Monet: The Bridge at Argenteuil

The Spinal Cord

Not Just an Passive Conduit!

Spinal Cord

• Extends from foramen magnum to L2

• Central Gray matter (association neurons/processes) and peripheral white matter (myelinated nerves)

• Gray matter shaped like “H” with posterior, anterior and lateral horns

Posterior: Sensory Neurons, Association Neurons (reflexes)

Anterior: Motor NeuronsLateral: Sympathetic Autonomic Motor Neurons

Nerve Pathways: groups of ascending and descending nerve axons within white tissue of cord.

Nerve PathwaysNames tell function (first part = origin)i.e Spinothalamic: originates in spinal cord and terminates in thalamus

Ascending Patways: 2-3 neurons in sequence

Somatic (motor) nerves are in 2 locations :

Motor NervesLower motor neurons: located in spinal gray matter or brainstem

Axons extend to musclesUpper motor neurons: Motor Cortex, Cerebellum, or Brainstem: Descend to medulla, cross to opposite side of cord and connect to lower neurons

Cerebrospinal Fluid bathes brain and spinal cord (flows) providing protection

Produced by Choroid Plexus in brain: Capillary/Ependymal structure surrounding ventricles

Chemicals can get into this fluid & influence brain activity

i.e. altitude incr. CO2 & H+ in CSF, this stimulates the hypothalamus to incr. breathing & incr. urine output.

Assignment:

Read: 211-217 and 202-203 (Reflexes and Neuronal Circuits)

First Exam will be the week of Sept. 18 (Either Weds/Friday)

The Exam will cover the Nervous System: Chapter 8

The Spinal Cord

Anatomy and Reflexes

Spinal Cord: Coloring GuideAs the spinal cord exits the skull, it

is continuous with the medulla: Color the “cervical segment” Red (AC: C1-C8)

Note: At the Cervical Enlargement, nerves exit to serve the upper limbs

Color Guide:The second segment is the Thoracic

Segment: Color Blue (AT: T1-T12)

The final segment to be colored is the Lumbar Segment: Color Green (AL: L1-L5)*

Note: The Lumbar enlargement serves the lower limbs (A2)

Spinal Cord Cross Section: Note: Nerves exit between

adjacent vertebrae via the intervertebral foramen

The spinal nerves exiting the cord are bundles of both ascending and descending nerve fibers: Color Purple (D)

Spinal Nerves:Nerves extending from the ventral

aspect of the spinal cord are called the ventral root: Color red (C2)These are descending motor nerves

Nerves extending from the dorsal spinal cord are the dorsal root: Color blue (C1)These are ascending sensory nerves

Gray Matter: Color Green (B)Dorsal (Posterior) Horn: Think

“Dorsal root” – Sensory neurons and association neurons

Ventral (Anterior) Horn: Think “Ventral root” – motor neurons

Lateral Horn: Sympathetic neurons (more later!)

Reflex Activity

What happens when you accidentally touch your hand to a hot stove?

Do you sit and think? NO! You withdraw your hand

almost before you even realize it’s fried!

!

The sensory signal is sent directly to the spinal column

It crosses association neurons-motor neurons, which initiate an immediate response

sensory info is also sent to CNS (but response has already begun)

Stimulus!To CNS

Response!

The “Reflex Arc”

Sensory receptorAfferent NeuronAssociation NeuronsEfferent (motor) NeuronEffector Organ (Skeletal or

Smooth)

Cranial and Spinal NervesCranial Nerves: 12 pairs (right and left)

originating from brainstem (10) and cerebrum (2)

Afferent and/or Efferent:Somatic Parasympathetic

Names/Roman Numeral designations (Vagus: X)

Interesting Cranial NervesTrigeminal (V): Both sensory and

motorSenses: facial skin, teeth and

dentists love to dismantle this nerve!Motor: Well, you know how fun it is

to leave the dentist with this one deadened!

Another interesting one…Vagus (X): Sensory to airways,

viscera; Motor to the smooth muscle of the airways, and PSNS to the heart/lung/gut etc.Vagus From “vagabond” to wonderVagal Tone: seen in well trained

athletes with very low heart rates

Spinal Nerves:

31 pairs exit intervertebral foramenAfter exit: Join to become

“Plexus”Afferent and Efferent: Somatic and Autonomic

Interesting Spinal Nerves:Phrenic Nerve: Originating from

the cervical plexus, innervates the diaphragm muscle (BREATHINGThe “wind knocked out of me”…Hiccups after heart surgeryPredict question: page223?

Radial and Ulnar Nerves

Radial: “Crutch paralysis”

Ulnar: Ever hit your “Funny Bone”? It’s not a bone at all – but the ulnar nerve!

Peripheral Nervous System: Definition: Neurons and processes found

outside the central nervous system – Includes:All Sensory Neurons (Afferent)Axons from motor neurons (somatic

efferent)Autonomic Motor neurons:

preganlionic axons and all postganlions

Begin Reviewing Nervous System:Summary (Page 228-230)

Check your understanding by reviewing the topics covered up to Peripheral Nervous System

Be able to answer Content Review Questions: (1-10, 12-17, 20-24)