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Nervous system - Coggle Diagram
Nervous system
ageing in the nervous system
risk of stroke
As fatty deposits accumulate in the blood vessels, there is a decrease in blood flow to the brain.
This can increase the chances that an affected vessel will rupture, leading to symptoms of a stroke (cerebrovascular accident)
slower reaction time
Because the brain processes nerve impulses more slowly, performance of certain tasks and reaction times often become slower
An elderly person who exercises (both mentally and physically) often loses fewer nerve cells in the brain.
Consumption of two or more drinks of alcohol every day reduces brain function.
loss of neurons
Neuronal loss occurs. The amount and location of the loss varies substantially among different regions of the brain.
Some neurons may shrink.
Neuronal loss and shrinkage causes a decrease in brain weight and size.
The nervous system has large numbers of neurons, more than we probably ever use, so age-related neuron loss may not affect behavior appreciably until very old age.
increase in neuroglia and deposits
neuroglia increases
Brain neurons accumulate abnormal intracellular deposits. Extracellular plaques may affect memory processing. When deposits and plaques exceed normal amounts caused by aging, clinical abnormalities may occur.
These particular changes are also characteristic of the brains of those with Alzheimer’s disease
changes in transmission efficiency
Decreased numbers of functional nerve cells may reduce the strength of the message being transmitted.
Fewer nerve cells result in more space to cross, and the coherence of the message may be disrupted, or random background noise (neural noise) could interfere with the clarity of the message.
The motor part of the older cerebral cortex may continue to respond for a time after stimulation ceases, and such aftereffects could blur or interfere with subsequent incoming messages. These changes could then account for the increased time older people usually need to perform simple tasks as well as for their poorer retention and increased susceptibility to distraction in learning and memory tasks.
somatic nervous system vs autonomic
somatic (voluntary)
Somatic motor fibers transmit impulses from the CNS to the skeletal muscles.
Includes 12 pairs of cranial nerves, which connect sensory organs.
The cranial nerves that only have sensory functions include the olfactory and optic nerves. Each of these has no parasympathetic fibers.
31 pairs of spinal nerves, which bring information into the spinal cord and carry messages from the cord to the effectors
autonomic (involuntary)
The ANS contains visceral motor nerve fibers regulating glandular, cardiac muscle, and smooth muscle activity.
Subdivides into the sympathetic and parasympathetic divisions.
The ANS is divided into the sympathetic and parasympathetic divisions. Certain visceral organs have fibers from both divisions, controlling the activation or inhibition of their actions.
The sympathetic division prepares the body for stressful or emergency situations and is part of the fight-or-flight response.
The parasympathetic division functions in an opposite manner and is part of the rest-and-digest response.
In the ANS, preganglionic neurons are the cell bodies of the first neurons and are found in the brain or spinal cord. Their axons synapse with second motor neurons, also known as postganglionic neurons. Their cell bodies are in autonomic ganglia outside the CNS. Their axons extend to effector organs.
Preganglionic axons are thin and lightly myelinated. Postganglionic axons are thinner and unmyelinated. Conduction through the autonomic efferent chain is, therefore, slower than conduction in the somatic motor system.
Autonomic motor neurons have a resting level of spontaneous activity even when there are no stimuli. This determines the autonomic tone, which is an important function of the ANS. By keeping a resting level of activity constant, an autonomic nerve can decrease or increase its activity, allowing for better control.
Preganglionic neurons are cholinergic neurons that originate in the brainstem or spinal cord.
They travel to ganglia, which are collections of nerve cells outside the central nervous system
sensory system
olfaction( sense of smell)
olfactory receptors
work with the sense of taste as well. The olfactory organs are masses of epithelium covering the upperpart of the nasal cavity, superior nasal conchae, and part of the nasal septum.
Olfactory receptor cells have hair-like cilia, which help to differentiate among odors.
Odorant molecules must partially condensate from gases to fluids before receptors can detect them. Impulses are analyzed by olfactory bulbs and interpreted in the olfactory complex of the brain.
Gustatory- Sense of taste
Taste pores have tiny projections called taste hairs, which are the sensitive parts of the taste receptor cells. Stimulation triggers an impulse on a nearby nerve fiber traveling to the brain.
The sense of taste is actually mostly based on the sense of smell to about 80%. Food lacks taste when the nasal passages are congested. This is why food doesn't taste good when you're having a flu.
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Without smell, the sense of taste would be very inefficient and much of what we enjoy from various flavors could no longer be appreciated.
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The five primary taste sensations are sweetness, sourness, saltiness, bitterness, and umami (deliciousness).
Auditory- Sense of hearing
The human ear is an organ that serves two special sensory functions: the detection of sound and the detection of body position, which enables us to maintain balance.
The ear consists of three separate portions: the external (outer), middle, and inner parts.
The middle ear structures include the auditory ossicles (malleus, incus, and stapes), ligaments, and oval window.
The inner ear structure include the osseous labyrinth, membranous labyrinth, three semicircular canals, the cochlea, round window, and organ of Corti.
external ear
Auricle (pinna): A funnel-shaped structure composed of elastic cartilage, thin skin, and small amounts of hair; most people refer to this structure as “the ear.” The auricle functions to funnel sound waves to the external acoustic meatus.
External acoustic meatus. Glands secrete cerumen, a yellow-brown waxy substance commonly referred to as earwax. Cerumen helps to trap foreign particles and repel insects from entering the ear.
Eardrum (tympanic membrane): A semitransparent membrane covered by thin skin on the outside and mucous membrane on the inside that actually
moves back and forth in response to sound waves; it is the boundary between the outer and middle ear.
middle ear
The middle ear (tympanic cavity) inside the petrous portion of the temporal bone is filled with air and contains the auditory ossicles (the malleus, incus, and stapes). These bones are attached to the tympanic cavity wall by ligaments and bridge the eardrum and inner ear to transmit vibrations
Vibrations are passed to the auditory ossicles, which is held to an opening
(the oval window) by ligaments. Vibration of the stapes moves fluid within the inner ear to stimulate hearing receptors
inner ear
The internal ear is complex, with chambers and tubes forming the bony labyrinth.
Inside the labyrinth structures are three semicircular canals, which aid in equilibrium, and a cochlea, which functions in hearing.
The vestibule and its two expanded chambers (the utricle and saccule),with a tiny macula containing many sensory hair cells function in equilibrium.
When the head is upright, the hairs project upward into a gelatinous material. When the head bends forward, backward, or to one side, the hairs bend to signal nerve fibers.
The organs of dynamic equilibrium are the three semicircular canals in the labyrinth. A swelling called an ampulla houses sensory organs, each known as a crista ampullaris. Hair cells within a cupula are bent to signal the brain.
Cells of the nervous system
Neurons
Nerve tissue contains neurons and glial cells (neuroglia). Neurons are the structural units of the nervous system, whereas neuroglia support the functions of the neurons.
Each neuron consists of a cell body, soma, with extensions called an axon and one or more (sometimes many) extensions called dendrites.
Dendrites receive electrical nerve impulses and conduct them toward the cell body and the axon.
Axons conduct nerve impulses away from the cell body. Most neurons have a single axon arising from the axonal hillock on the cell body.
Neurons are closely associated with neuroglia.
Neuroglia comprise almost half the brain and spinal cord tissue and are much more numerous than neurons. They support, nourish, and protect neurons.
CNS neurons are not able to replace themselves if injured or destroyed, although there may be a few exceptions.
Functional Classification of Neurons
sensory
Conduct action potentials toward the CNS(central nervous system) . Sensory neurons detect the internal and external environments (such as from the skin and viscera) and facilitate motor coordination (such as in joints and muscles).
motor
conduct action potentials away from the CNS toward muscles or glands
interneuron
Conduct action potentials within the CNS from one neuron to another, primarily between sensory and motor neurons.
Myelin Sheath
Certain neuroglia wrap themselves around the axons of neurons to create a structure known as the myelin sheath. Myelin is a whitish protein-lipoid. An axon with a myelin sheath is called myelinated, whereas those without myelin sheaths are called unmyelinated.
how do neurons communicate
Synapses (connections between neurons, how they "talk" to one another
axodendritic synapse
An axodendritic synapse is a nerve synapse between the axon of one neuron and the dendrite of another neuron. It is the most common type of synapse in the human body.
axosomatic synapse
An axosomatic synapse is a nerve synapse between the axon of one neuron and the cell body of another neuron
neuromuscular junction
synapse between neuron and muscle cell
postsynaptic neuron
synaptic cleft is the space between the axon of one neuron and the dendrites of another.
the neuron receiving the neuron impulse is called a postsynaptic neuron. The process of the impulse crossing the synaptic cleft is called a synaptic transmission.
presynaptic neuron, he neuron carrying the impulse into the synapse is called a presynaptic neuron.
chemial synapse
]Chemical synapses release and receive chemical neurotransmitters.
Information is transferred across chemical synapses beginning when an action potential arrives at an axon terminal.
electrical synapse
Electrical synapses are less common than chemical synapses. Electrically coupled neurons allow for rapid transmission across electrical synapses.
neurotransmissions.
The actions of neurotransmitters include effects on sleeping, anger, thinking, hunger, movement, memory, and many other functions.
Synaptic transmission is commonly affected by either the enhancing or inhibiting effects of neurotransmitters, their destruction, or the blocking of receptor binding.
Anything that reduces neurotransmitter activity may slow the brain’s ability to communicate with the rest of the body
Cell Membrane Potential
A cell membrane’s surface is usually electrically charged (polarized) compared with its inner contents. This is due to unequal amounts of positive and negative ions.
Adequate stimulation of a neuron causes generation of an electrical impulse in response. An action potential is a change in neuron membrane polarization and a return to its resting state.
An action potential forms a nerve impulse propagated along an axon
(1) the central nervous system (CNS) and (2) the peripheral nervous system (PNS).
CNS
consists of the brain and spinal cord, located in the dorsal body cavity. It is the control centre of the nervous system, integrating all its activities.
receives information from and sends information to the body. key decision maker
the brain
The brain and spinal cord are connected via the brain stem, which allows communication to flow in both directions. The spinal cord also provides a two-way communication, between the CNS and PNS.
The brain is surrounded first by grey matter and then by white matter. The grey matter (cortex) consists mostly of neuron cell bodies, whereas the white matter consists of myelinated fiber tracts.
This pattern is different in the spinal cord, in which the gray matter is located in the center with the white matter outside.
brain protection
Between the bony coverings and the soft brain tissues are layered membranes known as meninges that protect the brain and spinal cord.
Cerebrospinal Fluid
CSF surrounds the brain and spinal cord, maintaining a stable ionic concentration and protecting CNS structures. The brain floats in CSF, which cushions it and prevents the bottom of the brain from being crushed by its own weight. The CSF also helps to nourish the brain and may assist in carrying chemical signals concerning sleep and appetite.
Blood- Brain Barrier
BBB acts to selectively allow certain molecules to pass and to keep others from reaching the brain. The maintenance of a constant environment keeps the brain’s neurons from firing uncontrollably.
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Spinal cord
The spinal cord is a thin column of nerves leading from the brain to the vertebral canal.
It provides two ways of communication, to and from the brain, and contains the spinal reflex centers.
PNS
consists of 12 cranial nerves and 31 spinal nerves information to the body. detects stimuli in and around the body and sends that information to the CNS. Communicates messages from the CNS to the body.messenger
sensory receptors.
The sensory receptors of the PNS are specialized to respond to stimuli. They are sensitive to certain types of environmental changes.
Types of sensory receptors include-
Chemoreceptors-respond to chemicals in solution, including smelled or tasted molecules, changes in blood chemistry, and changes in interstitial fluid chemistry.
Mechanoreceptors- respond to mechanical forces such as pressure, touch, stretching, and vibrations.
Nociceptors- respond to stimuli that may be damaging, such as extreme heat or cold, excessive pressure, and inflammatory chemicals, resulting in pain.
Thermoreceptors- respond to temperature changes
general senses
The general senses of touch, pressure, temperature, and pain are spread throughout the body via muscle, joint, skin, and visceral receptors.
General sensory receptors are nerve endings of two types:
nonencapsulated (free) - mostly respond to temperature and painful stimuli in the skin and internal tissues, except for the brain.
encapsulated
reflex arc
A reflex is actually defined as a fast, automatic response to a specific stimulus. Reflex activity in the human body can be either inborn (innate) or learned (acquired).
Inborn reflexes are rapid and predictable motor responses to stimuli that are formed between neurons during human development.
They are involuntary and subconsciously maintain body posture, help to avoid pain, and control visceral activities. For example, a response to pain is triggered by an inborn spinal reflex that operates without assistance from the brain.
In a reflex arc, sensory impulses from receptors can reach their effectors without being processed by the brain. Some reflex arcs use interneurons. The five basic components of a reflex arc are a receptor, a sensory neuron, an integration center, a motor neuron, and an effector.
sensory
Impulses are carried toward the CNS from the body’s sensory receptors.
Somatic sensory fibers transmit impulses from the joints, skeletal muscles, and skin.
Visceral sensory fibers transmit impulses from the visceral organs of the ventral body cavity.
This sensory division informs the CNS of all events happening inside and outside the body.
motor
Impulses are carried from the CNS to the effector organs, activating muscles to contract and glands to secrete.
They affect (cause) motor responses.
The two main parts of this motor division are the somatic nervous system and the autonomic nervous system (ANS).