1. Central Nervous System (CNS) BIO 161 Chapter 11 & 12 – part 1

2. Review –Nervous Tissue Two types of tissues –Neurons – excitable cells that transmit electrical signals –Neuroglia - supporting cells – cells that surround and wrap neurons

3. Parts of a Neuron a)Cyton (cell body) –sometimes form ganglia – a group of cell bodies outside the CNS –eg. sensory nerves have cell bodies located in the dorsal root ganglion b)Axon – leads away from cyton c)Dendrite – brings stimuli into cyton d)myelin sheath – lipoprotein (insulating) e)Neuroglia – helper cells 1.Schwaan cells – ~1 mm long - make myelin in PNS 2.Oligodendrocytes – make myelin in CNS Recall –grey matter = unmyelinated cells –white matter = myelinated cells

4. Parts of a Neuron f)Nodes of Ranvier – speed up impulse g)Axon terminals – store neurotransmitter in synaptic vessicles to release into synapse  communicate impulse to next cell across the synapse. h)Synapse – space between neurons –where neurotransmitter goes from one axon to the next, or to a muscle, organ, or gland

5. DendritesCell body (Cyton) Axon Axon terminals Node of Ranvier Impulse direction Schwann cell (one internode) myelin sheathSynapse (gap) Dendrites (new cell) Impulse direction

6. Types of Nerves Sensory receptors are often unipolar one short process from cell body, splits T-like in two directions distal process is the receptor end proximal process goes into CNS cell bodies usually in ganglion Some sensory neurons are bipolar cell body is central, one process from each end of cell body dendrite one way, axon the other carry info from body to CNS – eg olfactory, retina (RARE) Motor neurons are often multipolar multiple processes from cell body carry info from CNS to body – eg Muscle contraction (99% of all)

7. Resting Potential Flux of Na+ and K+ is the action potential Normally, Na+ is pumped out of the cell, K+ is pumped in More Na+ out than K+ in  inside is negative compared to outside the result  -70 mV

8. ..Nerve Conduction Theory The action potential –electrical event causes change in ion gates –Na+ rushes in, making cell more positive inside –disturbs adjacent area of cell to do the same –disturbance moves along the axon  conduction

9. Figure 11.13: Propagation of an action potential (AP), p. 405. –70 +30 (a) Time = 0 ms(b) Time = 2 ms(c) Time = 4 ms Voltage at 2 ms Voltage at 4 ms Voltage at 0 ms Resting potential Peak of action potential Hyperpolarization Membrane potential (mV))

10. Saltatory Conduction

11. Protective Coverings (b) Fascicle Perineurium Blood vessels Endoneurium Nerve fibers Axon Endoneurium Perineurium Epineurium Myelin sheath Blood vessels Fascicle page 498

12. Synapse Connection between –nerve  nerve (axon  dendrite) –nerve  muscle axon ends in terminal space = “synapse” chemicals cross synapse = neurotransmitters –eg. acetylcholine (ACh), norepinephrine (NE) aka adrenaline

13. Figure 11.18: Events at a chemical synapse in response to depolarization, p. 410. Synaptic vesicles Axon terminal Synaptic cleft Presynaptic membrane Postsynaptic membrane Mitochondria Ion channel closed Ion channel open Neurotransmitter Degraded neurotransmitter Na + Action Potential 1 2 3 4 5 Neurotransmitter molecules Dendrite

14. Types of reflexes Monosynaptic –2 neurons sensory neuron  motor neuron eg. knee jerk Polysynaptic –multiple neurons sensory neuron  interneuron  brain  motor neuron eg. touching a hot stove (withdrawal)

15. Subdivisions of the Nervous System Central Nervous System - CNS –brain and spinal cord Peripheral Nervous System - PNS –everything outside the CNS –12 pairs of cranial nerves –31 pairs of spinal nerves –includes 2 divisions sensory – afferent (TO the CNS) motor – efferent (AWAY FROM the CNS)

16. CNS- Spinal cord –adult to ~L2 –infant to ~L3 or L4 conus medullaris –end of spinal cord filum terminale –end of pia cauda equina = “horse’s tail” –last spinal nerves 2 enlargements –cervical  arms –lumbar  legs

17. CNS - Brain 2% of body weight yet 20% of blood flow 3 main parts –forebrain cerebrum diencephalon –thalamus, hypothalamus, retina –midbrain midbrain –hindbrain pons cerebellum medulla oblongata

18. The Forebrain Cerebral cortex –80%+ of brain mass –voluntary and conscious –memory, intelligence –2 hemispheres left – usually dominant (90%) –problem solving, speech, logical integration right –motor, intuition, creativity, emotion

19. The Forebrain Sulcus –valley Fissure –deep valley Gyrus –bump

20. The Forebrain Cerebral lobes –Temporal hearing, memory of visual/auditory patterns, –Occipital vision –Frontal higher intelligence, motor action –Parietal Sensory – pain, temperature, touch, pressure

21. The Forebrain Diencephalon thalamus –relays spinal info  correct area of cortex hypothalamus –makes antidiuretic hormone –monitors hunger –controls temperature –monitors thirst –regulates sleep pituitary –anterior –posterior pineal gland

22. CNS Surrounded by –meninges - 3 layers dura mater –outermost –very tough arachnoid –diffuse fibres, spider web –space beneath is subarachnoid space – CSF and blood vessels pia –very light film – “soft” – collagen, elastin, reticulin –secretes CSF into subarachnoid space (rich vascularization) –what is meningitis?

24. Figure 12.31a: Anatomy of the spinal cord, p. 473. Epidural space (contains fat) Pia Spinal meninges Arachnoid Dura Subdural space Subarachnoid space Dorsal root ganglion

25. CSF derived from blood (choroid plexuses) ~150 ml in CNS, replaced ~ 3x/day  450-500 ml/day choroid plexuses in ventricles – capillary clusters –functions buoys brain (would crush under its own weight) shock absorbance nutritive –locations ventricles subarachnoid space central canal (in spine) –returns to blood in subarachnoid space

26. Figure 12.5: Ventricles of the brain, p. 434. (b)(a)Left lateral viewAnterior view Lateral ventricle Posterior horn Third ventricle Cerebral aqueduct Anterior horn Inter- ventricular foramen (Munroe) Inferior horn Central canal Lateral ventricle Third ventricle Cerebral aqueduct (Sylvius) Fourth ventricle Central canal Lateral ventricle Posterior horn Third ventricle Cerebral aqueduct Anterior horn Inter- ventricular foramen (Munroe) Inferior horn Lateral ventricle Third ventricle Cerebral aqueduct (Sylvius) Fourth ventricle

27. Peripheral Nervous System (PNS) Reflex arcs are commonly used –to test level of damage/disease in spinal cord eg. biceps reflex points to C5

28. Reflexes and Nerves p. 521 Spinal reflexes –do NOT go to the brain –afferent goes to spine (“at”) –efferent comes from spine (“effect”) The spinal reflex is a 5 step process –stimulus –afferent signal to spine –integration at spine –efferent signal to effector –‘effect’

29. Figure 13.14: The basic components of all human reflex arcs, p. 521. Stimulus Receptor Skin Sensory neuron Spinal cord (in cross section) Integration center Interneuron Motor neuron Effector 1 5 4 2 3

30. The Knee Jerk AKA The Patellar Reflex 1.tendon is struck rectus femoris is stretched stretch receptor is stimulated 2.signal travels on afferent (sensory) neuron from receptor to spine travels along fibres in femoral nerve 3.synapse with effector (motor) neuron in spine

31. The Knee Jerk 4.signal travels on efferent (motor) neuron from spine to receptor travels along fibres in femoral nerve 5.effect – rectus femoris contracts stops stretch that was initial stimulus Tests spine at level of L4-L6

32. Other spinal reflexes Biceps – C5, C6 Brachioradialis – C6 Triceps – C7 Knee jerk (patellar tendon) – L4 – L6 Ankle jerk (Achilles tendon) – S1 Abdominal – light scratch in 4 quadrants – umbilicus should move

33. Other spinal reflexes Abdominal –light scratch in 4 quadrants –lateral to medial –umbilicus should move –Upper Quadrants – T7-T9 –Lower Quadrants – T11, T12 Plantar –toes should flex –Babinski sign – extension of toes Pupil response –shine light into eyes briefly –pupil should contract – CN III (Occulomotor)

34. Spinal Nerves 31 pairs –supply body (not head) –8 cervical (C 1 -C 8 ) – how come 8? –12 thoracic (T 1 -T 12 ) –5 Lumbar (L 1 -L 5 ) –5 Sacral (S 1 -S 5 ) –1 Coccygeal (C 0 )

35. Figure 13.6: Distribution of spinal nerves, p. 509. Cervical nerves C 1 – C 8 Thoracic nerves T 1 – T 12 Lumbar nerves L 1 – L 5 Sacral nerves S 1 – S 5 Coccygeal nerve C 0

36. Spinal Nerve Anatomy Each spinal nerve is mixed fibres –at cord ventral root is motor fibres dorsal root is sensory fibres –come together to exit vertebral foramen as spinal nerve (mixed fibres) –as it exits foramen, the nerve splits into –Ventral ramus - to limbs and ventrum –Dorsal ramus – to dorsum –NOTE: both rami are mixed fibres

38. Distribution of the Ventral Rami Ventral rami for plexuses (blending of fibres from several spinal nerves) –Note: ONLY IN VENTRAL RAMI Does not happen for Thoracic Spinal Nerves Fibres from Cervical, Lumbar, Sacral and Coccygeal mix and blend –fibres from several spinal nerves go to one area –fibres from one spinal nerve arrive via different paths

39. Figure 13.6: Distribution of spinal nerves, p. 509. Cervical nerves C 1 – C 8 Thoracic nerves T 1 – T 12 Lumbar nerves L 1 – L 5 Sacral nerves S 1 – S 5 Coccygeal nerve C 0 Cervical plexus Intercostal nerves Cervical enlargement Lumbar enlargement Cauda equina Brachial plexus Lumbar plexus Sacral plexus

40. Plexuses Cervical –C1-C4 mostly to neck muscles incl. phrenic nerve – diaphragm (mostly C4 fibres) Brachial –C5-T1 to arm Lumbar –L1 – L4 legs Sacral –L4-S4 legs

41. Thoracic Rami Each Thoracic ramus, except T1, innervates muscles in a band at the same level of the spine –run between ribs  T1-T11 are intercostal nerves –only T12 is different (below the 12 th rib) called subcostal nerve