Basal Ganglia Structure and Function
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Questions and Answers

What is the main function of the basal ganglia?

  • To process auditory information
  • To act as a unified functional unit to control movement (correct)
  • To regulate body temperature
  • To process visual information

    • Which of the following is NOT a nucleus of the basal ganglia?

  • Cerebellum (correct)
  • Striatum
  • Globus pallidus
  • Substantia nigra

    • What is the main function of the Subthalamic nucleus?

  • To regulate emotions
  • To process sensory information
  • To control limb and trunk movements
  • To receive and send signals to the globus pallidus and substantia nigra (correct)

    • Which part of the Globus pallidus is one of the major output structures of the basal ganglia?

    <p>Internal segment</p> Signup and view all the answers

    What is the function of the Pars compacta of the Substantia nigra?

    <p>To project heavily to the striatum</p> Signup and view all the answers

    Which nucleus participates in eye movement control and cognition?

    <p>Caudate nucleus</p> Signup and view all the answers

    What is the function of the Striatum?

    <p>To receive afferent projections from the cerebral cortex</p> Signup and view all the answers

    Which part of the Substantia nigra can be viewed as a single output structure with the internal segment of the Globus pallidus?

    <p>Pars reticulata</p> Signup and view all the answers

    What is the effect of cholinergic striatal interneurons on motor activity?

    <p>Decrease motor activity</p> Signup and view all the answers

    Which of the following is NOT a function of basal ganglia?

    <p>Regulation of heart rate</p> Signup and view all the answers

    What is the role of basal ganglia in motor activity?

    <p>Planning and programming of movement</p> Signup and view all the answers

    Lesions in which part of the basal ganglia can lead to athetosis?

    <p>Globus pallidus</p> Signup and view all the answers

    What is the result of lesions in the substantia nigra?

    <p>Parkinson's disease</p> Signup and view all the answers

    What is the effect of lesions in the caudate nucleus and putamen?

    <p>Huntington's chorea</p> Signup and view all the answers

    What is the function of basal ganglia in speech?

    <p>Disturbed speech (dysarthria)</p> Signup and view all the answers

    What is the role of basal ganglia in movement timing and scaling?

    <p>Timing and scaling of movement</p> Signup and view all the answers

    What type of information is received from the parietal cortex by the basal ganglia?

    <p>primary and secondary somatosensory information</p> Signup and view all the answers

    What is the consequence of the direct pathway in the cortico-Basal Ganglia-thalamocortical circuit?

    <p>increase the excitatory drive from thalamus to cortex</p> Signup and view all the answers

    Which of the following neurotransmitters is NOT mentioned in the modulation of direct and indirect pathways?

    <p>serotonin</p> Signup and view all the answers

    What is the effect of the dopaminergic nigrostriatal projection on motor activity?

    <p>increase motor activity</p> Signup and view all the answers

    What is the function of the indirect pathway in the cortico-Basal Ganglia-thalamocortical circuit?

    <p>inhibit movement</p> Signup and view all the answers

    What is the role of the striatum in the direct pathway?

    <p>project directly to GP(internal)</p> Signup and view all the answers

    What is the function of the GPi/SNr in the cortico-Basal Ganglia-thalamocortical circuit?

    <p>modulate the thalamocortical connection</p> Signup and view all the answers

    What is the role of the D2 receptor in the direct pathway?

    <p>inhibit the direct pathway</p> Signup and view all the answers

    What is the average lifespan of olfactory receptor cells?

    <p>30-60 days</p> Signup and view all the answers

    What is the function of Bowman's glands in the olfactory system?

    <p>To secrete mucus onto the olfactory membrane</p> Signup and view all the answers

    What is the diameter of the cilia on olfactory receptor cells?

    <p>0.1-0.3 µm</p> Signup and view all the answers

    What is the resting membrane potential of olfactory receptor cells?

    <p>-55 mV</p> Signup and view all the answers

    How many different odors can humans discriminate?

    <p>1000-10,000</p> Signup and view all the answers

    What is the mechanism by which odorants stimulate olfactory receptor cells?

    <p>Chemical mechanism</p> Signup and view all the answers

    What is required for a substance to be detected by the olfactory system?

    <p>It must be volatile and slightly water soluble</p> Signup and view all the answers

    What is the structure where olfactory axons converge and synapse with mitral cells?

    <p>Glomerulus</p> Signup and view all the answers

    What is the region of the brain where the medial olfactory area is located?

    <p>Midbasal portions of the brain</p> Signup and view all the answers

    How many olfactory axons converge at each glomerulus?

    <p>25,000</p> Signup and view all the answers

    What is the primary function of the Lateral Olfactory Area?

    <p>Associating certain smells with nausea and vomiting</p> Signup and view all the answers

    What can cause anosmia as a result of nasal problems?

    <p>Nasal polyps and respiratory tract infections</p> Signup and view all the answers

    Which of the following senses are classified as visceral senses?

    <p>Taste and smell</p> Signup and view all the answers

    What type of receptors are smell receptors?

    <p>Chemoreceptors and extereceptors</p> Signup and view all the answers

    What is hyperosmia?

    <p>An enhanced sense of smell</p> Signup and view all the answers

    What is the result of damage to the olfactory nerves?

    <p>Anosmia</p> Signup and view all the answers

    How many different odorant receptors do humans have?

    <p>350</p> Signup and view all the answers

    What is the term for a distorted sense of smell?

    <p>Dysosmia</p> Signup and view all the answers

    What is the role of smell in lower animals?

    <p>For finding direction, seeking prey, avoiding predators, and sexual attraction</p> Signup and view all the answers

    What is the cause of congenital anosmia?

    <p>Genetic defect</p> Signup and view all the answers

    Why do humans spend millions of dollars annually?

    <p>To smell better and be more socially attractive</p> Signup and view all the answers

    What can cause hyposmia?

    <p>Nasal congestion</p> Signup and view all the answers

    Where is the olfactory membrane located?

    <p>In the superior part of the nasal cavity</p> Signup and view all the answers

    What is the surface area of the olfactory membrane in each nostril?

    <p>2.4-5 cm2</p> Signup and view all the answers

    What is the role of the Lateral Olfactory Area in feeding responses?

    <p>Learning to like or dislike certain foods</p> Signup and view all the answers

    How many bipolar olfactory neurons are there?

    <p>10 million-100 million</p> Signup and view all the answers

    What can lead to anosmia in patients with Alzheimer's disease?

    <p>Olfactory nerve damage</p> Signup and view all the answers

    What is the result of partial damage to the olfactory nerves?

    <p>Dysosmia</p> Signup and view all the answers

    What is the role of smell in humans?

    <p>It is less important in influencing our behavior</p> Signup and view all the answers

    What is the result of stimulation of the taste or smell receptors?

    <p>Pleasurable or objectionable sensations</p> Signup and view all the answers

    What is the primary function of the taste and smell sensations?

    <p>To distinguish between up to 30 million compounds and seek nutritionally useful food and avoid toxic substances</p> Signup and view all the answers

    How many probable chemical receptors have been identified in scientific studies?

    <p>13</p> Signup and view all the answers

    What type of receptors are taste receptors classified as?

    <p>Chemoreceptors</p> Signup and view all the answers

    What is the classification of taste and smell senses?

    <p>Visceral senses</p> Signup and view all the answers

    What stimulates the taste receptors?

    <p>Dissolved chemical molecules in saliva</p> Signup and view all the answers

    How many primary sensations of taste have been grouped into?

    <p>5 general categories</p> Signup and view all the answers

    What is the function of taste and smell sensations in seeking nutritionally useful food?

    <p>To induce pleasurable sensations</p> Signup and view all the answers

    What is the primary receptor involved in bitter taste?

    <p>Gustducin</p> Signup and view all the answers

    What is the typical diameter of a taste bud?

    <p>1/30 mm</p> Signup and view all the answers

    What is the threshold concentration for quinine to stimulate bitter taste?

    <p>0.000008 M</p> Signup and view all the answers

    What is the primary neurotransmitter involved in umami taste?

    <p>Glutamate</p> Signup and view all the answers

    What is the function of phospholipase C (PLC) in bitter taste?

    <p>Release of Ca2+ from intracellular stores</p> Signup and view all the answers

    How many different bitter receptors are associated with G-protein in humans?

    <p>24</p> Signup and view all the answers

    What is the function of PKA in sweet taste?

    <p>Phosphorylation of K+ channels</p> Signup and view all the answers

    What is the primary cause of the sour taste?

    <p>Influx of H+ ions</p> Signup and view all the answers

    What type of channels are responsible for the salty taste?

    <p>Epithelial sodium channels</p> Signup and view all the answers

    What is the result of Na+ influx into the salt receptors?

    <p>Depolarization and release of glutamate</p> Signup and view all the answers

    What is the effect of amiloride on the tongue?

    <p>Inhibition of ENaC receptors</p> Signup and view all the answers

    What is the primary function of ENaC receptors in the mouth?

    <p>Detection of salty taste</p> Signup and view all the answers

    What is the role of TRP channels in the taste system?

    <p>Detection of sour taste</p> Signup and view all the answers

    What is the result of inhibition of ENaC receptors on the tongue?

    <p>Decreased sensitivity to salty taste</p> Signup and view all the answers

    What is the approximate number of taste buds on the surface of the tongue in adults?

    <p>3000-10000</p> Signup and view all the answers

    Where are salty and sweet taste buds primarily located on the tongue?

    <p>Tip of the tongue</p> Signup and view all the answers

    Which nerve transmits signals from the anterior two-thirds of the tongue?

    <p>Lingual nerve</p> Signup and view all the answers

    What is the final destination of signals from the taste buds?

    <p>Gustatory cortex</p> Signup and view all the answers

    What is the function of microvilli in taste buds?

    <p>To provide a receptor surface for taste</p> Signup and view all the answers

    Where are moderate numbers of taste buds located on the tongue?

    <p>Fungiform papillae</p> Signup and view all the answers

    How many taste buds are located on the roof of the mouth and wall of the throat?

    <p>1000</p> Signup and view all the answers

    What is the lifespan of taste receptor cells in lower mammals?

    <p>10 days</p> Signup and view all the answers

    What is the purpose of the transmission of taste signals to the superior and inferior salivatory nuclei?

    <p>To regulate salivation</p> Signup and view all the answers

    What type of fibers are innervated by gamma motor neurons?

    <p>Intrafusal fibers</p> Signup and view all the answers

    What is the function of the static nuclear bag and nuclear chain fibers?

    <p>To respond to slow stretch</p> Signup and view all the answers

    What is the 'dynamic response' of the muscle spindle?

    <p>A rapid increase in impulses in response to rapid stretch</p> Signup and view all the answers

    What type of fibers are innervated by 1a afferents?

    <p>All three types of fibers</p> Signup and view all the answers

    What is the main function of the spinal cord apart from being a conduit for nerve fibers?

    <p>to contain neuronal circuits for walking and various reflexes</p> Signup and view all the answers

    What is the characteristic of alpha motor neurons?

    <p>they are 50-100% bigger than other neurons</p> Signup and view all the answers

    What is the function of the primary endings?

    <p>To respond to rapid stretch</p> Signup and view all the answers

    What is the function of muscle spindles?

    <p>to sense muscle length and change in length</p> Signup and view all the answers

    What is the characteristic of interneurons in the spinal cord?

    <p>they are small and very excitable</p> Signup and view all the answers

    What is the function of propriospinal fibers?

    <p>to provide pathways for multisegmental reflexes</p> Signup and view all the answers

    What is the result of coactivation of alpha and gamma motor neurons?

    <p>Contraction of the muscle and shortening of the spindle</p> Signup and view all the answers

    What is the function of the gamma system?

    <p>All of the above</p> Signup and view all the answers

    What initiates a stretch reflex in the knee jerk reflex?

    <p>Striking the patellar tendon with a hammer</p> Signup and view all the answers

    What is the location of the area that excites the gamma signal?

    <p>Bulboreticular facilitatory area of the brain stem</p> Signup and view all the answers

    What is the significance of the gamma efferents in the knee jerk reflex?

    <p>They facilitate the stretch reflex</p> Signup and view all the answers

    What is the function of the Golgi tendon reflex?

    <p>To equalize force among muscle fibers</p> Signup and view all the answers

    What is the speed at which muscle spindle and Golgi tendon signals are transmitted to higher centers?

    <p>120 m/sec</p> Signup and view all the answers

    What is the purpose of the crossed extensor reflex?

    <p>To push the body away from the stimulus and shift weight to the opposite limb</p> Signup and view all the answers

    What is the result of a painful stimulus on the affected limb?

    <p>Flexor reflex in the affected limb and an extensor reflex in the opposite limb</p> Signup and view all the answers

    What is the purpose of pressure on the bottom of the feet?

    <p>To cause an extensor reflex</p> Signup and view all the answers

    What is the function of gamma motor nerves to the spindle?

    <p>To innervate the contractile ends of the intrafusal fibers</p> Signup and view all the answers

    What happens when the muscle is stretched without contracting the ends of the spindle?

    <p>The stretch response is unavailable</p> Signup and view all the answers

    What is the role of the muscle spindle in the stretch reflex?

    <p>To return the muscle to its original length</p> Signup and view all the answers

    What is the result of sudden stretch of the muscle?

    <p>Excitation of the muscle spindle</p> Signup and view all the answers

    What is the purpose of the comparator of length between the intrafusal and extrafusal muscle fibers?

    <p>To compare the length of the intrafusal and extrafusal muscle fibers</p> Signup and view all the answers

    Study Notes

    Basal Ganglia

    • A group of nuclei that act as a unified functional unit, closely associated with the cerebral cortex and corticospinal motor control system.
    • Receives most input signals from the cerebral cortex and returns almost all output signals back to the cortex.

    Basal Ganglia Structure

    • Consists of four principal nuclei:
      • Striatum (input nucleus)
      • Globus pallidus (two separate nuclei: external and internal segments)
      • Subthalamic nucleus
      • Substantia nigra (two separate nuclei: pars compacta and pars reticulata)

    Striatum

    • Receiving afferent projections from the cerebral cortex
    • Comprised of three subnuclei:
      • Caudate nucleus (participates in eye movement control and cognition)
      • Putamen (participates in control of limb and trunk movements)
      • Nucleus accumbens (participates in emotions)

    Globus Pallidus

    • Internal segment: one of the major output structures of the basal ganglia
    • External segment: part of the intrinsic circuitry of the basal ganglia

    Substantia Nigra

    • Pars compacta: contains dopaminergic cells that project heavily to the striatum
    • Pars reticulata: can be viewed as a single output structure with the internal segment of the globus pallidus

    Subthalamic Nucleus

    • Small nucleus situated between the thalamus and the substantia nigra
    • Receives projections from the external segment of the globus pallidus, the cerebral cortex, thalamus, and brain stem
    • Sends output to both segments of the globus pallidus and to the substantia nigra pars reticulata

    Basal Ganglia Input

    • Receives input from various cortical regions:
      • Parietal cortex (primary and secondary somatosensory information, secondary visual information)
      • Temporal cortex (secondary visual and auditory information)
      • Cingulate cortex (limbic and emotional status information)
      • Frontal cortex (primary and secondary motor information)
      • Prefrontal cortex

    Cortico-Basal Ganglia-Thalamocortical Circuits

    • Two important pathways through which striatal information reaches the globus pallidus (internal):
      • Direct pathway: striatal cells project directly to the globus pallidus (internal)
      • Indirect pathway: striatal cells project to the globus pallidus (external)
    • The direct pathway increases the excitatory drive from the thalamus to the cortex, facilitating movement
    • The indirect pathway decreases the excitatory drive from the thalamus to the cortex, inhibiting movement

    Neurotransmitters in the Basal Ganglia

    • Dopaminergic modulation: increases motor activity
    • Cholinergic modulation: decreases motor activity by inhibiting striatal cells of the direct pathway and exciting striatal cells of the indirect pathway

    Functions of Basal Ganglia

    • Voluntary movement
    • Postural control
    • Control of muscle tone
    • Role in arousal mechanism
    • Speech
    • Cognitive control of motor activity
    • Planning and programming of movements
    • Timing and scaling of intensity of movements
    • Subconscious execution of some movements

    Lesions of Basal Ganglia

    • Globus pallidus: athetosis (spontaneous writing movements of the hand, arm, neck, and face)
    • Putamen: chorea (flicking movements of the hands, face, and shoulders)
    • Substantia nigra: Parkinson's disease (rigidity, tremor, and akinesia)
    • Subthalamus: hemiballismus (sudden flailing movements of the entire limb)
    • Caudate nucleus and putamen: Huntington's chorea (loss of GABA-containing neurons to the globus pallidus and substantia nigra)

    Chemical Senses: Smell

    • Smell (olfaction) and taste (gustation) are classified as visceral senses, physiologically related to each other.
    • Smell receptors are chemoreceptors and extereceptors, stimulated by dissolved chemical molecules in mucus.

    Olfactory Receptors

    • Humans have approximately 350 different odorant receptors, belonging to the G protein-coupled receptor superfamily.
    • Odorant receptors can distinguish between estimates of up to 30 million compounds.

    Physiological Importance of Smell

    • Smell plays a major role in finding direction, seeking prey, avoiding predators, and sexual attraction in lower animals.
    • In humans, the sense of smell is less sensitive and less important in influencing behavior.

    Olfactory Membrane and Cells

    • The olfactory membrane lies in the superior part of the nasal cavity, with a surface area of about 2.4-5 cm2 in each nostril.
    • There are 10 million-100 million bipolar olfactory neurons, with a lifespan of about 30-60 days, continuously replaced from a layer of basal stem cells.
    • Each cell has 4-25 cilia, with olfactory cilia projections reaching into the mucus that coats the inner surface of the nasal cavity.

    The Structure of the Olfactory System

    • Bowman glands secrete mucus onto the surface of the olfactory membrane.
    • Odorant molecules bind to olfactory receptors, activating adenyl cyclase, leading to depolarization.

    Physiologic Factors for Olfactory Stimulation

    • Substances must be volatile, slightly water-soluble, and slightly lipid-soluble to stimulate olfactory cells.

    Olfactory System

    • At each glomerulus, there are 25 mitral cells, 60 tufted cells, and 25,000 olfactory axons.
    • The medial olfactory area, composed of nuclei in the midbasal portions of the brain, is associated with primitive responses to olfaction.

    Abnormalities in Odor Detection

    • Anosmia (inability to smell) and hyposmia (diminished olfactory sensitivity) can result from nasal congestion, polyps, damage to olfactory nerves, tumors, respiratory tract infections, and prolonged use of nasal decongestants.
    • Hyperosmia (enhanced olfactory sensitivity) is less common, but can occur in pregnant women.
    • Dysosmia (distorted sense of smell) can be caused by sinus infections, partial damage to olfactory nerves, and poor dental hygiene.

    Chemical Senses: Taste

    • Taste (gustation) and smell (olfaction) are classified as visceral senses and are physiologically closely related to each other.
    • Taste receptors are chemoreceptors and exteroceptors that are stimulated by dissolved chemical molecules in saliva.

    Taste and Smell Sensations

    • Taste and smell sensations allow individuals to distinguish between estimates of up to 30 million compounds.
    • Stimulation of the taste or smell receptors induces pleasurable or objectionable sensations, leading to seeking nutritionally useful food or avoiding potentially toxic substances.

    Chemical Receptors in Taste Cells

    • At least 13 probable chemical receptors have been identified in taste cells, including:
      • 2 sodium receptors
      • 2 potassium receptors
      • 2 sweet receptors
      • 2 bitter receptors
      • 1 chloride receptor
      • 1 adenosine receptor
      • 1 inosine receptor
      • 1 glutamate receptor
      • 1 hydrogen ion receptor

    Primary Sensations of Taste

    • Primary sensations of taste have been grouped into five general categories:
      • Sour
      • Salty
      • Sweet
      • Bitter
      • Umami (delicious)

    Taste Substances

    • Sour taste is caused by acids (H+ ions) and is triggered by the Epithelial sodium channels (ENaC) that allow protons to enter the cytoplasm.
    • Salty taste is mediated by Na+ influx through amiloride-sensitive Na+ channels, with the main receptor being the epithelial sodium channel (ENaC).
    • Bitter taste is associated with gustducin (a heterotrimeric G protein) receptor and is caused by different compounds, most of which are poisons.
    • Sweet taste is triggered by sweet tastants, G protein (gustducin), and adenylyl cyclase, leading to the release of cAMP and depolarization.
    • Umami taste is triggered by amino acids and is mediated by the activation of the metabolic glutamate receptors (mGluR4) in taste buds.

    Threshold for Stimulation

    • Sour: 0.0009 N HCl
    • Salty: 0.01 M NaCl
    • Sweet: 0.01 M Sucrose
    • Bitter: 0.000008 M Quinine

    Taste Buds

    • Taste buds are composed of 50-100 modified epithelial cells (taste and supporting cells) with a diameter of 1/30 mm and a length of 1/16 mm.
    • Microvilli provide receptor surface for taste.
    • Adults have 3,000-10,000 taste buds on the surface of the tongue, with about 1,000 taste buds in the roof of the mouth and wall of the throat.

    Location of Taste Buds

    • Taste buds are located on:
      • Circumvallate papillae (V line on the surface of the posterior tongue)
      • Fungiform papillae (top side)
      • Foliate papillae
      • Palate
      • Tonsillar pillars
      • Epiglottis
      • Proximal esophagus

    Distribution of Taste on the Tongue

    • Salty and Sweet taste buds are located on the tip of the tongue.
    • Sour taste buds are located on the lateral edges of the tongue.
    • Bitter taste buds are located on the root of the tongue and soft palate.

    Transmission of Taste Signals

    • Signals from the anterior two-thirds of the tongue pass through the lingual nerve, chorda tympani, and facial nerve into the nucleus tractus solitarius (NTS).
    • Signals from the circumvallate papillae and posterior regions of the mouth and throat are transmitted through the glossopharyngeal nerve into the NTS.
    • Signals from the base of the tongue and pharyngeal region are transmitted into the NTS by way of the Vagus nerve.
    • Signals from the NTS pass to the Ventral posterior nucleus of the thalamus and then to the Gustatory cortex.

    Taste Reflexes

    • From the NTS, many taste signals are transmitted to the superior and inferior salivatory nuclei.

    Motor Functions of the Spinal Cord

    • The spinal cord is not just a conduit for nerve fibers, but contains neuronal circuits for walking and various reflexes that can be activated and commanded by higher brain centers.
    • The spinal cord is organized to transmit sensory information to higher centers and to elicit motor reflexes locally.

    Anterior Motor Neurons

    • Alpha motor neurons:
      • Give rise to large type A alpha fibers (~14 microns)
      • Stimulation can excite 3-100 extrafusal muscle fibers collectively called a motor unit
    • Gamma motor neurons:
      • Give rise to smaller type A gamma fibers (~5 microns)
      • Stimulation excites intrafusal fibers, a special type of sensory receptor

    Interneurons and Propriospinal Fibers

    • Interneurons:
      • 30 times as many as anterior motor neurons
      • Small and very excitable
      • Comprise the neural circuitry for motor reflexes
    • Propriospinal fibers:
      • Travel up and down the cord for 1-2 segments
      • Provide pathways for multisegmental reflexes

    Sensory Receptors of the Muscle

    • Muscle spindle:
      • Senses muscle length and change in length
    • Golgi tendon organ:
      • Senses tendon tension and change in tension

    The Muscle Spindle

    • The center has no contractile elements and responds to stretch
    • Ends have contractile elements
    • Three types of fibers:
      • Primary (1a) afferents innervate all three fiber types
      • Secondary (Group II) afferents innervate static bag and chain fibers
      • Gamma motor neurons innervate the ends of intrafusal fibers

    Response of the Muscle Spindle

    • Static response:
      • When the center of the spindle is stretched slowly, the number of impulses generated by the primary and secondary endings increases in proportion to the degree of stretch
    • Dynamic response:
      • When the center of the spindle is stretched rapidly, the number of impulses generated by the primary endings increases in proportion to the rate of change of length

    Gamma Motor Nerves to the Spindle

    • Divided into gamma s and gamma d, which innervate the contractile ends of the respective intrafusal fibers
    • Contraction of the ends will stretch the middle of the fiber

    Physiologic Function of the Muscle Spindle

    • Comparator of length between the intrafusal and extrafusal muscle fiber
    • Opposes a change in length of the muscle
    • When the muscle is stretched, the spindle returns it to its original length, leading to the stretch reflex

    The Stretch Reflex

    • Opposes further stretch of the muscle
    • Afferent impulses to the cord excite the alpha motor neuron, resulting in contraction of the muscle
    • Sudden stretch of the muscle excites the muscle spindle

    Changing Muscle Length

    • Coactivation of alpha and gamma motor neurons causes contraction of the muscle and the ends of the spindle, resulting in a shortened spindle with an intact stretch response

    Function of the Gamma System

    • Controls the intensity of the stretch reflex
    • Performs a damping function by adjusting sensitivity
    • The spindle is normally tonically active as a result of input from higher brain centers

    Clinical Application of the Stretch Reflex

    • Knee jerk reflex:
      • Striking the patellar tendon with a hammer stretches the quadriceps muscle and initiates a stretch reflex
      • Can be done with almost any muscle
      • Index of the facilitation of the gamma efferents

    Golgi Tendon Reflex

    • Mediated by the Golgi tendon organ receptor located in the tendon
    • Responds to tension
    • Function is to equalize force among muscle fibers

    Transmission of Stretch Information to Higher Centers

    • Muscle spindle and Golgi tendon signals are transmitted to higher centers
    • Informs the brain of the tension and stretch of the muscle
    • Important for feedback control of motor activity

    The Withdrawal Reflexes

    • A painful stimulus causes the limb to automatically withdraw from the stimulus
    • Neural pathways for reflex:
      • Nociceptor activation transmitted to the spinal cord
      • Synapses with pool of interneurons that diverge to the muscles for withdrawal, inhibit antagonist muscles, and activate reverberating circuits to prolong muscle contraction
    • Duration of the after discharge depends on the strength of the stimulus

    Crossed Extensor Reflex

    • Painful stimulus elicits a flexor reflex in the affected limb and an extensor reflex in the opposite limb
    • Extensor reflex begins 0.2-0.5 seconds after the painful stimulus
    • Serves to push the body away from the stimulus and shift weight to the opposite limb

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    Related Documents

    Basal Ganglia PDF
    Smell - PDF
    Taste Receptors & Sensations PDF
    Chapter 54 Motor Functions of the Spinal Cord PDF

    Description

    Learn about the basal ganglia, a group of nuclei that play a crucial role in motor control and cognition. Explore its structure, consisting of four principal nuclei, and their functions.

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