Anatomy Final

CNS (Central Nervous System)’s Role

• Integration center: interprets incoming sensory information

• Initiates motor output

• Coordinates higher functions (memory, learning, emotion)

CNS (Central Nervous System)’s Protection

• Bones: skull, vertebral column

• Meninges: dura, arachnoid, pia mater

• CSF: cushioning, buoyancy, chemical stability

CNS (Central Nervous System)’s Neurons

Contains interneurons, which form complex processing circuits

PNS (Peripheral Nervous System)

• Includes all neural tissue outside CNS

• Role: Link between CNS and body

PNS (Peripheral Nervous System) Function Divisions

Afferent (Sensory) & Efferent (Motor)

Afferent PNS

• Somatic Sensory: skin, skeletal muscles, joints

• Visceral Sensory: organs, internal environment

Efferent PNS

• Somatic motor: voluntary → skeletal muscle

• Visceral motor: involuntary → smooth muscle, cardiac muscle, glands

Somatic Nervous System (SNS)

• Voluntary control

• Innervates: skin, skeletal muscle, joints

• Includes cranial & spinal nerves

• Responsible for conscious movement & general sensations

Autonomic Nervous System (ANS)

• Involuntary; regulates homeostasis

• Manages internal functions: BP, HR, digestion, body temperature, respiration

Sympathetic Division (Fight/Flight) Origin

Thoracolumbar (T1-L2)

Sympathetic Division (Fight/Flight) Effects

• Increases HR & contractility

• Pupils dilate (mydriasis)

• Bronchodilation

• Vasodilation to skeletal muscle

• Vasoconstriction to skin & GI tract

• Inhibits digestion, urination, defecation

• Releases glucose from liver

• Stimulates sweat glands (unique sympathetic cholinergic fibers)

Parasympathetic Nervous System (Rest/Digest) Origin

Craniosacral (CN III, VII, IX, X + S2-S4)

Parasympathetic Nervous System (Rest/Digest) Effects

• Decreased HR

• Pupils constrict (miosis)

• Stimulates digestion (motility + secretions)

• Promotes urination & defecation

• Conserves energy

• Dual innervation: most organs receive both → dynamic balance=homeostasis

Spinal Cord Major Functions

• Pathway for sensory input → brain

• Pathway for motor output → body

• Reflex integration centers (fast, automatic responses independent of the brain)

Spinal Cord Superficial Anatomy

• Cervical enlargement: upper limb innervation

• Lumbar enlargement: lower libs, pelvis

• Conus medularis: tapered end (L1-L2)

• Cauda equina: bundle of spinal nerves below L2

• Filum Terminale: pia extension anchoring cord to coccyx

Cross-Sectional Anatomy of the Spinal Cord

• Gray Matter

• White Matter

• Roots & Spinal Nerve

• Landmarks

Gray Matter (Central, Butterfly-Shaped)

• Posterior (dorsal) horn: sensory processing

• Anterior (ventral) horn: motor neuron cell bodies

• Lateral horn: visceral motor neurons (T1-L2, S2-S4)

White Matter

• Organized into ascending (sensory) and descending (motor) tracts

• Columns: anterior, lateral, and posterior

Roots & Spinal Nerve

• Dorsal root: sensory input → dorsal horn

• Dorsal root ganglion → sensory neuron cell bodies (pseudounipolar)

• Ventral root: motor output from anterior horn

• Spinal Nerve: mixed sensory + motor

Landmarks

• Anterior median fissure: deep grove, ventral side

• Posterior median sulcus: shallow groove, dorsal side

Spinal Meninges

• Dura Matter

• Arachnoid Matter

• Pia Mater

Dura Mater

• Outermost: dense connective tissue

• Forms dural sac (foramen magnum → S2)

• Covers spinal nerve roots

• Epidural space: adipose tissue, blood vessels → epidural blocks

Arachnoid Matter

• Thin, avascular

• Subarachnoid space: filled with CSF

• Lumbar puncture site: L3-L4 or L4-L5 (below spinal cord)

Pia Mater

• Highly vascular, adhered to spinal cord surface

• Forms: denticulate ligaments: lateral stabilization, filum terminale: anchors cord downward

Dermatomes Location

Skin regions supplied by one spinal nerve

Dermatomes Clinical Uses

• Localizing spinal cord injury

• Detecting nerve root compression

• Identifying viral infections (shingles)

Referred Pain Mechanism

Visceral + somatic afferents synapse on same spinal interneurons → brain misinterprets source

Referred Pain Examples

• Heart attack → left arm/jaw

• Gallbladder → right shoulder

• Kidney stones → groin

Shingles (Herpes Zoster)

• Reactivation of varicella-zoster virus in dorsal root ganglia

• Painful, unilateral, dermatomal rash

• Often thoracic

• Increased risk in aging & immunosuppression

Nervous Plexuses

• Networks of ventral rami

• Redistribute fibers → multiple pathways to limbs

• Damage protection: if one spinal nerve injured, muscle still gets partial innervation

• Cervical Plexus

• Phrenic Nerve

• Brachial Plexus

• Lumbar Plexus

• Sacral Plexus

Cervical Plexus (C1-C5)

• Innervates: Neck, scalp, upper shoulders

• Phrenic Nerve

Phrenic Nerve (C3-C5)

Diaphragm → essential for breathing

Brachial Plexus (C5-T1)

• Supplies upper limb

• Major terminal nerves

Musculocutaneous

Anterior arm (biceps)

Axillary

Deltoid, shoulder sensation

Median

Forearm flexors, carpal tunnel

Radian

Posterior arm/forearm (extension)

Ulnar

Intrinsic hand muscles (“funny bone”)

Lumbar Plexus (L1-L4)

• Femoral nerve: quadriceps, anterior thigh

• Pudendal nerve: medial thigh adductors

Sacral Plexus (L4-S4)

• Sciatic nerve: largest nerve → tibial + common fibular

• Pudendal nerve: external genitalia, perineum

Reflex Arc Components (5 Steps)

1. Receptor: detects stimulus

2. Sensory neuron: sends signal to CNS

3. Integration center: one or more synapses

4. Motor neuron: carries command to effector

5. Effector: muscle or gland responds

Reflex Classification by Development

• Innate: genetically determined (withdrawal, blinking, patellar)

• Acquired: learned reflexes (driving, conditioned responses)

Reflex Classification by Processing Site

• Spinal: processed in spinal cord

• Cranial: processed in brainstem

Reflex Classification by Response Type

• Somatic: skeletal muscle

• Autonomic: smooth/cardiac muscle, glands

Reflex Classification by Complexity

• Monosynaptic: 1 synapse (patellar reflex)

• Polysynaptic: multiple synapses (withdrawal, crossed extensor)

Diagnostic Reflex Testing

Babinski reflex

• Normal adult: toes curl (plantar flexion)

• Abnormal adult: toes fan → indicates corticospinal tract damage→ (normal in infants due to incomplete myelination)

Somatosensory System

Senses Detected

• Touch, pressure, vibration

• Temperature

• Pain

• Proprioception

• Itch

Sensory Fiber Types

• Aa (I)

• AB (II)

• A8 (III)

• C fibers (IV)

Aa (I)

Diameter: largest

Myelin: thick

Speed(m/s): fastest

Sensation: proprioception (muscle spindles, GTOs)

AB (II)

Diameter: large

Myelin: myelinated

Speed(m/s): 2nd fastest

Sensation: touch, vibration, pressure

A8 (III)

Diameter: small

Myelin: thin

Speed(m/s): 3rd fastest

Sensation: fast, sharp pain; cold

C Fibers (IV)

Diameter: smallest

Myelin: none

Speed(m/s): slowest

Sensation: slow, dull pain; warmth; itch

Somatic Receptors

• Mechanoreceptors

• Thermoreceptors

• Nociceptors (pain receptors)

• Proprioceptors

Mechanoreceptors

• Merkel cells

• Meissner corpuscles

• Pacinian corpuscles

• Ruffini endings

• Hair follicle receptors

Merkel Cells

• Slow adapting; small receptive fields

• Fine detail, edges, shapes

• High spatial resolution

Meissner Corpuscles

• Rapid adapting; small receptive fields

• Light touch, flutter, low-frequency vibration

• Grip control

Pacinian Corpuscles

• Rapid adapting; large receptive fields

• Skin stretch, finger position, hand shape

• Important for proprioception

Ruffini Endings

• Slow adapting; large receptive fields

• Skin sketch, finger position, hand shape

• Important for proprioception

Hair Follicle Receptors

• Rapid adapting

• Detect hair movement & light touch

Somatic Receptor-Thermoreceptors

• Free nerve endings

• Cold receptors: peak ~25C

• Warm receptors: peak ~45C

• Extreme temps activate nociceptors

Nociceptors (Pain Response)

• Mechanical

• Thermal

• Polymodal

• Silent (visceral)

• Chemical Nociceptors

Nociceptors Mechanical

Strong pressure, cutting

Nociceptors Thermal

Extreme heat >45C or extreme cold

Nociceptors Polymodal

Mechanical + thermal + chemical

Nociceptors Silent (Visceral)

Activated only in inflammation

Chemical Nociceptors

Causing hyperalgesia (increased sensitivity) and allodynia (pain from non-painful stimuli)

Proprioceptors

• Muscle Spindles

• Golgi Tendon Organs (GTOs)

• Joint Receptors

Proprioceptor Muscle Spindles

• Detect muscle stretch/length

• Initiate stretch reflex

• Maintain tone & posture

Proprioceptor Golgi Tendon Organs (GTOs)

• Detect muscle tension

• Prevent damage

Proprioceptor Joint Receptors

Detect joint angle extremes, pressure, acceleration

The Brain

1. Cerebrum: conscious thought, memory, voluntary movement

2. Diencephalon: thalamus, hypothalamus, epithalamus

3. Brainstem: midbrain, pons, medulla

4. Coordination, balance

Cerebrum Anatomical Features

• Largest region

• Two hemispheres separated by longitudinal fissure

• Corpus callosum connects hemispheres

Cerebrum Surface Features

• Gyri: folds

• Sulci: shallow grooves

• Fissures: deep grooves

Cerebral Lobes

• Frontal Lobe

• Parietal Lobe

• Temporal Lobe

• Occipital Lobe

• Insula

Frontal Lobe

• Primary motor cortex (precentral gyrus) → voluntary movement

• Broca’s area → speech production (LEFT hemisphere)

• Prefrontal cortex → judgement, planning, personality

Parietal Lobe

• Primary somatosensory cortex (postcentral gyrus)

• Touch, pressure, pain, temperature, proprioception

Temporal Lobe

• Primary auditory cortex

• Wernicke’s area → language comprehension

• Hippocampus → memory formation

• Olfactory cortex

Occipital Lobe

Primary visual cortex

Insula

• Taste (gustatory cortex)

• Emotional awareness

• Interoception (internal body state)

Major Sulci & Gyri

• Central Sulcus

• Lateral Sulcus

• Parieto-occipital Sulcus

Central Sulcus

• Separates frontal & parietal lobes

• Marks boundary between motor (precentral) and sensory (postcentral) cortices

Lateral Sulcus

Separates temporal from frontal/parietal

Parieto-Occipital Sulcus

Separates parietal from occipital

The Diencephalon

• Thalamus

• Hypothalamus

• Epithalamus/Pineal Gland

• Subthalamus

Thalamus

• Sensory relay station

• Filters + directs signals to cortex

• Roles: consciousness, alertness, motor modulation

Hypothalamus

Homeostasis MASTER regulator

Functions:

• Temperature

• Hunger/thirst

• Autonomic control

• Endocrine control (via pituitary)

• Emotional responses

Epithalamus/Pineal Gland

• Produces melatonin → circadian rhythm

• Light-sensitive pathways from retina

Subthalamus

Assists in motor control with basal nuclei

Brainstem

• Midbrain

• Pons

• Medulla Oblongata

Midbrain

• Superior colliculi → visual reflexes

• Inferior colliculi → auditory reflexes

• Cerebral peduncles → motor tracts

• Substantia nigra → dopamine (degeneration → Parkinson’s)

Pons

• Relay between cerebellum & cerebrum

• Respiratory centers → pneaumotaxic & apneustic

Medulla Oblongata

• Continuous with the spinal cord

• Vital autonomic centers: cardiac (HR), Vasomotor (BP), Respiratory rhythmicity

• Controls reflexes: coughing, sneezing, vomiting

• CN IX-XII

Cerebellum

Two hemispheres,

Cranial Nerves (CN I-XII)

I - Olfactory

II - Optic

III - Oculomotor

IV - Trochlear

V - Trigeminal

VI - Abducens