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Anatomy and Physiology > Chapter 13 Nervous System > Flashcards

Chapter 13 Nervous System Flashcards

1
Q

Central nervous system

A

Brain and spinal cord
Processing centers

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2
Q

Peripheral nervous system

A

Cranial nerves and spinal nerves
Sensory input and motor response pathways

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3
Q

Reflexes

A

Quick, automatic nerve responses triggered by specific stimuli

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4
Q

Spinal reflexes

A

Controlled by the spinal cord alone without input from the brain
Example: dropping a hot pan. Reflex causes release of the pan before the information reaches the brain and the pain is perceived

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5
Q

Sensory Receptors

A

Cranial Nerves: In from the PNS sensory to brain out to Cranial motor Nerves
Spinal Nerves: In from the PNS and out to the Spinal Nerves
Effectors are
Muscles, Glands and Adipose Tissue

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6
Q

Spinal cord

A

Housed membranes (meninges) and vertebral column

Carries sensory and motor information between brain and out
Gives rise to spinal nerves

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7
Q

Gross anatomy of the spinal cord

A

About 18 in. (45 cm) long, 1/2 in. (14 mm) wide

brain only to vertebrae L1 and L2 (stops lengthening around age 4, but the vertebral column still grows)

4 regions (cervical, thoracic, lumbar, sacral)

Has bilateral symmetry

31 segments; give rise to spinal nerves

Grooves divide spinal cord into left and right
Posterior median sulcus—posterior side
Anterior median fissure—deeper, anterior groove

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8
Q

Central canal contains cerebrospinal fluid (CSF)

A
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9
Q

Enlargements of the spinal cord

A

Areas of the spinal cord that supply the limbs have more gray matter and are visibly wider.

Cervical enlargement
Supplies shoulder and upper limb
Lumbosacral enlargement
Supplies pelvis and lower limb

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10
Q

Distal end of the spinal cord

A

Conus medullaris
Tapered, conical end of cord below lumbar enlargement
Cauda equina
Nerve roots extending below conus medullaris
Looks like a horse’s tail, hence the name
Filum terminale
Thin thread of fibrous tissue at end of conus medullaris
Attaches to coccygeal ligament

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11
Q

Spinal roots and ganglia

A

Two branches form spinal nerves
Anterior root (ventral root)—axons of motor neurons
Posterior root (dorsal root )—axons of sensory
neurons
Spinal nerve roots divide into rootlets before entering or leaving the spinal cord

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12
Q

Spinal ganglia (also called dorsal root ganglia)

A

Contain cell bodies of sensory neurons that form the posterior root
Located between pedicles of adjacent vertebrae

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13
Q

Spinal nerves

A

Formed by union of posterior and anterior roots
Pairs—one from each side at each vertebral level
Each has a white ramus communicans and a gray ramus communicans that innervate glands and smooth muscle
Mixed nerves—contain both afferent (sensory) and efferent (motor) fibers
Each spinal nerve quickly divides into rami
Posterior ramus supplies skin/muscles of back
Anterior ramus supplies most of body wall, skin, limbs

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14
Q

Naming the spinal nerves:

A

Designated by vertebral region and number
C1 runs above first cervical vertebra
C8 below seventh cervical vertebra
All others named for vertebrae above
Example: T1 is below first thoracic vertebra

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15
Q

spinal meninges
Three specialized membranes surrounding spinal cord

A

Dura mater—outermost layer
Arachnoid mater—middle layer
Pia mater—innermost layer

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16
Q

Functions of the spinal meninges include:

Meningitis
Viral or bacterial infection of meninges

A

Protect spinal cord
Carry blood supply
Continuous with cranial meninges

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17
Q

The dura mater—outermost meningeal layer

A

Tough with dense collagen fibers
Continuous with cranial dura mater and fuses with periosteum of occipital bone
Distal end tapers to dense cord of collagen fibers; joins filum terminale in coccygeal ligament

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18
Q

Epidural space

A

Between vertebrae and dura mater (superficial to dura mater)
Contains loose connective and adipose tissue

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19
Q

Subdural space = potential space deep to dura mater

A
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20
Q

arachnoid mater—middle meningeal layer

A

Two components
Arachnoid membrane—weblike layer of simple squamous epithelia
Arachnoid trabeculae—network of collagen/elastic fibers between arachnoid membrane

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21
Q

Subarachnoid space

A

Space with arachnoid trabeculae, between arachnoid mater and pia mater
Filled with cerebrospinal fluid (CSF) that carries dissolved gases, nutrients, wastes

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22
Q

Lumbar puncture or spinal tap withdraws CSF from subarachnoid space

A
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23
Q

pia mater—innermost meningeal layer

A

Is a mesh of collagen and elastic fibers
Firmly attached to underlying neural structures it surrounds
Blood vessels for spinal cord are on surface of the pia mater, within subarachnoid space

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24
Q

Paired denticulate ligaments

A

Anchor pia mater to dura mater
Prevent lateral movement of spinal cord

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25
Gray matter—cell bodies of neurons, neuroglia, and unmyelinated axons
Functional organization of gray matter Masses of gray matter within CNS are called nuclei and are organized into regions called horns Posterior horns—somatic and visceral sensory nuclei (incoming information from receptors) Anterior horns—somatic motor nuclei (outgoing information to effectors) Lateral horns—thoracic and lumbar segments; visceral motor nuclei
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Gray Matter continued
Gray commissures Narrow bands of gray matter around central canal Axons cross here to the other side of spinal cord Sensory or motor nucleus location within gray matter determines which body part it controls
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WHITE MATTER - FUNCTION
Three columns (regions) Posterior white columns—between posterior horns and posterior median sulcus Anterior white columns—between anterior horns and anterior median fissure Anterior white commissure—where axons cross from one side of spinal cord to the other Lateral white columns—on each side of spinal cord, between anterior and posterior columns
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White Matter
Tract—bundle of axons in CNS Relay same type of information in same direction Ascending tracts—sensory information up toward the brain Descending tracts—motor commands down to the spinal cord
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Three connective tissue layers surround spinal nerves
Epineurium—outermost; network of collagen fibers Perineurium—middle layer; separates nerve into fascicles (axon bundles) Endoneurium—innermost; surrounds individual axons
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Spinal nerves
Pair of spinal nerves emerges laterally from each spinal cord segment Form by junction of anterior and posterior roots All spinal nerves are mixed nerves
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Peripheral nerves
Form from branching and re-sorting of spinal nerves. All are mixed nerves (sensory and motor) Same connective tissue layers as spinal nerves (continuous with each other)
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Peripheral distribution of spinal nerves Shingles—rash/symptoms occur along dermatomes
Sensory nerves In addition to motor impulses: Posterior, anterior, and white rami also carry sensory information Dermatome—specific bilateral region of skin supplied by a single pair of spinal nerves Peripheral neuropathies—regional losses of neural function that affect dermatomes, often from nerve trauma, compression, various illnesses
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Nerve plexuses
Complex, interwoven networks of nerve fibers Formed from blended fibers of anterior rami of adjacent spinal nerves Allows multiple spinal nerves to supply the same structures
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Four major nerve plexuses
Cervical plexus Brachial plexus Lumbar plexus Sacral plexus
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The cervical plexus Includes anterior rami of spinal nerves C1–C5 Innervates scalp behind ear, neck, and diaphragm
Major cervical plexus nerves Phrenic nerve—from C3–C5; controls diaphragm Lesser occipital nerve Great auricular nerve Transverse cervical nerve Supraclavicular nerves
36
brachial plexus
Innervates pectoral girdle, upper back, upper limb Anterior rami of C5–T1 These rami first form three large trunks (superior, middle, and inferior trunks) Trunks re-sort their axons to form three cords (lateral, posterior, and medial cords) Cords are named by their positions relative to the axillary artery Most nerves of brachial plexus come off the cords; a few originate at the trunks
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Major brachial plexus nerves
Musculocutaneous nerve (lateral cord) Median nerve (lateral and medial cords) Ulnar nerve (medial cord) Axillary nerve (posterior cord) Radial nerve (posterior cord)
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The hand is innervated by the ulnar, median, and radial nerves
Median nerve passes through the small carpal tunnel on the anterior wrist, along with several muscle tendons Carpal tunnel syndrome—compression of median nerve, usually when adjacent tendons are swollen (repetitive stress) Causes change or loss of sensation in the areas supplied by the median nerve
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lumbar plexus
Includes anterior rami of spinal nerves T12–L4 Major nerves Iliohypogastric nerve Ilio-inguinal nerve Femoral nerve Obturator nerve Genitofemoral nerve Lateral femoral cutaneous nerve
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sacral plexus
Includes anterior rami of spinal nerves L4–S4 Major nerves Sciatic nerve Superior and inferior gluteal nerves Pudendal nerve Two branches of the sciatic nerve Fibular nerve (common fibular nerve) Tibial nerve
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Sensory innervation of foot Mapping touch/pain perception and checking muscle function can determine damage to specific peripheral nerves
Branches from these peripheral nerves supply the foot/ankle Saphenous nerve Sural nerve Fibular nerve Tibial nerve
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Functional organization of neurons
Sensory neurons About 10 million; Motor neurons About 1/2 million; Interneurons About 20 billion; Interpret, plan, and coordinate signals coming in and out
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Neuronal pools
Interneurons organized into functional groups of interconnected neurons Each has limited input sources and output destinations May stimulate or depress parts of brain or spinal cord Five patterns of neural circuits in neuronal pools Divergence Convergence Serial processing Parallel processing Reverberation
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Patterns of neural circuits in neuronal pools
Divergence—spreads information from one neuron or neuronal pool to many Especially common in sensory pathways Convergence—several neurons synapse on a single neuron Example: subconscious and conscious control of the diaphragm in breathing—two neuronal pools synapse with the same motor neurons
45
Patterns of neural circuits in neuronal pools (continued)
Serial processing—information moves along a single path, sequentially from one neuron or neuronal pool to the next Example: pain signals pass sequentially through two neuronal pools to reach conscious brain Parallel processing—several neurons/neuronal pools process the same information at the same time Example: step on a bee. Signals spread through several neuronal pools so you can shift your weight, lift your foot, yell in pain at about the same time
46
Patterns of neural circuits in neuronal pools (continued)
Reverberation—collateral branches of neurons extend back and continue stimulating presynaptic neurons Forms positive feedback loop; continues until synaptic fatigue or inhibition occurs Examples: may maintain consciousness, breathing, muscle coordination
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Neural reflexes
Rapid, automatic responses to specific stimuli Basic building blocks of neural function A specific reflex produces the same motor response each time
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reflex arc
Sensory receptor Sensory neuron Information processing in CNS Motor neuron Effector
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Events in a spinal reflex arc
Step 1: Stimulus activates a receptor (review receptor types, Chapter 12) Step 2: With enough stimulation, action potential is generated in sensory neuron. Axon enters spinal cord via posterior root Step 3: Information processing in spinal cord usually occurs at one or more interneurons Step 4: Interneurons stimulate action potentials in motor neuron; its axon leaves via anterior root Step 5: Motor neuron stimulates effector (muscle/gland)
50
Four types of classification of reflexes
Development Motor response Complexity of neural circuit Site of information processing
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Development of reflexes—innate or acquired
Innate reflexes Basic neural reflexes formed before birth Genetically programmed (inborn) Examples: withdrawal, chewing, visual tracking Acquired reflexes Rapid, automatic learned motor patterns Repetition enhances them Examples: braking a car in emergency
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Motor response
Somatic reflexes Control skeletal muscle contractions Superficial reflexes—stimuli in skin/mucous membranes Stretch or deep tendon reflexes (such as patellar, or “knee-jerk,” reflex) Immediate—important in emergencies (slipping, cutting finger) Visceral reflexes (autonomic reflexes) Control other effectors Smooth muscle, cardiac muscle, or glands
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Monosynaptic reflex Single synapse—simplest reflex arc Sensory neuron synapses directly with motor neuron Fast response Polysynaptic reflex At least one interneuron between sensory neuron and motor neuron; most common Slower response; delay increase with number of synapses involved (longer path = longer delay) Intersegmental reflex arcs —many spinal cord segments interact; produce variable response
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Muscle spindle structure (continued)
Dendrites of sensory neurons wind around central region of intrafusal fibers. Sensory neuron axon enters CNS in posterior root Sensory neurons synapse in spinal cord directly with motor neurons Gamma efferents complete reflex arc by synapsing back at the intrafusal fibers Muscle contracts back to its resting length
55
Postural reflexes ed
Include both stretch reflexes (monosynaptic) and also complex polysynaptic reflexes Maintain normal upright posture Often involve multiple muscle groups (e.g., back and abdominal muscles) Maintain firm muscle tone Extremely sensitive receptors allow constant fine adjustments to be made as need
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Polysynaptic reflexes
More complicated than monosynaptic reflexes Interneurons can control multiple muscle groups Produce either EPSPs or IPSPs, stimulating some muscles and inhibiting others. Examples Tendon reflex Withdrawal reflexes Crossed-extensor reflexes
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tendon reflex
Prevents skeletal muscles from: Developing too much tension Tearing or breaking tendons Sensory receptors are Golgi tendon organs Stimulated when collagen fibers are overstretched Stimulate inhibitory interneurons in spinal cord More muscle tension leads to more muscle inhibition
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Withdrawal reflexes s
Move body part away from stimulus (pain or pressure) Example: flexor reflex in limbs; pulls hand from hot pan Strength and extent of response depends on intensity and location of stimulu
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Reciprocal inhibition
For flexor reflex to work, stretch reflex of antagonistic (extensor) muscles must be inhibited (reciprocal inhibition) by interneurons in spinal cord. When flexors contract, extensors relax When extensors contract, flexors relax
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Reflex arcs
Ipsilateral reflex arcs Occur on same side of body as stimulus Stretch, tendon, and withdrawal reflexes Crossed extensor reflexes involve contralateral reflex arcs Occur on side opposite stimulus
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Crossed extensor reflexes
Coordinated with flexor reflex Step on something sharp; before flexor reflex can lift injured foot, crossed extensor reflex straightens opposite limb to receive body weight, then flexor reflex can occur Maintained by reverberating circuits
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Five general characteristics of polysynaptic reflexes
Involve pools of interneurons May cause excitation or inhibition Involve more than one spinal segment Can activate muscles in multiple areas Involve reciprocal inhibition Coordinates contractions and reduces resistance Have reverberating circuits Prolongs reflexive motor response Several reflexes may cooperate To produce coordinated, controlled response
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Voluntary movements and reflex motor patterns
Spinal reflexes produce characteristic response for a given stimulus. Brain can also activate these same motor patterns through descending pathways Can facilitate, inhibit, or “fine-tune” the established motor response Examples: walking, running, jumping
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Reinforcement of spinal reflexes
Higher centers can adjust sensitivity of reflexes by stimulating excitatory or inhibitory interneurons in brainstem or spinal cord When excitatory synapses are chronically stimulated, postsynaptic neurons can be in general facilitation This reinforcement enhances spinal reflexes
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Inhibition of spinal reflexes
Higher centers inhibit spinal reflexes by: Stimulating inhibitory neurons Creating IPSPs at reflex motor neurons Suppressing postsynaptic neurons, thus inhibiting the reflex
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Plantar reflex s
Normal in adults Stroke lateral sole, causes reflexive toe-curling
67
The Babinski reflex
Normal in infants May indicate CNS damage in adults

Anatomy and Physiology (18 decks)

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