1. The Nervous System (Pgs. 196-217)

2. The Nervous System Organs of the nervous system are divided into
Central Nervous System (CNS)
Peripheral Nervous System (PNS)

3. 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)

4. Anatomical and Functional Organizaton

5. 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

6. Brain

7. 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)

8. 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)

9. 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

10. 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

11. 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

13. 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

14. 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

15. 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

16. 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

17. 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.

18. Basic Structure of a Nerve

19. 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

21. Spinal Nerves Fig. 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

22. Spinal Nerves Fig. 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.

24. 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 (left side of picture)

27. 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 (right side of picture)
Made up of motor neurons that conduct impulses to cardiac and smooth muscle tissue & glandular epithelial tissue

28. 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

30. 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

31. 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

32. 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