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Home , Arachnoid mater, Central nervous system, Decussation, Dura mater, Hindbrain, Interneuron

Guyton & Hall – Figure 45.2 Fundamentals of

General Design of Nervous System:

Analogy = Computer

Processing = Integrative System Input = Sensory System • 99% of sensory information Output = discarded Receptors: Effectors: • determine pathway Tactile of signals Visual • Information stored for future use Smooth muscle Auditor Glandular secretion Memory: Olfactory Highly facilitated synaptic pathways (sensory input not required to excite pathway)

1 Fundamentals of Nervous System

Organization of Nervous System:

Nervous system

Integration Peripheral nervous system (CNS) (PNS) Motor Sensory output input

Brain Motor division Sensory division (efferent) (afferent)

Autonomic nervous system (involuntary; smooth & cardiac muscle) (voluntary; skeletal muscle)

Sympathetic division Parasympathetic division

Fundamentals of Nervous System

Histology of Nervous System:

A. Neuroglia (supporting cells – “ glue”)

Central Nervous System (CNS) ciliated (most common)

Astrocytes: : Ependymal cells: • anchor to • ; engulf invaders • line canals / ventricles of • repair damaged neural • produce (CSF) • maintain “blood / brain barrier”

Peripheral Nervous System (PNS)

Schwann cells: • Insulate neurons ( sheath)

Oligodendrocytes: Satellite cells: • Insulate neurons (myelin sheath) • Function similar to

2 Fundamentals of Nervous System

Histology of Nervous System: • Long-lived (~ 100 years) • High metabolic rate B. Neurons • Specialized “excitable” cells • Allow for communication throughout body (via electrical impulses)

Neuron : 1) : Receive information (environment / other neurons) 2) Cell body (): Integrates information / initiate response 3) : Conducts (AP – electrical impulse) 4) Synaptic terminals: Transmit signal (other neurons / effector organs)

Axon hillock (AP generation)

Axon Dendrites Synaptic terminals Schwann Cells (PNS) Centrioles

(Can not divide) Cell body

Fundamentals of Nervous System

Histology of Nervous System: • Long-lived (~ 100 years) • High metabolic rate B. Neurons • Specialized “excitable” cells • Allow for communication throughout body (via electrical impulses)

Functional Classification of Neurons:

1) Sensory (Afferent) neurons: • Carry information from sensory receptors to CNS

2) Motor (Efferent) neurons: • Carry information from CNS to effector organs

3) Association neurons (): • Interconnects neurons in brain / spinal cord

3 Fundamentals of Nervous System

Histology of Nervous System: • Long-lived (~ 100 years) • High metabolic rate B. Neurons • Specialized “excitable” cells • Allow for communication throughout body (via electrical impulses)

Structural Classification of Neurons (# of processes) :

Multipolar Bipolar Unipolar ( 3 processes) (2 processes) (1 process)

Axon Axon Axon

Dendrites Trigger zone Dendrites Trigger zone Trigger zone

Dendrites

• Motor neurons • Sensory neurons • Sensory neurons • Interneurons (e.g., special organs) (PNS)

Central Nervous System

4 Central Nervous System

Organization of Nervous System:

Nervous system

Integration Central nervous system Peripheral nervous system (CNS) (PNS) Motor Sensory output input

Brain Spinal cord Motor division Sensory division (efferent) (afferent)

Autonomic nervous system Somatic nervous system (involuntary; smooth & cardiac muscle) (voluntary; skeletal muscle)

Sympathetic division Parasympathetic division

Central Nervous System

Brain: No correlation exists between and … • ~ 3.5 lbs (35 billion neurons) • ♂ brain ~ 10% larger than ♀ brain

Cerebrum Gross Anatomy: ()

Diencephalon ()

Brainstem ()

5 Marieb & Hoehn – Figure 12.1 Central Nervous System

Embryonic Development of Brain:

3 week old embryo

Neural crest

Neural plate Step 3: cells migrate; form Step 1: • Neural crest gives rise to PNS forms from surface

4 week old embryo Neural fold

Neural groove Step 2: Step 4: Neural plate invaginates; forms Neural groove becomes neural tube; sinks deep • Neural folds flank neural groove • Neural tube gives rise to CNS

Marieb & Hoehn – Figure 12.2 Central Nervous System

Embryonic Development of Brain: How we will consider brain anatomy

5 week old embryo

Neural Primary brain vesicles Secondary brain vesicles Adult brain structures tube

Telencephalon (endbrain)

Anterior Proencephalon Diencephalon (forebrain) (interbrain)

Mesencephalon Mesencephalon Brain stem (midbrain) (midbrain) (midbrain)

Metencephalon Brain stem () Rhombencephalon (afterbrain) (hindbrain) Cerebellum (spinalbrain) Brain stem (medulla) Posterior Spinal cord

6 Central Nervous System Space restriction greatly affects Embryonic Development of Brain: brain development

Brain stem (pons) Brain stem (midbrain) Cerebellum Midbrain

Diencephalon Brain stem (medulla)

Cerebrum Cervical flexure 5 week old embryo 13 week old embryo • Flexures develop to fit rapidly growing brain into membranous • Cerebrum forced to grow posterior and lateral (‘horseshoe’)

• Convolutions develop to Newborn increase surface area 26 week old embryo of brain Marieb & Hoehn – Figure 12.3

Central Nervous System Nuclei: Groups of cell bodies located in Basic Layout of Neurons: the central nervous system (analogous to ganglia in PNS)

White matter: Regions of myelinated in CNS Gray matter: Regions of unmyelinated axons / cell bodies in CNS

Cortex White White Gray matter matter Gray matter matter

Nucleus

Spinal cord Cerebrum

• Basic pattern observed in CNS • Cortex formed by migration of neurons • Cerebellum similar to cerebrum in its external cortex

Marieb & Hoehn – Figure 12.4

7 Marieb & Hoehn – Figure 12.5 Central Nervous System

Brain Anatomy:

A. Ventricles: Hollow chambers enclosed within brain (continuous with each other…)

Lateral ventricle Cerebrospinal fluid (CSF) • Provide constant, controlled environment for brain cells • Protect brain from toxins • Prevent escape of local

Choroid : Vascular network; produces CSF

Fourth ventricle • Similar ion composition to blood plasma •  protein content

Ventricles lined with ependymal cells (circulate CSF) • Gasses cross freely • 0.5 L / day produced

Costanzo – Figure 3.36

Central Nervous System

CSF Circulation: Presence of CSF in subarachnoid space Arachnoid villus gives buoyancy to brain (97% weight reduction)

1) CSF produced by in ventricles 2) CSF flows through ventricles and into subarachnoid space via lateral and median apertures 3) CSF exits subarachnoid space via arachnoid villi

Lateral aperture

puncture (spinal tap) (‘water on the brain”) Marieb & Hoehn – Figure 12.26

8 Central Nervous System

Cerebrum (forebrain)

Diencephalon (midbrain)

Brainstem Cerebellum (hindbrain)

Central Nervous System ~ 85% of brain mass

Brain Anatomy:

B. Cerebrum (cerebral hemispheres): Central

Parietal Frontal lobe lobe Parieto-occipital sulcus

Gyrus Sulcus Occipital (ridge) (groove) lobe Insula

Temporal lobe Lateral Fissure sulcus (deep groove) Marieb & Hoehn – Figure 12.6

9 Central Nervous System

Brain Anatomy:

B. Cerebrum (cerebral hemispheres):

Basic regions: Cerebral (superficial to deep)

1) Cerebral cortex (gray matter) 2) Cerebral white matter 3) Basal nuclei

Corpus callosum: White tract connecting cerebral hemispheres

Basal nuclei

Central Nervous System

Brain Anatomy: The cerebral B. Cerebrum (cerebral hemispheres): cortex is the 1) Cerebral cortex: seat of conscious behavior • Contains 3 types of functional areas: 1) Motor areas (send output) Only 2 - 4 mm thick but comprises 40% 2) Sensory areas (receive input) of the brain’s mass 3) Association areas (interpret data) 2.5 ft2 of surface area

Functional MRI scan (measure blood flow)

Neural cartography (electrostimulation)

10 Marieb & Hoehn – Figure 12.8 Central Nervous System

Brain Anatomy: Primary motor B. Cerebrum (cerebral hemispheres): cortex 1) Cerebral cortex: Conscious control of skeletal muscle movements • Motor areas:

Somatotopic mapping: The entire body is spatially represented in the cerebral cortex Pyramidal cells extend long axons to the spinal cord, forming , or corticospinal tracts

Central Nervous System

Homunculus (“little man”):

Note: One-to-one correspondence between cortical neurons and muscles misleading; map really “fuzzy”

Marieb & Hoehn – Figure 12.9

11 Marieb & Hoehn – Figure 12.8 Central Nervous System

Brain Anatomy: Primary motor B. Cerebrum (cerebral hemispheres): cortex Conscious control of skeletal 1) Cerebral cortex: communicates muscle movements directly with • Motor areas: primary

Frontal eye field Controls voluntary Premotor cortex movement of eyes Controls learned motor skills of repetitious or patterned nature (e.g., typing)

Broca’s area Controls muscles involved in speech production (often more pronounced in one hemisphere of brain)

Marieb & Hoehn – Figure 12.8 Central Nervous System

Brain Anatomy: Primary somatorsensory cortex B. Cerebrum (cerebral hemispheres): Receives information from Spatial sensory receptors in skin & 1) Cerebral cortex: discrimination proprioreceptors in joints • Sensory areas: Somatosensory association Gustatory cortex cortex Receives / interprets Integrates / interprets sensations of somatosensory inputs (e.g., temp. / pressure)

Primary visual Primary auditory cortex cortex Receives visual Receives auditory information information Medial (retinotopic mapping) (tonotopic mapping) Visual Auditory association Association area Olfactory cortex area Integrates / interprets Integrates / interprets Receives olfactory auditory inputs visual inputs information (e.g., music / thunder) (e.g., color / form) • Part of (‘nose brain’)

12 Marieb & Hoehn – Figure 12.8 Central Nervous System

Brain Anatomy: Locations where sensations, , B. Cerebrum (cerebral hemispheres): and become conscious 1) Cerebral cortex: (makes us who we are…)

• Association areas (multimodal):

(matures slowly) Anterior association area (Prefrontal cortex) • Intelligence • Complex • Recall • Personality

Central Nervous System Phrenology: Phineus Gage (1823 – 1860) The brain is the organ of the ; contains localized, specific modules

Franz Gall (1758 – 1828)

The American Crowbar Case

Introduction

13 Marieb & Hoehn – Figure 12.8 Central Nervous System

Brain Anatomy: Locations where sensations, thoughts, B. Cerebrum (cerebral hemispheres): and emotions become conscious 1) Cerebral cortex: (makes us who we are…)

• Association areas (multimodal):

Anterior association Posterior association area area • Pattern recognition • Spatial recognition • Sensory grouping • Language centers (Wernicke’s area)

Limbic association area Processes emotions related to personal / social interactions

Central Nervous System

Brain Anatomy: The cerebral B. Cerebrum (cerebral hemispheres): cortex is the 1) Cerebral cortex: seat of conscious behavior • Contains 3 types of functional areas • Contralateral control (e.g., left hemisphere controls right body) Only 2 - 4 mm thick but comprises 40% : of the brain’s mass Location where neural pathways cross 2.5 ft2 of surface area • Occur at different locations in CNS

• Lateralization (i.e., hemisphere specialization)

14 Central Nervous System

Categorical Representational

Central Nervous System

Brain Anatomy:

B. Cerebrum (cerebral hemispheres):

Basic regions: Cerebral cortex Cerebral (superficial to deep) white matter

1) Cerebral cortex (gray matter) 2) Cerebral white matter 3) Basal nuclei

Basal nuclei

15 Central Nervous System

Brain Anatomy:

B. Cerebrum (cerebral hemispheres): Commissural Association fibers 2) Cerebral white matter: fibers

Fiber tracts responsible for communication between cerebral areas and lower CNS

A) Commissural Fibers (form commissures) : • Interconnect cerebral hemispheres B) Association Fibers: • Interconnect areas of neural cortex within a single hemisphere

C) Projection Fibers: • Interconnect cerebral hemispheres with other regions of the brain

Corona radiata: Projection : Point where projection fibers radiate fan-like fibers Compact band of projection through cerebral white matter fibers near diencephalon

Marieb & Hoehn – Figure 12.10

Central Nervous System

Brain Anatomy:

B. Cerebrum (cerebral hemispheres):

Basic regions: Cerebral cortex Cerebral (superficial to deep) white matter

1) Cerebral cortex (gray matter) 2) Cerebral white matter 3) Basal nuclei

Basal nuclei

16 Central Nervous System

Brain Anatomy:

B. Cerebrum (cerebral hemispheres): 3) Basal nuclei: • Composed of gray matter ( cell bodies) • Function: 1) Subconscious control of skeletal muscle tone 2) Control stereotypical motor movements (e.g., arm swing) • Regulate intensity / inhibit unnecessary movements

Caudate

Putamen Corpus Lentiform Striped appearance nucleus due to passage of Globus internal capsule fibers pallidus

Central Nervous System

Cerebrum (forebrain)

Diencephalon (midbrain)

Brainstem Cerebellum (hindbrain)

17 Central Nervous System

Brain Anatomy:

C. Diencephalon: “Gateway to the Thalamus: cerebral cortex” • Composes 80% of diencephalon • Relay station for all information entering / exiting the cerebral cortex

Hypothalamus: • Autonomic control center • Center for emotional response • Body temperature regulation • Regulation of food / water intake • Regulation of sleep-wake cycles • Control of

Epithalamus: • Houses (melatonin) and choroid plexus (forms CSF) “Control center of body” Marieb & Hoehn – Figure 12.12 / 12.13

Central Nervous System “Emotional brain” Brain Anatomy: Diencephalon structures: (functional brain system): • Thalamus (anterior thalamic nuclei) • Hypothalamus Cerebral cortex structures: • Cingulate • Parahippocampal gyrus • • : Fiber tract linking regions together

 Alzheimer’s Disease:

• Control emotional states (e.g., fear) / behavioral drives (e.g., sex drive) Progressive degenerative disease of the brain • Link conscious (cerebral cortex) with unconscious function (brain stem) • Memory loss • Psychosomatic illnesses = -induced illness • Disorientation • Long-term memory storage / retrieval • Moodiness / confusion

18 Central Nervous System

Cerebrum (forebrain)

Diencephalon (midbrain)

Brainstem Cerebellum (hindbrain)

Central Nervous System

Brain Anatomy:

D. Brain stem: • Deep gray matter; superficial white matter • Produce rigidly programmed, autonomic behaviors necessary for survival • Conduction pathways between higher Thalamus and lower brain centers Midbrain: Midbrain • Visual / auditory centers

Pons: • Regulate respiration rate / depth

Medulla oblongata: Pons • Location where fiber tracts from Medulla (decussation) spinal cord cross over oblongata • Autonomic reflex center • rate / • Respiratory rhythm • / hiccupping / etc. Marieb & Hoehn – Figure 12.15

19 Marieb & Hoehn – Figure 12.19 Central Nervous System

Brain Anatomy: Aggregation of loosely Reticular Activating System (RAS - functional brain system): clustered neurons:

Lateral group Medial group Raphe nucleus • (midline) • Medial (large cell) group (small cell) visual • Lateral group Twisting of brain stem can stimuli lead to irreversible auditory LSD stimuli

general stimuli

• Maintains cerebral cortical alertness (e.g., on / off switch) • Filters out repetitive stimuli (~ 99% of stimuli filtered…)

Central Nervous System

Cerebrum (forebrain)

Diencephalon (midbrain)

Brainstem Cerebellum (hindbrain)

20 Central Nervous System

Brain Anatomy:

E. Cerebellum: “Small brain” • Gray matter superficial; white matter deep (11% TBM) • Precise timing of muscle coordination (balance, posture, repeated movements) Folia • All activity subconscious

Cerebellar Processing:

Cerebral cortex sends signal to move

Sensory information Maintain from body body coordination

Commands to motor neurons of spinal cord Marieb & Hoehn – Figure 12.17

Central Nervous System : Protection of the Brain: of the 1) Bone (Skull – cranium portion) 2) Meninges (specialized membranes)

A) (“tough mother”) C) (“gentle mother”) • Fibrous outer coating (2 layers) • Thin inner membrane • Protects CNS • Contains blood vessels B) (“ mother”) Two layers enclose • Delicate middle layer • Nourishes CNS

Bone Dura mater (periosteal layer) Dura mater (meningeal layer) Subarachnoid Arachnoid mater space (filled with CSF)

Pia mater

Marieb & Hoehn – Figure 12.24

21 Central Nervous System

Protection of the Brain: Constant internal environment necessary for proper neuronal functioning in brain 1) Bone (Skull – cranium portion) 2) Meninges (specialized connective tissue membranes) 3) Blood-brain barrier: -maintained barrier lining blood capillaries

Three layers of protection: A. endothelium B. Thick basal lamina C. Bulbous ‘feet’ of astrocytes • Signal tight junction formation

Tightly regulate substances bathing brain: In: glucose, amino acids, selected electrolytes Out: metabolic waste (urea), proteins, toxins,

• Displays differentially permeable (e.g., vomit center  brain stem)

Marieb & Hoehn – Figure 11.3

Central Nervous System

Homeostatic Imbalances of the Brain: Leading cause of accidental death in North America 1)

Concussion Subdural hemorrhage Alteration in brain function Bleeding into subarachnoid Swelling of the brain following blow to head space via ruptured vessels

2) Cerebrovascular accident Third leading cause of death in North America 3) Degenerative brain disorders Ischemic • Alzheimer’s disease Blockage of blood supply • Parkinson’s disease to brain due to blood clot • Huntington’s disease • May be transient

22 Central Nervous System

Organization of Nervous System:

Nervous system

Integration Central nervous system Peripheral nervous system (CNS) (PNS) Motor Sensory output input

Brain Spinal cord Motor division Sensory division (efferent) (afferent)

Autonomic nervous system Somatic nervous system (involuntary; smooth & cardiac muscle) (voluntary; skeletal muscle)

Sympathetic division Parasympathetic division

Central Nervous System Protected by / meninges Spinal Cord: • Provides conduction pathway to / from brain • Contains major reflex centers Cervical region • Independently initiates patterns of motor (8)(8) activity (e.g., walking) Gross Anatomy: Lumbar Thoracic • ~ 18 inches long (via vertebral foramen) enlargement region (12) • Two enlargements (cervical / lumbar) (12) Cornus • Innervation of limbs medullaris • Cord proper ends at L 1 Cauda Lumbar • (“horse’s tail”) equina region • Spinal (31 pairs) (5)(5) Sacral region (5) (5) (1)(1) Marieb & Hoehn – Figure 12.29

23 Central Nervous System Ascending tracts: Carry information to brain Spinal Cord: Descending tracts: Cross-sectional Anatomy: Carry information from brain Posterior median sulcus Transverse tracts: Posterior Carry information across cord White matter

Central canal Lateral Gray funiculus matter

Characteristics: 1) Decussation present 2) Multi-neuron pathways Anterior median fissure 3) Somatotopy exhibited 4) Symmetrical arrangement

Central Nervous System

Spinal Cord: Cross-sectional Anatomy:

Marieb & Hoehn – Figure 12.33

24 Central Nervous System

Spinal Cord: Cross-sectional Anatomy: Posterior median sulcus Posterior Posterior funiculus horn White (interneurons) matter

Central canal Lateral Lateral Gray funiculus matter horn (visceral motor neurons)

Gray commissure

Anterior Anterior funiculus horn Anterior median fissure (somatic motor neurons)

Central Nervous System

Spinal Cord: Cross-sectional Anatomy:

Dorsal Root

Dorsal root

Sensory neuron

Interneuron

Motor neuron

Ventral Root

25 Central Nervous System

Spinal Cord: Organization of Gray Matter:

Central Nervous System

Homeostatic Imbalances of the Spinal Cord: 1) Spinal cord trauma

Paralysis / Paraplegia Quadriplegia Damage to spinal cord leading Transection of spinal cord Transection of spinal cord

leading to functional / sensory loss between T1 and L1 between C4 and C7 2) Poliomyelitis 3) Amyotrophic lateral sclerosis (ALS)

Lou Gehrig’s disease

Destruction of ventral horn Progressive destruction of ventral motor neurons by horn motor neurons (autoimmune?)

26