Ch. 6 Pt 2 CNS

What are the 4 functions of the spinal cord?

Conduction, integration, locomotion, reflexes

How are the 31 pairs of spinal nerves divided?

Based on where they emerge from:

C1-L1 = spinal cord

L2-S5 = cauda equina

what are the 4 functional regions of the spine in order from top to bottom?

Cervical (neck/upper limbs)

Thoracic (chest)

Lumbar (abdomen/lower limbs)

Sacral (genitalia)

What are the 3 meninges of the spine?

Dura mater (tough stuff)

Arachnoid mater (spidery stuff)

Pia mater (delicate stuff)

What is the epidural space?

Space between vertebrae and dural sheath (covering dura mater). Usually filled with fat

What is the subarachnoid space?

Space between arachnoid mater and pia mater. Contains cerebrospinal fluid (CSF)

1. epidural space

2. Subarachnoid space

3. Dura mater

4. Arachnoid mater

5. Pia mater

Matter with little or no myelin. Association neurons (interneurons). Synapses between peripheral nerves and interneurons

Gray matter

Lot of myelin (mostly membrane→ rich in lipid content). Axons of ascending and descending neurons

White matter

1. Posterior (dorsal) root of spinal nerve

2. Posterior (dorsal) horn

3. Lateral horn

4. Anterior (ventral) root of spinal nerve

5. Anterior (ventral) horn

What are the areas of white matter running up and down the spinal cord and what kind of fibers do they contain?

Posterior column (top; all sensory fibers)

Lateral columns (left & right; mixed fibers)

Anterior column (bottom; mostly motor fibers)

Motor =

descending

sensory =

ascending

Clusters of nerves in parallel arrangements in the CNS. Ascending & descending

Nerve tracts

What is the naming rule for sensory tracts?

spino - [destination to brain]

What are the 3 neurons involved with sensory pathways?

3rd order neuron: From thalamus to postcentral gyrus of cerebral cortex (sensory region of brain)

2nd order: From brainstem or spinal cord to the thalamus (“gateway”) in brain

1st order: Detects a stimulus and sends it to the brainstem or posterior horn of spinal cord

What is the naming rule for motor tracts?

[origin in the brain] - spinal

What are the 3 neurons involved with motor pathways?

Upper motor neuron: From precentral gyrus of cerebral cortex to brain stem or spinal cord (motor region of the brain)

Lower motor neuron: Synapses with upper motor neuron and terminates at target organs

What is a nerve?

cord-like organs composed of nerve fibers (axons)

sheath that wraps around single nerve fibers and their myelin sheaths

endoneurium

sheath that wraps around groups of nerve fibers (nerve fascicle)

Perineurium

wrapping that covers the entire nerve

Epineurium

What are the 4 ways nerves are classified as?

By location of soma, by function, by innervation, and by range of organs innervated

What are the two locations for nerve somas?

cranial (innervate head)

spinal (innervate rest of body)

What are the 3 functions of nerves?

afferent/sensory nerves

efferent/motor nerves

mixed nerves

What are the two types of nerve innervations?

somatic & visceral fibers

What are the two ranges of organs innervated by nerves?

General fibers (innervate widespread organs: muscles, skin, viscera)

Special fibers (innervate more localized organs: eyes, ears, taste)

What 2 diseases cause destruction of motor neurons and production of skeletal muscle atrophy from lack of innervation?

Poliomyelitis and ALS

Caused by the poliovirus

Destroys motor neurons in brainstem and anterior horn of spinal cord

Causes muscle pain, weakness, and loss of some reflexes, followed by paralysis, muscular atrophy, and respiratory arrest

Virus spreads by fecal contamination of water (outbreaks in first half of 1900s)

Poliomyelitis

Destruction of motor neurons and muscular atrophy

Scarring of lateral regions of the spinal cord

The neurotransmitter glutamate accumulates to toxic levels

Causes muscular weakness, difficulty speaking, swallowing, and use of hands

Sensory and intellectual functions remain unaffected

Amyotrophic lateral sclerosis (ALS)

cluster of neurosomas outside the CNS

ganglion

contains somas of unipolar sensory neurons

posterior root ganglion

1. Posterior (dorsal) root ganglion

2. Gray commissure

3. Posterior (dorsal) root nerve

4. Spinal nerve

5. Anterior (ventral) root of spinal nerve

6. Central canal

What are the 4 nerve plexuses?

Cervical, brachial, lumbar, sacral

What are the key spinal nerves for each plexus?

cervical - phrenic nerve (diaphragm)

brachial - radial & ulnar nerve

lumbar - femoral nerve (quads)

sacral - sciatic nerve (hamstrings)

Each zone of the skin ( _____________) is innervated by sensory branches of the spinal nerves

dermatomes

Common disease of early childhood. Caused by varicella virus. Produces itchy rash that clears up (usually without complications). Virus remains for life in the posterior (dorsal) root ganglia (sensory neuron somas)

Chickenpox

Localized disease caused by the virus from chickenpox traveling along sensory nerves (when immune system is compromised). Painful trail of skin discoloration and fluid-filled vesicles along path of nerve (usually along one dermatome)

Shingles

Quick, involuntary, stereotyped (predictable) reactions to glands and muscles to stimulation. Automatic responses to sensory input that occur without our intent or often even our awareness. Can include glands and all 3 types of muscle

Reflexes

unlearned skeletal muscle reflexes mediated by brainstem/spinal cord

Somatic reflexes

What is the fastest/simplest reflex arc that goes from Somatic Sensor → afferent nerve fiber → efferent nerve fiber → effector?

Monosynaptic

Which reflex arc is most common that allows for integration that goes from Somatic receptor → afferent nerve fiber → interneuron(s) → efferent nerve fiber → effector?

Polysynaptic

What is the stretch reflex?

The tendency to cause a muscle to contract when it is rapidly stretched. Almost always involves reciprocal inhibition (Antagonists are inhibited during a reflex)

What is an example of reciprocal inhibition where there’s suppressed contraction of hamstrings when the quadriceps are contracting?

patellar tendon reflex

How do muscles know they are rapidly stretched?

Muscle spindles: stretch receptors that feed back info to the CNS about muscle tone/movement

The process of moving a body part away from a noxious stimulus. Requires a prolonged stimulation of flexor muscle

Flexor (withdrawl) reflex or ipsilateral reflex

The contraction of extensor muscles (and relaxation of flexor muscles) in limb opposite of the one that is withdrawn. Maintains balance by extending other leg

Crossed extension reflex