1. STRUCTURE AND FUNCTION OF THE NEUROLOGIC SYSTEM

2. Organization Central nervous system (CNS)
Anatomical structures
Brain enclosed -- cranial vault
Spinal cord enclosed -- bony spine
Peripheral nervous system (PNS)
Anatomical organization (Fig.12-26)
Nerves
Cranial – 12 pairs
Spinal pairs
Can be afferent or efferent

4. Functional organization
Somatic nervous system
Regulates voluntary, motor control
Neurotransmitter = acetyl choline (ACh)
Autonomic nervous system
Regulates internal environment

5. Most organs dually innervated:
Sympathetic neurons (Fig.12-24,23)
From thoracic, lumbar spinal regions
Important for “fight or flight” (incr’d heart rate/resp’n, decr’d digestion)
Neurotransmitters: ACh and epinephrine/norepi

7. Parasympathetic neurons (Fig.12-25,23)
From other spinal regions
Important to conserve energy and maintain homeostasis (decr’d heart rate, incr’d digestion)
Neurotransmitter: ACh

8. Neural tissue Neuron = primary cell of nervous system
About 1011 neurons/body
Each neuron adapted for specific function
Functions of neurons
Detect env’l changes
Initiate body response to changes
Fuel source -- mostly glucose

9. Anatomic components (Fig.12-1)
Cell body = soma
Most in CNS
Those in PNS grouped together as ganglia
Dendrites
Extensions of cell body
Carry information TOWARD cell body

10. Axon Usually one per neuron
Long projection; carries impulses AWAY from cell body
Myelin – insulating lipid covering
Forms sheath
Allows fast flow of ions in one direction  proper impulse conduction (away from cell body)
Interruptions in myelin coating = nodes of Ranvier
Nec for ions from ISF to enter axon for proper impulse

12. Supporting cells of neurological system (Fig.12-3,Table12-1)
Schwann cells – in PNS
Form myelin sheath around axons
Neuroglia -- “nerve glue”
Support CNS neurons
About ½ volume of the brain and spinal cord

14. Several types of neuroglial cells:
Astrocytes -- star shape
Form contact between neurons, circulatory system
“Buffer zone” between neurons (delicate) and molecules circulating in blood
Oligodendroglia
Deposit myelin in CNS (similar job as the Schwann cells in PNS)
Microglia
Phagocytic cells; digest debris in CNS
Ependymal cells
Help produce cerebrospinal fluid (csf)

18. Nerve injury and regeneration (Fig.12-4)
Mature neurons don’t divide, proliferate
Injury can  permanent loss of function
Regeneration of some PNS neurons is possible
Axon of neuron (so only myelinated fibers) repaired
Regeneration more optimistic if cell crushed
If cut, scar tissue can form  impede ion flux through cell membrane, so impede proper impulses

19. Regeneration more optimistic if injury further away from cell body
With regeneration, see:
Swelling distal to injury
Filaments hypertrophy
Myelin sheath and axon begin to degenerate, BUT
Proximal to injury, see projection of new neurofibriles
Neurilemma (membrane that surrounds the myelin sheath) acts as guide
Not in CNS, where myelin somewhat different
Scar tissue forms, and decr’d/no regeneration of neuronal tissue

20. Nerve impulses Action potentials generated
Neuron selectively changes electrical potential of its plasma membrane
 Influx of Na+ through selective channels (gated Na+ channels) at dendrite or soma
In response to biochemical signal from a neurotransmitter released from an impinging neuron
 Changes electrical potential of membrane in that region

22. Neurons influence neighboring neurons (Fig.12-2)
Release neurotransmitters (biochemicals signal an action potential in a neighboring neuron)
Synapse – region between two nearby neurons
First neuron in a series = “presynaptic”
Second neuron =“postsynaptic”
Presynaptic impinges on postsynaptic
Neurotransmitters synth’d, stored in vesicles near end of presynaptic neuron

24. When action potential reaches end of presynaptic neuron:
Signals vesicle holding neurotransmitters to merge with neuron’s plasma membrane in presynaptic area
Neurotransmitters released into synapse
Neurotransmitters travel through synapse, where they encounter postsynaptic neuron
On plasma membrane of postsynaptic neuron is a receptor specific for a particular neurotransmitter

25. Neurotransmitter binds the receptor on the postsynaptic neuron
Signals opening of nearby Na+ channels
 Membrane potential changes in the postsynaptic neuron
 Generation of action potential
Action potential travels through postsynaptic neuron’s dendrite, cell body and axon to axon ending (now presynaptic)
Signals neurotransmitter release to next neuron or muscle fiber on which it impinges, and changes occur within that cell

26. Some widely studied neurotransmitters
Norepinephrine, epinephrine, dopamine, ACh, serotonin (and MANY others)(Table12-2)
Excitatory neurotransmitters cause Na+ to flood into neuron  depolarization and action potential
Inhibitory neurotransmitters dampen Na+ influx into neuron  inhibition of depolarization, so no action potential
Different neurotransmitters have different functions (some excitatory, some inhibitory)

27. Central Nervous System (CNS)
The brain
Allows reasoning, intelligence, personality, mood
Weighs about 3 lb. in average adult
Receives about 20% of cardiac output
Divisions (Table 12-3;Fig.12-6)
Different regions, each associated with different function (Fig.12-7)
BUT some functions controlled by more than one region
Ex: cerebrum -- centers for sensory/motor, reasoning, memory, intelligence

29. Characteristics/Structures
Gyri – convolutions of tissue along brain surface
Importance: increase surface area of brain
Sulci – grooves between gyri
Gray matter – cerebral cortex
Cell bodies of neurons (so not myelinated)
White matter – myelinated nerve fibers (= axons)
Lies beneath cerebral cortex

30. Spinal cord (Fig.12-9,10,11) Long nerve cable Continuous with brain
Lies in vertebral canal
Surrounds, protects spinal cord
Divided into 31 anatomical sections
Gray matter (Fig.12-11)
In center of spinal cord
Butterfly shaped
Divided  3 horns
Composed of neuronal cell bodies

31. White matter Motor neurons (Fig.12-12,13) Surrounds gray matter
Myelinated tissue (so axons)
Forms ascending, descending tracts
Motor neurons (Fig.12-12,13)
Directly influence the muscle cells
Cell bodies of motor neurons lie in gray matter of spinal cord
Axons extend out of spinal cord
Regulate motor activity

33. Protective structures of the CNS
Cranium
8 fused bones; encloses and protects the brain
Epidural space
Lies between cranium and meninges
Site of blood collection ( epidural hematoma) if trauma  disruption of blood vessels of scalp/skull

35. Meninges – 3 protective membranes (Fig.12-14):
Dura mater – 2 layers of tissue
Arachnoid membrane – named for appearance (spider web)
Pia mater – cells to produce cerebrospinal fluid
Spaces between layers -- also sites where blood may collect if hemorrhage

37. Cerebrospinal fluid (csf)
Clear, colorless fluid similar to ISF and plasma (Table )
Helps cushion CNS
Produced within pia mater (about 600 mL/day)
Circulates within cranium in cavities, subarachnoid space
Exerts pressure within brain, spinal cord
Forms pressure gradient between arteries, cavities of CNS
Reabsorbed into venous circulation
Valves in arachnoid membrane move fluid into venous circulation (and opposite)

39. Vertebral column (Fig.12-15,16)
Vertebrae 33
Intervertebral discs
Between vertebrae
Pulpy, absorb shock
Prevent damage to nervous system structures
If rupture  back pain

41. Vertebral circulation
Arises from aortic arch  internal carotid arteries and  vertebral arteries (Fig.12-18; Table 12-5)
May be conducting ( brain surface), OR
Penetrating ( structures below the cortex)
Healthy brain can regulate its blood supply to maximize oxygen supply
Can increase extraction of oxygen from blood when systemic bp decreases (for awhile)
Can decrease resistance in cerebral vessels when systemic bp decreases (up to a point)

43. Selectively allow partic blood components from blood  brain
Blood-brain barrier
Supporting neural cells and blood capillaries have rel. tight junctions
Selectively allow partic blood components from blood  brain
Important in brain chemotherapy