Neural Integration and Spinal Cord Structure

Neural Integration and Conduction

• Neural integration is the process of executing an appropriate output in response to input signals from neurons.
• The brain and spinal cord work together to regulate locomotion, with the spinal cord functioning as a central pattern generator for alternating and repetitive muscle movements.

Meninges and Spinal Cord Structure

• The spinal cord has three meninges: Dura Mater, Arachnoid Mater, and Pia Mater.
• The Dura Mater is attached to the vertebral foramen and forms a loose-fitting dural sheath.
• The Arachnoid Mater adheres to the deep surface of the Dura Mater, and the subarachnoid space is filled with CSF.
• The Pia Mater is directly on the surface of the spinal cord, and the Denticulate Ligaments of the Pia Mater anchor the spinal cord.
• The Terminal Filum is an extension of the Pia Mater that anchors the conus medullaris to the coccyx.

Gray and White Matter

• A cross-section of the spinal cord reveals clear regions of gray and white matter.
• Gray matter regions are the site of synapse between incoming sensory neurons, interneurons, and outgoing motor neurons.
• The Posterior Horn, Anterior Horn, and Lateral Horn are all part of the gray matter.
• The Gray Commissure is a median bridge connecting the right and left sides of gray matter.
• White matter regions contain bundles of neurons traveling up and down the spinal cord, organized into Anterior, Lateral, and Posterior Columns (Funiculi).

Sensory and Motor Pathways

• Ascending Tracts are a relay of sensory neurons that transmit signals from the PNS up to higher centers.
• First-Order neurons are unipolar sensory neurons that transmit impulses from PNS receptors to the spinal cord.
• Second-Order neurons are excited by First-Order Neurons in the medulla oblongata and undergo decussation to the opposite side of the Medulla Oblongata.
• Third-Order neurons (if present) arise from the thalamus and ascend to the appropriate region of the cerebral cortex.
• Descending Tracts contain motor neurons that transmit signals from the brain, brain stem, or upper regions of the spinal cord to lower regions of the spinal cord.

Organization of Nerves

• A nerve is a parallel bundle of peripheral axons enclosed by connective tissue.
• Most nerves are a mix of sensory (afferent) and motor (efferent) fibers, but some are purely one or the other.
• Connective tissue sheaths include the Endoneurium, Perineurium, and Epineurium.

Spinal Nerves

• Spinal nerves are short and immediately divide into Posterior Ramus and Anterior Ramus.
• The Posterior Ramus innervates muscles of that region and joints of skin and back.
• The Anterior Ramus innervates anterior and lateral skin and muscles of the trunk and limbs.

Plexuses

• Plexuses are interlacing nerve networks that serve the limbs.
• There are five plexuses: Cervical, Brachial, Lumbar, Sacral, and Coccygeal.
• Each plexus is formed by branching Anterior Rami that join one another lateral to the vertebral column.

Reflexes

• Reflexes are quick, involuntary responses to specific stimuli that occur without the involvement of the primary motor cortex.
• Reflexes can be classified as Somatic or Autonomic, and Innate or Conditioned.
• The four important properties of reflexes are:
  • They require stimulation of specific receptors.
  • They are quick and utilize a minimal number of synapses.
  • They are involuntary, occurring without involvement of the primary motor cortex.
  • They are stereotyped and predictable.

Muscle Spindles

• Muscle spindles are proprioceptors that monitor the length of skeletal muscles, ligaments, and tendons.
• They are composed of 3-10 Intrafusal Fibers bundled in connective tissue.
• The gamma motor neuron innervates the Intrafusal fibers to adjust their length and sensitivity.

Reflex Arcs

• Reflex arcs are pathways that transmit signals from the sensory receptors to the effector organ.
• There are two types of reflex arcs: Monosynaptic and Polysynaptic.
• Monosynaptic reflex arcs lack an interneuron in the spinal cord gray matter, resulting in very fast responses.
• Polysynaptic reflex arcs involve one or more interneurons, allowing for more delayed reflex responses.

Examples of Reflexes

• Patellar Tendon Reflex: a polysynaptic reflex that responds to excessive tension in the tendon to prevent muscles and tendons from tearing.
• Flexor Reflex: a polysynaptic reflex that initiates the withdrawal of a threatened body part from the threat.
• Crossed Extensor Reflex: a polysynaptic reflex that couples ipsilateral flexion with contralateral extension to maintain balance.
• Plantar Reflex: a reflex that tests the function of corticospinal tracts from L4-S2.
• Abdominal Reflex: a reflex that tests the function of Ventral Rami from T8-T12.

Neural Integration and Conduction

• Neural integration is the process of executing an appropriate output in response to input signals from neurons.
• The brain and spinal cord work together to regulate locomotion, with the spinal cord functioning as a central pattern generator for alternating and repetitive muscle movements.

Meninges and Spinal Cord Structure

• The spinal cord has three meninges: Dura Mater, Arachnoid Mater, and Pia Mater.
• The Dura Mater is attached to the vertebral foramen and forms a loose-fitting dural sheath.
• The Arachnoid Mater adheres to the deep surface of the Dura Mater, and the subarachnoid space is filled with CSF.
• The Pia Mater is directly on the surface of the spinal cord, and the Denticulate Ligaments of the Pia Mater anchor the spinal cord.
• The Terminal Filum is an extension of the Pia Mater that anchors the conus medullaris to the coccyx.

Gray and White Matter

• A cross-section of the spinal cord reveals clear regions of gray and white matter.
• Gray matter regions are the site of synapse between incoming sensory neurons, interneurons, and outgoing motor neurons.
• The Posterior Horn, Anterior Horn, and Lateral Horn are all part of the gray matter.
• The Gray Commissure is a median bridge connecting the right and left sides of gray matter.
• White matter regions contain bundles of neurons traveling up and down the spinal cord, organized into Anterior, Lateral, and Posterior Columns (Funiculi).

Sensory and Motor Pathways

• Ascending Tracts are a relay of sensory neurons that transmit signals from the PNS up to higher centers.
• First-Order neurons are unipolar sensory neurons that transmit impulses from PNS receptors to the spinal cord.
• Second-Order neurons are excited by First-Order Neurons in the medulla oblongata and undergo decussation to the opposite side of the Medulla Oblongata.
• Third-Order neurons (if present) arise from the thalamus and ascend to the appropriate region of the cerebral cortex.
• Descending Tracts contain motor neurons that transmit signals from the brain, brain stem, or upper regions of the spinal cord to lower regions of the spinal cord.

Organization of Nerves

• A nerve is a parallel bundle of peripheral axons enclosed by connective tissue.
• Most nerves are a mix of sensory (afferent) and motor (efferent) fibers, but some are purely one or the other.
• Connective tissue sheaths include the Endoneurium, Perineurium, and Epineurium.

Spinal Nerves

• Spinal nerves are short and immediately divide into Posterior Ramus and Anterior Ramus.
• The Posterior Ramus innervates muscles of that region and joints of skin and back.
• The Anterior Ramus innervates anterior and lateral skin and muscles of the trunk and limbs.

Plexuses

• Plexuses are interlacing nerve networks that serve the limbs.
• There are five plexuses: Cervical, Brachial, Lumbar, Sacral, and Coccygeal.
• Each plexus is formed by branching Anterior Rami that join one another lateral to the vertebral column.

Reflexes

• Reflexes are quick, involuntary responses to specific stimuli that occur without the involvement of the primary motor cortex.
• Reflexes can be classified as Somatic or Autonomic, and Innate or Conditioned.
• The four important properties of reflexes are:
  • They require stimulation of specific receptors.
  • They are quick and utilize a minimal number of synapses.
  • They are involuntary, occurring without involvement of the primary motor cortex.
  • They are stereotyped and predictable.

Muscle Spindles

• Muscle spindles are proprioceptors that monitor the length of skeletal muscles, ligaments, and tendons.
• They are composed of 3-10 Intrafusal Fibers bundled in connective tissue.
• The gamma motor neuron innervates the Intrafusal fibers to adjust their length and sensitivity.

Reflex Arcs

• Reflex arcs are pathways that transmit signals from the sensory receptors to the effector organ.
• There are two types of reflex arcs: Monosynaptic and Polysynaptic.
• Monosynaptic reflex arcs lack an interneuron in the spinal cord gray matter, resulting in very fast responses.
• Polysynaptic reflex arcs involve one or more interneurons, allowing for more delayed reflex responses.

Examples of Reflexes

• Patellar Tendon Reflex: a polysynaptic reflex that responds to excessive tension in the tendon to prevent muscles and tendons from tearing.
• Flexor Reflex: a polysynaptic reflex that initiates the withdrawal of a threatened body part from the threat.
• Crossed Extensor Reflex: a polysynaptic reflex that couples ipsilateral flexion with contralateral extension to maintain balance.
• Plantar Reflex: a reflex that tests the function of corticospinal tracts from L4-S2.
• Abdominal Reflex: a reflex that tests the function of Ventral Rami from T8-T12.

Neural Integration and Conduction

• Neural integration is the process of executing an appropriate output in response to input signals from neurons.
• The brain and spinal cord work together to regulate locomotion, with the spinal cord functioning as a central pattern generator for alternating and repetitive muscle movements.

Meninges and Spinal Cord Structure

• The spinal cord has three meninges: Dura Mater, Arachnoid Mater, and Pia Mater.
• The Dura Mater is attached to the vertebral foramen and forms a loose-fitting dural sheath.
• The Arachnoid Mater adheres to the deep surface of the Dura Mater, and the subarachnoid space is filled with CSF.
• The Pia Mater is directly on the surface of the spinal cord, and the Denticulate Ligaments of the Pia Mater anchor the spinal cord.
• The Terminal Filum is an extension of the Pia Mater that anchors the conus medullaris to the coccyx.

Gray and White Matter

• A cross-section of the spinal cord reveals clear regions of gray and white matter.
• Gray matter regions are the site of synapse between incoming sensory neurons, interneurons, and outgoing motor neurons.
• The Posterior Horn, Anterior Horn, and Lateral Horn are all part of the gray matter.
• The Gray Commissure is a median bridge connecting the right and left sides of gray matter.
• White matter regions contain bundles of neurons traveling up and down the spinal cord, organized into Anterior, Lateral, and Posterior Columns (Funiculi).

Sensory and Motor Pathways

• Ascending Tracts are a relay of sensory neurons that transmit signals from the PNS up to higher centers.
• First-Order neurons are unipolar sensory neurons that transmit impulses from PNS receptors to the spinal cord.
• Second-Order neurons are excited by First-Order Neurons in the medulla oblongata and undergo decussation to the opposite side of the Medulla Oblongata.
• Third-Order neurons (if present) arise from the thalamus and ascend to the appropriate region of the cerebral cortex.
• Descending Tracts contain motor neurons that transmit signals from the brain, brain stem, or upper regions of the spinal cord to lower regions of the spinal cord.

Organization of Nerves

• A nerve is a parallel bundle of peripheral axons enclosed by connective tissue.
• Most nerves are a mix of sensory (afferent) and motor (efferent) fibers, but some are purely one or the other.
• Connective tissue sheaths include the Endoneurium, Perineurium, and Epineurium.

Spinal Nerves

• Spinal nerves are short and immediately divide into Posterior Ramus and Anterior Ramus.
• The Posterior Ramus innervates muscles of that region and joints of skin and back.
• The Anterior Ramus innervates anterior and lateral skin and muscles of the trunk and limbs.

Plexuses

• Plexuses are interlacing nerve networks that serve the limbs.
• There are five plexuses: Cervical, Brachial, Lumbar, Sacral, and Coccygeal.
• Each plexus is formed by branching Anterior Rami that join one another lateral to the vertebral column.

Reflexes

• Reflexes are quick, involuntary responses to specific stimuli that occur without the involvement of the primary motor cortex.
• Reflexes can be classified as Somatic or Autonomic, and Innate or Conditioned.
• The four important properties of reflexes are:
  • They require stimulation of specific receptors.
  • They are quick and utilize a minimal number of synapses.
  • They are involuntary, occurring without involvement of the primary motor cortex.
  • They are stereotyped and predictable.

Muscle Spindles

• Muscle spindles are proprioceptors that monitor the length of skeletal muscles, ligaments, and tendons.
• They are composed of 3-10 Intrafusal Fibers bundled in connective tissue.
• The gamma motor neuron innervates the Intrafusal fibers to adjust their length and sensitivity.

Reflex Arcs

• Reflex arcs are pathways that transmit signals from the sensory receptors to the effector organ.
• There are two types of reflex arcs: Monosynaptic and Polysynaptic.
• Monosynaptic reflex arcs lack an interneuron in the spinal cord gray matter, resulting in very fast responses.
• Polysynaptic reflex arcs involve one or more interneurons, allowing for more delayed reflex responses.

Examples of Reflexes

• Patellar Tendon Reflex: a polysynaptic reflex that responds to excessive tension in the tendon to prevent muscles and tendons from tearing.
• Flexor Reflex: a polysynaptic reflex that initiates the withdrawal of a threatened body part from the threat.
• Crossed Extensor Reflex: a polysynaptic reflex that couples ipsilateral flexion with contralateral extension to maintain balance.
• Plantar Reflex: a reflex that tests the function of corticospinal tracts from L4-S2.
• Abdominal Reflex: a reflex that tests the function of Ventral Rami from T8-T12.

Neural Integration and Conduction

• Neural integration is the process of executing an appropriate output in response to input signals from neurons.
• The brain and spinal cord work together to regulate locomotion, with the spinal cord functioning as a central pattern generator for alternating and repetitive muscle movements.

Meninges and Spinal Cord Structure

• The spinal cord has three meninges: Dura Mater, Arachnoid Mater, and Pia Mater.
• The Dura Mater is attached to the vertebral foramen and forms a loose-fitting dural sheath.
• The Arachnoid Mater adheres to the deep surface of the Dura Mater, and the subarachnoid space is filled with CSF.
• The Pia Mater is directly on the surface of the spinal cord, and the Denticulate Ligaments of the Pia Mater anchor the spinal cord.
• The Terminal Filum is an extension of the Pia Mater that anchors the conus medullaris to the coccyx.

Gray and White Matter

• A cross-section of the spinal cord reveals clear regions of gray and white matter.
• Gray matter regions are the site of synapse between incoming sensory neurons, interneurons, and outgoing motor neurons.
• The Posterior Horn, Anterior Horn, and Lateral Horn are all part of the gray matter.
• The Gray Commissure is a median bridge connecting the right and left sides of gray matter.
• White matter regions contain bundles of neurons traveling up and down the spinal cord, organized into Anterior, Lateral, and Posterior Columns (Funiculi).

Sensory and Motor Pathways

• Ascending Tracts are a relay of sensory neurons that transmit signals from the PNS up to higher centers.
• First-Order neurons are unipolar sensory neurons that transmit impulses from PNS receptors to the spinal cord.
• Second-Order neurons are excited by First-Order Neurons in the medulla oblongata and undergo decussation to the opposite side of the Medulla Oblongata.
• Third-Order neurons (if present) arise from the thalamus and ascend to the appropriate region of the cerebral cortex.
• Descending Tracts contain motor neurons that transmit signals from the brain, brain stem, or upper regions of the spinal cord to lower regions of the spinal cord.

Organization of Nerves

• A nerve is a parallel bundle of peripheral axons enclosed by connective tissue.
• Most nerves are a mix of sensory (afferent) and motor (efferent) fibers, but some are purely one or the other.
• Connective tissue sheaths include the Endoneurium, Perineurium, and Epineurium.

Spinal Nerves

• Spinal nerves are short and immediately divide into Posterior Ramus and Anterior Ramus.
• The Posterior Ramus innervates muscles of that region and joints of skin and back.
• The Anterior Ramus innervates anterior and lateral skin and muscles of the trunk and limbs.

Plexuses

• Plexuses are interlacing nerve networks that serve the limbs.
• There are five plexuses: Cervical, Brachial, Lumbar, Sacral, and Coccygeal.
• Each plexus is formed by branching Anterior Rami that join one another lateral to the vertebral column.

Reflexes

• Reflexes are quick, involuntary responses to specific stimuli that occur without the involvement of the primary motor cortex.
• Reflexes can be classified as Somatic or Autonomic, and Innate or Conditioned.
• The four important properties of reflexes are:
  • They require stimulation of specific receptors.
  • They are quick and utilize a minimal number of synapses.
  • They are involuntary, occurring without involvement of the primary motor cortex.
  • They are stereotyped and predictable.

Muscle Spindles

• Muscle spindles are proprioceptors that monitor the length of skeletal muscles, ligaments, and tendons.
• They are composed of 3-10 Intrafusal Fibers bundled in connective tissue.
• The gamma motor neuron innervates the Intrafusal fibers to adjust their length and sensitivity.

Reflex Arcs

• Reflex arcs are pathways that transmit signals from the sensory receptors to the effector organ.
• There are two types of reflex arcs: Monosynaptic and Polysynaptic.
• Monosynaptic reflex arcs lack an interneuron in the spinal cord gray matter, resulting in very fast responses.
• Polysynaptic reflex arcs involve one or more interneurons, allowing for more delayed reflex responses.

Examples of Reflexes

• Patellar Tendon Reflex: a polysynaptic reflex that responds to excessive tension in the tendon to prevent muscles and tendons from tearing.
• Flexor Reflex: a polysynaptic reflex that initiates the withdrawal of a threatened body part from the threat.
• Crossed Extensor Reflex: a polysynaptic reflex that couples ipsilateral flexion with contralateral extension to maintain balance.
• Plantar Reflex: a reflex that tests the function of corticospinal tracts from L4-S2.
• Abdominal Reflex: a reflex that tests the function of Ventral Rami from T8-T12.

Neural Integration and Conduction

• Neural integration is the process of executing an appropriate output in response to input signals from neurons.
• The brain and spinal cord work together to regulate locomotion, with the spinal cord functioning as a central pattern generator for alternating and repetitive muscle movements.

Meninges and Spinal Cord Structure

• The spinal cord has three meninges: Dura Mater, Arachnoid Mater, and Pia Mater.
• The Dura Mater is attached to the vertebral foramen and forms a loose-fitting dural sheath.
• The Arachnoid Mater adheres to the deep surface of the Dura Mater, and the subarachnoid space is filled with CSF.
• The Pia Mater is directly on the surface of the spinal cord, and the Denticulate Ligaments of the Pia Mater anchor the spinal cord.
• The Terminal Filum is an extension of the Pia Mater that anchors the conus medullaris to the coccyx.

Gray and White Matter

• A cross-section of the spinal cord reveals clear regions of gray and white matter.
• Gray matter regions are the site of synapse between incoming sensory neurons, interneurons, and outgoing motor neurons.
• The Posterior Horn, Anterior Horn, and Lateral Horn are all part of the gray matter.
• The Gray Commissure is a median bridge connecting the right and left sides of gray matter.
• White matter regions contain bundles of neurons traveling up and down the spinal cord, organized into Anterior, Lateral, and Posterior Columns (Funiculi).

Sensory and Motor Pathways

• Ascending Tracts are a relay of sensory neurons that transmit signals from the PNS up to higher centers.
• First-Order neurons are unipolar sensory neurons that transmit impulses from PNS receptors to the spinal cord.
• Second-Order neurons are excited by First-Order Neurons in the medulla oblongata and undergo decussation to the opposite side of the Medulla Oblongata.
• Third-Order neurons (if present) arise from the thalamus and ascend to the appropriate region of the cerebral cortex.
• Descending Tracts contain motor neurons that transmit signals from the brain, brain stem, or upper regions of the spinal cord to lower regions of the spinal cord.

Organization of Nerves

• A nerve is a parallel bundle of peripheral axons enclosed by connective tissue.
• Most nerves are a mix of sensory (afferent) and motor (efferent) fibers, but some are purely one or the other.
• Connective tissue sheaths include the Endoneurium, Perineurium, and Epineurium.

Spinal Nerves

• Spinal nerves are short and immediately divide into Posterior Ramus and Anterior Ramus.
• The Posterior Ramus innervates muscles of that region and joints of skin and back.
• The Anterior Ramus innervates anterior and lateral skin and muscles of the trunk and limbs.

Plexuses

• Plexuses are interlacing nerve networks that serve the limbs.
• There are five plexuses: Cervical, Brachial, Lumbar, Sacral, and Coccygeal.
• Each plexus is formed by branching Anterior Rami that join one another lateral to the vertebral column.

Reflexes

• Reflexes are quick, involuntary responses to specific stimuli that occur without the involvement of the primary motor cortex.
• Reflexes can be classified as Somatic or Autonomic, and Innate or Conditioned.
• The four important properties of reflexes are:
  • They require stimulation of specific receptors.
  • They are quick and utilize a minimal number of synapses.
  • They are involuntary, occurring without involvement of the primary motor cortex.
  • They are stereotyped and predictable.

Muscle Spindles

• Muscle spindles are proprioceptors that monitor the length of skeletal muscles, ligaments, and tendons.
• They are composed of 3-10 Intrafusal Fibers bundled in connective tissue.
• The gamma motor neuron innervates the Intrafusal fibers to adjust their length and sensitivity.

Reflex Arcs

• Reflex arcs are pathways that transmit signals from the sensory receptors to the effector organ.
• There are two types of reflex arcs: Monosynaptic and Polysynaptic.
• Monosynaptic reflex arcs lack an interneuron in the spinal cord gray matter, resulting in very fast responses.
• Polysynaptic reflex arcs involve one or more interneurons, allowing for more delayed reflex responses.

Examples of Reflexes

• Patellar Tendon Reflex: a polysynaptic reflex that responds to excessive tension in the tendon to prevent muscles and tendons from tearing.
• Flexor Reflex: a polysynaptic reflex that initiates the withdrawal of a threatened body part from the threat.
• Crossed Extensor Reflex: a polysynaptic reflex that couples ipsilateral flexion with contralateral extension to maintain balance.
• Plantar Reflex: a reflex that tests the function of corticospinal tracts from L4-S2.
• Abdominal Reflex: a reflex that tests the function of Ventral Rami from T8-T12.

Neural Integration and Conduction

• Neural integration is the process of executing an appropriate output in response to input signals from neurons.
• The brain and spinal cord work together to regulate locomotion, with the spinal cord functioning as a central pattern generator for alternating and repetitive muscle movements.

Meninges and Spinal Cord Structure

• The spinal cord has three meninges: Dura Mater, Arachnoid Mater, and Pia Mater.
• The Dura Mater is attached to the vertebral foramen and forms a loose-fitting dural sheath.
• The Arachnoid Mater adheres to the deep surface of the Dura Mater, and the subarachnoid space is filled with CSF.
• The Pia Mater is directly on the surface of the spinal cord, and the Denticulate Ligaments of the Pia Mater anchor the spinal cord.
• The Terminal Filum is an extension of the Pia Mater that anchors the conus medullaris to the coccyx.

Gray and White Matter

• A cross-section of the spinal cord reveals clear regions of gray and white matter.
• Gray matter regions are the site of synapse between incoming sensory neurons, interneurons, and outgoing motor neurons.
• The Posterior Horn, Anterior Horn, and Lateral Horn are all part of the gray matter.
• The Gray Commissure is a median bridge connecting the right and left sides of gray matter.
• White matter regions contain bundles of neurons traveling up and down the spinal cord, organized into Anterior, Lateral, and Posterior Columns (Funiculi).

Sensory and Motor Pathways

• Ascending Tracts are a relay of sensory neurons that transmit signals from the PNS up to higher centers.
• First-Order neurons are unipolar sensory neurons that transmit impulses from PNS receptors to the spinal cord.
• Second-Order neurons are excited by First-Order Neurons in the medulla oblongata and undergo decussation to the opposite side of the Medulla Oblongata.
• Third-Order neurons (if present) arise from the thalamus and ascend to the appropriate region of the cerebral cortex.
• Descending Tracts contain motor neurons that transmit signals from the brain, brain stem, or upper regions of the spinal cord to lower regions of the spinal cord.

Organization of Nerves

• A nerve is a parallel bundle of peripheral axons enclosed by connective tissue.
• Most nerves are a mix of sensory (afferent) and motor (efferent) fibers, but some are purely one or the other.
• Connective tissue sheaths include the Endoneurium, Perineurium, and Epineurium.

Spinal Nerves

• Spinal nerves are short and immediately divide into Posterior Ramus and Anterior Ramus.
• The Posterior Ramus innervates muscles of that region and joints of skin and back.
• The Anterior Ramus innervates anterior and lateral skin and muscles of the trunk and limbs.

Plexuses

• Plexuses are interlacing nerve networks that serve the limbs.
• There are five plexuses: Cervical, Brachial, Lumbar, Sacral, and Coccygeal.
• Each plexus is formed by branching Anterior Rami that join one another lateral to the vertebral column.

Reflexes

• Reflexes are quick, involuntary responses to specific stimuli that occur without the involvement of the primary motor cortex.
• Reflexes can be classified as Somatic or Autonomic, and Innate or Conditioned.
• The four important properties of reflexes are:
  • They require stimulation of specific receptors.
  • They are quick and utilize a minimal number of synapses.
  • They are involuntary, occurring without involvement of the primary motor cortex.
  • They are stereotyped and predictable.

Muscle Spindles

• Muscle spindles are proprioceptors that monitor the length of skeletal muscles, ligaments, and tendons.
• They are composed of 3-10 Intrafusal Fibers bundled in connective tissue.
• The gamma motor neuron innervates the Intrafusal fibers to adjust their length and sensitivity.

Reflex Arcs

• Reflex arcs are pathways that transmit signals from the sensory receptors to the effector organ.
• There are two types of reflex arcs: Monosynaptic and Polysynaptic.
• Monosynaptic reflex arcs lack an interneuron in the spinal cord gray matter, resulting in very fast responses.
• Polysynaptic reflex arcs involve one or more interneurons, allowing for more delayed reflex responses.

Examples of Reflexes

• Patellar Tendon Reflex: a polysynaptic reflex that responds to excessive tension in the tendon to prevent muscles and tendons from tearing.

• Flexor Reflex: a polysynaptic reflex that initiates the withdrawal of a threatened body part from the threat.

• Crossed Extensor Reflex: a polysynaptic reflex that couples ipsilateral flexion with contralateral extension to maintain balance.

• Plantar Reflex: a reflex that tests the function of corticospinal tracts from L4-S2.

• Abdominal Reflex: a reflex that tests the function of Ventral Rami from T8-T12.### White Matter Regions

• Contain bundles of neurons traveling up and down the spinal cord, organized into Anterior, Lateral, and Posterior Columns (Funiculi)

• Have Sensory and Motor Pathways

Sensory Pathways

• Ascending Tracts transmit signals from the Peripheral Nervous System (PNS) to higher centers
• First-Order neurons transmit impulses from PNS receptors to the spinal cord
• Second-Order neurons are excited by First-Order Neurons in the medulla oblongata and undergo decussation to the opposite side
• Third-Order neurons arise from the thalamus and ascend to the appropriate region of the cerebral cortex

Descending Tracts

• Transmit signals from the brain, brain stem, or upper regions of the spinal cord to lower regions of the spinal cord

Organization of Nerves

• A nerve is a parallel bundle of peripheral axons enclosed by connective tissue
• Most nerves are a mix of sensory (afferent) and motor (efferent) fibers
• Connective tissue sheaths include the Endoneurium, Perineurium, and Epineurium

Spinal Nerves

• Spinal nerves are short and immediately divide into Posterior Ramus and Anterior Ramus
• Posterior Ramus innervates muscles of that region and joints of skin and back
• Anterior Ramus innervates anterior and lateral skin and muscles of the trunk and limbs

Plexuses

• Are interlacing nerve networks that serve the limbs
• There are five plexuses: Cervical, Brachial, Lumbar, Sacral, and Coccygeal
• Each plexus is formed by branching Anterior Rami that join one another lateral to the vertebral column

Reflexes

• Are quick, involuntary responses to specific stimuli that occur without the involvement of the primary motor cortex
• Can be classified as Somatic or Autonomic, and Innate or Conditioned
• Have four important properties:
  • Require stimulation of specific receptors
  • Are quick and utilize a minimal number of synapses
  • Are involuntary, occurring without involvement of the primary motor cortex
  • Are stereotyped and predictable

Muscle Spindles

• Are proprioceptors that monitor the length of skeletal muscles, ligaments, and tendons
• Are composed of 3-10 Intrafusal Fibers bundled in connective tissue
• The gamma motor neuron innervates the Intrafusal fibers to adjust their length and sensitivity

Reflex Arcs

• Are pathways that transmit signals from the sensory receptors to the effector organ
• There are two types of reflex arcs: Monosynaptic and Polysynaptic
• Monosynaptic reflex arcs lack an interneuron in the spinal cord gray matter, resulting in very fast responses
• Polysynaptic reflex arcs involve one or more interneurons, allowing for more delayed reflex responses

Examples of Reflexes

• Patellar Tendon Reflex: a polysynaptic reflex that responds to excessive tension in the tendon
• Flexor Reflex: a polysynaptic reflex that initiates the withdrawal of a threatened body part
• Crossed Extensor Reflex: a polysynaptic reflex that couples ipsilateral flexion with contralateral extension
• Plantar Reflex: a reflex that tests the function of corticospinal tracts from L4-S2
• Abdominal Reflex: a reflex that tests the function of Ventral Rami from T8-T12