1. ANATOMY & PHYSIOLOGY OF THE NEURON

4. How does the human body facilitate communication between nearly 100 trillion cells ?

5. The Neuron Doctrine
Santiago Ramon y Cajal (1887): Neurons are the functional unit of the nervous system
Neurons are discrete, metabolic units
Neurons are electrochemically excitable cells

6. How many neurons?
320
1 Trillion?

7. Anatomy of the Neuron

8. Anatomy of the Neuron Soma
The cell body of the neuron; contains the nucleus and other organelles necessary for survival of the cell
Dendrite
Branches of the neuron that receive chemical messages (neurotransmitters) from another neuron
Axon
Long “arm(s)” of the neuron that propagate electrical messages (action potentials) from within the neuron
Axon hillock
The site of the soma where the axon stems from and most often the site of action potential origination

9. Neuroglia Functions: Example: Astrocytes, Oligodendrocytes
Surround neurons and hold them in place
Supply nutrients and oxygen
Insulate one neuron from another
Destroy pathogens and remove dead neurons

10. Types of Neurons Sensory (afferent)
Transmits signals from sensory receptors to the spinal cord/brain.
Motor (efferent)
Transmit signals from the brain/spinal cord to muscle fibers, resulting in muscle contractions, and affect glands.
Interneurons (association)
Connect neurons to other neurons within the same region of the brain or spinal cord.

12. Action Potential
Electrochemical message that can stimulate or inhibit another neuron

13. The Action Potential Electrochemical changes that occur along the axon
Voltage change caused by migration of sodium and potassium ions across the cell membrane of the axon
Action potentials may be excitatory (EPSP’s) or inhibitory (IPSP’s) of the next neuron

14. Schwann Cells & Myelin
The axons of many neurons are wrapped in glial tissue called Schwann cells
Schwann cells produce a fatty tissue called myelin that wraps around regions of the axon
The spaces between the wrapped layers of myelin are called Nodes of Ranvier

15. Saltatory Conduction
The myelin sheaths insulate the axon, preventing excessive leakage of K+ ions
Depolarization at one Node of Ranvier is sufficient to propagate the action potential at an adjacent node.
As less gated channels need to be opened and closed along the axon, the effective speed of the action potential is greater

17. Neurotransmitters
Neurotransmitters (NT) are endogenous chemicals that transmit signals from a neuron to a target cell across a synaptic cleft
Synthesis of the NT can take place in the cell body, in the axon, or in the axon terminal.
Storage of the NT in storage granules or vesicles in the axon terminal.

18. Major Neurotransmitters
Acetylcholine (ACH)
Stimulates motor neurons
Inhibits cardiac contraction
Norepinephrine
Increases cardiac contraction rate & strength

19. Synaptic Transmission
Calcium enters the axon terminal during an action potential, releasing the neurotransmitter (NT) into the synaptic cleft.
The NT binds to and activates a receptor in the postsynaptic membrane.
The neurotransmitter is either destroyed enzymatically, or taken back into the terminal from which it came, where it can be reused, or degraded and removed.

23. The Nervous System
The nervous system is the part of an animal’s body that coordinates voluntary and involuntary actions of the animal and transmits signals between the different parts of its body.

25. Central v. Peripheral Divisions
Central (CNS)
Form: Brain, Spinal Cord, Optic Nerve
Form: Protected by bone and/or blood-brain barrier
Function: Integrates messages received from extremities, sensory organs and internal organs
Peripheral (PNS):
Form: Nerves and Ganglia outside of CNS. Includes 10 of 12 cranial nerves
Form: Not protected by bone or blood-brain barrier
Function: Relays messages between CNS and extremities.

26. Autonomic v. Somatic Divisions of PNS
Autonomic Divison (ANS)
Function: Involuntary control over heart rate, breathing, perspiration, salivation, pupillary dilation and digestion
Form: Afferent (sensory) & Efferent (motor) neurons
Subdivided in Sympathetic and Parasympathetic Divisions
Somatic Division (SoNS)
Function: Voluntary control of body via efferent motor neurons
SoNS also encompasses reflex arcs, which do NOT travel to brain but instead rely on association neurons
Form: Comprised of three types of nerves
Spinal
Cranial
Association

27. Somatic Division (SoNS)
The SoNS is responsible for controlling voluntary movements, using efferent (motor) neurons, and reflex arcs, using association (inter-) neurons.
Three types of nerves:
Spinal: Innervate much of the body, and connect through the spinal column to the spinal cord. (letter-number designations according to the vertebra through which they connect to the spinal column)
Cranial: Innervate the head, and connect directly to the brain (especially the brainstem). (Roman Numerals descriptive names).
Association: Connects other neurons (not “projection” neurons)

28. Somatic Reflex Arcs
A reflex arc is a neural pathway that controls action reflexes (ex: patellar reaction) by synapsing in the spinal cord (not the brain).
This allows for faster response time. Sensory information is still relayed to your brain, as the reflex action occurs.

29. Autonomic Division (ANS)
The ANS is responsible for controlling involuntary movements, such as heart rate, breathing, perspiration, salivation, pupillary dilation,digestion.
It is composed of afferent (sensory) and efferent (motor) neurons.
The ANS is further subdivided two divisions:
The Sympathetic Division (“Fight or Flight”)
The Parasympathetic Division (“Feed & Breed”)

31. Sympathetic and Parasympathetic Divisions of the ANS
Sympathetic (Fight or Flight)
Elevates blood pressure via vasoconstriction
Increases respiratory volume via dilation of bronchioles
Inhibition of peristalsis
Dilation of pupil
Parasympathetic (Feed & Breed)
Decreased blood pressure via vasodilation
Decreased respiratory rate
Increased digestion, urination and defecation

32. Parasympathetic Shock?