Chapter 13: The Spinal Cord, Spinal Nerves, and Somatic Reflexes

In the spinal cord, the somas of the lower motor neurons are found in

Anterior Horns

Spinoreticular tract

Ascending Tract Anterolateral System carries pain signals resulting from tissue injury decussate Create reticular formation in the medulla and pons

Spinothalamic

Ascending Tract Anterolateraly System carries signals for pain, temp, pressure, tickle, itch and light or crude touch Decussate at second order neurons

Gracile Fasciculus

Ascending Tract carries signals from the midthoracic and lower parts of the body, below T6 Carry signals for vibration, viceral pain, deep and discriminative touch, proprioception

Posterior and Anterior Spinocerebellar

Ascending Tract carry proprioceptive signals from the limbs and trunk to the cerebellum at the rear of the brain Decussate

Cuneate Fasciculus

Ascending Tract occupies the lateral portion of the posterior column and forces the gracile fasciculus medially. carries same type of sensory signals as the gracile. T6 and up. Decussate at the medial lemniscus

Which plexus gives rise to the Axillary nerve?

Brachial Plexus

Which plexus gives rise to the Radial nerve?

Brachial Plexus

The brachial Plexus gives rise to all of the following nerves except a. axillary nerve b. radial nerve c. obturator nerve d. median nerve e. ulnar nerve

C. Obturator Nerve

Which plexus gives rise to the Phrenic nerve?

Cervical Plexus

Name the four major regions and two enlargements of the spinal cord

Cervical, Thoracic, lumbar, and Sacral regions Cervical Enlargement and Lumbar Enlargement

In the ____reflex, contraction of flexor muscles in one limb is accompanied by the contraction of extensor muscles in the contralateral limb

Crossed Extension

Decribe the distal end of the spinal cord and the contents of the vertebral canal from level L2 to S5

The cord tapers to a point called the medullary cone. Arising from the lumbar enlargement and medullary cone is a bundle of nerve roots that occupy the vertebral canal from L2 to S5. This bundle is the Cauda Equina.

The sciatic nerve is composite of two nerves, ______ and ______

Tibial, Common Fibular

At teh inferior end, the adult spinal cord ends before the vertebral column does

True

Each spinal cord segment has only one pair of spinal nerves

True

The anterior and posterior horns of the spinal cord are composed of gray matter

True

The corticospinal tracts carry motor signals down the spinal cord

True

The tendon reflex acts to inhibit muscle contraction

True

Thre crossing of a nerve fiber or tract from the right side of the CS to the left or vice cersa is called

decussation

Brachial Plexus

near the shoulder

Lumbar plexus

the lower back

The outermost connective tissue wrapping of a nerve is called the

Epineurium

Somatic reflexes are those that do not involve the brain

False

Some spinal nerves are sensory and others are motor

False

The dermatomes are nonoverlapping regions of skin innervated by different spinal nerves

False

The dura mater adheres tightly to the bone of the vertebral canal

False

The gracile fasciculus is a descending spinal tract

False

Nerve fibers that adjust the tension in a muscle spindle are called

Gamma Motor Neurons

Outside the CNS, the somas of neurons are clustered in swellings called ______

Ganglia

Name five structural components of a typical somatic reflex arc.

I. somatic receptors II. Afferent nerve fibers III. Integrating Center IV. Efferent Nerve fibers V. Effectors

Modified muscle fibers serving primarily to detect strech are called______

Intrafusal Fibers

Which plexus gives rise to the Ilioinguinal nerve?

Lumbar Plexus

Which plexus gives rise to the Obturator nerve?

Lumbar Plexus

Which plexus gives rise to the Sciatic nerve?

Lumbar Plexus

Sacral plexus

immediately inferior

Give an anatomical explanation of why a stroke in the right cerebral hemisphere can paralyze the limbs of the left side of the body

Decussation: meaning that they cross over from the left side of the body to the right side or vice versa. As a result the left side of the brain receives sensory information from the right side of the body and sends motor commands to that side, while the right side of the brain senses and controls the left side of the body

Tectospinal Tract

Descending Tract begins in midbrain - tectum involved in reflex turning of head

Corticospinal Tract

Descending Tract carry motor signals from the cerebral cortex for precise, finely coordinated limb movement. Decussate

Lateral and Medial Reticulospinal

Descending Tract originate in the reticular formation of the brainstem. Control muscles of the upper and lower limbs, maintain psture and balance

Lateral and Medial Vestibulospinal

Descending Tract Begin in brainstem, vestibular nuclei, which receives impulses for balance from the inner ear. Important in reponding to body tilt.

Which of these is not a region of the spinal cord? a. cervical b. thoracic c. pelvic d. lumbar e. sacral

Pelvic

The _____ nerves arise from the cervical plexus and innervate the diaphragm

Phrenic

The _____ganglion contains the somas of neurons that carry sensory signals to the spinal cord

Posterior root

Distal to the intervertebral foramen, a spinal nerve branches into an anterior and posterior ____

Ramus

A strech reflex requires the action of _______ to prevent an atagonistic muslce from interfering with the agonist

Reciprical inhibition

Which plexus gives rise to the Pudendal nerve?

Sacral and Coccygeal Plexuses

Anterior Root (Ventral)

Six to eight nerve rootlets emerge from the anterior survace and converge Motor

Posterior Root (dorsal)

Six to eight rootlets emerg from the posterior surface adn converge Sensory

The Cerebellum receives feedback from the muscles and joints by way of the ____ tracts of the spinal cord

Spinorcerebellar

A patient has a gunshot wound that caused a bone fragement to nick the spinal cord. The patient now feels no pain or temperature sensations from that level of the body down. Most likely the ______ was damaged

Spinothalamic

Below L2, the vertebral canal is occupied by a bundle of spinal nerve roots called

The Cauda Equina

Intrafusal Fiber

The muscle fibers within the spindle

Cervical Plexus

The neck

Coccygeal Plexus

adjacent to the lower sacrum and coccyx

Anulospiral Ending

after entering the muscle spindle, the fiber divides into two flat, ribbonlike branches that wind themselves in rings or spirals about the intrafusal muscle fibers.

The nonvisual awareness of the body's position and movements is called____

proprioception

Gamma Motor Neuron

relatively small-diameter, slow motor nerve fibers

All Somatic reflexes share all of the following properties except: a. they are quick b. they are monosynaptic c. they require stimultion d. they are involuntary e. they are sterotyped

they are monosynatpic