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The Nervous System (Pgs. 196-217). The Nervous System. Organs of the nervous system are divided into Central Nervous System (CNS) Peripheral Nervous System (PNS). Vertebrate Nervous System. Central Nervous System Brain Spinal Cord - PowerPoint PPT Presentation
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The Nervous System
(Pgs. 196-217)
The Nervous System
Organs of the nervous system are divided into• Central Nervous System (CNS)• Peripheral Nervous System (PNS)
Vertebrate Nervous System Central Nervous System
Brain Spinal Cord
Peripheral Nervous system – cranial & spinal nerves & ganglia Somatic (voluntary) – connect to skin and Skeletal
Muscles Autonomic (involuntary, homeostatic control) – cardiac
muscle, smooth muscle, and glands Sympathetic – dominates in times of stress; “fight or flight”
syndrome (increases heart rate, blood pressure, breathing) Parasympathetic – acts as counterbalance, conserves
energy (decreases heart rate, blood pressure, breathing rate)
Anatomical and Functional Organizaton
Central Nervous System
Brain – largest & most complex part of NS. Contains nerve centers associated with sensations. Issues motor commands & carries on higher mental functions: Fig. 8-9, 8-10
Brain
Brain stem Extends from base of the cerebrum to the
spinal cord Consists of midbrain, pons, & medulla
oblongata Medulla oblongata – transmits all ascending &
descending impulses, & contains several vital & nonvital relex centers (cardiac, respiratory, vasomotor)
Pons- transmits impulses between the cerebrum & other parts of the NS, and contains centers that help regulate the rate & depth of breathing
Midbrain – contains reflex centers associated with eye & head movements (visual & auditory impulses)
Diencephalon
Thalamus – central relay station for incoming sensory impulses; emotions and alerting or arousal mechanisms
Hypothalamus – maintain homeostasis, regulation of body temp., water balance, sleep-cycle control, appetite & sexual arousal (**very important gland of the endocrine system)
Cerebellum Consists of two hemispheres that are
connected by the vermis Composed of white matter surrounded
by a thing cortex of gray matter Functions primarily as a reflex center in
the co-ordination of skeletal muscle movements & the maintenance of equilibrium
Cerebrum Two hemisphere connected by the corpus
callosum Surface marked by convolutions (ridges)
and gyri (grooves); 4 lobes each hemisphere – frontal, parietal, temporal, occipital
Composed of thin layer of gray matter near surface; white matter found deeper
Higher brain functions such as thought, reasoning, interpretations of sensory impulses, control of voluntary muscles, and storage of memory
Spinal Cord Nerve column
that extends from the brain into the vertebral canal. It terminates at the level between L1 and L2; fig. 8-11, 8-12
Spinal Cord - Structure Composed of 31 segments, each of which
gives rise to a pair of spinal nerves Characterized by two deep longitudinal
grooves that divide it into right and left halves
Has a central core of gray matter that is surrounded by white matter
White matter is composed of bundles of myelinated nerve fibers
Spinal Cord - Function Provides a two way communications
system between the brain & body parts outside the NS
Primary reflex center Ascending tracts carry sensory impulses
to the brain; descending tracts carry motor impulses to muscles and glands
Many of the fibers in the ascending and descending tracts cross over in the spinal cord or brain
Coverings & Fluid spaces of the Brain & Spinal Cord
Meninges – protective membrane covering brain & spinal cord; three layers; Fig. 8-13 Dura mater – outer layer Arachnoid – middle layer Pia mater – inner layer Cerebrospinal fluid occupies the space
between the arachnoid & pia mater
Coverings & Fluid spaces of the Brain & Spinal Cord
Ventricles – interconnected cavities within the cerebral hemisphere & brain stem that are filled with cerebrospinal fluid: Fig. 8-14
Peripheral Nervous System Consists of cranial and spinal nerves that
branch out from the brain and spinal cord to all body parts. Subdivided into somatic & autonomic portions.
Basic Structure of a Nerve
Cranial Nerves Fig. 8-16, Table 8-2
12 pairs that connect the brain to parts in the head, neck, & trunk
Most cranial nerves are mixed (sensory & motor); some are pure sensory & other primarily motor
Some cranial nerve fibers are somatic & others are autonomic
Spinal NervesFig. 8-17, 8-18
31 pairs originate from the spinal cord These mixed nerves provide a two way
communication system between the spinal cord & parts in the arm, legs, neck, and trunk
Each nerve emerges by a dorsal and ventral root Dorsal (posterior) root contains sensory fibers and
is characterized by the presence of a dorsal root ganglion
Ventral root contains motor fibers
Spinal NervesFig. 8-17, 8-18
Each spinal nerve divides into several branches & then combines with other spinal nerves to form plexuses in which nerve fibers are sorted and recombined so that those fibers associated with a particular part reach it together.
Somatic Nervous System Skeletal muscle & skin Conduction of nerve impulse is all the way
from the spinal cord or brain to the effector
No synapses Fig. 8-19 (left side of picture)
Autonomic Nervous System
Portion of nervous system that function without conscious effort
Concerned primarily with the regulation of visceral activities that aid in maintaining homeostasis
Fig. 8-19 (right side of picture) Made up of motor neurons that conduct
impulses to cardiac and smooth muscle tissue & glandular epithelial tissue
Autonomic Nervous System
Conduction pathway is a 2 neuron relay – in the ganglia the impulses are integrated before passing out to effectors
ANS is divided into 2 divisions Sympathetic Parasympathetic
Sympathetic Prepares the body for stressful and emergency
conditions “fight or flight syndrome” Increase in heart rate, breathing, decrease in
activities of digestive tract Sympathetic preganglionic dendrites and cell
bodies are located in the gray matter of the thoracic and upper lumbar segments of the spinal cord
Sympathetic preganglionic axons synapse with many postganglionic neurons in sympathetic ganglion & these postganglionic neurons frequently terminate in widely separated organs; therefore, sympathetic responses are usually widespread
Parasympathetic Most active under ordinary conditions Decreases heart rate and breathing Opposite (antagonist) to sympathetic Parasympathetic preganglionic dendrites and
cell bodies are located in gray matter of brain stem and sacral segments of the spinal cord; axons extend some distance before terminating in parasympathetic ganglion
Parasympathetic postganglionic neurons have short axons that extend into nearby structures; therefore parasympathetic stimulation usually involved responses by only one organ
Neurotransmittters – chemical compounds released by axons
The different effects of the autonomic divisions are due to the different neurotransmitters released by the postganglionic fibers
There are various types of receptors present on the cell membranes and a cell’s response to neurotransmitters depends upon the number and type of receptors present in their membranes.
Fig. 8-20