The Nervous system

1. The Nervous system Some parts of our brains stay as malleable as a baby’s, so we can create neurons and learn new things throughout our lives. - John Medina

2. Functions • Collect infromation about the bodies internal and external environment. • Process that information and respond to it.

3. Central Nervous System • Coordinates the voluntary and involuntary actions. • Consists of the Brain and the Spinal Cord. • Information is sent to the brain via the Spinal Cord. • The Brain interprets the information and makes a response

4. 3 types of neurons • Sensory neurons – carry impulses from sense organs to spinal cord and brain. • Motor neurons – carry impulses from brain and spinal cord to muscles and glands. • Interneurons process info from sensory and send impulses to motor or brain

6. Resting Potential • Active transport pumps Na+ out and K+in. • Ungated K+ channel proteins allow more K+to diffuse back in. • Because of higher K+ inside cell, K+ diffuse out of cell. • This results in a net negative charge of 70 mV inside the cell

7. Action Potential • When a stimulus reaches a resting neuron, the neuron transmits the signal as an impulse called an action potential. • During an action potential, ions cross back and forth across the membrane, causing electrical changes that transmit the nerve impulse.

8. Action Potential revisited • If the signal is strong enough and the voltage reaches a threshold, it triggers the action potential. • More gated ion channels open, allowing more Na+ ions inside the cell. • The cell depolarizes so that the charges across the membrane are reversed.

9. Action Potential

10. Impulse crossing a synapse

11. Three main regions of the brain Cerebrum, Cerebellum & brain stem

12. Spinal Cord • It is around 45 cm long and varies in width from ½ inch in the cervical and lumbar regions to ¼ inch thick in the thoracic area. • 3 main functions • A link for brain to motor nerves. • A link for sensory nerves to the brain. • A center for coordinating reflexxes

13. Cross Section of cervical vertebrae

17. Spinal Cord facts • 31 pairs of nerves that leave the spinal cord. • Other nerves travel to the spinal cord. • The cord runs through the spinal canal. • The canal is bathed in fluid and protected by the vertebrae.

18. Spinal Cord Injury • The spinal cord cannot heal itself. • The cord can be damaged by trauma, loss of blood, compression, infection or tumor. • 12,000 cases of spinal cord injury each year.

19. Types of Spinal Cord injury • Either complete or incomplete. • Complete is a complete loss of sensation and muscle function below the injury. • Incomplete, there is some function below the level of injury. • In most cases, both sides of the body are affected equally

20. Types of injury II • An injury to the upper portion can cause quadriplegia – paralysis of both arms and both legs. • An injury in the lower back can cause paraplegia – paralysis of both legs only.

21. Causes of Spinal Cord Injury • Trauma is most common cause. • Nearly half are caused by motor vehicle accidents. • Others include stabbing or gunshots, sports, tumor compression, infection or inflammation. • Loss of blood supply through an aneurysm is another cause.

22. Traumatic injury to spinal cord • A sudden blow to the spine can fracture vertebrae sending pieces to bruise or tear spinal cord tissue. • Most of the time the spinal cord is not cut but bruised. • The injury may damage a few, many or almost all of the axons. • Recovery ranges from complete recovery to complete paralysis.

23. Treatment • Improved first aid and treatment can minimize damage to the nervous system. • 1/3 of those with an injury to the neck will need help breathing. • Methlyprednisilone appears to reduce damage. • Physical therapy, electrical stimulation,and counseling help

24. Prognosis • Incomplete injuries allow for some recovery. • Treatment of chronic pain and bladder and bowel dysfunction is often necessary.

25. Cerebrum • Involved in several functions of the body including: • Intelligence, Personality, Thinking, perceiving, producing and understanding language, interpretation of sensory impulses, motor function, planning and organization and touch sensation

26. Limbic System • Emotion, behavior, memory. • Amygdala associated with emotional learning, including fear and anxiety, and long term memories • Brains pleasure center, produces good feelings.

27. Thalamus and Hypothalamus • Thalamus – relays messages from sensory neurons to the proper region of the brain. • Hypothalamus – control center for hunger, thirst, fatigue, anger and body temp.

28. Cerebellum • Coordinates and balances the actions of muscles • Enables graceful movements. • Cerebellum learns movements involved in muscle activities like hitting a baseball, golf ball, skiing, playing tennis or shooting a basketball.

29. Brain Stem • Includes midbrain, pons and medulla oblongata. • Regulates of information between brain and rest of body. • Controls blood pressure, hear rate, breathing, ans swallowing. • Keeps you going when unconscious

30. How drugs affect Dopamine neurotransmitters. • Cause the release of a flood of dopamine. • Simulate receptors elsewhere in the brain that lead to dopamine release. • Brain reacts to this by reducing the number of dopamine receptors, so larger and larger doses have to be taken for same effect.

31. Peripheral Nervous System • All the nerves and cells not part of the CNS. • Main function is to connect the CNS to the limbs and organs. • It is not protected by bone or chemical barriers. • It is divided into the Sensory division, motor division, Somatic division, sympathetic division, autonomic division

32. Somatic Nervous System • Part of the Peripheral nervous system. • It is associated with voluntary control of body movements. • It is responsible for stimulating muscle contraction

33. Reflex arc – sensory neuron to spinal cord interneuron, motor neuron, hand jerked away

34. Autonomic Nervous System • Acts as a control system on involuntary activities. • Heart rate, digestion, respiratory rate, salivation, pupillary dilation, urination, breathing and swallowing. • Some of these functions can be partially controlled by the somatic nervous systme.

35. Sympathetic – fight or flee, prepares body for activityParasympathetic – rest and digest, prepares body for inactivity

36. Touch • Touch sensors located on the skin. • Distribution is not even. • Cold receptors stop below 300 and pain takes over. • Pain and pressure receptors also located in joints and organs, but not the brain!

37. Skin cross section – 450 X

38. Olfaction • The sense of smell depends on specialized sensory cells in the nasal cavity. • When molecules bind to specific sites a signal is sent to the olfactory bulb in the brain.

39. Dog sense of smell • Dog’s brain 1/10 human. • The part that controls smell is 40 times larger. • Dog’s sense of smell is 1,000 to 10,000,000 more sensitive than a human’s.

41. Olfactory lobe of human Olfactory lobe of dogBel

42. Sense of Taste • Taste buds react to specific chemicals. • They are located on the tongue in small bumps called papillae. • 2,000 to 5,000 taste buds are located on the tongue. • Each bud contains 50 to 100 receptor cells. • There are 5 tastes, sweet, sour, salty, bitter and umami. • Other factors in taste include smell, texture, and temperature

44. Scanning electron microscope picture of taste buds

45. Generalized taste areas of the tongue

46. Ears • Two functions, hearing and equilibrium. • Outer ear, pinna, is composed of collagenous cartilage. • Auditory canal is a hole through the temporal bone. • Modified pieces of the temporal bone form the malleaus, incus and staper of the inner ear.

47. Hearing • Vibrations – ear canal- ear drum- malleus – incus- stapes – oval window – cochlea – hair cells – impulses – brain – interpretation.

48. Cochlea sensitivity • The higher the frequency the higher the sound. • The round window acts as a pressure relief membrane dissipating the sound energy. • As people age they tend to lose the ability to hear the higher frequencies.

49. Semicircular canals • Fluid filled canals with sensitive hair cells. • As the head is moved so is the fluid, stimulating the hairs and sending signals to the brain. • The brain interprets this signals as movement. • Dizziness is caused by sustained motion that is stopped suddenly.

50. Otoliths • The otolith organ provides information on the position of the head. • When the head is tilted tiny crystals of CaCO3 pull on the hairs sending signals to the brain. • This helps people to know how the position of the head has changed.