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Nervous and sensory systems - Coggle Diagram
Nervous and sensory systems
nervous system
most complex systems in the body in controlling, coordinating, and integrating all body activities.
Along with the endocrine system, it regulates and maintains homeostasis (to stop/prevent bleeding).
The nervous system is fast acting and communicates with cells by electrical impulses.
neurons
structure
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.
divisions of nervous system
Peripheral Nervous System (PNS)
consists of 12 cranial nerves and 31 spinal nerves
detects stimuli in and around the body and sends that information to the CNS. Communicates messages from the CNS to the body.
messenger
communicates with internal organs and glands
sympathetic division (arousal)- fight or flight (sending signals to brain on danger- increased heartbeat)
parasympathetic division (calming)- rest and digest
communicates with sense organs and voluntary muscles
sensory (afferent) nervous system (sensory output)
motor (efferent) nervous system (motor output)
examples: peripheral nerves and connects CNS to other parts of the body
Central Nervous System (CNS)
consists of the brain and spinal cord, located in the dorsal body cavity. It is the control center of the nervous system, integrating all its activities.
receives information from and sends information to the body.
key decision maker
Brain
brain components
cerebum
: largest part of the brain (controls higer brain functions, interprets sensory impulses ,initiates muscle movements
Basal nuclei
- masses of grey matter that are deep inside celebral hemispheres- relays motor impulses from the celebral cortex, passing into brain stem and spinal cord, assisting the coordination of voluntary movements
Diencephalon
- masses of grey matter (thalamus and hypothalamus)
thalamus- relays sensory impulses ascending from other areas of the CNS to the celebral cortex
Hypothalamus- helps maintain haemostasis by regulating visceral activities- links nervous system and endocrine systems
cerebellum- large tissue mass, inferior to cerebrum, posterior to brain stems: has 2 lateral hemispheres; connected by the vermis
Brain stem; midbrain, pons, medulla oblongata- connects cerebrum to spinal cord
Brain protection
Between the bony coverings and the soft brain tissues are layered membranes known as meninges that protect the brain and spinal cord.
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.
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.
Brain and spinal cord
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.
Neurons are the structural units of the nervous system, whereas neuroglia (glial cells) support the functions of the neurons.
classification
Types of Neurons and functions
->
Sensory (afferent)
: Conduct action potentials toward the CNS. 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 (efferent)
: conduct action potentials away from the CNS towards muscles or glands
->
Interneuron
: conduct action potentials within the CNS from one neuron to another, primarily between sensory and motor neurons
communication
chemical synapses
chemical synapses-
release
and
receive
chemical neurotransmitters.
Information is transferred across chemical synapses beginning when an action potential arrives at an axon terminal.
example:
axodendritic
synapses (between axon ending of a neuron and dendrites of other neurons)
axosomatic
synapses (between axon ending of one neuron and soma of others.
neuromuscular junction
(synapse between neuron and muscle cell)
postsynaptic neuron
(the neuron receiving this impulse & process of impulse crossing the synapse cleft is called
synaptic transmission
)
presynaptic neuron
(carry impulse into synapse)
electrical synapses
electrical synapses-
less
common than chemical synapses. Electrically coupled neurons allow for rapid transmission across electrical synapses.
neurotransmitters
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.
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.
cell membrane's potential
surface is usually electrically charged (polarized) compared with its inner contents- 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, forming a nerve impulse propagated along an axon.