Chapter 15 Sensory Pathways & SNS

Sensory pathways: sensory information travels from receptors to CNS.

Sensory receptors: detect incoming stimuli, which can be specialized cells or cell processes, action potentials are sent along sensory pathways.

Receptive field: size is inversely related. Area monitored by a single receptor cell. Sensitive areas overlap fields.

Transduction: conversion of arriving stimuli into action potential by the sensory receptor.

Sensation: arriving info to the cortex(input).

Perception: conscious awareness of a sensation(processing).

Afferent division: somatic and visceral sensory pathways bring info. to CNS.

Efferent division: somatic and visceral motor commands from the motor cortex in the brain.

What are the general senses? Temperature, Pain, Touch, Pressure, Vibration, Proprioception (body position). Also widely distributed over the body and more externally than internally. They are simple structures.

What are special senses? Olfaction (smell), Gustation (taste), Vision (sight), Equilibrium (balance), and Hearing

What is the labeled line? Path of incoming stimuli to CNS.

What is adaptation? reduction of receptor sensitivity due to constant stimuli.

What are the types of adaptation? Peripheral adaptation and Central adaptation

Which body system quickly adapts to painless constant stimuli? Temperature is an example. The Nervous System

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What are tonic receptors? Are always active, slow-adapting receptors. Eg. pain receptors

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What are phasic receptors? normally inactive, fast-adapting receptors. Eg. phasic, and temp receptors adapt quickly.

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What are the general sensory receptors? Nociceptors (pain), Thermoreceptors (temp), Mechanoreceptors(physical distortion), Chemoreceptors (chemical concentration)

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What is Phantom Limb Syndrome? A sensory neuron or interneuron activity without limb causing perceived pain.

What is referred pain: sensation shares a spinal pathway leading to 1 sensory cortex in the brain.

{{Fun fact: There are 3-4 more cold receptors than warm receptors.{{

Fine touch: narrow receptive fields, more sensitive.

Crude touch: large receptive fields, less sensitive.

Free nerve endings: Sensitive to touch and pressure. Situated between epidermal cells and small receptive fields.

Root hair plexus nerve endings: monitor distortions and movements wherever hairs are located. Adapt rapidly.

Tactile discs: Fine touch and pressure receptors. Very small receptive fields.

Bulbous corpuscles: Sensitive to pressure and distortion of skin. Located in the reticular (deep) dermis. Encapsulate dermal collagen fibers and wrap them with dendrites.

Lamellar corpuscles: sensitive to deep pressure and vibration. A single dendrite lies within a series of concentric layers of collagen fibers. Deep dermis.

Tactile corpuscles: perceive sensations of fine touch, pressure, and low-frequency vibration. The most abundant in eyelids, lips, fingertips, nipples, and external genitalia. Dermis.

Baroreceptors: detect pressure changes.

Proprioceptors: monitor positions

Tactile receptors: touch, vibrations, and pressure.

Chemoreceptors: respond to water and lipid soluble substances that are dissolved in body fluids (example: blood O2 & CO2). Adapt quickly, and monitors pH, carbon dioxide, and oxygen levels in arterial blood at carotid bodies and aortic bodies. Includes CN IX and X.

Spinothalamic Pathway: Carry sensations of crude touch, pressure, pain, and temperature. Includes referred pain and phantom limb syndrome.

Posterior Column Pathway: tracts in the posterior column. Carries sensation of fine touch, vibration, pressure, and proprioception.

Sensory homunculus: functional map of primary somatosensory cortex. The area devoted to a particular body region is proportional to the density of sensory neurons and not proportional to the size of the region.

Spinocerebellar Pathway: conveys info about positions of muscles, tendons, and joints from the spinal cord to the cerebellum and this info does not reach our awareness.

What are the spinocerebellar tracts? Posterior and anterior spinocerebellar tracts

What is the Visceral Sensory Pathway? Interceptors detect stimuli for viscera in thoracic and abdominopelvic cavities. Includes nociceptors, baroreceptors, thermoreceptors, tactile receptors, and chemoreceptors. Not as numerous as in somatic tissues. Sensory info from the mouth, palate, pharynx, larynx, trachea, and esophagus is carried by cranial nerves: V, VII, IX, and X.

What is a solitary nucleus?

A large nucleus on each side of the medulla oblongata. Also, a major processing center for visceral sensory information. Has connections with cardiovascular and respiratory centers and reticular formation.

Somatic motor pathways: carries motor commands from the motor cortex to the brain stem or spinal cord and then to PNS. Always involve at least an upper or lower motor neuron.

What is an upper motor neuron? The neuron cell body lies in a CNS processing center. Cell bodies in the cerebral cortex then descend down to the spinal cord.

What is a lower motor neuron? The neuron cell body lies in a nucleus of the brainstem or spinal cords, and axons extend outside CNS.

Somatic nervous system: control contractions of skeletal muscles

Corticospinal pathway: from the cortex down to the spinal cord.

Corticobulbar tracts- allow conscious movement of eyes, jaw, face, and some muscles in the neck and pharynx.

Corticospinal tracts- visible along the anterior surface of medulla oblongata as a pair of thick bands called pyramids.

Lateral corticospinal tracts- contains axons that decussate at pyramids.

Anterior corticospinal tracts-contains axons that cross over in anterior white commissure.

What is motor homunculus? Functional map of the primary motor cortex. Motor control is available and similar to the sensory homunculus.

What is the medial pathway? Helps control movements of the trunk and proximal limb muscles. Include upper neurons.

What is the lateral pathway? helps control distal limb muscles that perform precise movements.

What tract is included in the lateral pathway? Rubrospinal tract

What type of receptor detects pressure changes from organs within our bodies? Baroreceptors.

What type of receptor detects levels of O2 and CO2 in our blood? Chemoreceptors.

What type of neuron carries sensory information from the thalamus to the cerebral cortex? Third-order neuron.

Second-order neuron- sensory info from first order to third order in the thalamus.

First-order neuron- sensory info from the periphery into CNS.

What sensory pathway carries crude touch and temperature sensations? Spinothalamic pathway

What sensory pathways carry proprioception sensations? Posterior column pathway.

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