The Nervous System

The Nervous System Master control & communicating system Functions: Sensory input – senses changes Integration – interprets changes Motor output – reacts to changes Two Sub-divisions: Central Nervous System (CNS) Brain & spinal cord Peripheral Nervous System (PNS) Spinal & cranial nerves

Nervous Tissue Two Types Neuroglia (“nerve glue”) Support, insulate, & protect neurons Neurons – three parts Dendrites – detect impulses Cell body – interpret impulses Axon – conduct impulses

Classification of Neurons Based on structure & function Functional: Sensory/Afferent Neurons Carries message to CNS Motor/Efferent Neurons Carries impulses from the CNS Interneurons Connect sensory & motor neurons Structural: Based on # of processes extending from the cell Multipolar Neurons (most common), Bipolar Neurons (rare), & Unipolor Neurons (rare)

Neuroglial Cells Supportive, protective, and connective tissue of the CNS Glial cells are stromal (framework) tissue, whereas neurons carry nervous impulses Astrocytes Star-like appearance (astr/o = star) Transports water & salts between capillaries & neurons Microglial cells Protect neurons in response to inflammation Oligodendrocytes Few dendrites (olig/o = few or scanty) Form the myelin sheath in the CNS Ependymal cells Line membranes where cerebrospinal fluid (CSF) circulates

Neurons Continued… Neurons do not touch Tiny gap separates neurons Neurons release chemicals called neurotransmitters that carry the impulse to the next neuron or muscle cell Most are covered with myelin (fatty material) Cells of the PNS are covered with Schwann cells (myelin sheath) In CNS: Gray matter is unmyelinated fibers White matter is myelinated fibers

Synapse Space where the nervous impulse jumps from one neuron to the other. Aka synaptic cleft or synapse Neurotransmitter Chemical substance that transfers the impulse Acetylcholine, norepinephrine, epinephrine, dopamine, serotonin, endorphins

Nerve Physiology How is a signal transmitted down a neuron? Dendrites Cell Body Axon Transmission of Nerve Impulse nerve impulse is an electrical signal that travels along an axon. electrical difference between the inside of the axon and its surroundings When activated, there is a sudden change in the voltage across the wall of the axon caused by the movement of ions in and out of the neuron. triggering a wave of electrical activity that passes from the cell body along the length of the axon to the synapse.

Transmission of Impulses Neuron at rest has a (+) charge outside the cell & a (-) charge within the cell Stimulus excites a neuron Gated sodium channels open, allowing Na+ to enter & make the inside of the cell (+) & outside (-) Depolarization Action potential starts As the impulse passes, gated Na+ channels close & gated potassium channels open, releasing K+ Repolarizes the neuron Known as the Na+/K+ pump

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Connections Between Neurons When an impulse reaches the end of an axis… Calcium channels open & Ca+ enters the axis & causes the release of neurotransmitters Neurotransmitters diffuse across the synapse & bind to receptors on the dendrites of the next neuron Initiating a new impulse

General Structure Central Nervous System (CNS) Brain & spinal cord Coordinates all of body’s activities Interprets incoming information & issues instructions Peripheral Nervous System (PNS) Cranial nerves Carry impulses between the brain & the head & neck Exception: Vagus Nerve Spinal nerves Plexuses Plexus = large network of nerves Peripheral nerves

The Brain Control center 4 main sections Cerebral Hemispheres The Cerebrum Superior portion of the brain Speech, memory, logic, emotional responses, consciousness, voluntary movement, & interpretation of sensations. Lots of creases & folds Increases surface area Consists of both gray & white matter

The Brain Diencephalon – interbrain Sits on top of the brain stem; enclosed by the cerebral hemispheres Includes: Thalamus – relay station Hypothalums Regulates body temp., water balance, & metabolism Controls drives & emotions Regulates the pituitary gland

The Brain Brain Stem – 3 inches long Cerebellum Includes: Midbrain involved in functions such as vision, hearing, eye movement, and body movement. Pons involved in motor control and sensory analysis Medulla oblongata responsible for maintaining vital body functions, such as breathing and heart rate Cerebellum Back of the brain Balance, posture, & coordination

Brain Dysfunctions Concussion Contusion Cerebral edema Violent jarring or shaking that results in a disturbance of brain function Contusion Bruise to the brain Cerebral edema Swelling Cerebrovascular accidents strokes Alzheimer’s Disease

Peripheral Nervous System Nerves that carry messages to & from CNS Afferent Division (Sense receptors) For sight, hearing, balance, smell, touch & Sensory (afferent) nerves Carry messages toward the spinal cord & brain Efferent Division (Motor nerves) Travel from the spinal cord & brain to muscles, telling them how to respond

Peripheral Nervous System Somatic Nervous System Voluntary pathways Ex: turning head when tapped on shoulder Autonomic Nervous System Connects CNS to internal organs Involuntary pathways Carries impulses away from the CNS to the glands, heart, blood vessels, & involuntary muscles (intestines, stomach, bladder) Autonomic nerves Sympathetic nerves Stimulate the body in times of stress & crisis Increase heart rate, dilate airways, increase BP, stimulate the adrenal glands, inhibit intestinal contractions Parasympathetic nerves Slow down heart rate, lower BP & stimulate intestinal contractions

Cranial Nerves – PNS ~12 pairs in the head & neck Olfactory Facial smell Taste, Face expression Optic Vestibulocochlear vision Hearing & balance Oculomotor Glossopharyngeal eyes Throat control Trochlear Vagus mouth digestion Trigeminal Accessory face + nose + mouth neck Abducens Hypoglossal eye roll tongue

Nervous System Disorders Poliomyelitis viral infection, may lead to partial or full paralysis Cerebral palsy group of disorders that can involve brain and nervous system functions, such as movement, learning, hearing, seeing, and thinking. Parkinson’s disease Multiple Sclerosis (MS) Epilepsy Dyslexia Tay-Sachs Disease Rabies – viral infection Dementia - Senility