1. Nervous System Basics

2. Nervous System Overview

3. Nervous System Overview
Central Nervous System (CNS)
Composed of brain and spinal cord
Peripheral Nervous System (PNS)
Composed of nerves outside the CNS
Autonomic Nervous System (ANS)
Part of the PNS, controls the involuntary organs and muscles

4. Nervous Tissue
Left Photo: Glial cells - red, neurons - green. Right Photo: Glial cells - green, neurons – red, nuclei - blue

5. Nervous Tissue Nervous tissue is composed of two types of cells
Neurons: transmit nerve messages
Glial Cells: support cells in the nervous system that help to protect the neurons, as well as produce the myelin sheaths of nerves, secrete cerebrospinal fluid, defend against bacteria, regulate ions
About 50% of the weight of the brain is glial cells.

6. Neurons

7. Neurons Functional unit of the nervous system Composed of three parts:
Humans have about 100 billion neurons in their brain!
Composed of three parts:
Dendrite: receives information from another cell and transmits to the cell body
Cell Body: contains nucleus, mitochondria, and other organelles
Axon: conducts messages away from the cell body

8. Neuron Types

9. Neuron Types
Sensory Neuron: long dendrite, short axon; carry messages from sensory receptors to CNS
Motor Neuron: long axon, short dendrite; transmit messages from CNS to muscles/glands
Interneuron: only in CNS, connect neuron to neuron

10. Specialization

11. Specialization
Many axons have a myelin sheath, which acts like insulation, wrapped around them
Formed from the plasma membrane of specialized Glial cells called Schwann cells
Schwann cells serve as supportive, nutritive, and serve facilities for neurons
Gap between Schwann cells is called the node of Ranvier
Signals jumping node to node travel hundreds of times faster than along the surface of axons
Allows your brain to communicate with your toes in a few thousandths of a second

12. Synaptic Communication

13. Synaptic Communication
Synapse: junction where neurons communicate
Neurons normally do not touch each
Synaptic cleft: separation gap
Presynaptic neuron: transmitting cell
Postsynaptic neuron: receiving cell
Electrical activity in the neuron causes the release of chemicals called neurotransmitters into the synaptic cleft
This causes electrical activity in another neuron
Synaptic vesicles: neurotransmitter releasers

14. Neurotransmitters
Chemicals which relay, amplify, and modulate signals between a neuron and another cell
Acetylcholine: triggers muscle contraction
Norepinephrine: flight or fight response; increases blood flow to muscles, releases glucose, increases heart rate
Dopamine: important in treatment of Parkinson’s
Serotonin: relates anger, aggression, body temp, mood, sleep, human sexuality, appetite, and metabolism
Endorphin – natural “pain relievers”

15. CNS: The Brain

16. CNS: The Brain Cerebrum Cerebellum Hypothalamus
Largest part of the human brain, associated with higher brain function such as thought and action
Cerebellum
“Little brain”, associated with regulation and coordination of movement, posture, and balance.
Hypothalamus
Produces hormones that control body temp, hunger, moods, hormones, sleep, thirst, and sex drive

17. Peripheral Nervous System

18. Peripheral Nervous System
Afferent Neurons: Some peripheral neurons collect info and transmit it towards the CNS
Efferent Neurons: Others transmit info away from the CNS
Nerves are bundled axons and dendrites of neurons outside the CNS

19. Autonomic Nervous System
Has two subdivisions that stimulate or inhibit body systems
Sympathetic division – can be activated by physical or emotional stress
Parasympathetic division – controls the internal environment during routine conditions

20. Reflex Arc

21. Reflex Arc Part of the PNS’ motor division
Controls the movement of skeletal muscles
Voluntary, but can be operated without conscious control (balance)
Reflexes such as knee-jerk
Sensory neurons connect sensory receptors to the CNS. The CNS processes the signal, and transmits a message back to an effector organ (an organ that responds to a nerve impulse from the CNS) through a motor neuron.

22. Resting Potential

23. Resting Potential
Outside the neuron’s plasma membrane has a positive charge, while inside has a negative charge
Passage of ions across the cell membrane passes the electrical charge along the cell
The voltage potential is -70mV of a cell at rest
Resting potential results from differences between sodium and potassium positively charged ions and negatively charged ions in the cytoplasm
Sodium ions are more concentrated outside the membrane, while potassium ions are more concentrated inside the membrane  Active transport due to the Sodium Potassium Pump

24. Action Potential

25. Action Potential
A temporary reversal of the electrical potential along the membrane for a few milliseconds
Begins at one spot on the membrane, but spreads to adjacent areas of the membrane
After, there is a refractory period, which prevents the message from being transmitted backward along the membrane.

26. Steps in an Action Potential

27. Step in an Action Potential
At rest the outside of the membrane is more positive than the inside
Sodium channels open and sodium moves into the cell, causing the membrane potential to become positive.
At some point, the potassium channels open allowing potassium ions to flow out of the cell.
The sodium channels close and stop the inflow of positive charge. Potassium channels are open, allowing positive charges to outflow and the membrane potential plunges.
When the membrane potential reaches its resting state, the potassium channels close.
Sodium/potassium pump pumps sodium out of the cell and potassium into the so it is ready for the next action potential.