Chapter 14 The Nervous System The Spinal Cord

Introduction • The Central Nervous System (CNS) consists of: • The spinal cord •

Gross Anatomy of the Spinal Cord • Features of the Spinal Cord • •

Gross Anatomy of the Spinal Cord • Features of the Spinal Cord • Consists

Figure 14. 1 a Gross Anatomy of the Spinal Cord Cervical spinal nerves C

Figure 14. 1 d Gross Anatomy of the Spinal Cord Posterior median sulcus Dorsal

Gross Anatomy of the Spinal Cord • Features of the Spinal Cord • Transverse

Gross Anatomy of the Spinal Cord • Features of the Spinal Nerves • Classified

Spinal Meninges • Features of Spinal Meninges • Specialized membranes that provide protection, physical

Figure 14. 2 c The Spinal Cord and Spinal Meninges Spinal cord Anterior median

Spinal Meninges • Features of Spinal Meninges • Made of three layers • Dura

Figure 14. 2 a The Spinal Cord and Spinal Meninges Gray matter White matter

Spinal Meninges • The Dura Mater • Tough fibrous outermost layer of the meninges

Spinal Meninges • The Arachnoid Mater • Middle meningeal layer • Separated from the

Spinal Meninges • The Pia Mater • Deepest meningeal layer • Blood vessels are

Sectional Anatomy of the Spinal Cord • Gray Matter • Central canal • Consists

Sectional Anatomy of the Spinal Cord • Organization of Gray Matter • Somas are

Sectional Anatomy of the Spinal Cord • Organization of Gray Matter • Posterior gray

Figure 14. 4 b Sectional Organization of the Spinal Cord Posterior median sulcus From

Sectional Anatomy of the Spinal Cord • Organization of White Matter • • •

Figure 14. 4 c Sectional Organization of the Spinal Cord Leg Posterior white column

Spinal Nerves • There are 31 pairs of spinal nerves • • • 8

Spinal Nerves • Each peripheral nerve consists of: • Epineurium • Outer layer—becomes continuous

Figure 14. 5 a Anatomy of a Peripheral Nerve Blood vessels Connective Tissue Layers

Spinal Nerves • Peripheral Distribution of Spinal Nerves • Spinal nerves from two branches

Spinal Nerves • Peripheral Distribution of Spinal Nerves • Motor impulses leave the spinal

Figure 14. 6 a Peripheral Distribution of Spinal Nerves Motor Commands Postganglionic fibers to

Figure 14. 6 b Peripheral Distribution of Spinal Nerves Sensory Information From interoceptors of

Spinal Nerves • Dermatomes • Each pair of spinal nerves monitors specific surface areas

Figure 14. 7 Dermatomes C 2–C 3 NV C 2–C 3 C 2 C

Nerve Plexuses • There are four nerve plexuses • • Cervical plexus Brachial plexus

Figure 14. 8 Peripheral Nerves and Nerve Plexuses Cervical plexus Brachial plexus C 1

Nerve Plexuses • The Cervical Plexus (C 1–C 5) • Consists of cutaneous and

Nerve Plexus • The Cervical Plexus • Consists of cutaneous and muscular branches •

Figure 14. 9 The Cervical and Brachial Plexuses © 2015 Pearson Education, Inc.

Nerve Plexus • The Brachial Plexus (C 5–T 1) • Innervates the pectoral girdle

Nerve Plexus • The Brachial Plexus (C 5–T 1) • The trunks form the

Figure 14. 10 a The Brachial Plexus Dorsal scapular nerve C 4 C 5

Figure 14. 10 b The Brachial Plexus b This posterior view of the brachial

Nerve Plexus • The Cords of the Brachial Plexus (details) • Lateral cord: extends

Figure 14. 10 c The Brachial Plexus Cervical plexus Clavicle, cut and removed Right

Nerve Plexus • The Lumbar and Sacral Plexuses (T 12–S 4) • Also called

Figure 14. 11 The Lumbar and Sacral Plexuses © 2015 Pearson Education, Inc.

Nerve Plexus • The Lumbar and Sacral Plexuses (T 12–S 4) • Lumbar plexus

Nerve Plexus • The Lumbar and Sacral Plexuses (T 12–S 4) • Sacral plexus

Figure 14. 12 a Peripheral Nerves Originating from the Lumbar and Sacral Plexuses Nerves

Figure 14. 12 b Peripheral Nerves Originating from the Lumbar and Sacral Plexuses Nerves

Nerve Plexus • Summary of the Spinal Nerves • • • Cervical spinal nerves

Nerve Plexus • Summary of the Nerve Plexuses • • • Cervical plexus nerves

Figure 14. 3 Posterior View of Vertebral Column and Spinal Nerves Occipital bone Spinal

Reflexes • Reflex • An immediate involuntary motor response • Reflex Arc • The

Reflexes • Pathway of a Reflex Arc 1. 2. 3. 4. 5. Activation of

Reflexes • Classification of Reflexes • Reflexes are classified according to: • Their development

Figure 14. 13 A Reflex Arc 1 2 Arrival of stimulus and activation of

Figure 14. 14 The Classification of Reflexes can be classified by Development Innate Reflexes

Reflexes • Classification of Reflexes • Spinal reflexes can be: • Monosynaptic • Involves

Figure 14. 15 Neural Organization and Simple Reflexes Ganglion CENTRAL NERVOUS SYSTEM Sensory neuron

Reflexes • Spinal Reflexes • Stretch reflex 1. 2. 3. 4. 5. © 2015

Figure 14. 16 a Stretch Reflexes 1 Stimulus. Stretching of muscle stimulates muscle spindles

Figure 14. 16 b Stretch Reflexes Receptor (muscle spindle) Stretch Stimulus Spinal cord REFLEX

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Introduction • The Central Nervous System (CNS) consists of: • The spinal cord • Integrates and processes information • Can function with the brain • Can function independently of the brain • The brain • Integrates and processes information • Can function with the spinal cord • Can function independently of the spinal cord © 2015 Pearson Education, Inc.

Gross Anatomy of the Spinal Cord • Features of the Spinal Cord • • 45 cm in length Passes through the foramen magnum Extends from the brain to L 1 Consists of: • • • Cervical region Thoracic region Lumbar region Sacral region Coccygeal region © 2015 Pearson Education, Inc.

Gross Anatomy of the Spinal Cord • Features of the Spinal Cord • Consists of (continued): • • • Cervical enlargement Lumbosacral enlargement Conus medullaris Cauda equina Filum terminale: becomes a component of the coccygeal ligament • Posterior and anterior median sulci © 2015 Pearson Education, Inc.

Figure 14. 1 a Gross Anatomy of the Spinal Cord Cervical spinal nerves C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 Cervical enlargement 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 Lumbosacral enlargement T 12 L 1 Conus medullaris L 2 Lumbar spinal nerves L 3 L 4 Inferior tip of spinal cord Cauda equina L 5 Sacral spinal nerves S 1 S 2 S 3 S 4 S 5 Coccygeal nerve (Co 1) Filum terminale (in coccygeal ligament) a 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, however, extends from the brain only to the level of vertebrae L 1–L 2. © 2015 Pearson Education, Inc.

Gross Anatomy of the Spinal Cord • Features of the Spinal Cord • Consists of (continued): • 31 spinal segments • Each segment consists of: • • © 2015 Pearson Education, Inc. Dorsal root ganglia Ventral root Spinal nerve

Figure 14. 1 d Gross Anatomy of the Spinal Cord Posterior median sulcus Dorsal root ganglion White matter Gray matter Central canal Spinal Ventral nerve root Anterior median fissure C 3 T 3 L 1 S 2 d Inferior views of cross sections through representative segments of the spinal cord showing the arrangement of gray and white matter. © 2015 Pearson Education, Inc.

Gross Anatomy of the Spinal Cord • Features of the Spinal Cord • Transverse view • • • White matter Gray matter Central canal Anterior median fissure Posterior median sulcus © 2015 Pearson Education, Inc.

Gross Anatomy of the Spinal Cord • Features of the Spinal Nerves • Classified as mixed nerves • Sensory nerves (afferent nerves) • Transmit impulses toward the spinal cord • Motor nerves (efferent nerves) • Transmit impulses away from the spinal cord © 2015 Pearson Education, Inc.

Spinal Meninges • Features of Spinal Meninges • Specialized membranes that provide protection, physical stability, and shock absorption • Continuous with the cranial (cerebral) meninges • Denticulate ligaments help anchor the spinal cord in position © 2015 Pearson Education, Inc.

Figure 14. 2 c The Spinal Cord and Spinal Meninges Spinal cord Anterior median fissure Pia mater Denticulate ligaments Arachnoid mater (reflected) Dura mater (reflected) Spinal blood vessel Dorsal root of sixth cervical nerve Ventral root of sixth cervical nerve c Anterior view of spinal cord shows meninges and spinal nerves. For this view, the dura and arachnoid membranes have been cut longitudinally and retracted (pulled aside); notice the blood vessels that run in the subarachnoid space bound to the outer surface of the delicate pia mater. © 2015 Pearson Education, Inc.

Spinal Meninges • Features of Spinal Meninges • Made of three layers • Dura mater • Tough, fibrous outermost layer • Arachnoid mater • Middle layer • Pia mater • Innermost layer © 2015 Pearson Education, Inc.

Figure 14. 2 a The Spinal Cord and Spinal Meninges Gray matter White matter Ventral root Dorsal root ganglion Spinal nerve Dorsal root Meninges Pia mater Arachnoid mater Dura mater a Posterior view of the spinal cord shows the meningeal layers, superficial landmarks, and distribution of gray and white matter. © 2015 Pearson Education, Inc.

Spinal Meninges • The Dura Mater • Tough fibrous outermost layer of the meninges • Stabilizes the spinal cord within the vertebral canal • Cranial and sacral attachments stabilize the longitudinal axis of the spinal cord © 2015 Pearson Education, Inc.

Spinal Meninges • The Arachnoid Mater • Middle meningeal layer • Separated from the pia mater by the subarachnoid space • Cerebrospinal fluid flows within this space • Arachnoid trabeculae extend from the arachnoid to the outer layer of the pia mater © 2015 Pearson Education, Inc.

Sectional Anatomy of the Spinal Cord • Gray Matter • Central canal • Consists of somas (cell bodies) surrounding the central canal • Consists of glial cells • White Matter • Consists of axons • Nerves are organized into tracts or columns • Located outside the gray matter area © 2015 Pearson Education, Inc.

Sectional Anatomy of the Spinal Cord • Organization of Gray Matter • Somas are organized into groups called nuclei • Sensory nuclei • Motor nuclei • Transverse view shows: • • Posterior gray horns Lateral gray horns Anterior gray horns Gray commissure © 2015 Pearson Education, Inc.

Sectional Anatomy of the Spinal Cord • Organization of Gray Matter • Posterior gray horns • Somatic sensory and visceral nuclei • Lateral gray horns • Visceral motor nuclei • Anterior gray horns • Somatic motor nuclei • Gray commissure • Consists of axons crossing from one side to the other © 2015 Pearson Education, Inc.

Figure 14. 4 b Sectional Organization of the Spinal Cord Posterior median sulcus From dorsal root Posterior gray horn Posterior gray commissure Somatic Visceral Lateral gray horn Visceral Anterior gray horn Somatic Anterior gray commissure Sensory nuclei Motor nuclei To ventral root Anterior median fissure b The left half of this sectional view shows important anatomical landmarks; the right half indicates the functional organization of the gray matter in the anterior, lateral, and posterior gray horns. © 2015 Pearson Education, Inc.

Sectional Anatomy of the Spinal Cord • Organization of White Matter • • • Consists of columns of nerves (funiculi) Posterior white column Anterior white column Lateral white column Columns convey either: • Sensory tracts (ascending tracts) • Motor tracts (descending tracts) © 2015 Pearson Education, Inc.

Figure 14. 4 c Sectional Organization of the Spinal Cord Leg Posterior white column (funiculus) Hip Trunk Arm Lateral white column (funiculus) Flexors Extensors Hand Forearm Arm Shoulder Trunk Anterior white column (funiculus) c Anterior white commissure The left half of this sectional view shows the major columns of white matter. The right half indicates the anatomical organization of sensory tracts in the posterior white column for comparison with the organization of motor nuclei in the anterior gray horn. Note that both sensory and motor components of the spinal cord have a definite regional organization. © 2015 Pearson Education, Inc.

Spinal Nerves • Each peripheral nerve consists of: • Epineurium • Outer layer—becomes continuous with the dura mater • Perineurium • Layer surrounding a fascicle—a fascicle is a bundle of axons • Endoneurium • Layer surrounding a single axon © 2015 Pearson Education, Inc.

Figure 14. 5 a Anatomy of a Peripheral Nerve Blood vessels Connective Tissue Layers Epineurium covering peripheral nerve Perineurium (around one fascicle) Endoneurium Schwann cell Fascicle a A typical peripheral nerve and its connective tissue wrappings © 2015 Pearson Education, Inc. Myelinated axon

Spinal Nerves • Peripheral Distribution of Spinal Nerves • Spinal nerves from two branches • Dorsal ramus • Ventral ramus • Spinal nerves T 1 to L 2 have two additional branches • White ramus • Gray ramus • White and gray rami are collectively called rami communicantes © 2015 Pearson Education, Inc.

Spinal Nerves • Peripheral Distribution of Spinal Nerves • Motor impulses leave the spinal cord via the ventral root • Sensory information enters the spinal cord via the dorsal root • Rami communicantes (white and gray rami) • Innervates smooth muscles, glands, and organs • Dorsal ramus • Innervates skeletal muscles of the neck and back • Ventral ramus • Innervates skeletal muscles of the limbs © 2015 Pearson Education, Inc.

Figure 14. 6 a Peripheral Distribution of Spinal Nerves Motor Commands Postganglionic fibers to smooth muscles, glands, etc. , of back To skeletal muscles of back Dorsal root ganglion Dorsal root Visceral motor Somatic motor Dorsal ramus Ventral ramus To skeletal muscles of body wall, limbs Ventral root Postganglionic fibers to smooth muscles, glands, etc. , of body wall, limbs Spinal nerve Sympathetic ganglion White ramus (preganglionic) Rami communicantes Gray ramus (postganglionic) Sympathetic nerve KEY Somatic motor commands Visceral motor commands a The distribution of motor neurons in the spinal cord and motor fibers within the spinal nerve and its branches © 2015 Pearson Education, Inc. Postganglionic fibers to smooth muscles, glands, visceral organs in thoracic cavity Preganglionic fibers to sympathetic ganglia innervating aboominopelvic viscera

Figure 14. 6 b Peripheral Distribution of Spinal Nerves Sensory Information From interoceptors of back From exteroceptors, proprioceptors of back Dorsal root Somatic sensory Visceral sensory Dorsal ramus Ventral ramus From exteroceptors, proprioceptors of body wall, limbs Dorsal root ganglion From interoceptors of body wall, limbs Rami communicantes KEY Ventral root Somatic sensations Visceral sensations From interoceptors of visceral organs b A comparable view detailing the distribution of sensory neurons and sensory fibers © 2015 Pearson Education, Inc.

Figure 14. 7 Dermatomes C 2–C 3 NV C 2–C 3 C 2 C 3 T 2 C 6 L 1 L 2 C 8 C 7 T 1 L 3 L 4 L 5 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 S 2 C 3 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 L 4 L 3 L 5 C 4 C 5 T 2 C 6 T 1 C 7 S 4 S 3 L 1 S 1 L 5 S 5 C 8 L 2 S 2 L 3 S 1 L 4 ANTERIOR © 2015 Pearson Education, Inc. POSTERIOR

Nerve Plexuses • There are four nerve plexuses • • Cervical plexus Brachial plexus Lumbar plexus Sacral plexus • Sometimes the lumbar and sacral are combined to form the lumbosacral plexus © 2015 Pearson Education, Inc.

Figure 14. 8 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 Lesser occipital nerve Great auricular nerve Transverse cervical nerve Supraclavicular nerve Phrenic nerve Axillary nerve T 8 Musculocutaneous nerve T 9 Thoracic nerves T 10 T 11 T 12 L 1 Lumbar plexus Radial nerve L 2 Ulnar nerve L 3 Median nerve L 4 Sacral plexus L 5 S 1 S 2 S 3 S 4 S 5 Co 1 Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Femoral nerve Obturator nerve Superior Inferior Gluteal nerves Pudendal nerve Sciatic nerve Lateral femoral cutaneous nerve Saphenous nerve Common fibular nerve Tibial nerve Medial sural cutaneous nerve © 2015 Pearson Education, Inc.

Nerve Plexus • The Cervical Plexus • Consists of cutaneous and muscular branches • Muscular branch innervates: • Omohyoid, sternohyoid, geniohyoid, thyrohyoid, sternothyroid • Rhomboids • Serratus anterior • Sternocleidomastoid • Diaphragm (controlled by the phrenic nerve of the cervical plexus) © 2015 Pearson Education, Inc.

Nerve Plexus • The Brachial Plexus (C 5–T 1) • Innervates the pectoral girdle and upper limbs • The ventral rami emerging from C 5 to T 1 form the trunks • Superior trunk • Middle trunk • Inferior trunk © 2015 Pearson Education, Inc.

Nerve Plexus • The Brachial Plexus (C 5–T 1) • The trunks form the divisions • Anterior • Posterior • The divisions form the cords • Posterior • Lateral • Medial • The cords form the spinal nerves © 2015 Pearson Education, Inc.

Figure 14. 10 a The Brachial Plexus Dorsal scapular nerve C 4 C 5 C 6 C 7 C 8 T 1 Suprascapular nerve BRACHIAL PLEXUS Superior trunk Middle trunk Inferior trunk Musculocutaneous nerve Median nerve Ulnar nerve Radial nerve Lateral antebrachial cutaneous nerve Anterior antebrachial interosseous nerve Superficial branch of radial nerve Ulnar nerve Median nerve Palmar digital nerves Anterior interosseous nerve Deep branch of ulnar nerve Superficial branch of ulnar nerve Radial nerve Ulnar nerve a In this anterior view of the brachial plexus and upper limb, the distribution of major peripheral nerves can be seen. Median nerve Anterior © 2015 Pearson Education, Inc.

Figure 14. 10 b The Brachial Plexus b This posterior view of the brachial plexus shows the location and distribution of the nerves. Musculocutaneous nerve Axillary nerve Branches of axillary nerve Radial nerve Ulnar nerve Median nerve Posterior antebrachial cutaneous nerve Deep branch of radial nerve Radial nerve Superficial branch of radial nerve Ulnar nerve Dorsal digital nerves Median nerve Posterior © 2015 Pearson Education, Inc.

Nerve Plexus • The Cords of the Brachial Plexus (details) • Lateral cord: extends to form the musculocutaneous nerve • The lateral cord and medial cord extend to form the median nerve • Medial cord extends to form the ulnar nerve • Posterior cord: branches to form the radial nerve and axillary nerve © 2015 Pearson Education, Inc.

Figure 14. 10 c The Brachial Plexus Cervical plexus Clavicle, cut and removed Right common carotid artery Brachial plexus (C 5–T 1) Deltoid muscle Sternocleidomastoid muscle, sternal head Musculocutaneous nerve Sternocleidomastoid muscle, clavicular head Right axillary artery over axillary nerve Median nerve Radial nerve Right subclavian artery Biceps brachii, long and short heads Ulnar nerve Coracobrachialis muscle Retractor holding pectoralis major muscle (cut and reflected) Skin Right brachial artery Median nerve c This dissection shows the major nerves arising from the cervical and brachial plexuses. © 2015 Pearson Education, Inc.

Nerve Plexus • The Lumbar and Sacral Plexuses (T 12–S 4) • Also called the lumbosacral plexus • Lumbar plexus arises from L 1 to L 4 • Sacral plexus arises from L 4 to S 4 © 2015 Pearson Education, Inc.

Nerve Plexus • The Lumbar and Sacral Plexuses (T 12–S 4) • Lumbar plexus nerves L 1 to L 4 • • • Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve Iliohypogastric nerve Ilioinguinal nerve Obturator nerve © 2015 Pearson Education, Inc.

Nerve Plexus • The Lumbar and Sacral Plexuses (T 12–S 4) • Sacral plexus nerves L 4 to S 4 • Sciatic nerve (branches to form the common fibular nerve and the tibial nerve) • Pudendal nerve • Superior gluteal nerve • Inferior gluteal nerve • Posterior femoral cutaneous nerve © 2015 Pearson Education, Inc.

Figure 14. 12 a Peripheral Nerves Originating from the Lumbar and Sacral Plexuses Nerves Originating from the Lumbar Plexus Iliohypogastric nerve Illioinguinal nerve Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve Obturator nerve Saphenous nerve Common Fibular Nerve and Its Branches Common fibular nerve Superficial fibular nerve Deep fibular nerve a The lumbar and sacral © 2015 Pearson Education, Inc. plexuses, anterior view Subcostal nerve Nerves Originating from the Sacral Plexus Superior gluteal nerve Inferior gluteal nerve Posterior femoral cutaneous nerve Pudendal nerve Sciatic nerve

Figure 14. 12 b Peripheral Nerves Originating from the Lumbar and Sacral Plexuses Nerves Originating from the Sacral Plexus Superior gluteal nerve Inferior gluteal nerve Posterior femoral cutaneous nerve Pudendal nerve Sciatic nerve Branches of the Sciatic Nerve Tibial nerve Common fibular nerve Medial sural cutaneous nerve Lateral sural cutaneous nerve Sural nerve Medial plantar nerve Lateral plantar nerve b The sacral plexus, posterior view © 2015 Pearson Education, Inc.

Nerve Plexus • Summary of the Spinal Nerves • • • Cervical spinal nerves emerge from C 1–C 8 Thoracic spinal nerves emerge from T 1–T 12 Lumbar spinal nerves emerge from L 1–L 5 Sacral spinal nerves emerge from S 1–S 5 Coccygeal spinal nerves emerge from Co 1 © 2015 Pearson Education, Inc.

Nerve Plexus • Summary of the Nerve Plexuses • • • Cervical plexus nerves emerge from C 1–C 5 Brachial plexus nerves emerge from C 5–T 1 There is not a thoracic plexus Lumbar plexus nerves emerge from T 12–L 4 Sacral plexus nerves emerge from L 4–S 4 There is not a coccygeal plexus © 2015 Pearson Education, Inc.

Figure 14. 3 Posterior View of Vertebral Column and Spinal Nerves Occipital bone Spinal cord emerging from foramen magnum Cervical plexus (C 1–C 5) Cervical spinal nerves (C 1–C 8) Brachial plexus (C 5–T 1) Thoracic spinal nerves (T 1–T 12) Lumbar plexus (T 12–L 4) Sacral plexus (L 4–S 4) Coccygeal nerves (Co 1) © 2015 Pearson Education, Inc. Lumbar spinal nerves (L 1–L 5) Sciatic nerve Sacral spinal nerves (S 1–S 5) emerging from sacral foramina

Reflexes • Reflex • An immediate involuntary motor response • Reflex Arc • The neural “wiring” of a single reflex • Begins at a sensory receptor and ends at a peripheral receptor © 2015 Pearson Education, Inc.

Reflexes • Pathway of a Reflex Arc 1. 2. 3. 4. 5. Activation of a sensory receptor Relay of information to the CNS Information processing Activation of a motor neuron Response by the effector © 2015 Pearson Education, Inc.

Reflexes • Classification of Reflexes • Reflexes are classified according to: • Their development • Innate or acquired • The site where information is processed • Spinal or cranial (cerebral) • The nature of the resulting motor response • Somatic, visceral, or autonomic • The complexity of the neural circuit • Monosynaptic or polysynaptic © 2015 Pearson Education, Inc.

Figure 14. 13 A Reflex Arc 1 2 Arrival of stimulus and activation of receptor Dorsal root Activation of a sensory neuron Sensation relayed to the brain by collateral REFLEX ARC Receptor Stimulus Effector 5 Response by effector Ventral root 4 Activation of a motor neuron 3 Information processing in CNS KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated) © 2015 Pearson Education, Inc.

Figure 14. 14 The Classification of Reflexes can be classified by Development Innate Reflexes • Genetically determined Acquired Reflexes • Learned © 2015 Pearson Education, Inc. Response Somatic Reflexes Complexity of Circuit Processing Site Monosynaptic Spinal Reflexes • Control skeletal muscle contractions • Include superficial and stretch reflexes • One synapse • Processing in the spinal cord Visceral (Autonomic) Reflexes Polysynaptic Cranial Reflexes • Control actions of smooth and cardiac muscles, glands • Multiple synapses (two to several hundred) • Processing in the brain

Reflexes • Classification of Reflexes • Spinal reflexes can be: • Monosynaptic • Involves a single segment of the spinal cord • Polysynaptic • Integrates motor output from several spinal segments © 2015 Pearson Education, Inc.

Figure 14. 15 Neural Organization and Simple Reflexes Ganglion CENTRAL NERVOUS SYSTEM Sensory neuron Ganglion Sensory neuron CENTRAL NERVOUS SYSTEM Circuit 2 Motor neuron Circuit 1 Motor neurons Sensory receptor (muscle spindle) Skeletal muscle 1 Skeletal muscle a A monosynaptic reflex circuit involves a peripheral sensory neuron and a central motor neuron. In this example, stimulation of the receptor will lead to a reflexive contraction in a skeletal muscle. © 2015 Pearson Education, Inc. Interneurons Sensory receptor Skeletal muscle 2 b A polysynaptic reflex circuit involves a sensory neuron, interneurons, and motor neurons. In this example, the stimulation of the receptor leads to the coordinated contractions of two different skeletal muscles.

Reflexes • Spinal Reflexes • Stretch reflex 1. 2. 3. 4. 5. © 2015 Pearson Education, Inc. Stimulus stretches a muscle Activates a sensory neuron Information is processed in the spinal cord Motor neurons are activated Muscle (effector) contracts

Figure 14. 16 a Stretch Reflexes 1 Stimulus. Stretching of muscle stimulates muscle spindles 2 Activation of a sensory neuron 3 4 5 Information processing at motor neuron Activation of motor neuron Response. Contraction of muscle a Steps 1– 5 are common to all stretch reflexes. © 2015 Pearson Education, Inc.

Figure 14. 16 b Stretch Reflexes Receptor (muscle spindle) Stretch Stimulus Spinal cord REFLEX ARC Effector Contraction KEY Sensory neuron (stimulated) Motor neuron (stimulated) b The patellar reflex is controlled by Response © 2015 Pearson Education, Inc. muscle spindles in the quadriceps muscle group. The stimulus is a reflex hammer striking the muscle tendon, stretching the spindle fibers. This results in a sudden increase in the activity of the sensory neurons, which synapse on spinal motor neurons. The response occurs upon the activation of motor units in the quadriceps group, which produces an immediate increase in muscle tone and a reflexive kick.