nervous system 12.4

 

12.3 The Function of Nervous Tissue

•  the major functions of the nervous system: sensation, integration, and response.
•  Testing the Water: 

1.  The sensory neuron has endings in the skin that sense a stimulus such as water temperature. The strength of the signal that starts here is dependent on the strength of the stimulus.
2.   The graded potential from the sensory endings, if strong enough, will initiate an action potential at the initial segment of the axon (which is immediately adjacent to the sensory endings in the skin). 
3.  The axon of the peripheral sensory neuron enters the spinal cord and contacts another neuron in the gray matter. 
4. The contact is a synapse where another graded potential is caused by the release of a chemical signal from the axon terminals.
5.  An action potential is initiated at the initial segment of this neuron and travels up the sensory pathway to a region of the brain called the thalamus. 
6. Another synapse passes the information along to the next neuron. 
7.  The sensory pathway ends when the signal reaches the cerebral cortex. 
8. After integration with neurons in other parts of the cerebral cortex, a motor command is sent from the precentral gyrus of the frontal cortex.
9. The upper motor neuron sends an action potential down to the spinal cord. The target of the upper motor neuron is the dendrites of the lower motor neuron in the gray matter of the spinal cord. 
10.  The axon of the lower motor neuron emerges from the spinal cord in a nerve and connects to a muscle through a neuromuscular junction to cause contraction of the target muscle.

• Found in the skin of your fingers or toes is a type of sensory receptor that is sensitive to temperature, called a thermoreceptor .
• The amount of change is dependent on the strength of the stimulus (how hot the water is). This is called a graded potential
• . If the stimulus is strong, the voltage of the cell membrane will change enough to generate an electrical signal that will travel down the axon. You have learned about this type of signaling before, with respect to the interaction of nerves and muscles at the neuromuscular junction. The voltage at which such a signal is generated is called the threshold, and the resulting electrical signal is called an action potential. 
• In this example, the action potential travels—a process known as propagation—along the axon from the axon hillock to the axon terminals and into the synaptic end bulbs.
• When this signal reaches the end bulbs, it causes the release of a signaling molecule called a neurotransmitter

When the molecular signal binds to the receptor, the cell membrane of the target neuron changes its electrical state and a new graded potential begins.

• If graded potential is strong enough to reach threshold, the second neuron generates an action potential at its axon hillock. 

The upper motor neuron is in this region, called the precentral gyrus of the frontal cortex, which has an axon that extends all the way down the spinal cord. 

• At the level of the spinal cord at which this axon makes a synapse, a graded potential occurs in the cell membrane of a lower motor neuron.
• This second motor neuron is responsible for causing muscle fibers to contract.
• The axon terminates on muscle fibers at the neuromuscular junction.
• Acetylcholine is released at this specialized synapse, which causes the muscle action potential to begin, following a large potential known as an end plate potential.
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Nervous system 12.2

1.  Nervous tissue is composed of two types of cells, neurons and glial cells.
2. Glial cells, or glia, are known to play a supporting role for nervous tissue. 
3. Neurons are important, but without glial support they would not be able to perform their function.
4. Neurons are responsible for the electrical signals that communicate information about sensations, and that produce movements in response to those stimuli, along with inducing thought processes within the brain.
5. There are 3 types of neurons cell.
6.  Unipolar cells have one process that includes both the axon and dendrite. 
7. Bipolar cells have two processes, the axon and a dendrite. 
8. Multipolar cells have more than two processes, the axon and two or more dendrites.
9. The other processes of the neuron are dendrites, which receive information from other neurons at specialized areas of contact called synapses.
10. There are six types of glial cells. Four of them are found in the CNS and two are found in the PNS.
11. Satellite cell found in PNS the function is support the neuron.
12. Astrocyte found in CNS its support neurons
13. Oligodendrocyte found in CNS it function insulation, myelination.
14. Schwann cell found in PNS its function Insulation and myelination.
15. Ependymal cell it creating CSF .
16. Microglia found in CNS it function immune surveillance and phagocytosis.
17. Many axons are wrapped by an insulating substance called myelin, which is actually made from glial cells.
18. Nutrient molecules, such as glucose or amino acids, can pass through the BBB, but other molecules cannot. 
19. Where the axon emerges from the cell body, there is a special region referred to as the axon hillock.
20. The main part of a neuron is the cell body, which is also known as the soma (soma = “body”).
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Nervous system 12.1

The nervous system includes brain and spinal cord.

https://www.researchgate.net/figure/Organization-of-human-nerve-system_fig5_221719508

• Central Nervous Systems

• Peripheral Nervous Systems

• Nervous tissue, present in both the CNS and PNS.
• Neurons are cells and therefore have a soma.

• White matter is white because axons are insulated by a lipid-rich substance called myelin.
• Neuron cell bodies in the CNS is referred to as a nucleus.
•  In the PNS, a cluster of neuron cell bodies is referred to as a ganglion.
• A bundle of axons, or fibers, found in the CNS is called a tract whereas the same thing in the PNS would be called a nerve. 
• Attributed to different regions of the brain (such as the cerebral cortex or the hypothalamus)
• the optic nerve carries signals from the retina that are either used for the conscious perception of visual stimuli, which takes place in the cerebral cortex,
• First, the basic functions of the nervous system are sensation, integration, and response. 
• The nervous system not involving the brain or spinal cord is called  Peripheral Nervous System (PNS)
• Myelin sheath-White matter is found on the inside of the brain and the outside of the spinal cord. It is made up of this part of the neuron.
• Spinal cord-Forms part of the Central Nervous System along with the brain.
• Brain -Forms part of the Central Nervous System along with the spinal cord.
• Cerebrum-Largest part of the brain involved in information processing. Forms the connections between different parts of the brain (mostly white matter)
• Cerebellum-Part of brain responsible for balance and coordination
• Corpus callosum-Connects the left and right hemispheres of the brain
• Nervous system responses are FAST or SLOW
• Thalamus collects information from the body and sends it to the relevant part of the brain Post office'
• Dendrite are Part of a neuron that receives signals from other neurons or receptors.
• Cell body-Part of a neuron responsible for normal cell function.
• Axon terminal-The end of a neuron from where the signal changes from an electrical impulse into a chemical signal before it crosses the synapse.
• Neurotransmitter-The chemical which is released from an axon terminal and travels across a synapse to the next neuron.
• Stimulus-Causes a receptor to send a signal to a neuron
• Chemoreceptors -Receptors that detect chemicals eg. taste, smell.
• Mechanoreceptors-Receptors that detect movement eg. touch, hearing.
• Photoreceptors-Receptors that detect light eg. eyes
• Effector-The muscle or gland in which a response occurs due to stimulation of a motor neuron.
• Reflex-A fast and automatic response to immediate danger!
• Frontal lobe-Part of brain responsible for risk taking, emotions, and decision making. Underdeveloped in teenagers.
• Temporal Lobe-sitting close to ear level within the skull it is associated with processing auditory information and with the encoding of memory.
• Parietal Lobe-roughly located at the upper back area in the skull, it processes sensory information it receives from the outside world, mainly relating to touch, taste, and temperature.
• Occipital Lobe-Responsible for vision.
• Autonomic-The set of motor nerves that automatically control the operation of vital glands and organs; also called the involuntary nervous system( autonomic nervous system)
• Receptor-A sensory cell which receives information from the environment and passes it to the dendrite of a neuron.
• https://quizlet.com/591935885/nervous-system-flash-cards/
  

Important notes chapter 12

• Nervous tissue, present in both the CNS and PNS.
• Nervous tissue, contains two basic types of cells: neurons and glial cells.
• Neurons are cells and therefore have a soma.
• There is one important process that every neuron has called an axon, which is the fiber that connects a neuron with its target. 
• Another type of process that branches off from the soma is the dendrite.
• These two regions within nervous system structures are often referred to as gray matter (the regions with many cell bodies and dendrites) or 
• white matter (the regions with many axons). 
• But white matter is white because axons are insulated by a lipid-rich substance called myelin. 
• The distinction between gray matter and white matter is most often applied to central nervous tissue, which has large regions that can be seen with the unaided eye.
• A brain removed during an autopsy, with a partial section removed, shows white matter surrounded by gray matter.
•  Gray matter makes up the outer cortex of the brain. (credit: modification of work by “Suseno”/Wikimedia Commons)
• A localized collection of neuron cell bodies in the CNS is referred to as a nucleus.
• In the PNS, a cluster of neuron cell bodies is referred to as a ganglion. 
• Nucleus it is the center of a cell, where the DNA is found; and it is a center of some function in the CNS.
• Terminology applied to bundles of axons also differs depending on location. 
• A bundle of axons, or fibers, found in the CNS is called a tract whereas the same thing in the PNS would be called a nerve.
• Nervous system function 
• The nervous system is involved in receiving information about the environment around us (sensation) and generating responses to that information (motor responses) 
• The nervous system can be divided into regions that are responsible for sensation (sensory functions) and for the response (motor functions).
• Sensory input needs to be integrated with other sensations, as well as with memories, emotional state, or learning (cognition).
• 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.
• The stimuli for taste and smell are both chemical substances (molecules, compounds, ions, etc.), 
• Touch is physical or mechanical stimuli that interact with the skin,
•  sight is light stimuli, and hearing is the perception of sound, which is a physical stimulus similar to some aspects of touch.
• Those five are all senses that receive stimuli from the outside world, and of which there is conscious perception.
• Additional sensory stimuli might be from the internal environment (inside the body), such as the stretch of an organ wall or the concentration of certain ions in the blood. for example can detect high sodium level in blood or high potassium level in blood .
• Response. The nervous system produces a response 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. (motor response). 
• The nervous system can cause the contraction of all three types of muscle tissue. For example, skeletal muscle contracts to move the skeleton, cardiac muscle is influenced as heart rate increases during exercise, and smooth muscle contracts as the digestive system moves food along the digestive tract.
• Responses also include the neural control of glands in the body as well, such as the production and secretion of sweat by the eccrine and merocrine sweat glands found in the skin to lower body temperature.
•  Voluntary responses are governed by the somatic nervous system and 
• Involuntary responses are governed by the autonomic nervous system.
• Stimuli that are received by sensory structures are communicated to the nervous system where that information is processed. ( eye , ear, touch, taste ,smell) 
• Controlling the Body ( Somatic nervous system and autonomic nervous system) 
• somatic nervous system (SNS) is responsible for conscious perception and voluntary motor responses.
• Voluntary motor response means the contraction of skeletal muscle.
• The autonomic nervous system (ANS) is responsible for involuntary control of the body, usually for the sake of homeostasis. (blood pressure, heart rate , respiration, temperature) 
• The role of (ANS)the autonomic system is to regulate the organ systems of the body, which usually means to control homeostasis. 
• The enteric nervous system (ENS) is responsible for controlling the smooth muscle and glandular tissue in your digestive system. It is a large part of the PNS.and is not dependent on the CNS. It is sometimes valid, however, to consider the enteric system to be a part of the autonomic system because the neural structures that make up the enteric system are a component of the autonomic output that regulates digestion. 
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April 12 2024 -1st day of class