Neuroscience of Motor Control

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Questions and Answers

Which cells are classified as upper motor neurons involved in motor control?

Cerebellar granule cells

Interneurons

Sensory neurons

Pyramidal cells (correct)

What is the role of the internal capsule in the context of movement?

It connects the cerebral cortex to other brain regions (correct)

It generates auditory signals

It regulates balance

It processes visual information

Which part of the brain is primarily responsible for coordinating voluntary movement?

Cerebellum (correct)

Cerebrum

Pons

Midbrain

Which pathway is associated with the corticospinal tract in motor control?

Lateral corticospinal pathway Signup and view all the answers

Which structure connects the brainstem to the forebrain and is significant in motor control?

Cerebral peduncle Signup and view all the answers

What is the function of the cervical enlargement in the spinal cord?

Nerves to the upper limbs Signup and view all the answers

Which of the following correctly describes the cauda equina?

A bundle of nerve roots extending from L2 to S5 Signup and view all the answers

What marks the point where the spinal cord tapers?

Medullary cone Signup and view all the answers

Which of the following statements about the spinal cord's structure is true?

Longitudinal grooves are present on both anterior and posterior sides Signup and view all the answers

What regions does the spinal cord primarily divide into?

Cervical, thoracic, lumbar, and sacral Signup and view all the answers

Which pathway is associated with the transmission of proprioceptive information to the cerebellum?

Spinocerebellar pathway Signup and view all the answers

In spinal cord ascending pathways, which structure is primarily involved in processing and relaying sensory information to the cortex?

Thalamus Signup and view all the answers

Which of the following correctly identifies one of the primary functions of the dorsal column–medial lemniscal pathway?

Transmission of touch and proprioception Signup and view all the answers

Where do third-order neurons synapse before sending sensory information to the primary somatosensory cortex?

Thalamus Signup and view all the answers

Which part of the brain is involved in fine motor control and coordination, receiving information from the spinocerebellar pathway?

Cerebellum Signup and view all the answers

The dorsal column–medial lemniscal and spinocerebellar pathways are both components of which system?

Central nervous system Signup and view all the answers

Which ascending pathway is primarily responsible for the sensation of temperature and crude touch?

Lateral spinothalamic pathway Signup and view all the answers

Which statement about the spinocerebellar pathway is true?

It transmits proprioceptive information to the cerebellum. Signup and view all the answers

Which neurons are responsible for carrying sensory information from the body to the spinal cord?

Somatic sensory neurons Signup and view all the answers

What is the role of interneurons located in the dorsal horn of the spinal cord?

They connect sensory and motor neurons. Signup and view all the answers

Which component of the spinal cord contains both sensory and motor pathways?

Spinal nerve Signup and view all the answers

Which type of neuron is involved in autonomic responses?

Visceral motor neuron Signup and view all the answers

What type of information do visceral sensory neurons convey to the spinal cord?

Internal organ sensations Signup and view all the answers

What structure is primarily associated with motor neuron output in the spinal cord?

Ventral horn Signup and view all the answers

Which neurons would you expect to find receiving input from somatic sensory neurons?

Interneurons in the dorsal horn Signup and view all the answers

What distinguishes the somatic motor neuron from the visceral motor neuron?

Somatic motor neurons innervate skeletal muscles. Signup and view all the answers

How many pairs of spinal nerves are there in total?

31 pairs Signup and view all the answers

What type of information does the posterior (dorsal) root carry?

Sensory input to the spinal cord Signup and view all the answers

From where does the first cervical nerve exit?

Between the skull and atlas Signup and view all the answers

Which root carries motor output from the spinal cord?

Anterior (ventral) root Signup and view all the answers

What structure is formed from the roots arising from the lower spinal cord?

Cauda equina Signup and view all the answers

How many thoracic spinal nerves are there?

12 thoracic nerves Signup and view all the answers

What does the posterior (dorsal) root ganglion contain?

Neurosomas of sensory neurons Signup and view all the answers

Which of the following is the correct number of lumbar spinal nerves?

5 lumbar nerves Signup and view all the answers

What type of fibers do mixed nerves contain?

Both afferent and efferent fibers Signup and view all the answers

Which type of nerves carry signals from sensory receptors to the CNS?

Sensory (afferent) nerves Signup and view all the answers

How are neurosomas in a ganglion arranged?

In bundles with nerve fibers leading in and out Signup and view all the answers

What envelops the ganglion, ensuring continuity with the nerve?

Endoneurium Signup and view all the answers

What is the main function of motor (efferent) nerves?

To transmit signals to muscles and glands Signup and view all the answers

What type of fibers can both sensory and motor fibers be described as?

Somatic or visceral Signup and view all the answers

Where is the posterior root ganglion located?

Near the spinal cord Signup and view all the answers

Which statement about nerves is incorrect?

Sensory nerves only carry signals from the CNS Signup and view all the answers

Study Notes

Introduction

Thousands of Americans are paralyzed by spinal cord injury each year.
The spinal cord is the information highway connecting the brain to the lower body.
The chapter will study the spinal cord and spinal nerves.

Functions of the Spinal Cord

Nerve fibers conduct sensory and motor information up and down the spinal cord.
Spinal neurons receive input from multiple sources (e.g., bladder control), integrate it, and execute appropriate output.
The spinal cord contains central pattern generators that coordinate repetitive movement sequences like walking.
Reflexes are involuntary responses to stimuli vital for posture, coordination and protection.

Surface Anatomy 1

The spinal cord is a cylinder of nervous tissue arising from the brainstem at the foramen magnum of the skull.
It occupies the upper two-thirds of the vertebral canal.
The inferior margin ends at the first lumbar vertebra (L1) or slightly beyond.
It averages 1.8 cm thick and 45 cm long.
It gives rise to 31 pairs of spinal nerves.
A segment is a part of the spinal cord supplied by a pair of spinal nerves.

Surface Anatomy 2

The spinal cord has longitudinal grooves on the anterior and posterior sides.
These include the anterior median fissure and posterior median sulcus.
The spinal cord is divided into cervical, thoracic, lumbar, and sacral regions.
Two areas are thicker than elsewhere: cervical and lumbar enlargements.
- Cervical enlargement supplies nerves to the upper limb.
- Lumbar enlargement supplies nerves to the pelvic region and lower limbs.
The medullary cone (conus medullaris) is where the cord tapers to a point below the lumbar enlargement.
The cauda equina is a bundle of nerve roots that occupy the vertebral canal from L2 to S5.

The Spinal Cord, Posterior

The spinal cord is a complex structure surrounded by the meninges containing the spinal nerves, roots, and ganglia.
It is divided into various regions and has different segmentations.
Key anatomical structures like the spinal cord, spinal nerves, rootlets, and meninges (dura, arachnoid, pia mater) are shown in the illustration.

Meninges of the Spinal Cord 1

Meninges are three fibrous membranes that enclose the brain and spinal cord.
They separate soft tissue from cranium and vertebral bones.
From superficial to deep: dura mater, arachnoid mater, and pia mater.
The dural sheath surrounds the spinal cord, separated from vertebrae by the epidural space.
Arachnoid membranes adhere to dura, separated from pia by fiber containing subarachnoid space with cerebrospinal fluid (CSF).
Lumbar puncture (spinal tap) collects CSF for examination.
The pia mater follows spinal cord contours and continues as a fibrous terminal filum to fuse with dura to form coccygeal ligament.

Meninges of the Spinal Cord 2

The meningeal coverings include dura mater, arachnoid mater, and pia mater, and are depicted here in relation to the spinal cord and surrounding structures.

Meninges of the Spinal Cord 3

The spinal cord is shown with its gray and white matter structures.
The meninges and their relationship with the spinal cord are also clearly highlighted.

Spina Bifida

Spina bifida is a congenital defect where one or more vertebrae fail to fully develop a vertebral arch around the spinal cord.
The defect is common in the lumbosacral region of the spine.
Spina bifida cystica is a serious form.
Folic acid supplementation for pregnant women helps reduce the risk.

Spina Bifida Cystica

This image showcases the appearance of spina bifida cystica in a newborn.

Cross-Sectional Anatomy 1

The central area is gray matter shaped like a butterfly with columns surrounding white matter.
Gray matter comprises neuron cell bodies with little myelin—the site of information processing and synaptic integration.
White matter consists of abundantly myelinated axons carrying signals within the central nervous system.

Cross-Sectional Anatomy 2

A cross-section of the spinal cord with gray and white matter, meninges, and spinal nerve structures are shown in relation to the vertebral column.

Gray Matter

The spinal cord has a central core of butterfly- or H-shaped gray matter in cross section.
It consists of posterior (dorsal) horns; posterior (dorsal) root of spinal nerve carries only sensory fibers thick anterior (ventral) horns.
The anterior (ventral) root carries only motor fibers.
Gray commissure connects right and left sides; lined with ependymal cells and filled with cerebrospinal fluid (CSF).
Lateral horn visible from T2 through L1 contains sympathetic neurons.

White Matter

White matter surrounds gray matter in the spinal cord as bundles of axons.
It provides pathways for communication between different CNS levels.
White matter is organized into columns (funiculi) on each side: posterior (dorsal), lateral, and anterior (ventral).
Subdivisions of each column are called tracts or fasciculi.

Spinal Tracts

Tracts in the spinal cord share similar origins, destinations and functionality.
Ascending tracts carry sensory information upwards.
Descending tracts carry motor information downwards.
Decussation is the crossing over of tracts; the brain controls the opposite side of the body.
Contralateral tracts originate and end on opposite sides, while ipsilateral tracts stay on the same side.

Tracts of the Spinal Cord

The diagram displays the various ascending and descending tracts in the spinal cord.
These tracts play a critical role in conducting nerve impulses.

Spinal Tracts (2)

Important ascending (sensory) and descending (motor) tracts are shown and labeled in the spinal cord.

Spinal Nerve Structure (1)

Diagram illustrating a spinal nerve's constituent parts (sensory and motor components), the dorsal root ganglion (containing cell bodies of sensory neurons), and sensory/motor neurons.

Spinal Nerve Structure (2)

Diagram emphasizing the component parts of a spinal nerve including the components of the dorsal and ventral roots.

General Anatomy of Nerves and Ganglia 1

The spinal cord communicates with the rest of the body using spinal nerves.
Nerves are cord-like structures composed of multiple nerve fibers (axons) bound together by connective tissue.
Mixed nerves contain sensory and motor fibers.

General Anatomy of Nerves and Ganglia 3

Sensory nerves carry signals from sensory receptors to the CNS.
Motor nerves carry signals from the CNS to muscles and glands.
Mixed nerves contain both sensory and motor fibers.

General Anatomy of Nerves and Ganglia 4

Ganglia are clusters of neurosomas that are enveloped by endoneurium.
Neurosomas contain bundles of nerve fibers that enter and leave the ganglion.
The posterior root ganglion is associated with spinal nerves.

Anatomy of a Ganglion

A diagram clearly showing the different parts of a ganglion in relation to a spinal nerve with labeled sensory and motor pathways.

Spinal Nerves

31 pairs of mixed spinal nerves exist.
8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.
Cervical nerves exit spaces between skull and atlas. Others emerge through intervertebral foramina.

Proximal Branches

Each spinal nerve arises from two roots.
The posterior (dorsal) root conveys sensory information to the spinal cord and has a dorsal root ganglion containing sensory neuron cell bodies.
The anterior (ventral) root conveys motor information out of the spinal cord.
Rootlets form the anterior and posterior roots.

The Spinal Nerve Roots

The diagram illustrates the spinal nerve roots and their relationship to the spinal cord and peripheral nerves.

Nerve Plexuses 1

Anterior rami branch and repeatedly anastomose to form five main nerve plexuses: cervical, brachial, lumbar, sacral, and coccygeal.
Cervical plexus supplies the neck, which includes the phrenic nerve to the diaphragm.
Brachial plexus supplies the upper limbs.
Lumbar plexus supplies the abdominal wall, anterior thigh and genitalia.
Sacral plexus supplies the remainder of the lower trunk and lower limb.
Coccygeal plexus is small and supplies a small area at the coccyx.

Nerve Plexuses 2

Somatosensory function involves carrying sensory signals from bones, joints, muscles, skin.
This is often referred to as proprioception because the brain receives information about body position and movements from sensory nerve endings in muscles, tendons, and joints.
Motor function primarily stimulates muscle contraction.

The Cervical Plexus

This illustration showcases the anatomical arrangement of the cervical plexus nerves.

The Brachial Plexus 1

The brachial plexus emerges from the ventral rami of the brachial region.
Structure and branching patterns of peripheral nerves are displayed.

The Brachial Plexus 2

The illustration displays the intricate structure of the brachial plexus, including its cords and major branches of the brachial nerves such as the axillary, median, ulnar, and radial.

The Lumbar Plexus

This diagram details the lumbar plexus and its anatomical structure, including the nerves supplying the lower extremities.

The Sacral and Coccygeal Plexuses

An image illustrating the lumbar plexus and the intricate connections of nerve bundles.

Nerve Injuries

Radial nerve injury: passes through axilla, can result in crutch paralysis and wrist drop.
Sciatic nerve injury: sharp pain traveling from the gluteal region to the leg; commonly due to herniated intervertebral discs or spinal osteoporosis.

Cutaneous Innervation and Dermatomes

Dermatomes are specific areas of skin that convey sensory information to a spinal nerve.
Dermatome maps illustrate cutaneous regions served by each spinal nerve.
Dermatomes overlap, requiring anesthetizing 3 successive spinal nerves to completely eliminate sensation from a specific dermatome.

A Dermatome Map

A visual representation of dermatomes over the human body displaying the sensory distribution related to each spinal nerve segment.

The Nature of Reflexes

Reflexes are quick, involuntary, and stereotyped reactions initiated by stimuli to glands or muscles.
They require stimulation and are not spontaneous.
Reflexes are quick, involve few to no interneurons, and have a minimal synaptic delay.
They are involuntary, difficult to suppress, and stereotyped (recurring similarly each time).

The Nature of Reflexes 2

Reflexes include glandular secretions and contraction of all three muscle types.

The Nature of Reflexes 3

The pathway of a somatic reflex includes somatic receptors in skin, muscles, or tendons.
Afferent nerve fibers carry information from receptors, either to the posterior horn of the spinal cord or brainstem.
The integrating center is the point where synaptic contact happens in gray matter of cord or brainstem; it determines if efferent neurons signal muscles.
Efferent nerve fibers carry motor impulses to effectors (muscles).

A Representative Reflex

Illustration of a reflex arc showing the flow of information from a stimulus to the response within the body in relation to the spinal cord.

The Muscle Spindle

Muscle spindles are stretch receptors found within skeletal muscles.
They are proprioceptors, specialized sense organs that monitor body position and movement.
Muscle spindles inform the brain about muscle length and movement of body parts.
This allows the brain to send motor commands to coordinate movement, regulate reflexes, muscle tone, and posture.

A Muscle Spindle and Its Structure

A highly detailed illustration of a muscle spindle, its components, and their connections, such as the peripheral nerve, intrafusal fibers (stretching), muscle fibers, and the nerve supply (alpha and gamma motor neurons).

Poliomyelitis and ALS 1

Poliomyelitis and ALS both lead to motor neuron destruction resulting in skeletal muscle atrophy from lack of innervation.
Poliomyelitis is caused by the poliovirus and destroys motor neurons in the brainstem and anterior horn of the spinal cord.
Early signs include muscle pain, weakness, and loss of some reflexes, which progress to paralysis and respiratory arrest.
The poliovirus spreads via fecal contamination of water supplies.

Poliomyelitis and ALS 2

Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, damages motor neurons, leading to muscular atrophy.
Scarring (sclerosis) of lateral spinal cord regions is also a feature.
Astrocytes (specialized glial cells), which normally reabsorb neurotransmitters like glutamate, fail to do so in ALS, leading to glutamate buildup and toxicity.
Early signs include muscle weakness, problems with speaking, swallowing, and using hands.
Sensory functions remain unaffected.

Studying That Suits You

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Description

Test your knowledge on the neural mechanisms involved in motor control with this quiz. Explore key components such as upper motor neurons, the internal capsule, and the cortico-spinal tract. Understand the structures that play a significant role in coordinating and executing voluntary movements.