Essentials of Human Anatomy Physiology Elaine N Marieb
Essentials of Human Anatomy & Physiology Elaine N. Marieb Seventh Edition The Nervous System Modified by J. Kalinowski 1/2014 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Functions of the Nervous System Sensory input – gathering information Uses sensory receptors to monitor changes (stimuli) occurring inside and outside the body Integration To process and interpret sensory input and decide if action is needed Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 1 a
Functions of the Nervous System Slide 7. 1 b Motor output A response to integrated stimuli The response activates muscles or glands Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Functions of Neuroglia § § Myelin production Structural support Communication Environmental monitoring
Neuroglia can replicate but cannot conduct Supports neurons
Neuroglial cells – write functions by the diagram • Microglia - scavenge and degrade dead cells, protecting the brain from invading microorganisms • Oligodendrocytes - form myelin sheaths around axons in the CNS • Schwann cells - form myelin sheaths around axons in the PNS
Neuroglial Cells • Ependymal cells - produce cerebrospinal fluid in brain and spinal cords • Astrocytes - provide nutrients to neurons, give synapses structural support, and block toxic substances
Nervous Tissue: Neurons = nerve cells Cells specialized to transmit messages – can conduct but cannot replicate Have 3 specialized characteristics Longevity: with nutrition, can live as long as you do Amitotic: unable to reproduce themselves (so cannot be replaced) High metabolic rate: require continuous oxygen & glucose (due to lots of activity) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 8
Neuroglia vs. Neurons Neuroglia divide. Neurons do not. Most brain tumors are “gliomas. ” Involve the neuroglia cells, not the neurons. As neuroglia grow out of control, they press on the neurons impairing their function
Neurilemma Why is the outer covering (neurilemma) of a neuron so important? It is the site of electrical signaling – also plays a crucial role in cell to cell interactions during development
Major Regions of Neurons Cell body Contains the metabolic/biosynthetic center of the cell (location of the nucleus) Does not contain centrioles (reflects amitotic nature) but has the other organelles Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 8
Neuron Anatomy Dendrites hundreds per cell – diffusely branched – close to cell body Receptive sites conduct impulses toward the cell body Immense surface area for reception Figure 7. 4 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 10
Neuron Anatomy • Axon hillock: site of summation for incoming information where the "decision" to initiate or not initiate a nerve impulse takes place
Neuron Anatomy Axons Transmit impulses away from cell body Vary in length and diameter Larger diameter = faster conduction Figure 7. 4 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 10
Neuron Anatomy Axons Axon terminals located at end of axon branches Figure 7. 4 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 10
Axon terminals Contain vesicles with neurotransmitters – chemicals which transmit electrical impulses Axonal terminals are separated from the next neuron or effector by the Synaptic cleft Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 11
Axon terminals Synaptic knob – site where action potential is converted into a chemical message Synapse – the entire junction between 2 nerves OR a nerve and another structure Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 11
Myelin Sheath Function: Protects & insulates fibers Increases speed of transmission through a process known as Saltatory Conduction Figure 7. 5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 12
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Functional Classification of Neurons Sensory (afferent) Nerve fibers that carry information from sensory receptors to the central nervous system (CNS) Ends of dendrites associated with specialized receptors Figure 7. 1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Sensory Receptors • Cutaneous receptors: pressure, nociceptors (pain), thermoreceptors (heat & cold) • Proprioceptors: muscles, tendons, organs: amount of stretch or tension • Specialized receptors in sense organs: photoreceptors (light), mechanoreceptors (hearing & equilibrium), chemoreceptors (smell & taste)
Functional Classification Motor (efferent) division Nerve fibers that carry impulses from the central nervous system to muscles & glands Association or Interneurons Responsible for integration & reflex – connect motor & sensory neurons Make up over 99% of neurons Figure 7. 1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 3 b
Reflex Activity Reflex: rapid predictable motor response to stimuli that the body is programmed to do Unlearned, unpremeditated, involuntary Withdrawal from pain Learned or acquired reflexes result from repetition or practice. Example: experienced driver drives a car Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 58
Reflex Activity Two types: Autonomic: regulate the activity of smooth muscles, the heart, and glands Examples: salivary reflex, pupilary reflex, digestion, blood pressure Somatic reflexes: skeletal muscle reflexes Example: knee jerk reflex Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 58
Reflex – define 5 elements of Know your diagram
Functional Properties of Neurons Two major functional properties of neurons resulting in electrochemical event Irritability - ability to respond to stimuli & convert it into a nerve impulse Conductivity – ability to transmit an impulse to other neurons, muscles, or glands Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 17
Synapse – know the diagram Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 11
Regeneration • Mature neurons are incapable of mitosis. • PNS nerve axons can regenerate successfully if cell body is not destroyed • Uninjured cell body swells to prepare to synthesize proteins to support regeneration
Regeneration Axons regenerate at a rate of 1. 5 mm/day The greater the distance between severed nerve endings, the less chance of recovery. Axonal sprouts may grow into surrounding areas and form a mass called a neuroma. Surgical realignment can help. Retraining may be necessary once the connection is completed Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 14 b
Neuroma Acoustic neuroma MRI
Regeneration PNS vs CNS In PNS axon regeneration, macrophages clean out the debris from the injury. Schwann cells will form a tunnel of neurolemma to guide severed nerve ending together. A growth factor is also released In CNS – No Schwann cells to do this. Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 7. 14 b
Age related changes Degenerative changes Loss of dendritic & synaptic connections Accumulation of lipofuscin
Age related changes Lead to: Loss of balance Insomnia Increased risk of depression, Alzheimer’s & Parkinson’s disease Fading memory Slowed responses & reflexes
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