Nervous System

Roles

• Monitors changes– What are the changes?

• Processes and interprets sensory input

• Effects a response

Organization

• CNS– Organs?

• PNS– Organs?

PNS

• Sensory (afferent) - delivers messages from the sensory receptors toward the CNS

• Motor (efferent) - delivers messages from the CNS to organs– Somatic nervous system - messages sent to

muscles– Autonomic nervous system - messages sent to

smooth muscle, cardiac muscles, and glands.– Which would be considered the involuntary

nervous system? Why?

Nervous Tissue

• Neuroglial cells of CNS– Astrocytes - form a barrier between capillaries and

neurons– Microglia - phagocytes– Ependymal - use cillia to circulate cerebrospinal fluid– Oligodendrocytes - form myelin sheath

• Neuroglial cells of PNS– Schwann cells - form myelin sheath– Satellite cells

• Neurons

Neurons

• Cell body– What is all here?

• Dendrites - receive incoming electrical stimulus– Neurons have hundreds of dendrites

• Axons - send out electrical stimulus– Neurons only possess one– mm to m in length. Where could an axon a meter

in length be found?

Axons

• Possess hundreds or thousands of axon terminals

• Terminals contain hundreds of vesicles– What are found in the vesicles (think about

the axon innervating the muscle)?– Why are these chemical messengers

needed?

Axons

• Most nerve fibers are covered with myelin– It is a fatty material. Function?

• What cells make up the myelin sheath?

• Gaps between cells are called nodes of Ranvier

Neuron classification

• Afferent (sensory neuron)– Examples?

• Efferent (motor neuron)

• Interneurons– What do you think these do?

Neuron Physiology

• Based on balance of what ions?

• Threshold stimulus

• All-or-none response

Neuron Physiology

• Resting membrane potenial (polarized)

• Na+ is highly concentrated outside the cell

• K+ is highly concentrated inside the cell

Neuron Physiology

• Stimulus initiates an action potential

• Causes Na+ channels to open– What will this cause?– Depolarization

• Once a small area is depolarized it stimulates adjacent areas– Creates an action potential

Neuron Physiology

• After depolarization, K+ channels open– What will this cause?– Repolarization

• What has to happen in order to get back to resting potential?

Neuron Physiology

• Myelin sheath speeds up the propagation of the action potential

• The impulse can travel at speeds up to 120 m/sec

• How does the nerve impulse get from one neuron to the next?

Reflex

• Rapid, predictable, involuntary motions• What would a reflex be called that stimulates

a skeletal muscle? Smooth muscles, heart, glands?

• Reflex arcs – Sensory receptor– Effector organ– Sensory neurons– Motor neurons– Integration center (CNS)

Central Nervous SystemProtection

• Meninges - connective tissue membranes– Dura mater– Arachnoid mater– Pia mater

• What do you think meningitis is?

Central Nervous SystemProtection

• Blood Brain Barrier– There are not spaces between cells in the

brain capillaries– Significance?– What glial cells help form tight junctions

between epithelial cells?– Lipid soluble molecules can easily pass.

What types of molecules would not pass?

Central Nervous SystemProtection

• Blood Brain Barrier– Glucose is water soluble. How does it

cross the BBB– The BBB is weaker in the emetic center of

the brain. Why?

Central Nervous SystemCerebrospinal Fluid

• Colorless liquid similar to blood plasma

• Surrounds the brain and spinal cord

• Role?

Central Nervous SystemBrain

• Cerebrum - most superior portion of the brain– Gyri - ridges– Sulci - grooves– Fissures - deeper grooves– These separate the lobes of the cerebrum

Cerebrum

• Motor areas, sensory areas, association areas

• Each hemisphere is concerned with the functions of the opposite side of the body.

• Hemispheres are not equal in function

• No functional area works alone

Cerebral lobes

• Parietal - somatic sensory (primary and association) area– Impulses travel to and from sensory receptors

(pain, cold, touch)– Sensory pathways are crossed

• Occipital - visual (primary and association) area

• Temporal - auditory association area– olfactory

Cerebral Lobes

• Frontal - primary motor area (patways are crossed)– Intellectual reasoning– Social acceptability– Complex memories (shared with temporal)– Language comprehension

Cerebral Hemispheres

• Gray matter - outermost (cerebral cortex)

• White matter - inner– Consists of fiber tracts - bundles of nerve

fibers that carry impulses to and from the cortex

– Corpus callosum - connects the two hemispheres and allows for communication

Central Nervous SystemDiencephalon

• Thalamus - sensation is determined pleasant or unpleasant

• Hypothalamus - regulation of body temperature, water balance, metabolism– Thirst, appetite, pain, pleasure, and sex centers – Regulates pituitary

• Pituitary Gland - major hormone producer

Central Nervous SystemBrain Stem

• About the size of a large thumb

• Midbrain - involved with vision and hearing

• Pons - breathing center

• Medulla Oblongata - controls vital visceral activities– Like what?

Central Nervous SystemCerebellum

• Coordinates muscle movement

• Monitors cerebrums intentions with actual performance

• Contains the arbor vitae

Spinal Cord• Extends from _________ to _________• What are the layers of protection?

Fluid?• Two way conduction• Major reflex center• Where would be a good location for

CSF testing?• Cauda equina

Peripheral Nervous SystemNerves

• Axon, fascicle, and nerve

• endoneurium, perineurium, and epineurium

• How would you describe the structure of a nerve?