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Introduction to Physiological Principles Physiology
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Uploaded: 7 years ago
Category: Anatomy
Type: Lecture Notes
Tags: spinal, nervous, neurons, sensory, system, motor, brain, autonomic, matter, complex, integrating, information, synapse, postganglionic, center, axons, neuronal, efferent, region, functional, blood, regions, memories, neuron, cortex, wraps, afferent, sympa
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Transcript
Functional Organization of Nervous Systems
Maguire et al. 2000 http://www.pnas.org/cgi/reprint/97/8/4398
Figure 4
For surgical planning, a series of simple tasks (e.g., auditory, visual, motor, and language tasks) may be performed in a sequence to identify critical functional areas. These may then be superimposed on high-resolution anatomic images.
J Clin Invest. 2003 July 1; 112(1): 4–9.
Practice Does Make Perfect!
Overview of the Nervous System
One of the body’s homeostatic control systems
Contains sensors, integrating centers, and output pathways
More interneurons in a pathway ? greater number of interconnections and ability to integrate information
Cnidarians
Most nervous systems are organized into three functional divisions
Afferent sensory, integrating, and efferent motor
Cnidarians are an exception
Nervous system is an interconnected web or nerve net
Neurons carry action potentials in both directions
Neurons are not only sensory or only motor
Organism can still perform complex behaviors
Nervous System Terms
Bilaterally symmetrical – right and left side are mirror images
Cephalization – sense organs and nervous integrating centers are concentrated at the anterior end
Ganglia – groups of neuronal cell bodies
Nuclei – groups of neuronal cell bodies within the brain
Brain – an integrating center made up of clusters of nuclei
Tracts – bundles of many axons within the CNS
Nerve – a bundle of many axons outside of the CNS
Structure of a Nerve
Bundles of myelinated and unmyelinated axons enclosed in several layers of connective tissue
Endoneurium – wraps each axon
Perineurium – wraps a bundle (fascicle) of axons
Epineurium – wraps the entire nerve
Mixed nerves – contain both afferent and efferent neurons
Each neuron is either afferent (sensory) or efferent (motor)
Nervous Systems Across Animal Groups
Cephalization occurs in most animals and is more apparent in more complex nervous systems
Cnidarians and Echinoderms are exceptions in that they lack cephalization
Organisms with more complex nervous systems have more neurons; and therefore, more synapses
Increased numbers of synapses ? more integration of information ? more complex behaviors
Since memories are stored in synapses, a complex nervous system provides greater potential for learning
The Vertebrate Central Nervous System
High degree of Cephalization
Unique in having a hollow dorsal nerve cord (spinal cord)
How evolve from invertebrate?
Is still segmented!
Part of the nervous system is encased within cartilage or bone
CNS – brain and spinal cord
Part of the nervous system extends to the periphery of the body
PNS – nerves outside of the CNS
Cranial and Spinal Nerves (PNS)
Cranial nerves
Exit directly from skull
13 pairs (labeled with roman numerals)
Some afferent, some efferent, some mixed
Spinal nerves
Branch from spinal cord
Enter and exit between adjacent vertebrae
Named based on region of vertebral column from which they emerge
Cervical, thoracic, lumbar, sacral, and coccygeal
Mixed nerves
Segmented Ancestor?
Gray and White Matter
Brain and spinal cord contain two types of tissue
Gray matter – neuronal cell bodies
White matter – tracts of axons and their myelin sheaths
Spinal cord: white matter on surface, gray matter inside
Cerebral cortex: gray matter on surface, white matter inside
The CNS Is Isolated and Protected
Meninges
Layers of connective tissue that surround brain and spinal cord
Fish have one
Mammals have three
Cerebral spinal fluid (CSF)
Fills spaces within the CNS and acts as shock absorber
Blood-brain barrier
Tight junctions in brain capillaries limit passage of solutes from blood into the CSF
The Vertebrate Brain
Extension of the spinal cord
Nerve tracts extend between brain and spinal cord
Has several cavities called ventricles containing CSF
Three main regions
Rhombencephalon (hindbrain)
Reflexes and involuntary behaviors
Mesencephalon (midbrain)
Coordination of sensory information
Relay center in mammals
Prosencephalon (forebrain)
Integration of sensory information
Regulation of body temperature, reproduction, eating, emotion
Learning and memory in mammals
Hindbrain and Midbrain
Three regions
Pons – located above medulla
Pathway between medulla, cerebellum, and forebrain
Controls alertness, initiates sleep and dreaming
Cerebellum – two hemispheres at back of brain
Responsible for motor coordination
Contains half of the neurons in the brain
Medulla oblongata – located at top of spinal cord
Regulates breathing, heart rate, diameter of blood vessels, blood pressure
Contains pathways between spinal cord and brain
Primary center for coordinating and initiating behavioral responses in fish and amphibians
Size and function reduced in mammals
Relay center between spinal cord and forebrain
Sometimes grouped with the pons and medulla and termed the brainstem
Forebrain (Prosencephalon)
Involved in processing and integrating sensory information, and in coordinating behavior
Greatly enlarged in birds and mammals
Main regions:
Cerebrum
Thalamus – integrates sensory information
Epithalamus – hunger, thirst and melatonin secretion
Hypothalamus
Figure 7.10
Cerebrum and Hypothalamus
Outer layer is the cortex
Divided into two cerebral hemispheres
Left side controls right side of body
Right side controls left side of body
Neurons pass between the two sides via the corpus callosum
Located at base of forebrain
Under the thalamus
Helps maintain homeostasis
Body temperature, thirst, hunger, reproduction, etc.
Interacts with ANS
Regulates secretion of pituitary hormones
Limbic System “emotional brain”
Network of connected structures that lie between the cortex and the rest of the brain
Influences emotions, motivation, memory
Includes hypothalamus and other parts
Amygdala – aggression and fear responses
Hippocampus – converts short-term memory to long-term memory
Olfactory bulbs – sense of smell
Cortex (Isocortex in mammals)
Integrates and interprets sensory information and initiates voluntary movements
Has taken over many of the midbrain functions of lower vertebrates
Necessary for cognition and higher brain functions
More folded in more advanced mammals
Gyri (singular: gyrus) = folds; Sulci (singular: sulcus) = grooves
Cortical Topology/Functionality
Figure 8.5
Each region of the cortex corresponds to a specific part of the body that it controls by motor output, or from which it receives sensory input
Size of the brain region devoted to different parts of the body varies widely
(Functional regions)
Figure 7.16
Peripheral Nervous System Divisions
Autonomic Nervous System
“Involuntary nervous system”
Involved in maintaining homeostasis
Branches
Sympathetic
Most active during periods of stress or physical activity
“Fight-or-flight” system
Parasympathetic
Most active during periods of rest
“Resting and digesting” system
Enteric
Independent of other two systems
Innervates organs of alimentary canal
Maintaining Homeostasis
Balancing sympathetic and parasympathetic branches
Three mechanisms:
Dual innervation
Most organs receive input from both systems
Antagonistic action
One system stimulates while the other inhibits
Basal tone
Even under resting conditions autonomic neurons carry APs
Figure 7.17
Dual Innervation
Table 7.3
Antagonistic Action
Similarities in Autonomic Pathways
Two neurons in series
Preganglionic
May synapse with many postganglionic neurons and intrinsic neurons
Postganglionic
Neurotransmitter is released at effector organ from varicosities
pre- and postganglionic neurons synapse in the autonomic ganglia
Differences in Autonomic Pathways
Preganglionic cell body location
S – thoracic and lumbar regions of spinal cord
PS – hindbrain and sacral region of spinal cord
Ganglia location
S – chain that runs close to spinal cord
PS – chain that runs close to the effector
Number of postganglionic neurons that synapse with a single preganglionic neuron
S – ten or more
PS – three or fewer
Neurotransmitter released at the effector organ
Figure 7.20
Only Sympathetic Innervation
Some effectors receive only sympathetic innervation
Adrenal medulla
Collection of modified postganglionic neurons
Sweat glands
Arrector pili muscles in skin
Kidneys
Most blood vessels
Figure 7.21
Regulation of the Autonomic System
Set of neurons in brainstem
Figure 7.22
Autonomic Reflex Arcs
Most autonomic changes occur via simple neural circuits that do not involve conscious centers of the brain
Somatic Motor Pathways
“Voluntary nervous system”
Control of skeletal muscles
Usually under conscious control
Cerebrum
Somatic Motor Pathway Characteristics
Control only one type of effector, skeletal muscle
Cell bodies of motor neurons are located in the CNS
Monosynaptic
Axons are very long, and extend all the way to the muscle
Axon splits into a cluster of axon terminals at the neuromuscular junction
Release the neurotransmitter acetylcholine
Synaptic cleft between the motor neuron and the muscle is very narrow
Effect on the muscle cell always excitatory
For example, causes depolarization and contraction
Animal Behaviors
Three categories:
Reflex behaviors
Involuntary and simple
Convergence (retina) versus divergence (ANS)
Rhythmic behaviors
Underlie locomotion, breathing, and the function of the heart
Governed by pattern generators
Groups of neurons that produce self-sustaining, rhythmic depolarizations
Voluntary behaviors
Most complex and diverse
Consciously planned and coordinated by brain
Learning and Memory
Most animals can learn and form memories due to the plasticity of the nervous system
Learning
Process of acquiring new information
Memory
Retention and retrieval of information
Plasticity
Changes in synaptic and neuronal function in response to stimuli
Memory in Mammals
Hippocampus involved in long-term memory, but memories are “stored” in cerebrum
Memories are “stored” by increasing the efficiency of the synapse between two neurons
Long-term potentiation (LTP) – repetitive stimulation of hippocampal tissue leads to an increase in the response of the postsynaptic neuron
Table 7.4
Sympathetic vs. Parasympathetic Systems
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