Test 3- Ch. 12

second lumbar vertebrae

the spinal cord extends from the foramen magnum to the _____

segments of the spinal cord

• cervical (8)

• thoracic (12)

• lumbar (5)

• sacral (5)

spinal nerves

the spinal cord gives rise to 31 pairs of _____

not uniform in diameter through length

cervical enlargement

______ supplies upper limbs

lumbar enlargement

_____ supplies lower limbs

conus medullaris

• tampered inferior end of the spinal cord

• extends inferiorly to the second lumbar vertebrae

cauda equina

origins of the spinal nerves extending inferiorly from lumbosacral enlargement comes off the conus medullaris

same

a ganglion is a bunch of cell bodies together at axons moving in the _____ direction and boosts signals into the spinal cord. They decide if the signal goes to an interneuron or not.

important info to the brain

survival, food, and reproduction

interneuron

• middle man

• once activated by a ganglion, it sends the brain a message but tells the arm to move and stimulates it instead of waiting for the brain to decide what to do

Meninges of the Spinal Cord

Connective tissue membranes surrounding the spinal cord and brain

1. dura mater

2. arachnoid mater

3. pia mater

Spaces

1. epidural

2. subdural

3. subarachnoid

Dura mater (Thecal Sac)

• continuous with epineurium of the spinal nerves

• wrap that goes CNS to PNS

Arachnoid mater

• spiny layer

• thin and wispy

Pia mater

• bound tightly to the surface of the brain and spinal cord

• forms the filum terminale, which anchors spinal cord to coccyx and the denticulate ligaments that attach the spinal cord to dura mater

epidural

• location for epidural anesthesia

• layer of adipose tissue above and around dura mater

• contains blood vessels, areolar CT, and fat

subdural

• serous fluid

• under/below dura mater

subarachnoid

CSF (cerebrospinal fluid) and blood vessels with web-like strands of arachnoid tissue

anterior median fissue and posterior median sulcus

deep clefts partially separating left and right halves of the spinal cord

white mater

• myelinated axons forming tracts

• three columns (funiculi): ventral, dorsal, lateral

  • each of these divided into tracts (fasciculi; pathways)

gray matter

• neuron cell bodies, dendrites, axons

• Horns (multipolar neurons)

  • posterior (dorsal) horn

  • anterior (ventral) horn

  • lateral horn (associated with ANS)

posterior (dorsal) horn

contains neurons that receive information from the dorsal root neurons

anterior (ventral) horn

contains cell bodies of multipolar neurons that innervate skeletal muscle

lateral horn

cell bodies of multipolar neurons of the autonomic nervous system

commissures

connections between left and right halves

• gray with central canal in the center

• white

roots

spinal nerves that arise as rootlets then combine to form roots

dorsal root

the _____ is sensory

has a ganglion

ventral root

the _____ is motor

laterally

the dorsal and ventral roots merge _____ to form a spinal nerve

ascending and descending nerve tracts

• certain spots in the spinal cord consists of ________

• ascending is afferent or sensory infromation that goes up to the brain

• descending is efferent or motor information being sent to the PNS

Dorsal Root Ganglion

• collections of cell bodies of pseudo-unipolar sensory neurons forming dorsal roots

• motor neuron cell bodies are in anterior and lateral horns of spinal cord gray mater

somatic

multipolar ______ mtor neurons are located in the anterior (motor) horn

autonomic

_____ neurons are located in the lateral horn

Axons of motor neurons form ventral roots and pass into spinal nerves

Reflex

• self-preservation

• autonomic response to a stimulus that occurs without conscious thought; homeostasis

Reflex Arc

neural pathway that controls a reflex; sometimes involves an interneuron

components of a reflex arc

Sensory receptor→ sensory neurpne → interneuron → motor neuron → effector organ (muscle)

reflexes based on number of synapses

1. monosynaptic reflexes

2. polysynaptic reflexes

reflexes based on development

1. innate reflexes

2. learned reflexes

reflexes based on effector type

1. somatic reflexes

2. autonomic (visceral) reflexes

reflexes based on location of integration center

1. cranial reflexes- brain

2. spinal reflexes- spinal cord

monosynaptic reflex

no interneurons

polysynaptic reflex

multiple synapses with interneurons

innate reflex

• part of normal development

• ex: pulling foot back when stepping on lego

learned reflex

• develop as activities are repeated

• ex: athlete catching a ball coming at its face

somatic reflexes

____ have an effector type of skeletal muscle

autonomic (visceral) reflexes

____ have an effector type of smooth muscle, cardiac muscle, and glands

Reflex Arc Steps

1. a sensory receptor detects a sstimulus, generating action potentials

2. a sensory neuron conducts action potentials through a nerve and dorsal root to the spinal cord

3. in the spinal cord, the action potential is carried to the integra- ion (integration) center, which can involve an interneuron. (Simple reflexes do NOT involve an interneuron)

4. the interneuron synapses with the motor neuron

5. the motor neuron axon conducts action potentials through the ventral root and spinal nerve to an effector organ

Example of Reflex Arc

1. you felt the mosquito bite

2. action potential happens

3. sensory receptor sends AP down the dorsal root

4. into ganglion projecting into the spinal cord

5. brain says ow, smack it

6. motor signal goes down spinal cord

7. out the ventral root it goes

8. you swing at the mosquito

muscle spindle

specialized muscle cells that respond to a stretch (stretch reflex)

Stretch Reflex Information (monosynaptic reflex)

• muscles contract in response to a stretching force applied to them.

• (UNIQUE because no interneurons)

• muscle spindle: specialized muscle cells that respond to stretch

• innervated by specific motor neurons: gamma motor neurons (small diameter neurons) control sensitivity of muscle spindles

• sensory neurons innervate the noncontractile centers of the muscle spindle cells

• these sensory neurons synapse with motor neurons of the spinal cord called alpha motor neurons which cause the muscle to contract

gamma motor neurons

small diameter neurons that control the sensitivity of muscle spindles

alpha motor neurons

motor neurons of the spinal cord that cause the muscle to contract

Example of Stretch Reflex

1. when the patellar ligament is tapped, the tendons and muscles of the quadriceps femoris muscle group stretch. Muscle spindle receptors within the muscle stretch, which activates the stretch reflex

2. axons of these sensory neurons extend to the spinal cord

3. in the spinal cord, the sensory neurons synapse directly with the alpha motor neurons

4. alpha motor neurons then stimulate the muscle in which the muscle spindle is embedded

5. the same muscle that was stretched not contracts in response to the action potentials stimulated by the alpha motor neurons

6. gamma motor neurons, contract the muscle spindles to allow them to detect further stretching

Teacher Example of a Stretch Reflex

at the doctor’s, they do a patellar test w the hammer. They hit the patellar tendon, reflex causes leg to move to protect the leg muscles. The tendon goes in, pulling the muscle down with it, so response is to pop out the leg so the leg muscles don’t get damaged.

-have spindles wrapped around muscles (muscle spindle fibers) with neurons that can detect movement (sensory neurons)

-tap patellar, sensory neurons alert SC, 1 neuron goes to brain and other connects to Alpha Motor Neuron to cause contraction

Golgi Tendon Reflex

• prevents contracting muscles from applying excessive tension to tendons

• monosynpatic reflex

• contains a golgi tendon organ

Golgi tendon organ

• encapsulated nerve endings that have at their ends numerous terminal branches with small swellings associated with bundles of collagen fibers in the tendon. Located in tendon near muscle

• prevent damage to tendons that could be caused by excessive tension

• produces sudden relaxation of the muscles

Example of a golgi tendon reflex

weight lifter suddenly drops heavy weight. Sudden movement of “clean and jerk” put so musch tension on tendons like achilles, they could break

Teacher example of Golgi Tendon Reflex

a weightlifter is lifting and if the weight becomes too much, the body sends the brain a signal, brain says no and hands open to drop the weight or knee goes down due to inhibitory neuron stopping AP from occuring and Alpha Moton Neuron is affected and stops action potential so muscle relaxes

Components of the Golgi Tendon Reflex

golgi tendon organ → sensory neuron → inhibitory interneurons inhibit alpha motor neuron → muscle relaxes

Explained Steps of Golgi Tendon Reflex

1. as a muscle contracts, the attached tendons stretch, resulting in increased tension in the tendons

2. the increased tension stimulates action potentials in the sensory neurons from the Golgi tendon organs. The sensory neurons pass through the dorsal root to the spinal cord and enter the dorsal gray horn

3. at the integration center in the dorsal horn, the sensory neurons branch and synapse with inhibitory interneurons

4. the interneurons synapse with alpha motor neurons that innervate the muscle to which the Golgi tendon organ is attached

5. inhibition of the alpha motor neurons result in relaxation of the muscle and a reduction in tension in the tendon

withdrawl reflex

function is to remove a body limb or other part from a painful stimulus

reciprocal innervation

• causes relaxation of extensor muscle when flexor muscle contracts

• involved in stretch and withdraw reflexes

• where 1 muscle contracts, and 1 reflexes (bicep/tricep)

crossed extensor reflex

when a withdrawal reflex is initiated in one lower limb, the ______ causes extension of opposite lower limb

1. pain receptors detect a painful stimulus

2. sensory neurons conduct action potentials to the spinal cord

3. sensory neurons synapse with excitatory interneurons in the spinal cord that synapse with alpha motor neurons

4. excitation of the alpha motor neurons results in contraction of the flexor muscles

5. withdrawal of the limb from the painful stimulus

withdrawal reflex with reciprocal innervation

1. during the withdarawal reflex, sensory neurons conduct action potentials from pain receptors to the spinal cord

2. at the integration center sensory neurons synapse with excitatory interneurons, which are part of the withdrawal reflex

3. collateral axons of sensory neurons that carry action potential from pain receptors synapse with inhibitory interneurons in the dorsal horn of the SC

4. the inhibitory interneurons synapse with and inhibit alpha motor neurons of extensor (antagonist) muscles. When the withdrawal reflex is initiated, flexor muscles contract and _________ causes the extensor muscles to relax. This reduces the resistance to movement that the extensor muscles would otherwise generate

Withdrawal Reflex with Crossed Extensor Reflex

1. during the withdrawal reflex, sensory neurons conduct action potentials from pain receptors to spinal cord

2. at the integration center, sensory neurons synapse with excitatory interneurons, which are part of the withdrawal reflex

3. collateral axons from the sensory synapse with excitatory interneurons that extend through the white commisure to the opposite side of the spinal cord

4. these interneurons synapse with alpha motor neurons that innervate extensor muscles in the opposite side of the body. When a withdrawal reflexis initiated in one lower limb, the _______ causes extension of the opposite lower limb

interactions with spinal cord reflexes

• sensory information goes to the brain ex: pain

• descending tracts from the brain carry info to the reflexes

• neurotransmitters produce either EPSP or IPSPs modifying the reflex