Spinal Cord and Reflexes

Spinal Cord and Reflexes

Muse: Lecture #9

11/22/10

Spinal cord, nerves and reflexes

Figure 13–1 An Overview of Chapters 13 and 14.

Figure 13.1

Central nervous system (CNS) Peripheral nervous system (PNS)

Motor (efferent) divisionSensory (afferent)division

Somatic nervoussystem

Autonomic nervoussystem (ANS)

Sympatheticdivision

Parasympatheticdivision

accelerator brake

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 CordFigure 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)


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


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


Control and Location

Sensory or motor nucleus location within the

gray matter determines which body part it

controls


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


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


Figure 13–5a The Sectional Organization of the Spinal Cord.


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


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


Figure 13–6a A Peripheral Nerve.


Peripheral Nerves

Interconnecting branches of spinal nerves

Surrounded by connective tissue sheaths



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


Figure 13–7b Peripheral Distribution of Spinal Nerves.


Figure 13–8 Dermatomes.


Peripheral Neuropathy

Regional loss of sensory or motor function

Due to trauma or compression

chronic can be due to diabetes


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


The Four Major Plexuses of Ventral Rami

Cervical plexus

Brachial plexus

Lumbar plexus

Sacral plexus


Figure 13–10 Peripheral Nerves and Nerve Plexuses.


Figure 13–10 Peripheral Nerves and Nerve 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)


Figure 13–11 The Cervical Plexus.



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)

Includes ventral rami of spinal nerves C5–T1


Figure 13–12a The Brachial Plexus.


Figure 13–12b The Brachial Plexus.


Figure 13–12c The Brachial Plexus.



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


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


Figure 13–13b The Lumbar and Sacral 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

1 SENSORY RECEPTOR(responds to a stimulusby producing a generatoror receptor potential)

1SENSORY NEURON(axon conducts impulses from receptor to integrating center)

SENSORY RECEPTOR(responds to a stimulusby producing a generatoror receptor potential)

2 1SENSORY NEURON(axon conducts impulses from receptor to integrating center)


INTEGRATING CENTER(one or more regions within the CNSthat relay impulses from sensory tomotor neurons)

Interneuron

2

3




MOTOR NEURON(axon conducts impulses fromintegrating center to effector)

Interneuron

2

3

4




MOTOR NEURON(axon conducts impulses fromintegrating center to effector)

EFFECTOR(muscle or gland thatresponds to motornerve impulses)

Interneuron

2

3

4 5

Reflex Arc

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 “knee-

jerk”, 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

1

Increased tensionstimulatesSENSORYRECEPTOR (tendon)

1

Spinalnerve

SENSORYNEURONexcited

To brain


2 ++

1

Within INTEGRATINGCENTER (spinal cord),sensory neuron activatesinhibitory interneuron

Excitatoryinterneuron

Spinalnerve

Inhibitoryinterneuron


+

To brain


++2

3

–

+1

–



Antagonisticmusclescontract

Spinalnerve

MOTOR NEURONinhibited



+

To brain


Motor neuron toantagonisticmuscles is excited

+

+

+

+2

3

4

1

–

EFFECTOR(muscle attachedto same tendon)relaxes andrelieves excesstension



Antagonisticmusclescontract

Spinalnerve

MOTOR NEURONinhibited



+

To brain


Motor neuron toantagonisticmuscles is excited

+

+

+2

3

45

+

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


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


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


Inhibition of Spinal Reflexes

Higher centers inhibit spinal reflexes by

Stimulating inhibitory neurons

Creating IPSPs at reflex motor neurons

Suppressing postsynaptic neurons


The Babinski Reflexes

Normal in infants

May indicate CNS damage in adults


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


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


Figure 14–4 The Formation and Circulation of Cerebrospinal Fluid.


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


Figure 21–23 Arteries of the Brain.


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


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


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


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


Figure 14–5a The Diencephalon and Brain Stem.


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

Spinal Cord and Reflexes

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