CNS Anatomy and Cerebral Cortex: Brain, CSF, and Sensory-Motor Areas

Rostral

Toward the front (nose/head end) of the CNS

Caudal

Toward the tail end of the CNS

Dorsal vs. ventral

Dorsal = back/posterior side - ventral = belly/anterior side

Gray matter (CNS)

Unmyelinated nerve cell bodies and axon terminals - clusters of cell bodies are nuclei

White matter (CNS)

Myelinated axons - axon bundles connecting CNS regions are tracts - very few cell bodies

Nuclei (CNS)

Clusters of neuron cell bodies in the CNS

Tracts (CNS)

Axon bundles connecting regions of the CNS

Limbic system

Link between cognitive functions and emotions

Amygdala

Emotion and memory

Hippocampus

Learning and memory

Basic pattern of the spinal cord

Central cavity surrounded by a gray matter core / with white matter (myelinated fiber tracts) external to it

Protection of the brain and spinal cord (bone)

Brain is encased in the bony skull (cranium) - spinal cord runs through the vertebral column

Meninges

Connective tissue between bone and neural tissue that stabilizes it and protects it from bruising

Three meningeal layers (outside to inside)

Dura mater / arachnoid membrane / pia mater

Subarachnoid space

Space between arachnoid membrane and pia mater - contains cerebrospinal fluid (CSF)

Cerebrospinal fluid (CSF)

Clear / colorless fluid that bathes the entire CNS - secreted by the choroid plexus

Ventricles

Ependymal cell-lined / fluid-filled cavities of the brain that contain CSF

Choroid plexus

Makes CSF - found in the lateral / 3rd / and 4th ventricles

CSF production and turnover

Made and drained into the blood constantly - total volume ~150 mL / replaced every 8 hours

Why is CSF composition (especially pH) important?

Essential in the control of cerebral blood flow and breathing

CSF: mechanical protection

Cushion and shock absorber - lets the brain float in the cranial cavity / reducing its effective weight by 97%

CSF: chemical protection

Provides optimal ionic composition for neuronal signaling - carries chemical signals such as hormones that control sleep and appetite

CSF: circulation

Allows exchange of nutrients and wastes between the blood and the CNS

Hydrocephalus

Build-up of CSF

Causes of hydrocephalus

CSF overproduction - obstruction in the ventricular system - problems with absorption - inflammation of CSF space (e.g. / meningitis / infection / or blood entry from hemorrhage/trauma)

Meningitis

Bacterial or viral inflammation of the meninges/CSF space - can cause hydrocephalus

Cerebral hemispheres

Superior part of the brain - make up 83% of its mass - contain gyri / sulci / and fissures

Gyri

Ridges on the cerebral hemispheres

Sulci

Shallow grooves on the cerebral hemispheres

Fissures

Deep grooves in the cerebral hemispheres

Five lobes of the cerebral hemisphere

Frontal / parietal / temporal / occipital / insula

Lateralization of cortical function

Each hemisphere has abilities not shared with its partner

Cerebral dominance

Designates the hemisphere dominant for a function / e.g. / language (usually the left)

Left hemisphere function

Language / math / and logic

Right hemisphere function

Visual-spatial skills / emotion / and artistic skills

Cerebral cortex

Superficial gray matter - ~40% of brain mass - gyri convolutions increase surface area

Contralateral control

Each cerebral hemisphere controls the opposite side of the body

Three types of functional areas of the cerebral cortex

Motor areas (voluntary movement) / sensory areas (conscious awareness of sensation) / association areas (integrate diverse information)

Motor areas of the cortex

Control voluntary movement

Sensory areas of the cortex

Conscious awareness of sensation

Association areas of the cortex

Integrate diverse information

Primary motor cortex

Contains pyramidal cells whose axons make up the corticospinal tracts - allows conscious control of precise / skilled / voluntary movements

Cortical body representation

No correspondence between cortical area size and size of the body part served

Deep insula

Integration of sensory information / especially pain

Four major sensory areas

Primary somatosensory cortex - somatosensory association cortex - visual and auditory areas - olfactory / gustatory / and vestibular cortices

Primary somatosensory cortex

Receives information from the skin and skeletal muscles - exhibits spatial discrimination

Somatosensory association cortex

Integrates sensory information - forms a comprehensive understanding of the stimulus - determines size / texture / and relationship of parts

Primary visual (striate) cortex

At the extreme posterior tip of the occipital lobe - receives visual information from the retinas

Visual association area

Surrounds the primary visual cortex - interprets visual stimuli (color / form / movement)

Primary auditory cortex

Superior margin of the temporal lobe - receives information on pitch / rhythm / and loudness

Auditory association area

Posterior to the primary auditory cortex - stores memories of sounds and permits perception of sounds

Prefrontal cortex

Anterior frontal lobe - intellect / cognition / recall / personality - judgment / reasoning / persistence / conscience - closely linked to the limbic system

Broca's area

Left hemisphere only - motor speech area that directs tongue muscles - active when preparing to speak (word formation) - damage causes inability to speak

Broca's aphasia

Inability to speak/produce speech resulting from damage to Broca's area

Wernicke's area

Language comprehension (spoken and written words) - sounding out unfamiliar words - damage causes inability to understand speech and to read

Wernicke's area damage

Person can speak without difficulty / but the words don't make sense - cannot attach meaning to words or convey thoughts

Arcuate fasciculus

Fiber tract connecting Wernicke's area and Broca's area

Conduction aphasia

Language disorder caused by damage to the arcuate fasciculus

Visceral association area

In the cortex of the insula - conscious perception of visceral sensations (upset stomach / full bladder / need for a bowel movement)

Cerebral white matter: three fiber types

Commissures / association fibers / projection fibers

Commissures

Connect corresponding gray areas of the two hemispheres so they function as one - the largest and most important is the corpus callosum

Corpus callosum

Largest commissure - connects the two cerebral hemispheres

Association fibers

Connect different parts of the same hemisphere

Projection fibers

Enter the hemispheres from lower brain or cord centers - tie the cortex to the rest of the nervous system and to receptors and effectors

Sagittal plane

Plane dividing the body/brain into left and right parts

Coronal plane

Plane dividing the body/brain into anterior and posterior (front/back) parts

Diencephalon

Central core of the forebrain (deep gray matter) / almost surrounded by the cerebral hemispheres - includes thalamus / hypothalamus / part of the pituitary gland / and pineal gland

Thalamus

Receives sensory input (except smell) - sorts / edits / and relays it as a group - all inputs ascending to the cortex pass through it - mediates sensation / motor activities / cortical arousal / learning / and memory

Which sensory input does NOT go through the thalamus?

Smell (olfaction)

Lateral geniculate nuclei

Part of the thalamus - relays visual information to the occipital lobe

Medial geniculate nuclei

Part of the thalamus - relays auditory information to the temporal lobe

Hypothalamus

Maintains homeostasis and regulates the autonomic system - controls the endocrine system and pituitary hormone secretion

Hypothalamic centers (list)

Hunger/satiety and thirst - body temperature - sleep and wakefulness - sexual arousal and performance - emotions (fear / anger / pain / pleasure) - endocrine control

Preoptic area (hypothalamus)

Temperature control - regulates shivering / hyperventilation / vasodilation / and sweating

Supraoptic nucleus

Produces antidiuretic hormone (ADH / vasopressin) to control urine volume/osmolarity by water reabsorption

Paraventricular nucleus

Produces oxytocin / which stimulates uterine contraction

Limbic system: connections

Very few connections to the cerebral cortex - "emotional" and "primal"

Limbic system: primal functions

Rage and aggression - fear - hunger/satiety (addiction) - sex/sex drive (addiction) - reward (addiction) and punishment

Memory: role of hippocampus

Critical component of memory acquisition and consolidation

Short-term memory

Memory of recent events - transferred to long-term memory by memory consolidation

Memory consolidation

Transfer of short-term to long-term memory - sleep is needed for optimum consolidation

Long-term memory (LTM)

Requires actual structural changes - in the hippocampus this is termed long-term potentiation (LTP)

Long-term potentiation (LTP)

Structural/synaptic strengthening in the hippocampus underlying long-term memory

Nondeclarative (implicit) memory

Memory of simple skills and conditioning (e.g. / tying a shoe / riding a bike)

Declarative (explicit) memory

Memory that can be verbalized - impaired in amnesia

Semantic memory

Declarative memory of facts (e.g. / names of the bones of the body)

Episodic memory

Declarative memory of events (e.g. / taking a practical exam on the skeletal system)

LTP step 1: glutamate and AMPA receptor

Glutamate binds AMPA receptor / allowing Na+ in

LTP step 2: NMDA receptor activation

Cell depolarizes / activating NMDA receptor channels (previously inactive because Mg2+ blocked the pore)

LTP step 3: NMDA receptor

Allows Ca2+ and Na+ to enter

LTP step 4: calcium signaling

Ca2+ binds calmodulin / which activates CaMKII (Ca2+/calmodulin-dependent protein kinase II)

CaMKII in LTP

Causes more AMPA receptors to fuse to the plasma membrane / strengthening the synapse (more sensitive to glutamate release - EPSP)

CREB

cAMP response element binding protein - transcription factor activated in LTP that turns on genes for mRNA/proteins / including dendritic spines with AMPA receptors

Ion that stimulates genetic transcription for learning and memory

Ca2+

Magnesium (Mg2+) in LTP

Blocks the pore of the NMDA receptor until the cell is depolarized

Emotions and memory

Emotions can strengthen or weaken memory formation - the amygdala is involved in the emotional component of memory

Stress and memory

Stress impairs memory consolidation in the hippocampus and working memory function of the prefrontal cortex

PTSD and memory

May result in hippocampal atrophy - memories are stored but retrieval is hindered

Cortisol and memory

Cortisol strengthens emotional memory formation via the amygdala but weakens hippocampal memory formation and retrieval

Suprachiasmatic nuclei (SCN)

Main control of circadian rhythms - ~20 /000 "clock cells" oscillating every 24 hours