Nervous System - Chapter 10

Definition of Node of Ranvier

A small gap or indentation in the myelin sheath that surrounds an axon

Definition of Perineurium

A specialized layer of connective tissue that surrounds and protects nerve fascicles

Definition of Axon Hillock

A specialized region of a neuron where the axon originates from the cell body

Definition of Oligodendrocyte

A type of glial cell that produces and maintains myelin in the central nervous system (CNS)

Definition of Cranial Nerve

A type of nerve that emerges from the brain or brainstem rather than the spinal cord

Definition of Spinal Nerve

A type of nerve that is connected to the spinal cord

Definition of Postsynaptic cell

Cell that receives signals from a presynaptic cell at a synapse

Definition of Synapses

A junction between two nerve cells (neurons) or between a neuron and a muscle cell, wheere information is transmitted from one cell to another

Definition of Microglial Cells

Type of glial cell that act as the primary immune cells in the CNS. They are small, non-neuronal cells that make up approximately 10-15% of all cells in the brain and spinal cord.

Definition of Ependymal Cells

Type of glial cell that line the ventricles of the brain and the central canal of the spinal cord. They are specialized epithelial cells that form a thin layer of tissue that separates the cerebrospinal fluid (CSF) from the brain and spinal cord tissue.

Definition of Schwann Cell

Type of glial cells that are found in the peripheral nervous system (PNS) and are responsible for producing the myelin sheath that surrounds and insulates axons of peripheral neurons

1. Explain the differences between unipolar, bipolar, and multipolar neurons, including their structure, location, and function.

Unipolar Neurons

1. Describe the locations and functions of the primary, secondary, and tertiary afferent neurons in a sensory pathway.

1. Primary afferent neurons: These neurons are located in the dorsal root ganglia of the spinal cord and the sensory ganglia of the cranial nerves. They are responsible for detecting and transmitting sensory information from the body's periphery to the spinal cord or brainstem. Primary afferrent neurons have specialized receptors in their dendrites that detect different types of sensory stimuli, such as touch, pressure, temperature, and pain. 2. Secondary afferent neurons These neurons are located in the spinal cord or brainstem and receive input from primary afferent neurons. They are responsible for relaying sensory information to higher centers in the brain, such as the thalamus. Secondary afferent neurons may also integrate and process sensory information before transmitting it to higher brain regions 3. Tertiary afferent neurons These neurons are located in the thalamus and receive input from secondary afferent neurons. They are responsible for relaying sensory information to the primary sensory cortex in the brain. Tertiary afferent neurons may also play a role in sensory perception and discrimination.

Definition of Fascicles

A bundle of skeletal muscle fibers or nerve fibers that are organized and surrounded by a layer of connective tissue

Definition of Neurotransmitter

A chemical messenger that transmits signals across the synapse

Definition of Endoneurium

A delicate layer of connective tissue that surrounds and protects individual nerve fibers within a nerve fascicle

Definition of Axon

A fiber that emerges from the cell body and projects to target cells

Definition of Bipolar Neurons

Bipolar Neurons have two processes that extend from each end of the cell body, opposite to each other. One is the axon and one the dendrite. Bipolar cells are found in the special senses, including the olfactory epithelium (where smell stimuli are sensed), the retina (wherer visual stimuli are sensed), and the inner ear (where auditory stimuli and equilibrium are detected).

Definition of Nerves

Bundles of Axons in the PNS

Definition of Peripheral Nervous System (PNS)

Everything else including nerves and ganglia

Definition of Ganglia

Groups of neuron cell bodies in the peripheral nervous system

Definition of Nuclei

Groups of neuron cell bodies that form round aggregates

Definition of Cortex

Groups of neuron cell bodies that line up in layers

Explain the direction that information flows through neurons.

Information flows through neurons in one direction, from the dendrites (or cell body) oof the receiving neuron, to the axon terminals of the transmitting neuron

Definition of Somatic Sensation

Information from skin, joints, and skeletal muscles

Definition of Neurites

Many extensionos of their cell membranes

Definition of Multipolar Neurons

Multipolar neurons have one axon and two or more dendrites (usually many more). With the exception of the uniplar sensory ganglion cells and the two specific biplar cells mentioned above, all other neurons are multipolar. Almost all neurons in the central nervous system and all motor neurons are multipolar.

Definition of Presynaptic Neuron

Neuron sending the message

Definition of Astrocyte

One cell providing support to neurons of the CNS. Astrocytes have many processes extending from their main cell body. Those processes extend to interact with neurons, blood vessels, or the connective tissue covering the CNS. Some ways in which they support neurons in the central nervous system are by maintaining the concentration of ions in the extracellular space, removing excess signaling molecules, reacting to tissue damage, and inducing formation of the blood-brain barrier (BBB)

Definition of Dendrites

Projections of the cell body that receive information from other neurons

Definition of Sensation

Receiving informationo about the environment to gain input about what is happening outside the body (or, sometimes, within the body). The sensory functions of the nervous system register the presence of a change from homeostasis or a particular event in the environment, known as a stimulus. The senses we think of most are the "big five": taste, smell, touch, sight, and hearing.

Definition of Somatic Nervous System (SNS)

Responsible for conscious perception and voluntary motor responses

Definition of Autonomic Nervous System (ANS)

Responsible for involuntary control of the body, usually for the sake of homeostasis (regulation of the internal environment)

Definition of Neurotransmitter Receptors

Specialized proteins located on the surface of cells that bind to neurotransmitters

Definition of Cell Body (Soma)

The cell body contains the nucleus and most of the major organelles

Definition of Integration

Stimuli that are received by sensory structures are communicated to the nervous system stem where that information is processed

Definition of Central Nervous System (CNS)

The brain and the spinal cord

Discuss the structure and function of myelin and how myelin is formed in the CNS and the PNS.

The insulation for axons in the nervous system is provided by glial cells: oligodendrocytes in the CNS and Schwann cells in the PNS. Myelin is a lipid-rich sheath that surrounds and supports the axon. It speeds up transmission of electrical signals along the axon. The lipids are essentially the phospholipids of the glial cell membrane. Myelin, however, is more than just the membrane of the glial cell. It also includes important proteins that are integral to that membrane. Some of the proteins help to hold the layers of the glial cell membrane closely together. Breaks in the myelin sheath, called nodes of Ranvier, are essential for the proper functioning of myelin in speeding up transmission of nerve impulses.

Explain the locations and functions of the upper and lower motor neurons in a motor pathway.

The motor pathway consists of two types of neurons: upper motor neurons and lower motor neurons. These neurons work together to transmit motor signals from the brain to the muscles of the body. Upper motor neurons: These neurons originate in the motor cortex of the brain and descend through the brainstem and spinal cord to synapse onto lower motor neurons in the spinal cord or brainstem. They are responsible for initiating and modulating voluntary movements and maintaining muscle tone. Upper motor neurons receive input from other brain regions, such as the basal ganglia and cerebellum, which help to coordinate and refine motor movements. Lower motor neurons: These neurons are located in the ventral horn of the spinal cord or in motor nuclei of the brainstem. They receive input from upper motor neurons and directly innervate skeletal muscles to produce movement. Lower motor neurons are responsible for executing the final motor output and are necessary for muscle contraction and movement.

Definition of Response (Motor)

The nervous system produces responses (termed motor responses) on the basis of the stimuli perceived by sensory structures. An obvious response would be the movement of muscles, such as withdrawing a hand from a hot stove, but there are broader uses of the term.

Definition of White Matter

The regions with many axons

Definition of Gray Matter

The regions with many cell bodies and dendrites

Definition of Satelite Cells

They provide support, performing similar functions in the periphery as astrocytes do in the CNS

Definition of Epineurium

Tough layer of connective tissue that surrounds and protects peripheral nerves

1. Explain in basic terms what a neuronal network is and what neuronal networks do.

A compelx system of interconnected neurons that work together to process and transmit information in the brain and nervous system. These networks can involve thousands or even millions of neurons, and they play a crucial role in the functioning of the brain and the body.

Definition of Myelin

A fatty substance that forms a sheath around the axons of many neurons in the nervous system (made up of glial cells)

1. Describe the structure of a nerve and its organization.

A nerve is a bundle of many nerve fibers or axons, along with their surrounding connective tissue, blood vessels, and support cells, which is responsible for transmitting electrical signals between the brain, spinal cord, and other parts of the body

Definition of Synapse

A specialized junction between two nerve cells (neurons) or between a neuron and a target cell, such as a muscle or gland cell. It is the point where the axono terminal of one neuron meets the dendrite or cell body of another neuron or a target cell, forming a tiny gap called the synaptic cleft

Describe the ganglia and nerves of the peripheral nervous system. Explain the contents of each.

Ganglia can be categorized, for the most part, as either sensory ganglia or autonomic ganglia, referring to their primary functions. The most common type of sensory ganglion is a dorsal (posterior) root ganglion. These ganglia are the cell bodies of neurons with axons that are sensory endings in the periphery, such as in the skin, and that extend into the CNS through the dorsal nerve root. The ganglion is an enlargement of the nerve root. Under microscopic inspection, it can be seen to include the cell bodies of the neurons, as well as bundles of fibers that are the dorsal nerve root. The cells of the dorsal root ganglion are unipolar cells, classifying them by shape. Also, the small round nuclei of satelite cells can be seen surrounding - as if they were orbiting - the neuron cell bodies. Other examples of ganglia are the cranial nerve ganglia associated with cranial nerves and the sympathetic and parasympathetic ganglia associated with the autonomic nervous system.

1. Explain what is known about the following clinical issues relating to nervous tissue. Multiple sclerosis Alzheimer's disease

Multiple Sclerosis: It is an example of an autoimmune disease. The antibodies produced by lymphocytes (a type of white blood cell) mark myelin as something that should not be in the body. This causes inflammation and the destruction of the myelin in the central nervous system. As the insulation around the axons is destroyed by the disesase, scarring becomes obvious. Alzheimer's Disease: One of the strongest theories of what causes Alzheimer's disease is based on the accumulation of extracellular beta-amyloid plaques and intracellular tau tangles, dense conglomerations proteins that are not functioning correctly.

Differentiate between sensory (afferent) neurons and motor (efferent) neurons.

Sensory neurons, also known as afferent neurons, are responsible for carrying sensory information from the body's sensory receptors, such as the skin, eyes, ears, nose, and tongue, to the central nervous system (CNS). They transmit information about sensations such as touch, temperature, pain, pressure, and sound to the CNS. Sensory neurons have specialized endings called receptors that detect changes in the environment and convert them into electrical signals that can be transmitted along the neuron. Motor neurons, also known as efferent neurons, are responsible for carrying signals from the CNS to the muscles, glands, and other effector organs of the body. They transmit information that controls movement, secretion, and other functions of the body. Motor neurons have specialized endings called axon terminals that release neurotransmitters, which stimulate or inhibit the activity of the target cells.

Definition of Axon Terminals

Specialized structures located at the end of the axons of neurons. They are the sites where the axon comes into close contact with other neurons or target cells, such as muscles of glands

Definition of Glial Cells, Neuroglia, or Simply Glia

The other type of cell found in nervous tissue. They are considered to be supporting cells, and many functions are directed at helping neurons complete their function for communication

Synaptic Cleft

The small space between the membranes of the two cells

Definition of Unipolar Neurons

Unipolar Neurons have only one process emerging from the cell. Human unipolar cells have an axon that emerges from the cell body, but it splits so that the axon can extend along a very long distance. At one end of the axon are dendrites, and at the other end, the axon forms synaptic connections with a target. Unipolar cells are exclusively sensory neurons and have two unique characteristics. First, their dendrites are receiving sensory information, sometimes directly from the stimulus itself. Secondly, the cell bodies of unipolar neurons are always found in ganglia. The axon projects from the dendrite endings, past the cell body in a ganglion, and into the central nervous system.

Definition of Special Sensation

Vision, hearing, taste, smell, balance/equilibrium