The Spinal Cord, Spinal Nerves, and Spinal Reflexes

Transcription

1 13 The Spinal Cord, Spinal Nerves, and Spinal Reflexes PowerPoint Lecture Presentations prepared by Jason LaPres Lone Star College North Harris

2 An Introduction to the Spinal Cord, Spinal Nerves, and Spinal Reflexes Spinal Reflexes Rapid, automatic nerve responses triggered by specific stimuli Controlled by spinal cord alone, not the brain

3 Figure 13-1 An Overview of Chapters 13 and 14 CHAPTER 14: The Brain Sensory receptors Sensory input over cranial nerves Reflex centers in brain Motor output over cranial nerves Effectors Muscles CHAPTER 13: The Spinal Cord Glands Sensory receptors Sensory input over spinal nerves Reflex centers in spinal cord Motor output over spinal nerves Adipose tissue

4 13-2 Spinal Cord Gross Anatomy of the Spinal Cord About 18 inches (45 cm) long 1/2 inch (14 mm) wide Ends between vertebrae L 1 and L 2 Bilateral symmetry Grooves divide the spinal cord into left and right Posterior median sulcus on posterior side Anterior median fissure deeper groove on anterior side

5 13-2 Spinal Cord Enlargements of the Spinal Cord Caused by: Amount of gray matter in segment Involvement with sensory and motor nerves of limbs Cervical enlargement Nerves of shoulders and upper limbs Lumbar enlargement Nerves of pelvis and lower limbs

6 13-2 Spinal Cord Gross Anatomy of the Spinal Cord The distal end Conus medullaris Thin, conical spinal cord below lumbar enlargement Cauda equina Nerve roots extending below conus medullaris

7 Figure 13-2 Gross Anatomy of the Adult Spinal Cord L 1 Conus medullaris Lumbar spinal nerves L 2 L 3 L 4 Inferior tip of spinal cord Cauda equina L 5 L 1

8 Figure 13-2 Gross Anatomy of the Adult Spinal Cord Dorsal root Dorsal root ganglion Posterior median sulcus White matter C 1 C 2 Central canal Gray matter Cervical spinal nerves C 3 C 4 C 5 C 6 C 7 C 8 Cervical enlargement Spinal nerve Ventral root Anterior median fissure C 3 T 1 T 2 T 3 T 4 T 5 T 6 T 7 Thoracic spinal nerves T 8 T 9 Posterior median sulcus T 10 T 11 Lumbar enlargement T 3 T 12 L 1 Conus medullaris Lumbar spinal nerves L 2 L 3 L 4 Inferior tip of spinal cord Cauda equina L 5 L 1 Sacral spinal nerves S 1 S 2 S 3 S 4 S 5 Coccygeal nerve (Co 1 ) Filum terminale (in coccygeal ligament) S 2

9 Figure 13-2 Gross Anatomy of the Adult Spinal Cord Posterior median sulcus Dorsal root Dorsal root ganglion White matter Cervical spinal nerves C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 Cervical enlargement Central canal Spinal nerve Ventral root Gray matter Anterior median fissure C 3 The superficial anatomy and orientation of the adult spinal cord. The numbers to the left identify the spinal nerves and indicate where the nerve roots leave the vertebral canal. The spinal cord extends from the brain only to the level of vertebrae L 1 L 2 ; the spinal segments found at representative locations are indicated in the cross sections. Inferior views of cross sections through representative segments of the spinal cord, showing the arrangement of gray matter and white matter.

10 Figure 13-2 Gross Anatomy of the Adult Spinal Cord T 1 T 2 T 3 T 4 T 5 T 6 T 7 Thoracic spinal nerves T 8 T 9 Posterior median sulcus T 10 T 11 T 12 Lumbar enlargement Conus medullaris T 3

11 Figure 13-2 Gross Anatomy of the Adult Spinal Cord L 1 Conus medullaris Lumbar spinal nerves L 2 L 3 L 4 Inferior tip of spinal cord Cauda equina L 5 L 1

12 Figure 13-2 Gross Anatomy of the Adult Spinal Cord Inferior tip of spinal cord Cauda equina Sacral spinal nerves S 1 S 2 S 3 S 4 S 5 Coccygeal nerve (Co 1 ) Filum terminale (in coccygeal ligament) S 2

13 13-2 Spinal Cord 31 Spinal Cord Segments Based on vertebrae where spinal nerves originate Positions of spinal segment and vertebrae change with age Cervical nerves Are named for inferior vertebra All other nerves Are named for superior vertebra

14 13-2 Spinal Cord Roots Two branches of spinal nerves 1. Ventral root Contains axons of motor neurons 2. Dorsal root Contains axons of sensory neurons Dorsal root ganglia Contain cell bodies of sensory neurons

15 13-2 Spinal Cord The Spinal Nerve Each side of spine Dorsal and ventral roots join To form a spinal nerve Mixed Nerves Carry both afferent (sensory) and efferent (motor) fibers

16 Figure 13-3a The Spinal Cord and Spinal Meninges White matter Ventral root Dorsal root Gray matter Dorsal root ganglion Spinal nerve Meninges Pia mater Arachnoid mater Dura mater A posterior view of the spinal cord, showing the meningeal layers, superficial landmarks, and distribution of gray matter and white matter

17 Figure 13-3b The Spinal Cord and Spinal Meninges Meninges Subarachnoid space Rami communicantes ANTERIOR Vertebral body Dura mater Arachnoid mater Pia mater Autonomic (sympathetic) ganglion Ventral root of spinal nerve Ventral ramus Spinal cord Adipose tissue in epidural space Denticulate ligament Dorsal root ganglion Dorsal ramus A sectional view through the spinal cord and meninges, showing the peripheral distribution of spinal nerves POSTERIOR

18 13-2 Spinal Cord The Spinal Meninges Specialized membranes isolate spinal cord from surroundings Functions of the spinal meninges include: Protecting spinal cord Carrying blood supply Continuous with cranial meninges Meningitis Viral or bacterial infection of meninges

19 13-2 Spinal Cord The Three Meningeal Layers 1. Dura mater Outer layer of spinal cord 2. Arachnoid mater Middle meningeal layer 3. Pia mater Inner meningeal layer

20 13-2 Spinal Cord The Dura Mater Tough and fibrous Cranially Fuses with periosteum of occipital bone Is continuous with cranial dura mater Caudally Tapers to dense cord of collagen fibers

21 13-2 Spinal Cord The Dura Mater The Epidural Space Between spinal dura mater and walls of vertebral canal Contains loose connective and adipose tissue Anesthetic injection site

22 13-2 Spinal Cord The Arachnoid Mater Middle meningeal layer Arachnoid membrane Simple squamous epithelia Covers arachnoid mater

23 13-2 Spinal Cord The Interlayer Spaces of Arachnoid Mater Subarachnoid space Between arachnoid mater and pia mater Contains collagen/elastin fiber network (arachnoid trabeculae) Filled with cerebrospinal fluid (CSF)

24 13-2 Spinal Cord The Pia Mater Is the innermost meningeal layer Is a mesh of collagen and elastic fibers Is bound to underlying neural tissue

25 13-2 Spinal Cord Blood vessels Along surface of spinal pia mater Within subarachnoid space

26 Figure 13-4 The Spinal Cord and Associated Structures Spinal cord Anterior median fissure Pia mater Denticulate ligaments Dorsal root Ventral root, formed by several rootlets from one cervical segment Arachnoid mater (reflected) Dura mater (reflected) Spinal blood vessel

27 13-3 Gray Matter and White Matter Sectional Anatomy of the Spinal Cord White matter Is superficial Contains myelinated and unmyelinated axons Gray matter Surrounds central canal of spinal cord Contains neuron cell bodies, neuroglia, unmyelinated axons Has projections (gray horns)

28 13-3 Gray Matter and White Matter Organization of Gray Matter The gray horns Posterior gray horns contain somatic and visceral sensory nuclei Anterior gray horns contain somatic motor nuclei Lateral gray horns are in thoracic and lumbar segments; contain visceral motor nuclei Gray commissures Axons that cross from one side of cord to the other before reaching gray matter

29 13-3 Gray Matter and White Matter Organization of Gray Matter The cell bodies of neurons form functional groups called nuclei Sensory nuclei Dorsal (posterior) Connect to peripheral receptors Motor nuclei Ventral (anterior) Connect to peripheral effectors

30 13-3 Gray Matter and White Matter Organization of White Matter Posterior white columns lie between posterior gray horns and posterior median sulcus Anterior white columns lie between anterior gray horns and anterior median fissure Anterior white commissure area where axons cross from one side of spinal cord to the other Lateral white columns located on each side of spinal cord between anterior and posterior columns

31 13-3 Gray Matter and White Matter Organization of White Matter Tracts or fasciculi In white columns Bundles of axons Relay same information in same direction Ascending tracts Carry information to brain Descending tracts Carry motor commands to spinal cord

32 Figure 13-5a The Sectional Organization of the Spinal Cord Posterior white column Dorsal root ganglion Lateral white column Posterior gray horn Lateral gray horn Anterior gray horn Anterior white column The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior gray horns.

33 Figure 13-5a The Sectional Organization of the Spinal Cord Posterior median sulcus Posterior gray commissure Somatic Visceral Visceral Somatic Functional Organization of Gray Matter The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groups called nuclei. Sensory nuclei Motor nuclei The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior gray horns. Anterior gray commissure Anterior white commissure Anterior median fissure Ventral root

34 Figure 13-5b The Sectional Organization of the Spinal Cord POSTERIOR Posterior gray commissure Dura mater Arachnoid mater (broken) Central canal Anterior gray commissure Anterior median fissure Pia mater ANTERIOR A micrograph of a section through the spinal cord, showing major landmarks in and surrounding the cord.

35 Figure 13-5b The Sectional Organization of the Spinal Cord POSTERIOR Posterior median sulcus Structural Organization of Gray Matter The projections of gray matter toward the outer surface of the spinal cord are called horns. Posterior gray horn Lateral gray horn Dorsal root Anterior gray horn ANTERIOR Dorsal root ganglion Ventral root A micrograph of a section through the spinal cord, showing major landmarks in and surrounding the cord.

36 13-3 Gray Matter and White Matter Spinal Cord Summary Spinal cord has a narrow central canal Surrounded by gray matter Containing sensory and motor nuclei Sensory nuclei are dorsal Motor nuclei are ventral

37 13-3 Gray Matter and White Matter Spinal Cord Summary Gray matter Is covered by a thick layer of white matter White matter Consists of ascending and descending axons Organized in columns Contains axon bundles with specific functions Spinal cord is so highly organized It is possible to predict results of injuries to specific areas

38 13-4 Spinal Nerves and Plexuses Anatomy of Spinal Nerves Every spinal cord segment Is connected to a pair of spinal nerves Every spinal nerve Is surrounded by three connective tissue layers That support structures and contain blood vessels

39 13-4 Spinal Nerves and Plexuses Three Connective Tissue Layers of Spinal Nerves 1. Epineurium Outer layer Dense network of collagen fibers 2. Perineurium Middle layer Divides nerve into fascicles (axon bundles) 3. Endoneurium Inner layer Surrounds individual axons

40 Figure 13-6 A Peripheral Nerve Blood vessels Connective Tissue Layers Epineurium covering spinal nerve Perineurium (around one fascicle) Endoneurium Myelinated axon Fascicle Schwann cell

41 Figure 13-6 A Peripheral Nerve Blood vessels Perineurium (around one fascicle) Endoneurium

42 13-4 Spinal Nerves and Plexuses Peripheral Nerves Interconnecting branches of spinal nerves Surrounded by connective tissue sheaths

43 13-4 Spinal Nerves and Plexuses Peripheral Distribution of Spinal Nerves Spinal nerves Form lateral to intervertebral foramen Where dorsal and ventral roots unite Then branch and form pathways to destination

44 13-4 Spinal Nerves and Plexuses Peripheral Distribution of Spinal Nerves Motor nerves The first branch White ramus Carries visceral motor fibers to sympathetic ganglion of autonomic nervous system Gray ramus Unmyelinated nerves Return from sympathetic ganglion to rejoin spinal nerve

45 13-4 Spinal Nerves and Plexuses Peripheral Distribution of Spinal Nerves Motor nerves Dorsal and ventral rami Dorsal ramus Contains somatic and visceral motor fibers Innervates the back Ventral ramus Larger branch Innervates ventrolateral structures and limbs

46 Figure 13-7 Peripheral Distribution of Spinal Nerves To skeletal muscles of back Postganglionic fibers to smooth muscles, glands, etc., of back The spinal nerve forms just lateral to the intervertebral foramen, where the dorsal and ventral roots unite. The ventral root of each spinal nerve contains the axons of somatic motor and visceral motor neurons. Dorsal root Dorsal root ganglion The dorsal ramus contains somatic motor and visceral motor fibers that innervate the skin and skeletal muscles of the back. The axons in the relatively large ventral ramus supply the ventrolateral body surface, structures in the body wall, and the limbs. Visceral motor nuclei Somatic motor nuclei Somatic motor commands Visceral motor commands Postganglionic fibers to smooth muscles, glands, visceral organs in thoracic cavity Preganglionic fibers to sympathetic ganglia innervating abdominopelvic viscera Sympathetic ganglion A sympathetic nerve contains preganglionic and postganglionic fibers innervating structures in the thoracic cavity. Rami communicantes To skeletal muscles of body wall, limbs Postganglionic fibers to smooth muscles, glands, etc., of body wall, limbs The white ramus is the first branch from the spinal nerve and carries visceral motor fibers to a nearby sympathetic ganglion. Because these preganglionic axons are myelinated, this branch has a light color and is therefore known as the white ramus. The gray ramus contains postganglionic fibers that innervate glands and smooth muscles in the body wall or limbs. These fibers are unmyelinated and have a dark gray color.

47 13-4 Spinal Nerves and Plexuses Peripheral Distribution of Spinal Nerves Sensory nerves In addition to motor impulses Dorsal, ventral, and white rami also carry sensory information Dermatomes Bilateral region of skin Monitored by specific pair of spinal nerves

48 Figure 13-7 Peripheral Distribution of Spinal Nerves The dorsal ramus carries sensory information from the skin and skeletal muscles of the back. The ventral ramus carries sensory information from the ventrolateral body surface, structures in the body wall, and the limbs. From exteroceptors, proprioceptors of body wall, limbs From interoceptors of back From exteroceptors, proprioceptors of back Dorsal root ganglion The dorsal root of each spinal nerve carries sensory information to the spinal cord. Somatic sensory nuclei From interoceptors of body wall, limbs Somatic sensations Visceral sensations Rami communicantes The sympathetic nerve carries sensory information from the visceral organs. Ventral root Visceral sensory nuclei From interoceptors of visceral organs

49 Figure 13-8 Dermatomes C 2 C 3 N V T 2 C 6 C 8 C 2 C 3 C 2 C 3 C 3 L 1 L 2 L 3 C 4 C 5 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 L 1 L 2 L3 L4L5 C 8 T C 1 L 1 S 7 5 L 5 L 4 S 2 S 4 S 3 L S 2 2 S 1 C 4 T 2 C 5 C 6 C 7 T 1 L 5 L 3 S 1 L 4 ANTERIOR POSTERIOR

50 Figure 13-9 Shingles

51 13-4 Spinal Nerves and Plexuses Nerve Plexuses Complex, interwoven networks of nerve fibers Formed from blended fibers of ventral rami of adjacent spinal nerves Control skeletal muscles of the neck and limbs

52 13-4 Spinal Nerves and Plexuses The Four Major Plexuses of Ventral Rami 1. Cervical plexus 2. Brachial plexus 3. Lumbar plexus 4. Sacral plexus

53 Figure Peripheral Nerves and Nerve Plexuses Cervical plexus Brachial plexus C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 Lesser occipital nerve Great auricular nerve Transverse cervical nerve Supraclavicular nerve Phrenic nerve Axillary nerve Musculocutaneous nerve T 9 Thoracic nerves T 10 T 11

54 Figure Peripheral Nerves and Nerve Plexuses T 12 Lumbar plexus L 1 L 2 L 3 L 4 Radial nerve Ulnar nerve Median nerve Sacral plexus L 5 S 1 S 2 S 3 S 4 S 5 Co 1 Iliohypogastric nerve Ilioinguinal nerve Lateral femoral cutaneous nerve Genitofemoral nerve Femoral nerve Obturator nerve Superior Inferior Gluteal nerves Pudendal nerve Saphenous nerve Sciatic nerve

55 13-4 Spinal Nerves and Plexuses The Cervical Plexus Innervates neck, thoracic cavity, diaphragmatic muscles Major nerve Phrenic nerve (controls diaphragm)

56 Figure The Cervical Plexus Cranial Nerves Accessory nerve (XI) Hypoglossal nerve (XII) Lesser occipital nerve Nerve Roots of Cervical Plexus C 1 C 2 C 3 C 4 C 5 Supraclavicular nerves Clavicle

57 Figure The Cervical Plexus Great auricular nerve Geniohyoid muscle Transverse cervical nerve Thyrohyoid muscle Ansa cervicalis Omohyoid muscle Phrenic nerve Sternohyoid muscle Sternothyroid muscle

58 13-4 Spinal Nerves and Plexuses The Brachial Plexus Innervates pectoral girdle and upper limbs

59 13-4 Spinal Nerves and Plexuses The Brachial Plexus Major nerves Musculocutaneous nerve (lateral cord) Median nerve (lateral and medial cords) Ulnar nerve (medial cord) Axillary nerve (posterior cord) Radial nerve (posterior cord)

60 Figure 13-12a The Brachial Plexus Trunks of Brachial Plexus Superior Middle Inferior Dorsal scapular nerve Suprascapular nerve Spinal Nerves Forming Brachial Plexus C 4 C 5 C 6 C 7 C 8 T 1 Musculocutaneous nerve Median nerve Ulnar nerve Radial nerve Lateral antebrachial cutaneous nerve Superficial branch of radial nerve Deep radial nerve Ulnar nerve Median nerve Palmar digital nerves Major nerves originating at the right brachial plexus, anterior view

61 Figure 13-12b The Brachial Plexus Anterior Posterior Radial nerve Ulnar nerve Median nerve Areas of the hands serviced by nerves of the right brachial plexus

62 13-4 Spinal Nerves and Plexuses The Lumbar Plexus Major nerve Femoral nerve

63 13-4 Spinal Nerves and Plexuses The Sacral Plexus Major nerves Sciatic nerve Two branches of the sciatic nerve 1. Fibular nerve 2. Tibial nerve

64 Figure 13-13a The Lumbar and Sacral Plexuses Nerves of the Lumbar Plexus Iliohypogastric Ilioinguinal Genitofemoral Lateral femoral cutaneous Femoral Obturator T 12 L 1 L 2 L 3 L 4 L 5 Spinal Nerves Forming the Lumbar Plexus T 12 nerve L 1 nerve L 2 nerve L 3 nerve L 4 nerve Lumbosacral trunk Lumbar plexus, anterior view

65 Figure 13-13b The Lumbar and Sacral Plexuses Lumbosacral trunk Nerves of the Sacral Plexus Superior gluteal Inferior gluteal Sciatic Posterior femoral cutaneous S 5 Spinal Nerves Forming the Sacral Plexus L 4 nerve L 5 nerve S 1 nerve S 2 nerve S 3 nerve S 4 nerve Co1 Pudendal Sacral plexus, anterior view

66 Figure 13-13c The Lumbar and Sacral Plexuses Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve Obturator nerve Superior gluteal nerve Inferior gluteal nerve Pudendal nerve Posterior femoral cutaneous nerve (cut) Sciatic nerve Saphenous nerve Common fibular nerve Superficial fibular nerve Deep fibular nerve Nerves of the lumbar and sacral plexuses, anterior view

67 Figure 13-13d The Lumbar and Sacral Plexuses Sural nerve Saphenous nerve Sural nerve Fibular nerve Saphenous nerve Tibial nerve Saphenous nerve Tibial nerve Sural nerve Fibular nerve Cutaneous distribution of the nerves in the foot and ankle

68 Figure 13-13e The Lumbar and Sacral Plexuses Superior gluteal nerve Inferior gluteal nerve Pudendal nerve Posterior femoral cutaneous nerve Sciatic nerve Tibial nerve Common fibular nerve Sural nerve Nerves of the sacral plexus, posterior view

69 13-5 Neuronal Pools Functional Organization of Neurons Sensory neurons About 10 million Deliver information to CNS Motor neurons About 1/2 million Deliver commands to peripheral effectors Interneurons About 20 billion Interpret, plan, and coordinate signals in and out

70 13-5 Neuronal Pools Five Patterns of Neural Circuits in Neuronal Pools 1. Divergence Spreads stimulation to many neurons or neuronal pools in CNS 2. Convergence Brings input from many sources to single neuron 3. Serial processing Moves information in single line

71 13-5 Neuronal Pools Five Patterns of Neural Circuits in Neuronal Pools 4. Parallel processing Moves same information along several paths simultaneously 5. Reverberation Positive feedback mechanism Functions until inhibited

72 Figure 13-14a Neural Circuits: The Organization of Neuronal Pools Divergence A mechanism for spreading stimulation to multiple neurons or neuronal pools in the CNS

73 Figure 13-14b Neural Circuits: The Organization of Neuronal Pools Convergence A mechanism for providing input to a single neuron from multiple sources

74 Figure 13-14c Neural Circuits: The Organization of Neuronal Pools Serial processing A mechanism in which neurons or pools work sequentially

75 Figure 13-14d Neural Circuits: The Organization of Neuronal Pools Parallel processing A mechanism in which neurons or pools process the same information simultaneously

76 Figure 13-14e Neural Circuits: The Organization of Neuronal Pools Reverberation A positive feedback mechanism

77 13-6 Reflexes Reflexes Automatic responses coordinated within spinal cord Through interconnected sensory neurons, motor neurons, and interneurons Produce simple and complex reflexes

78 13-6 Reflexes Neural Reflexes Rapid, automatic responses to specific stimuli Basic building blocks of neural function One neural reflex produces one motor response Reflex arc The wiring of a single reflex Beginning at receptor Ending at peripheral effector Generally opposes original stimulus (negative feedback)

79 13-6 Reflexes Five Steps in a Neural Reflex Step 1: Arrival of stimulus, activation of receptor Physical or chemical changes Step 2: Activation of sensory neuron Step 3: Information processing by postsynaptic cell Triggered by neurotransmitters Step 4: Activation of motor neuron Action potential Step 5: Response of peripheral effector Triggered by neurotransmitters

80 Figure Events in a Neural Reflex Arrival of stimulus and activation of receptor Activation of a sensory neuron Dorsal root Sensation relayed to the brain by axon collaterals Stimulus Receptor REFLEX ARC Information processing in the CNS Response by effector Effector Ventral root Activation of a motor neuron KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated)

81 13-6 Reflexes Four Classifications of Reflexes 1. By early development 2. By type of motor response 3. By complexity of neural circuit 4. By site of information processing

82 13-6 Reflexes Development of Reflexes Innate reflexes Basic neural reflexes Formed before birth Acquired reflexes Rapid, automatic Learned motor patterns

83 13-6 Reflexes Motor Response Nature of resulting motor response Somatic reflexes Involuntary control of nervous system Superficial reflexes of skin, mucous membranes Stretch or deep tendon reflexes (e.g., patellar, or knee-jerk, reflex) Visceral reflexes (autonomic reflexes) Control systems other than muscular system

84 13-6 Reflexes Complexity of Neural Circuit Monosynaptic reflex Sensory neuron synapses directly onto motor neuron Polysynaptic reflex At least one interneuron between sensory neuron and motor neuron

85 13-6 Reflexes Site of Information Processing Spinal reflexes Occur in spinal cord Cranial reflexes Occur in brain

86 Figure The Classification of Reflexes Reflexes can be classified by development response complexity of circuit processing site Innate Reflexes Somatic Reflexes Monosynaptic Spinal Reflexes Genetically determined Control skeletal muscle contractions Include superficial and stretch reflexes One synapse Processing in the spinal cord Acquired Reflexes Visceral (Autonomic) Reflexes Polysynaptic Cranial Reflexes Learned Control actions of smooth and cardiac muscles, glands, and adipose tissue Multiple synapse (two to several hundred) Processing in the brain

87 13-7 Spinal Reflexes Spinal Reflexes Range in increasing order of complexity Monosynaptic reflexes Polysynaptic reflexes Intersegmental reflex arcs Many segments interact Produce highly variable motor response

88 13-7 Spinal Reflexes Monosynaptic Reflexes A stretch reflex Have least delay between sensory input and motor output For example, stretch reflex (such as patellar reflex) Completed in msec Receptor is muscle spindle

89 Figure A Stretch Reflex Stimulus Stretch Receptor (muscle spindle) REFLEX ARC Spinal cord Effector Contraction KEY Sensory neuron (stimulated) Motor neuron (stimulated) Response

90 13-7 Spinal Reflexes Postural reflexes Stretch reflexes Maintain normal upright posture Stretched muscle responds by contracting Automatically maintain balance

91 13-7 Spinal Reflexes Polysynaptic Reflexes More complicated than monosynaptic reflexes Interneurons control more than one muscle group Produce either excitatory or inhibitory effects

92 13-7 Spinal Reflexes Withdrawal Reflexes Move body part away from stimulus (pain or pressure) For example, flexor reflex Pulls hand away from hot stove Strength and extent of response Depend on intensity and location of stimulus

93 Figure A Flexor Reflex Distribution within gray horns to other segments of the spinal cord Painful stimulus Flexors stimulated Extensors inhibited KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated) Motor neuron (inhibited) Inhibitory interneuron

94 13-7 Spinal Reflexes Reciprocal Inhibition For flexor reflex to work The stretch reflex of antagonistic (extensor) muscle must be inhibited (reciprocal inhibition) by interneurons in spinal cord

95 13-8 The Brain Can Alter Spinal Reflexes Integration and Control of Spinal Reflexes Reflex behaviors are automatic But processing centers in brain can facilitate or inhibit reflex motor patterns based in spinal cord