Chapter 11

1. Chapter 11 Nervous System II

2. PROTECTION OF THE CNS The brain and spinal cord are protected (surrounded) by bones, membranes, and fluid.

3. Meningies • membranes surrounding and protecting CNS • three layers • dura mater – outer, tough • DM splits into two layers where it encloses the dural sinuses (that collect venous blood from the brain) • arachnoid mater – thin, weblike • Beneath the arachnoid mater lies a wide space called the sub-arachnoid space • This space is filled with cerebrospinal fluid (CSF) and serves as a cushion for the brain • pia mater – inner, very thin • dips into grooves & contours • The space between the dura mater and the bone is called the epidural space and is filled with loose CT and fat • CSF fills the subarachnoid space and central canal

5. Ventricles of the Brian • (interconnected cavities) within the cerebral hemispheres and brain stem • The Ventricles: • are continuous with central canal of spinal cord • are filled with cerebrospinal fluid (CSF) • are lined by ependymal cells • neuroglial cell in CNS

7. Cerebrospinal Fluid • secreted by choroid plexus • circulates in ventricles, central canal of spinal cord, and subarachnoid space • completely surrounds brain and spinal cord • clear liquid • provides nutrition and protection • helps maintain stable ion concentrations in CNS

9. THE SPINAL CORD The spinal cord is a nerve column that passes downward from brain into the vertebral canal. Recall that it is part of the CNS

10. Structure of the Spinal Cord • Length = about 17 inches • Start = foramen magnum • End = tapers to point (conus medullaris) and terminates near the intervertebral disc that separates the 1st - 2nd lumbar (L1-L2) vertebra • Contains 31 segments (and therefore gives rise to 31 pairs of spinal nerves) • Note cervical and lumbar enlargements

11. Structure of the Spinal Cord cont. • cauda equina (“horse’s tail”) in which the lower lumbar and sacral nerves travel downward • i.e. lower spinal nerves must “chase” their points of exit) • filum terminale that represents distal portion of the tail (pia mater) • No actual nerve tissue • A cross-section of the spinal cord resembles a butterfly with its wings outspread (gray matter) surrounded by white matter

12. Functions of the Spinal Cord • Nerve Pathway = the route traveled by a nerve impulse through the nervous system • Reflex arc = the simplest demonstration of a nerve pathway (spinal reflexes) • involves 2-3 neurons • involuntary response • often does not involve the brain • Examples include: • knee-jerk or patellar reflex

13. Spinal Nerves • Spinal nerves extend to/from the spinal cord and are part of the PNS • Ganglion = a bundle of cell bodies outside the CNS • Dorsal Root Ganglion contains the cell bodies of sensory (afferent) neurons bringing impulses to the CNS • The fusion of the dorsal and ventral roots designates the beginning of the spinal nerve which then passes through its intervertebral foramen

14. Ascending and Descending Tracts • The white matter of the spinal cord represents the location of our major nerve pathways called "nerve tracts" • provide a 2-way system of communication: • ascending tracts conduct sensory (afferent) impulses from body parts to brain • descending tracts conduct motor (efferent) impulses from brain to effectors • All pathways are paired (right and left)

15. BRAIN The brain is the largest and most complex portion of the nervous system.

16. Introduction • It occupies the cranial cavity and is composed of one hundred billion multipolar neurons. • The brain oversees the function of the entire body and also provides characteristics like personality • The brain is composed of 5 major portions • cerebrum, cerebellum, diencephalon, basal nuclei and brain stem

17. Structure of the Cerebrum • Cerebrum = the largest portion of the brain, which is divided into two cerebral hemispheres. • Hemispheres are connected by a deep bridge of nerve fibers called the corpus callosum • Surface ridges are called convolutions (gyri) • Convolutions are separated by two types of grooves. (Sulci and Fissures) • Each hemisphere is divided into lobes, which are named for the bones that cover them including frontal, parietal, temporal, and occipital lobes

20. Structure/Function of the Cerebrum • Composition: • Bulk of cerebrum is white matter. • bundles of myelinated nerve fibers (by oligodendrocyte) • Cerebral cortex or the outer portion of cerebrum is composed of gray matter • bundles of neuron cell bodies • contains 75% of all neurons in nervous system • Functional Regions of theCerebral cortex • Responsible for all conscious behavior by containing three kinds of functional areas, which include motor, sensory and association areas

21. Sensory Areas • Sensory Areas are concerned with conscious awareness of sensations and are located in the parietal, occipital, and temporal cortex • The include the • Cutaneous Sensory Area • Visual Area • Auditory Area • Sensory Area for Taste • Sensory Area for Smell

24. Association Areas • regions that are not primary motor or primary sensory areas • widespread throughout the cerebral cortex • Association traits include: • analyzing & interpreting sensory experiences • help provide memory, reasoning, verbalizing, judgment and emotions

25. Hemisphere Dominance • The left hemisphere is dominant is most individuals • Dominant hemisphere controls • speech • writing • reading • verbal skills • analytical skills • computational skills • Nondominant hemisphere controls • nonverbal tasks • motor tasks • understanding and interpreting musical and visual patterns • provides emotional and intuitive thought processes

26. Memory • Memory is the consequence of learning. Whereas learning is the acquisition of new knowledge, memory is the persistence of that learning, with the ability to access it at a later time • Two types of memory: • Short Term: working memory • Long Term: changes structure or function of neurons

27. Motor Areas Motor Areas are located in the frontal cortex: • Primary motor cortex • initiates all voluntary muscle movements • Broca's area • motor speech area • Frontal Eye Field • controls voluntary movements of eyes and eyelids

30. Basal Nuclei • masses of gray matter located deep within the white matter of the cerebral hemispheres • Release dopamine, which inhibits excess movements • control certain muscular activities • primarily by inhibiting motor functions • caudate nucleus, putamen, globus pallidus

31. Diencephalon • includes two important areas of gray matter: • Thalamus • gateway for sensory impulses heading to cerebral cortex • receives all sensory impulses (except smell) • channels impulses to appropriate part of cerebral cortex for interpretation • Hypothalamus • maintains homeostasis by regulating visceral activities • links nervous and endocrine systems

32. Limbic System • Limbic System = involved in Emotional response • interprets sensory impulses • includes structures in the frontal and temporal cortex, basal nuclei, thalamus, hypothalamus, and deep nuclei • controls emotional experience and expression • produces feelings • recognizes life threatening upsets in a person's physical or psychological condition and counters them

33. Brain Stem • The brain stem is composed of three major parts • midbrain, pons, and medulla oblongata • The brain stem serves as a pathway for fiber tracts running to (sensory impulses) and from (motor impulses) the cerebrum and is the sight where many cranial nerves (PNS) arise

34. Midbrain • Corpora quadrigemina = 4 dome-like protrusions on the dorsal midbrain surface • centers for visual and auditory reflexes • Cerebral peduncles – bundles of nerve fibers • acts in reflex actions (visual and auditory) • also contains areas associated with reticular formation • contains bundles of fibers that join lower parts of brainstem and spinal cord with higher part of brain • cerebral aqueduct

36. Pons • "bridge" or pathway of conduction tracts • helps regulate rate and depth of breathing • also contains areas associated with reticular formation • relays nerve impulses to and from medulla oblongata and cerebellum

38. Medulla Oblongata • conducts ascending and descending impulses between brain and spinal cord • contains an autonomic reflex center involved in maintaining homeostasis of important visceral organs • contains cardiac, vasomotor, and respiratory control centers • contains various nonvital reflex control centers (coughing, sneezing, swallowing, vomiting)

40. Reticular Formation Types pf Sleep • Slow wave (90min) overall decrease in reticular formation activity • person is tired • restful • reduced blood pressure and respiratory rate • Rapid eye movement sleep (REM) certain areas of brain are active • responsible for dreaming • lasts 15 minutes • some areas of brain active • heart and respiratory rates irregular • complex network of nerve fibers scattered throughout the brain stem • controls brains alertness • inhibited = sleep, alcohol, tranquilizers • extends into the diencephalon • connects to centers of hypothalamus, basal nuclei, cerebellum, and cerebrum • filters incoming sensory information • arouses cerebral cortex into state of wakefulness

42. Cerebellum • note pattern of white matter (within gray matter) = "arbor vitae" • integrates sensory information concerning position of body parts • coordinates skeletal muscle activity • maintains posture

43. PERIFERAL NERVOUS SYSTEM

44. PSN Introduction • The peripheral nervous system (PNS) consists of nerves that extend to and from the CNS organs • Cranial nerves arising from the brain • Somatic fibers connecting to the skin and skeletal muscles • Autonomic fibers connecting to viscera • Spinal nerves arising from the spinal cord • Somatic fibers connecting to the skin and skeletal muscles • Autonomic fibers connecting to viscera • The PNS is divided into a sensory and motor branch • The motor branch of the PNS is further subdivided into a somatic nervous system (from CNS to skin and skeletal muscles) and autonomic nervous system (from CNS to smooth muscle, cardiac muscle and endocrine glands)

45. Structure Of Peripheral Nerves • A nerve is a cord-like bundle of axons wrapped in CT • Structureof a Nerve: • Three types of CT wrappings (similar to muscle): • endoneurium around each axon (and myelin) • perineurium around each fascicle (bundle) of axons • epineurium around each nerve

47. Nerve Fiber Classification • MixedNerves • Nerves that carry impulses both to and from the CNS • contain both sensory and motor axons • most common; 2-way communication • Sensory (afferent)Nerves • Nerves that only carry sensory impulses toward the CNS • rare (only three pairs of cranial nerves) • Motor (efferent)Nerves • Nerves that only carry motor impulses away from CNS • rare (only five pairs of cranial nerves)

48. General somaticefferent fibers carry motor impulses from CNS to skeletal muscles General somatic afferent fibers carry sensory impulses to CNS from skin and skeletal muscles General visceral efferent fibers carry motor impulses away from CNS to smooth muscles and glands General visceral afferent fibers carry sensory impulses to CNS from blood vessels and internal organs Special somatic efferent fibers carry motor impulses from brain to muscles used in chewing, swallowing, speaking, and forming facial expressions Special visceral afferent fibers carry sensory impulses to brain from olfactory and taste receptors Special somatic afferent fibers carry sensory impulses to brain from receptors of sight, hearing, and equilibrium Nerve Fiber Classification cont.

49. Cranial Nerves • 12 pairs • 2 pairs to/from forebrain • 10 pairs to/from brain stem • Memorize by using one of many mnemonic devices: • One example is: "Oh, Oh, Oh, To Touch And Feel Very Good Velvet AH!" • See www.medicalmnemonics.com for more.