Bio 209 Ch. 13

• (1) Pathway for sensory info – axons of sensory neurons enter spinal cord and travel through spinal cord to brain
• (2) Pathway for motor info – axons of motor neurons travel from brain through the spinal cord; when axons of motor neurons exit spinal cord, they travel to effectors

rigid structure that protects the spinal cord; spinal cord located within vertebral canal (vertebral canal formed by vertebral foramina; vertebral foramen is the opening in the middle of vertebra)

Dura Mater: outer, tough layer of meninges

Arachnoid: middle layer of meninges

Pia Mater: inner layer of meninges (denticulate ligaments: lateral extensions of pia mater – help hold spinal cord in place)

acts as a shock absorber

located between wall of vertebral column and dura mater; contains adipose and connective tissue that cushion the spinal cord

injection of anesthetic into the epidural space

inflammation of the meninges caused by an infection

insertion of a needle into the subarachnoid space to collect CSF for a diagnostic

• Begins: base of the Medulla Oblongata where the spinal cord passes thru the Foramen Magnum à Extends to the superior border of the second lumbar vertebra
• - In infants, the spinal cord extends to the third/fourth lumbar vertebra. Difference due to growth, until it ends at the age of 4-5 years

located within cervical region of vertebral column; enlarged due to sensory & motor neuron axons that serve the upper limbs enter and leave the spinal cord from here; these axons form the nerves that serve the upper limbs

located within lower thoracic region of vertebral column; enlarged due to sensory & motor neurons that serve the lower limbs and enter and leave the spinal cord from here; these axons form the nerves that serve the lower limbs

tapering end of spinal cord that is inferior to lumbar enlargement; located at level of intervertebral disc between L1 & L2

pia mater that extends from conus medullaris; anchors spinal cord to coccyx

spinal cord ends between L1 & L2; lumbar sacral and coccygeal spinal nerves exit vertebral column inferio to the conus medullaris; bundles of axons that form the lumbar, sacral and coccygeal spinal nerves exit spinal cord and hang inferiorly to conus medullaris (looks like a “horse’s tail” hence cauda = tail equine = horse)

bundles of sensory and motor axons; 31 pairs (each pair is named for the spinal segment from which it arises)

contain only axons of sensory neurons

contain only axons of motor neurons

swelling in posterior root that contains sensory neuron cell bodies

Posterior Root: carries nerve impulses to the spinal cord FROM sensory receptors

Anterior Root: carries nerve impulses from the spinal cord TO the effectors

wide groove on anterior (ventral) surface of spinal cord

narrow groove on posterior (dorsal) surface of spinal cord

crossbar of letter “H”

space in middle of spinal cord that is filled with CSF

anterior TO gray commisure; connects white matter of right and left sides of spinal cord

contain clusters of somatic motor neuron cell bodies (nuclei)

contain clusters of autonomic motor nuclei and are only found in the thoracic and upper lumbar segments of spinal cord

Anterior: initiates nerve impulses that control skeletal muscle

Lateral: initiates nerve impulses that control cardiac & smooth muscles, and glands

Posterior:

The Anterior Horn of the Spinal Cord is affected by the Polio Virus

Cause: Chicken Pox Virus

Located: Posterior Dorsal Root Ganglion

Blisters located along sensory nerve belonging to the infected dorsal root ganglion

• Sensory (Ascending) Tracts: TO the brain
• Motor (Descending) Tracts: FROM the brain

(1) Sensory and Motor Tracts are severed

(2) Loss of Sensory Input and Motor Output of spinal nerves that emerge inferior to the transaction à loss of sensation and loss of motor function (paralysis)

Anterior and Posterior Roots at each Spinal Cord Segment combine to form spinal nerve (all spinal nerves mixed nerves contain sensory & motor info)

• - 8 Cervical
• - 12 Thoracic
• - 5 pairs of Lumbar
• - 5 pairs of Sacral
• - 1 pair of Coccygeal

connective tissue that surrounds each axon within a nerve; can be found surrounding both myelinated & unmyelinated axons

bundles of axons with their endoneurium

connective tissue that surrounds fascicles

outermost connective tissue covering of nerve

branch of spinal nerves after passing thru intervertebral foramen

network of axons; axons from anterior rami of spinal nerves (except thoracic nerves T1-T12) form plexuses on right and left side of body

Cervical: C1-C5; innervates skin and muscles of head, neck, shoulder; Phrenic Nerve is most important (supplies diaphragm)

Brachial: C5-C8 & T1; innervates muscles and skin of upper limbs; Major nerves it innervates = Axillary (deltoid and teres minor), Musculocutaneous (muscle on anterior arm), Median (muscles on anterior forearm and hand, Radial (muscles on posterior arm and forearm), Ulnar (muscles on medial forearm and hand)

Lumbar: L1-L4; innervates skind and muscles of abdomen, pelvis, partial lower limbs; Major nerves it innervates = Femoral (flexor muscles of thigh and extensor muscles of legs), Obturator (adductor muscles)

• Sacral: L4-L5 & S1-S4; innervates skin and muscles of butt, perineum, lower limbs; Major nerves it innervates = Pudendal (muscles of perineum), Sciatic (two nerves tibial
• and common fibular bound together by connective tissue), Tibial (supplies muscles of posterior and lateral leg), Common Fibular (supplies muscles of
• anterior leg and foot)

In the case of a spinal cord, when it is completely severed, cutting all sensory & motor tracts resulting loss of motor & sensory functions below transection

• At C3: no function from neck down, ventilator required for breathing
• At C4-C5: diaphragm functional
• At T1-T3: complete arm function
• At T10-L1: most thigh muscles, walk with LONG braces
• At L1-L2: most leg muscles, walk with SHORT braces

• Dermatome: area of skin that is served by one spinal nerve or the trigeminal (V) nerve (cranial nerve)
• - Stimulating a dermatome can help determine if a spinal cord is damaged

fast, predictable, automatic responses to stimuli

Spinal : involves spinal nerves and spinal cord

Cranial : involves cranial nerves and brain

Somatic : involve skeletal muscles, consciously perceived

Autonomic : involved smooth muscle, cardiac muscle, glands ; not consciously perceived

• Sensory Receptor: responds to stimulus
• - Induces Graded Potential
• (Generator Potential) in dendrite of sensory neuron
• - If Graded Potential depolarizes axon to threshold an action potential is generated
• Sensory Neuron Axon: carries nerve impulse to CNS
• - Intensity of stimulus coded by frequency of nerve impulse
• Integration Center:
• - Monosynaptic Reflex – integrating center is single synapse between sensory and motor neuron
• - Polysynaptic Reflex – integrating center consists of one or more interneurons; interneuron synapses onto the motor neuron
• Motor Neuron: interneurons initiate nerve impulses in motor neuron
• - Axon of motor neuron leaves CNS
• Effector: innervated by motor neuron
• - Somatic Reflex: effector skeletal muscle
• - Autonomic Reflex: effector is cardiac muscle, smooth muscle, gland

• - Monosynaptic Reflex – integrating center is single synapse between sensory and motor neuron
• - Polysynaptic Reflex – integrating center consists of one or more interneurons; interneuron synapses onto the motor neuron

Stretch Reflex: controls muscle length by causing contraction of stretched muscle; important for maintaining posture

Tendon Reflex: controls muscle tension and causes muscle relaxation before muscle force becomes great enough to tear tendons

Flexor Reflex: response to painful stimulus and causes movement of limb away from stimulus

Crossed Extensor Reflex: controls balance; flexor reflex causes one leg to move away from a painful stimulus while crossed extensor reflex causes opposite leg to extend and maintain balance

• (1) Reflexes are predictable responses to stimuli
• (2) Reflex testing indicates health of nervous system
• (3) Abnormalities in reflex may indicate problem in reflex pathway (arc)

Patellar: stretch reflex; tapping of leg at knee joint causes contraction of quad muscle and entension of knee

Achilles: stretch reflex; tapping Achilles tendon causes contraction of the gastrocnemius and soleus muscles and plantar flexion

Banbinski Sign: gentle stroking of outer margin of sole of foot normally causes plantar flexion (curling toes) or a negative sign after 1.5 years; Positive sign occurs when great toe dorsiflexes (normal before 1.5 years)