What are the primary structures and functions of the central nervous system? 11/14 and 11/16

1. What are the primary structures and functions of the central nervous system? 11/14 and 11/16 CH 13 and 14 What are landmark structures of the CNS? What are the structures of a spinal nerve? What are the structures of the spinal cord? Blood Brain Barrier: how does it protect us? Meninges: how do they protect us? Cerebral Spinal Fluid: Where does it come from?

3. Central nervous system can be broken down into two parts: brain and spinal cord Embryonic Origin: CNS forms as an in-folding of epithelium -Implications for spina bifida and folic acid Three Major Regions of the Brain: • Cerbrum (cerbral hemispheres): the neurons of the “cortex” controls voluntary thoughts and actions -Consists of folds (gyri) and grooves (sulchi) -The corpus callosum connects the two cerebral halves • Cerebellum: helps coordinate the wishes of the cortex -It contains half the neurons of the brain! -It makes an “action” possible • Brain Stem: coordinates baseline functions: breathing/heart rate -Medulla Oblongata is the last part of brain • CNS continues as the “Spinal Cord”

4. Nerve: cluster of axons/dendrites located outside of the CNS Ganglion: cluster of nerve cell bodies (soma) outside CNS

5. Neurons Need Constant Oxygen! PERIOD! • Neurons are specialized for maintaining specific membrane potentials and forming action potentials at the “right” moment. • Neurons are mostly dependent upon glycolysis because they have very few mitochondria. • The few mitochondria neurons we “DO” have are in need of a constant supply of oxygen to maintain the tenuous balance of ATP production and demand in neurons. • Blood supply to capillaries where gas/nutrient exchange occurs are under low pressure (10-20 mmHg), while the blood pressure in the aorta is typically 120/80.

6. How do oxygen and other nutrient molecules reach neurons? The oxygen and nutrient demands of the brain are met by nutrients that must first enter capillaries and diffuse out to the surrounding tissues. The blood vessels are permeable to glucose, Na+, oxygen and CO2. They extend deep into the neural tissues! Blockages in cerebral vessels can cause brain injury (ischemia) or a CerbralVascular Accident/ CVA/stroke (infarct or brain cell death ). Causes of Blockage: Blood clot or external pressure (tamponade) Stoppage of the Heart does lead to stoppage of cerebral blood flow! Three Considerations: 1) What happens to intracranial pressure and capillary flow when a cerebral artery undergoes an aneurism or a rupture? 2) How do we know that stoppage of blood flow to the brain stops for more than about 20 seconds, you black out? 3) How do we know that stoppage of 3-5 minutes causes cell infarct?

7. Blood vessels pass through the nervous tissues of a nerve, however these blood vessels have a very limited permeability due to the BBB. Note: Endoneurium surround/support axons with or without Schwann cells.

8. Important Features: Ventral Root: MOTOR Dorsal Root: SENSORY D. Root “Ganglia”: Nerve Plexus Functions: 31 spinal nerves total! C1-8+T1-12+L1-5+ S1-5 and 1 coccygeal Each with a left/right branch Spinal nerves exit the spinal cord via the intervertebral notchs (foramen) of every vertebra. This permits “afferent” nerves to enter and “efferent” nerves to leave the spinal cord (CNS).

9. After a spinal nerve exits the intervertebral foramen it splits into three major branches • 1) Dorsal Ramus: to dorsal region • 2) Ventral Ramus: to ventral region • 3) Communicating Rami: to the sympathetic chain ganglion • Sometimes a plexus is formed when several ventral rami merge (cervical, brachial, lumbar, sacral and coccygeal)

10. Dermatomes overlap by about 50% Novacaine blocks Na+-voltage gated channels! When applied to a spinal nerve it prevent AP conduction of afferent neurons. Knock out any three adjacent Spinal Nerves and you can do local surgery on the skin! “Painless ” Consider the Dentist! Dermatomes can also be used for: locating spinal injury sites accupuntcure Each spinal nerve is responsible for sensation in a band of skin that extends around the body in a band roughly adjacent to the nerves origin. This band of skin is called a dermatome.

11. Parts: D/V Sulchi D/V/L Horns Central Canal Conus Medullaris Cauda Equina Why are spinal cord injuries less common when you fracture L3-L5? The spinal cord conducts APs to and from the brain, it controls locomotion, and it mediates reflex actions so that some APs need not travel all the way to/from the brain.

12. White Matter: axons/dendrites Grey Matter: somas Grey Commissure: crossing Tracts: cluster with similar source or destination. Motor vs. Sensory Tracts: Ascending: Dorsal/Lateral Descending: Ventral/Lateral Three layers of protection: Dura M-Arachnoid M.- Pia M. Three spaces: Epidural-Dural-Subarachnoid There are specialized regions within the spinal cord called ascending and descending tracts (Lab Review)

13. The blood brain barrier (BBB) provides critical protection to the CNS from materials in the blood! Endothelial cell Tight junctions create the BBB in adults! What about the BBB neonates? Why is the blood brain barrier significant? • Prevents some pathogenic organisms from entering the CSF • Prevents some toxins from entering the CSF • Prevents some drugs from entering CSF • What can happens to BBB function and formation if you have high blood pressure or a concussion (trauma)? • Why does the BBB create drug transport problems? Consider Parkinsons’ Disease, L-DOPA and Michael J. Fox • Circumventricular organs provide a back door for toxins to reach the CSF directly from the blood! • Spinal Tap: provides a way to detect pathogens in CSF!

14. The CNS is protected by several structures: fluids, bones and meninges! • Skull plates/Vertebrae: protection #1 • Three sheaths (meninges) of connective tissue cover the brain/spinal cord: protection #2 • 2a: Dura mater (Periosteal and Meningeal)- “tough mother” Tough CT for protection Falx cerebri and Tentorium cerebelli “Subdural Space” • 2b: Archanoid mater- “Spider-like mother” CSF reabsorption Some protection Extends across sulcus “Subarachnoid Space” • 2c: Pia mater- “Delicate mother” Extends into sulcusLast line of defense Epidural Space: located between dura mater and lumbar vertebrae Perivascular Space: space filled by blood vessels that penetrate the pia mater and enter the neural tissue where nutrient exchange occurs

15. The brain has special fluid filled spaces called ventricles that are filled with cerebral spinal fluids that protect the brain. Functions of Cerebrospinal Fluid: • 1) Brain Buoyancy: Why are plasma membranes fatty acid rich why does this help achieve neutral buoyancy? Why is this good? • 2) Shock absorption: When do we receive most concussions? • 3) Chemical Protection: Why is the brain so sensitive to pH? Where are the ventricles and what do they do? • Two Lateral Ventricles: one per cerebral hemisphere • Interventricular foramen to link lateral ventricles- • One Third ventricle: one between the two hemispheres • Mesencephalic or Cerebral Aqueduct- • One Fourth ventricle: one at base of brain stem/cerebellum Central Canal extends from fourth ventricle into the length of the spinal

16. Where is the cerebral spinal fluid formed, how much fluid is produced and where does the fluid go? • What is CSF composed of relative to blood? • How much CSF we have/produce? • CSF is produced at: choroid plexus, subarachnoid plexus and by ependymal lining • Excess CSF is removed by arachnoid villi where it enters the venous blood stream. • What is Hydroencephally? • What color is your CSF if you have an infection of the CNS? • Why do we perform “Lumbar” Spinal Taps and not “cervical” taps?

17. Rarely people create excess CSF and intracranial pressure when they travel to high altitude causing a potentially fatal condition called HACE. You could even see this on a ski trip to Colorado! 

18. The hindbrain consists of two subdivisions: myelencephalon and metencephalon • Myelencephalon: This region becomes the medulla oblongata • Cardiac Center-heart rate • Vasomotor Center-blood pressure • Respiratory Centers- PO2 and PCO2 • MO ends at foramen magnum and becomes the spinal cord • What is life like in an ancephalic neonate? What is needed for “life”?

19. Metencephalon=Pons+Cerebellum Pons: next after medulla • Helps Medulla Regulate Breathing: pneumotaxic/apneustic areas • Coordinates passage of APs between cerebrum-cerebellum Cerebellum: coordinates higher motor neuron output before APs sent into the spinal cord • Maintains muscle tone- • Control limb proprioception- Structures of the Cerebellum: • L/R hemispheres • Vermis and Folia • Abundant dendrite rich Purkinji cells Cerebellum helps turn ideas of cerebrum into action potentials sent to muscles for action!

20. RF has special nuclei that: Control arousal Moderate pain Control autonomic functions Help control somatic motor activity Anesthetics work here! Mesencephalon: Midbrain sits between hypothalmus, reticular formation, and pons The reticular formation is in three different parts of the brain: medulla, pons and midbrain

21. Forebrain1-front, middle and back Diencephalon • Hypothalmus: front Hunger and satiety centers Thermostat: losing or gaining Heart rate modification Osmoreceptors/thirst detection Releasing hormones to Ant. Pituitary Post. Pituitary: is an extension of the hypothalamusoxytocin + ADH Time keeping and secretions Centers for emotions/pleasure • Thalamus: middle Info gateway to cerebral cortex • Epithalamus: back Pineal gland and diurnal secretions

22. Grey mater: 2-3mm,4 lobesX2sides Gyri/Sulchi increase SA X3 times! Frontal Lobe: Voluntary motor actions, foresight/planning, and social judgments Parietal Lobe: central sulcus to parietoccipital sulcus Sensory Integration Occipital Lobe: visual interpreting Temporal Lobe: visual recognition, hearing, learning, memory, smell Pete was hit by a baseball and lost the ability to name people by their face, but could name people by their voice. What lobe may have been effected? Forebrain: The cerebral cortex (telencephalon) associates sensory input APs to create/implement thoughts, value sensory strengths/ weaknesses, create reason and generate voluntary motor functions.

23. Cerebral white (cortex) matter consists of inter communicating axons and dendrites allowing billions of cells to modify each others membrane potentials and ability to make action potentials!! THIS IS AMAZING!! • Lies underneath the Grey Matter! • Projection Tracts: higher (cortex) to lower brain function • Commissural Tracts: hemisphere to hemisphere • Association Tracts: area-to-area in one hemisphere • Short-term and Long-term potentiation: changing the resting membrane potential of the right cellmemory • Learning occurs with repetitive action potentials being sent along these synapses and tracts.

24. Sensory Association Areas: primarily behind the central sulchi. Information enters the cortex via the thalamus! Where are the Areas? V.I.P. for lab test: Primary Somato-Sensory Area: Primary Visual Area: Primary Auditory Area: Primary Gustatory Area: Primary Olfactory Area: Cognition is the sum of our awareness, knowledge, and memory. Its function is dependent upon the integrative functions of association areas in the cortex.

25. Where are the motor areas? • Reference Points: • Central Sulchus- • Precentral Gyrus- Two Main Motor Regions in Cortex: • 1) Premotor/Motor Association area: Coordinated or learned muscle sequences originate here! • How do you step from here to there? • What muscles will be used in what sequence? • 2) Precentral Gyrus is the Primary Motor Area: • Action potentials from motor association area arrive here. This is where action potentials are integrated and leave the cortex • Next Step: Brainstem

26. Humunculi for sense and motor functions line up on the precentral or postcentral gyri. How can this be used to characterize the location of a injury/stroke? Why is it important to know where the injury occurred?

27. Hearing involves several different association areas in the cortex. Interneurons are critical for processing of visual information between the visual association areas of the brain.

28. Damage to the brain comes in different forms, degrees of severity, and permanence. • Brain concussion- • Brain laceration- • Meningitis- • Encephalitis- • What does trauma do to the BloodBrainBarrier? Consequences of BBB damage? • “Cerebral vascular accident”/ “Stroke”- Blood flow changes and Hypoxia • Transient ischemic attack- Hypoxia/Ischemia/Cell Death (Necrosis or Infarct): • Dementia and Alzheimer Disease

29. Damage to one side of the brain often appears as a loss of function/sensation in the contralateral side! The corpus callosum lets action potentials cross along commissural tracts (decussation) between the two hemispheres!

30. Some classic brain injury stories: Phineus Gage, Red Barron, auto/motorcycle injury victims. Remember: brain/body may live on, but the personality may never be the same!

31. Memory entails the modification of nerve cell membrane potentials, neurotransmitter release and excitability. How do we create memories that last a few seconds, minutes, days, years or decades? • Hippocampus organizes input and determines what/if info goes to long-term locations in the cerebral cortex. • Long-term potentiation means neurons permanently change their resting membrane potential. This means memory has occurred. How this creates “memory” is poorly understood. • Amnesia can be of two types: 1) Retrograde Amnesia: you cannot remember your past Example: music you forgot from your past (Ozzy?) 2) Anterograde Amnesia: you cannot remember new things Example: music today that you forgot (Miley Cyrus?) Remember: With regards to neuronal function ones amnesia can be temporary (sometimes due to hypoxia) or permanent (sometimes due to infarct).

32. Why doesn’t the pre-frontal cortex always have the capacity to prevent our emotions from getting the best of us? • Sob sessions, violent anger, revenge, love, pleasure, passion, involuntary manslaughter……these are our emotions! • The farther we go from the cortex, the less control we have over the brain function! • Pre-frontal cortex: Judgments, Intent, Premeditation, and Self-Control • The amygdala and hypothalmus (Limbic System) are inferior to the cortex and work together to mitigate emotions! • Because these structures sit below the cortex, they can over-ride the cortex! • Hypothalmus: mitigates the senses of reward and punishment! • Hypothamlus: mitigates sleep and circadian rhythms

33. Review of action potentials moving into (sensory info)/out of (motor info) the brain. Most control is exerted in a contra-lateral fashion!

34. Review For Lab Exam: There are 12 (I-XII) cranial nerves numbered by sequence of exit starting at the rostral end of the brain and can have motor, sensory or mixed function. • I-Olfactory: Mostly sensory, cribiform plate • II-Optic: Mostly sensory, retina • III-Oculomotor: Mostly motor Constrict pupils Control Rectus and inf. Obliques • IV-Trochlear: Mostly motor-Superior obliques • V-Trigeminals: Massive and Mixed: Three branches *Often cut by accident or injury *Sensation from the face! *Important for chewing!

35. NOTE: almost every time a facial nerve innervates a muscle, there are also sensory fibers (from spindles) running back along the same nerve that indicate the degree of stretch (proprioception) in the muscle to prevent overstretch of the target muscle! VI-Abducens: Mostly motor to the lateral rectus muscles of the eye VII-Facial: Mixed Nerve Function Taste or gustation comes from tongue! Proprioception comes from the scalp! *Motor activity to facial muscles…huge nerve *Motor activity to lacrimal glands: please don’t cry! VIII-Cranial/ Vestibulocochlear/or/Auditory Nerve Mainly sensory! @Semicircular canals and equilibrium info sent here! @Inner ear and hearing info sent here! *Motor functions adjust sensitivity of haircells!

36. XI-Spinal Accessory Motor: throat, trapezius sternocleidomastoid Sensory: proprioceptor throat/voice box XII-Hypoglossal: mixed Tongue proprioceptors Motor functions help control: speech and swallowing IX-Glossopharyngeal: Mixed Nerve Afferent: Taste, touch, temperature on the tongue. Efferent: muscles for swallowing in the throat