Introduction to Nervous System

Composition of Nervous System Two main divisions Two main divisions 1) Central Nervous system (CNS) brain and spinal chord 1) Central Nervous system (CNS) brain and spinal chord 2)Peripheral Nervous System (PNS) nerves 2)Peripheral Nervous System (PNS) nerves

Remember from Homeostasis Message is received from sensory receptor along sensory neuron (afferent pathway) Message is received from sensory receptor along sensory neuron (afferent pathway) Messages reaches brain and is integrated (control center) Messages reaches brain and is integrated (control center) Reaction command sent down efferent pathway along motor neuron (motor output) Reaction command sent down efferent pathway along motor neuron (motor output)

Types of Motor Actions Somatic Somatic Happens in skeletal muscle Happens in skeletal muscle voluntary voluntary Autonomic Autonomic Happens in smooth and cardiac muscle Happens in smooth and cardiac muscle Involuntary Involuntary 2 parts 2 parts Sympathetic and parasympathetic Sympathetic and parasympathetic

Cells of the Nervous System Broken down into two groups Broken down into two groups 1) supporting cells 1) supporting cells 2) neurons 2) neurons

Examples of Neuroglia (supporting cells) 1) astrocytes – anchor neurons to capillaries 1) astrocytes – anchor neurons to capillaries 2) microglia – phagocytes (digest debris and dead cells) 2) microglia – phagocytes (digest debris and dead cells) 3) Ependymal cells- ciliated; always on surface near spinal fluid; circulates fluid 3) Ependymal cells- ciliated; always on surface near spinal fluid; circulates fluid

One more Neuroglial cell (in CNS) 4)Oligodendrocytes – fatty; insulated nerve fibers 4)Oligodendrocytes – fatty; insulated nerve fibers Produce myelin sheath which surround and insulate the nerve fiber Produce myelin sheath which surround and insulate the nerve fiber

In PNS Instead of oligodendrocytes, they have Schwann cells, which insulate the nerve fiber Instead of oligodendrocytes, they have Schwann cells, which insulate the nerve fiber Satellite cells – form protective layer around nerve cell body Satellite cells – form protective layer around nerve cell body

Neurons Specifically designed to transmit message (nerve impulse) Specifically designed to transmit message (nerve impulse)

Parts of a Neuron 1)Cell Body- contains nucleus 1)Cell Body- contains nucleus 2) fiber (process)- carries message to next neuron 2) fiber (process)- carries message to next neuron Toward cell body = dendrites Toward cell body = dendrites Away from cell body = axon Away from cell body = axon

Axonal Terminal As an axon ends, it branches into hundreds of synapses. As an axon ends, it branches into hundreds of synapses. Releases neurotransmitters to next neuron or muscle Releases neurotransmitters to next neuron or muscle

Myelination of Neurons In CNS, the fatty covering is oligodendrocyte In CNS, the fatty covering is oligodendrocyte In PNS, fatty myelin forms Schwann cells, which increase transmission rate. In PNS, fatty myelin forms Schwann cells, which increase transmission rate. Gaps between Schwann cells= Nodes of Ranvier Gaps between Schwann cells= Nodes of Ranvier