CHAPTER 14: Nervous System: Spinal Cord and Spinal Nerves

anterior corticospinal tract

(also called the ventral corticospinal tract, "Bundle of Turck", medial corticospinal tract, direct pyramidal tract, or anterior cerebrospinal fasciculus) is a small bundle of descending fibers that connect the cerebral cortex to the spinal cord.

Monosynaptic

(of a reflex pathway) involving a single synapse.

ulnar nerve

A major nerve in the upper extremity that supplies both sensory and motor innervation to parts of the forearm and hand.

tendon reflex

A myotatic or deep reflex in which the muscle stretch receptors are stimulated by percussing the tendon of a muscle.

phrenic nerve

A nerve that runs from the spinal cord to the diaphragm (the thin muscle below the lungs and heart that separates the chest from the abdomen). It causes the diaphragm to contract and relax, which helps control breathing.

upper motor neuron

A neuron that starts in the motor cortex of the brain and terminates within the medulla (another part of the brain) or within the spinal cord.

spinal cord (corticospinal tract)

AKA, the pyramidal tract, is the major neuronal pathway providing voluntary motor function. This tract connects the cortex to the spinal cord to enable movement of the distal extremities

withdrawal reflex

Causes flexor muscles to contract in response to a painful or discomforting stimulus. This helps to withdraw part of the body from a painful stimulus to avoid damage.

crossed-extensor reflex

Complex reflex that consists of an ipsilateral withdrawal reflex and a contralateral extensor reflex. This keeps you from falling over, for example if you step on something painful. When you pull your foot back, the other leg responds to hold you up.

anterolateral pathway

a collection of ascending pathways that carry pain and temperature--as well as related touch--sensations from the spinal cord to the brainstem or thalamus.

lateral corticospinal tract

a descending motor pathway that begins in the cerebral cortex, decussates in the pyramids of the lower medulla (also known as the medulla oblongata or the cervicomedullary junction, which is the most posterior division of the brain[2]) and proceeds down the contralateral side of the spinal cord.

reciprocal inhibition

a general phenomenon in which the stretch of one muscle inhibits the activity of the opposing muscle

musculocutaneous nerve

a large branch of the Brachial Plexus, it supplies the muscles of the front of the arm and skin of lateral side of forearm

sciatic nerve

a major nerve extending from the lower end of the spinal cord down the back of the thigh, and dividing above the knee joint. It is the nerve with the largest diameter in the human body.

spinal nerves

a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body.

anterior horns

a motor neuron that projects from the anterior portion of the grey matter in the spinal cord to the skeletal muscle

sacral plexus

a nerve plexus that provides motor and sensory nerves for the posterior thigh, most of the lower leg, the entire foot, and part of the pelvis

cervical plexus

a network of nerves branching from the spinal nerves of the neck region and innervating the neck, chest, diaphragm, and part of the face

brachial plexus

a network of nerves in the shoulder that carries movement and sensory signals from the spinal cord to the arms and hands

motor pathways

a neural pathway that originates in the brain or brainstem and descends down the spinal cord to control the motor neurons.

indirect pathways

a neuronal circuit through the basal ganglia and several associated nuclei within the central nervous system (CNS) which helps to prevent unwanted muscle contractions from competing with voluntary movements

deep fibular nerve

a peripheral nerve of the calf. It's a terminal branch of the common peroneal nerve, which is a branch of the sciatic nerve.

common fibular nerve

a short, thin nerve located in the posterior compartment of the lower extremity. It arises as a terminal branch of the sciatic nerve around the apex of the popliteal fossa.

brainstem (corticobulbar tract)

a two-neuron path which unites the cerebral cortex with the cranial nerve nuclei in the brainstem involved in motor functions (apart from the oculomotor nerve).

tibial nerve

enables the lower leg to receive messages from the brain. It starts above the knee in the back of the leg. The nerve connects to 21 muscles that make it possible to move your leg, foot and toes.

radial nerve

helps you move your elbow, wrist, hand and fingers. It runs down the back of the arm from the armpit to the hand.

Polysynaptic

involving two or more synapses in the central nervous system

lower motor neuron

motor neuron that extends (mainly from the spinal cord or brainstem) to elicit responses in muscles or glands.

median nerve

one of the three major nerves of the forearm and hand. It courses from the brachial plexus in the axilla to innervate the intrinsic muscles of the hand.

stretch reflex

or myotatic reflex refers to the contraction of a muscle in response to its passive stretching.

lumbar puncture

or spinal tap may be done to diagnose or treat a condition. For this procedure, your healthcare provider inserts a hollow needle into the space surrounding the spinal column (subarachnoid space) in the lower back to withdraw some cerebrospinal fluid (CSF) or inject medicine.

superior trunk

part of the brachial plexus. It is formed by joining of the ventral rami of the fifth (C5) and sixth (C6) cervical nerves.

nerve plexuses

proximal segments of peripheral nerves emerging from the foramina of the spine with interchanging and intertwining nerves from different spinal levels that then form individual nerves more distally

Contralateral

relating to or denoting the side of the body opposite to that on which a particular structure or condition occurs.

muscle spindle

stretch receptors that signal the length and changes in length of muscles. They lie within an independent capsule, parallel to the main muscle. They are therefore stretched when the muscle lengthens but shorten when the muscle contracts

conus medullaris

the bundled, tapered end of the spinal cord nerves. Situated near the first two lumbar vertebrae, the conus medullaris ends at the cauda equina, a bundle of spinal nerves and nerve roots.

Middle trunk

the continuation of the ventral ramus of the seventh cervical nerve; it contributes fibers to the posterior and lateral cords (fasciculi) of the brachial plexus.

femoral nerve

the largest of five nerve branches of the lumbar plexus. This network of nerves is in the abdominal part of the torso (lower spine)

superficial fibular nerve

the main nerve of the lateral compartment of the leg. It begins at the lateral side of the neck of fibula, and runs through the fibularis longus and fibularis brevis muscles.

Thoracic

the middle section of your spine. It starts at the base of your neck and ends at the bottom of your ribs. It's the longest section of your spine. Your thoracic spine consists of 12 vertebrae, labeled T1 through T12.

Cervical

the neck region of your spinal column or backbone. It consists of your first seven bones (C1-C7).

reflex arc

the nerve pathway involved in a reflex action, including at its simplest a sensory nerve and a motor nerve with a synapse between.

cauda equina

the sack of nerve roots (nerves that leave the spinal cord between spaces in the bones of the spine to connect to other parts of the body) at the lower end of the spinal cord. These nerve roots provide the ability to move and feel sensation in the legs and the bladder.

spinocerebellar pathway

tract that travels from the spinal cord to the cerebellum, carrying proprioceptive and other information that the cerebellum utilizes to coordinate movement.

direct pathways

a circuit in the basal ganglia thought to be involved in the facilitation of movement.

anterior rami

One of the primary branches of a spinal nerve that supplies the lateral and ventral portions of the body wall, limbs, and perineum

inferior trunks

The anterior division of the lower trunk passes down on the medial side of the axillary artery, and forms the medial cord or fasciculus of the brachial plexus.

posterior (dorsal) root ganglion

a cluster of neurons (a ganglion) in a dorsal root of a spinal nerve.

anterior spinocerebellar tracts

conveys proprioceptive information from the body to the cerebellum.

obturator nerve

a branch of the lumbar plexus that arises from the second, third, and fourth lumbar nerves and that supplies the hip and knee joints, the adductor muscles of the thigh, and the skin

gray commissure

a bundle of nerve fibers that surrounds the central canal of the spinal cord and connects the anterior and dorsal horns of gray matter in each half of the cord

axillary nerve

also known as the circumflex nerve, is one of five peripheral nerves that run through your shoulder.

lateral spinothalamic tract

also known as the lateral spinothalamic fasciculus, is an ascending pathway located anterolaterally within the peripheral white matter of the spinal cord. It is primarily responsible for transmitting pain and temperature as well as coarse touch.

anterior spinothalamic tract

also known as the ventral spinothalamic fasciculus, is an ascending pathway located anteriorly within the spinal cord, primarily responsible for transmitting coarse touch and pressure

Reflexes

an action that is performed as a response to a stimulus and without conscious thought

Shingles

an acute, painful inflammation of the nerve ganglia, with a skin eruption often forming a girdle around the middle of the body. It is caused by the same virus as chickenpox.

Dermatomes

an area of skin in which sensory nerves derive from a single spinal nerve root

lumbar plexus

an essential collection of nerves that arise from mostly the lumbar spinal cord.

filum terminale

an extension of the pia mater that extends from the terminal end of the spinal cord to the tailbone.

Sacral

at the bottom of the spine and lies between the fifth segment of the lumbar spine (L5) and the coccyx (tailbone).

ipsilateral

belonging to or occurring on the same side of the body.

intercostal nerves

branches of the anterior divisions of the thoracic spinal nerves and innervate the thoracic and abdominal walls

anterior root

carries motor signals from the brain out to the muscles

posterior root

carries sensory signals from the skin to the brain

terminal branches

change electrical impulses or action potentials within a neuron into chemical messages in the form of neurotransmitters. These neurotransmitters are released from terminal branches into synapses to relay messages to other neurons or other types of cells like muscle cells.

Lumbar

consists of the five bones (vertebra) in your lower back

pyramidal pathway

consists of upper motor neurons extending from the cortex to the brainstem or spinal cord that make up two major pathways of voluntary movement: the corticospinal and corticobulbar tracts

posterior spinocerebellar tracts

conveys proprioceptive information from proprioceptors in the skeletal muscles and joints to the cerebellum.