The Nervous system - Mission College

The Nervous system - Mission College

Nervous System Chapter 7 1 Outline Functions of the Nervous System Nervous Tissue: Neuron Structure and Types The Nerve Impulse Synaptic Transmission System Organization: Main Divisions of the Nervous System

Central Nervous System Brain Spinal Cord Peripheral Nervous System Central Nervous System (CNS) Peripheral Nervous System (PNS) (Spinal Cord), Nerves and Ganglia

Homeostasis 2 Functions of the Nervous System Helps coordinate all the other systems of the body in conjunction with the endocrine system. Helps govern all organ function and the composition of

blood. Helps coordinate movement. Helps regulate blood pressure, heart rate, breathing rate. Helps regulate peristalsis in digestive tract. Involved in reproduction. Involved in control of urination and defecation. Provides us with the ability to reason and communicate. Allows positive interaction with environment. 3 Nervous Tissue: Neuron Structure and Types Nervous Tissue contains two types of cells. Neurons transmit nerve impulses between parts of the nervous system. Neuroglia support and nourish neurons. 4

Types of Neuroglial Cells Central Nervous System Neuroglia 1. Astrocytes- most abundant; have projections around 2. 3. 4. neurons & blood capillaries, anchor neurons to nutrient supply, help determine capillary permeability, control chemical environment of the neurons Microglia- spider-like phagocytes, remove debris & bacteria Oligodendrocytes- wrap plasma membranes around neurons, create myelin sheath for CNS neurons,

increases conduction speed of neuronal impulse Ependymal Cells- line cavities in the brain, cilia circulates the cerebrospinal fluid- cushioning fluid in the brain 5 Figure 7.3 Supporting (glial) cells of nervous tissue. Capillary Myelin sheath Neuron Process of oligodendrocyte Nerve fibers Astrocyte (a) Astrocytes are the most abundant and versatile neuroglia.

(d) Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers. Satellite cells Neuron Microglial cell (b) Microglial cells are phagocytes that defend CNS cells. Fluid-filled cavity Ependymal cells Brain or spinal cord tissue (c) Ependymal cells line cerebrospinal fluid-filled cavities. 2015 Pearson Education, Inc.

Cell body of neuron Schwann cells (forming myelin sheath) Nerve fiber (e) Satellite cells and Schwann cells (which form myelin) surround neurons in the PNS. Types of Neuroglial Cells (Cont.) Peripheral Nervous System Neuroglia 1. Schwann Cells- wrap plasma membranes around 2. neurons, create myelin sheath for PNS neurons, increases conduction speed of neuronal impulse Satellite Cells- act as protective, cushioning cells

7 Figure 7.5 Relationship of Schwann cells to axons in the peripheral nervous system. Schwann cell cytoplasm Axon Schwann cell plasma membrane (a) Schwann cell nucleus (b) Neurilemma Myelin

sheath (c) 2015 Pearson Education, Inc. Figure 7.3 Supporting (glial) cells of nervous tissue. Capillary Myelin sheath Neuron Process of oligodendrocyte Nerve fibers Astrocyte (a) Astrocytes are the most abundant and versatile neuroglia. (d) Oligodendrocytes have processes that form

myelin sheaths around CNS nerve fibers. Satellite cells Neuron Microglial cell (b) Microglial cells are phagocytes that defend CNS cells. Fluid-filled cavity Ependymal cells Brain or spinal cord tissue (c) Ependymal cells line cerebrospinal fluid-filled cavities. 2015 Pearson Education, Inc. Cell body of neuron

Schwann cells (forming myelin sheath) Nerve fiber (e) Satellite cells and Schwann cells (which form myelin) surround neurons in the PNS. Neuron Structure Neurons contain three basic parts. Cell body contains nucleus and other organelles. Dendrites receive signals from sensory receptors or other neurons. Axon conducts nerve impulses to another neuron. 10 Figure 7.4a Structure of a typical motor neuron.

Mitochondrion Dendrite Cell body Nissl substance Axon hillock Axon Neurofibrils Nucleus Collateral branch One Schwann cell Axon terminal

(a) 2015 Pearson Education, Inc. Node of Ranvier Schwann cells, forming the myelin sheath on axon Neuron Types Neurons are classified according to function. Sensory neurons take impulses from sensory receptors to the CNS. Interneurons receive input from sensory neurons, and other neurons, and then communicate with other interneurons connected to the brain and with motor neurons. Motor neurons take nerve impulse away from the CNS to an effector that carries out responses to environmental change.

12 Types of Neurons 13 Figure 7.6 Neurons classified by function. Central process (axon) Sensory Spinal cord Cell neuron (central nervous system) body Ganglion Dendrites Peripheral process (axon) Afferent transmission

Interneuron (association neuron) Peripheral nervous system Receptors Efferent transmission Motor neuron To effectors (muscles and glands) 2015 Pearson Education, Inc. The Nerve Impulse

The nervous system uses the nerve impulse to convey information. Resting potential is the voltage level when an axon is not conducting an impulse. Sodium-potassium pump (requires ATP) causes greater concentration of Na+ outside the axon, and greater concentration of K+ inside the axon. Unequal ion distribution causes inside of axon to be negative relative to the outside. 15 Action Potential An action potential is a rapid change in polarity across an axomembrane as the nerve impulse occurs. All-or-none once threshold is reached. Sodium gates open, allowing Na+ to

move inside the axon. Potassium gates open, allowing K+ to move outside the axon. 16 Propagation of an Action Potential Each preceding portion causes an action potential in the next portion of an axon. As soon as an action potential has moved on, the previous portion of an axon undergoes a refractory period in which the sodium gates are unable to open. 17 Maintenance of the Resting Membrane Potential Bio 130 Human Biology

Figure 11.3 Resting and Action Potential 19 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the Normal or Slide Sorter views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Interstitial fluid

Interstitial fluid Axon cytoplasm Axon cytoplasm 2 1 REPOLARIZATION Sodium channels close Potassium channels open Potassium diffuses out Membrane repolarizes DEPOLARIZATION Sodium channels open Sodium diffuses in Membrane depolarizes

Membrane potential (mV) +30 0 PNa Threshold PK 70 0 1 2 3 4

5 6 Time (milliseconds) 3 RESTING POTENTIAL Sodium and potassium channels closed Na+-K+ pump matches rate of leakage REESTABLISHMENT OF RESTING POTENTIAL Potassium channels close Interstitial fluid Interstitial fluid Axon cytoplasm

Axon cytoplasm Figure 11.5 Transmission Across a Synapse Synapse is point of interaction between neurons. Not a direct interaction; a space between called synaptic cleft. Transmission across a synaptic cleft is carried out by chemicals called neurotransmitters stored in synaptic vesicles. Neurotransmitter binds to receptor on postsynaptic

membrane. Depending on the neurotransmitter and the receptor, response of postsynaptic neuron can be towards excitation or inhibition. 22 Figure 7.10 How neurons communicate at chemical synapses. Axon of transmitting neuron Receiving neuron 1 Action potential arrives. Vesicles Dendrite

Axon terminal Synaptic cleft 2 VesicleTransmitting neuron fuses with 4 Neurotrans3 Neurotrans- mitter binds plasma membrane. mitter is released into synaptic cleft. to receptor on receiving neurons membrane.

Neurotransmitter Na+ Receptor Synaptic cleft Ion channels Receiving neuron 2015 Pearson Education, Inc. Neurotransmitter is broken down and released. Na+ Neurotransmitter molecules

5 Ion channel opens. 6 Ion channel closes. System Organization Details Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. brain Central Nervous System (CNS) cranial nerves brain spinal cord spinal cord spinal nerves Peripheral Nervous System (PNS) sensory (afferent) nerves carry sensory information into brain and spinal cord

somatic sensory nerves: signals from skin, muscles, joints, special senses a. The two divisions of the nervous system. b. autonomic visceral sensory nerves: signals from body organs motor (efferent) nerves

carry motor information from CNS to effectors somatic motor nerves: signals to skeletal muscles, voluntary autonomic motor nerves: signals to smooth muscle, cardiac muscle, glands, involuntary sympathetic division fight or flight parasympathetic

division rest and digest System Organization Central Nervous System The central nervous system (CNS) is made up of the spinal cord and the brain. Both are wrapped in protective membranes, meninges, with spaces between meninges filled with cerebrospinal fluid. CNS is composed of two types of nervous tissue. Gray matter Cell bodies and short, nonmyelinated fibers.

White matter - Myelinated axon bundles or tracts. 25 CNS: The Brain The Cerebrum. The cerebrum, telencephalon, is the largest portion of the human brain. Communicates with, and coordinates activities of, other parts of the brain. Divided into left and right cerebral hemispheres. Divided by longitudinal fissure. 26 The Human Brain 27

Lobes of Cerebral Hemisphere 28 The Brain Diencephalon is made up of hypothalamus and thalamus, and circles the third ventricle. Hypothalamus: Hunger, sleep, thirst, body temperature, water balance; control pituitary gland Thalamus: Visual, auditory, somatosensory

Cerebellum is separated from the brain stem by the fourth ventricle. Input from eyes, ears, joints, muscles for maintenance of posture and balance; coordinated voluntary movements The brain stem contains the midbrain, pons, medulla oblongata, reticular formation. Medulla oblongata: Regulation of heartbeat, breathing, vasoconstriction Reticular formation is a complex network of nuclei and fibers in the brain stem; regulates alertness, waking up. 29

CNS & PNS Functions of the Spinal Cord. The spinal cord extends from the base of the brain through the foramen magnum into the vertebral canal. The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord, and is a center for reflex actions. 30 CNS & PNS: Spinal Cord and Spinal Nerves 31 CNS & PNS: Spinal Cord; Reflex Arc

Reflex Arc Animation 32 System Organization 33 CNS & PNS: Spinal Cord and Spinal Nerves Peripheral Nervous System The peripheral nervous system (PNS) is composed of nerves and ganglia. Nerves are bundles of axons.

Both sensory and motor axons exist in the nerves. Ganglia are areas of nerves containing collections of cell bodies. The sensory neurons are subdivided into two categories: 1. somatic sensory (head, body wall, limbs, special senses), 2. autonomic sensory (visceral organs) The motor neurons are subdivided into two categories: Somatic motor (skeletal muscle; voluntary) Autonomic motor (smooth, cardiac muscle, glands; involuntary)

The autonomic motors are subdivided into two categories: Sympathetic division (fight or flight) Parasympathetic division (rest and digest) 34 Somatic sensory & Autonomic sensory Somatic motors Autonomic motors Sympathetic Parasympath. 35 PNS: Autonomic System

Autonomic system regulates the activity of cardiac and smooth muscles and glands. This system covers all motor output to all the organs and blood vessels of the body. Broken down to two divisions, both use two neurons and one ganglion. Sympathetic division brings about fight or flight responses; ganglion close to spinal cord. Parasympathetic division brings about rest or digest, vegetative responses; ganglion close to or within effector organ. 36 Sympathetic Division 37

Parasympathetic Division 38 39 40 Homeostasis

Helps coordinate all the other systems of the body in conjunction with the endocrine system. Helps govern all organ function and the composition of blood. Helps coordinate movement. Helps regulate blood pressure, heart rate, breathing rate. Helps regulate peristalsis in digestive tract. Involved in reproduction. Involved in control of urination and defecation. 41 Need to Know Functions of the Nervous System 1. A. B.

C. D. E. F. G. 2. Coordination of body functions; assisted by endocrine system Govern organ function Regulation of heart rate, breathing, blood pressure Regulation of coordinated movement Provides ability to reason and communicate Regulation of peristalsis Regulation of urination and defecation Neuron types A. Sensory neurons B.

Interneurons C. Motor neurons 42 Need to Know (Cont.) 3. Nervous System Organization A. CNS; brain and spinal cord B. PNS; nerves and ganglia C. Sensory neurons; somatic & autonomic; dorsalroot ganglia D. Motor neurons; somatic and autonomic E. Autonomic motor neuron divisions; sympathetic and parasympathetic F.

Placement of ganglia in sympathetic and parasympathetic divisions G. Functionality of both divisions (sympathetic & parasympathetic) 43 4. 5. Need to Know (Cont.) Spinal Cord Organization A. White and gray matter, what are they? B. Dorsal-root ganglia and dorsal roots and ventral roots C. Spinal cord reflex arcs, understand how they work

Brain A. Function of hypothalamus, cerebellum, medulla oblongata 44

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