Interneurn -> A nerve cell fund entirely within the central nervus system that acts as a link between sensry neurns and mtr neurns Infrmatin sent frm brain t perfrm a gal, has a purpse Tw Types f Mtr Behavir: Vluntary Reflexive -> ut f cntrl & awareness Extensin: Tw interacting muscles; extensr and flexr muscles The extensr muscle cntracts while the flexr muscle relaxes Agnist -> muscle that cntracts while ther relaxes Antagnist -> muscle that ppses the actin f the agnists muscle There is an increase in the angle arund the jint T relax a muscle, inhibit the neurns in them Flexin: The flexr muscle cntracts while the extensin muscle relaxes The angle arund the jint decreases Reciprcal innervatin f muscles means activating bth muscles Bth are crdinated in activatin and relaxatin Balance between the muscles tensins Mtr neurns: Only excitatry neurns release acetylchline (ACh)
Alpha neurns -> innervate skeletal (extradusal) muscles (big muscles that cause yu t mve) Gamma neurns -> innervate muscle spindle (intrafusal) (muscle fibers) Lcated in the gray matter in spinal crd and the cranial nerves in spinal crd Receive infrmatin frm interneurns The sensry infrmatin travels up t the brain but als synapses with interneurns in the spinal crd The brain sends infrmatin t the spinal crd and the neurn synapses with the same interneurn as befre and then innervates the muscles The mtr neurn leaves thrugh the ventral rt Descending mtr neurns innervate ther spinal interneurns Spinal interneurns: Neurns in the gray matter Drive a lt f infrmatin Vluntary infrmatin cming frm descending pathways and innervating these interneurns (sme can inhibit and sme can verride infrmatin) Receives prpriceptive feedback, tensin infrmatin, length mnitring, crdinates cmplex mvements (help walk autmatically) Interneurns integrate all this infrmatin Spinal Reflexes 1. Withdrawal reflexes -> prtects limbs frm injury 2. Stretch reflex -> cntrls muscle length 3. Inverse stretch reflex -> cntrls muscle tensin Mst spinal reflexes can be verridden. 1. Withdrawal Reflexes: Flexin Withdrawal Reflex: Plysynaptic (ges thrugh 2 synapses befre reaching mtr neurn, interneurns between sensry input and mtr utput):
This is befre the brain knws it Experience pain and usually the withdrawal reflex ccurs Pain afferents travel up the muscle thrugh the drsal rt ganglin crssing the central canal in the spinal clumn and ging up the anterlateral side t the brain The pain afferent als synapses with 2 efferent in the spinal crd: Inhibitry interneurn -> inhibits mtr neurn (in ventral hrn) that innervates ipsilateral extensr, the leg will nt extend Excitatry interneurn -> will excite the mtr neurn (in ventral hrn) that innervates the ipsilateral flexr, the leg will flex and yu will withdraw frm painful stimulus Crss extensr reflex: Autmatic respnse that stabilizes persn by inhibiting and exciting muscles in the ther leg The leg that isn't intrduced t the stimuli gets innervated in the OPPOSITE WAY
Als plysynaptic Interneurns als inhibit the cntralateral leg's flexr muscle t prevent it frm flexing Interneurns als excite the cntralateral leg's extensr muscle s that it extends weight n ther leg. CONTRALATERAL COMPENSATION The magnitude f the withdrawal reflex depends n the magnitude f the pain stimulus The mre painful, the mre it withdraws After discharge -> increased duratin f withdrawal mediated by the feedback lps in the spinal crd The mre painful, the harder it is t readjust it later Irradiatin -> increase in rate & magnitude f withdrawal respnse is prprtinal t increase in stimulus' strength Larger # f actin ptentials prduced by painful stimulus activate a larger number f interneurns (recruited) that innervate the mtr neurns that increase withdrawal This reflex can be verridden 2. Stretch Reflex: Prpriceptive feedback that infrms abut the muscle's length Mnsynaptic (primary) and plysynaptic (secndary) cmpnents Mnsynaptic stretch reflex (knee jerk): The prpriceptive receptrs get activated when stretch muscle, measures it's length
Sends signal up the drsal rt t drsal hrn and up the drsal clumn int the brain The afferents branch ff in the ventral hrn and then synapse with mtr neurns that leave thrugh the ventral rt They activate the same muscle that was stretched (excite the mtr neurn f the ipsilateral extensr) -> causes it t EXTEND They inhibit the mtr neurns innervating the ipsilateral flexr -> prevents frm FLEXING The dctr usually hits the stretch muscle which causes leg t kick, if it desn't then there is a prblem with the CNS The muscle that is activated is stretched (excites the stimulated muscle) Muscle Spindle & Glgi Tendn Organ:
i. Glgi tendn rgan -> detects tensin in the muscle ii. Tendn -> attaches muscle t the bne iii. Muscle spindle -> small, embedded, parallel in the muscle, desn't cntribute t frce iv. Stretch receptr -> mechanreceptr activated by changes in length v. Intrafusal muscle fibers -> activated by gamma mtr neurns, smaller fibers within the muscle spindles vi. Muscle tensin -> sends inf t brain vii. Extrafusal muscle fibers -> causes yu t mve, main mtr neurns, activated by alpha mtr neurns Muscle Spindles: Tw types f afferents cming ut Ia and II Activated by mechanreceptrs in stretch receptr prtin La in nuclear bag fibers Ll in nuclear chain fibers Gamma mtr axns innervate bth ends f the interfusal muscle fibers La (primary) afferents: Adapting afferents, give infrmatin abut the changes in muscle length Als give infrmatin abut sme static length (tap) LL (secndary) afferents: Inf abut static muscle length Muscle spindles can lse sensitivity: An increase in external lad can stretch the muscle spindles even mre, they extend Vluntary flexin can cause extrafusal muscles (alpha mtr neurn activity) t cntract, muscles shrten Muscle spindles shrten and cllapse, reducing sensitivity
Muscles cntract -> get lse & flppy -> lse sensitivity Gamma mtr neurns maintain muscle spindle sensitivity Alpha-gamma c-activatin -> wrk alngside Muscle spindles dn't cntribute t frce f muscle cntractin They cntract n each side, being pulled and this makes them tighter and maintains their sensitivity Intrafusal muscles maintain muscle spindle sensitivity Muscle tne -> clinical term used t describe muscles pulled back 3. Inverse Stretch Reflex: Cntrls muscle tensin Invlves the Glgi tendn rgan Glgi tendn rgan: Respnds t tensin Detects changes in frces There are prpriceptive afferents cming frm the tendn It's in series with the muscle Active cntractin f a muscle prduces mre tensin than stretching CONTRACT -> A LOT OF FORCE
The cllagen fibers wrap arund the free nerve ending f the Ib afferents that g t the spinal crd When the rgan is stretched with frce, cllagen pinch and defrm free-ending, which causes mechanreceptr ins t pen. This leads the Ib afferents t becme pen. Glgi tendn rgan reflex (inverse stretch):
Tensin in the stretching muscle sends signals up Ib afferents The afferent branches in the ventral hrn It inhibits the mtr neurn fr the extensr muscle -> preventing it frm extending It excites the mtr neurn fr the flexr muscle -> causing it t flex/cntract When it cntracts, the Glgi can say n. It regulates the amunt f frce that's generated Can verride the rgan Inhibit same muscle that was stimulated Inverse f stretch reflex -> inhibits Mtr Cntrl & Brain
Crticspinal (skilled mvement) -> descending pathways, direct fine mtr skills (muth & hands) Extrapyramidal (trunk & psture) -> regulated things like walking, pathway that interacts with the spinal crd Muscle spindle & Glgi tendn The basal nuclei and the Cerebellum help mtr system decide which muscle t mve s that yu dn't have t think abut it The middle level sets a timing n when each muscle cntracts and makes crrectins based n sensry infrmatin. Gal (ex: think f lifting a bx) is generated in the rstral end f the crtex (in circle) which is sent t the mtr system and put int actin Think -> Premtr crtex (decdes visual inf t mtr inf) -> primary mtr crtex (synthesizes small mvements) Supplementary mtr area (yellw) cntains internally generated respnses Organizatin f primary mtr crtex: Muscles that are next t ne anther are cntrlled by neurns that are next t each ther in the brain (systematic layut) The size f bdy structure in the primary mtr crtex is prprtinal t the number f neurns dedicated t their mtr cntrl and the degree f skill required t perate that area f bdy.
Example: the hands take up a great deal f space thus they require a lt f skill. Require a lt f neurns in fingers fr skilled manners. Descending mtr pathways: Crsses at the medulla belw spinal crd Leaves thrugh ventral rt Muscle tne -> resistance if skeletal muscles t stretch (pull n muscle t pull it back) 1. Damage t descending pathways (increase reflexes): Inhibitry pathway usually Hypertnia -> abnrmally high muscle tne, pulls back t much can increase r decrease muscle tne Spasticity -> veractive mtr reflexes (big kick) Rigidity -> cnstant muscle cntractin, t much activity 2. Damage t mtr neurns (reflexes g away): Hyptnia -> abnrmally lw muscle tne (desn't d much) Atrphy -> lss f muscle mass
Decreased r missing reflexes Fasciculatins -> visible muscle twitches, a.p fired randmly when nt necessary Neurgenic -> mtr neurn r axn Mypathic -> neurmuscular junctin r muscle Basal nuclei (ganglia) -> helps with timing f mvement and smthly perfrm an actin Basal Nuclei mvement disrders: Parkinsn disease -> affects basal nuclei Cmmn Reduced dpamine input in basal nuclei (tremrs/shaky) Akinesia -> reduced mvements Bradykinesia -> slw mvements Muscular ridgitiy Resting tremr Treatment -> give dpamine Huntingtn disease -> genetic mutatin that causes widespread lss f neurns in the bran Shws later in life Preferentially lst nuclei Hyperkinetic disrder -> excessive mtr mvements Chreifrm mvements -> jerky, randm invluntary mvements f face and limb Cerebellum -> invlved with timing, errr crrectin & learning new mtr skills Receives sensry infrmatin, vestibular, visual, auditry, smatsensry prpriceptive Massive cnnectin with sensry infrmatin ut interacts with descending & ascending Cerebellar deficits:
Asynergia -> smth muscles are subdivided their separate cmpnents, divided int cmpnents Dysmetria -> unable t target mvements crrectly "pass pinting", miss target Ataxia -> uncrdinated Intentian tremr -> vluntary mvements, tremr r grabbing bject