A&P: Ch.13 (Ex.24) - The Spinal Cord, Spinal Nerves, Spinal Reflexes

Monosynaptic Reflexes

A stretch reflex Have the 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

Illiohypogastric & Illioinguinal

Abdominal Muscles Nerve of lumbar plexus

Gross Anatomy of the Spinal Cord

About 18 inches (45 cm) long 1/2 inch (14 mm) wide Growth of cord stops at age 5 Starts at medulla oblongata Ends between vertebrae L1 and L2

Obturator nerve

Adductor muscles Nerve of lumbar plexus

Enlargements of the Spinal Cord Caused by:

Amount of gray matter in segment Involvement with sensory and motor nerves of limbs

Lateral femoral cutaneous nerve

Anterior thigh Nerve of lumbar plexus

Visceral reflexes (autonomic reflexes)

Control or adjust activities of smooth & cardiac muscle, glands, and adipose tissues Control systems other than muscular system

Epineurium

Covering of entire nerve dura mater blends into it at intervertebral foramen outermost layer consisting of dense network of collagen fibers

Axillary nerve

Deltoid & teres minor part of brachial plexus

Sensory nuclei

Dorsal (posterior) Connect to peripheral receptors receive and relay senesory info from peripheral receptors 3&2

Inhibition of Spinal Reflexes

Higher centers inhibit spinal reflexes by: - Stimulating inhibitory neurons - Creating IPSPs at reflex motor neurons - Suppressing postsynaptic neurons

Reinforcement (Facilitation) 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

Cauda equina

Horses Tail Nerve roots extending below conus medullaris distal end of spinal cord

White matter

Is superficial Contains myelinated and unmyelinated axons

Denticulate ligaments

Prevent lateral movement of spinal cord 4

Coccygeal ligament

Prevent superior-inferior movement of spinal cord - Dural connections at foramen magnum

The Tendon Reflex

Prevents skeletal muscles from: - Developing too much tension - Tearing or breaking tendons Golgi Tendons - Sensory receptors unlike muscle spindles or proprioceptors

Divergence

Spread of information from one neuron to many Permits broad distribution of a specific input Example: Sensory information coming to CNS Divergence

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

The spinal cord is protected by

The meninges - Connective tissue The vertebral column - Provides a bony covering of the spinal cord Cerebrospinal fluid.

Endoneurium

Wrapping of each nerve fibers around an axon innermost layer, extend from perinerium and surround indiv. axons

MOTOR INFORMATION TO THE VENTRAL RAMUS

axons in relatively large ventral ramus supply the ventrolateral body surface, structures in the body wall, and the limbs TO skeletal muscles of body wall, limbs, postganglionic fibers TO smooth muscles, glands, etc.. of body wall, limbs

subarachnoid space

between the arachnoid mater and pia mater and contains cerebrospinal fluid (CSF).

epidural space

bw dura mater and walls of vertebral canal, contains areolar tissue, blood vessels, and a protective padding of adipose tissues filled w/ fat

SENSORY INFORMATION FROM THE DORSAL RAMUS

dorsal ramus carries sensory info from the skin and skeletal muscles of the back FROM interoceptors oback FROM extereceptors of back

MOTOR INFORMATION TO THE DORSAL RAMUS

dorsal ramus contains somatic motor and visceral motor fibers that innervate the skin and skeletal muscles of the back TO the skeletal muscles of back postganglionic fibers TO smoother muscles, glands, etc. of back

meningitis

inflammation of meningeal membranes can disrupt normal circulation of CSF

Muscle spindles

inform the nervous system of the length of the muscle to maintain healthy muscle tone

pia mater

innermost menigeal layer, consists of a meshwork of elastic and collagen fibers firmly bound to underlying neural tissue

arachnoid mater

middle meningeal layer Spider web of collagen fibers

Golgi tendon

organs inform the brain as to the amount of tension in the muscle and tendons

The anterior (ventral) median fissure and the posterior (dorsal) median sulcus

penetrate the white matter of the spinal cord and divide it into right and left sides.

Spinal Meninges

three coverings that run continuously around the spinal cord and brain and are continuous with the cranial meninges (surround the brain). The dura mater - The outermost layer. The arachnoid - The middle layer. The pia mater - The innermost meninx

Dura mater

tough layer that forms the outermost covering of the spinal cord contians dense collagen fibers that are oriented along the longitudinal axis of the cord dense irregular CT

SENSORY INFORMATION FROM THE VENTRAL RAMUS

ventral ramus carries senseory info from the ventrolateral body surface, strucs in the body wall, and the limbs FROM extereceptors, propireceptors of body wall, limbs From interoceptors of body wall, limbs

Median & Ulnar nerves

- Flexors of wrist & hand - Ulnar (funny bone) - Median Carpal tunnel Pincer grasp Suicide finger part of brachial plexus

Radial nerve

- Shoulder & elbow extensors - Damage causes wrist drop

Five General Characteristics of Polysynaptic Reflexes

1. Involve pools of interneurons 2. Are intersegmental in distribution **Extend across the spinal cord to activate muscles in many parts of the body 3. Involve reciprocal inhibition **Antagonistic Muscles 4. Have reverberating circuits - Which prolong reflexive motor response 5. Several reflexes cooperate - To produce coordinated, controlled respons

31 Spinal Cord Segments

Are the paths of communication between the spinal cord and most of the body. Named & numbered by the cord level of their origin 8 pairs of cervical nerves - C1 to C8 12 pairs of thoracic nerves - T1 to T12 - 5 pairs of lumbar nerves L1 to L5 5 pairs of sacral nerves - S1 to S5 1 pair of coccygeal nerves Positions of spinal segment and vertebrae change with age

Sacral Plexuses

Arises from L4-S4 Innervates mostly posterior surfaces Major nerve - Sciatic nerve -- Longest & largest nerve in body -- Formed by two nerves --- Tibial nerve --- Fibular nerve

Reflexes

Automatic responses coordinated within spinal cord The wiring of a single reflex - Through interconnected sensory neurons, motor neurons, and interneurons Produce simple and complex reflexes - Beginning at receptor - Ending at peripheral effector - Generally opposes original stimulus --Negative feedback)

Gray commissures

Axons that cross from one side of cord to the other before reaching gray matter

Branches off Brachial Plexus Upper (Superior) Trunk

BRACHIAL (C5 - T1) - ARM Upper Trunk (C5,C6)

Anterior white column

Between anterior gray horns and median fissure

Posterior white column

Between posterior gray horns and posterior median sulcus

Saphenous

Branch of femoral Medial leg Medial foot Nerve of lumbar plexus

*Rami communicates

Branches of the branches which are part of the autonomic nervous system. I

Convergence

Brings input from many sources to single neuron Several neurons synapse on single postsynaptic neuron Example: Breathing movements of diaphragm and ribs can be controlled subconsciously or consciously

Tracts or fasciculi

Bundle of axons relatively uniform in diameter, myelination, conduction speed, and functional type In white columns Relay same information in same direction

Dorsal root

Contains axons of sensory neurons brings sensory info into the spinal cord

Phrenic nerve

C3, C4 & C5 Controls diaphragm Breathing stops because the phrenic nerves no longer send impulses to the diaphragm. major nerve of cervical plexus

Mixed Nerves

Carry both afferent (sensory) and efferent (motor) fibers carry somatic and autonomic (visceral) impulses The four types of mixed nerves are: Somatic afferent Somatic efferent Visceral afferent Visceral efferent

Descending tracts

Carry motor commands to spinal cord

Ascending tracts

Carry sensroy information to brain

Dorsal root ganglia

Contain cell bodies of sensory neurons

Ventral root

Contains axons of motor neurons that extend into the periphery to control somatic and visceral effectors

The Spinal Nerve

Each side of spine - Dorsal and ventral roots join - To form a spinal nerve

Lateral white column

Either side between anterior and posterior columns

Musculocutaneous nerve

Elbow flexors

Caudal or Lumbar Anesthesia

Epidural anesthesia is the most popular means for pain relief during labor. Over 50% of women giving birth at hospitals use epidural anesthesia. The goal of an epidural is to provide analgesia, or pain relief, rather than complete anesthesia, which is total lack of feeling.

Crossed Extensor Reflexes

Example: stepping on a tack - Flexor reflex pulls injured foot away (ipsilateral) -- Flexor muscles stimulated -- Extensor muscles inhibited Crossed extensor reflex straightens uninjured leg and supports shifting weight (Contralateral) Activated by collaterals of excitatory and inhibitory interneurons - Extensor muscles stimulated - Flexor muscles inhibite motor response occurs on opposite side of stimulus

Genitofemoral nerve

External genitalia & and thigh Nerve of lumbar plexus

Femoral nerve

Flexors of thigh Extensors of leg Nerve of lumbar plexus

*Ventral (anterior) ramus

Form plexus supply anterior trunk & limbs

Brachial Plexus

Formed by C5-T1 It gives rise to the nerves that innervate the shoulder and upper limb. There are four major branches of this plexus - Roots - five ventral rami (C5-T1) (Purple) - Trunks - upper, middle, and lower, which form divisions (Green) = Divisions - anterior and posterior serve the front and back of the limb (Pink) - Cords - lateral, medial, and posterior fiber bundles (Blue) A number of nerve disorders may result from injury to the here

Sciatic nerve

Formed by two nerves Tibial nerve * Flexors of knee * Extensors of ankle * Plantar surface of foot Fibular nerve (Peroneal) * Biceps femoris * Toes *Peroneal nerve injury produces foot drop or numbness

Neuronal pools

Functional groups of interconnected neurons Most cases are interneurons in CNS - May involve several regions of brain - May involve neurons in one specific location in brain or spinal cord - Estimated number of pools ~100s to 1000s - Patterns of neuronal interactions suggest functional classifications Neural circuit ("wiring diagram")

The Cervical Plexus

Includes ventral rami of spinal nerves C1-C5 Innervates neck, thoracic cavity, diaphragmatic muscles Major nerve

Lumbar Plexus

Includes ventral rami of spinal nerves T12-L4 Innervates the abdominal wall, external genitalia, psoas & the anterior thigh

Flexor (withdrawal) Reflex

Initiated by a painful stimulus - Step on tack -- Pain fibers send signal to spinal cord I nterneurons branch to different spinal cord segments Motor fibers in several segments are activated More than one muscle group activated to lift foot off of tack - Causes automatic withdrawal of the threatened body part - Ipsilateral and polysynaptic

Spinal Anesthesia

Injected into the sub arachnoid space where the CSF delivers the anestesia along the spinal cord Temporary muscle paralysis and sensory loss

Spinal Somatic Reflexes

Integration center is in the spinal cord - Most do not involve higher learning centers - The brain remains "advised" of spinal reflex activity and can facilitate, inhibit or adapt it if needed. - Effectors are skeletal muscle Testing of somatic reflexes is important clinically to assess the condition of the nervous system

Anterior white commissure

Interconnects anterior white columns region where axons cross from one side of the spinal cord to the other

Inborn Reflex (innate)

Involuntary & unlearned action Prevent us from having to think about things like maintaining posture or controlling visceral activities Patterned response (same every time) Tendon reflex Pupillary reflex Swallowing Withdrawal reflex Sucking

Somatic reflexes

Involuntary control of skeletal system - Superficial reflexes of skin, mucous membranes - Stretch or deep tendon reflexes *Patellar, or "knee-jerk," reflex

Polysynaptic reflex

Involve at least one interneuron, one sensory neuron, and one motor neuron Longer delay between stimulus and response due to increased number of synapses - Produce more complex reflexes

Nerve Plexuses

Joining of ventral rami of spinal nerves to form nerve networks or plexuses

Postural reflexes

Many stretch reflexes that help maintain upright posture Coordinated activities of opposing muscles to keep body's weight over feet - Example: leaning forward stretches calf muscle receptors which stimulate the muscles to increase tone -- Returns body to upright position Postural muscles generally have firm muscle tone and extremely sensitive stretch receptors - Allow for very fine, subconscious adjustments

Polysynaptic Reflexes

More complicated than monosynaptic reflexes Responsible for automatic actions involved in complex movements - Examples: walking and running Interneurons control more than one muscle group - Produce either EPSPs or IPSPs May involve sensory and motor responses on the same side of body or opposite sides - Same side: ipsilateral reflexes (OCCUR ON THE SAME SIDE OF THE BODY) -- Examples: stretch reflex, withdrawal reflex Opposite sides: contralateral reflexes - Example: crossed extensor reflex

Spinal Cord coverings and Support

Most superficial to the deepest: Vertebrae Epidural space - Filled with fat Dura mater - Dense irregular CT Subdural space - Filled with interstitial fluid Arachnoid - Spider web of collagen fibers Subarachnoid space - Filled with CSF Pia mater - Thin layer adhering to the surface of spinal cord & brain - Denticulate ligaments hold in place - Contains blood vessels

Motor Information

Motor information leaves the spinal cord via three different routes: Dorsal Rami Ventral Rami Rami Communicates

Reverberation

Positive feedback mechanism Once activated it functions until inhibited

Withdrawal Reflexes

Move body part away from stimulus (pain or pressure) Show tremendous versatility because sensory neurons activate many pools of interneuron Strength and extent of response - Depend on intensity and location of stimulus Example: - Flexor reflex - Crossed extensor reflexes Withdrawal reflex example: flexor reflex - Grabbing an unexpectedly hot pan causes pain receptors in hand to be stimulated - Sensory neurons activate interneurons in spinal cord - Interneurons --- Activate motor neurons in anterior gray horn to contract flexor muscles --- Activated inhibitory interneurons keep extensors relaxed = Reciprocal inhibition

Serial processing

Moves information in single line Information relayed from one neuron or neuronal pool to another (stepwise fashion) Example: Sensory relay from one brain part to another

Parallel processing

Moves same information along several paths simultaneously Several neurons or neural pools process same information simultaneously Many responses can occur simultaneously Example: Stepping on a tack

Lumbar enlargement

Nerves of pelvis and lower limbs

Cervical enlargement

Nerves of shoulders and upper limbs

Spinal Nerve Innervation: Back, Anterolateral Thorax, and Abdominal Wall

No nerve plexus in thoracic region T1 toT12 Called - Thoracic nerves - Intercostal nerves.

Cranial reflexes

Occur in nuclei of brain

Spinal Reflexes

Occur in nuclei of spinal cord Two types - Single segmental ---Within one spinal segment Intersegmental - Multiple spinal segments

Motor commands

Rami communicantes ("communicating branches") White ramus - Preganglionic fibers that are myelinated - Visceral motor fibers to sympathetic ganglion Gray ramus - Postganglionic fibers that are unmyelinated - Innervate glands and smooth muscles of body wall or limbs Sympathetic nerve - Preganglionic and postganglionic fibers to structures of thoracic cavity

Brain influences on spinal reflexes

Reflex motor behavior occurs automatically However, can have an effect on the performance of the reflex Motor control is a series of interacting levels. Lower level neurons are monosynaptic and rapid Higher level centers in the brain will build on those simple reflexive patterns Can facilitate or inhibit motor neurons or interneurons involved

spinal tap (lumbar puncture)

Removal of cerebrospinal fluid from the subarachnoid space is This procedure is used to diagnose pathologies and to introduce antibiotics, contrast media, anesthetics, and chemotherapeutic drugs.

Sciatic Pain

Sciatica pain extends from the buttock down the leg to the foot Sciatic nerve injury can occur due to a - Ruptured disc - Dislocated hip - Osteoarthritis of the lumbosacral spine, - Pressure from the uterus during pregnancy - An improperly administered gluteal injection.

Sensory Information in Spinal Rami

Sensory commands Rami communicantes - "Communicating branches" to the ANS White ramus - Delivers sensory information from the visceral organs via the sympathetic nerve

Sensory Information

Sensory information enters the spinal cord via three different routes: Dorsal Rami Ventral Rami Rami Communicates

Control and Location

Sensory or motor nucleus location within the gray matter determines which body part it controls For Example: The cervical enlargement Anterior gray horns contain somatic nuclei which control muscles in the upper limb. Moving medially to lateral are separate nuclei that control (1)Muscles that position the pectoral girdle (2)Muscles that move the arm (3)Muscles that move the forearm and hand (4)Muscles that move the hand and fingers

Monosynaptic reflex

Simplest reflex arc involving one sensory and one motor neuron Faster response time due to only one synapse

The Stretch Reflex

Simplest reflex arc involving one sensory and one motor neuron Have the 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 automatically regulates skseletal muscle length

Babinski reflex

Stroking lateral side of sole of foot Positive response: - Toes fan due to lack of inhibitory control of reflex response from descending motor pathways - Normal in infants - Can indicate damaged higher centers or descending tracts in adults Negative response: - Toes curl due to development and normal reflex response in adults - = Plantar reflex

*Meningeal branches

Supply meninges, vertebrae & blood vessels D

*Dorsal (posterior) ramus

Supply skin & muscles of back

Thoracic Nerves

Supply the back Innervated by dorsal rami via several branches

Intercostal nerves

Supply the thorax Intercostal nerves supply muscles of the ribs, anterolateral thorax, and abdominal wall

Gray matter

Surrounds central canal of spinal cord Contains neuron cell bodies, neuroglia, unmyelinated axons Has projections - Gray horns

Perineurium

Surrounds group of nerve fibers, forming a fascicle middle layer, extend inward from the epinerium, connective tissue partitions divide nerve into series of compartments that contain bundles of axons, or fascicles

Nuclei

The cell bodies of neurons form functional groups called masses of gray matter w/in CNS

Ascending Pathways

The central processes of fist-order neurons branch diffusely as they enter the spinal cord and medulla Some branches take part in spinal cord reflexes Others synapse with second-order neurons in the cord and medullary nuclei Fibers from touch and pressure receptors form collateral synapses with interneurons in the dorsal horns

Muscle Spindles

The receptors in stretch reflexes Bundles of small, specialized intrafusal muscle fibers - Innervated by sensory and motor neurons Surrounded by extrafusal muscle fibers - Which maintain tone and contract muscle

Dermatomes

The skin over the entire body is supplied by spinal nerves that carry somatic sensory nerves impulses into the spinal cord. All spinal nerves except C1 innervate specific, constant segments of the skin; the skin segments are called dermatomes. Clinical Application - Knowledge of dermatomes helps a physician to determine which segment of the spinal cord or which spinal nerve is malfunctioning. - Damaged regions of the spinal cord can be distinguished by patterns of numbness over a dermatome region specific bilateral region of the skin surface monitored by a single pair of spinal nerves

Somatic spinal reflexes include

The stretch reflex Tendon reflex Flexor (withdrawal) reflex Crossed extensor reflex

Filum terminale

Thin thread of fibrous tissue at end of conus medullaris Attaches to coccygeal ligament distal end of spinal cord

Conus medullaris

Thin, conical spinal cord below lumbar enlargement distal end of spinal cord

Motor nuclei

Ventral (anterior) Connect to peripheral effectors issue motor commands to peripheral effectors G&H

Shingles

Viral infection of dorsal root ganglia Painful, blistering skin rash due to the varicella-zoster virus, the virus that causes chickenpox. After you get chickenpox, the virus remains inactive (becomes dormant) in certain nerves in the body. Shingles occurs after the virus becomes active again in these nerves years later. The reason the virus suddenly become active again is not clear. -- Often only one attack occurs. Shingles may develop in any age group, but you are more likely to develop the condition if: - You are older than 60 - You had chickenpox before age 1 - Your immune system is weakened by medications or disease

Learned (acquired) Reflex

Voluntary & premeditated action Slower than an inborn reflex Varied response (learning occurs) Enhanced by repetition Meter stick catch Driving

cerebrospinal fluid

acts as a shock absorber and a diffusion medium for dissolved gases, nutrients, chemical messangers, and waste

Lateral gray horns

are in thoracic and lumbar segments; contain visceral motor nuclei

Posterior gray horns

contain somatic and visceral sensory nuclei

Anterior gray horns

contain somatic motor nuclei

subdural space

seps the dura mater from deeper meningeal layer