General Properties of the Nervous System

The sensory nervous system enables us to sense the world by detecting specific forms of energy and converting them into signals the brain can interpret.
Perception involves the conscious interpretation of sensory information, influenced by memory and other neural processes.
Sense organs, like the ear and eye, are complex structures containing sensory receptors.
Sensory receptors are specialized structures that detect specific forms of energy from the environment, like light, pressure, or chemicals. They can be nerve endings or separate cells.
Sensory units consist of a single afferent neuron and its associated receptor.
Receptor field is the area where an adequate stimulus can activate the afferent neuron.
Afferent neurons transmit sensory information from the periphery to the central nervous system (CNS).

Afferent neurons: Send signals to the body.
- Somatic afferent: Receive input from the surface of the body.
- Visceral afferent: Receive input from internal organs.
Interneurons: Connect neurons within the CNS. They form the majority of neurons (~99%).
Efferent neurons: Send signals from the CNS to the periphery, controlling muscles, glands, and other organs.

Photoreceptors: Detect light.
Chemoreceptors: Detect chemical stimuli.
Thermoreceptors: Detect temperature.
Mechanoreceptors: Detect pressure or mechanical stimuli.
Proprioceptors: Detect body position and movement.
Sensory receptors can be classified by their complexity, from simple nerve endings to complex sense organs.

Sensory receptors convert different forms of energy into electrical signals, which are then transmitted to the CNS.
Sensory coding refers to the conversion of sensory information into a neural code that the brain can understand.
Receptors differ in their sensitivity to specific stimuli.
Variations in the frequency and pattern of action potentials carry information about the intensity and type of stimulus.
The brain interprets sensory information based on the pattern of neural activity.

Pain is a complex sensory experience that signals tissue damage or potential harm.
Nociceptors are specialized sensory receptors that detect pain stimuli.
Analgesic systems in the body reduce pain perception by releasing neurochemicals that block the transmission of pain signals.

The peripheral nervous system (PNS) consists of all nerves outside the CNS.
Nerves are bundles of axons and dendrites that carry signals between the CNS and the body.

The somatic nervous system controls voluntary movements of skeletal muscles.
The autonomic nervous system regulates involuntary processes, such as heart rate, digestion, and breathing.

The sympathetic nervous system prepares the body for "fight-or-flight" responses, increasing heart rate and blood pressure.
The parasympathetic nervous system promotes "rest-and-digest" activities, slowing heart rate and promoting relaxation.

Reflexes are involuntary, rapid responses to stimuli that bypass conscious processing in the brain.
Reflex arcs are neural circuits that mediate reflexes.
They involve sensory receptors that detect stimuli, interneurons that process the information, and motor neurons that activate muscles or glands.

Sensory systems allow us to perceive the world through specialized receptors that detect specific forms of energy, such as light or sound.
Perception is the conscious interpretation of sensory information, influenced by memory and other neural processes.
Sensory perception is not absolute, meaning our perception of the world is influenced by various factors, such as our previous experiences and the context in which we are perceiving the stimulus.

A sense is the detection of a stimulus, which is a form of physical energy.
Special senses include vision, hearing, taste, smell, and balance.
Somatic senses are touch, temperature, pain, itch, and proprioception.
Proprioception is the awareness of body movement and position in space.
Sensory systems can be both complex and simple.
Sensory receptors can be nerve endings or specialized cells.
Sensory units are a single afferent neuron and its associated receptor.
A receptor field is the area in which a stimulus can elicit a response in a specific afferent neuron.

Neurons are classified based on their function.
Afferent neurons send signals towards the central nervous system (CNS).
- Somatic afferent neurons receive input from the surface of the body.
- Visceral afferent neurons receive input from internal organs.
Interneurons connect to efferent neurons and are found exclusively in the CNS.
Efferent neurons send signals away from the CNS to target organs, glands, muscles, etc.

Sensory receptors detect a specific form of energy from the environment.
Receptors are highly specific for the type of energy they detect.
Not all receptors are nerve endings; some are separate cells.
Sensory units are a single afferent neuron with its associated receptor.
Receptor field is the area over which a stimulus in the environment can elicit a response in the afferent neuron.

Photoreceptors detect light.
Chemoreceptors detect chemicals.
Thermoreceptors detect temperature.
Mechanoreceptors detect pressure.
Proprioceptors detect movement and position.
Sensory units can be simple or complex and are classified by their special sense.
Perception is the conscious understanding of a stimulus, which is influenced by the type of energy, the intensity and the location of the stimulus, as well as previous experiences, and the context of the stimulus.
The sensory system is a complex network of specialized cells, neurons, and pathways work together to detect, process, and interpret information from the environment.