Neuro

2636

Medical Vocabulary — Nervous System

Define the medical vocabulary components related to the nervous system.

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Word Roots & Meanings

Root / Prefix	Meaning	Example Term
neuro-	nerve	neuron, neuroglia
glia	glue	neuroglia (supporting cells)
axon	axis	axon (long conducting process)
af- / ferre	to / to carry	afferent (carries TO CNS)
ef- / ex-	from	efferent (carries FROM CNS)
syn-	together	synapse (junction between neurons)
saltare	to leap	saltatory propagation
meninx	membrane	meninges (coverings of CNS)
dura	hard	dura mater (tough outer meningeal layer)
pia	delicate	pia mater (innermost meningeal layer)
arachne	spider	arachnoid (web-like middle meningeal layer)
astro-	star	astrocyte (star-shaped glial cell)
oligo-	few	oligodendrocytes (fewer cell processes)
ganglio	knot	ganglion (cluster of neuron cell bodies)
hypo-	below	hypothalamus (below the thalamus)
inter-	between	interneurons (between other neurons)
cauda / equus	tail / horse	cauda equina (horse's tail — spinal nerve roots)
vagus	wandering	vagus nerve (N X — wide distribution)
vas	vessel	vasomotor center (controls vessel diameter)
meso-	middle	mesencephalon (midbrain)

2637

Two Anatomical Divisions & General Functions

Communicate the two anatomical divisions of the nervous system and their general functions.

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Two Anatomical Divisions

Division	Components	General Function
CNS	Brain + Spinal cord	Integrates and coordinates sensory data; transmits motor commands; seat of intelligence, memory, emotion
PNS	All neural tissue outside CNS	Connects CNS to body; carries sensory information in and motor commands out

Functional Divisions of the PNS

Division	Direction	Function
Afferent division	TO the CNS	Carries sensory information from receptors to CNS
Efferent division	FROM the CNS	Carries motor commands from CNS to effectors (muscles and glands)

Subdivisions of the Efferent Division

Somatic NS (SNS)

Voluntary control over skeletal muscle — under conscious control.

Autonomic NS (ANS)

Involuntary regulation of smooth muscle, cardiac muscle, and glands. Includes sympathetic (fight or flight) and parasympathetic (rest and digest) — typically have opposing effects.

⚠ Exam TrapAfferent = arriving (sensory, TO CNS). Efferent = exiting (motor, FROM CNS). Root: af- means "to," ef- means "from." Mixing these is the most common NS question error.

2638

Neurons & Neuroglia: Structure & Function

Distinguish between neurons and neuroglia on the basis of their structure and function.

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Neuron Structure

Four main parts: cell body (nucleus, Nissl bodies) → dendrites (receive signals) → axon hillock (AP origin) → axon → axon terminals (synapse with next cell). Most CNS neurons cannot divide (lack centrioles).

Structural Classification

Type	Structure	Where Found
Multipolar	2+ dendrites, single axon	Most common in CNS; ALL skeletal motor neurons
Unipolar	Dendrites and axon continuous; cell body offset	Most PNS sensory neurons
Bipolar	One dendrite, one axon; cell body between	Special sense organs (sight, smell, hearing)

Functional Classification

Type	Number	Function
Sensory (afferent)	~10 million	Carry info FROM receptors TO CNS
Motor (efferent)	~500,000	Carry motor commands FROM CNS to effectors
Interneurons	~20 billion	Entirely in brain/spinal cord; interconnect neurons; higher functions

CNS Neuroglia — 4 Types

Cell	Size/Number	Key Function
Astrocytes	Largest, most numerous	Blood-brain barrier; structural support; repair damaged neural tissue
Oligodendrocytes	Smaller, fewer processes	Myelinate CNS axons — each myelinates segments of SEVERAL axons; creates internodes; gaps = nodes of Ranvier
Microglia	Smallest, least numerous	Phagocytic — engulf waste and pathogens; derived from white blood cells
Ependymal cells	—	Line ventricles and central canal; produce and circulate CSF

PNS Neuroglia — 2 Types

Cell	Key Function
Schwann cells	Cover ALL PNS axons; myelinate ONE segment of ONE axon only; outer surface = neurilemma
Satellite cells	Support neuron cell bodies in PNS ganglia

⚠ Oligodendrocyte vs Schwann CellOligodendrocyte: CNS, myelinates MULTIPLE axons. Schwann cell: PNS, myelinates ONE segment of ONE axon only. Both produce myelin but are entirely different cells in different locations.

Nuance — White vs Gray MatterWhite matter = myelinated axon regions (lipid-rich myelin appears white). Gray matter = neuron cell body regions (Nissl bodies appear gray). This distinction applies throughout the entire CNS.

2639

Events That Generate Action Potentials

Communicate the events that generate action potentials in the membranes of nerve cells.

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Process Objective — Steps in OrderKnow which ion moves in which direction at each phase, and which voltage value triggers each event.

Resting Conditions

Condition	Value / Detail
Resting membrane potential	–70 mV (inside more negative than outside)
Na+ concentration	High OUTSIDE the cell
K+ concentration	High INSIDE the cell
Na+/K+ exchange pump	Pumps 3 Na+ OUT and 2 K+ IN — requires ATP
Threshold	–60 mV — must depolarize to this level to fire an AP

Steps of Action Potential Generation

1

Graded depolarization to threshold (–70 → –60 mV): Stimulus opens chemically gated Na+ channels. Na+ enters → local depolarization. Graded potential decreases with distance from stimulus site.

2

Rapid depolarization (–60 → +30 mV): At threshold, voltage-gated Na+ channels OPEN. Na+ rushes in rapidly. Inner membrane surface becomes positive. Membrane potential rises to +30 mV.

3

Repolarization begins (+30 → –70 mV): Voltage-gated Na+ channels CLOSE (inactivate). Voltage-gated K+ channels OPEN. K+ moves OUT of the cell → membrane potential falls back.

4

Hyperpolarization and return (–90 → –70 mV): K+ channels close slowly. K+ briefly overshoots → ~–90 mV (hyperpolarization). K+ channels fully close → returns to –70 mV resting potential.

All-or-none principle: Every stimulus reaching threshold generates an identical AP. Stronger stimuli produce MORE FREQUENT APs, not stronger ones.

Refractory period: From Na+ channel opening until repolarization is complete — membrane cannot respond to further stimulation. Ensures one-way propagation. Maximum rate ~500–1000 APs/second.

Propagation

Type	Axon	Mechanism	Speed
Continuous propagation	Unmyelinated	AP spreads step by step along entire membrane	~1 m/s (2 mph)
Saltatory propagation	Myelinated	AP leaps from node of Ranvier to node; myelin blocks ion flow between nodes	18–140 m/s (40–300 mph)

Clinical — Multiple SclerosisMS destroys CNS myelin (oligodendrocytes). Loss of myelin converts fast saltatory propagation to slow degraded conduction → progressive sensory loss, motor deficits, visual problems.

2640

Mechanism of Nerve Impulse Transmission at the Synapse

Communicate the mechanism of nerve impulse transmission at the synapse.

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Process Objective — Cholinergic Synapse: 4 StepsKnow what triggers each step. Step 2 (calcium mechanism) and Step 4 (AChE) are high-probability exam targets.

Synapse Structure

Presynaptic neuron → axon terminal (synaptic vesicles contain neurotransmitter) → synaptic cleft → postsynaptic membrane (receptors). Transmission is ONE-DIRECTIONAL only.

Events at a Cholinergic Synapse

1

AP arrives at axon terminal: Depolarizes the presynaptic membrane.

2

Ca2+ enters; ACh released: Depolarization opens calcium channels → Ca2+ enters axon terminal → triggers exocytosis of synaptic vesicles → ACh released into synaptic cleft. Release stops when Ca2+ is actively removed from cytoplasm.

3

ACh binds; postsynaptic membrane depolarizes: ACh diffuses across cleft → binds to Na+ channels on postsynaptic membrane → Na+ enters → graded depolarization. If threshold reached → AP generated.

4

ACh removed by AChE: Acetylcholinesterase breaks ACh into acetate + choline. Effect terminates. Terminal reabsorbs choline to resynthesize ACh.

Major Neurotransmitters

Neurotransmitter	Type	Typical Effect	Inactivated by
ACh	Cholinergic	Usually excitatory	AChE
Norepinephrine (NE)	Adrenergic	Usually excitatory	Monoamine oxidase (MAO)
Dopamine	—	Usually inhibitory	—
GABA	—	Usually inhibitory (hyperpolarization)	—
Serotonin	—	Usually inhibitory	—

⚠ What Triggers ACh Release?Ca2+ entering the axon terminal — NOT the AP directly. The AP opens calcium channels; calcium triggers exocytosis. Block calcium → no ACh even if APs keep arriving.

2641

Three Meningeal Layers of the CNS

Identify the three meningeal layers that surround the central nervous system.

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The Three Meninges — Outer to Inner

Layer	Characteristics	Associated Space / Structures
1. Dura mater	Outermost; tough, fibrous. Brain = 2 layers; spinal cord = 1 layer (not fused to vertebral bone).	Dural sinuses (large collecting veins); dural folds (anchor brain). Epidural space (spinal only): fat + blood vessels.
2. Arachnoid	Middle; squamous cells with web-like collagen/elastic fibers below it.	Subdural space (small lymphatic fluid). Subarachnoid space (CSF); arachnoid granulations return CSF to venous blood.
3. Pia mater	Innermost; delicate; firmly bound to neural tissue surface; highly vascular.	Blood vessels supplying brain and spinal cord run here within subarachnoid space.

Cerebrospinal Fluid (CSF)

Produced by the choroid plexus in all 4 ventricles at ~500 mL/day. Total volume: ~150 mL (replaced every 8 hours). Functions: cushioning, buoyancy (brain weighs 1400 g in air, ~50 g in CSF), nutrient/waste transport.

⚠ Space LocationsEpidural = OUTSIDE the dura (spinal cord only). Subdural = BETWEEN dura and arachnoid. Subarachnoid = BETWEEN arachnoid and pia — where CSF lives. Epidural anesthesia = injected into epidural space.

2642

Structure & Functions of the Spinal Cord

Define the structure and functions of the spinal cord.

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Gross Anatomy

~45 cm long; 31 segments → 31 pairs of spinal nerves. Ends at L1–L2 in adults. Enlargements: cervical (shoulder/upper limb) and lumbar (pelvis/lower limb). Below cord tip: long nerve roots = cauda equina.

Dorsal roots: sensory axons, associated with dorsal root ganglia. Ventral roots: motor axons. Both unite → spinal nerve. All 31 pairs of spinal nerves are mixed nerves (sensory + motor).

Functions

Highway for sensory impulses ascending TO the brain
Highway for motor impulses descending FROM the brain
Integrates information independently; controls spinal reflexes

Gray Matter — H-Shape

Horn	Contains	Function
Posterior (dorsal) horn	Sensory nuclei	Receives and processes incoming sensory information
Anterior (ventral) horn	Somatic motor nuclei	Controls skeletal muscle contractions
Lateral horn	Visceral motor neurons	ANS control: smooth muscle, cardiac muscle, glands

White Matter — Three Columns

Column	Direction
Posterior white column	Ascending (sensory) — fine touch, vibration, proprioception
Anterior white column	Descending (motor) — voluntary motor commands
Lateral white column	Both ascending and descending tracts

Clinical — Spinal Cord Injury LevelsC4/C5 damage → quadriplegia (all four limbs). Thoracic damage → paraplegia (lower limbs only). Spinal cord does not regenerate — damaged tracts seldom repair.

2643

Major Regions of the Brain & Their Functions

Communicate the major regions of the brain and their functions.

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Classification Objective — 6 RegionsKnow each region's location and specific function. Clinical questions: "Damage to X — what function is lost?"

Six Major Brain Regions

Region	Location	Key Functions
Cerebrum	Largest; most superior	Conscious thought, intellectual functions, voluntary movement, sensory awareness, memory storage and processing
Diencephalon	Below cerebrum; surrounds 3rd ventricle	Relay/switching center integrating conscious and unconscious sensory and motor pathways
Midbrain	Superior brain stem	Visual and auditory reflex responses; maintains consciousness (reticular activating system); muscle tone and posture
Pons	Middle brain stem	Connects cerebellum to brain stem; involuntary control of respiration pace and depth
Medulla oblongata	Inferior brain stem; connects to spinal cord	Vital reflex centers: cardiovascular (cardiac center + vasomotor center) and respiratory rhythmicity center
Cerebellum	Posterior; covered by cerebrum	Adjusts postural muscles for balance; programs and fine-tunes voluntary and involuntary movements

Diencephalon — Three Components

Structure	Function
Thalamus	Final relay for ALL ascending sensory info EXCEPT olfactory — filters what reaches conscious awareness
Hypothalamus	Homeostasis: hunger, thirst, body temperature, circadian rhythms; primary link between nervous and endocrine systems (pituitary gland connection); secretes ADH and oxytocin
Epithalamus	Contains pineal gland → secretes melatonin; regulates day/night cycles

Key Internal Cerebrum Structures

Structure	Function
Basal nuclei	Subconscious control of skeletal muscle tone; coordinate learned movement patterns
Limbic system	Establishes emotional states; links conscious cortex to unconscious brain stem; aids long-term memory (hippocampus)
Corpus callosum	White matter band linking the two hemispheres; 200+ million axons

⚠ Thalamus vs HypothalamusThalamus = relay point for sensory information (all except smell). Hypothalamus = homeostatic control and endocrine link to pituitary. Mixing these is a high-frequency error.

Clinical — Parkinson's DiseaseSubstantia nigra (midbrain) releases dopamine to inhibit basal nuclei. Damage → less dopamine → basal nuclei overactive → excess muscle tone → difficulty initiating voluntary movement, rigidity, tremor.

2644

Motor, Sensory & Association Areas of the Cerebral Cortex

Identify the motor, sensory, and association areas of the cerebral cortex and their functions.

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Lobes and Their Primary Areas

Lobe	Location	Key Areas
Frontal lobe	Anterior to central sulcus	Primary motor cortex (precentral gyrus); premotor cortex; prefrontal cortex; speech center (Broca's area); gustatory cortex
Parietal lobe	Posterior to central sulcus	Primary sensory cortex (postcentral gyrus); somatic sensory association area
Temporal lobe	Below lateral sulcus	Auditory cortex; auditory association area; olfactory cortex
Occipital lobe	Most posterior	Visual cortex; visual association area

Primary Motor and Sensory Areas

Area	Gyrus	Function
Primary motor cortex	Precentral gyrus (frontal)	Directs voluntary movements by controlling somatic motor neurons in brain stem and spinal cord
Primary sensory cortex	Postcentral gyrus (parietal)	Receives somatic sensory information (touch, pressure, pain, temperature) — conscious awareness requires thalamic relay to this area

Association and Higher-Order Areas

Area	Location	Function
Somatic sensory association area	Parietal lobe	Interprets incoming sensory data (e.g., recognizes a mosquito landing)
Premotor cortex (somatic motor association)	Frontal lobe	Coordinates learned motor movements; instructs primary motor cortex
Visual association area	Occipital lobe	Interprets meaning of visual information
Auditory association area	Temporal lobe	Interprets auditory information
General interpretive area (Wernicke's area)	Temporal/parietal junction — usually LEFT hemisphere	Integrates all sensory information; essential for language comprehension
Speech center (Broca's area)	Frontal lobe — same side as Wernicke's	Regulates breathing and vocalization required for normal speech production
Prefrontal cortex	Anterior frontal lobe	Abstract thought; predicts consequences; planning; emotional interpretation

Hemispheric Lateralization

Left — Categorical Hemisphere

Language, reading, writing, speaking, mathematical calculation, logical reasoning. Contains general interpretive and speech centers in most people.

Right — Representational Hemisphere

Spatial relationships, face recognition, emotional context of language, artistic and musical processing, three-dimensional analysis.

Sensory and Motor HomunculusCortical area devoted to a body region reflects the NUMBER OF RECEPTORS or motor units there — not physical size. Hands, lips, and tongue are grossly oversized on the homunculus; trunk and back are tiny.

2645

Cranial Nerves & Their Principal Functions

Identify the cranial nerves, and relate each pair of cranial nerves to its principal functions.

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Classification Objective — 12 PairsMnemonic: Oh Once One Takes The Anatomy Final, Very Good Vacations Are Heavenly
Each nerve is Sensory, Motor, or Mixed.

All 12 Cranial Nerve Pairs

Number	Name	Type	Principal Function
N I	Olfactory	Sensory	Smell — only CN attached to cerebrum directly
N II	Optic	Sensory	Vision from retina; fibers cross at optic chiasm
N III	Oculomotor	Motor	4 of 6 extrinsic eye muscles; pupil constriction and lens shape (parasympathetic)
N IV	Trochlear	Motor	Superior oblique eye muscle — smallest cranial nerve
N V	Trigeminal	Mixed	Largest CN; 3 branches: sensory from face/head; motor to chewing muscles (temporalis, masseter, pterygoids)
N VI	Abducens	Motor	Lateral rectus eye muscle (abducts the eyeball)
N VII	Facial	Mixed	Motor: facial expression, lacrimal/salivary glands. Sensory: taste from anterior 2/3 of tongue
N VIII	Vestibulocochlear	Sensory	Cochlear branch: hearing. Vestibular branch: balance, position, movement
N IX	Glossopharyngeal	Mixed	Sensory: taste posterior 1/3 tongue; blood pressure/gas monitoring. Motor: pharyngeal muscles (swallowing)
N X	Vagus	Mixed	Wandering nerve; ~75% of all parasympathetic outflow; thoracic and abdominal visceral organs
N XI	Accessory	Motor	Sternocleidomastoid and trapezius muscles
N XII	Hypoglossal	Motor	Voluntary control of tongue muscles

⚠ Three Eye Movement NervesN III (oculomotor): 4 muscles. N IV (trochlear): superior oblique only. N VI (abducens): lateral rectus only. Can't look laterally → N VI damaged. Can't look down-and-in → N IV damaged.

2646

Distribution Pattern of Spinal Nerves

Communicate the distribution pattern of spinal nerves to the regions they innervate.

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31 Pairs of Spinal Nerves

Region	Pairs	Plexus	Regions Innervated
Cervical	8 (C1–C8)	Cervical (C1–C5); Brachial (C5–T1)	Neck; phrenic nerve → diaphragm; shoulder, arm, forearm, hand
Thoracic	12 (T1–T12)	No major plexus (intercostal nerves)	Thoracic and abdominal wall; intercostal muscles
Lumbar	5 (L1–L5)	Lumbar plexus (T12–L4)	Hip, anterior/medial thigh; femoral and obturator nerves
Sacral	5 (S1–S5)	Sacral plexus (L4–S4)	Posterior thigh, leg, foot; sciatic nerve and gluteal nerves
Coccygeal	1 (Co1)	—	Skin over coccygeal region

Dermatomes: Each spinal nerve monitors a specific skin region. Damage produces characteristic sensory loss in that dermatome — used clinically to localize spinal cord lesions. Shingles (varicella-zoster infecting dorsal root ganglia) produces a painful rash along the affected dermatome.

⚠ All Spinal Nerves = Mixed NervesEvery one of the 31 pairs contains BOTH sensory and motor fibers. Unlike cranial nerves (which can be purely sensory or purely motor), all spinal nerves are mixed by definition.

2647

Components of a Reflex Arc

Identify the components of a reflex arc.

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Process Objective — 5 Components in OrderA reflex is an automatic, involuntary motor response to a specific stimulus. Always produces the same result.

Five Components of a Reflex Arc

1

Arrival of stimulus → activation of receptor: Receptor detects a specific change (stretch, pain, pressure).

2

Activation of a sensory neuron: Afferent neuron carries signal to CNS via dorsal root.

3

Information processing in the CNS: Monosynaptic: sensory synapses DIRECTLY on motor neuron. Polysynaptic: one or more interneurons process the signal first.

4

Activation of a motor neuron: Efferent neuron carries command out via ventral root.

5

Response by effector: Muscle contracts or gland secretes. Response typically opposes the original stimulus (negative feedback).

Monosynaptic vs Polysynaptic

Type	Synapses	Speed	Response Complexity	Example
Monosynaptic	Sensory directly on motor	Fastest	Simple, stereotyped	Stretch reflex (patellar/knee-jerk)
Polysynaptic	1+ interneurons	Slower	Can control multiple muscle groups	Flexor (withdrawal) reflex

Stretch reflex: Receptor = muscle spindles. Stimulus = muscle stretch. Response = contraction of stretched muscle. Clinically tests spinal cord and peripheral nerve integrity.

Reciprocal inhibition: When flexors are stimulated, interneurons simultaneously inhibit antagonist extensor motor neurons — preventing competing contractions.

Clinical — Babinski SignNormal in infants: stroking sole → toes fan out. Normal adult response: toes curl (plantar reflex). Positive Babinski in an adult = damage to descending inhibitory pathways → used to detect CNS injury.

2648

Principal Sensory & Motor Pathways

Identify the principal sensory and motor pathways.

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Sensory (Ascending) Pathways

Pathway	Sensations Carried	Crosses At	Destination
Posterior column pathway	Fine touch, pressure, vibration, proprioception (highly localized)	Medulla oblongata	Primary sensory cortex (opposite side)
Spinothalamic pathway	Crude touch, pressure, pain, temperature (poorly localized)	Spinal cord	Primary sensory cortex via thalamus
Spinocerebellar pathway	Proprioception — muscle, bone, joint positions	Does not cross (subconscious)	Cerebellar cortex

Posterior Column Pathway — 3 Neurons

1

First-order neuron: receptor → dorsal root → ascends in posterior column to medulla oblongata.

2

Second-order neuron: synapses in medulla → crosses to opposite side → ascends to thalamus.

3

Third-order neuron: thalamus → relays to appropriate region of primary sensory cortex.

Motor (Descending) Pathways

Pathway	Also Called	Control Type	Crosses Where
Corticospinal pathway	Pyramidal system	Conscious voluntary skeletal muscle control	Mostly medulla oblongata
Medial and lateral pathways	Extrapyramidal system	Subconscious: muscle tone, posture, learned movements, reflexive responses	Various

Contralateral ControlBoth posterior column and corticospinal pathways cross the midline. Left hemisphere controls and receives sensation from the RIGHT side of the body. Right-sided stroke → left-sided deficits.

⚠ Tract Naming ConventionSpino- prefix = ascending (sensory, going TO brain). -spinal suffix = descending (motor, going FROM brain). Middle = brain region involved. Corticospinal = cortex to spinal cord (motor, descending).

2649

Sympathetic & Parasympathetic Divisions of the ANS

Communicate the functions and structures of the sympathetic and parasympathetic divisions.

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Classification Objective — Structural & Functional ComparisonKnow origin of preganglionic fibers, ganglion location, fiber length ratio, and neurotransmitter for each division.

Structural Comparison

Feature	Sympathetic	Parasympathetic
Nickname	"Fight or flight"	"Rest and digest"
Preganglionic origin	T1–L2 (thoracolumbar)	Brain stem (N III, VII, IX, X) + S2–S4 (craniosacral)
Preganglionic fiber length	Short	Long
Ganglion location	Near vertebral column (chain ganglia) OR anterior to it (collateral ganglia)	In or near target organ (terminal / intramural ganglia)
Postganglionic fiber length	Long	Short
Postganglionic neurotransmitter	Norepinephrine — NE (adrenergic)	Acetylcholine — ACh (cholinergic)
Scope	Widespread — visceral AND somatic structures throughout body	Restricted — visceral structures only

⚠ Universal Preganglionic RuleALL preganglionic autonomic fibers (both divisions) are cholinergic — release ACh — always excitatory. Only postganglionic fibers differ. Sympathetic postganglionic = adrenergic (NE). Parasympathetic postganglionic = cholinergic (ACh).

Functional Effects on Key Organs

Structure	Sympathetic Effect	Parasympathetic Effect
Heart	↑ rate and force of contraction	↓ rate and force of contraction
Airways	Dilate (bronchodilation)	Constrict (bronchoconstriction)
Pupils	Dilate	Constrict
Digestive system	↓ activity	↑ activity (digestion, peristalsis, secretions)
Urinary bladder	Constricts sphincter, relaxes bladder (retains urine)	Contracts bladder wall, relaxes sphincter (eliminates urine)
Sweat glands	↑ secretion	Not innervated
Adrenal medulla	Releases NE + epinephrine into blood	Not innervated

Dual InnervationMost vital organs receive BOTH sympathetic and parasympathetic input with opposing effects. Structures receiving sympathetic only: sweat glands, arrector pili, most blood vessels, adipose tissue. Vagus nerve (N X) provides ~75% of all parasympathetic outflow.

2650

Effects of Aging on the Nervous System

Communicate the effects of aging on the nervous system.

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Age-Related Anatomical Changes

Change	Details
Reduced brain size and weight	Primarily from decreased volume of cerebral cortex; narrower gyri and wider sulci
Reduced neuron number	Cortical neuron loss (brain stem nuclei less affected)
Decreased blood flow to brain	Arteriosclerosis (fatty deposits in vessel walls) reduces blood flow; increases stroke risk
Synaptic changes	Fewer dendritic branchings; synaptic connections lost; neurotransmitter production declines
Intracellular/extracellular deposits	Abnormal proteins and pigments accumulate inside neurons; extracellular protein plaques — in excess, associated with Alzheimer's disease

Functional Consequences

Memory consolidation (short-term → long-term) becomes more difficult
Sensory systems less acute — brighter light, louder sounds, stronger smells needed
Reaction times slow
Reflexes weaken or disappear
Motor precision decreases
~85% of elderly still function relatively normally

Clinical — Alzheimer's DiseaseMost common cause of senility; affects ~15% over age 65. Progressive loss of hippocampal and cortical neurons → memory loss → verbal/reading/emotional deficits → loss of motor abilities. Characterized by extracellular protein plaques and intracellular abnormal protein deposits. No cure; medications slow progression in some patients.

2651

Interrelationships Between the Nervous System & Other Organ Systems

Communicate the interrelationships between the nervous system and other organ systems.

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System Interrelationships

Body System	NS Does FOR That System	That System Does FOR the NS
Integumentary	Controls arrector pili muscles and sweat glands	Provides sensations of touch, pressure, pain, vibration, temperature; hair insulates skull and peripheral nerves
Skeletal	Controls skeletal muscle contractions → determines bone position; maintains bone mass through mechanical stress	Provides calcium for neural function; skull and vertebral column protect brain and spinal cord
Muscular	Controls all skeletal muscle contractions; coordinates respiratory and cardiovascular activities	Facial muscles express emotional state; laryngeal muscles allow speech; muscle spindles provide proprioceptive sensation to NS

The nervous system monitors all other systems and adjusts their activities. The muscular system cannot function without nervous system input. The cardiovascular system is relatively independent — the NS primarily coordinates and fine-tunes it to meet demands of other systems.

SOMAPL18

The Nervous System