Chapter 7 (part 1) : The Nervous System

Nissel Substance

A Nissl body, also known as Nissl substance, is a large granular body found in neurons. These granules are of rough endoplasmic reticulum (RER) with rosettes of free ribosomes, and are the site of protein synthesis. It was named after Franz Nissl, a German neuropathologist who invented the Nissl staining method.

Ganglia

A ganglion is a nerve cell cluster or a group of nerve cell bodies located in the autonomic nervous system and sensory system. Ganglia house the cells bodies of afferent nerves and efferent nerves.

Neuron

A neuron or, also known as a neurone, "a nerve cell"; "by the late 20th century the term neuron was commoner than neurone ... and standard in scientific usage" or nerve cell) is an electrically excitable cell that receives, processes, and transmits information through electrical and chemical signals. These signals between neurons occur via specialized connections called synapses. Neurons can connect to each other to form neural networks. Neurons are the primary components of the central nervous system, which includes the brain and spinal cord, and of the peripheral nervous system, which comprises the autonomic nervous system and the somatic nervous system.

Action Potential

Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and endocrine cells, as well as in some plant cells. In neurons, action potentials play a central role in cell-to-cell communication by providing for (or assisting in, with regard to saltatory conduction) the propagation of signals along the neuron's axon towards boutons at the axon ends which can then connect with other neurons at synapses, or to motor cells or glands. In other types of cells, their main function is to activate intracellular processes. In muscle cells, for example, an action potential is the first step in the chain of events leading to contraction. In beta cells of the pancreas, they provoke release of insulin. Action potentials in neurons are also known as "nerve impulses" or "spikes", and the temporal sequence of action potentials generated by a neuron is called its "spike train". A neuron that emits an action potential is often said to "fire".

Interneuron

An interneuron (also called internuncial neuron, relay neuron, association neuron, connector neuron, intermediate neuron or local circuit neuron) is a broad class of neurons found in the human body. Interneurons create neural circuits, enabling communication between sensory or motor neurons and the central nervous system (CNS). They have been found to function in reflexes, neuronal oscillations, and neurogenesis in the adult mammalian brain.

Astrocytes

Astrocytes (Astro from Greek astron = star and cyte from Greek "kytos" = cavity but also means cell), also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. The proportion of astrocytes in the brain is not well defined.

Autonomic Reflex

Autonomic reflexes are unconscious motor reflexes relayed from the organs and glands to the CNS through visceral afferent signaling.

Axon

Axon, also called nerve fibre, portion of a nerve cell (neuron) that carries nerve impulses away from the cell body. A neuron typically has one axon that connects it with other neurons or with muscle or gland cells.

Efferent Neuron

Efferent Neurons (also known as efferent nerve fibers) are conducting cells that carry information from the central nervous system (the brain and spinal cord) to muscles and organs throughout the body. These neurons carry electrical impulses that tell organs and muscles what to do.

Gray Matter

Grey matter (or gray matter) is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and myelinated as well as unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distinguished from white matter, in that it contains numerous cell bodies and relatively few myelinated axons, while white matter contains relatively few cell bodies and is composed chiefly of long-range myelinated axon tracts. The colour difference arises mainly from the whiteness of myelin. In living tissue, grey matter actually has a very light grey colour with yellowish or pinkish hues, which come from capillary blood vessels and neuronal cell bodies.

Repolarization

In neuroscience, repolarization refers to the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential has changed the membrane potential to a positive value.

Support Cells

In the central nervous system, there are four types of supporting cells. 1. Oligodendrocytes. The axons of many neurons are insulated by a myelin sheath, which increases the rate at which an axon can conduct an action potential. 2. Microglia These types of cell are less common. They have a role in immune defence and become phagocytic in response to infections or tissue damage. 3. Astrocyte These cells are the most common type of supporting cell. They are involved in metabolic exchange between neurons and blood. 4.Ependymal cells. These cells line the vetricles and spinal canal. They have cilia on their luminal surface.

Proprioceptors

In the limbs, the proprioceptors are sensors that provide information about joint angle, muscle length, and muscle tension, which is integrated to give information about the position of the limb in space. The muscle spindle is one type of proprioceptor that provides information about changes in muscle length.

Afferent Neuron

In the peripheral nervous system (PNS), an afferent nerve fiber is the axon of a sensory neuron. It is a long process extending far from the nerve cell body that carries an action potential from the sensory neuron toward the central nervous system (CNS).

Microglia

Microglia are a type of neuroglia (glial cell) located throughout the brain and spinal cord. Microglia account for 10-15% of all cells found within the brain. As the resident macrophage cells, they act as the first and main form of active immune defence in the central nervous system (CNS).

Myelin

Myelin is a fatty white substance that surrounds the axon of some nerve cells, forming an electrically insulating layer. It is essential for the proper functioning of the nervous system. It is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination or myelinogenesis.

Myelin Sheath

Myelin is a fatty white substance that surrounds the axon of some nerve cells, forming an electrically insulating layer. It is essential for the proper functioning of the nervous system. It is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination or myelinogenesis.

Neuroglia

Neuroglia, also called glial cells, or simply glia are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the central and peripheral nervous systems. In the central nervous system, glial cells include oligodendrocytes, astrocytes, ependymal cells and microglia, and in the peripheral nervous system glial cells include Schwann cells and satellite cells

Neurilemma

Neurolemma (also known as neurilemma or sheath of Schwann (Schwann's Sheath)) is the outermost nucleated cytoplasmic layer of Schwann cells (also called neurolemmocytes) that surrounds the axon of the neuron. It forms the outermost layer of the nerve fiber in the peripheral nervous system.

Neurotransmitter

Neurotransmitters, also known as chemical messengers, are endogenous chemicals that enable neurotransmission. They transmit signals across a chemical synapse, such as a neuromuscular junction, from one neuron (nerve cell) to another "target" neuron, muscle cell, or gland cell. Neurotransmitters are released from synaptic vesicles in synapses into the synaptic cleft, where they are received by receptors on the target cells. Many neurotransmitters are synthesized from simple and plentiful precursors such as amino acids, which are readily available from the diet and only require a small number of biosynthetic steps for conversion. Neurotransmitters play a major role in shaping everyday life and functions. Their exact numbers are unknown, but more than 100 chemical messengers have been uniquely identified.

Schwann Cells

Schwann cell, also called neurilemma cell, any of the cells in the peripheral nervous system that produce the myelin sheath around neuronal axons. Schwann cells are named after German physiologist Theodor Schwann, who discovered them in the 19th century.

Nodes of Ranvier

The action potential travels from one location in the cell to another, but ion flow across the membrane occurs only at the nodes of Ranvier. As a result, the action potential signal jumps along the axon, from node to node, rather than propagating smoothly, as they do in axons that lack a myelin sheath.

Autonomic Nervous System

The autonomic nervous system is the part of the nervous system that supplies the internal organs, including the blood vessels, stomach, intestine, liver, kidneys, bladder, genitals, lungs, pupils, heart, and sweat, salivary, and digestive glands.

Central Nervous System

The central nervous system (CNS) is the part of the nervous system consisting of the brain and spinal cord. The central nervous system is so named because it integrates information it receives from, and coordinates and influences the activity of, all parts of the bodies of bilaterally symmetric animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish—and it contains the majority of the nervous system.

Motor Division

The motor division of the PNS is subdivided into several branches. The somatic motor branch carries voluntary (willed) commands to the skeletal muscles, allowing a person to perform such action as swatting a mosquito or sticking out the tongue.

Peripheral Nervous System

The peripheral nervous system (PNS) is one of the two components of the nervous system, the other part is the central nervous system (CNS). The PNS consists of the nerves and ganglia outside the brain and spinal cord. The main function of the PNS is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body.

Sensory Division

The sensory division is a part of peripheral nervous system, it runs from sensory organs to the CNS (brain and spinal cord). The sensory division collects information (touch, pain, pressure, vision, taste etc) from outside (somatic sensory) and inside (visceral sensory) of the body and carries them to the CNS

Somatic Nervous System

The somatic nervous system (SoNS or voluntary nervous system) is the part of the peripheral nervous system associated with the voluntary control of body movements via skeletal muscles. The SoNS consists of afferent nerves or sensory nerves, and efferent nerves or motor nerves.

Involuntary Nervous System

The somatic system is the part of the peripheral nervous system that is responsible for carrying motor and sensory information both to and from the central nervous system. This system is made up of nerves that connect to the skin, sensory organs, and all skeletal muscles.

Oligodendrocytes

Their main functions are to provide support and insulation to axons in the central nervous system of some vertebrates, equivalent to the function performed by Schwann cells in the peripheral nervous system. Oligodendrocytes do this by creating the myelin sheath, which is 80% lipid and 20% protein.

Somatic reflex

There are two types of reflex arcs:the autonomic reflex arc, affecting inner organs, and the somatic reflex arc, affecting muscles. When a reflex arc consists of only two neurons, one sensory neuron, and one motor neuron, it is defined as monosynaptic. Monosynaptic refers to the presence of a single chemical synapse.

Depolarization

medical Definition of depolarization. : loss of polarization; especially : loss of the difference in charge between the inside and outside of the plasma membrane of a muscle or nerve cell due to a change in permeability and migration of sodium ions to the interior.

Synaptic Cleft

medical Definition of synaptic cleft. : the space between neurons at a nerve synapse across which a nerve impulse is transmitted by a neurotransmitter — called also synaptic gap.

White Matter

White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distribution of action potentials, acting as a relay and coordinating communication between different brain regions.

Dendrite

a short branched extension of a nerve cell, along which impulses received from other cells at synapses are transmitted to the cell body.

Reflex Arc

the nerve pathway involved in a reflex action including at its simplest a sensory nerve and a motor nerve with a synapse between.