Exercise 5 Flashcards
2.What is another name for the neuron?
Another name for the neuron is nerve cell. The neuron or nerve cell is the basic unit of function of the nervous system
- Neurons are classified according to their function. List the three classes or types of neurons and briefly describe what each does.
- The three classes or types of neurons are: sensory neurons, interneurons and motor neurons.
Sensory neurons take nerve impulses, electrical or chemical messages, from a sensory receptor to the central nervous system (spinal cord and brain).
Interneurons receive input from sensory neurons or other interneurons, add up these messages and then send them on to the motor neuron for action. Interneurons are found only in the CNS.
Motor neurons receive nerve impulses from the interneuron and then send a nerve impulse out of the CNS to a muscle or gland, referred to as an effector, for action.
4.What are sensory receptors? What are effectors?
A sensory receptor is a specialized cell found in the sense organs that receives internal or external stimuli depending on its location in our body.
An effector refers to a muscle fibre or gland that receives the nerve impulse from a motor neuron and then exhibits a response.
Name the three basic parts of a neuron and briefly describe each.
Neurons vary in appearance but all have three basic parts. They are:
Cell body – contains the nucleus and other organelles
Dendrites – numerous, short extensions that receive nerve impulses from sensory receptors or other neurons
Axon – is usually quite long in comparison to the dendrites. It conducts nerve impulses away from the cell body to an effector (muscle or gland), or another neuron.
What is the basic structural difference between a sensory neuron, a motor neuron and an interneuron?
Sensory neurons are unipolar having a single extension that leads away from the cell body and then divides. The axon in a sensory neuron, by-passes the cell body and passes the nerve impulse directly from the dendrites into the spinal cord. Most neurons in the body are multipolar. They include interneurons and motor neurons. These neurons have one axon that carries the impulse away from the cell body, after the cell body has received the impulse from the dendrites.
7.What is myelin sheath? What produces the myelin sheath? What is the purpose of a myelin sheath?
Myelin sheath is a protective lipid covering that is found on some axons. In the PNS myelin is formed by Schwann cells, a type of neuroglia. These cells have myelin in their plasma membrane. The purpose of the myelin is to protect and to insulate against the loss of ions in nerve transmission.
8.What are the gaps called on the axon that have no myelin sheath? Explain why they appear.
The gaps on the axon where no myelin occurs are called the nodes of Ranvier. They form as a result of individual Schwann cells wrapping around the axon and leaving a space between cells.
9.Which nerve fibres have a myelin sheath covering their axon? What name do we give to these fibres?
Long axons tend to have myelin sheath. Axons that contain myelin appear white and glistening. In the CNS, these axons are referred to as white matter. In the brain white matter lies in the interior but in the spinal cord it lies to the outside.
Which nerve fibres do not have a myelin sheath covering their axon? What name do we give to these fibres?
Short axons tend not to have a myelin sheath. In the CNS these axons are referred to as gray matter. The surface area of the brain is gray matter but in the spinal cord gray matter is found in the centre of the cord
Name and briefly describe a disorder that interferes with the function of the myelin sheath.
Multiple sclerosis is a disease of the myelin sheath in the CNS. Lesions form and harden into scars that interfere with the normal conduction of nerve impulses.
What parts of a neuron are located in the gray matter of the brain and spinal cord?
The parts of a neuron contained in gray matter are the cell body, dendrites and nonmyelinated axons.
Which part of a neuron makes up the white matter of the brain and spinal cord?
The part of a neuron that makes up the white matter of the brain and spinal cord is the myelinated axon.
1.Name and briefly describe the role of the two types of cells contained in nervous tissue.
- Nervous tissue contains two types of cells: neurons sometimes called nerve cells, and neuroglia sometimes called neuroglial cells. The role of the neuron is to transmit nerve impulses between the various parts of the nervous system. The role of the neuroglia is to support and nourish neurons.
