Honors Anatomy & Physiology

1. Honors Anatomy & Physiology Nervous System

2. Neuron Structure • Characteristics • Life-long cell once it has established a connection to another neuron or to muscles • Neurons have high metabolism • Require oxygen 24/7 • Don’t do well when deprived of O2 past 10 min • Amitotic • Can repair damaged dendrites and axons in PNS • Cannot replicate themselves to repair dead or dying neurons

3. Excitability • Ability to respond to stimuli • Irritability • Sensory adaptation • With prolonged stimulation, signal is temporarily lost (e.g. smell) • Conductivity • Ability to transmit an impulse

4. Structure • Dendrites • Receive the message or stimuli (pain, pressure, temperature, etc.) • Carry the message to the cell body • Cell Body • Message travels through cell body to axon hillock • Cell body contains • Nucleus • Lots of mitochondria • No centrioles – Not needed! • Rough ER – needed for protein synthesis • Neurotransmitter used to transmit the message to the next neuron is made in cell body and sent to axon terminal branches

5. Axon Hillock (This is where it all happens!) • If message is strong enough and triggers the axon hillock, then message is allowed to travel down the axon • Axon • Carry messages away from cell body/axon hillock • Axon Branches • Many axons have multiple terminal branches • The end of the branch flattens into a disc shape called the synaptic bulb • Contains small vacuoles that contain the neurotransmitter • Synaptic cleft, or synapse • Space between the 2 neurons, or neuron & muscle

6. Neuron

7. Shapes of Neurons • Unipolar • “uni” = one uninterrupted unit • Cell bodies are housed off to the side • Always sensory • Bipolar • Cell body in middle of cell, creating 2 parts – “bi” • In adult, make up Cranial Nerves I (Olfactory) and II (Optic) • Sensory

8. Multipolar • Many dendrites = “multi” • In PNS – multipolar neurons are always motor neurons • All neurons in CNS ARE multipolar

10. Neurophysiology • Resting Membrane Potential • Every cell has sodium potassium (NaK) pumps in their cell membranes • NaK pump uses ATP to force 3 Na+ out and 2 K+ into cell • Continual process for the cell • Sets up unequal balance of positive charges • Outside of cell has a slightly positive charge • Inside of cell has a less positive charge = relatively “negative” • Electrical charge across the membrane = difference of -70 mv • Polarization = outside +, inside – = Resting Membrane Potential

11. ONLY Neurons and Muscle Cells can CHANGE the charge to do work • Depolarization - Open the gates and let Na+ IN • Causes inside of the cell to become less negative • If enough gates open, Na+ floods the cell • Inside of cell becomes as positive as outside = roughly equal charges • Repolarization - Close the gates to end the “message” and “reset” the membrane • Enzyme destroys the neurotransmitter • K+ leaks out • NaK pump pulls 2 K+ back inside and kicks 3 Na+ back outside • Resting membrane potential is re-established

12. Threshold Stimulus • Enough Na+ must enter to change the charge on the dendrite • Graded Potential • Small electrical change small depolarization -55mv -60 mv • Action Potential • Once threshold has been reached, Na+ pours in all along the axon • Charge inside the axon changes from -60mv +30mV = Action Potential! • All-or-None Principle • Either neuron’s threshold is met and it fires all the way, or it is not met and doesn’t fire at all

14. Supporting Cells • Neuroglia • Dense network of supporting cells for nerve tissue, each has a specific job • Can replace themselves • Speed of gray neuron vs. a white neuron • Gray Neurons • Carry their messages through dendrite cell body axon hillock axon branches synaptic knob • Because most of cell membrane surface area is involved, nerve impulse travels 1-4 mph

15. White Neurons • Special cell that insulates along the length of the dendrite and axon • Form insulating bundles with small gaps in between the cells • Myelin Sheath • CNS • Myelin created by oligodendrocytes • Shaped like an octopus; ‘arms’ can reach out to myelinate from a few neurons to up to 50 neurons • Also creates structural framework of the CNS

16. PNS • Myelin created by Schwann cells • Wraps around the axon or dendrite like a towel. It takes up to 1000 Schwann cells to myelinate an axon • Can help dendrites and axons if damaged • Gaps between myelin • Nodes of Ranvier • Only the gaps can depolarize • Nerve impulse skips across the neuron’s membrane *skipping = saltatory conduction • Speed of nerve impulse = 250 mph (300 meters/sec)

17. Other Supporting Cells • Astrocytes – CNS = “spider cell” or star-shaped cell • Most abundant, cling to capillaries and neurons • Forms blood-brain barrier • Feed transfer the nutrients from capillary to neuron • Protect “foot” on capillary prevents transfer of material to neuron Blood-Brain Barrier • Support Structural support for brain and spinal cord • Blood volume – Influence the amount of blood flowing through a part of brain • Outnumber neurons 10:1

19. Microglia – CNS = “Janitors” – small cell • Clean-up anything in CNS that is illegal Phagocytosis • Ependymal – CNS • Line ventricles & central canal of the spinal cord • Helps form cerebral spinal fluid • Cilia circulate the CSF

22. Introduction to Body Communication • CNS (Central Nervous System) – Located in “center” of body • Brain – main communication organ in the body • Spinal cord • Integration center “Choice Maker” • PNS (Peripheral Nervous System) • “Peri-“ around • Pathways TO and FROMthe CNS • Afferent pathways = Input • Carry messages to the brain • Carry messages from the 5 senses • Known as “Sensory Pathways”

23. Efferent Pathways = Output • Carry messages away from CNS to the body • Known as “Motor Pathway” • Output is determined by INPUT • You are what you think! • Brain doesn’t know ‘real’ input from ‘false’ input • Somatic Motor – Voluntary movements • Cerebellum plus skeletal muscles • Movements made using conscious thinking • Autonomic Motor – Involuntary movements • Midbrain, cerebellum, and brain stem

24. Affects • Smooth muscles • Sphincter muscles of blood vessels & gastrointestinal system • Cardiac muscle • Two Divisions • Sympathetic Nervous System • Speeds us up. If not controlled, can kill us! • “Fight or Flight” (or Freeze!) • Parasympathetic Nervous System • Dominates the sympathetic • Only allows body to work as hard and as fast as it needs to

25. Central Nervous System: The Choice Maker! • Brain Landmarks • Gyrus= bumps • Sulcus= shallow grooves • Fissure = deep groove or division • Longitudinal fissure • Separates 2 hemispheres of brain • Corpus callosum – connects L & R hemispheres; allows neurons to communicate between 2 halves • Major Areas of Cerebrum • Frontal Lobe • Responsible for • Personality

26. Morals and ethics • Ability to form words for speaking – Broca’s area • Skeletal muscle movement (voluntary movement) • Output center of the brain • Pre-central gyrus • Mapped to show what part of brain instructs that particular part of the body’s voluntary muscles • The larger the body part drawn – on that part of brain the MORE brain area used for that part! • Motor Homunculus = “Little Man”

28. Parietal Lobe • Major input center • Memory • Repetition helps put a memory into “Long term storage” • Short-term memory hasn’t had enough repetition to stay filed, so can be lost quickly • “Learning” takes short-term memory, followed up with 1-3 weeks of repetition • Memory Problems • Alzheimer’s • Short-term loss, but can remember what happened when they were 5 yrs old • As brain deteriorates, more long-term memory files are broken down; relatives & important dates are forgotten

29. Head injury patients • Recover reading, writing, speech & motor skills, but will struggle in school • Short-term memory loss prevents them from remembering lesson long enough to be able to reinforce it • Understanding speech – Wernicke’s area • Recognition of objects, people, places & events • Memory of events and outcome of choices (files of the hard drive) • Post-central gyrus • Mapped to show what part of the brain receives input from that particular part of the body • Sensory Homunculus

31. Occipital Lobe • Receives images from eyes upside down • Breaks patterns down into familiar items • Parietal lobe helps identify these items with the use of language • You “see” with your brain • Temporal Lobe • Responsible for hearing and balance • Parietal lobe helps place an identification with sounds that are heard

32. Cerebellum • Controls coordination = traffic controller - movement, balance, posture • Quite developed at birth, continues to develop as the infant uses repetitive movements • “Brain Stem” • Pons – controls inspiration “breathing” • Medulla Oblongata • Controls vital functions – heart rate & respiration* (rate, rhythm, and depth) • Exits skull at magnum foramen • Ends at C2

33. Effects of Alcohol on brain • Impacted by rate of absorption into bloodstream • Slows brain cell’s capacity to carry messages slows everything down • Parietal lobe – CTZ (chemical trigger zone) • Causes nausea and vomiting • If alcohol level is too high or too much is absorbed too quickly, it can shut the cerebrum down, then the brainstem causes death

34. Meaning of “Brain Dead” • If oxygen is cut off to the brain, a bleed or swelling in the brain due to a blow to the head occurs, or too much of a chemical agent causes cerebrum to lose the ability to carry messages • If brain stem is still operating and maintains vital signs, but voluntary brain is no longer functioning ** organ donation

36. Grey vs. White Matter • Nerve cells (neurons) carry messages one way • White matter • Special cells wrap around neuron to insulate and help message move at up to 250 mph • In CNS, the insulating cell is the oligodendrocyte • Insulated neurons = white neurons – make up “white matter” • White neurons responsible for carrying messages to & from specific areas of CNS, especially to cerebral cortex

37. Grey matter • Cortex of brain • Outer layer • Composed of cell bodies and neurons that are not wrapped or insulated • Grey neurons carry messages much more slowly; 1-4 mph • Cortex is where choices are made!

38. Ventricles of Brain and Cerebral Spinal Fluid (CSF) • Four ventricles • 1st Ventricle - 2 lateral ventricles that count as 2 ventricles • 3rd Ventricle • 4th Ventricle • Central Canal • Cerebral Spinal Fluid • Functions as shock absorber • 400 – 500 mL produced daily • Ependymal cells • Line ventricles & central canal • Contain microvilli & cilia to help the flow of CSF

39. Hydrocephalic Condition • If ventricles do not form correctly, or a blockage develops, CSF cannot flow or drain correctly • Fetus/infant – build-up of fluid pushes skull bones to form larger head and compress brain development • Adult – tumors or head injuries can cause problems with CSF draining or flowing properly. Skull is fused, CSF build-up in ventricles. Pressure forces brain into skull. Pathways become disconnected and major problems develop. • Correction = “Shunt” • Tube inserted into ventricles that drains CSF into abdominal cavity

41. Spinal Cord • Interstate that connects brain to body • Receives sensory input from body and delivers motor output to specific areas of body • Spinal cord ends at T12 – past that point, it becomes a loose collection of nerves known as “caudal equina” (Horse’s tail) • Sensory and motor tracts – Interstate lanes • Sensory tracts go up to brain with input. - Found on dorsal side of spinal cord • Motor tracts go from brain with the output choice. - Found on ventral side of spinal cord • Nerve pathways are 1-way!

42. Cross Section of the Spinal Cord • Entry and exit ramps • Gray matter of spinal cord is located on inside • Forms an “X” shape • Tips of X known as “horns” • Dorsal side = Dorsal horns • Entry ramps • All sensory pathways enter the spinal cord here on their way up to the brain • Ventral side = Ventral horns • Exit ramps • Motor pathways leave the spinal cord here to deliver motor output to voluntary muscles

45. Gray matter • Can switch pathways from one side of the body to the other • Houses the components of reflex arcs • White matter – myelinated pathways carrying messages to & from brain. • Protection of CNS • Meninges 3 membrane layers that surround brain & spinal cord • Pia mater = Inner layer • “Pia” = tender • Fragile membrane – sits directly on surface of brain • Arachnoid membrane = Middle layer • Legs that look like spider legs

46. Space between arachnoid and pia = subarachnoid space • Blood vessels and cerebral spinal fluid located here • Dura mater = Outermost Layer • Thicker and toughest membrane: Dura = tough • Lies directly under the skull • Space between dura mater and arachnoid membrane = sub-dural space • Meningitis – infection of one or more of the 3 membranes. Can be caused by bacteria or virus • Vaccine – protects you from neisseriameningiditis, a routinely lethal form of bacteria causing menengitis! Should be vaccinated before leaving for college!

48. Peripheral Nervous System • Relationship of communication between the spinal cord and nerves • ALWAYS statements • Nerves are ALWAYS found in the PNS (tracts are the pathways in CNS) • Sensory nerves ALWAYS go to the CNS • Sensory nerves ALWAYS have a ganglion to house their nuclei • Sensory nerves ALWAYS enter the dorsal horn to pass their messages along

49. Pathway • Once the message has arrived at the spinal cord, it travels via sensory tracts up to brain’s cortex for interpretation • Choice is made • Output travels along motor tracts down the spinal cord • Message exits the spinal cord through the ventral horn • Travels along a motor nerve to the skeletal muscle • When a motor nerve “hooks up” with a muscle to tell it to move = innervation • Combination of sensory and motor nerve wrapped together = spinal nerve

50. 31 pairs of spinal nerves that enter & leave the spinal cord • 12 pairs of cranial nerves that enter & leave the brain only • Nerve protection – nerves are wrapped up in connective tissue membranes & many times hide under muscles for protection • Endoneurium – connective tissue membrane that surrounds individual neuron • Perineuriumsurrounds • Fascicles – bundles of neurons surrounded by connective tissue membrane • Epineurium– membrane that surrounds collection of fascicles