Anatomy Ch. 14 Spinal Cord and Spinal Nerves

Naming of spinal nerves

C1-C8, T1-T12, L1-L5, S1-S5, 1 Coccygeal

Gray matter

Centrally located Resembles a letter H or a butterfly Subdivided into anterior horns, lateral horn, posterior horns, and they gray commissure.

Subarachnoid Space

Cerebral Spinal Fluid (CSF)

Patellar (knee-jerk) Reflex

Clinically important reflexes. Spinal nerve segments tested: L2-L4 Normal Action of Effector: Extends knee when patellar ligament is tapped.

Dorsal-Column/Medial-Lemniscal System

Decussates in medulla oblongata - Discriminative touch - Proprioception - Pressure - Vibration - Visceral pain

Peripheral Nerve Structure

Deep to superficial: endoneurium, perineurium, epineurium

Thoracic

Lies inferior to the cervical part

Descending Tracts

more medial and anterior

Lower Motor Neurons

spinal cord to periphery

Anterior Spinocerebellar

feedback from receptors (proprioception)

Posterior Spinocerebellar

feedback from receptors (proprioception)

Somatic sensory nuclei

Receive information from sensory receptors, such as pain or pressure receptors in the skin.

Lateral Vestibulospinal

balance and posture

3 Neuron Circuits

-First order detects stimulus -Second order relays to brainstem (thalamus) -Third order takes signal to sensory cortex (cerebrum)

Reflex Testing in a Clinical Setting

-Testing reflexes can be used to test specific muscle groups and specific spinal nerves or segments of the spinal cord. -Hypoactive reflex: reflex response is diminished or absent May indicate damage to a segment of the sc May indicate muscle disease or damage to a neuromuscular junction -Hyperactive reflex: Reflex response is abnormally strong May indicate damage somewhere in the brain or spinal cord

Ascending Tract Types

2 neurons Gracile Fasciculus, Cunate Fasciculus, Spinothalamic, Spinoreticular, Posterior Spinocerebellar, Anterior Spinocerebellar

Descending Tract Types

2 neurons Lateral and Anterior Corticospinal, Tectospinal, Lateral and Medial Reticulospinal, Lateral and Medial Vestibulospinal

Spinothalamic Tracts

3 neurons Decussates in spinal cord - Pain - Temperature - Touch - Pressure - Tickle and itch

Nerve Plexus

A network of interweaving anterior rami of spinal nerves. The anterior rami of most spinal nerves form nerve plexuses on both the right and left sides of the body These nerve plexuses then split into multiple "named" nerves that innervate various body structures. The principal plexuses are the cervical plexuses, brachial plexuses, and lumbar plexuses, and sacral plexuses.

Ipsilateral

A reflex arch may be ipsilateral or contralateral. When both the receptor and effector organs of the flex are on the same side of the spinal cord. Ex. left arm contracts to pull your left hand away from a hot object.

Contralateral

A reflex arch may be ipsilateral or contralateral. When the sensory impulses from a receptor organ cross over through the spinal cord to activate effector organs in the opposite limb. Ex. A contralateral effect occurs when you step on a sharp object with your left foot and then contract the muscles in your right leg to maintain balance as you withdraw your left leg from the damaging object.

Lumbar Part

A shorter segment of the spinal cord

Dermatome

A specific segment of the skin supplied by a single spinal nerve. All spinal nerves except C1 innervate a segment if skin, and so each of these nerves is associated with a dermatome. Clinically important because they can indicate potential damage to one or more spinal nerves.

Anterior Ramus

After leaving the intervertebral foramen, a typical spinal nerve almost immediately splits into branches, termed rami. The larger of the two main branches. This splits into multiple other branches, which innervate the anterior and lateral portions of the trunk, the upper limbs, and the lower limbs. Many of the anterior rami go on to form nerve plexuses. Additional rami, called the rami communicantes, are also associated with spinal nerves. These rami contain axons associated with the autonomic nervous system. Each set of rami eommunicantes extends between the spinal nerve and a ball-like structure called the sympathetic trunk ganglion. These ganglia are interconnected and form a beaded necklace-like structure called the sympathetic trunk.

Posterior Ramus

After leaving the intervertebral foramen, a typical spinal nerve almost immediately splits into branches, termed rami. The smaller of the two main branches. Innervates the deep muscle of the back and the skin of the back.

Plantar Reflex

Clinically important reflexes. Spinal nerve segments tested: L5, S1 Normal Action of Effector: Plantar flexes foot; flexes toes when plantar side of foot is briskly stroked.

Ankle (Archilles) Reflex

Clinically important reflexes. Spinal nerve segments tested: S1, S2 Normal Action of Effector: Plantar flexes ankle when calcaneal tendon is tapped.

Spinal nerves

Connect the CNS to muscles, glands, and receptors. Contains three types of successive CT wrappings: endoneurium, perineurium, and epineurium. Motor axons in a spinal nerve originate from the spinalcord. Contains both motor axons (from the anterior root) and sensory axons (from the posterior root).

Meninges

Dura Mater, Arachnoid Mater, Pia Mater

Lumbosacral enlargement

Extends through the lumbar and sacral parts of the spinal cord and innervates the lower limbs

Lateral horns

Found in the T1-L2 parts of the spinal cord Contain cell bodies of autonomic motor neurons, which innervate cardiac muscle, smooth muscle, and glands.

Polysynaptic Reflexes

Have more complex neural pathways that exhibit a number of synapses involving interneurons within this reflex arc. Because this reflex arc has more components, there is a more prolonged delay between stimulus and response. Ex. The crossed-extensor reflex, which is the reflex that supports postural muscle activity when you withdraw your foot from a painful stimulus. Enables you to balance for example.

Motor nuclei

In the anterior and lateral horns contain motor neuron cell bodies that send nerve impulses to muscles and glands.

Somatic motor nuclei

In the anterior horns innervate skeletal muscle

Autonomic motor nuclei

In the lateral horns innervate smooth muscle, cardiac muscle, and glands.

Cauda equina

Inferior to conus medullaris a group of axons project inferiorly from the spinal cord

Anterior horns

Left and right anterior masses Primarily houses the cell bodies of somatic motor neurons, which innervate skeletal muscle.

Posterior horns

Left and right posterior masses of gray matter. The axons of sensory neurons and the cell bodies of interneurons are located in this region.

Epidural Space

Lies between the dura mater and the periosteum covering the inner walls of the vertebra, and houses areolar CT, blood vessels, and adipose CT. * Epidural anesthetic is given here.

Sacral Part

Lies inferior to the lumbar part

Cervical enlargement

Located in the inferior cervical part of the spinal cord Contains neurons that innervate the upper limbs

Coccygeal Part

Most inferior "tip" of the spinal cord One pair of coccygeal spinal nerves arises from this region

Spinal Cord Meninges

Protects and encapsulates the spinal cord Continuous with the cranial meninges Spaces between some of the meninges have clinical significance. Outermost to innermost: vertebra, epidural space, dura mater, subdural space, arachoid mater, subarachnoid space, and pia mater.

Visceral sensory nuclei

Receives information from sensory receptors such as the stretch receptors in the smooth muscle walls of viscera.

Stretch Reflex

Spinal Reflex A monosynaptic reflex that monitors and regulates skeletal muscle length. Stretch in a muscle is monitored by stretch receptors called muscle spindles. When a stimulus results in the stretching of a muscle, that muscle reflexively contracts. The patellar reflex is an example. The stimulus stretches the quadraceps femoris muscle and initiates contraction of the muscle, thereby extending the knee joint.

Withdrawal (Flexor) Reflex

Spinal Reflex A polysynaptic reflex arc that is initiated by a painful stimulus, such as touching something very hot. Stimulation of a receptor organ causes the transmission of sensory information to the spinal cord. Interneurons receive the sensory information and stimulate motor neurons to direct flexor muscles to contract in response. Simultaneously, antagonistic (extensor) muscles are inhibited so that the traumatized body part may be quickly withdrawn from the harmful situation.

Cervical

Supermost region of spinal cord Continuous with the medulla oblongata

Tracts

The axons within each white matter funiculs are organized into smaller structural units called tracts or fasciculi. Individual tracts conduct either sensory impulses or motor commands only. Each funiculus region contains both ascending and descending tracts. Thus, each funiculus contains both motor and sensory axons.

Reflex arc

The neural wiring of a single reflex. Always begins at a receptor in the PNS, communicates with the CNS, and ends at a peripheral effector, such as a muscle or gland cell. Five steps: 1. Stimulus activates receptor. 2. Nerve impulse travels through sensory neuron to the CNS. 3. Information from nerve impulse is processed in the integration center by interneurons. 4. Motor neuron transmits nerve impulse to effector. 5. Effector (peripheral target organ) responds to nerve impulse from motor neuron.

Monosynaptic Reflexes

The simplest of all reflexes. Sensory axons synapse directly on the motor neurons, whose axons project to the effector. Interneurons are not involved in processing this reflex. Very minor synaptic delay is incurred in the single synapse of this reflex arc, resulting in a very prompt reflex response. Ex. The patellar (knee-jerk) reflex.

Anatomy of spinal cord

The spinal cord is partitioned into an inner gray matter region and an outer white matter region. The gray matter is dominated by dendrites and cell bodies of neurons and glial cells and unmyelinated axons, whereas the white matter is composed primarily of myelinated axons.

Medullary Cones

The tapering inferior end of the spinal cord Marks the official "end" of the spinal cord proper (usually at the level of the first lumbar vertebrae)

Funiculus

The white matter of the spinal cord is external to the gray matter. White matter on each side of the cord is partitioned into three regions, called funiculus.

Lateral and Medial Reticulospinal

balance and posture, regulation of awareness of pain

Upper Motor Neurons

brain to lower motor

Two enlargments of the spinal cord

cervical and lumbar

Medial Vestibulospinal

control of head position

Lateral and Anterior Corticospinal

fine control of limbs

Ascending Tracts

more lateral and posterior

Tectrospinal

reflexive head turning in response to visual and auditory stimuli

Cunate Fasciculus

sensation in limb and trunk, movement/position, deep discriminative touch, vibration, and visceral pain above T6

Gracile Fasciculus

sensation in limb and trunk, movement/position, deep discriminative touch, vibration, and visceral pain below T6

Spinothalamic

sensation of light, touch, tickle, itch, temperature, pain, and pressure

Spinoreticular

sensation of pain from tissue injury