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

nPosterior: Sensory Neurons, Association Neurons (reflexes) nAnterior: Motor Neurons nLateral: Sympathetic Autonomic Motor Neurons nNerve Pathways: groups of ascending and descending nerve axons within white tissue of cord.

Nerve Pathways nNames tell function (first part = origin) ni.e Spinothalamic: originates in spinal cord and terminates in thalamus nAscending Patways: 2-3 neurons in sequence nSomatic (motor) nerves are in 2 locations :

Motor Nerves nLower motor neurons: located in spinal gray matter or brainstem nAxons extend to muscles nUpper motor neurons: Motor Cortex, Cerebellum, or Brainstem: Descend to medulla, cross to opposite side of cord and connect to lower neurons

Cerebrospinal Fluid n bathes brain and spinal cord (flows) providing protection n Produced by Choroid Plexus in brain: Capillary/Ependymal structure surrounding ventricles n Chemicals can get into this fluid & influence brain activity n i.e. altitude incr. CO2 & H+ in CSF, this stimulates the hypothalamus to incr. breathing & incr. urine output.

Assignment: Read: and (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 Guide As the spinal cord exits the skull, it is continuous with the medulla: Color the “cervical segment” Red (A C : 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 (A T : T1-T12) The final segment to be colored is the Lumbar Segment: Color Green (A L : 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 n What happens when you accidentally touch your hand to a hot stove? n Do you sit and think? NO! n You withdraw your hand almost before you even realize it’s fried! !

u The sensory signal is sent directly to the spinal column u It crosses association neurons-motor neurons, which initiate an immediate response u sensory info is also sent to CNS (but response has already begun) Stimulus! To CNS Response!

The “Reflex Arc” Sensory receptor Afferent Neuron Association Neurons Efferent (motor) Neuron Effector Organ (Skeletal or Smooth)

Cranial and Spinal Nerves Cranial 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 Nerves Trigeminal (V): Both sensory and motor Senses: 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 wonder Vagal Tone: seen in well trained athletes with very low heart rates

Spinal Nerves: 31 pairs exit intervertebral foramen After 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 (BREATHING The “wind knocked out of me”… Hiccups after heart surgery Predict 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 ) 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)