3 Neuroanatomy refers to the study of the parts and function of neurons. Neurons are individual nerve cells.The entirety of the human body’s neurons make up the nervous system, from the brain to the tips of the toes.
4 Neuron The basic building block of the nervous system -- a nerve cell Neurons perform three basic tasksReceive informationCarry the informationPass the information on to the next neuron
6 A. DendritesThin, branching fibers lined with receptors at which the dendrite receives information from other neurons. The greater the surface area, the greater the amount of information. Some dendrites are covered with spines which greatly increase its surface area.
7 B. Cell Body/SomaContains the (C) nucleus and other parts of the cell needed to sustain life
8 D. AxonWire-like structure ending in the terminal buttons that extends from the cell body
9 E. Myelin SheathAn insulating, fatty covering around the axon that speeds neural transmissions. Axons that are myelinated appear white. Known as “white matter.”
10 F. Schwann CellsProvide for the growth of the myelin sheath.
11 G. Nodes of RanvierRegularly spaced gaps in the myelin sheath around an axon or nerve fiber. This is where depolarization takes place.
12 H. Terminal ButtonsThe branched end of the axon that contains neurotransmitters
18 At the terminal buttons, neurotransmitters are released into the synapse and passed along to the dendrites of the next neuron.
19 If enough neurotransmitters have been sent, the next neuron will fire If enough neurotransmitters have been sent, the next neuron will fire. If not, the message ends. This is called the all-or-nothing principle.
20 All-or-None Principle The principle that if a neuron fires it will always fire at the same intensityAll action potentials are of the same strength.A neuron does NOT fire at 30%, 45% or 90% but at 100% each time it fires.
23 Resting PotentialThe state of a neuron when it is at rest and capable of generating an action potentialThe neuron is set and ready to fire
24 Resting PotentialWhile in resting potential, a neuron is said to be “Polarized”negative ions are within the cell. Surrounding the cell are positively charged ions.The ions cannot mix while in this stage
25 A neuron has a pre-set level of stimulation that needs to be met or exceeded in order for it to pass the received impulses on to the next neuron. This is called a neuron’s threshold.
26 If the threshold has been met a chain reaction begins. The cell becomes depolarized and allows positively charged ions into the axon at the nodes of ranvier.
29 Action PotentialThis mix of positive and negative ions causes an electrical charge to form (an action potential).A brief electrical charge that travels down the axon of the neuron.A neural impulseConsidered an “on” condition of the neuron
30 Once the refractory period is complete the neuron can fire again The “recharging phase” when a neuron, after firing, cannot generate another action potentialOnce the refractory period is complete the neuron can fire again
31 Refractory PeriodExcess neurotransmitters are reabsorbed by the sending neuron – this is called re-uptakeThe cell becoming polarized once again.
35 Neuron firing like a Toilet Like a Neuron, a toilet has an action potential. When you flush, an “impulse” is sent down the sewer pipe
36 Neuron firing like a Toilet 2. Like a neuron, a toilet has a refractory period. There is a short delay after flushing when the toilet cannot be flushed again because the tank is being refilled
37 Neuron firing like a Toilet Like a Neuron, a toilet has a resting potential. The toilet is “charged” when there is water in the tank and it is capable of being flushed againLike a Neuron, a toilet operates on the all-or-none principle – it always flushes with the same intensity, no matter how much force you apply to the handle
39 Click here to see a neuron in action! Click here to see a quick summary!
40 Depending on what type of neurotransmitter has been released, the next neuron will react differently.….so, since the entire body is a connection of nerves, …
41 Inhibitory vs Excitatory Inhibitory neurotransmitters decrease the likelihood of the firing action potential of a cell whileExcitatory neurotransmitters increase the likelihood of action potential
42 Acetylcholine (ACh)ExcitatoryInvolved in muscle action, learning, and memoryUndersupply - Alzheimer’s disease
43 DopamineInhibitory:Pleasure, Reward and Motivation, Motor Control over Voluntary MovementsExcessive dopamine linked to schizophrenia;
44 Serotonin Inhibitory Affects mood, hunger, sleep, and arousal Undersupply is linked to depression; Prozac and other anti-depressants raise serotonin levels
45 Epinephrine and Norepinephrine Excitatory: Used for arousal in the flight/fight response, plays a role in learning and memory retrievalAdrenaline Burst of Energy (small amounts in brain)Undersupply can depress mood
46 GABAInhibitory:offsets excitatory messages (see Glutamate); helps regulate daily sleep-wake cyclesUndersupply linked to anxiety, seizures, tremors, and insomnia
47 Glutamate Excitatory Involved in memory, learning and movement Oversupply can overstimulate the brain, producing migraines or seizures (epilepsy)
48 EndorphinsInhibitory: Natural opiates that are involved in pain perception and positive emotionsreleased in response to pain and vigorous exercise
49 Drugs and Chemicals Interact with Neural Transmission
50 Some drugs that people put into their bodies are classified as agonists. Agonists may either speed up the neural process, cause an over-release or absorption of a neurotransmitter, or block the re-uptake process.
52 Some agonists mimic the effects of a naturally occurring neurotransmitter Agonist (like morphine – replacing natural endorphines)Dendrite of receiving Neuron
53 If re-uptake is blocked, the lingering neurotransmitters in the synapse will continue to be absorbed until it is gone.Therefore, a lingering feeling will occur
54 Cocaine – blocks the re-uptake of dopamine Examples of AgonistsCocaine – blocks the re-uptake of dopamineMDMA (Ecstasy) – blocks the reuptake of serotoninRepeated use destroys serotonin producing cells
55 Some drugs that people put into their bodies are classified as antagonists. Antagonists may slow or stop the transmission of a neurotransmitter, or they may bind themselves to receptors on a neuron’s dendrite, thus not allowing a message to be passed on.
56 Examples of Antagonists Curare – a poison that stops the flow of Ach – causes paralysisAntagonist (like curare)Neurotransmitter (such as Ach)Dendrite of receiving Neuron
57 There are three types of neurons: Afferent Neurons (Sensory Neurons)InterneuronsEfferent Neurons (Motor Neurons)
58 Types of NeuronsAfferents, or “sensory neurons”, carry information from the body to the brain
59 Types of NeuronsInterneurons, found in the spinal cord and the braininterpret incoming information and determine the next course of action
60 Types of NeuronsEfferents, or “motor neurons”, carry information from the spinal cord or the brain to the rest of the body in order to initiate behavior
61 The exceptions to the “general pathway” of neural activity are reflexes.
62 Reflexes are controlled by the spinal cord without any conscious effort on behalf of the brain.
63 Reflexes are primitive responses protect our bodies from danger
64 Yawning (too much carbon dioxide in the blood) ReflexCoughingBlinkingYawning (too much carbon dioxide in the blood)….etc…….
65 Reflex Sensory to spinal cord to motor… no brain processing involved….