Chp 14 (Brain and Cranial Nerves)

Brains Contribution to Homeostasis

-receiving sensory input

-integrating new and stores info

-making decisions and responses through motor activities

What protects the brain?

-Cranial Meninges (same as spinal) And Bones

• dura has 2 layers: periosteal (external) meningeal (internal) and 3 extensions:

  • Falx Cerebri: splits cerebrum hemispheres

  • Falx Cerebelli: splits cerebellum hemispheres

  • Tentarium Cerebelli: splits cerebrum and cerebellum

• venous sinus drains blood and CSF

Brain Circulation

Blood flows TO brain: internal carotid → vertebral arteries

Blood flow away from brain TO heart: dural venous → int. Jugular veins

-interruption of oxygen can lead to weakening/damage of braiN

-measured by fMRI

Blood-Brain Barrier

-prevents harmful substances entering, formed by

• Tight junctions: seal brain capillaries’ endothelial cells

• Basement membrane: thick, surrounds endothelial cells

• Astrocytes: press against cap’s, secretes substance to allow passage btw blood n neurons

Cerebrospinal Fluid (CSF) Functions

-colourless, mainly water, bathes CNS

• mechanical protection: absorbs shock n protects the delicate tissues of the CNS from jolts, allows brain to float

• Chemical Protection: optimal chemical environment for neuronal signlaing

• Circulation: medium for nutrient, waste, exchange btw blood and nervous tissue

4 CSF Filled Ventricles

2 Lateral: for each hemisphere in cerebrum

• seperated by septum pellucidum

3rd: along midline, above hypothalamus, btw R/L of thalamus

4th: btw brainstem and cerebellum

Where is CSF produced?

-choroid plexuses (Cap’s covered by ependymal cells found in ventricle walls)

• cells secerete CSF via blood plasma filtration, and joined by tight junctions to make blood-CSF barrier

Circulation of CSF

Venous blood: Lat ventricles → 3rd → 4th → subarachnoid space → arachnoid villi of dural venous sinuses → heart n lungs

THEN

Arterial blood: 4th’s choroid plexuses → 3rd’s choroid plexuses → lat’s choroid plexuses

Reabsorption of CSF

-reabsorbed through arachnoid villi (looks like grapes)

Hydrocephalus

-build of CSF pressure due to drainage blockage of CSF (eg; tumour, inflammation)

• allowed in babies (for fontanels to expand)

Brainstem Parts

• medulla oblangata

• Pons

• Midbrain

Reticular foramen covers brain stem

Medulla Oblangata

-Has ascending sensory + descending motor tracts, nuclei

-pyramids = ventral surface bulge

• motor tracts that pass from cerebrum to spinal cord

• Control voluntary movement in limbs n trunk

-decussation (crossing) of pyramids, crosses over

• L side of brain controls R side body functions (and vice versa)

Body Functions Medulla Controls

Cardiovascular Centre: force n rate of heartbeat, BV diameter

Respiratory Center: rhythm of breathing

Reflex Center: coughing, sneezing, swallowing

-gustatory, cochlear, and vestibular nuclei, and nuclei for cranial nerves (8-12)

• somatic sensation nuclei (eg; touch, proprioception)

Pons

-has nuclei and tracts

-connects brain parts via tracts

-helps in breathing

-has nuclei from cranial nerves (5-8)

Midbrain

-has cerebral aqueduct, connects 3rd n 4th ventricle

-has sensory + motor tracts, nuclei (visual and auditory info)

Anterior and Posterior Midbrain

Ant. (descending): cerebral peduncles = paired axons

Post. (Ascending): tectum = 4 rounded elevations

• 2 superior elevation (superior colliculi)

  • Reflex center for visual (eg; object tracking)

• 2 inferior elevation (inferior colliculi)

  • Auditory pathway, relays from ear to thalamus, reflex center for startle reflex

Substantia nigra: release dopamine (death of these cells = Parkinsons)

Nuceli from cranial nerves (3-4)

Reticular Formation

-area in brainstem where white + grey matter have netlike arrangement

-has reticular activating system (RAS)

• maintains consciousness with stimuli

• Alerts cerebral cortex to sensory signals to wake up

Cerebellum

-evaluates movements initiated by motor areas in cerebrum being carried out

-adjusts posture

-programs and fine tunes voluntary and involuntary movements

-store memories of learned movements (eg; typing)

-dmg can cause atoxia (inability to coordinate movements)

• no proprioception, act drunk

Thalamus

-2 halves held tgt by interthalamic adhesion, has 7 major nuclei groups

-relay station for sensory and motor functions

• sensory

  • Small piece of received Sensory info from spinal cord n brainstem goes through thalamus → cerebral cortex (like focusing on one sound in a noisy room, like a filter)

  • Pain, temp, pressure, hearing

• Motor

  • Send info from cerebellum n basal nuclei → primary motor area of cortex

  • Relay station btw cerebrum parts

-consciousness, learning, memory, emotions

Hypothalamus

-has 12 nuclei in 4 regions

-controls many body activities, a major regulator of homeostasis

-connects to pituitary gland, ECF → blood (where endocrine n nervous meet)

Hypothalamus Functions

1. Control of ANS: regulator of visceral activities (eg; regulation of HR, food movement in GI tract)

2. Hormone Production: releasing or inhibiting hormones released into capillary network (stimulate/inhibit secretion of anterior pituitary hormones), make ADH

3. Regulation of Emotional n Behavioural Patterns: w/ limbic system, expression of rage, pain, pleasure

4. Regulation of eating and drinking: thirst, feeding, and satiety centers

5. Control of Body Temp: when blood flowing through hypo is too high/low, hypo directs ANS accordingly

6. Regulation of Circadian Rhythms n Consciousness: linked to input from retina to establish 24hr cycle

Epithalamus

-above behind thalamus, contains pineal gland

• endocrine gland, secretes melatonin during darkness, promotes sleepiness

Circumventricular Organs

-lie in 3rd ventricle’s wall, no BBB

-monitors chemical changes in blood

-coordinate homeostatic activities of endocrine and nervous

-regulates BP, hunger, thirst

Cerebrum

-gives us high thinking

-outer cerebral cortex, inner cerebral white matter, deep gray matter nuclei, gyri (bumps)

-fissures (deep grooves) and sulcus (shallower grooves) in btw folds

Cerebral Hemispheres n Lobes

5 lobes: Frontal, Temporal, Occipital, Parietal, insula (deep)

• All split by longitudinal fissure

Pre-Central Gyrus: primary MOTOR area

Post-Central Gyrus: primary SOMATO SENSORY area

Each hemisphere receives sensory input n generates motor outputs to OPPOSITE side of body

Cerebral White Matters

Under cortex, myelinated axons running in 3 directions

Association tracts: connect/transmit NI’s btw gyri in SAME hemisphere

Commisural Tracts: from gyri of 1 hemisphere to other

Projection Tracts: form descending/ascending tracts that transmit impulses from cerebrum to other parts of brain and spinal cord (eg; diencephalon)

Limbic System

-establishment of emotional states

• pain, pleasure, anger, memory, etc

3 Types of Areas in Cerebral Cortex

Sensory Areas: perception of sensations

Motor Areas: initiate movements

Association Areas: memory, emotions, reasoning, personality

Sensory Areas

-reception and interpretation of sensory impulses

-primary visual, auditory, gustatory, olfactory, somatosensory areas

Primary Somatosensory Area

-postcentral gyrus

-input from touch, proprioception, pain, tickle, thermal sensations

-mainly for localization of origin and intensity of sensation

Primary Visual Area

-tip of occipital bone

-receives impulses that convey info (eg; shape, color, movement) for vision

Primary Auditory Area

-superior part of temporal lobe