Reflexes Flashcards
What is a stretch reflex, what do they measure?
The stretch reflex (myotatic reflex) is a muscle contraction in response to stretching within the muscle. It is a monosynaptic reflex which provides automatic regulation of skeletal muscle length.
When a muscle lengthens, the muscle spindle is stretched and its nerve activity increases. This increases alpha motor neuron activity, causing the muscle fibers to contract and thus resist the stretching. A secondary set of neurons also causes the opposing muscle to relax. The reflex functions to maintain the muscle at a constant length.
Golgi tendon reflex
The Golgi tendon reflex is a normal component of the reflex arc of the peripheral nervous system. In a Golgi tendon reflex, skeletal muscle contraction causes the agonist muscle to simultaneously lengthen and relax. This reflex is also called the inverse myotatic reflex, because it is the inverse of the stretch reflex. Though muscle tension is increasing during the contraction, alpha motor neurons in the spinal cord supplying the muscle are inhibited
Name the examinable stretch reflexes and their nerve roots
Biceps reflex (C5, C6)
Brachioradialis reflex (C5, C6, C7)
Extensor digitorum reflex (C6, C7)
Triceps reflex (C6, C7, C8)
Patellar reflex or knee-jerk reflex (L2, L3, L4)
Ankle jerk reflex (Achilles reflex) (S1, S2)
Describe the pupillary reflex
The pupillary light reflex pathway has an afferent limb (within CN II) and efferent limb (within CN III).
The ganglion cells of the retina project bilaterally to the pretectal nuclei. The pretectal nuclei projects crossed and uncrossed fibers to the Edinger-Westphal nucleus, which gives rise to the preganglionic parasympathetic fibers. These fibers exit the midbrain with CN III and synapse with postganglionic parasympathetic neurons of the ciliary ganglion, which innervates the sphincter muscle of the iris
Describe the accommodation reflex
The accommodation reflex is a reflex action of the eye, in response to focusing on a near object, then looking at distant object (and vice versa), comprising coordinated changes in vergence, lens shape and pupil size (accommodation).
It is dependent on cranial nerve II (afferent limb of reflex), superior centers (interneuron) and cranial nerve III (efferent limb of reflex). The change in the shape of the lens is controlled by the ciliary muscles inside the eye. Changes in contraction of the ciliary muscles alter the focal distance of the eye, causing nearer or farther images to come into focus on the retina; this process is known as accommodation.[1] The reflex, controlled by the parasympathetic nervous system, involves three responses; pupil accommodation, lens accommodation, and convergence.
What is the jaw jerk reflex?
The jaw jerk reflex or the masseter reflex is a stretch reflex used to test the status of a patient’s trigeminal nerve (CN V)
Describe the corneal reflex
The corneal reflex, also known as the blink reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea (such as by touching or by a foreign body), or bright light, though could result from any peripheral stimulus. Stimulation should elicit both a direct and consensual response (response of the opposite eye).
The reflex is mediated by:
the nasociliary branch of the ophthalmic branch (V1) of the 5th cranial nerve (trigeminal nerve) sensing the stimulus on the cornea, lid, or conjunctiva (i.e. it is the afferent).
the temporal and zygomatic branches of the 7th cranial nerve (Facial nerve) initiating the motor response (i.e. it is the efferent).
Mediated by centre in the pons of brainstem.
Describe the glabellar reflex
Sensory - CNV Motor - CNVII
Glabellar reflex (also known as the “glabellar tap sign”) (Glabella) is a primitive reflex. It is elicited by repetitive tapping on the forehead.
Subjects blink in response to the first several taps. If the blinking persists, this is known as Myerson’s sign and is abnormal and a sign of frontal release; it is often seen in people who have Parkinson’s disease.
The afferent sensory signals are transmitted by the trigeminal nerve, and the efferent signals come back to orbicularis oculi muscle via the facial nerve, which in turn reflexively contracts causing blinking.
What is the vestibule-ocular reflex?
Sensory CNIII, Motor CN III, IV, VI +T
he vestibulo-ocular reflex (VOR), sometimes known as but not completely synonymous with the oculocephalic reflex (which itself is colloquially known as the “doll’s head reflex” and is used to assess the health of coma patients, along with VOR) is a reflex eye movement that elicits eye movement by stimulating the vestibular system. This reflex functions to stabilize images on the retinas (in yoked vision) during head movement by producing eye movements in the direction opposite to head movement, thus preserving the image on the center of the visual field(s).
Describe the gag reflex and its function
Sensory CN IX Motor CN X
The pharyngeal reflex or gag reflex (also known as a laryngeal spasm) is a reflex contraction of the back of the throat - prevents choking
Nerve roots for the cremasteric reflex
L1-L2
What is the withdrawal reflex
The withdrawal reflex (nociceptive or flexor withdrawal reflex) is a spinal reflex intended to protect the body from damaging stimuli. It is polysynaptic, causing stimulation of sensory, association, and motor neurons
What is the tympanic reflex
The tympanic reflex helps prevent damage to the inner ear by muffling the transmission of vibrations from the tympanic membrane to the oval window
The reflex works by contracting the muscles of the inner ear, the tensor tympani and the stapedius. This pulls the manubrium of the malleolus inwards and tightens it. This tightening prevents the vibrations from disturbing the perilymph.
