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Gabriela Samson P:1 Nervous - Coggle Diagram
Gabriela Samson P:1 Nervous
Disorders/Diseases
Alzheimer's Disease- A form of dementia associated with age.
Spinal Cord Injury- Damage to the Spinal Cord.
Autism- Brain disorder that makes it difficult to communicate.
Meningitis- Infection in the meninges surrounding the brain.
Cerebrovascular Accident (Stroke)- Occurs when blood flow to a portion of the brain is halted.
Multiple Sclerosis- Autoimmune disease that damages the myelin sheath.
Major functions of the nervous system
Central nervous system (CNS): Made up of the brain and spinal cord. Responsible for integration of information and decision-making.
Peripheral nervous system (PNS): Made up of cranial and spinal nerves that connect the CNS to the rest of the body.Contains sensory (afferent) and motor (efferent) divisions.
General functions of the nervous system: sensory, integrative, and motor. Organs of the nervous system can be divided 2 groups:
Motor functions: Somatic nervous system: controls voluntary skeletal muscles. Autonomic nervous system: controls involuntary effectors (smooth and
cardiac muscles and glands).
Neurotransmitters are the chemical messengers in a synapse, that convey an electrical impulse from a neuron to another cell.
Sensory function: Provided by sensory receptors, which detect internal or external changes. Information travels from receptors to sensory neurons, which transport information into the CNS.
Neuroglia: cells that support, nourish, protect, and insulate neurons.
Integrative function: Coordination of sensory information in the CNS. Processing of this information is the basis for decision-making.
Main cell types in the nervous system: Neurons: cells that communicate, via electrical impulses, with other neurons or other tissues.
Motor function: Nerve impulses (CNS) are conducted along motor neurons to effectors.
Functions of the nervous system: thinking, movement, internal processes of physiology.
Effectors are muscles or glands that respond to decisions made in the CNS.
Major aspects of nervous system: sensory input, integration and processing (decision-making), and motor output (response).
Compare & contrast the autonomic nervous system
Impulses are conducted to the brain or spinal cord; then motor impulses travel through cranial and spinal nerves, then through ganglia, and finally to effectors (muscles or glands).
Two divisions of the ANS, which exert opposing effects on target organs in many cases:
Sympathetic division: active in conditions of stress or emergency (fight or flight).
Autonomic activities are regulated by reflexes that have sensory receptors in the viscera and skin.
Parasympathetic division: active under normal, restful conditions (rest and digest).
Controls heart rate, blood pressure, breathing rate, body temperature.
ANS neurons are all motor neurons. In the ANS, motor pathways consist of 2 neurons:
Helps maintain homeostasis, responds to emotional stress, and prepares the body for strenuous activity.
Controls visceral motor functions of smooth muscle, cardiac muscle, and glands.
A preganglionic neuron, that leaves the CNS, and synapses with one or more neurons, which have cell bodies in an autonomic ganglion in the PNS.
A postganglionic neuron, whose fiber (axon) leaves an autonomic ganglion, and innervates a visceral effector.
Autonomic nervous system (ANS): Portion of the PNS that functions constantly and independently, without conscious effort.
Major parts and functions of the spinal cord
The spinal cord consists of 31 segments, each of which connects to a pair of spinal nerves.
White matter, made up of bundles of myelinated nerve fibers (nerve tracts), surrounds a butterfly-shaped core of gray matter housing interneurons and neuron cell bodies.
Consists of spinal nerves in the lumbar & sacral areas.
Cell bodies of sensory neurons that enter the spinal cord are found in the dorsal root ganglia outside the spinal cord.
Cauda equina (horse’s tail): Structure formed where spinal cord tapers to a point inferiorly.
The upper and lower wings of gray matter form the posterior and anterior horns; between them is the lateral horn.
Gives rise to nerves that serve the lower limbs.
A central canal in the middle of the gray matter contains cerebrospinal fluid.
Lumbar enlargement: A thickened region near the bottom of the spinal cord.
Major functions: transmit impulses to and from the brain, and to house spinal reflexes.
Ascending tracts carry sensory information to the brain; descending tracts carry motor information from brain to muscles or glands.
Provides nerves to upper limbs.
Cervical enlargement: A thickened area near top of spinal cord.
Spinal reflexes: controlled by reflex arcs that pass through the spinal cord.
Spinal cord: Begins at the base of the brain.
Connective Tissue Coverings
The axon conducts impulses away from the cell body; it arises from a thickening extending from the cell body, called the axon hillock.
There is only 1 axon in each neuron.
Dendrites conduct impulses toward the cell body; they are short and branching, and they provide the receptive surface for communication with other neurons.
Myelin Sheath: Larger axons are enclosed by myelin sheaths; they are called myelinated fibers.
The cell body (soma) contains major organelles including nucleus.
Narrow gaps in the myelin sheath are called nodes of Ranvier.
Neuron (Nerve Cell) Structure: A neuron contains a cell body, tubular cytoplasm-filled dendrites, and a tubular, cytoplasm-filled axon.
Myelin sheath increases conduction speed of nerve impulses.
Action potential & the Nerve Impulse
It occurs when the charge reaches -55 mV.
When action potential is reached, cell responds by returning to resting potential (-70 mV) by process of repolarization.
Action potential either occurs or does not.
Action potentials of a neuron are all of the same strength.
Reaching an action potential is all-or-none response:
Repolarization returns the polarized state, and is accomplished by outward flow of potassium ions through potassium channels.
Change from negative to positive charge inside neuron is called depolarization, since now, inside and outside are both positive.
At end of repolarization, a slight overshoot called hyperpolarization occurs, in which potential dips below -70 mV.
Upon reaching threshold potential, voltage-gated Na+ channels open, changing charge to about +30 mV; this is called an action potential.
Finally, the Na+/K+ pump moves Na+ ions back out of cell, and K+ back into the cell.
Threshold stimulus: a stimulus strong enough to cause so many Na+ ions to enter neuron, that potential changes from -70 to -55 mV (the threshold potential).
An action potential at the trigger zone causes an electrical current to flow to adjacent regions of the axon’s membrane.
An excitatory stimulus opens chemically-gated Na+ channels; Na+ ions flow into cells due to concentration gradient, causing the inside of neuron to become less negative.
Refractory period: period during and after an action potential, during which a threshold stimulus will not cause another action potential:
A stimulus can change resting potential in either direction.
Limits frequency of action potentials. Ensures the impulse is only transmitted in one direction – down the axon.
A neuron remains at rest until stimulated.
Continuous conduction: Occurs in unmyelinated axons.
Conduct impulses sequentially over the entire length of their membrane.
Saltatory conduction: Occurs in myelinated axons.
The myelin sheath insulates axons from ion movement across the cell membrane.
Impulses “jump” from one Node of Ranvier to the next, since sodium and potassium channels occur only at the nodes.
Major parts and functions of the brain
Sensory fibers from the PNS cross over in the spinal cord or the brainstem; this results in sensory impulses from the right side of the body being interpreted by centers in the left cerebral hemisphere.
Association areas of the brain analyze and interpret sensory impulses, and function in reasoning, judgment, emotions, verbalizing ideas, and storing memory:
Smell area: deep in temporal lobe.
Association areas of the frontal lobe control a number of higher intellectual processes (planning, problem solving).
Taste area: base of central sulcus and insula.
Association areas of the parietal lobe function in understanding speech and choosing the proper words.
Auditory area: posterior temporal lobe.
Association areas in occipital lobe help analyze visual patterns and combine visual images with other sensory information.
Visual area: posterior occipital lobe.
Association areas next to sensory areas are important for analyzing the sensory input.
Cutaneous senses: anterior parietal lobe.
A general interpretive area is found at the junction of the parietal, temporal, and occipital lobes, and plays a primary role in complex thought processing and integration.
The sensory areas are located in several areas of the cerebrum; they interpret sensory input, producing feelings or sensations:
Not all association areas are bilateral; Wernicke’s area of the temporal lobe is usually on the left side only; it helps with understanding of written and spoken language.
The functional areas of the brain overlap, but the cortex can generally be divided into sensory, association, and motor areas.
The primary motor cortex (areas) lie in the posterior frontal lobes, anterior to the central sulcus.
The cerebrum provides higher brain functions: Interpretation of sensory input, Initiating voluntary muscular movements, Stores information for memory, Integrates information for reasoning, Intelligence and Personality
There is also crossover in the brainstem in motor systems, so that the right cerebral hemisphere controls muscles on the left side of the body.
Broca’s motor speech area is in the frontal lobe, usually on the left side; controls muscle movements for speech.
Drugs of abuse (Mouse Party)
Methamphetamine- Meth is highly addictive because it works directly on the brain's reward pathway, making the user feel intense pleasure and exhilaration.
Alcohol- Alcohol particularly affects areas of the brain involved in memory formation, decision making and impulses control.
Marijuana- Anandamide is known to be involved in removing unnecessary short term memories. It is also responsible for slowing down movement, making us feel relaxed and calm.
Cocaine- Like other drugs, cocaine concentrates in the reward pathway. However, it also active in the part of the brain controlling voluntary movements. This is why cocaine abusers are fidgety and unable to be still.
Ecstasy- Ecstasy affects serotonin pathways responsible for mood, sleep, perception and appetite. Ecstasy also indirectly interacts with the reward pathways. The excess serotonin stimulates a milder release of dopamine along the reward pathway giving ecstasy slightly addictive properties.
LDS- LSD and other hallucinogens excite a particular region of the brain known as the locus coeruleus (LC). A single neuron from the LC may branch to many different sensory areas of the brain. The LC is responsible for feelings of wakefulness and evoking a startle response to unexpected stimulus.
Heroine- The transmission of pain signals, stress response, and emotional attachment.
Tissues (structure & function of neurons and neuroglia)
Astrocytes: lie between blood vessels and neurons; functions: Structural support.
Formation of the blood-brain barrier, which protects brain tissue from chemical fluctuation and prevents entry of many substances.
Ependymal cells: produce cerebrospinal fluid in CNS.
Oligodendrocytes: form the myelin sheath around axons in the brain and spinal cord.
Peripheral nervous system neuroglia: Schwann cells: the myelin-producing neuroglia of the PNS.
Satellite cells: provide protective coating around cell bodies of neurons in the PNS.
Central nervous system neuroglia: Microglia: small cells that function as phagocytes for bacterial cells and cellular debris, and produce scar tissue in sites of injury.
Damaged PNS neurons are able to regenerate their axons.
Neuroglia (glial cells, “nerve glue”) are cells that support neurons. Functions: fill spaces, structurally support, protect, and insulate neurons. Do not generate or conduct nerve impulses. 4 types in CNS, 2 types in PNS.
CNS axons are myelinated by oligodendrocytes, which lack a neurilemma, so they usually do not regenerate.
Spinal nerves
Each dorsal root contains a dorsal root ganglion which houses the cell bodies of sensory neurons entering the spinal cord.
A ventral root and dorsal root unite to form a spinal nerve which extends out the vertebral canal through the intervertebral foramen.
Each arises from two roots: A sensory dorsal root and a motor ventral root.
The main branches of spinal nerves, expect in the thoracic region, from networks called plexuses:
Numbered in sequence: 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves, and 1 pair of coccygeal nerves.
Cervical plexuses (C1-C4): Lie on either side of the neck; supply muscles and skin of the neck; include the phrenic nerves, which control the diaphragm.
Grouped according to the level from which they arise.
Brachial plexuses (C5-T1)- Arise from lower cervical and upper thoracic nerves; supply muscles and skin of arms,forearms, and hands; lead into the upper limbs; include the musculoskeletal ulnar, median, radial, and axilllary nerves.
All except the first pair are mixed nerves.
Lumbosacral plexuses (L1-S4)- Arise from the lower spinal cord; supply muscle and skin of the lower abdomen, external genitalia, buttocks, and legs; include the obturator, femoral, and sciatic nerves.
31 pairs of spinal nerves arise from spinal cord.
Anterior branches of the thoracic spinal nerves do not form plexuses, but become the intercostal nerves.
Neurotransmitters
Some neurons produce one type of neurotransmitter, while others produce two or three.
Action potential passes along an axon and over the surface of its synaptic knob.
Action of neurotransmitter depends on type of receptors in a specific synapse.
Synaptic knob membrane becomes more permeable to calcium ions, and they diffuse inward.
Neurotransmitters include acetylcholine, amino acids, neuropeptides.
In the presence of calcium ions, synaptic vesicles fuse to synaptic knob membrane.
There are more than 100 neurotransmitters
Synaptic vesicles release their neurotransmitter into synaptic cleft.
Cranial nerves
The first pair arises from the cerebrum, and the second pair from the thalamus, but most arise from the brainstem.
The 12 pairs are designated by number and name; the numbers are in order, from superior to inferior.
Most are mixed nerves, containing sensory & motor nerve fibers, but some are only sensory, and others are primarily motor.
Twelve pairs of cranial nerves arise from the underside of the brain.
Classification of neurons
Unipolar neurons have only 1 process extending from the cell body; outside the cell body, it soon splits into 2 parts that function as 1 axon; the peripheral process has dendrites near a peripheral body part, and the central process runs into the CNS; the cell bodies are found in ganglia outside the CNS; these are sensory neurons.
Sensory (afferent) neurons: conduct impulses from peripheral receptors to the CNS; usually unipolar, although some are bipolar.
Bipolar neurons have 2 processes extending from the cell body, a dendrite and an axon; found in some of the special senses, such as the eyes, nose, and ears.
Interneurons (association or internuncial neurons): multipolar neurons lying within the CNS that form links between other neurons; the cell bodies of some interneurons aggregate in specialized masses called nuclei.
Neurons differ in size, shape, and structure: Multipolar neurons: have many dendrites and one axon arising from their cell bodies; most neurons with cell bodies in CNS (interneurons and motor neurons) are multipolar.
Motor (efferent) neurons: multipolar neurons that conduct impulses from the CNS to peripheral effectors (muscles or glands).
Major divisions and subdivisions of the nervous system
Peripheral nervous system (PNS) Cranial nerves arising from the brain and brainstem
Sensory fibers connecting peripheral sensory receptors to the CNS
Central nervous system (CNS) Brain, and Spinal cord.
Somatic fibers connecting to skin and skeletal muscles
Autonomic nervous system, which connects the CNS to viscera, and controls subconscious activities.
Autonomic fibers connecting to viscera
Somatic nervous system, which connects the CNS to skeletal muscles and the skin, and oversees conscious activities.
Spinal nerves arising from the spinal cord
The motor part of the PNS is made up of 2 portions:
Sensory fibers connecting peripheral sensory receptors to the CNS
Contains sensory and motor divisions.
Somatic fibers connecting to skin and skeletal muscles
Consists of cranial nerves, arising from the brain, and spinal nerves, arising from the spinal cord.
Peripheral nervous system (PNS): Consists of nerves that connect the CNS to body parts.
Autonomic fibers connecting to viscera
Reflex arc (major parts & functions)
Striking the patellar ligament stretches the quadriceps femoris muscle and tendon, stimulating stretch receptors.
Sensory neurons transmit nerve impulses to the spinal cord, where they synapse with motor neurons, and issue a motor command.
The patella (knee-jerk) reflex is an example of a simple reflex; it has only 2 neurons, sensory & motor, and lacks an inter neuron.
Motor neurons transmit the impulses to the quadriceps muscle,which contracts in response; this extends the knee.
Reflexes control heart rate, blood pressure, etc. and carry out automatic responses such as vomiting, sneezing, swallowing, etc.
This reflex helps maintain upright posture.
Reflexes: automatic responses to changes (stimuli) inside or outside of the body, that help maintain homeostasis.
Withdrawal reflex- Occurs in response to touching something painful, such as stepping on a tack (or laying a hand on a hot stove).
Effector: Muscle or gland. Responds to stimulation (or inhibition) by motor neuron and produces reflex or behavioral action.
Involves sensory neurons, interneurons, and motor neurons:
Motor Neuron: Dendrite, cell body, and axon of a motor neuron. Carries instructions from brain or spinal cord out to effector.
Sensory receptors send pain messages along sensory neurons to the spinal cord.
Interneuron: Dendrite, cell body, and axon of a neuron within the brain or spinal cord. Carries information from the receptor into brain or spinal cord.
Sensory neurons send impulses to interneurons, where information is coordinated.
Sensory Neuron: Dendrite, cell body, and axon of a sensory neuron. Carries information from the receptor into brain or spinal cord.
Interneurons issue motor commands to motor neurons.
Receptor: Receptor end of a dendrite or a specialized receptor cell in a sensory organ. Senses specific type of internal or external change.
Motor signals are sent to flexor muscles to contract.