Spinal Cord, Spinal Nerves, and Reflexes

Flashcards based on lecture notes about spinal cord, spinal nerves, and reflexes.

What two main components make up the central nervous system?

Brain and spinal cord

What two main components make up the peripheral nervous system?

Cranial and spinal nerves

What is the function of reflexes?

Quick, automatic nerve responses triggered by specific stimuli

What controls spinal reflexes?

Spinal cord alone, without input from the brain

What protects the spinal cord?

Membranes (meninges) and the vertebral column

What is the function of the spinal cord?

Carries sensory and motor information between brain and body; gives rise to spinal nerves

Approximately how long is the spinal cord?

About 18 in. (45 cm) long

Where does the spinal cord extend from?

From the brain to L1 and L2

What are the four regions of the spinal cord?

Cervical, thoracic, lumbar, sacral

How many segments give rise to spinal nerves?

31

What is the posterior median sulcus?

A groove that divides the spinal cord into left and right sides on the posterior side

What is the anterior median fissure?

A deeper, anterior groove that divides the spinal cord into left and right sides

What does the central canal contain?

Cerebrospinal fluid (CSF)

What is gray matter?

Unmyelinated cell bodies of neurons, neuroglia, and unmyelinated axons

What is white matter?

Myelinated and (some) unmyelinated axons

What does the cervical enlargement supply?

The shoulders and upper limbs

What does the lumbosacral enlargement supply?

The pelvis and lower limbs

What is the conus medullaris?

Tapered end of cord below lumbosacral enlargement

What is the cauda equina?

Nerve roots that extend from the conus medullaris

What is the filum terminale?

Thread of tissue at end of conus medullaris that extends down and anchors the spinal cord to the coccyx

What forms spinal nerves?

Two branches: anterior root (ventral root) and posterior root (dorsal root)

What do anterior roots contain?

Axons of motor neurons

What do posterior roots contain?

Axons of sensory neurons

What do spinal ganglia contain?

Cell bodies of sensory neurons that form the posterior root

What forms spinal nerves?

Union of posterior and anterior roots

What are mixed nerves?

Nerves that contain both afferent (sensory) and efferent (motor) fibers

What are the three specialized membranes surrounding the spinal cord?

Dura mater, arachnoid mater, and pia mater

What is the function of spinal meninges?

Surround and protect the spinal cord (and the brain)

What is the dura mater?

Outermost meningeal layer; tough layer of dense irregular CT; distal end joins filum terminale

What is the arachnoid mater?

CT layer with fibers that form a web-like structure

What is the pia mater?

Areolar CT; contains numerous blood vessels

What is the epidural space?

Space between vertebrae and dura mater (superficial to dura mater)

What is the subdural space?

Space between the dura mater and arachnoid mater

What is the subarachnoid space?

Space between arachnoid and pia mater that is filled with cerebrospinal fluid (CSF)

What are nuclei (in the context of the spinal cord)?

Masses of gray matter within CNS organized into regions called horns

What do dorsal horns contain?

Somatic and visceral sensory nuclei

What do ventral horns contain?

Somatic motor nuclei

What do lateral horns contain?

Visceral motor nuclei

What are dermatomes?

Specific bilateral regions of skin monitored by a single pair of spinal nerves

What is a neural reflex?

Rapid, automatic responses to specific stimuli; basic building blocks of neural function

What are the five components of a reflex arc?

Sensory receptor, sensory neuron, CNS (integration center), motor neuron, effector

What is a monosynaptic reflex?

Single synapse; sensory neuron synapses directly with motor neuron; fastest, simplest reflex arc

What is a polysynaptic reflex?

At least one interneuron between sensory and motor neuron; slower response

Where does processing occur in spinal reflexes?

In the spinal cord

Where does processing occur in cranial reflexes?

In the brain

What is a stretch reflex?

Regulates skeletal muscle length throughout the body; very rapid; example: patellar reflex

What are muscle spindles made of?

Bundles of small, specialized skeletal muscle cells called intrafusal muscle fibers

What monitors stretch in intrafusal fibers?

Dendrites of sensory neurons wind around the central region of intrafusal fibers

What surrounds muscle spindles?

Larger skeletal muscle cells called extrafusal muscle fibers

What innervates extrafusal muscle fibers?

Alpha-motor neurons

What occurs when stretching the intrafusal fibers?

Increases the frequency of action potentials fired by the sensory neuron

What does the alpha neuron stimulate?

The extrafusal fibers to contract (increase muscle tone), to prevent further overstretching of the muscle

What initially happens when a patellar ligament is struck?

Stretches tendon and quadriceps femoris muscle

What does the activation of Golgi tendon organs do?

Inhibits firing of alpha-motor neuron (motoneuron), reducing muscle contraction; avoids excessive contraction of muscle and damage to tendon

What is the withdrawal reflex?

A protective mechanism that allows quick withdrawal from a painful stimulus

What is reciprocal innervation?

When interneurons are stimulated in the spinal cord to inhibit antagonistic muscles

What is the crossed extensor reflex?

More complex reflexes that require control of muscles on the contralateral limb; also called double reciprocal innervation