collections of myelinated fibers
What is Gray matter?
1) Mostly neuron cell bodies and unmyelinated fibers 2) Outer most layer of the cortex