Chapter 10. Central Nervous System, Spinal Nerves, and Cranial Nerves. Copyright 2010, John Wiley & Sons, Inc.

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1 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves

2 End of Chapter 10 Copyright 2010 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.

3 Spinal Cord Structure: Protection and Coverings Vertebrae Spinal meninges Three layers of connective tissue Dura mater Arachnoid mater Pia mater Continuous with cranial meninges Cerebrospinal fluid (CSF)

4 Spinal Meninges and Spaces Epidural space: between vertebrae and dura mater Dura mater- tough,dense connective tissue Extends to vertebra S2 (well beyond spinal cord) Arachnoid mater: resembles spider s web Extends into subarachnoid space Subarachnoid space CSF circulates in this space Pia mater: thin, delicate layer Adheres to surface spinal cord (and brain) Contains blood vessels

5 Spinal Meninges and Spaces

6 Gross Anatomy of Spinal Cord Extends from medulla of brain to L2 vertebra Cauda equina (horse s tail) Extends inferior to end of spinal cord Consists of roots of lumbar, sacral and coccygeal spinal nerves Left and right halves partially separated by Anterior median fissure and posterior median sulcus Small central canal (filled with CSF) in middle Enlargements: cervical and lumbar regions Points of origins of nerves to upper and lower limbs

7 Gross Anatomy of Spinal Cord

8 Internal Structure of Spinal Cord Gray matter forms H (or butterfly ) Three horns on each side; sites of cell bodies Posterior gray horns: contain sensory neurons Anterior gray horns: contain somatic motor neurons Lateral: contain autonomic motor neurons White matter (surrounds gray H ) Consists of white columns Posterior, anterior, and lateral columns Contain tracts (bundles of axons) Sensory tracts: ascending to brain Motor tracts: descending from brain

9 Internal Structure of Spinal Cord

10 Spinal Nerves 31 pairs Named according to level of vertebra C1-C8, T1-T12, L1-L5, S1-S5, 1 coccygeal Emerge from spinal cord through intervertebral foramina Nerves attached to spinal cord by 2 roots Dorsal root: made of axons of sensory neurons Dorsal root ganglion: swelling containing cell bodies of sensory neurons Ventral root: composed of axons of motor neurons Both somatic motor and autonomic motor

11 Spinal Nerve Composition Formed by 2 spinal nerve roots Are mixed: Formed from dorsal root (sensory) and ventral root (motor) root Connective tissue coverings Individual axons wrapped in endoneurium Axons grouped in fascicles wrapped in perineurium Outer covering = epineurium

12 Spinal Nerve Composition

13 Distribution of Spinal Nerves Spinal nerves branch after pass through intervertebral foramina Some join with branches from neighboring nerves to form plexuses Nerve names relate to region innervated Spinal nerves T2-T12 do not form plexuses Called intercostal nerves Supply abdominal muscles, skin of chest and back, and muscles between ribs.

14 Plexuses Cervical plexus Supplies posterior head, neck, shoulders, and diaphragm Important nerves: phrenic to diaphragm Brachial plexus Supplies upper limbs + some neck and shoulder muscles Important nerves: radial, ulnar, axial, median to arm, forearm, hand

15 Plexuses Lumbar plexus Supplies abdominal wall, external genitalia, and part of lower limbs Important nerves: femoral (to anterior thigh: quads) Sacral plexus Supplies buttocks, perineum, and most of lower limbs Important nerves: gluteal, sciatic (to posterior thigh and all of leg and foot)

16 Spinal Cord

17 Spinal Cord Functions Pathways for nerve impulses within tracts Ascending (sensory). Example: spinothalamic Descending (motor). Example: corticospinal Reflexes: fast, involuntary sequences of actions in response to stimuli Can be simple (withdrawal) or complex (learned sequence such as driving car) Levels Spinal (reflex arc): simple Cranial: more complex

18 Reflex Arc 1. Sensory receptor: responds to stimulus 2. Sensory neuron: through dorsal root ganglion and root posterior horn 3. Integrating center: single synapse between sensory and motor neurons 4. Motor neuron: from anterior horn ventral root spinal nerve 5. Effector: muscle responds

19 Example of Reflex Arc: Patellar Reflex 1. Sensory receptor is stimulated by tap on patellar tendon 2. Sensory neuron: through dorsal root spinal cord 3. Integrating center: single synapse in spinal cord 4. Motor neuron: through ventral root spinal nerve femoral nerve 5. Effector: quads contract, extend leg

20 Example of Reflex Arc: Patellar Reflex

21 Brain: Major Parts Brain stem: continuous with spinal cord Medulla oblongata, pons, midbrain Diencephalon: superior to brain stem Thalamus, hypothalamus, and pineal gland Cerebrum: largest part and most superior Surface covered with gray matter: cortex Deep to cortex is cerebral white matter Cerebellum: posterior and inferior Means little brain Cranial meninges: dura mater, arachnoid mater, and pia mater

22 Brain: Major Parts

23 Brain: Major Parts

24 Brain Blood Supply and Blood-Brain Barrier Requires 20% of the body s O 2 supply 4 min lack permanent damage Requires continuous glucose supply Protected by blood-brain barrier Allows passage of lipid soluble materials: O 2, CO 2, alcohol, anesthetic agents But controls entry of most harmful materials Created by tight capillaries and astrocytes

25 Cerebrospinal Fluid (CSF) Formed in the 4 ventricles of brain Lateral (#1 and 2) 3rd 4th ventricle Formed in choroid plexuses By filtration and secretion of blood plasma Pathway In specialized capillary networks (covered by ependymal cells) in walls of ventricles Through 4 ventricles central canal of spinal cord and within subarachnoid space Reabsorbed through arachnoid villi into blood in superior sagittal sinus Cushions brain and provides nutrients

26 Cerebrospinal Fluid (CSF)

27 Brain Stem: Medulla Oblongata Most inferior part of brainstem White matter connects spinal cord and other parts of brain Contains vital nuclei Cardiovascular center Regulates heart rate, blood pressure Medullary rhythmicity area Adjusts respiratory rhythm Other sensory and reflex motor areas Cranial nerves VIII-XII attached here

28 Brain Stem: Pons Serves as a bridge Connects medulla to midbrain and above Contains ascending and descending tracts Connects left and right sides of cerebellum Contains nuclei Motor relays from cerebrum to cerebellum Helps control breathing Cranial nerves V-VIII attached here

29 Brain Stem

30 Brain Stem: Midbrain Connects pons to diencephalon Large tracts: cerebral peduncles Nuclei: Substantia nigra: related to Parkinson disease Red nuclei: help coordinate movements Origin of cranial nerves III and IV (control eye movements) Superior colliculi: nuclei involved in Scanning eye movements Responses to visual stimuli Inferior colliculi: responses to auditory input

31 Reticular Formation Netlike arrangement of gray and white matter Contains ascending and descending tracts Ascending part = reticular activating system (RAS) Carries sensory pathways to cerebral cortex Helps maintain consciousness Helps induce sleep

32 Reticular Formation

33 Diencephalon Thalamus: major sensory relay center Also motor, autonomic, and consciousness functions Hypothalamus: lies inferior to thalamus Control of pituitary and hormone production Works with ANS regulating many viscera Involved with feelings and behavior patterns Regulation of eating, drinking, fluid levels Control of body temperature Regulation of circadian rhythms, sleep, waking Pineal gland: secretes melatonin Controls sleep, biological clock

34 Diencephalon

35 Cerebellum Location: posterior to medulla and pons, inferior to cerebrum Attached to brain stem by cerebellar peduncles Structure: Two cerebellar hemispheres Cerebellar cortex: gray matter Tree-like appearance (seen in sagittal section) of white matter and gray nuclei

36 Cerebellum Functions Receives wide range of sensory input from muscles, joints, tendons, eyes, inner ears Compares actual movements with intended ones Helps produce smooth, coordinated movements Helps execute skilled motor activities Regulates posture and balance

37 Cerebrum: Structure Cerebral cortex Internal white mater Deep gray nuclei Surface folds of cerebral cortex: gyri Grooves between gyri: sulci Longitudinal fissure: divides cerebrum into left and right hemispheres Hemispheres connected by corpus collosum

38 Cerebrum: Structure Each hemisphere has 4 lobes Frontal, parietal, temporal, occipital Central sulcus separates frontal, parietal Precentral gyrus anterior to sulcus: primary motor area Postcentral gyrus: primary somatosensory area Deep gray nuclei: basal ganglia Globus pallidus, putamen, caudate nucleus

39 Cerebrum

40 Cerebrum

41 Limbic System Ring of structures on inner border of cerebrum and floor of diencephalon Called emotional brain : plays primary role in pain, pleasure, anger, affection and in behavior Involuntary activity related to survival Important in memory development

42 Limbic System

43 Functional Areas of Cerebral Cortex Specialized areas in specific regions of cerebral cortex Sensory areas receive input perception Motor areas initiate movements Associative areas complex integration: memory, emotion, reasoning, judgment

44 Sensory Areas Primary somatosensory area: postcentral gyrus Input includes: touch, proprioception, pain, itching, tickle, temperature Primary visual area: occipital lobe Primary auditory area: temporal lobe Primary gustatory (taste) area: base of postcentral gyrus Primary olfactory (smell) area: medial aspect of temporal lobe

45 Motor Areas Located anterior to central sulcus Primary motor area: precentral gyrus Broca s speech area Interacts with premotor area and primary motor area to regulate breathing and speech muscles Is in left hemisphere in 97% of persons

46 Association Areas Adjacent to sensory and motor areas and connected via association tracts Integrate and interpret information Examples Somatosensory association area Posterior to primary somatosensory area Integrates sensation: exact shape and texture of object compared with stored memories Wernike s area: left temporal, parietal lobes Interprets meaning of speech: words thoughts Right hemisphere adds emotional content

47 Cerebrum: Functional Areas

48 Somatic Sensory Pathways Relay sensory information from periphery to cerebral cortex 3 neurons in each pathway Cell body #1 in dorsal root ganglion Cell body #2 in spinal cord or brain stem Cell body #3 in thalamus; axon extends to cerebral cortex (somatosensory area in postcentral gyrus) Most sensory input to right side of body reaches left side of brain (and vice versa)

49 Somatic Sensory Pathways Posterior column - medial lemniscus pathway senses Fine touch: body location, texture, size Proprioception: position and motion of body parts Vibrations: fluctuating touch stimuli Spinothalamic pathways Anterior and lateral spinothalamic tracts Relay impulses for pain, tickle, itch, hot, and cold sensations

50 Somatic Sensory Pathways

51 Somatic Motor Pathways Signals come from Upper motor neurons: via corticospinal tracts Basal ganglia: help with muscle tone Cerebellum: coordination Sensory neurons or interneurons via reflexes Impulses activate lower motor neurons Cell bodies in anterior gray of spinal cord Axons ventral root spinal nerve muscle voluntary movements

52 Somatic Motor Pathways

53 Somatic Sensory and Motor Pathways Interactions Animation Somatic Sensory and Motor Pathways You must be connected to the internet to run this animation.

54 Lateralization Brain controls opposite side of the body: all sensory and motor pathways cross in CNS Left side of the brain controls right side of body Right side of brain controls left side of body Left hemisphere important for spoken and written language, numerical and scientific skills, and reasoning Right side more involved with spatial and pattern recognition and emotional content

55 Memory Process for storing and retrieving information Involves structural and functional changes Involves association areas, parts of limbic system, and diencephalon Skill memory also involves cerebellum and basal ganglia

56 Cranial Nerves (Table 10.2) I. Olfactory: special sensory smell II. Optic: special sensory vision III. Oculomotor: motor control of eye movements IV. Trochlear: motor control of eye movements V. Trigeminal: mixed General sensory: touch, pain, pressure, hot, cold in face Motor: to muscles used for chewing

57 Cranial Nerves VI. Abducens: motor control of eye movements VII.Facial: mixed Special sensory (taste) from anterior of tongue Motor to muscles of facial expression, tear glands, and some salivary glands VIII.Vestibulocochlear: special sensory ear

58 Cranial Nerves IX. Glossopharyngeal: mixed Sensory for posterior of tongue, pharynx, and palate; blood pressure Motor to pharyngeal muscles (swallowing), salivary gland (parotid

59 Cranial Nerves X. Vagus: mixed (the major parasympathetic nerve) Sensory from pharynx, ear, diaphragm, visceral organs in thoracic and abdominal cavities Motor to palatal and pharyngeal muscles (swallowing and voice); to viscera in thoracic and abdominal cavities

60 Cranial Nerves XI. Accessory: motor to voluntary muscles including sternocleidomastoid and trapezius (move head, shoulders) XII.Hypoglossal: motor to tongue (swallowing and speech)

61 Aging Rapid brain growth during first few years of life Due to increase in size of neurons and proliferation of neuroglia Increase in development of dendritic branches and synaptic contacts From early adulthood through old age: Decline in brain mass Fewer synaptic contacts brain function Some decrease in brain function