Chapter 10: The Nervous System I

What are the Nodes of Ranvier?

In between the beads of myelin sheath are uninsulated spaces called Nodes of Ranvier. The nerve impulses travel down the axon by jumping from node to node. This jumping action allows the impulse to travel much faster than if it had to travel down the entire length of the axon.

Describe interneurons.

Interneurons are found within the spinal cord or brain. They transmit impulses from one part of the brain or spine to another. These are multipolar neurons.

Discuss the regeneration of nerve axons.

Mature neurons don't divide, so they are only replaced if neural stem cells are stimulated to divide. If a peripheral axon is damaged, the proximal end may develop sprouts and begin regrowth. Growth is very slow, but the regenerated axon may reconnect. If the axon regenerates in the wrong place, full function will not occur. If an axon is separated from its cell body in the central nervous system, system regeneration may occur, but the CNS lacks cells that help guide the axon. Regeneration in the CNS is unlikely.

Describe motor neurons.

Motor neurons (efferent neurons) carry nerve impulses out of the brain or spinal cord to effectors. Effectors are structures that respond like muscles or glands. Motor neurons are multipolar.

Describe multipolar neurons.

Multipolar neurons have multiple processes arising from the cell body. One process is the axon and the others are dendrites. Multipolar neurons are found within the brain or spinal cord.

What are nerves?

Nerves are bundles of axons.

What are two types of neural tissue?

Neuron-nerve cell Neuroglia Cells- special cells of the nervous system that produce myelin, communicate between cell, and maintain the ionic environment

What happens when a neurotransmitter is released?

Once the neurotransmitter is released, it diffuse across the synaptic cleft until reaching another neuron or cell. Receptor molecules on the receiving cell's membrane accepts the neurotransmitter and then resulting in a nerve impulse. Once the impulse is transferred, the neurotransmitter is broken down by enzymes or reabsorbed by the transmitting neuron preventing further impulses from being generated.

Describe sensory neurons.

Sensory neurons (afferent neurons) carry impulses from peripheral body parts to the spinal cord or brain. The dendrites of sensory neurons have specialized structures that detect changes in the outside world (eyes, ears, touch receptors in the skin), or within the body (temperature and blood pressure changes). Most of these are unipolar.

What is the CNS?

The CNS is the central nervous system. The central nervous system consists of the brain and spinal cord.

What does the axon do?

The axon carries nerve impulses away from the body of the neuron and towards other cells.

What is the myelin sheath?

The axons of most neurons are insulated by a myelin sheath. The myelin sheath is made up of a fatty material produced by Schwann cells. This material prevents nerve impulses from traveling down the axon.

What is at the end of an axon?

The end of the axon had knobbed branches at its end that play a role in the transmission of neurological information to other neurons or cells.

What is the PNS?

The peripheral nervous system consists of the nerves (cranial and spinal) that connects the CNS to the other parts of the body.

Describe unipolar neurons.

Unipolar neurons have a single process extended from the cell body. unipolar neurons are found outside of the brain and spinal cord.

What is a chemical synaptic transfer?

A chemical synaptic transfer occurs when an electrical nerve signal travels down an axon toward the axon's knobs. This electrical impulse causes the axon to release a tiny vesicle containing a neurotransmitter. Neurotransmitters are the biological messenger molecules that transmit the information through the synapse.

How many types of fibers does a neuron have?

A neuron has two types of fibers projecting from the cell body, dendrites and axons.

What is a synapse?

A synapse is the small space between the knobs on an axon and another cell. Synapses are important to the nervous system. The nervous system must be able to send and receive electro-chemical messages from neurons to neurons or neurons to other cells.

What is an electrical synaptic transfer?

An electrical synaptic transfer occurs when an electrical signal is sent from the presynaptic neuron to the postsynaptic cell. This type of transfer across the synapse is common in the heart and digestive system, where nerve signals must maintain steady, rhythmic contractions.

Describe bipolar neurons.

Bipolar neurons have two process extending from each end of the cell body. One process is the axon and the other is the dendrite. Bipolar neurons are found in specialized areas of the eyes, ears and nose.

What do dendrites do?

Dendrites receive nerve impulses and transfer the information t the body on the neuron.

What are the two types of synaptic transfers?

Electrical or chemical