Nervous System

3 Functions of the Nervous System

• 1. Monitor changes inside and outside the body.– Changes are stimuli and the gathered information is

the sensory input.• 2. Processes and interprets the sensory input

and makes decisions about what should be done at each moment this is integration.

• 3. It then effects a response by activation muscles or glands this is called motor output.

Structural Classification

• Central Nervous System-(CNS)- brain and spinal cord – Interpret incoming sensory information and issue

instructions based on past experience and current conditions.

• Peripheral Nervous System-(PNS)- nerves that extend from the brain and spinal cord.– Carry impulse to and from the brain.

Functional Classification

• Functional Classification has to only with the PNS structures. – Sensory division-(afferent)- convey impulses to the CNS• Somatic sensory fibers- transmit impulses from the skin,

skeletal muscles and joints.• Visceral sensory fibers- transmit impulses from the visceral

organs.– Motor division-(efferent)- carries impulse from the CNS

to effector organs, muscles and glands. Bring about motor response.

Functional Classification

• Motor division has two subdivisions– Somatic nervous system- allows us to consciously,

or voluntarily, control our skeletal muscles.• Voluntary Nervous System

– Autonomic Nervous System- regulates events that are automatic or involuntary.• Involuntary Nervous System

Structure and Function

• Neuroglia- supporting cells in the CNS are lumped together. Literally meaning “nerve glue”– Astrocytes-star-shaped cells that account for

nearly half of the neural tissue. These cells protect by picking up excess ions and recapturing released neurotransmitters.

– Microglia- spiderlike phagocytes that dispose of debris, including dead cells and bacteria

Cont.– Ependymal- line the cavities of the brain and the spinal cord.

Helps circulate cerebrospinal fluid that fills those cavities that cushion the brain.

– Oligodendrocytes- glia that wrap their flat extensions tightly around the nerve fibers, producing fatty insulating coverings called myelin sheaths.

• Glia cannot transmit nerve impulses• This is what most tumors are formed from in the brain.• In the PNS support cells are:

– Schwann cells – form myelin sheath– Satellite cells- act as protective cushioning cells

Neurons Anatomy

• Neuron- nerve cell that transmit messages from one part of the body to another.– All have:

• Cell body that contains a nucleus • One or more slender processes extending from the cell body.

– Cell body- metabolic center of the neuron.• Have all organelles except centrioles

– Nissl substance- rough ER– Neurofibrils- intermediate filaments that are important

in maintaining cell shape

Neuron Anatomy

• Fibers- vary in length from microscopic to 3-4 feet long

• Dendrites- convey incoming messages toward the cell body.– Branch like projections off of the cell body but not

long arms.• Axons- generate nerve impulses and typically

conduct them away from the cell body.– Long arm like projection from the cell body.

Neuron Anatomy• Axonal Terminal- contain little sacs that have

neurotransmitters in them that send and receive nerve impulses.

• Synaptic cleft- tiny gas– Neurons never actually touch each other.

• Myelin- covers axons and is a white fatty material. Increases nerve impulse speed.

• CNS nerves are called tracts• PNS nerves are called nerves• White matter is mylinated and Grey matter has no myelin.

Classification

• Multipolar Neuron-Many processes coming off of the cell body

• Bipolar Neuron- two processes coming off of the cell body

• Unipolar Neuron- one processes coming off of the cell body

PhysiologyNerve Impulse

Central Nervous System

• In the embryonic development the CNS first appears as a tube (Neural Tube).

• Then it expands to four regions of the brain to form chambers called ventricles.

Functional Anatomy of the Brain

• Weighs a little over 3 lbs.

• Four Regions- – Cerebral hemisphere– Diencephalon– Brain stem– cerebellum

Cerebral Hemisphere

• Most superior part of the brain• Largest region of the brain• Gyri- covers the entire surface of the cerebral

hemispheres exhibits elevated ridges of tissue.• Sulci- shallow grooves• Fissures- deeper grooves

Lobes

• Parietal lobe- recognize pain, coldness, or a light touch. – Most sensitive areas are the lips and the

fingertips.• Occipital lobe- visual area• Temperal lobe- auditory area– Deep inside the temporal lobe is the olfactory area

Lobes

• Frontal lobe- primary motor area– Allows us to move and have motor control

• Broca’s area- ability to speak• Speech area- located on the temporal,

parietal, and occipital • Corpus Callosum-connects the cerebral

hemispheres. Allows the hemispheres to communicate.

Diencephalon

• Sits atop the brain stem and is enclosed by the cerebral hemispheres.

• Major structures-– Thalamus-sensory impulses– Hypothalamus- regulation of body temp., water

balance, and metabolism. Thirst, appetite, sex, and pain. Regulates the pituitary gland.

– Pituitary gland- anterior floor by a slender stalk. – Epithalamus- roof of 3rd ventricle. Pineal body and the

choroid plexus.

Brain Stem• Size of your thumb in diameter.• Structures are the midbrain, pons, and medulla oblongata.

– Controls breating and blood pressure.• Midbrain- reflex centers involved with vision and hearing.• Pons- control of breathing.• Medulla Oblongata- vital visceral activities. Heart rate,

breathing, swallowing, and vomiting.• Reticular Formation- motor control of visceral organs.

– RAS- plays a role in consciousness and the awake/sleep cycles. Damage to this area can result in coma.

Cerebellum

• Large cauliflowerlike • Skeletal muscle activity• Equilibrium apparatus of the inner ear, eye• Compared to the auto pilot.• If damaged movement becomes clumsy like a

drunk person

Brain Injuries

• Concussion- slight brain injury– Dizzy, loss of consciousness briefly, no permanent

damage– Contusion- marked tissue destruction.– Cerebral edema- swelling of the brain due to

injury.