Miscellaneous

http://faculty.plattsburgh.edu/donald.slish/DA.html The above link will show drugs and impact at synapse

Chapter 13aOrganization of the Nervous System

Kathleen Cercone PT, PhDhttp://www.mmi.mcgill.ca/mmimediasampler/default.htm

Go down, will see what we talked about last class

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You can viewThe relationship of the spinal nerve and the vertebrae that they exit under or aboveCervical, C1 spinal nerve, above the vertebraeC8 is below C7T1 now under T1

To right: The conus medullaris, horses tail and the spinal nerve from the spinal cord must travel to exit under the vertebrae is belongs under

In Ch. 13, we focus on the spinal cord—we will deal with cranial nerves later• sensory receptors / neurons

(Chap. 15)• spinal cord and spinal nerves

(Chap. 13) motor neurons / NMJs (Chap. 10)• spinal reflex arcs (Chap. 13)

A. Functional Organization

Spinal reflexes:What is a reflex?

• sensory receptors / neurons (Chap. 15)• spinal cord and spinal nerves (Chap. 13) motor neurons / NMJs (Chap. 10)• spinal reflex arcs (Chap. 13)

A. Gross Anatomy of the Spinal Cord

Spinal Nerve Numbering• 31 pairs, corresponding to spinal nerve origins• 8 cervical:

– nerve C1 – C7 above vertebra they are named for– nerve C8 below C7 and above T1)

• 12 thoracic, 5 lumbar (below vertebra they are named for)

• 5 sacral, 1 coccygeal

13-2 Spinal Cord

31 Spinal Cord SegmentsBased on vertebrae where spinal nerves originate Positions of spinal segment and vertebrae change with age

Cervical nervesNamed for inferior vertebra

All other nervesNamed for superior vertebra

Subarachnoid spaceContains cerebrospinal fluid (CSF) that acts as

shock absorber and diffusion mediumLumbar puncture (spinal tap) withdraws CSF

Epi=above

An anterior view of the cervical spinal cordshowing the meninges, supporting ligaments,and the roots of the spinal nerves

Denticulate ligaments

Blood vessels withinthe subarachnoid space

Spinal cord

Anterior median fissure

Pia mater

Dorsal rootVentral root, formed byseveral “rootlets” fromone cervical segment

Arachnoid mater (reflected)

Dura mater (reflected)

Supporting ligaments: Prevent lateral movement of spinal cordDenticulate ligaments; Extend from pia mater through arachnoid

to dura mater

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This cross section through thecervical region of the spinal cordshows some prominent features andthe arrangement of gray matter andwhite matter.

C3

Dorsal root

Dorsal rootganglion

Centralcanal

Spinalnerve

Ventralroot

Posterior median sulcus

White matter

Gray matter

Anterior median fissure

b

Figure 13-5 The Sectional Organization of the Spinal Cord.

Dorsal root ganglion

Lateral white column

Posterior gray horn

Lateral gray horn

Anterior gray horn

Anterior white column

Posterior white columnPosterior median sulcus

Posterior gray commissure

Somatic

Visceral

Somatic

Visceral

Ventral root

Sensory nuclei

Motor nuclei

The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groups called nuclei.

Functional Organization of Gray Matter

Posterior median sulcus

Anterior gray commissure

Anterior white commissureAnterior median fissure

Posterior gray commissure

Dura mater

Arachnoid mater (broken)

Central canal

Anterior gray commissure

Anterior median fissure

Pia mater ANTERIOR

POSTERIOR Structural Organization of Gray MatterThe projections of gray matter toward the outer surface of the spinal cord are called horns.

Posterior gray horn

Lateral gray horn

Dorsal root

Anterior gray horn

Dorsal root ganglion

Ventral root

A micrograph of a transverse section through the spinal cord, showing major landmarks in and surrounding the cord.

The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior gray horns.

a

Different levels along the spinal cord join together to form the spinal nerve.The nerve is a mixed nerveas it has afferent and efferent fibers, sensory, motor fibers join together as 1 spinal nerve

Spinal nerve

1. Dorsal ramus2. Ventral ramus3. Spinal Nerve4. Afferent5. Efferent

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Neuron Pathways and Nuclei Locations

White matter in spinal cord: 1. posterior white columns2. anterior white columns; 3. lateral white columns4. anterior white commissure – axons crossing to opposite side of spinal cord

Most of the spinal nerves are associated with specific dermatomes (an area of skin innervated by all the cutaneous neurons of a certain spinal or cranial nerve).

Sensation

Our bodies are constantly exposed to sensory information called stimuli.Sensation is a conscious or unconscious awareness of external or internal stimuli.

– information about conditions inside or outside the body

Perception is the conscious awareness and interpretation of sensations.

the conscious awareness and interpretation of a sensation

Sensory Transduction translates the sensory stimulus to an action potential

Free nerve endingsa Root hair plexusb

c d

e

Tactile discs Tactile corpuscle

Lamellated corpuscle

Hair Tactile disc

Tactile corpuscle

Free nerveending

Ruffini corpuscle

Sensorynerve

Lamellatedcorpuscle

Root hairplexus

Root hairplexus

f Ruffini corpuscle

Tactilecorpuscle

Sensorynerve fiber

Dermis

Dendrites

Capsule

Epidermis

Tactile corpuscle

Merkel cell

Nerveterminal(dendrite)

Tactile disc

Afferent nerve fiber

Dermis

Dendritic process

Accessory cells(specialized fibroblasts)

Concentric layers(lamellae) of collagen

fibers separatedby fluid

Lamellated corpuscle(cross section)

LM × 330

LM × 125

These are tactile receptors in the Skin

Reflexes and Neural Circuits

Neuronal poolsFunctional groups of interconnected neurons

Most cases are interneurons in CNSMay involve several regions of brainMay involve neurons in one specific location in brain or spinal cord

Estimated number of pools ~100s to 1000sPatterns of neuronal interactions suggest functional classifications

Neural circuit (“wiring diagram”)Simple circuits in PNS and spinal cord control reflexes

Preprogrammed responses to specific stimuli

Work like a “team” in a business

Arrival of stimulus and activation of receptor

Activation of a sensory neuron

Dorsal rootSensation relayed to the brain by axon collaterals

Spinal cord

ReceptorStimulus

EffectorResponse by a peripheral effector

Activation of a motor neuron

Ventral root

REFLEX ARC

KEYSensory neuron (stimulated)Excitatory interneuronMotor neuron (stimulated)

Information processing in the CNS

3

2

4

5

1

Steps in reflex: • muscle spindle detects stretch of muscle• sensory neuron is activated• sensory neuron signals across a synapse in the spinal cord to a motor

neuron• motor neuron is activated• motor neuron signals across a NMJ to skeletal muscle fibersSome reflexes are inborn, such as pulling your hand away from a hot surface before you even feel that it is hot

Methods of Classifying Reflexes

Response

REFLEX ARC

Stimulus

StretchReceptor (muscle spindle)

Contraction Effector

Spinal cord

Sensory neuron (stimulated)Motor neuron (stimulated)

KEY

http://www.sumanasinc.com/webcontent/animations/content/reflexarcs2.html

http://www2.sunysuffolk.edu/pickenc/Reflex%20Arc.swf

13-7 Spinal Reflexes

Muscle SpindlesThe receptors in stretch reflexesBundles of small, specialized intrafusal muscle fibers (receptors)

Innervated by sensory and motor neuronsSurrounded by extrafusal muscle fibers (effectors)

Which maintain tone and contract muscle

reflex arc:intrafusal fibers → sensory neuronextrafusal fibers ← motor neuron

Intrafusal muscle fibers of a muscle spindleSpecialized fibers with a central sensory region

has myofibrils in terminal regions onlyinnervated by 2 types of neurons:

1.sensory neurons: detect stretch of the sensory region2. gamma motor neurons: adjust tone by controlling the terminal regions

Sensory (stretch) receptorMonosynaptic reflex:Direct communication betweensensory and motor neuron

Polysynaptic reflex:Interneuron facilitatessensory-motor communication

Sensory receptor

Sensoryneuron

Interneuron

Motor neuron

Spinal cord

Sensoryneuron

Motor neuron

Effector organ

Effector organ

Monosynaptic and Polysynaptic Reflexes

Painful stimulus

Flexors stimulated

Extensors inhibited

Distribution within gray horns to other segments of the spinal cord

Withdrawal reflex—polysynaptic reflex arcPainful stimulus causes transmission of sensory information to the

spinal cord.

Interneurons receive the sensory information and stimulate the motor neurons to direct flexor muscles to contract in response.

Simultaneously, antagonistic extensor muscles are inhibited so that the traumatized body part may be quickly withdrawn from the harmful stimulation.

The crossed extensor reflex, which involvesa contralateral reflex arc To motor neurons

in other segmentsof the spinal cord

Painfulstimulus

ExtensorsstimulatedFlexorsinhibited

Extensorsinhibited

Flexorsstimulated

Sensory neuron(stimulated)ExcitatoryinterneuronMotor neuron(stimulated)

Motor neuron(inhibited)Inhibitoryinterneuron

Step on tackFlexor reflex pulls injured

foot awaya. Flexor muscles

stimulatedb. Extensor muscles

inhibitedCrossed extensor reflex straightens uninjured leg and supports shifting weight

Activated by collaterals of excitatory and inhibitory interneurons

Extensor muscles stimulatedFlexor muscles inhibited

b

Figure 13-17 The Babinski Reflexes.

The plantar reflex (negative Babinski reflex), a curling of the toes, is seen in healthy adults.

The Babinski sign (positive Babinski reflex) occurs in the absence of descending inhibition. It is normal in infants, but pathological in adults.

a

13-2 Spinal Cord

The Interlayer Spaces of Arachnoid Mater

Cerebrospinal Fluid (CSF)Carries dissolved gases, nutrients, and

wastesLumbar puncture or spinal tap withdraws CSF

Spinal nerve structure and distributionShingles: Viral infection of dorsal root gangliaCaused by varicella-zoster

virus Same herpes virus as

chickenpoxProduces painful rash and

blisters on dermatome served by infected nerves

Those who have had chickenpox are more at risk

Virus can remain dormant within anterior gray horns

Unknown trigger for reactivation