1. Processes reflexes

2. Site for integration of APs that aries locally (or triggered by impulses from PNS and brain)

3. Conduction pathway for sensory & motor nerve impulses

1. Vertebral Column

2. Meninges

3. Cerebrospinal Fluid

-tough CT

-spinal- surround spinal cord

-cranial- surround brain

Meninges Layers:

Dura Mater

outermost layer "leather jacket"

between Dura and arachnoid mater

-contains interstitial fluid

Meninges Layers:

Arachnoid mater

between arachnoid and pia mater

-contains cerebrospinal fluid (CSF)

Meninges Layers:

Pia Mater

innermost layer "t-shirt"

-thin, transparent CT layer

-adheres to surface of spinal cord and brain

Meninges Layers:

CSF

helps with protection

-shock absorber; supplies nutrients

-begins as continuation of medulla oblongata

-terminates at coneus medullary

-roughly cylindrical with slightly flattened regions

-16-18 inches long

-3/4 inch diameter

-contains cervical and lumbar enlargements (point of origin for nerves to extremities)

-31 pairs

-paths of communication between SC & most of body

-Named & numbered according to region & level of SC they emerge

-part of PNS

-connect CNS to sensory receptors, muscles, & glands

Cervical: 8

Thoracic: 12

Lumbar: 5

Sacral: 5

Coccygeal: 1

-connect each spinal nerve to a segment of SC

-2 points of attachment: posterior root and anterior root

-contains sensory fibers

-conducts impulses from PNS->CNS

-has swelling = posterior root ganglion: mass of cell bodies of sensory neurons

-contains motor neuron axons

-conducts impulses from CNS->PNS & effector cells

-cell bodies of motor neurons in gray matter of SC

1. Gray Matter

2. White matter

3. Central Canal

-shaped like H

-Consists of: cell bodies of neurons, neuroglia, unmyelinated axons, dendrites of interneurons, motor neurons

-receives & integrates incoming & outgoing information

-outside-surrounds gray matter

-consists of: bundles of myelinated & unmyelinated sensory axons, interneurons, motor neurons

-highways of impulse propagation to and from brain

CT covering of spinal nerves

-axons grouped within CT sheathes

-3 layers: epineurium, perineurium, and endoneurium 

-surrounds entire nerve

-surrounds individual axon

Distribution of Spinal Nerves:

Branches

a. posterior ramus: serves deep dorsal trunk muscles and skin

b. anterior ramus: serves muscles of upper and lower limbs; serves skin of lateral and ventral trunk

Distribution of Spinal Nerves:

Plexuses

-network of axons from many anterior rami

-cervical, brachial, lumbar, sacral, coccygeal

Distribution of Spinal Nerves:

Intercostal nerves

-thoracic nerves

-T2-T12 directly innervate structures they support

-skin is supplied by spinal nerves (carry somatic sensory nerve impulses to SC)

-spinal nerves innervate specific, constant skin segments (except C1, skin segments = DERMATOMES)

-helps physicians to determine segment of SC or which spinal nerve is malfunctioning

Spinal Cord Physiology:

2 Functions

1. White matter are highways for impulse conduction to and from brain

2. Gray matter receives and integrates incoming and outgoing information

-distinct bundles of axons

-have common origin or destination

-carry similar information

-may extend long distance up or down SC

Sensory Tract

-ascending

-axons conduct impulse towards brain

-descending

-axons conduct impulses down SC

-fast, predictable, automatic response to changes in environment

-helps to maintain homeostasis (permitting body to make exceedingly rapid adjustments)

Reflexes:

4 types

1. Spinal reflex: integration in SC gray matter

2. Cranial reflex: integration in Brain

3. Somatic reflex: skeletal muscle contracts

4. Autonomic (visceral) reflex: smooth and cardiac muscle, glands

-simplest type of pathway

-pathways = specific neuronal circuits

-include at least one synapse

Reflex Arc:

5 functional components

1. sensory receptor: responds to stimulus

2. sensory neuron: moves signal to CNS

3. Integrating center: processes input and starts response

4. motor neuron: carries response signal

5. effector: part that responds

Stretch Reflex:

monosynaptic

1 sensory neuron and 1 motor neuron

Stretch Reflex:

Ipsilateral reflex

-maintains muscle tone

-muscle coordination during exercise

-ex: patellar reflex

-polysynaptic: 2 nuerons

-ipsilateral

-prevents damage to muscles & tendons from stretching

-operates as a feedback mechanism

-controls muscle tension by causing relaxation when force too extreme

-polysynaptic

-ipsilateral

-intersegmental: several SC segments involved

-protective withdrawal reflex

-moves a limb to avoid pain

-contraction of flexor muscles to move a limb

-works with crossed extensor reflex to maintain balance