APH CH 9 nervous system

central nervous system

brain and spinal cord

CNS

can not repair itself

peripheral nervous system

nerves

Sensory-somatic nervous system

12 pairs of cranial nerves (eyes, ears, etc) and 31 pairs of spinal nerves

Sensory-somatic nervous system

Consciously controlled (skeletal muscles)

Autonomic nervous system

sensory neurons and motor neurons that run between the CNS

Autonomic nervous system

Heart, lungs, smooth muscles, glands

Autonomic nervous system

Two subdivisions

   1. Sympathetic nervous system

  - Fight or Flight

  2. Parasympathetic nervous system

  - “normal conditions”

Neurons (Nerve cells)

structural and functional units of the nervous system

Neurons (Nerve cells)

 Specialized to react to physical and chemical changes

Neurons (Nerve cells)

The brain is made up of about 200-100 billion nerve cells

Nerve Impulse

The electrochemical process of transmitting information from one neuron to another to cells outside the nervous system

Cell Body (soma)

contains cytoplasm, cell membrane, organelles (mitochondria, lysosomes, Golgi apparatus, nucleus, chromatophilic substance, and neurofibrils)

Dendrites

Numerous extensions from the neuron cell body that takes information to the cell body

Dendrites

Receives electrochemical messages (into cell)

Axon

The extension from the neuron cell body that takes information away from the cell body

Axon Terminal

End part of an axon that makes a synaptic contact with another cell

Neuroglial cells

Fill space, provide structural framework, produce myelin, and carry on phagocytosis

Neuroglial cells

Greatly out number neurons in the CNS (50x)

Neuroglial cells

They are cells- not nerve cells

CNS- Microglial cells

Support neurons and phagocytize (engulf bacteria debris)

CNS- Oligodendrocytes

Occur in rows along nerve fibers and they provide insulating layers of myelin around axons within the CNS

CNS- Astrocytes

Provide shape, support and structure

CNS- Astrocytes

Regulates nutrient and ion concentration

CNS- Astrocytes

Forms scar tissue to fill space following injury to CNS

CNS- Ependymal cells

Lines interior cavity of CNS

Ependymal cells make sure

nothing harmful gets in

PNS- Schwann cells

form a covering called myelin sheath

Myelin (CNS- Oligodendrocytes vs. PNS- Schwann cells)

Lipid-protein membrane layer

Myelin Sheath

Wraps around the axon and is necessary in order for the impulse to travel down the axon

Neurilemma

surrounds myelin sheath

Nodes of Ranvier

Narrow gaps in the myelin sheath between the Schwann cells

White Matter

Myelinated axons in the CNS

Gray Matter

Unmyelinated axon in the CNS

Afferent (sensory)

Travels towards the CNS

(Afferent) Sensory:

from outside body

(Afferent) Visceral:

Inside the body

Efferent (motor)

Travels away or out of the CNS

(Efferent) Somatic:

going to skeletal muscles

(Efferent) Autonomic:

smooth & cardiac muscles, glands

Interneurons

Within the CNS

Interneurons

Direct incoming impulses, process, interpret and re-direct

Bipolar Neurons

Has only 2 processes, one from each end

Bipolar Neurons

Found in eyes, nose and ear

Unipolar Neurons

Single process from cell body that divides into 2 branches (CNS + PNS)

Ganglia:

Unipolar neurons that are specialized masses of nervous tissue located outside the brain and spinal cord

Multipolar Neurons

Many processes (dendrites) arising from the cell body

Multipolar Neurons

One axon

Multipolar Neurons

Found mostly in the brain and spinal cord

10,000

specific types of neurons in the human brain

Active Transport

Movement of particles through the membrane from a region of low concentration to high concentration

Active Transport

ATP (energy) is required

Ex: Na+/K+ pump

Polarization =

electrically charged

Polarization

is important to the conduction of nerve impulses (& muscle contraction)

Polarization

is caused by the unequal distribution of positive and negative ions on either side of the cell membrane

Resting (membrane) potential

The difference between the electrical charges inside and outside the cell membrane

Na+ :

high concentration outside the cell and low inside (wants to go in)

K+ :

high concentration inside the cell and low outside (wants to go out)

Negatively charged particles inside cell

want to leave the cell but can’t get through the membrane

Threshold Potential

Stimulation level that must be exceeded to elicit a nerve impulse or a muscle contraction

Action Potential

The sequence of electrical changes when a nerve cell membrane is exposed to a stimulus that exceeds its threshold

Depolarization

When a cell responds to a stimulus causing the cell membrane’s resting potential to decrease

Depolarization

Inside the membrane becomes less negative compared to outside the cell

Depolarization

*Na+ channels open and rush into the cell

Repolarization

Membrane becomes negative again when membrane channels open up and K+ leaves the cell

Repolarization

*K+ channels open up and rush out of the cell

Na+/K+ pump- Pumps Na+ back outside and K+ back inside the cell

3 Na+ for every 2 K+

Threshold

The minimal amount of stimulus needed to produce an action potential

All or None Response

If a nerve fiber responds at all to a stimulus, it responds completely (like muscles)

All or None Response

Greater intensity of stimulation triggers more impulses per second, not a stronger impulse

Saltatory Conduction

Produced in myelinated neurons where the nerve impulse travels down the axon jumping from Node of Ranvier to Node of Ranvier

Reflexes

Rapid, automatic, subconscious response to a stimulus

Simple pathway including only a few neurons

Causes involuntary reaction

“Built in” or learned