Seeley's Essentials of Anatomy & Physiology Eleventh Edition Chapter 8 - Nervous System, PDF

Because learning changes everything.® Chapter 8 Nervous System Part 1 Lecture Outline Seeley’s ESSENTIALS OF ANATOMY & PHYSIOLOGY Eleventh Edition Cinnamon VanPutte Jennifer Regan Andrew Russo Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the...

Because learning changes everything.® Chapter 8 Nervous System Part 1 Lecture Outline Seeley’s ESSENTIALS OF ANATOMY & PHYSIOLOGY Eleventh Edition Cinnamon VanPutte Jennifer Regan Andrew Russo Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. Nervous System Figure 8.1 Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 2 Nervous System Functions 1. Receiving sensory input 2. Integrating information 3. Controlling muscles and glands 4. Maintaining homeostasis 5. Establishing and maintaining mental activity Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 3 Main Divisions of Nervous System 1 Central nervous system (CNS) brain and spinal cord Peripheral nervous system (PNS) All the nervous tissue outside the CNS Sensory division Conducts action potentials from sensory receptors to the CNS Motor division Conducts action potentials to effector organs, such as muscles and glands Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 4 Main Divisions of Nervous System 2 Somatic nervous system Transmits action potentials from the CNS to skeletal muscles. Autonomic nervous system Transmits action potentials from the CNS to cardiac muscle, smooth muscle, and glands Enteric nervous system A special nervous system found only in the digestive tract. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 5 Organization of the Nervous System Figure 8.2 Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 6 Cells of the Nervous System Neurons receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs. Glial cells supportive cells of the CNS and PNS, meaning these cells do not conduct action potentials. Instead, glial cells carry out different functions that enhance neuron function and maintain normal conditions within nervous tissue. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 7 Neurons A neuron (nerve cell) has a: Cell body – which contains a single nucleus Dendrite – which is a cytoplasmic extension from the cell body, that usually receives information from other neurons and transmits the information to the cell body Axon – which is a single long cell process that leaves the cell body at the axon hillock and conducts sensory signals to the CNS and motor signals away from the CNS Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 8 Typical Neuron Figure 8.3 Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 9 Structural Types of Neurons 1 Multipolar neurons have many dendrites and a single axon. Most of the neurons within the CNS and nearly all motor neurons are multipolar. Bipolar neurons have two processes: one dendrite and one axon. Bipolar neurons are located in some sensory organs, such as in the retina of the eye and in the nasal cavity. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 10 Structural Types of Neurons 2 Pseudo-unipolar neurons have a single process extending from the cell body, which divides into two processes as short distance from the cell body. One process extends to the periphery, and the other extends to the CNS. The two extensions function as a single axon with small, dendrite-like sensory receptors at the periphery. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 11 Types of Neurons Figure 8.4 Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 12 Glial Cells 1 Glial cells are the supportive cells of the CNS and PNS. Astrocytes serve as the major supporting cells in the CNS. Astrocytes can stimulate or inhibit the signaling activity of nearby neurons and form the blood-brain barrier. Ependymal cells line the cavities in the brain that contains cerebrospinal fluid. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 13 Glial Cells 2 Microglial cells act in an immune function in the CNS by removing bacteria and cell debris. Oligodendrocytes provide myelin to axons of neurons in the CNS. Schwann cells provide myelin to axons of neurons in the PNS. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 14 Types of Glial Cells Figure 8.5 Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 15 Myelin Sheath 1 Myelin sheaths are specialized layers that wrap around the axons of some neurons, those neurons are termed, myelinated. The sheaths are formed by oligodendrocytes in the CNS and Schwann cells in the PNS. Myelin is an excellent insulator that prevents almost all ion movement across the cell membrane. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 16 Myelin Sheath 2 Gaps in the myelin sheath, called nodes of Ranvier, occur about every millimeter. Ion movement can occur at the nodes of Ranvier. Myelination of an axon increases the speed and efficiency of action potential generation along the axon. Multiple sclerosis is a disease of the myelin sheath that causes loss of muscle function. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 17 Unmyelinated Neurons Unmyelinated axons lack the myelin sheaths. These axons rest in indentations of the oligodendrocytes in the CNS and the Schwann cells in the PNS. A typical small nerve, which consists of axons of multiple neurons, usually contains more unmyelinated axons than myelinated axons. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 18 Myelinated and Unmyelinated Axons Figure 8.6 Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 19 Organization of Nervous Tissue Nervous tissue varies in color due to the abundance or absence of myelinated axons. Nervous tissue exists as gray matter and white matter. Gray matter consists of groups of neuron cell bodies and their dendrites, where there is very little myelin. White matter consists of bundles of parallel axons with their myelin sheaths, which are whitish in color. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 20 Resting Membrane Potential 1 All cells have electrical properties which are evident at their cell membranes. The phospholipid bilayer of the cell membrane is impermeable to ions but ions can cross the membrane through ion channels. Ions flow through ion channels due to differences in concentration across the membrane and due to charge difference across the membrane. There are two types of ion channels: leak channels and gated channels. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 21 Resting Membrane Potential 2 Leak channels are always open so ions can diffuse across the membrane, down their concentration gradient. Gated channels are closed until opened by specific signals. Chemically gated channels are opened by chemicals such as neurotransmitters. Voltage-gated channels are opened by a change in the electrical property of the cell membrane. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 22 Resting Membrane Potential 3 In most cells the inside of the membrane has a negative charge relative to the outside of the membrane which has a positive charge. The membrane is said to be polarized. A small, but measurable, voltage exists across the membrane. When the cell is at rest, this voltage is called the resting membrane potential. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 23 Resting Membrane Potential 4 Membrane potentials are due to differences in concentrations of ions across the membrane In a resting cell, there is a higher concentration of K+ inside the cell membrane and a higher concentration of Na+ outside the cell membrane. Also, there are negatively charged proteins trapped inside the cell because they are too large to pass through the cell membrane. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 24 Resting Membrane Potential 5 Leak channels contribute to the difference in ion concentrations across the membrane during resting membrane potential. There are 50 to 100 times more K+ leak channels than Na+ leak channels. The resting membrane has much greater permeability to K+ than to Na+. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 25 Resting Membrane Potential 6 The sodium-potassium pump is also required to maintain resting membrane potential. The pump actively transports K+ into the cell and Na+ out of the cell. It is estimated that the sodium-potassium pump consumes 25% of all the ATP in a typical cell and 70% of the ATP in a neuron. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 26 Resting Membrane Potential 7 Figure 8.7(1) Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 27 Resting Membrane Potential 8 Figure 8.7(2) Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 28 Resting Membrane Potential 9 Figure 8.7(3) Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 29 Nerve Cell Communication Nerve cells are excitable. The resting membrane potential can change in response to a stimuli. In nerve cells, this change is a means by which the cell communicates with other cells. The changes in membrane potential that nerve cells use to communicate with other cells are called action potentials. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 30 Gated Membrane Channels The stimuli that cause action potentials activate gated channels which are closed until opened by specific signals. The opening and closing of gated ion channels changes the permeability of the membrane to ions and can therefore change the membrane potential. Action potentials may result. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 31 Action Potential 1 Action potentials are electrical signals that are conducted along the cell membrane similar to electricity travelling along an electrical wire. The channels responsible for the action potential are voltage-gated Na+ and K+ channels, which are closed during resting membrane potential. When a stimulus is applied to the nerve cell, following neurotransmitter activation of chemically gated channels, Na+ channels open very briefly, and Na+ diffuses quickly into the cell. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 32 Action Potential 2 This movement of Na+, which is called a local current, causes the inside of the cell membrane to become positive, a change called depolarization. If depolarization is not strong enough, the Na+ channels close again, and the local potential disappears without being conducted along the nerve cell membrane. If depolarization is large enough, Na+ enters the cell so that the local potential reaches a threshold value. This threshold depolarization causes voltage-gated Na+ channels to open, generally at the axon hillock. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 33 Action Potential 3 The opening of these channels causes a massive, 600- fold increase in membrane permeability to Na+. Voltage-gated K+ channels also begin to open. As more Na+ enters the cell, depolarization continues at a much faster pace, causing a brief reversal of charge – the inside of the cell membrane becomes positive relative to the outside of the cell membrane. The charge reversal causes Na+ channels to close and Na+ then stops entering the cell. During this time, more K+ channels are opening and K+ leaves the cell, resulting in repolarization. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 34 Action Potential 4 At the end of repolarization, the charge on the cell membrane briefly becomes more negative than the resting membrane potential; this condition is called hyperpolarization and occurs briefly. Action potentials occur in an all-or-none fashion. All-or-none refers to the fact that if threshold is reached, an action potential occurs; if the threshold is not reached, no action potential occurs. The sodium-potassium pump assists in restoring the resting membrane potential. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 35 Action Potential 5 Figure 8.9 (1) Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 36 Action Potential 6 Figure 8.9 (2) Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 37 Action Potential 7 Figure 8.9 (3) Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 38 Action Potential 8 Figure 8.10 Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 39 Action Potential Conduction Once an action potential is generated it is conducted down the cell membrane in one of two ways: continuous conduction or saltatory conduction. Glial cells insulate the axons of some neurons; a characteristic called myelination. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 40 Unmyelinated and Myelinated Axon Action Potentials Action potentials in unmyelinated axons travel more slowly than in myelinated axons. Action potentials along unmyelinated axons occur along the entire membrane in a process called continuous conduction. Action potentials on myelinated axons occur in a jumping pattern at the nodes of Ranvier. This type of action potential conduction is called saltatory conduction. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 41 Conduction along the Axon Figure 8.11 Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 42 Axon Conduction Speed The speed of action potential conduction varies widely, even among myelinated axons; it is based on the diameter of axon fibers. Medium-diameter, lightly myelinated axons, characteristic of autonomic neurons, conduct action potentials at the rate of about 3 to 15 meters per second (m/s). Large-diameter, heavily myelinated axons conduct action potentials at the rate of 15 to 120 m/s. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 43 Synapse 1 A neuroneuronal synapse is a junction where the axon of one neuron interacts with another neuron. The end of the axon forms a presynaptic terminal and the membrane of the next neuron forms the postsynaptic membrane, with a synaptic cleft between the two membranes. Chemical substances called neurotransmitters are stored in synaptic vesicles in the presynaptic terminal. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 44 Synapse 2 An action potential reaching the presynaptic terminal causes voltage-gated Ca2+ channels to open, and Ca2+ moves into the cell. This influx of Ca2+ causes the release of neurotransmitters by exocytosis from the presynaptic terminal. The neurotransmitters diffuse across the synaptic cleft and bind to specific receptor molecules on the postsynaptic membrane. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 45 Synapse 3 The binding of neurotransmitters to these membrane receptors causes chemically gated channels for Na+, K+, or Cl− to open or close in the postsynaptic membrane. The specific channel type and whether or not the channel opens or closes depend on the type of neurotransmitter in the presynaptic terminal and the type of receptors on the postsynaptic membrane. The response may be either stimulation or inhibition of an action potential in the postsynaptic cell. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 46 Synapse 4 If Na+ channels open, the postsynaptic cell becomes depolarized, and an action potential will result if threshold is reached. If K+ or Cl− channels open, the inside of the postsynaptic cell tends to become more negative, or hyperpolarized, and an action potential is inhibited from occurring. There are many neurotransmitters, with the best known being acetylcholine and norepinephrine. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 47 Synapse 5 Neurotransmitters do not normally remain in the synaptic cleft indefinitely, thus their effects are short duration. These substances become reduced in concentration when they are either rapidly broken down by enzymes within the synaptic cleft or are transported back into the presynaptic terminal. An enzyme called acetylcholinesterase breaks down acetylcholine. Norepinephrine is either actively transported back into the presynaptic terminal or broken down by enzymes. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 48 The Synapse Figure 8.12 Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 49 Neuronal Pathway (Converging) The CNS has simple to complex neuronal pathways. A converging pathway is a simple pathway in which two or more neurons synapse with the same postsynaptic neuron. This allows information transmitted in more than one neuronal pathway to converge into a single pathway. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 50 Neuronal Pathway (Diverging) A diverging pathway is a simple pathway in which an axon from one neuron divides and synapses with more than one other postsynaptic neuron. This allows information transmitted in one neuronal pathway to diverge into two or more pathways. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 51 Neuronal Pathways Converging pathway Diverging pathway Figure 8.13 Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 52 Summation 1 A single presynaptic action potential usually does not cause a sufficiently large postsynaptic local potential to reach threshold and produce an action potential in the target cell. Many presynaptic action potentials are needed in a process called summation. Summation of signals in neuronal pathways allows integration of multiple subthreshold local potentials. Summation of the local potentials can bring the membrane potential to threshold and trigger an action potential. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 53 Summation 2 Spatial summation occurs when the local potentials originate from different locations on the postsynaptic neuron—for example, from converging pathways. Temporal summation occurs when local potentials overlap in time. This can occur from a single input that fires rapidly, which allows the resulting local potentials to overlap briefly. Spatial and temporal summation can lead to stimulation or inhibition, depending on the type of signal. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 54