Examples of sensory neuron in the following topics:
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- A reflex arc defines the pathway by which a reflex travels—from the stimulus to sensory neuron to motor neuron to reflex muscle movement.
- In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord.
- The stimulus, such as a needle stick, stimulates the pain receptors of the skin, which initiate an impulse in a sensory neuron.
- When a reflex arc consists of only two neurons, one sensory neuron, and one motor neuron, it is defined as monosynaptic.
- It causes the stimulation of sensory, association, and motor neurons.
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- The peripheral nervous system (PNS) consists of sensory neurons, motor neurons, and neurons that communicate either between subdivisions of the PNS or connect the PNS to the CNS .
- The nervous system has three broad functions: sensory input, information processing, and motor output .
- In the PNS, sensory receptor neurons respond to physical stimuli in our environment, like touch or temperature, and send signals that inform the CNS of the state of the body and the external environment.
- This sensory information is then processed by the CNS, predominantly by the brain.
- Central neurons, which in humans greatly outnumber the sensory and motor neurons, make all of their input and output connections with other neurons.
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- A typical neuron consists of a cell body and neuronal processes such as dendrites and axon.
- These extensions are the conducting region of the neuron.
- The cell body is the major biosynthetic center of the neuron.
- For example, sensory neurons respond to touch, sound, light, and other sensory inputs.
- 1: Unipolar neuron, 2: Bipolar neuron, 3: Multipolar neuron, 4: Pseudounipolar neuron
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- Afferent neurons convey information from tissues and organs into the central nervous system (e.g. sensory neurons).
- Efferent neurons transmit signals from the central nervous system to the effector cells (e.g. motor neurons).
- Another way in which neurons are classified is by their effect on target neurons.
- A neuron releases a neurotransmitter that binds to chemical receptors on the target neuron .
- Other types of neurons include excitatory motor neurons in the spinal cord that release acetylcholine, and inhibitory spinal neurons that release glycine.
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- Autonomic ganglia are clusters of neuron cell bodies that transmit sensory signals from the periphery to integration centers in the CNS.
- A dorsal root ganglion (or spinal ganglion) is a nodule on a dorsal root of the spine that contains cell bodies of nerve cells (neurons) that carry signals from sensory organs towards the appropriate integration center.
- The nerve endings of dorsal root ganglion neurons have a variety of sensory receptors that are activated by mechanical, thermal, chemical, and noxious stimuli.
- In these sensory neurons, a group of ion channels thought to be responsible for somatosensory transduction have been identified.
- The pathways of the ciliary ganglion include sympathetic neurons (red), parasympathetic neurons (green), and sensory neurons (blue).
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- Broadly, sensory receptors respond to one of four primary stimuli:
- Sensory receptors perform countless functions in our bodies.
- During taste, sensory neurons in our taste buds detect chemical qualities of our foods including sweetness, bitterness, sourness, saltiness, and umami (savory taste).
- Adequate stimulus can be used to classify sensory
receptors.
- A sensory receptor's adequate
stimulus is the stimulus modality for which it possesses the
adequate sensory transduction apparatus.
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- It includes both sensory receptor neurons in the periphery (eg., skin, muscle, and organs) and deeper neurons within the central nervous system.
- In the periphery, the primary neuron is the sensory receptor that detects sensory stimuli like touch or temperature.
- Tertiary neurons have cell bodies in the thalamus and project
to the postcentral gyrus of the parietal lobe, forming a sensory homunculus in
the case of touch.
- At this location there is a map of sensory space referred to as a sensory homunculus.
- Image representing the cortical sensory homunculus.
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- The sensory information (touch, pain, temperature, etc.,) is then conveyed to the central nervous system by afferent neurons, of which there are a number of different types with varying size, structure, and properties.
- Generally, there is a correlation between the type of sensory modality detected and the type of afferent neuron involved.
- For example, slow, thin, unmyelinated neurons conduct pain whereas faster, thicker, myelinated neurons conduct casual touch.
- This is the main sensory receptive area for the sense of touch.
- Like other sensory areas, there is a map of sensory space called a homunculus at this location.
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- These functions are based on the sensory input, integration and motor output.
- Sensory input is based on the many sensory receptors that can monitor changes occurring both inside and outside the body.
- The total sum of the gathered information by these sensory receptors is called sensory input.
- It does this by extracting information from the environment using sensory receptors.
- Electrical impulses travel along the axon of a neuron.
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- Remarkably, specialized receptors have evolved to transmit sensory inputs from each of these sensory systems.
- Sensory receptors code four aspects of a stimulus:
- Sensory receptors are found throughout our bodies, and sensory receptors that share a common location often share a common function.
- Force-sensitive mechanoreceptors provide an example of how the placement of a sensory receptor plays a role in how our brains process sensory inputs.
- Mammalian muscle spindle showing typical position in a muscle (left), neuronal connections in spinal cord (middle), and an expanded schematic (right).