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Spinal Cord and Reflexes Muse: Lecture #13 7/9/12 Spinal cord, nerves and reflexes Figure 13–1 An Overview of Chapters 13 and 14. Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Motor (efferent) division Somatic nervous system Sympathetic division accelerator Autonomic nervous system (ANS) Parasympathetic division brake Figure 13.1 Spinal Cord Gross Anatomy of the Spinal Cord About 18 inches (45 cm) long 1/2 inch (14 mm) wide Ends between vertebrae L1 and L2 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 Spinal Cord Gross Anatomy of the Spinal Cord The Distal End Conus medullaris: – thin, conical spinal cord below lumbar enlargement Filum terminale: – thin thread of fibrous tissue at end of conus medullaris – attaches to coccygeal ligament Cauda equina: – nerve roots extending below conus medullaris Spinal Cord Figure 13–2 Gross Anatomy of the Adult Spinal Cord. Spinal Cord Figure 13–2 Gross Anatomy of the Adult Spinal Cord. Made by Honda? 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 Spinal Cord Roots Two branches of spinal nerves Ventral root: – contains axons of motor neurons Dorsal root: – contains axons of sensory neurons Dorsal root ganglia contain cell bodies of sensory neurons 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 Spinal Cord Figure 13–3 The Spinal Cord and Spinal Meninges Spinal Cord Figure 13–3 The Spinal Cord and Spinal Meninges Spinal Cord The Spinal Meninges Specialized membranes isolate spinal cord from surroundings Functions of the spinal meninges include Protect spinal cord Carry blood supply Continuous with cranial meninges Meningitis: Viral or bacterial infection of meninges Spinal Cord The Three Meningeal Layers Dura mater Outer layer of spinal cord Arachnoid mater Middle meningeal layer Pia mater Inner meningeal layer 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 Joins filum terminale in coccygeal ligament The Epidural Space Between spinal dura mater and walls of vertebral canal Contains loose connective and adipose tissue Anesthetic injection site Spinal Cord The Arachnoid Mater Middle meningeal layer Arachnoid membrane Simple squamous epithelia Covers arachnoid mater Spinal Cord The Interlayer Spaces of Arachnoid Mater Subdural space Between arachnoid mater and dura mater Subarachnoid space Between arachnoid mater and pia mater Contains collagen/elastin fiber network (arachnoid trabeculae) Filled with cerebrospinal fluid (CSF) Cerebrospinal Fluid (CSF) Carries dissolved gases, nutrients, and wastes Spinal tap: withdraws CSF Spinal Cord The Pia Mater Is the innermost meningeal layer Is a mesh of collagen and elastic fibers Is bound to underlying neural tissue Spinal Cord Figure 13–4 The Spinal Cord and Associated Structures 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) 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 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 Gray Matter and White Matter Control and Location Sensory or motor nucleus location within the gray matter determines which body part it controls 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 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 Gray Matter and White Matter Figure 13–5a The Sectional Organization of the Spinal Cord. Gray Matter and White Matter Figure 13–5b The Sectional Organization of the Spinal Cord. Spinal Cord Summary Spinal cord has a narrow central canal Surrounded by gray matter Containing sensory and motor nuclei Sensory nuclei are dorsal SounD Motor nuclei are ventral MoVe 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 Containing axon bundles with specific functions Spinal cord is so highly organized It is possible to predict results of injuries to specific areas 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 Spinal Nerves and Plexuses Three Connective Tissue Layers of Spinal Nerves Epineurium Outer layer Dense network of collagen fibers Perineurium Middle layer Divides nerve into fascicles (axon bundles) Endoneurium Inner layer Surrounds individual axons Spinal Nerves and Plexuses Figure 13–6a A Peripheral Nerve. Spinal Nerves and Plexuses Peripheral Nerves Interconnecting branches of spinal nerves Surrounded by connective tissue sheaths Spinal Nerves and Plexuses 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 Spinal Nerves and Plexuses Figure 13–7b Peripheral Distribution of Spinal Nerves. Spinal Nerves and Plexuses Figure 13–8 Dermatomes. Spinal Nerves and Plexuses Peripheral Neuropathy Regional loss of sensory or motor function Due to trauma or compression chronic can be due to diabetes 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 Spinal Nerves and Plexuses The Four Major Plexuses of Ventral Rami Cervical plexus Brachial plexus Lumbar plexus Sacral plexus Spinal Nerves and Plexuses Figure 13–10 Peripheral Nerves and Nerve Plexuses. Spinal Nerves and Plexuses Figure 13–10 Peripheral Nerves and Nerve Plexuses. Spinal Nerves and Plexuses The Cervical Plexus of the Ventral Rami Includes ventral rami of spinal nerves C1–C5 Innervates neck, thoracic cavity, diaphragmatic muscles Major nerve Phrenic nerve (controls diaphragm) Spinal Nerves and Plexuses Figure 13–11 The Cervical Plexus. Spinal Nerves and Plexuses Spinal Nerves and Plexuses Includes ventral rami of spinal nerves C5–T1 The Brachial Plexus of the Ventral Rami Major nerves of brachial plexus Musculocutaneous nerve (lateral cord) Median nerve (lateral and medial cords) Ulnar nerve (medial cord) Axillary nerve (posterior cord) Radial nerve (posterior cord) Spinal Nerves and Plexuses Figure 13–12a The Brachial Plexus. Spinal Nerves and Plexuses Figure 13–12b The Brachial Plexus. Spinal Nerves and Plexuses Figure 13–12c The Brachial Plexus. Spinal Nerves and Plexuses Spinal Nerves and Plexuses The Lumbar Plexus of the Ventral Rami Includes ventral rami of spinal nerves T12–L4 Major nerves Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve Spinal Nerves and Plexuses The Sacral Plexus of the Ventral Rami Includes ventral rami of spinal nerves L4–S4 Major nerves Pudendal nerve Sciatic nerve Branches of sciatic nerve Fibular nerve Tibial nerve 3D Rotation of Lumbar and Sacral Plexuses Spinal Nerves and Plexuses Figure 13–13b The Lumbar and Sacral Plexuses. Spinal Nerves and Plexuses Figure 13–13d The Lumbar and Sacral Plexuses. 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 Neuronal Pools Neuronal Pools Functional groups of interconnected neurons (interneurons) Each with limited input sources and output destinations May stimulate or depress parts of brain or spinal cord Neuronal Pools Five Patterns of Neural Circuits in Neuronal Pools Divergence Spreads stimulation to many neurons or neuronal pools in CNS Convergence Brings input from many sources to single neuron Serial processing Moves information in single line Neuronal Pools Five Patterns of Neural Circuits in Neuronal Pools Parallel processing Moves same information along several paths simultaneously Reverberation Positive feedback mechanism Functions until inhibited Neuronal Pools Figure 13–14 Neural Circuits: The Organization of Neuronal Pools. Reflexes Automatic responses coordinated within spinal cord Through interconnected sensory neurons, motor neurons, and interneurons Produce simple and complex reflexes Reflex Arc 2 SENSORY NEURON (axon conducts impulses from receptor to integrating center) 1 SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential) Interneuron 3 INTEGRATING CENTER (one or more regions within the CNS that relay impulses from sensory to motor neurons) 4 MOTOR NEURON (axon conducts impulses from integrating center to effector) 5 EFFECTOR (muscle or gland that responds to motor nerve impulses) 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) 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 Graded depolarization 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 Reflexes Figure 13–15 Events in a Neural Reflex. Reflexes Four Classifications of Reflexes By early development By type of motor response By complexity of neural circuit By site of information processing Reflexes Development How reflex was developed Innate reflexes: – basic neural reflexes – formed before birth Acquired reflexes: – rapid, automatic – learned motor patterns 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 “kneejerk”, reflex) Visceral reflexes (autonomic reflexes): – control systems other than muscular system 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 Site of Information Processing Spinal reflexes Occurs in spinal cord Cranial reflexes Occurs in brain Reflexes Figure 13–16 The Classification of Reflexes. 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 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 20–40 msec Receptor is muscle spindle Spinal Reflexes Figure 13–17 A Stretch Reflex. Spinal Reflexes Postural reflexes Stretch reflexes Maintain normal upright posture Stretched muscle responds by contracting Automatically maintain balance Spinal Reflexes Polysynaptic Reflexes More complicated than monosynaptic reflexes Interneurons control more than one muscle group Produce either EPSPs or IPSPs Excitory post synaptic potentials Spinal Reflexes The Tendon Reflex Polysynaptic Prevents skeletal muscles from Developing too much tension Tearing or breaking tendons Sensory receptors unlike muscle spindles or proprioceptors To brain Inhibitory interneuron 5 EFFECTOR (muscle attached to same tendon) relaxes and relieves excess tension 4 MOTOR NEURON inhibited + ++ 2 SENSORY NEURON excited – Increased tension stimulates 1 SENSORY RECEPTOR (tendon) + Spinal nerve 3 Within INTEGRATING + Antagonistic muscles contract CENTER (spinal cord), sensory neuron activates inhibitory interneuron Motor neuron to antagonistic muscles is excited Excitatory interneuron 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 Depends on intensity and location of stimulus Spinal Reflexes Figure 13–19 A Flexor Reflex. 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 Spinal Reflexes Reflex Arcs Ipsilateral reflex arcs Occur on same side of body as stimulus Stretch, tendon, and withdrawal reflexes Crossed extensor reflexes Involve a contralateral reflex arc Occur on side opposite stimulus Spinal Reflexes Crossed Extensor Reflexes Occur simultaneously, coordinated with flexor reflex For example, flexor reflex causes leg to pull up Crossed extensor reflex straightens other leg To receive body weight Maintained by reverberating circuits Spinal Reflexes Figure 13–20 The Crossed Extensor Reflex. Spinal Reflexes Five General Characteristics of Polysynaptic Reflexes Involve pools of neurons Are intersegmental in distribution Involve reciprocal inhibition Have reverberating circuits Which prolong reflexive motor response Several reflexes cooperate To produce coordinated, controlled response 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 The Brain Can Alter Spinal Reflexes Voluntary Movements and Reflex Motor Patterns Higher centers of brain incorporate lower, reflexive motor patterns Automatic reflexes Can be activated by brain as needed Use few nerve impulses to control complex motor functions Walking, running, jumping The Brain Can Alter Spinal Reflexes Reinforcement of Spinal Reflexes Higher centers reinforce spinal reflexes By stimulating excitatory neurons in brain stem or spinal cord Creating EPSPs at reflex motor neurons Facilitating postsynaptic neurons The Brain Can Alter Spinal Reflexes Inhibition of Spinal Reflexes Higher centers inhibit spinal reflexes by Stimulating inhibitory neurons Creating IPSPs at reflex motor neurons Suppressing postsynaptic neurons The Brain Can Alter Spinal Reflexes The Babinski Reflexes Normal in infants May indicate CNS damage in adults The Brain Can Alter Spinal Reflexes Figure 13–21 The Babinski Reflexes. An Introduction to the Brain and Cranial Nerves The Adult Human Brain Ranges from 750 cc to 2100 cc Contains almost 97% of the body’s neural tissue Average weight about 1.4 kg (3 lb) The Brain Six Regions of the Brain Cerebrum Cerebellum Diencephalon Mesencephalon Pons Medulla oblongata The Brain Figure 14–1 An Introduction to Brain Structures and Functions. The Brain Figure 14–2 Ventricles of the Brain. Brain Protection and Support Physical protection Bones of the cranium Cranial meninges Cerebrospinal fluid Biochemical isolation Blood–brain barrier Brain Protection and Support Cerebrospinal Fluid (CSF) Surrounds all exposed surfaces of CNS Interchanges with interstitial fluid of brain Functions of CSF Cushions delicate neural structures Supports brain Transports nutrients, chemical messengers, and waste products Brain Protection and Support Figure 14–4 The Formation and Circulation of Cerebrospinal Fluid. Brain Protection and Support Blood Supply to the Brain Supplies nutrients and oxygen to brain Delivered by internal carotid arteries and vertebral arteries Removed from dural sinuses by internal jugular veins Brain Protection and Support Figure 21–23 Arteries of the Brain. Brain Protection and Support Blood–Brain Barrier Isolates CNS neural tissue from general circulation Formed by network of tight junctions Between endothelial cells of CNS capillaries Lipid-soluble compounds (O2, CO2), steroids, and prostaglandins diffuse into interstitial fluid of brain and spinal cord Astrocytes control blood–brain barrier by releasing chemicals that control permeability of endothelium Brain Protection and Support Blood–CSF Barrier Formed by special ependymal cells Surround capillaries of choroid plexus Limits movement of compounds transferred Allows chemical composition of blood and CSF to differ Brain Protection and Support Four Breaks in the BBB Portions of hypothalamus Secrete hypothalamic hormones Posterior lobe of pituitary gland Secretes hormones ADH and oxytocin Pineal glands Pineal secretions Choroid plexus Where special ependymal cells maintain blood– CSF barrier The Medulla Oblongata The Medulla Oblongata Allows brain and spinal cord to communicate Coordinates complex autonomic reflexes Controls visceral functions Nuclei in the Medulla Autonomic nuclei: control visceral activities Sensory and motor nuclei: of cranial nerves Relay stations: along sensory and motor pathways The Medulla Oblongata Figure 14–5a The Diencephalon and Brain Stem. The Medulla Oblongata Figure 14–5c The Diencephalon and Brain Stem. The Cerebellum Functions of the Cerebellum Adjusts postural muscles Fine-tunes conscious and subconscious movements The Cerebellum Structures of the Cerebellum Purkinje cells Large, branched cells Found in cerebellar cortex Receive input from up to 200,000 synapses Arbor vitae Highly branched, internal white matter of cerebellum Cerebellar nuclei: embedded in arbor vitae: – relay information to Purkinje cells The Cerebellum Structures of the Cerebellum The peduncles Tracts link cerebellum with brain stem, cerebrum, and spinal cord: – superior cerebellar peduncles – middle cerebellar peduncles – inferior cerebellar peduncles The Cerebellum Disorders of the Cerebellum Ataxia Damage from trauma or stroke Intoxication (temporary impairment) Disturbs muscle coordination The Cerebellum Figure 14–7a The Cerebellum. The Cerebellum Figure 14–7b The Cerebellum. The Diencephalon Integrates sensory information and motor commands Thalamus, epithalamus, and hypothalamus The pineal gland Found in posterior epithalamus Secretes hormone melatonin The Diencephalon The Thalamus Filters ascending sensory information for primary sensory cortex Relays information between basal nuclei and cerebral cortex The third ventricle Separates left thalamus and right thalamus Interthalamic adhesion (or intermediate mass): – projection of gray matter – extends into ventricle from each side The Diencephalon The Thalamus Thalamic nuclei Are rounded masses that form thalamus Relay sensory information to basal nuclei and cerebral cortex The Diencephalon The Hypothalamus Mamillary bodies Process olfactory and other sensory information Control reflex eating movements Infundibulum A narrow stalk Connects hypothalamus to pituitary gland Tuberal area Located between the infundibulum and mamillary bodies Helps control pituitary gland function The Diencephalon Figure 14–10a The Hypothalamus in Sagittal Section. The Diencephalon Eight Functions of the Hypothalamus Provides subconscious control of skeletal muscle Controls autonomic function Coordinates activities of nervous and endocrine systems Secretes hormones Antidiuretic hormone (ADH) by supraoptic nucleus Oxytocin (OT; OXT) by paraventricular nucleus The Diencephalon Eight Functions of the Hypothalamus Produces emotions and behavioral drives The feeding center (hunger) The thirst center (thirst) Coordinates voluntary and autonomic functions Regulates body temperature Preoptic area of hypothalamus Controls circadian rhythms (day–night cycles) Suprachiasmatic nucleus The Limbic System The Limbic System Is a functional grouping that Establishes emotional states Links conscious functions of cerebral cortex with autonomic functions of brain stem Facilitates memory storage and retrieval The Limbic System Components of the Limbic System Amygdaloid body Acts as interface between the limbic system, the cerebrum, and various sensory systems Limbic lobe of cerebral hemisphere Cingulate gyrus Dentate gyrus Parahippocampal gyrus Hippocampus The Limbic System Components of the Limbic System Fornix Tract of white matter Connects hippocampus with hypothalamus Anterior nucleus of the thalamus Relays information from mamillary body to cingulate gyrus Reticular formation Stimulation or inhibition affects emotions (rage, fear, pain, sexual arousal, pleasure) The Limbic System Figure 14–11a The Limbic System. The Limbic System Figure 14–11b The Limbic System. The Limbic System The Cerebrum The Cerebrum Is the largest part of the brain Controls all conscious thoughts and intellectual functions Processes somatic sensory and motor information The Cerebrum Gray matter In cerebral cortex and basal nuclei White matter Deep to basal cortex Around basal nuclei The Cerebrum Figure 14–12c The Brain in Lateral View. The Cerebrum Special Sensory Cortexes Visual cortex Information from sight receptors Auditory cortex Information from sound receptors Olfactory cortex Information from odor receptors Gustatory cortex Information from taste receptors The Cerebrum Figure 14–15a Motor and Sensory Regions of the Cerebral Cortex. The Cerebrum The Cerebrum The Left Hemisphere In most people, left brain (dominant hemisphere) controls Reading, writing, and math Decision making Speech and language The Right Hemisphere Right cerebral hemisphere relates to Senses (touch, smell, sight, taste, feel) Recognition (faces, voice inflections) The Cerebrum Figure 14–16 Hemispheric Lateralization. The Cerebrum Monitoring Brain Activity Brain activity is assessed by an electroencephalogram (EEG) Electrodes are placed on the skull Patterns of electrical activity (brain waves) are printed out The Cerebrum Four Categories of Brain Waves Alpha waves Found in healthy, awake adults at rest with eyes closed Beta waves Higher frequency Found in adults concentrating or mentally stressed Theta waves Found in children Found in intensely frustrated adults May indicate brain disorder in adults Delta waves During sleep Found in awake adults with brain damage The Cerebrum Figure 14–17a-d Brain Waves. The Cerebrum Synchronization A pacemaker mechanism Synchronizes electrical activity between hemispheres Brain damage can cause desynchronization Seizure Is a temporary cerebral disorder Changes the electroencephalogram Symptoms depend on regions affected Cranial Nerves 12 pairs connected to brain Four Classifications of Cranial Nerves Sensory nerves: carry somatic sensory information, including touch, pressure, vibration, temperature, and pain Special sensory nerves: carry sensations such as smell, sight, hearing, balance Motor nerves: axons of somatic motor neurons Mixed nerves: mixture of motor and sensory fibers Cranial Nerves Figure 14–18 Origins of the Cranial Nerves. Cranial Nerves Optic Nerves (II) Primary function Special sensory (vision) Origin Retina of eye Pathway Optic canals of sphenoid Destination Diencephalon via optic chiasm Cranial Nerves Optic Nerve Structures Optic chiasm Where sensory fibers converge And cross to opposite side of brain Optic tracts Reorganized axons Leading to lateral geniculate nuclei Cranial Nerves Figure 14–20 The Optic Nerve. Cranial Nerves The Vagus Nerves (X) Primary function Mixed (sensory and motor) Widely distributed in thorax and abdomen Origins Sensory: – – – – part of pharynx auricle and external acoustic meatus diaphragm visceral organs of thoracic and abdominopelvic cavities Motor: – motor nuclei in medulla oblongata Cranial Nerves The Vagus Nerves (X) Pathway Jugular foramina Between occipital and temporal bones Destination Sensory: – sensory nuclei and autonomic centers of medulla oblongata Visceral motor: – muscles of the palate and pharynx – muscles of the digestive, respiratory, and cardiovascular systems in thoracic and abdominal cavities Cranial Nerves Figure 14–26 The Vagus Nerve. Cranial Nerves Figure 14–26 The Vagus Nerve. Cranial Nerves The Accessory Nerves (XI) Primary function Motor to muscles of neck and upper back Origin Motor nuclei of spinal cord and medulla oblongata Pathway Jugular foramina between occipital and temporal bones Destination Internal branch: – voluntary muscles of palate, pharynx, and larynx External branch: – sternocleidomastoid and trapezius muscles Cranial Nerves Cranial Nerves Cranial Reflexes Cranial Reflexes Monosynaptic and polysynaptic reflex arcs Involve sensory and motor fibers of cranial nerves Clinically useful to check cranial nerve or brain damage Cranial Reflexes