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Nervous Tissue Will Kleinelp Associate Professor Department of Biology

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1 Nervous Tissue Will Kleinelp Associate Professor Department of Biology

2 Comprised of brain cranial nerves spinal cord spinal nerves ganglia enteric plexus sensory receptors

3 Functions sense changes in internal and external environment via sensory receptors analyze sensory information, store information and decision making processes respond to stimuli via muscles glands or other nerves

4 Organization Central nervous System (CNS) brain spinal cord
Peripheral nervous System (PNS) cranial nerves spinal nerves sensory and motor components ganglia receptors Peripheral Nervous System Subdivisions somatic nervous system - voluntary autonomic nervous system (ANS) - involuntary sympathetic division parasympathetic division enteric nervous system - enteric plexi throughout GI tract

5 Peripheral Nervous System

6 Autonomic Nervous System
• Responsible for involuntary visceral motor activity • conducts impulses from the CNS to • cardiac muscle • smooth muscles • glands • Two Divisions SYMPATHETIC Engages body systems during activity PARASYMPATHETIC Conserves energy antagonist of sympathetic system

7 Enteric Nervous System
• Sensory receptors and neurons located in GI tract and enteric plexuses • Involuntary motor neurons in the enteric plexuses • Effects smooth muscle, gastroitestinal and endocrine glands of the GI tract

8 Cells of the Nervous System
• Supporting cells - neuroglia smaller thean neurons comprise 1/2 mass of the brain approximately 10x more numerous than neurons • Neurons

9 Astocytes NEUROGLIA most abundant
contains radiating processes that adhere neurons to nearby blood capillaries make exchanges between capillaries and neurons guide developing neurons aid in synapse formation aid in cleaning up leaked K ions recapture neurotransmitters aid in information processing in the brain

10 Microglia NEUROGLIA contains thorny extensions
function to monitor health of nearby neurons migrate towards injured or unhealthy neurons converts macrophages to destroy/remove neuronal debris and microorganisms only protecting within the CNS

11 Ependymal Cells NEUROGLIA shaped from squamous to columnar
some ciliated located in the central cavities of brain and spinal cord form a permeable barrier between the CSF of these cavities and surrounding tissue

12 Oligodendrocytes NEUROGLIA similar to astrocytes
position themselves along thick neuron fibers in CNS wrap processes around neuron produce insulating myelin sheaths

13 Satellite & Schwann Cells
NEUROGLIA Satellite & Schwann Cells both located in the PNS Satellite cells surround neuron cell bodies with unknown function Schwann cells are also called neurolemmocytes these surround the myelin sheath aid in the formation of myelin similar to oligodendrocytes aid to repair damaged PNS nerve fibers

14 THE NEURON Functional cell of the nervous system
transmit and conduct impulses from one part to another found as afferent or sensory efferent or motor internuncial or association CHARACTERISTICS longevity - with adequate nutrition will last a lifetime amitotic - once fucntional they lose the ability to divide and cannot be replaced...EXCEPT olfactory epithelium memory cells o the hippocampus retain a high metabolic rate - require continuous and abundant supplies of glucose and oxygen

15 100,000,000,000

16 cell body dendrites axon collateral nucleus axon hillock neurofibrils neurilemma nissl bodies axon cylinder myelin sheath node of Ranvier axon terminals synaptic end bulbs

17 D CB D D CB AX AX AX CB AT AT AT Multipolar Unipolar Bipolar one dendrite; one axon; fond in retina if eye, inner ear and olfactory area of the brain begin as bipolar in fetus multiple dendrites; one axon; found in brain and spinal cord

18 Kinesin Movement Review References
Review References

19 Ion Channels

20 Ion channels control the movement of ions through the neuronal cell membrane. Ion channels are
selective passive or active regionally located functionally unique

21 Selective Ion Channels
Selective channels select ions for passage based on the charge of the ion, the size of the ion and how much water the ion can attract and hold around it

22 Ion Channels Ion channels are either active or passive
Active channels have gates that either open or close the channel passive channels or leakage channels are always open and allow ions to flow continuously. These channels are located throughout all parts of the neuron.

23 Voltage Regulated Channels
When a neuron is at rest the voltage regulated gates are closed. During an action potential, the voltage across the membrane changes with the flux of Na-K causing the voltage channels to open and close Ions move through open channels Found in axon hillock, nodes of Ranvier, all along unmyelinated axons

24 Chemically Regulated Channels or Ligand Gates
Some neurons have active channels that contain chemically controlled gates. Neurotransmitters such as acetylcholine (ACH) and GABA bind to chemically gated channels causing them to open. This then permits ions to move across the membrane. Located on dendrites and cell body.

25 Uniqueness of Ion Channels
Passive channels are responsible for resting membrane potential Passive channels Chemically gated channels are responsible for synaptic potentials or the incoming signals to a neuron Chemically gated channels Voltage gated channels are responsible for the generation and propagation of an action potential - the outgoing signal from the neuron Voltage gated channels

26 Impulse Conduction





31 Synapses



34 ELECTRICAL SYNAPSES When one neuron forms a gap junction with another neuron, an electrical synapse is made. Electrical current in the form of ions, flows directly from one neuron to another through the gap junction. These synapses are ALWAYS excitatory

35 CHEMICAL SYNAPSES at a chemical synapse the neuronal membranes are separated by a gap called the synaptic cleft. Electrical current CANNOT flow directly from one neuron to another. A chemical called a neurotransmitter is released from the sending neuron and carries the signal to the next neuron.

36 Parts of the Chemical Synapse
postsynaptic neuron synaptic cleft Synaptic vesicles presynaptic neuron


38 voltage gated Ca channel
1. impulse moves down neuron to axon terminal nerve impulse impulse reaches voltage gated Ca channels and the wave of depolarization causes gate to open and Ca ions to move in Ca influx recruits synaptic vesicles to migrate to presynaptic neurons membrane voltage gated Ca channel synaptic vesicles synaptic cleft neurotransmitters postsynaptic neuron

39 synaptic vesicles release neurotransmitter into synaptic cleft
neurotransmitteractivates channel to open and causes an influx of Na ions triggering an postsynaptic action potential neurotransmitters attaches to specific receptor sites on closed ligand gated channel postsynaptic neuron

40 - + - + - + - + - + - + - + - + - + - - - + - - - + + + + +

41 ` + Teduplicatext At 47 - - - + - - - + + + + +



44 EPSP & Excitatory Synapses


46 IPSP & Inhibitory Synapses











57 Serial Processing whole system works in a predictable all-or-nothing manner. One neuron stimulates the next, which stimulates the next, and so on, eventually causing a specific, anticipated response. examples of serial processing are spinal reflexes, and straight-through sensory pathways from receptors to the brain

58 Parallel Processing inputs are segregated into many pathways, and information delivered by each pathway is dealt with simultaneously by different parts of the neural circuitry. smelling a pickle (the input) may cause you to remember picking cucumbers on a farm; or it may remind you that you don’t like pickles or that you must buy some at the market; or perhaps it will call to mind all these thoughts. For each person, parallel processing triggers some pathways that are unique. The same stimulus—pickle smell, in our example—promotes many responses beyond simple awareness of the smell. Parallel processing is not repetitious because the circuits do different things with the information, and each “channel” is decoded in relation to all the others to produce a total picture.

59 References

60 Neurotransmitters Acetylcholine Glutamate
Major NT found in PNS neuromuscular junction where it excites skeletal muscle, and inhibits cardiac muscle is also found in the CNS is degraded via acetylcholinesterase Glutamate Most common excitatory NT in the CNS removed by active pumping back into the presynaptic end bulb Gamma amino butyric acid (GABA) Most common inhibitory NT in the CNS Anti-anxiety drugs enhance the action of GABA Norepinephrine In the brain NE effects sleep and moods. In the PNS, NE and epinephrine are main neurotransmitters of sympathetic postganglion synapses NE and epinephrine are also produced by the adrenal glands and are responsible for flight or flight responses this is a biogenic amine and is degraded enzymatically by monoamine oxidase Dopamine Found in the brain is involved in emotional responses and skeletal muscle movement this is a biogenic amine and is degraded enzymatically by monoamine oxidase Seratonin Found in the brain is involved in temperature regulation, sleeping, sensory perception and moods this is a biogenic amine and is degraded enzymatically by monoamine oxidase

61 Neurotransmitters Continued
Neuropeptides widespread throughout CNS and PNS some act as hormones Endorphins and Enkephalins involved in natural pain killing biochemical derivatives of morphine and heroin produce euphoric effects Nitric Oxide is not produce by vesicles like other NE is lipid soluble and diffuses out of the neuron acts to cause changes in cellular enzymes instead of a membrane receptor causes blood vessel vasodilation Phagocytes release NO in higher toxic levels to destroy invading cells

62 Neurotransmitter Removal
NT removal is absolutely necessary for normal synaptic function. If the NT lingers at the postsynpatic neuron, muscle fiber or gland it would cause continuous stimulation of the postsynaptic neuron. NT are removed via Diffusion - some NT naturally diffuse away from receptors after their action closing the gates Enzymatic degradation - most NT are degraded by enzymes released at the postsynaptic neuron. Enzymes are released once the gate has been activated Uptake by cells - many NT are actively transported into the neuron that released them via neurotransmitter transporters. Some NT are blocked from reuptake by therapeutic drugs. Neuromodulators as Welbutin and Prozac are selective seratonin reuptake inhibitors (SSRI). By preventing reuptake, stimulation is prolonged.


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