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Neuronal Communication - Coggle Diagram
Neuronal Communication
Types of Neurones and Structure
General Structure
Dendrite
Receives a stimulus or chemical messenger from a dendron of a pre synaptic neurone,
Soma
Contains the nucleus and other organelles.
Schwann Cell
The cell that produces myelin
Node of Ranvier
Gaps in the neurone where the nervous signal jumps. (Saltatory Conduction)
Myelin Sheath
It is the protective covering of the axon. It causes the signal to increase in spped.
Axon
A long extension that carries the nervous signal.
Axon Terminal
Passes the action potential to the post synaptic neurone by using neurotransmitters to diffuse across the synapse to pass this signal.
Types of Neurones
Sensory Neurone
Neurones that convert a certain type of neurone into an action potential and pass it on to next neurone (relay)
Structure
Relay Neurone
Structure
Motor Neurone
Myelinated Neurones VS Myelinated Neurones
Myelinated
Structure
Myelinated neurons have an axon that is surrounded by a protective covering called myelin sheath, which is formed by specialized cells called Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS).
Myelin Sheath
The myelin sheath is made up of multiple layers of lipid-rich myelin, which insulates the axon and allows for faster conduction of nerve impulses.
Nodes of Ranvier: Between the segments of myelin, there are small gaps called nodes of Ranvier. These nodes play a crucial role in the saltatory conduction of the nerve impulse.
Saltatory Conduction
Myelinated neurons, the nerve impulse jumps from one node of Ranvier to another, resulting in faster conduction due to the insulation provided by the myelin sheath.
Location
Myelinated neurons are found in both the CNS and PNS. In the CNS, they are present in regions such as the white matter. In the PNS, they are found in motor neurons responsible for controlling skeletal muscles and sensory neurons that transmit signals from sensory organs.
Non Myelinated
Structure
Non-myelinated neurons lack a myelin sheath around their axons. Instead, they have Schwann cells or oligodendrocytes that wrap around multiple axons without forming distinct myelin sheaths.
Conduction Speed
The absence of a myelin sheath results in slower conduction of nerve impulses in non-myelinated neurons compared to myelinated neurons.
Continuous Conduction: In non-myelinated neurons, the nerve impulse propagates continuously along the entire length of the axon, without jumping between nodes.
Location
Non-myelinated neurons are commonly found in the autonomic nervous system (ANS), which controls involuntary functions of internal organs, as well as in certain sensory pathways, such as pain and temperature sensation.
Nervous Systems
Central Nervous System
Consists of the brain and spinal cord. Brain: Divided into different regions such as the cerebrum, frontal lobe, occipital lobe, temporal lobe, parietal lobe, hippocampus, and cerebellum. Spinal Cord: Responsible for relaying information between the brain and the rest of the body.
Peripheral Nervous System
Somatic
Controls voluntary movements and sensory perception. Involves sensory neurons that transmit information from the senses to the CNS and motor neurons that transmit signals from the CNS to muscles.
Autonomic
Parasympathetic
Activated during "rest and digest" responses. Slows down heart rate, constricts pupils, and increases digestive activity. Promotes relaxation and conserves energy.
Sympathetic
Activated during "fight or flight" responses. Increases heart rate, dilates pupils, and decreases digestive activity. Prepares the body for intense physical activity or emergencies.
Proteins
Voltage Gated Sodium Channels
Allows facilitated diffusion of sodium ions into the cell. This cause the depolarisation of a neurone.
Voltage Gated Potassium Channels
Allows facilitated diffusion of potassium ions into the cell. This cause the repolarisation and hyperpolarisation of a neurone.
Sodium Potassium Pump
Actively transports 3 sodium ion out of the cell and 2 potassium cells into the cell. This helps to maintain the resting potential.
Stretch Mediated Sodium Channel
Allows facilitated diffusion of sodium ions into the cell. This cause the depolarisation of a neurone. Only found in the Pacinian Corpuscle.
Cases Studies
Pacinian Corspule
Structure
Composed of concentric layers of connective tissue called lamellae. These lamellae surround a central core, which contains the nerve endings. The corpuscle is elongated in shape and has a fluid-filled cavity between the lamellae.
Function
Highly sensitive to mechanical pressure and vibrations. When a mechanical stimulus is applied to the corpuscle, it deforms the lamellae and generates a receptor potential. This potential triggers the generation of action potentials in the associated sensory neurons.
Location
found in the skin, particularly in areas sensitive to touch, such as the fingertips, palms, and soles of the feet. They are also present in other tissues, including muscles, joints, and some internal organs.
Sensory Perception
In the somatosensory system, it is responsible for detecting and interpreting touch and pressure sensations. They contribute to our perception of various tactile sensations, including fine touch, texture, and vibrations.
Definition
Neurone
A specialised cell that transmits an electrical signal
Neurotransmitter
A chemical messenger that is produced by the pre synaptic neurone which triggers an action potential in the post synaptic neurone.
Homeostasis
Regulation of an internal steady state despite internal and external factors.
Generation of an Action Potential
Production an Action Potential
Thershold
If the stimulus produces a volage that is greater than -55mV an action potental will be induced otherwise if it is equal to -55mV or below then an action potential won`t be produced.
Refractory Period
Actively transports 3 sodium ion out of the cell and 2 potassium cells into the cell by the carrier protein called the sodium potassium pump. This helps to maintain the resting potential.
Action Potential
When the stimulus passes the threshold of -55mv, depolarisation occurs where sodium ions diffuse into the cell through the voltage gated sodium channel which is a channel protein. It reaches its maximum voltage of 40mv and then becomes repolarised because of the facilitated diffusion of potassium ions out of the cell through the voltage gated potassium channel decreasing the voltage to -70mv.
Resting Potential
The potential at which there is no stimulus or activity in the neuron it remains at -70mv because of the sodium potassium pump which is a carrier protein
All of Nothing Principle
Synapses
Summary
Pre Synaptic Neurone
The presynaptic neuron is responsible for releasing acetylcholine into the synaptic cleft.
Acetylcholine is synthesized in the presynaptic neuron and stored in vesicles.
When an action potential reaches the presynaptic terminal, it triggers the release of acetylcholine into the synaptic cleft.
The release of acetylcholine is regulated by calcium ions, which enter the presynaptic terminal upon depolarization.
Acetylcholine is released through exocytosis, where the vesicles fuse with the presynaptic membrane and release their contents into the synaptic cleft.
The release of acetylcholine from the presynaptic neuron is essential for initiating the transmission of the nerve impulse across the synapse.
Post Synaptic Neurone
The postsynaptic neuron contains receptors called cholinergic receptors that are specific to acetylcholine.
Acetylcholine released into the synaptic cleft binds to these receptors on the postsynaptic neuron.
The binding of acetylcholine to cholinergic receptors initiates a series of events that lead to the generation of an action potential in the postsynaptic neuron.
The specific type of cholinergic receptor determines whether the synapse is excitatory or inhibitory.
In excitatory synapses, acetylcholine binding depolarizes the postsynaptic membrane, making it more likely to generate an action potential.
In inhibitory synapses, acetylcholine binding hyperpolarizes the postsynaptic membrane, making it less likely to generate an action potential.
What is involved in this process
Calcium Ions
Calcium ions are crucial for neurotransmitter release in the presynaptic neuron.
When an action potential reaches the presynaptic terminal, voltage-gated calcium channels open, allowing calcium ions to enter the presynaptic terminal.
The influx of calcium ions triggers the fusion of neurotransmitter-containing vesicles with the presynaptic membrane, leading to the release of acetylcholine into the synaptic cleft.
ACh
Acetylcholine is a neurotransmitter involved in transmitting signals across the synapse.
It is synthesized in the presynaptic neuron and stored in vesicles.
Upon depolarization of the presynaptic terminal, acetylcholine is released into the synaptic cleft.
Receptors
Cholinergic receptors are specific receptors located on the postsynaptic neuron.
Acetylcholine released into the synaptic cleft binds to these receptors.
The binding of acetylcholine to cholinergic receptors initiates a response in the postsynaptic neuron.
AChE
Acetylcholinesterase is an enzyme present in the synaptic cleft. Its role is to break down acetylcholine into acetyl and choline, terminating the action of acetylcholine at the synapse. By breaking down acetylcholine, acetylcholinesterase prevents continuous stimulation of the postsynaptic neuron.
Mitochondria
Energy Production
Mitochondria are responsible for generating adenosine triphosphate (ATP), the primary energy source for cellular processes, including neurotransmitter synthesis, release, and recycling.
Calcium Regulation
Mitochondria help regulate calcium ion levels within the presynaptic terminal. They take up excess calcium ions that enter during the action potential, maintaining calcium homeostasis and preventing excessive neurotransmitter release.
Recycling of Neurotransmitter
Mitochondria are involved in the recycling of neurotransmitters, including acetylcholine. They take up excess neurotransmitters released into the synaptic cleft and convert them back into precursors, such as choline, for reuse in neurotransmitter synthesis.
