Neurophysiology 7 Flashcards
What is the function of somatosensory systems?
The somatosensory systems inform us about objects in our external environment through touch (i.e., physical contact with skin) and about the position and movement of our body parts (proprioception) through the stimulation of muscle and joints.
Also monitor the temperature of the body, external objects and environment, and provide information about painful, itchy and tickly stimuli.
Describe the major somatosensory pathways
there are 2
The posterior (dorsal) column-medial lemniscal pathway carries discriminative touch and proprioceptive information from the body, and the main sensory trigeminal pathway carries this information from the face.
The spinothalamic pathways carry crude touch, pain and temperature information from the body, and the spinal trigeminal pathway carries this information from the face
List the aspects of somatosensory systems
- Somatic stimuli
- Sensory receptors
- Sensory transduction
- Peripheral somatosensory neurons
Describe the stimuli that evoke somatic sensory sensations
There are several modalities of somatic sensation.
The stimuli that evoke these sensations can be summarized as:
1. Tactile
2. Proprioceptive
3. Nociceptive (pain)
Describe tactile stimuli
These are external forces in physical contact with the skin that give rise to the sensations of touch, pressure, flutter, or vibration.
Touch often involves minimal force on-or-by an object that produces very little distortion of the skin.
In contrast, pressure involves a greater force that displaces the skin and underlying tissue.
Flutter (20 – 50 Hz) or vibration (100 – 300 Hz) are more complex sensations of touch. They are tactile stimuli that vary with time.
How do you clinically examine discriminative touch?
An initial clinical examination of discriminative touch often involves testing the vibratory sense by applying a 128 Hz tuning fork over a bony prominence
Describe propioceptive stimuli
These are internal forces that are generated by the position or movement of a body part.
Static forces on the joints, muscles and tendons, which maintain limb position against the force of gravity, indicate the position of a limb.
The movement of a limb is indicated by dynamic changes in the forces applied to muscles, tendons and joints.
How do you clinically examine proprioception?
An initial clinical examination of proprioception often involves testing the position sense by having the patient, with eyes closed, touch one finger with another after the target finger has been moved
Describe nociceptive stimuli
These are tissue-damaging sources of energy that may be external or internal to the body surface.
Sharp, cutting pain is the sensation elicited on initial contact with the painful stimulus.
The sensation of dull, burning pain may follow as a consequence of tissue inflammation.
How do you clinically examine pain sensation?
An initial clinical examination of the pain sense often involves testing sharp, cutting pain sensitivity by asking the patient, with her/his eyes closed, what they feel when pricked with a pin
Where are most sensory system receptors located?
The receptors of most sensory systems are located in:
specialized sensory receptor organs (e.g. the photoreceptors in the eye; the auditory and vestibular hair cells in the inner ear) or
within a restricted part of the body (e.g. the taste buds in the mouth; the olfactory receptors in the olfactory mucosa of the nose).
What is the specialised sensory receptor cell in the somatosensory system?
There is only one type of specialised sensory receptor cell in the somatosensory system, theMerkel cells, and they are found only in skin
What are cutaneous sensory receptors?
These are specialized dendritic endings of afferent nerve fibers, often associated with non-neural cells that surround it.
The sensitivity (modality specificity) of the somatosensory receptor is determined by its location and by the structure of the non-neural tissue surrounding the 1° afferent terminal.
The different mechanoreceptor types are located in different regions of the skin and are responsible for perception of different characteristics of a touch stimulus
Some sensory receptors are not housed within specialised structures but rather are free nerve endings.
Pain and temperature sensations arise from unmyelinated dendrites of sensory neurons located around hair follicles throughout the glaborous and hairy skin, as well as deep tissue.
List and describe the types of mechanoreceptors
Touch and pressure are sensed by four types of mechanoreceptors:
1. Meissner corpuscles – glabrous skin within the dermal papillae. Encapsulated dendrites that respond to changes in texture and slow vibrations.
2. Merkel cells (disks) – basal layer of the epidermis of both hairy and non-hairy skin. Expanded dendritic endings that respond to sustained pressure and touch.
3. Ruffini corpuscles – enlarged dendritic endings with elongated capsules that respond to sustained pressure
4. Pacinian corpuscles – subcutaneous tissue below the dermis. Unmyelinated dendritic endings encapsulated by concentric lamellae which respond to deep pressure and fast vibration
List and describe the propioceptive receptors
- Muscle spindles :: Are found in nearly all striated muscles.
Encapsulated and consists of small muscle fibers, called intra-fusal muscle fibers, and afferent and efferent nerve terminals. Specialized to monitor muscle length (stretch) and signal the rate of change in muscle length by changing the discharge rate of afferent APs. Most numerous in muscles that carry out fine movements (the extraocular muscles; intrinsic muscles of the hand and fewer in large muscles that control gross movements of the body (e.g. the muscles of the back). - Golgi tendon organs :: Found in the tendons of striated extra-fusal muscles near the muscle-tendon junction. Resemble Ruffini corpuscles. Encapsulated and contain intertwining collagen bundles, which are continuous with the muscle tendon, and fine branches of afferent fibers that weave between the collagen bundles. Monitors and signals muscle contraction against a force (muscle tension), whereas the muscle spindle is a proprioceptor that monitors and signals muscle stretch (muscle length)
- Joint receptors :: Found within the connective tissue, capsule and ligaments of joints.
The encapsulated endings resemble the Ruffini and Pacinian corpuscles and the Golgi tendon organs.
It has been suggested that information from muscles, tendons, skin and joints are combined to provide estimates of joint position and movement.
For example, when the hip joint is replaced — removing all joint receptors — the ability to detect the position of the thigh relative to the pelvis is not lost.
