MBBS1 Spinal Cord Reflexes Lecture 2024 PDF

4MBBS103 NBSS block neuro REFLEXES 14/3/24 Spinal cord systems & reflexes Dr M R Huett https://www.youtube.com/watch?v=55vA9MzWObM 1  Aim To provide an understanding of...

4MBBS103 NBSS block neuro REFLEXES 14/3/24 Spinal cord systems & reflexes Dr M R Huett https://www.youtube.com/watch?v=55vA9MzWObM 1  Aim To provide an understanding of reflexes Spinal cord systems & reflexes Dr M R Huett 2 14/3/24  objectives This lecture should enable students to: 1. Understand the function of simple monosynaptic reflexes 2. Describe the roles of the five elements of a reflex 3. Explain reciprocal inhibition / recurrent inhibition 4. Understand the basic concepts of reflex control of movement 5. Comprehend complex reflexes and their clinical importance Spinal cord systems & reflexes Dr M R Huett 3 14/3/24  Reflexes key points Key points 1.Definition reflex 2.Monosynaptic reflex arc 3.Poly synaptic reflex 4.Cross reflex 5.Intersegmental reflex 6. Brain stem reflexes 7.Vestibular reflexes 8.Cerebellar reflexes 9. Developmental reflexes 10. Clinical significance of reflexes 14/3/24 Spinal cord systems & reflexes Dr M R Huett 4  Reflexes definition Definition reflex Stereotyped involuntary response to stimulus not subject to conscious control Spinal cord systems & reflexes Dr M R Huett 5 14/3/24  Reflexes autonomic reflexes Autonomic reflexes mediated: autonomic nervous system activation: smooth muscle cardiac muscle glands Spinal cord systems & reflexes Dr M R Huett 6 14/3/24 http://www.tedmontgomery.com/the_eye/eyephotos/index-grphc.html  Reflexes somatic reflexes Somatic reflexes mediated: somatic nervous system activation: stimulation of skeletal muscle Spinal cord systems & reflexes Dr M R Huett 7 14/3/24  Reflexes foundation for movement Neural circuits = building blocks of CNS Simplest neural circuit = reflex Fast automatic behaviour Very old evolutionary survival No conscious effort Spinal cord systems & reflexes Dr M R Huett 8 14/3/24  Reflexes simple → complex circuit Brainbow Timing, coordination ….. Switch ….. control Circus of Light Spinal cord systems & reflexes Dr M R Huett 9 14/3/24 http://braintour.harvard.edu/archives/portfolio-items/brainbow  Reflexes Reflex 3 steps SENSORY INPUT INFORMATION PROCESSING MOTOR OUTPUT Spinal cord systems & reflexes Dr M R Huett 10 14/3/24  Reflexes 5 COMPONENTS 1. Receptor 2. Sensory neurone afferent pathway to CNS 3.Interpretation centre one or more synapse in CNS 4.Motor neurone efferent pathway from CNS 5.Effector e.g. muscle contracts / gland secretes 11 14/3/24 Spinal cord systems & reflexes Dr M R Huett  Reflexes 5 components 1 5 COMPONENTS 1. Receptor 2. Sensory neurone 2 afferent pathway to CNS 3.Interpretation centre one or more synapse in CNS 4.Motor neurone efferent pathway from CNS 5.Effector e.g. muscle contracts / gland secretes 3 5 4 Monosynaptic reflex 12 14/3/24 Spinal cord systems & reflexes Dr M R Huett  Reflexes monosynaptic reflex 1. Receptor A. Muscle spindle 2. Sensory neurone B. mylenated Large diameter 1A (Aα) afferent axon C. peripheral nerve D. dorsal root ganglion cell body 3.Interpretation centre E. spinal cord synapse 4. α motor neurone 1938 Mylenated large diameter 268.8 miles per hour (120m/s) : 5. Effector Mercedes-Benz W125 F. muscle extrafusal fibres13 14/3/24 Spinal cord systems & reflexes Dr M R Huett Neuromuscular junction  Reflexes monosynaptic Simplest ….. Monosynaptic reflex Role mono synaptic reflex: controls stretch leg muscles maintains upright posture Spinal cord systems & reflexes Dr M R Huett 14 14/3/24  Reflexes polysynaptic Most reflexes POLYSYNAPTIC More than one synapse interneurones More synapses = slower … synaptic delay 0.5 msec Signal can be changed Average number synapses per neurone = ~20,000 15 14/3/24 Spinal cord systems & reflexes Dr M R Huett  Reflexes skeletal muscle reflexes Proprioceptors located - skeletal muscle, tendons, joint capsules, and ligaments Proprioceptors carry input - sensory neurons to CNS CNS integrates input signal Somatic motor neurons carry output signal – Alpha motor neurons Effectors - contractile skeletal muscle fibers Spinal cord systems & reflexes Dr M R Huett 16 14/3/24  Proprioceptors Muscle spindles and Golgi tendon organs sensory receptors in muscle Extrafusal muscle fibers Alpha motor neuron Muscle spindle Golgi tendon organ Tendon 14/3/24 17 Spinal cord systems & reflexes Dr M R Huett  Proprioceptors Muscle spindles Gamma motor neurons To CNS Tonically active sensory neurons Central region lacks myofibrils. Gamma motor neurons from CNS Muscle spindle Intrafusal fibers Extrafusal fiber Muscle spindle 14/3/24 18 Spinal cord systems & reflexes Dr M R Huett  Proprioceptors Golgi tendon organs Extrafusal muscle fibers Afferent neuron Capsule Sensory receptor Collagen fiber Tendon Golgi tendon organ 19 14/3/24 Spinal cord systems & reflexes Dr M R Huett Muscle Spindles Muscle spindles monitor muscle length & rate change of length and prevent overstretching 1 1 Extrafusal muscle fibers at resting length Sensory neuron 3 endings 2 2 Sensory neuron is tonically active. Intrafusal fibers Sensory of muscle spindle neuron 3 Spinal cord integrates function. Alpha motor neuron Spinal cord 4 Alpha motor neurons to extrafusal fibers receive tonic 4 input from muscle spindles. 5 5 Extrafusal fibers maintain a certain level of tension even at rest. (a) Spindles are firing even when muscle is relaxed. 20 14/3/24 Spinal cord systems & reflexes Dr M R Huett  Alpha-Gamma Coactivation 21 14/3/24 Spinal cord systems & reflexes Dr M R Huett  Muscle Reflexes Help Prevent Damage Spinal cord systems & reflexes Dr M R Huett 22 14/3/24  Reflexes example polysynaptic Simple polysynaptic Withdrawal reflex Nb: total flexor pattern Spinal cord systems & reflexes Dr M R Huett 23 14/3/24  Reflexes polysynaptic Sensory detects excitatory synapse – motor neurone contraction ALSO branch to interneurone inhibits antagonist motorneurone Spinal cord systems & reflexes Dr M R Huett 24 14/3/24  Reflexes reciprocal inhibition Simple reflex & polysynaptic Reciprocal inhibition Reciprocal Innervation Excitation of one group muscles / inhibition their antagonists Sherrington = reciprocal innervation This a key principle of motor organisation 25 14/3/24 Spinal cord systems & reflexes Dr M R Huett  Reflexes stretch / muscle spindle Muscle spindle reflex www.colorado.edu/.../image/figure8-5.jpg Spinal cord systems & reflexes Dr M R Huett 26 14/3/24  Reflexes interlimb Cross cord reflexes not only one limb Opposite limb affected Effects reversed ipsilateral + flexors - extensors contralateral - flexors + extensors Ipsi for withdrawal …flex to remove Contra for stability … straight leg for support Spinal cord systems & reflexes Dr M R Huett 27 14/3/24  Reflexes flexor & cross extension reflex Spinal cord Ascending pathways to brain 3a Gray matter 2 Spinal White cord Sensory matter neuron 1 Painful stimulus activates nociceptor. 3b 3c - 2 Primary sensory neuron - enters spinal cord and diverges. One collateral activates ascending 3a pathways for sensation (pain) and Nociceptor postural adjustment (shift in center of gravity). 3b Withdrawal reflex pulls foot away from painful stimulus. Painful Alphamotor stimulus neurons 1 Crossed extensor reflex supports 3c body as weight shifts away from painful stimulus. Extensors inhibited Extensors contract As weight shifts to left leg. Flexors contract, moving foot away from painful stimulus. Flexors inhibited 14/3/24 28 Spinal cord systems & reflexes Dr M R Huett  Reflexes intersegmental Inter segmental reflexes E.g. Arm movements Leg movements 29 14/3/24 Spinal cord systems & reflexes Dr M R Huett  Reflexes intersegmental Spinal pattern generators Spinal motor patterns walking Building block = crossed extensor reflex Circuit wiring Timing: Rhythm generator ? Membrane has ‘pacemaker’ properties 14/3/24 Spinal cord systems & reflexes Dr M R Huett 30  Reflexes central pattern generators Central pattern generators - control of rhythmic movements neuronal circuits → rhythmic motor patterns such as walking, breathing, without sensory or descending inputs instructing specific timing precise temporal sequences of muscle contraction → coordinated movement Forward swim motor pattern recorded from 3 hindlimb muscle nerves: a knee extensor (red), a hip flexor (violet) a hip extensor (blue) "motor patterns“ = programmed sequences muscle activity "central pattern generators" (CPGs) = rhythmically active networks nerve cells Spinal – intersegmental simple movements e.g. stepping brain stem – complex movements e.g. turning Spinal cord systems & reflexes Dr M R Huett 31 14/3/24 http://cbns.ucr.edu/faculty/currie.html  Reflexes descending control Descending control pyramidal Change motor neurone pool excitability extra pyramidal clinical Jendrassik maneuver to reinforce knee-jerk Spinal cord systems & reflexes Dr M R Huett 32 14/3/24  Reflexes recurrent inhibition Recurrent inhibition Renshaw cells Collateral from spinal motor neurone Inhibitory interneurones regulate spinal motor neurones Spinal cord systems & reflexes Dr M R Huett 33 14/3/24  Reflexes descending control Pyramidal corticospinal corticobulbar Extrapyramidal vestibulospinal – vestibular N tectospinal – superior colliculus – mid brain reticulospinal – MRST- Pons, LRST-medulla rubrospinal – red N – mid brain Spinal cord systems & reflexes Dr M R Huett 34 14/3/24 http://instruct.uwo.ca/anatomy/530/descmoto.gif  Reflexes descending control Extrapyramidal Vestibulospinal – lateral VS - Ipsilateral Control balance & posture Innervate ‘antigravity muscles’ Flexors – upper limb; Extensors – lower limb Medial VS - bilateral – neck & shoulder Tectospinal → cervical spine Coord. Head movts. relation to visual stim. Reticulospinal - MRST- ↑ muscle tone – excite vol. LSRT - ↓ inhib. Muscle tone – inhibit Vol movt. Rubrospinal – contralateral -? Role - fine movts. Spinal cord systems & reflexes Dr M R Huett 35 14/3/24  Reflexes supra spinal reflexes Postural reflexes Vestibular reflexes Brain stem reflexes Spinal cord systems & reflexes Dr M R Huett 36 14/3/24  Reflexes supra spinal reflexes Supra spinal reflexes Labyrinthine righting reflex - vestibular reflex Lean off balance stimulate semicircular canals motor response neck and limbs maintain upright posture Spinal cord systems & reflexes Dr M R Huett 37 14/3/24  Reflexes brain stem vestibular reflexes Vestibular reflexes Lateral Vestibulospinal Tract to all spinal cord Excites ipsilateral extensor motor neurones Inhibits via interneurone flexor motor neurones (legs monosynaptic path, arms polysynaptic) Medial Vestibulospinal Tract to mid thorax Excites neck muscles 14/3/24 Spinal cord systems & reflexes Dr M R Huett 38  Posture reflex control Vestibular reflexes Need information orientation to vertical vestibular apparatus = sense organ Neural pathway: Inner ear vestibular nuclei spinal motor neurones Postural reflex body movements Lean to left Excite extensors on left recover vertical Spinal cord systems & reflexes Dr M R Huett 39 14/3/24  Higher CNS brain stem visual reflexes Visual reflexes Powerful input posture control Clouds moving give ‘sense’ moving Try to compensate …. Fall! 40 14/3/24 Spinal cord systems & reflexes Dr M R Huett  Posture reflex control Visual reflexes Powerful input posture control Eye lateral geniculate nucleus midbrain descending reflex pathways spinal motor neurones Spinal cord systems & reflexes Dr M R Huett 41 14/3/24  Posture feedback control Pressure receptors Important receptors for maintainence posture skin pressure receptors Stand - soles feet pressure receptors monitor distribution weight Clinically if destroyed eg tabes dorsalis Close eyes … fall Spinal cord systems & reflexes Dr M R Huett 42 14/3/24  Higher CNS somatosensory reflexes Sitting balance buttock pressure receptors Racing drivers ‘drive by the seat of their pants’ Spinal cord systems & reflexes Dr M R Huett 43 14/3/24  Reflexes cerebellar reflexes Cerebellar reflexes Reflex centre integrates sensory information position of the body coordinates complex movements maintains posture Spinal cord systems & reflexes Dr M R Huett 44 14/3/24  Reflexes clinical relevance Clinical relevance Reflexes lost before weakness Signs: absent Distorted exaggerated loss symmetry Spinal cord systems & reflexes Dr M R Huett 45 14/3/24  Reflexes clinical relevance Detect alterations: Indicate: degeneration demyelination or Other pathology before other signs Spinal cord systems & reflexes Dr M R Huett 46 14/3/24  Reflexes Hyporeflexia clinical relevance Weak or absent response ? damage to the nerves outside the spinal cord (peripheral neuropathy) damage to the motor neurons (motor neuron disease), or neuromuscular junction (myasthenia gravis) or muscle disease (myopathy) Spinal cord systems & reflexes Dr M R Huett 47 14/3/24  Reflexes hyperreflexia clinical relevance Excessive response ? spinal cord damage above the level controlling the hyperactive response higher CNS damage Disinhibition Spinal cord systems & reflexes Dr M R Huett 48 14/3/24  Reflexes clinical relevance Asymmetric response ? early onset of progressive disease localized nerve damage e.g. trauma Spinal cord systems & reflexes Dr M R Huett 49 14/3/24  Reflexes clinical relevance Spinal cord injury reflex tests determine area injury E.g. motor neurones above - unaffected below - absent Closed head injury eg bleed in or around brain increase pressure in cranium pressure on cranial nerve III - change eye reflex response ( occulomotor reflex) Spinal cord systems & reflexes Dr M R Huett 50 14/3/24  Reflexes clinical relevance Foot reflex 1896 Babinski "On the cutaneous plantar reflex in certain organic disorders of the nervous system" "phenomenon of the toes" Stroke lateral aspect of the sole reaction = anatomical extensor in the first two toes in hemiplegic and paraparetic patients….and neonates Small Cowper Madonna (1505) by Raphael (Raffaello Sanzio) 51 14/3/24 Spinal cord systems & reflexes Dr M R Huett  Reflexes developmental & clinical Flexor reflexes – neonates & young infant stand - flexor reflexes in the lower limbs controlled by the dorsal reticulospinal tract walk - flexor synergy for walking pattern Develop: Babinski sign disappears (stimulate - great toe goes down) Adults Babinski sign reappears = loss upper motor neurone control Spinal cord systems & reflexes Dr M R Huett https://www.youtube.com/watch?v=55vA9MzWObM 52 14/3/24  Reflexes developmental & clinical Complex reflex responses important developmentally Primitive and developmental reflexes At birth NO voluntary control movement Environmental stimuli – primitive reflexes Automatic stereotyped responses As CNS matures higher brain areas override primitive reflexes Spinal cord systems & reflexes Dr M R Huett 53 14/3/24  Reflexes developmental & clinical Survival pattern of response inhibited to allow mature patterns response Postural reflexes develop……. ….regulated higher movement control centres Important role of Inhibition Disinhibition causes clinical problems Spinal cord systems & reflexes Dr M R Huett 54 14/3/24  Reflexes developmental & clinical Clinical Cerebral palsy children do not make transition → movement random and uncontrolled Failed development higher control spectra of disorders retain primitive reflexes – affect sensory perception of movement not only limbs, eyes, balance, hearing Spinal cord systems & reflexes Dr M R Huett 55 14/3/24  Summary Revision spinal reflexes Intersegmental reflexes Supraspinal reflexes Developmental reflexes Clinical relevance Spinal cord systems & reflexes Dr M R Huett 56 14/3/24  The best reflex? smile And watch the effect on your neighbour Reflexes are FUN …… and a smile is one of your best therapeutic tools Spinal cord systems & reflexes Dr M R Huett 57 14/3/24  Hopefully not confused …. but now have foundation for neuro ! Spinal cord systems & reflexes Dr M R Huett 58 14/3/24  Additional slides For interest to introduce complex reflex patterns Spinal cord systems & reflexes Dr M R Huett 59 14/3/24  Reflexes developmental & clinical Neonate reflexes Spinal cord systems & reflexes Dr M R Huett 60 14/3/24  Developmental reflexes Moro response Left big toe Babinski age 5 months Spinal cord systems & reflexes Dr M R Huett 61 14/3/24  Reflexes developmental & clinical Asymmetric tonic neck reflex Tonic Neck (Fencing) Reflex head is rotated left left arm extends right arm flexes Opposite reaction if head rotated right Spinal cord systems & reflexes Dr M R Huett 62 14/3/24  Reflexes developmental & clinical Moro Reflex Moro Reflex (Startle Reflex) Hold supine infant a few inches above bed Gently drop infant back to elicit startle arms out in extension and grimaces Spinal cord systems & reflexes Dr M R Huett 63 14/3/24  Reflexes developmental & clinical Foot Stroke Inner Sole Toes curl around ("grasp") examiner's finger Stroke Outer Sole (Babinski) Toes spread, great toe dorsiflexion Walking Reflex Hold baby up with one hand across chest As feet touch ground, baby makes walking motion Protective Reflex Soft cloth is placed over the babies eyes and nose Baby arches head and turns head side to side Brings both hands to face to swipe cloth away Spinal cord systems & reflexes Dr M R Huett 64 14/3/24  Reflexes developmental & clinical Hand-to-Mouth (Babkin) Reflex Stroke newborns cheek or put finger in babies palm Baby will bring his fist to mouth and suck a finger Swimmer's (Gallant) Response Hold baby prone while supporting belly with hand Stroke along one side of babies' spine Baby flexes whole body toward the stroked side Spinal cord systems & reflexes Dr M R Huett 65 14/3/24  Reflexes developmental & clinical Dolls eyes Give one forefinger to each hand - baby grasps both Pull baby to sitting with each forefinger Eyes open on coming to sitting (Like a Doll's) Head initially lags Baby uses shoulders to right head position Rooting Reflex Touch newborn on either side of cheek Baby turns to find breast Sucking mechanism on finger is divided into 3 steps Front of tongue laps on finger Back of tongue massages middle of the finger Oesophagus pulls on tip of finger Spinal cord systems & reflexes Dr M R Huett 66 14/3/24  Useful web sites : http://neuroscience.uth.tmc.edu/s3/chapter02.html https://meded.ucsd.edu/clinicalmed/neuro3.htm http://braintour.harvard.edu/archives/portfolio-items/brainbow babinski reflex m ovie http://library.med.utah.edu/neurologicexam/html/home_exam.html Reflex Control of Posture and Movement: Ibro Symposium Pub: Elsevier, 22 Sep 2011 Diagrams / figs: Silverthron : Human Physiology pub: Pearson Spinal cord systems & reflexes Dr M R Huett 67 14/3/24