Nervous Tissue Chapter 12 12 1 Nervous Tissue

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Nervous Tissue Chapter 12 12 -1

Nervous Tissue Chapter 12 12 -1

Nervous Tissue • Overview of the nervous system • Nerve cells (neurons) • Supportive

Nervous Tissue • Overview of the nervous system • Nerve cells (neurons) • Supportive cells (neuroglia) • Electrophysiology of neurons • Synapses • Neural integration 12 -2

Overview of Nervous System • Master Control of the Body – Endocrine and nervous

Overview of Nervous System • Master Control of the Body – Endocrine and nervous system maintain internal coordination • endocrine = _______________ • nervous – ____________ receive information – brain and spinal cord determine responses – brain and spinal cord ____________________________________ 12 -3

Subdivisions of Nervous System Two major subdivisions • _____________ – brain and spinal cord

Subdivisions of Nervous System Two major subdivisions • _____________ – brain and spinal cord enclosed in bony coverings • _____________ – nerve = _______________________ – _______ = swelling of ______ in a nerve 12 -4

Functional Divisions of PNS • Sensory (______) divisions (receptors to CNS) – visceral sensory

Functional Divisions of PNS • Sensory (______) divisions (receptors to CNS) – visceral sensory and somatic sensory division • Motor (________) division (CNS to effectors) – visceral motor division (ANS) effectors: cardiac, smooth muscle, glands • sympathetic division (action) • parasympathetic division (digestion) – somatic motor division effectors: skeletal muscle 12 -5

Fundamental Types of Neurons • Sensory (afferent) neurons – _________________________ – Transmit info to

Fundamental Types of Neurons • Sensory (afferent) neurons – _________________________ – Transmit info to brain/spinal cord • ______________ – In between sensory and motor pathways in CNS – 90% of neurons are interneurons – _________________________ • ______________ – send signals to muscles and glands – organs respond called effectors 12 -6

Properties of Neurons • ______________ – ability to respond to changes (stimuli) in/out of

Properties of Neurons • ______________ – ability to respond to changes (stimuli) in/out of body • Conductivity – ________________ • ______________ – __________________ 12 -7

Structure of a Neuron • _________________________ – single, central nucleus – cytoskeleton • microtubules

Structure of a Neuron • _________________________ – single, central nucleus – cytoskeleton • microtubules and neurofibrils (bundles of actin filaments) • RER Nissl bodies • _____________ – ___________ • Singe axon (nerve fiber) arising from axon hillock for rapid conduction – _______________________ 12 -8

Variation in Neural Structure • __________ – most common – many dendrites/one axon •

Variation in Neural Structure • __________ – most common – many dendrites/one axon • Bipolar neuron – ______________________ • __________ – sensory from skin and organs to spinal cord • Anaxonic neuron – many dendrites/no axon – help in visual processes 12 -9

Types of Neuroglial Cells • ______________________ – wraps around nerve fibers • ___________________________________________ –

Types of Neuroglial Cells • ______________________ – wraps around nerve fibers • ___________________________________________ – in areas of infection, trauma or stroke 12 -10

Types of Neuroglial Cells • ________________ – – – _________________________ regulate composition of brain

Types of Neuroglial Cells • ________________ – – – _________________________ regulate composition of brain tissue fluid convert glucose to lactate to feed neurons secrete nerve growth factor promoting synapse formation electrical influence on synaptic signaling sclerosis – damaged neurons replace by hardened mass of astrocytes • ____________________ 12 -11

Myelin • ____________________ – formed from wrappings of plasma membrane • 20% protein and

Myelin • ____________________ – formed from wrappings of plasma membrane • 20% protein and 80 % lipid (looks white) – all myelination completed by late adolescence • In PNS, hundreds of layers wrap axon – ______________________ – covered by basal lamina and endoneurium 12 -12 • Gaps between myelin segments = _________

Speed of Nerve Signal • Diameter of fiber and presence of myelin • _______________________

Speed of Nerve Signal • Diameter of fiber and presence of myelin • _______________________ • Speeds – small, unmyelinated fibers = 0. 5 - 2. 0 m/sec – small, myelinated fibers = 3 - 15. 0 m/sec – large, myelinated fibers = up to 120 m/sec • Functions – slow signals supply the stomach and dilate pupil – fast signals supply skeletal muscles and transport sensory signals for vision and balance 12 -13

Regeneration of Peripheral Nerves • Soma and neurilemmal tube intact • Stranded end of

Regeneration of Peripheral Nerves • Soma and neurilemmal tube intact • Stranded end of axon and myelin sheath degenerate – cell soma swells, ER breaks up and some cells die • Axon stump puts out several sprouts • _____________________________ – schwann cells produce nerve growth factors 12 -14

Local Potentials • Local disturbances in membrane potential – ___________________ – depolarization (opens gated

Local Potentials • Local disturbances in membrane potential – ___________________ – depolarization (opens gated Na+ channels) decreases potential across cell membrane • Na+ rushes in • Na+ diffuses for short distance inside membrane producing a change in voltage called a local potential 12 -15

Local Potentials 2 • ______________ – vary in magnitude with stimulus strength – get

Local Potentials 2 • ______________ – vary in magnitude with stimulus strength – get weaker the farther they spread – are reversible as K+ diffuses out of cell – ____________________________________ 12 -16

Action Potentials • __________________________________________ • If threshold potential (-55 m. V) is reached voltagegated

Action Potentials • __________________________________________ • If threshold potential (-55 m. V) is reached voltagegated Na+ channels open (Na+ enters causing depolarization) • Slow K+ gates fully open • K+ exits repolarizing the cell • _____________________ 12 -17 – excessive exiting of K+

The Refractory Period • Resists stimulation • ____________ – as long as Na+ gates

The Refractory Period • Resists stimulation • ____________ – as long as Na+ gates are open – _____________ • ____________ – as long as K+ gates are open – __________________________ • Refractory period occurs to a small patch of membrane at one time (quickly recovers) 12 -19

Impulse Conduction - Unmyelinated Fibers 12 -20

Impulse Conduction - Unmyelinated Fibers 12 -20

________________ • Voltage-gated channels needed for APs – fewer than 25 per m 2

________________ • Voltage-gated channels needed for APs – fewer than 25 per m 2 in myelin-covered regions – up to 12, 000 per m 2 in nodes of Ranvier • Fast Na+ diffusion occurs between nodes 12 -21

Saltatory Conduction • Notice how the action potentials jump from node of Ranvier to

Saltatory Conduction • Notice how the action potentials jump from node of Ranvier to node of Ranvier. 12 -22

Chemical Synapse Structure • ___________ have synaptic vesicles with neurotransmitter and __________ have receptors

Chemical Synapse Structure • ___________ have synaptic vesicles with neurotransmitter and __________ have receptors 12 -26

Types of Neurotransmitters • ________________ – • • Amino acid neurotransmitters ________________ – –

Types of Neurotransmitters • ________________ – • • Amino acid neurotransmitters ________________ – – – • formed from acetic acid and choline replace –COOH in amino acids with another functional group ___________ (epi, NE and dopamine) indolamines (serotonin and histamine) ________ 12 -27

Synaptic Transmission 3 kinds of synapses with different actions • ________________ = ACh •

Synaptic Transmission 3 kinds of synapses with different actions • ________________ = ACh • Inhibitory GABA-ergic synapse = GABA • ________________ = NE Synaptic delay (. 5 msec) – time from arrival of nerve signal at synapse to start of AP in postsynaptic cell 12 -29

Neural Integration • More synapses a neuron has the greater its information-processing capability –

Neural Integration • More synapses a neuron has the greater its information-processing capability – cerebral cortex 40, 000 synapses • estimated to contain 100 trillion synapses • Chemical synapses are decision-making components – ___________________ 12 -30

Postsynaptic Potentials- EPSP • _________________ – a positive voltage change causing postsynaptic cell ___________

Postsynaptic Potentials- EPSP • _________________ – a positive voltage change causing postsynaptic cell ___________ • result from Na+ flowing into the cell – glutamate and aspartate are excitatory neurotransmitters • ACh and norepinephrine may excite or inhibit depending on cell 12 -31

Postsynaptic Potentials- IPSP • __________________ postsynaptic cell to be less likely to fire (hyperpolarize)

Postsynaptic Potentials- IPSP • __________________ postsynaptic cell to be less likely to fire (hyperpolarize) • result of Cl- flowing into the cell or K+ leaving the cell – glycine and GABA are inhibitory neurotransmitters • ACh and norepinephrine may excite or inhibit depending upon cell 12 -32