The nervous system
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The document provides an overview of the nervous system, including its major components and how it functions. It discusses how (1) the brain and spinal cord make up the central nervous system, which controls and coordinates the body's activities, and (2) the peripheral nervous system connects to and controls the rest of the body through nerves. It also describes how (3) neurons transmit signals through electrical and chemical processes, allowing the nervous system to sense the environment and direct the body's responses.
The nervous system
- 1. The Nervous System Ch. 37/38
- 2. Objectives Content Label and describe the major divisions of the nervous system and of neurons Skill Use models and representations
- 3. The command center of the body The brain contains over 100 billion neurons (nerve cells) Each one of those connected to 100s of others Incredibly complex MRIs have allowed scientists to “see” into the brain Have found that certain regions dedicated to certain tasks
- 4. Evolution of the Nervous System All animals (except sponges) have some sort of nervous system The arrangement of neurons is what is different between them Greater complexity of the nervous system evolved with cephalization
- 5. Quick Think The Unity of Life is an important theme in BIOLOGY All living things are able to RESPOND TO THEIR ENVIRONMENT With a partner – come up with at least 3With a partner – come up with at least 3 different organisms and how theydifferent organisms and how they respond to their environmentrespond to their environment Be prepared to share
- 13. The mammalian nervous system has 2 parts 1. Central Nervous System (CNS) 1. Brain + spinal cord 2. Peripheral Nervous System (PNS) 1. All the nerves that run throughout the body
- 14. Nervous system is made up of neurons & support cells
- 15. Neurons The cells of the nervous system Cell body – contains nucleus & organelles Dendrites – extensions of the cell body that receive incoming messages from other cells Axon – conveys message to the next cell
- 16. Axon – many are covered in a fatty layer called the myelin sheath This insulates the axon and helps the message travel faster
- 17. Synaptic terminal – the end of the axon Synapse – where the message is relayed from one neuron to the next Message is sent via a chemical messenger called a neurotransmitter
- 19. 3 main types of neurons Sensory neurons – collect info from inside (blood pressure, blood CO2 levels, etc) & outside the body (light, temperature, taste, etc)
- 20. Interneurons – neurons in CNS that analyze & interpret the info from the sensory neuron and connect to motor neurons to elicit a response
- 21. Motor neurons – send signals from the CNS to the body Messages sent to effector cells Effector cells are muscle cells or gland cells that carry out a particular response
- 22. An example of a nerve circuit The reflex arc – a reflex is a body’s automatic response to stimuli Sensory neuron receives info Passes message to spinal cord (interneurons) Message passed to motor neuron Motor neuron signals an effector cell Response is initiated
- 23. Dendrites, cell body, axon, sensory neuron, interneuron, motor neuron, stimulus, effect
- 24. Glia – support cells for neurons 3 kinds: Astrocytes – provide support to neurons Oligodendrocytes – form the myelin sheath in the CNS Schwann cells – form the myelin sheath in the PNS
- 25. Stop and Process – read description & color as you go A bracket – red B bracket – yellow C & D– pink E1 & E2 – orange F1 – blue F2 – green F3 – light green G bracket – gray Background of G area – gray Cell bodies and dendrites in G area – pink H bracket – white Axons in H area - purple
- 26. How neurons send messages Part 1: Electrical message within the neuron
- 27. Q: What is membrane potential?
- 28. All cells maintain an electrical potential difference (voltage) across their plasma membrane The membrane potential is maintained by a difference in ionic composition on either side of the membrane For neurons- the resting potential is the membrane potential when the cell is not transmitting a signal
- 29. Q: What is membrane potential? A: A difference in charge between the inside and outside of the cell membrane
- 30. Q: How is this membrane potential created?
- 31. Neurons have ion channels in the membrane The sodium/potassium pump protein (Na+ /K+ ) uses active transport (ATP) to maintain the resting potential
- 32. Q: How is this membrane potential created? A: by proteins in the cell membrane called sodium/potassium (Na+ /K+ ) pumps
- 33. Q: Why “potential”? I get “membrane”…but what does the “potential” part mean? A: It refers to potential energy – the potential to do work for the cell
- 34. Q: So how do Na+ /K+ pumps work? A: they move 3 Na+ out of cell and 2 K+ into cell so there is an overall negative charge inside the cell
- 35. Q: What is “resting” potential? A: normal voltage (~-70 mV) when a neuron is inactive
- 36. A stimulus of some sort affects the permeability of the membrane to certain ions This gives rise to a nerve impulse we call an action potential
- 37. Q: What is an “action” potential?
- 38. The Action PotentialAction Potential (aka nerve impulse) They are the signals conducted by the axons An all or none reaction It starts with a stimulus that causes the depolarization of the neuron Na+ ion channels open and Na+ enters the cell This reverses the charges (+ inside and – outside)
- 39. The action potential ends as Na+ channels are closed and K+ channels are opened This helps return the neuron to its resting potential
- 40. Action potentials move down the axon Saltatory conduction is the jumping of the nerve impulse between the nodes of Ranvier This speeds up nerve impulses
- 41. Q: What is an “action” potential? A: a stimulus opens ion channels in cell membrane that allow Na+ to rush into cell, reversing electrical potential. This impulse jumps from node of Ranvier to node of Ranvier until it reaches the synapse
- 42. Q: How does it all go back to normal? A: The Na+ /K+ pump
- 43. So… bioflix
- 44. How the message is passed to the next neuron From the axon of one cell to the dendrites of then next through the synapse Electrical synapse (a few) - electrical current flows from cell to cell via gap junctions Chemical synapse (most) - the release of a neurotransmitter
- 45. The Chemical Synapse Neurotransmitter binds to receptors on the plasma membrane of the next neuron This triggers an action potential in the next neuron
- 46. Neurotransmitters are then broken down by enzymes, diffuse away, or are taken up by neighboring cells Bioflix
- 47. 2 types of neurotransmitter response 1. Excitory postsynaptic potential (EPSP) - binding of neurotransmitter causes electrical charge (depolarization) of postsynaptic membrane - action potential can now be generated in this cell 2. Inhibitory postsynaptic potential (IPSP) - binding of neurotransmitter causes an electrical charge that makes it harder for the next neuron to generate an action potential
- 48. Acetylcholine - reduces the strength & rate of contraction of cardiac muscles Epinephrine & norepinephrine - “fight or flight” Important neurotransmitters Serotonin & Dopamine - affect sleep, mood, attention, learning
- 49. The Central and Peripheral Nervous Systems
- 50. Peripheral Nervous System Somatic nervous system - carries signals to skeletal muscles Autonomic nervous system - regulates automatic functions of smooth & cardiac muscle Sympathetic division - increased heart rate, adrenaline, fight-or-flight Parasympathetic division - opposite effect, calming
- 51. The Brain Cerebrum - 2 hemispheres, regulates learning, language, personality, etc. Contains a thick band of axons that connects the 2 sides called the corpus callosum
- 52. Each side has 4 lobes: Frontal Temporal Occipital Parietal
- 53. Cerebellum - coordination, decision making, consciousness, awareness of surroundings
- 54. Brainstem - medulla oblangata + pons + midbrain Controls breathing rate, arousal & sleep, swallowing, digestion
- 55. Diencephalon - epithalamus, thalamus, and hypothalamus Main center through which sensory and motor info passes to & from cerebrum Hypothalamus controls feeding, fighting, fleeing, reproduction, circadian rhythms
- 56. Sensory & Motor Mechanisms Ch. 49
- 57. Types of sensory receptors Mechanoreceptors - get info from physical stimuli (pressure, touch, motion, sound) Thermoreceptors - heat & cold , maintain body temp Chemoreceptors - solute concentration, taste, smell Electromagnetic receptors - detect electromagnetic light, electricity, magnetism Pain receptors - respond to excess stimuli
- 58. Mechanoreceptors for hearing detect settling particles & moving fluid Ear Outer ear - external pinna & auditory canal Collect sounds & direct them to tympanic membrane (eardrum)
- 59. Middle ear - vibrations conducted through 3 small bones (malleus, incus, stapes) Inner ear - contains cochlea - organ for hearing Organ of Corti - in cochlea, has hair cells that transduce vibrations into action potentials
- 60. Taste Tastebuds are modified epithelial cells on tongue & mouth
- 61. Eyes Compound eyes (insects,crustaceans) - have 1000s of light detectors and lenses Single lens eye (vertebrates, some inverts)
- 62. Eyeball - 2 outer layers Sclera & choroid Sclera becomes cornea - allows light in Pupil - hole in center of iris Retina - contains photorecptor cells Rods - very light sensitive cells Cones - cells that distinguish color Aqeuous humor - fills anterior of eye Vitreous humor - fills posterior of eye Rhodopsin - light absorbing pigment that triggers signal transduction pathways that lead to sight
- 63. Skeleton Exoskeleton - hard encasement on surface of animal Endoskeleton - hard parts buried within soft tissue
- 64. Skeletal muscle Attached to bone, responsible for movement Made up of long fibers that are the muscle cells Muscle fibers are made up of bundles of myofibrils Myofibrils have 2 kinds of myofilaments: thick
- 65. Basic contractile unit is sarcomere During contraction, the sarcomere length is reduced Sliding filament model - thick & thin filaments slide past each other Actin & myosin molecules in thick & thin filaments interact to cause the sliding
- 66. Slow twitch muscle fibers - slow, long lasting contractions (endurance) Fast twitch muscle fibers - fast, powerful contractions (speed)