1. How Nerve Signals Maintain Homeostasis
9.1 The Importance of the Nervous System
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2. 9.1: The Importance of the Nervous System
The nervous system is an elaborate communication system that has more than 100 billion nerve cells in the brain alone.
Memory, learning and language are all a part of the nervous system.
Has two divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).

3. CNS PNS Brain and spinal cord Protected by All the other neurons
Meninges
skull and vertebrae
PNS
All the other neurons
Serves limbs and organs
Sensory and motor branches
Exposed to toxins and more susceptible to injuries

5. CNS includes nerves of the brain and spinal cord and is the coordinating centre for incoming and outgoing information.
The PNS includes the nerves that carry information between the organs of the body and the CNS
PNS is divided further into the somatic and autonomic nerves.
Somatic: controls the skeletal muscle, bones and skin.
Autonomic: special motor nerves that control the internal organs of the body.
Autonomic can be subdivided into the sympathetic and the parasympathetic.

8. Peripheral Nervous System
Somatic Nerves:
Controls skeletal (voluntary) muscles, bones and skin
Brings information from the external environment to the CNS
Motor somatic nerves

9. Peripheral Nervous System
Autonomic Nerves:
Motor nerves that control smooth (involuntary) muscles, organs

11. Autonomic nervous system
Controls the internal organs of the body
operate without conscious control
constant interplay of balance between sympathetic and parasympathetic systems
autonomic nerves

13. Sympathetic nervous system
Prepares the body for stress:
increases heart rate,
increases the release of glucose,
dilates the pupils,
increases blood flow to the skin,
causes release of epinephrine

14. Parasympathetic nervous system
Restores normal balance:
decreases heart rate
stores glucose
constricts pupils
decreases blood flow to the skin

15. Nerves are responsible for sensory (input), integrative, and motor output.
Sensory Nerves
monitor external stimuli like temperature, light, and sound, etc.
Use internal body receptors to detect variations in pressure, pH, CO2 concentration, levels of various electrolytes etc.

16. Integrative Nerves
signals are brought together (integrated) to create sensations, to produce thoughts, or to add to memory.
Decisions are made based on the sensory input.

17. Motor nerve output / response
The nervous system responds to stimuli by sending signals to muscles, causing them to contract, or to glands, causing them to produce secretions.
Muscles and glands are called effectors
They cause an effect in response to directions from the nervous system.

18. Anatomy of a Nerve Cell

19. Cells of NS Non-neural cells (neuroglial or simply glial) Neurons
Provide oxygen and nutrients to neurons
Provide support, insulation and protection against pathogens
Remove dead neurons
Neurons
receive stimuli
conduct action potentials

20. Non-neural Glial Cells
Astrocytes
cover the surfaces of neurons and blood vessels.
provide structural support and help form the blood brain barrier, thus playing a role in regulating what substances from the blood reach the neurons.
Oligodendrocytes
form the myelin sheaths of axons in CNS
Schwann cells
form a myelin sheath called the neurilemma around each axon in PNS (sheath is 80% lipid + 20% protein)
very important in saltatory nerve conduction

21. Astrocyte

26. Types of Neurons Bipolar Unipolar Multipolar
has only two nerve fibers (axon & dendrite)
Unipolar
single nerve fiber
Multipolar
many nerve fibers
One is an axon, rest are dendrites

27. What are the 3 parts of all neurons?
Dendrites
The cell body
The axon

28. Neuron Structure Cell body: Contains nucleus Dendrites:
Receive information
Conduct nerve impulses toward the cell body
Axon:
Sends nerve impulses from the cell body to other neurons (effectors)
Myelin Sheath:
White coat of fatty protein that covers some axons

29. Schwann Cells:
Individual cells that compose the myelin sheath
Insulates the nerve cell
Nodes of Ranvier:
Areas between the sections of myelin sheath

30. Neurons Dendrites (“receivers”) Cell Body
Axon terminals (“Transmitters “)

32. Functional Differences b/w Neurons
Sensory (afferent) Neurons
carry nerve impulses from peripheral body parts into the brain or spinal cord
PNS to CNS
Have specialized dendrite ends
Interneurons (association)
within the brain or spinal cord
Link with other neurons
Motor (efferent) Neurons
carry nerve impulses out of the brain or spinal cord to effectors
CNS to PNS
Motor impulses stimulate muscles to contract and glands to release secretions

34. Sensory Neurons Afferent neurons
Sense and relay stimuli (information) from the environment to the CNS
Located in clusters outside of the spinal cord
Types of sensory receptors: thermoreceptors (temp.), photo (vision), pain, pressure, mechano (hearing), chemo (taste and smell)

35. Interneurons/Association Neurons
Neurons that link together neurons in the body
Mainly in the spinal cord and brain
human brain contains ~100 billion interneurons averaging 1000 synapses on each or some 1014 connections

36. Motor Neurons Efferent Neurons Relay information to the effectors
Muscles, organs and glands
The axons connecting your spinal cord to your foot can be as much as 1 m long (although only a few micrometers in diameter).

39. ANIMATIONS

40. Reflex Arcs Sensory neurons are stimulated by pricking rose thorns
Signal travels to spinal cord along sensory neurons
Synapse with interneurons within CNS
Interneurons stimulate motor neurons
Stimulus travels along motor axons to muscle
Muscle contracts to withdraw hand

41. Reflex arcs:
Sensory
Integrative
Motor

44. Reflex Arcs

46. The Speed of Nerve Impulses
Myelinated nerve fibres speed up nerve impulses
Nerve impulses jump from one node to another… speeding up nerve action (known as saltatory conduction)

47. Neuron Repair Neurilemma: Thin membrane that surrounds the axon
Promotes regeneration of damaged neurons
Not in all nerve cells
White Matter:
Nerve cells in the brain that contain myelinated fibres and a neurilemma
Grey Matter:
Nerve cells in the brain and spinal cord that lack a myelin sheath and neurilemma
Why are spinal and brain injuries often permanent?

48. How to Fix “Irreparable” Damage to the CNS
Reattach two torn nerves
- limited success
2. Grafts from the PNS
- more successful…CNS cells that are left alone however, had no regeneration

49. Stem Cells Cells that have not specialized into tissue cells
Experiments are being done on replacing damaged cells using stem cells
E.g. pp. 415…rats with reconnected spinal cords
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