1. Introduction to The nervous system
Anatomy Ch. 7 Part 1
Introduction to The nervous system

2. Introduction
The nervous system is the master controlling and communicating system of the body.
Communication with body cells is done by using electrical impulses.
In order to maintain homeostasis the nervous system works with the endocrine system
The nervous system conducts impulses
The endocrine system uses hormones

3. 3 Functions of the Nervous System
Monitor changes produced by stimuli, also known as sensory input
Process and interpret, also known as integration
Cause a response by activating muscles or glands (effectors) via motor output

4. Structural Classification of the Nervous System
Central Nervous System (CNS)
Brain and spinal cord
Integrating and command center
Interprets and issues instructions
Peripheral Nervous System (PNS)
Spinal and cranial nerves
Link receptors to the CNS and the CNS to glands or muscles

5. Functional Classification (PNS)
Sensory (afferent)
Carry impulses to the CNS from sensory receptors
Divided into the Somatic and Visceral
Somatic: skin, skeletal muscles, and joints
Visceral: visceral organs
Motor (efferent)
Carry impulses from the CNS to muscles or glands
Divided into Somatic and Autonomic
Somatic: Voluntary control of skeletal muscles
Autonomic: involuntary control of smooth and cardiac muscles and glands

6. Sympathetic and Parasympathetic Divisions of the Autonomic Nervous System
Neurotransmitter is acetylcholine
Rest and Digest division
Decreases the activity of the cardiovascular and respiratory systems and increases the activity of the digestive system.
Sympathetic
Neurotransmitters are acetylcholine, epinephrine, and norepinephrine
Fight or flight division
Increases the activity of the cardiovascular and respiratory systems and decreases the activity of the digestive system.

7. Common Neurotransmitters
Acetylcholine
skeletal muscle activity
Adrenaline (epinephrine)
fight or flight
Noradrenaline (norepinephrine)
stress hormone
Serotonin
mood
Dopamine
pleasure
Endorphins
Euphoria (excitement or happiness)
Glutamate
memory
GABA
calming

8. Nervous Tissue
Supporting Cells (neuroglial cells) support insulate, and protect neurons
Astrocytes: link capillaries and neurons
Microglia: phagocytes that dispose of debris
Ependymal: circulate CSF
Oligodendrocytes: insulate nerve fibers
Schwann cells: form myelin sheaths
Satellite cells: protect and cushion

10. Anatomy of a Neuron
Cell body: nucleus, Nissl bodies (ER), and neurofibrils which maintain shape
Dendrites: convey incoming messages to the cell body
Axons: conduct messages away from the cell body

11. Regions of axons
Hillock: area of the cell body where the axon originates
Terminals: branches of axons that contain neurotransmitters
Synaptic cleft: gap between an axon and the next neuron, the junction is called a synapse

12. Myelin sheaths: covering of axons that protect and insulate and increase transmission rates of impulses
Schwann cells: produce myelin sheaths
Nodes of Ranvier: gaps between Schwann cells
Neurilemma: surrounds the myelin sheaths
Only found in the PNS which allows for regeneration

14. Differences between the CNS and PNS
In the CNS clusters of cells bodies are called nuclei
In the PNS clusters of cell bodies are called ganglia
In the CNS bundles of nerve fibers are called tracts
In the PNS bundles of nerve fibers are called nerves

15. The terms white matter and gray matter refer to regions of the CNS.
White matter has myelinated fibers
Gray matter has unmyelinated fibers

16. Functional Classification
Direction of Impulses
Sensory (afferent): carry impulses from receptors to the CNS; the cell bodies are outside of the CNS
Free nerve endings – pain and temperature
Meissners corpuscles – touch
Lamellar corpuscles – deep pressure
Proprioceptors – muscles and tendons

17. Motor (efferent): carry impulses from the CNS to organs, muscles or glands; the cell bodies are found in the CNS
Interneurons (association): connect motor and sensory neurons; cell bodies are found in the CNS

18. Neurons have 2 major functional properties:
Irritability: respond to stimulus
Conductivity: transmit impulses

19. Structural Classification
Number of Processes
Multipolar
several extensions from the cell body
all motor and association neurons
most common
Bipolar
2 extensions from the cell body
only found in the eye and nose

20. Unipolar
A single short process that divides into proximal and distal processes
Sensory neurons of the PNS
Axons conduct impulses toward and away from the cell body.

22. Conduction of a Nerve Impulse
A resting neuron is polarized meaning there are more positive ions on the outside than on the inside
The major positive ion on the inside of the cell membrane is Potassium
The major positive ion on the outside of the cell membrane is Sodium

23. Steps of Impulse Conduction
1. As long the neuron is in the resting state it will be inactive. This is called the polarized state. Most neurons are excited by neurotransmitters.
2. When the neuron is stimulated, sodium quickly diffuses into the neuron. This changes the polarity of the membrane and is called depolarization.

24. 3. If the stimulus is strong enough, the depolarization will travel over the entire length of the neuron membrane. This is called action potential or nerve impulse. 4. As the impulse moves, the permeability changes. Potassium is now able to leave the neuron rapidly by diffusion. This causes the cell to become repolarized. There cannot be another impulse until the neuron is repolarized.

25. 5. After repolarization the sodium and potassium are returned to their original locations by the Na/K pump. This is an active process requiring ATP.

26. Action Potential

27. The previous process occurs in unmyelinated fibers
The previous process occurs in unmyelinated fibers. Fibers that have myelin conduct impulses much faster.
The impulse actually jumps from one node to another skipping myelinated regions. This is called saltatory conduction.

28. Impulses do not travel from one neuron to the next.
Instead neurotransmitters cross the synapse between neurons and carry the signal.

29. Steps of transmission from one neuron to the next (electrochemical)
1. When the action potential reaches the axon terminal, calcium enters the terminal 2. The calcium causes vesicles in the terminal to release the neurotransmitter 3. The neurotransmitter moves across the synapse and binds to receptors on the next neuron 4. If there are enough neurotransmitters to stimulate the next neuron then an impulse can be conducted. 5. Once the next neuron has been stimulated the neurotransmitter is removed.

30. Neuron Transmission

31. Reflexes
Most of what the body does everyday is programmed as reflexes.
Reflexes are rapid, predictable, and involuntary responses to a stimuli
The pathway of a reflex is called a reflex arc
Reflexes can be classed as somatic or autonomic.
Somatic: skeletal muscles
Autonomic: smooth and cardiac muscles and glands

32. All reflexes have 5 elements:
Sensory receptor: reacts to stimuli
Sensory neurons: send message to the CNS
Integration center: the CNS
Motor neurons: send message to the effector organ
Effector organ: the muscle or gland stimulated

33. Reflex arcs can have 2 or more neurons.
Additional neurons are called interneurons.
The more neurons, the longer the reflex takes to happen.
Spinal reflexes do not require the brain’s involvement.
Reflexes that involve the brain are those that require many types of information.

34. Reflex Arc