Unit 5 Terms Flashcards
Function of the Nervous System
Communication
Sensory Input
Monitoring changes using sensory receptors
Integration
Process and interpret senses and decide on required action.
Motor Output
Cause a response by activating muscles or glands.
Cell
The basic unit of a structure and function in the nervous system.
Supporting Cells
(Glia). Support, insulation, protection. Cannot transmit impulses. Do not lose their ability to divide.
Neurons
Specialized nervous system cell. Conduct electrical impulses that allow cells, tissues, and organs to detect and respond to stimuli. types of neurons.
Nerves
Composed of many different neurons bundled together.
Neurons are made up of…
-Cell body
-Dendrites
-Axon
Cell Body
-Contains nucleus and metabolic center
-Lacks centrioles so it can’t divide
Dendrites
Projections or extensions that receive signals from other neurons and carry impulses toward the cell body. Usually highly branched.
Axon
A single thin projection from the cell body. Carries impulses away from the cell body towards either other neurons or effectors. Ends in a series of branches with slight enlargements on their ends called axon terminals.
Myelin Sheath
Schwann cells in the peripheral nervous system forms a shiny white fatty protein (doesn’t conduct electricity well) wrapped around axons. Remains intact if damaged. Oligodendrocytes form myelin in the central nervous system.
The myelin sheath has three main functions…
-protection of nerve fibre
-good insulator
-increase rate of transmission of nerve impulses along the axon. (Gaps between sections of the sheath called nodes of ranvier allow the impulse to jump from node to node.) Allows them to travel much faster than unmyelinated nerves.
Sensory Neurons
Gather info from receptors and carry it towards brain or spinal cord. Can be specialized for heat, light, pressure, etc. Cell body is located in clusters called ganglia next to spinal cord. Axons usually terminate at interneurons.
Interneurons
Found entirely within CNS. Stimulated by sensory neurons. Information if brought together and a decision is made (sometimes involves brain/spinal cord). Relays the decision to the brain or motor neurons.
Motor Neurons
Muscles are glands that respond to stimuli. Effector organs. Carry the impulses from the brain/spinal cord to the effectors that causes a reaction or gland. Cell body is located in spinal cord or brain. Since impulses travel away from cell bodies they have long axons.
Reflex Arc
Basic nervous response. Has five basic parts; receptor, sensory neuron, interneuron (in the spinal cord), motor neuron, effector. Withdrawl or protective actions. Brain doesn’t participate. Some interneurons inform the brain so it is still aware. Startle response, blinking, knee jerk, etc.
What happens when the impulse is too important?
It is sent to the spinal cord and bypasses the brain causing a faster response.
Polar
Opposite charges
Nerve Membrane At Rest…
Inner area of the neuron contains more K and is negatively charged, outside area contains Na and is positively charged. This causes polarization and a large potential difference.
Action Potential Initiation and Generation…
A stimuli initiates an action potential. Membranes become more permeable and allow a rapid inward movement of sodium ions causing rapid depolarization. If the stimulus is strong enough it transmits a long distance signal called action potential. The huge influx of Na causes other channels to open allowing K ions to leave, repolarization. As the impulse moves forward the original potential is restored behind it.
Threshold value
The minimum input needed to initiate an action potential.
Movement of the Impulse along the Neuron…
A change in permeability causes a change in the adjoining section as the impulse moves along. In myelinated fibres this occurs only at the nodes of ranvier so it can be up to 4 times faster.
Repolarization must occur…
for a neuron to conduct another impulse.
Facts about Action Potentials
Neurons have an all or none response. If it’s below the threshold value it causes no impulse, no matter how high above it is it will cause the same impulse unless it’s so strong that it causes a reaction in more neurons. Sedatives block the altering of permeability.
Synaptic Cleft
Neurons aren’t directly connected to other neurons, so instead there is a space in between them called the synaptic cleft.
How do impulses get across the synaptic cleft?
When an impulse reaches the end of an axon, vesicles release a chemical known as a neurotransmitter into the space via, exocytosis. The neurotransmitter diffuses across the synapse to the membrane of the dendrite off the next neuron.
What does the neurotransmitter do?
The chemical alters the permeability of the dendrite’s membrane to sodium ions and a new impulse is initiated.
What happens to the neurotransmitter once it’s finished?
Almost as soon as the axon terminal has released the chemical transmitter some of it begins being reabsorbed by the dendrite. Enzymes released by the axon terminal break down the rest. This very fast action prevents the transmitter from continually firing impulses at the dendrite.
What keeps the neuron travelling in only one direction?
Only axon terminals release the chemical transmitters and only dendrites are sensitive to them. Therefore, impulses only move from axon terminals to dendrites and not the other way.
Two divisions of the nervous system
Central and peripheral.
Central Nervous System
Made up of brain and spinal cord and the interneurons carrying information in and out. Integrating and command centers. Interpret sensory information based on past experience and current conditions. Like a control panel that receives input signals, analyses them, and send out instructions. Stores information for future use.
Peripheral Nervous System
Made up of nerves that carry information between organs in the body and the central nervous system (sensory and motor neurons). Communication lines.
The Brain
Contains over 1 billion neurons. From the superior view we see two large hemispheres. Three protective meninges cover the entire brain. Between the second and third layers there is cerebrospinal fluid that is further protection. This fluid is secreted by clusters of capillaries. The fluid also functions in nutrient distribution, waste removal, movements of hormones, movement of white blood cells. Divided into forebrain, midbrain, and hindbrain.
Hindbrain
Made up of the cerebellum, the pons, and medulla oblongata.
Medulla Oblongata
Nerve impulses controlling some of the vital processes that are involuntary such as breathing, heartbeat, swallowing, blood pressure occur here. Damage equals coma or death.
