Chapter 13- Exam 4

What is the function of the spinal cord

Information high that has a connection between the body and the brain

Where does the spinal cord start and end?

From the occipital bone to all the way to L1

Which nervous system is the spinal cord and spinal nerve a part of.

• Spinal cord: Central Nervous System

• Spinal nerve: Peripheral Nervous System

What is the order of meninges sheets?

Dura mater, Arachnoid mater, Pia mater

How many pairs of spinal nerves are there?

• 31 pairs

What does each meninges sheet hold in each layer?

• Dura and Arachnoid→ hold cerebral spinal fluid that protects neural tissue

• Pia→ contact spinal cord

What is subarachnoid space?

• fluid-filled space between the arachnoid mater and pia mater surrounding the brain and spinal cord. It contains cerebrospinal fluid (CSF), which cushions and protects the central nervous system, and also provides nutrients and removes waste

What is the function of gray commissure?

• It. connects the left and right side of the spinal cord

• Left sensory info is gonna be processed on the right side

How do you know on posterior side of the cord?

• Landmark of dorsal root ganglion

• Afferent—> sensory towards spinal cord

What are the three functions of the spinal cord?

• Conduction- The spinal cord acts as a communication pathway between the brain and body.

  • 3-4 feet long

• Locomotion- The spinal cord contains central pattern generators that produce rhythmic muscle movements like walking. These can function without the brain, but normal movement requires brain control for balance and precision.

• Reflexes- Need to happen automatically/ rapidly with stimulus and responses

What is the significance of cervical and lumbar enlargements in the spinal cord?

• Synapses in the GRAY matter

  • take up more space meaning it contributes to these enlargements

What is gray matter ?

• Gray- soma and synapse

  • Dorsal, Ventral, Lateral horn, gray commissure that goes left to right that connects the two sides of the chord

  • Deeper to the chord

What is white matter?

•  Axons with more myelination which mean faster action potentials

• Periphery of chord is white matter 

• Dorsal, ventral, lateral column that are ALL myelinated 

What are white matter columns composed of?

White axons (myelinated nerve fibers)

What is another name for ascending pathways?

Afferent pathways→Sensory information from the body to the brain

What is another name for descending pathways?

Efferent pathways-→Motor commands from the brain to muscles

How long are the neurons?

The order of feeling from finger to brain→ VERY LONG NEURON

What is decussation?

Sensory impulses must cross from left to right then right to left

What do ascending pathways do, and what is the order from receptor to brain?

Ascending (afferent) pathways carry sensory information from the body to the brain. The sequence is: sensory receptor → first-order neuron → second-order neuron (to the thalamus) → third-order neuron → cerebral cortex.

What do descending pathways do, where do they start, and what happens before reaching the muscles?

Descending pathways control motor movements of skeletal muscles. They originate in the primary motor cortex, cross over (decussate) in the medulla before movement, and then synapse with efferent (lower motor) neurons.

What happens in poliomyelitis, and what function is affected?

Poliomyelitis causes death of neurons in the ventral (anterior) horn, leading to loss of somatic motor function.

What is the structure of a nerve, including its coverings and basic characteristics?

• A nerve is a bundle of axons (nerve fibers) in the peripheral nervous system.

• The simplest fibers are unmyelinated. Its structure is similar to muscle, with layers:

  • epineurium (covers the whole nerve), perineurium (surrounds fascicles), and endoneurium (separates individual nerve fibers).

  • Blood vessels penetrate only up to the perineurium.

What are “yellow nerve fibers,” and why do they appear yellow?

They are myelinated axons, which appear yellowish due to the fatty myelin sheath that insulates the fiber and speeds up nerve signal transmission.

What are nerve plexuses?

• Nerve plexuses are networks of intermixing spinal nerves

  • Cervical plexus (C1–C5)

  • Brachial plexus (C5–T1)

  • Lumbar plexus (L1–L4)

  • Sacral plexus (L4–S4)

What are dermatomes, how do they overlap, and what happens with nerve damage at different spinal levels?

• Dermatomes are areas of skin supplied by a single spinal nerve.

• They overlap at the edges by about 50%, meaning adjacent dermatomes (like T1 and T2) share sensory input.

• Because of this overlap, damage to one nerve (like L4) causes partial loss of sensation, such as in part of the toe.

• Complete loss of sensation requires damage to multiple adjacent nerves, such as L3, L4, and L5.

What is a myotatic reflex?

A reflex where a muscle contracts in response to being stretched.

What does myotatic reflex help maintain?

• Balance and equilibrium in posture

• Happens through spinal reflexes (no brain required for initial response)

What are the steps of Myotatic Reflex?

• Muscle stretches

• Sensory receptors (muscle spindles) detect stretch

• Signal sent to spinal cord (afferent neuron)

• Motor neuron sends signal back

• Muscle contracts to resist stretch

Agonist vs Antagonist

• Agonist: muscle that performs the action

• Antagonist: muscle that does the opposite action

During knee movement, which muscles act as the agonist and antagonist in both extension (straightening) and flexion (bending), and how do they work together?

• Extension (straightening):

  • Agonist → Quadriceps

  • Antagonist → Hamstrings

• Flexion (bending):

  • Agonist → Hamstrings

  • Antagonist → Quadriceps

💡 Think: Teeter-totter → when one contracts, the other relaxes

What is Reciprocal Inhibition?

When the agonist contracts, the antagonist is inhibited (relaxes).

Why is reciprocal inhibition important?

• Prevents muscles from working against each other

• Allows smooth movement

Example:

• Quadriceps contract → hamstrings are inhibited

What are the differences between extrafusal and intrafusal muscle fibers in terms of structure and function?

Extrafusal Muscle Fibers

• Main muscle fibers (most of the muscle)

• Responsible for:

  • Force production

  • Movement

• Involve:

  • Myofibrils

  • Calcium release for contraction

Intrafusal Muscle Fibers

• Found inside muscle spindles

• Function:

  • Detect changes in muscle length (stretch)

• Contain:

  • Sensory dendrites (afferent neurons)

How does maintaining posture work as a negative feedback system in muscles?

• Muscle stretches (body shifts)

• Sensory neurons send signal to spinal cord

• Motor response contracts muscle back

• Muscle returns to original length

➡ This is a negative feedback loop:

• Detect change → correct it → return to equilibrium

What is the flexor withdrawal reflex?

• A polysynaptic reflex that pulls a body part away from pain.

• Involves multiple neurons (polysynaptic)

• Happens quickly (protective reflex)

• Maintains balance by:

  • Extending the opposite leg (crossed-extensor reflex)

What is an example of the flexor withdrawal reflex?

• Step on something sharp → foot withdraws immediately

What is the Golgi tendon reflex?

• A reflex that prevents muscle damage from too much tension.

• Location:
  Golgi tendon organs (in tendons)

• Function:
  Detects excessive tension
  Sends inhibitory signals to stop contraction

• Result:
  Muscle relaxes to avoid injury