Muscle Tone Flashcards
Muscle Tone
The resting tension in a skeletal muscle.
Skeletal muscle described as voluntary but even relaxed slightly contracted.
Muscle is always in a state where it can contract.
Helps with joint stabilization and to maintain posture.
Reflexes
Unvoluntary, unconscious.
We need muscle tone so that we can have reflexes.
Hypotonia
Absence of low-level contractions that lead to muscle tone.
Hypertonia
Excessive muscle tone. Accompanied with hyperreflexia.
Cerebral palsy.
Reflex arc!
- Receptor
- Sensory neuron
- Interneuron/Integration center
- Motoneuron
- Effector
- Receptor
Detects stimulus (skin, organ, muscle, tendons). Corresponds to the end of a particular's dendrite or specialized receptor cell in a sensory organ.
- Sensory Neuron
Conveys the sensory info to the brain or spinal chord.
Corresponds to dendrite, cell body and axon of sensory nerve.
- Integration center
Relay neuron.
Corresponds to dendrite, cell body and axon of interneuron of brain or spinal chord.
- Motoneuron
Conducts the motor info to the periphery.
- Effector
Muscle or gland.
Sensory receptor classification
Type of stimulus they detect:
- Mechanoreceptors
- Thermoreceptors
- Photoreceptors
- Chemoreceptors
- Nociceptors
By their body location:
- Exteroceptors
- Interoceptors
- Proprioceptors
Mechanoreceptors
Detect change in movement.
Thermoreceptors
Detect change of temperature.
Photoreceptors
Detect change in light.
Chemoreceptors
Detect change in chemical state (stomach).
Nociceptor
Detect pain.
Exteroceptors
Near the surface of the body, monitor external environment.
Interoceptors
Deep, monitor internal environment, 99% of receptors in the body.
Proprioceptors
Monitors the relationship of external and internal environment. Position and movement.
Unencapsulated receptors
- Free nerve endings of sensory neurons
- Modified free nerve endings: Merkel discs
- Hair follicle receptors
Encapsulated receptors
- Meissner’s corpuscles
- Pacinian corpuscles
- Ruffini endings
- Muscle spindles
- Golgi tendon organs
- Joint kinesthetic receptors
Free nerve endings of sensory neurons
- Extero-, intero- and proprioceptors
- Thermo-, chemo- (itch), mechano- and nociceptors
Located in most body tissues: dense connective tissue and epithelia.
Modified free nerve endings (Merkel discs)
- Exteroceptors
- Mechanoreceptors (light pressure)
Slowly adapting.
Located in basal layer of epidermis (superficial).
Hair follicle receptors
- Exteroceptors
- Mechanoreceptors (hair deflection)
Rapidly adapting.
Superficial, surrounding hair follicles (goosebumps).
Meissner’s corpuscles
- Exteroceptors
- Mechanoreceptors (light pressure, discriminative touch,
low frequency vibration)
Dermal papillae of hairless skin.
Pacinian corpuscles
- Extero-, intero- and some proprioceptors
- Mechanoreceptors (deep pressure, stretch, high
frequency vibration)
Dermis, hypodermis, periostea, mesentery, tendons, lig., joint capsules.
Ruffini endings
- Extero- and proprioceptors
- Mechanoreceptors (deep pressure and stretch)
Deep in dermis, hypodermis and joint capsule.
Muscle spindle
- Proprioceptors
- Mechanoreceptors (muscle stretch, length, change in
force)
Skeletal muscles, particularly of extremities.
Golgi tendon organs
- Proprioceptors
- Mechanoreceptors (tendon stretch and tension)
Tendons
Reflex info first in the Golgi tendon organs than in muscle spindle.
Joint kinesthetic receptors
- Proprioceptors
- Mechanoreceptors and nociceptors
Joint capsules of synovial joints.
Spinal Reflexes
- Stretch reflex
- Golgi tendon reflex
- Flexor and crossed-extensor reflexes
- Superficial reflexes
Different reflexes for different receptors
Muscle spindle and Golgi tendon organs
They give spinal chord all the information it needs for changing in length of muscle. Muscle spindles in skeletal muscles: - Information about muscle length Golgi tendon organs in tendon: - Amount of tension in the muscle Important role in stretch reflexes.
Muscle spindle anatomy
Intrafusal muscle fibers enclosed in connective tissue capsule.
Central region: no myofilaments and receptive surfaces.
Two types of afferents:
- Type 1a fibers: Spindle center: Rate and degree of stretch.
- Type 2 fibers: Spindle ends: Degree of stretch.
Afferents
Nerve carrying a message towards the CNS.
Type 1a fibers
Heavily myelinated: allows for fast conduction.
Very high sensitivity, strongly reacts to muscle stretch.*
Play leading role in regulation of muscle activity.
1a and 2 have their own motor innervation with gamma MN.
Type 2 fibers
Myelinated.
Generate firing rates which correlate to changes in muscle length but do not change weather the muscle is actively stretched or length is stable.
Low dynamic sensitivity and sends signals about actual length of muscle.*
1a and 2 have their own motor innervation with gamma MN.
Gamma motoneurons
Maintain the sensitivity of the spindle during muscle contraction.
Motor drive induced by alpha MNs is accompanied by activation of gamma- MNs.
Coupling is commonly called “α - γ coactivation”.
Two types of gamma- MNs: dynamic and static.
Alpha-Gamma coactivation
Make sure muscle is always ready to contract! *
Activation of Gamma MNs prevents temporary insensitivity (after contraction, if only alpha MNs are activated, spindle becomes slack and no action potentials can be fired).
Gamma MNs cause weak contractions that keep spindle tout at all times.
Stretch reflex
Muscle spindle activated by stretch.
Sensory neurons transmit afferent impulses at higher frequency.
Sensory neuron synapse directly with alpha-MN, excite extrafusal fibers. Activate agonist.
Afferent fibers also synapse with interneurons that inhibit the motor neurons controlling the antagonist muscle.
Reciprocal inhibition
Efferent impulses of alpha-MNs cause stretched muscle to contract.
Efferent impulses of alpha-MNs to antagonist muscle are reduced.
Inhibition of antagonist muscle.
The activation of interneuron of antagonist muscle.
Cerebellum
Helps with regulation of muscle tone.
Spinocerebellar tract helps the muscle spindle.
Golgi tendon organ
Detects a stretch in muscle.
Mechanoreceptors inform about muscle tension via 1b afferents in the tendon.
Makes sure the agonist is not stretching too much and causing damage, by activating the antagonist muscle and inhibiting the agonist (opposite of muscle spindle).
Regulation of tension.
Function directly related to motor unit contraction and passive stretch of the muscle.
Flexion reflex pathway
Reaction to pain or deep pressure.
Cutaneous receptors.
F.ex. stepping on a nail. Stimulated leg flexes to withdraw. Sensory neuron from the foot will activate flexor muscle and inhibit extensor muscle. On the other leg it will activate extensor and inhibit flexor (for stability).
Superficial reflexes
Gentle cutaneous stimulation under the foot normally leads to flexion of the toes.
When superficial reflexes are not working the big toe would extend (Babinski sign).
If you are touched around the belly button you will suck it in, contract abdomen.
Babinski reflex
Reflex responsible for negative results of the Babinski reflex is flexion reflex (flexion of toes).
Positive results is extension of the big toe.
