1. The Nervous System PSE 4U1 Exercise Science Unit 4

2. Suggested Readings/Practice Text: p. 95-107 Workbook: p.84-89

3. Two Components of the Nervous System Central Nervous System (CNS) Peripheral Nervous System (PNS)

4. The Components of the Nervous System

5. The Central Nervous System (CNS) Brain –Cerebrum largest part, nerve centres, 4 lobes (frontal, temporal, parietal, occipital) –Cerebellum second largest region, behind and below the cerebrum, coordinates muscle movement, controls balance –Brain stem below cerebrum & in front of cerebellum, links cerebrum with spinal cord, autonomic functions, etc.

6. The Central Nervous System (CNS) Brain (con’t) –Diencephalon thalamus (sensory stimuli to brain, eg. pain) and hypothalamus (body temp., appetite, emotions) –Limbic system hippocampus, amygdala, pituitary, etc. regulates basic drives/emotions (eg. hunger, aggression, emotional drives) –Reticular activating system directs information to appropriate centres, maintains consciousness

8. This is an opposite view of the brain from the previous slide

9. The Central Nervous System (CNS) Con’t Spinal cord –runs through vertebrae (vertebral column) –starts at base of brain stem to second lumbar vertebra –spinal nerves branch off between each vertebra, and travel to various organs and tissues –spinal nerves carry sensory information TOWARDS the CNS and motor commands AWAY from the CNS

10. The Peripheral Nervous System (PNS) parts of nervous system that are outside the CNS massive road network “carrying traffic” (information) in and out of the CNS Composed of… PNS - Autonomic- Somatic sympathetic parasympathetic

11. PNS: The Autonomic Nervous System Controls heart and internal organs Sympathetic system - prepares the body for emergencies (e.g. increase heart rate, decreased digestive activity, increased breathing) - fight-or-flight responses - orders release of adrenaline from adrenal gland Parasympathetic - helps bring body back to “normal state” - parasympathetic system has opposite effect of sympathetic system (e.g. decreases HR, increases digestive activities

12. Functions of the Sympathetic Nervous System (in depth) Helps us cope with stress by sending impulses to many internal organs producing widespread changes: –Increase in: heart rate, blood pressure, blood supply to skeletal muscles, secretion of sweat, secretion by adrenal glands –Decreased secretion from digestive glands –Constriction of blood vessels –Prepares body for strenuous muscular work (eg exercise) –Prepares us for FIGHT or FLIGHT response

14. The Somatic Nervous System Makes us aware of the external environment. Consists of nerves that convey messages from the sensory organs to the CNS and from the CNS to the muscles. Composed of… Afferent nerve fibres - sends sensory information to the brain Efferent nerve fibres (E=Exit) - brain sends information through these fibres to instruct skeletal muscles to react

15. Reflex Arc Characteristics (p. 99)

16. Reflex Arc pathway (circuit) along which the initial stimulus and corresponding response message travel 1.the Receptor receives the initial stimulus 2.the Sensory (or Afferent) nerve carries the impulse to the spinal column or brain 3.the Intermediate nerve fibre (adjustor or interneuron) interprets the signal and issues an appropriate response 4.the Motor (or Efferent) nerve carries the response message from the spinal cord to the muscle or organ 5.the Effector organ (e.g. skeletal muscle) carries out the response

17. Suggested Work Read Textbook p. 95-99 Complete Workbook Ex. 6.3 (p. 87)

18. Coverings & Fluid Spaces of Brain and Spinal Cord Brain & spinal cord surrounded with tough, fluid-containing membrane called Meninges Meninges –A. the dura mater – tough outer layer –B. the arachnoid mater – middle cobweb like fluid filling in its spaces –C. the pia mater – delicate innermost layer (look at handout)

20. Cerebrospinal fluid –Forms continually from fluid filtering out of the blood, which circulated between the arachnoid and pia mater –Fills spaces inside of the brain that are called ventricles (2) – one inside the right half of cerebrum and one inside the left cerebrum –CSF moves from ventricles down and around spinal cord and returns to blood –Remember: this fluid forms continually from blood, circulates, and is reabsorbed into the blood Coverings & Fluid Spaces of Brain and Spinal Cord (Con’t)

21. Cells of the Nervous System Two types –Neurons: nerve cells –Neuroglia: specialized connective tissue

22. Neurons Consist of 3 main parts 1. Neuron Cell Body 2. Dendrites - branching projections from neuron cell body - transmit impulses to the neuron cell bodies 3. Axon - one elongated projection from the cell body - transmit impulses away from the neuron cell bodies (look at handout)

23. Are classified according to the direction in which they transmit impulses –Sensory neurons: transmit impulses to the spinal cord and brain from all parts of the body –Motor neurons: transmit impulses away from the brain and spinal cord to muscles and glands –Interneurons: conduct impulses from sensory neurons to motor neurons Neurons (Con’t)

24. Myelin –A white fatty substance which surrounds the axon –Good insulator covering the axon between nodes, allowing transmission to be fast –Formed by Schwann Cells that wrap around some axons outside the central nervous system –Neurilemma is the outer cell membrane of a Schwann Cell –Nodes of Ranvier are indentations that exist between adjancent Schwann Cells –Saltatory Conduction rapid nerve conduction along a myelinated axon where impulse jumps from node to node (look at handout) Neurons (Con’t)

25. Myelin (con’t) –An interesting note about neurilemma –Axons in brain and spinal cord have no neurilemma –Neurilemma plays an important part in regeneration of cut and injured axons, therefore, axons in brain and cord do not regenerate, but those in nerves do (albeit slowly) Neurons (Con’t)

27. Nerve Impulses On handout

28. Neuroglia Cells Do not transmit impulses Special type of connective tissue Maintain functioning of neurons by holding them together and protecting them 3 types –Astrocytes: large, star shaped, threadlike branches attached to neurons and blood vessels –Microglia: smaller than astrocytes, stationary, when brain tissue shows signs of inflammation or degeneration, they enlarge and move about acting as microbe-eating scavengers –Oligodendroglia: hold nerve fibres together, produce fatty myelin sheath that surrounds neurons in the brain and spinal cord

30. The Proprioceptor System Proprioceptors: –Specialized receptors located within tendons, muscles, and joints –Provide sensory information (ex. state of muscle contraction) through the primary use of two sensory receptors: golgi tendon organs and muscle spindles Continuously monitor muscle actions “Tell” the nervous system about the state of muscle contraction Act as a kind of safety device allowing the nervous system to respond accordingly

31. Golgi Tendons and Muscle Spindles Golgi Tendon Organs (GTOs) - located on the ends of tendons - detects increased tension exerted on tendon Muscle Spindles - help detect increased muscle length

32. Golgi Tendon Organs

33. The Muscle Spindle Motor neuron Sensory neuron (two branches within) Muscle spindle within muscle fibre (magnified) Muscle fibres

34. Golgi Tendon Organs & Muscle Spindles Golgi Tendon OrgansMuscle Spindles Location Where tendon meets muscle fibre In belly of muscle fibre Position In series with muscle fibre Parallel to muscle fibre Respond to Changes in muscle/tendon tension Changes in muscle length Sensory neurons 12

35. The Stretch Reflex Stretch reflex: –Simplest spinal reflex –Depends on the single connection between primary afferent fibres and motor neurons of same muscle

36. The Stretch Reflex Stretch reflex (con’t): –Sequence of nerve impulses and motions (e.g. tapping patella ligament): Receptor muscle senses action of hammer against patella ligament through the muscle spindle’s sensory neuron Message transmitted along afferent nerve axon to spinal cord Afferent neuron synapses with the efferent pathway of same muscle Impulse transmitted along efferent pathways to muscle Motor units contract–brings about knee-jerk action

37. Muscle Spindles at Work Motor neuron Sensory neuron (two branches within) Muscle fibres

38. Polysynaptic Reflexes Withdrawal reflex: –Rapid and occurs before brain has time to interpret the information –Involves the withdrawal of a body part from a painful stimulus –Reflex action involves transferring impulse from a sensory neuron to a motor neuron through a connecting interneuron Crossed-Extensor Reflex: –Observed when one leg or arm automatically compensates for a reflex action in opposing leg or arm –Involves multiple synapses and muscle groups

39. The Withdrawal Reflex and the Crossed-Extensor Reflex

40. Disorders & Diseases of the Nervous System Multiple Sclerosis (MS) –Autoimmune disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarringmyelinaxonsdemyelination

41. Disorders & Diseases of the Nervous System Parkinson’s Alzheimer’s Epilepsy Stroke Meningitis Schizophrenia

42. Spinal Cord and Head Injuries Spinal cord injuries: –Damage to the spine can result in an inability to send impulses to body parts –Nerves above injury keep working, nerves below may not –Paraplegia: Injury prevents use of legs but not arms –Quadriplegia: Injury prevents movement of both arms and legs –Causes: Car accidents, Falls, Sports, Diving © iStockphoto.com/”caracterdesign”

43. Spinal Cord and Head Injuries Head injuries: –Most common head injury is a concussion: Occurs when brain literally hits the skull; often involves injury to nerve fibres Ranges from mild to severe Symptoms can include: headaches, fatigue, dizziness, memory problems, or slurred speech © iStockphoto.com/”AlexKalina”