Somatic Nervous System and Motor Control

Flashcards covering the key concepts of the somatic nervous system, reflexes, and motor pathways.

Somatic Nervous System (SNS)

Part of the Motor Division.

Sensory Information (Afferent)

Sense organs receive information about changes in the body and the external environment, transmitting coded messages to the spinal cord and brain.

Motor Response (Efferent)

Brain and spinal cord issue commands to cells and organs (muscles and glands) to carry out a response.

Nerves

Communication pathway between sensory information processing and motor response.

Somatic Nervous System (SNS)

Controls contractions of skeletal muscles.

Autonomic Nervous System (ANS)

Controls visceral effectors like smooth muscle, cardiac muscle, and glands.

SNS Function

Controls contractions of voluntary skeletal muscles but can include reflexes.

Motor Neuron Cell Bodies

Located in the CNS (Brain Stem or Spinal Cord).

Efferent Pathway (Somatic)

Single long myelinated motor neuron from the CNS to the effector (Skeletal muscle).

Neural Reflexes

Rapid, automatic stereotyped responses mediated by the brain stem and spinal cord.

Reflex Arc

Neural pathways involved in reflexes.

Properties of a Reflex

Require stimulation, are fast, involuntary, and stereotyped.

Receptors

Site of stimulus action; responds to physical or chemical changes.

Sensory Neuron (Afferent)

Carries information to sensory neurons in the dorsal root ganglia to CNS.

Integration Center

Points of synapse between sensory & motor neurons: can be monosynaptic (simple) or polysynaptic (complex).

Motor Neuron (Efferent)

Conducts efferent impulses from the integration center to an effector.

Effector

Responds to efferent impulse.

Innate Reflexes

Unlearned and involuntary reflexes formed before birth.

Acquired Reflexes

Learned reflexes resulting from practice or repetition.

Somatic Reflexes

Activate skeletal muscle.

Visceral Reflexes (Autonomic)

Activate cardiac, smooth muscle, or glands.

Monosynaptic Reflex

Sensory neuron synapses directly onto motor neuron, with no interneuron.

Polysynaptic Reflex

At least 1 interneuron between sensory neuron and motor neuron; all autonomic reflexes are polysynaptic.

Spinal Reflexes

Occur in the spinal cord.

Cranial Reflexes

Occur in the brain.

Stretch Reflexes

Monosynaptic reflexes that automatically monitor skeletal muscle length.

Muscle Spindle

Proprioceptor located between muscle fibers that provides length information.

Patellar (Knee Jerk) Reflex

Example of a stretch reflex; involves tapping the patellar ligament.

Postural Reflex

Maintains upright position.

Tendon Organ

Proprioceptor located in the tendon that provides tension information.

Tendon Reflex (Golgi Tendon Reflex)

Automatically monitors skeletal muscle tone and prevents excessive tension.

Flexor (Withdrawal) Reflex

Moves body part away from stimulus (pain or pressure); an ipsilateral and polysynaptic reflex.

Reciprocal Inhibition

Inhibition of antagonistic (extensor) muscle during flexor reflex.

Crossed Extensor Reflex

Straightens other leg to receive body weight during flexor reflex; a contralateral reflex.

Ipsilateral Reflex Arc

Occurs on the same side of the body as the stimulus.

Contralateral Reflex Arc

Occurs on the side opposite the stimulus.

Upper Motor Neuron

Cell body lies in a CNS processing center, usually pyramidal neurons of precentral gyrus.

Lower Motor Neuron

Cell body lies in the brain stem or spinal cord (ventral horn) and directly innervates skeletal muscles.

Motor Homunculus

Diagrammatic representation of cortical areas proportional to the number of muscles and motor units in a body region.

Direct (Pyramidal) Pathways

Conscious motor commands including Corticobulbar and Corticospinal tracts.

Indirect (Extrapyramidal) Pathways

Subconscious motor commands including Medial and Lateral Pathways.

Corticobulbar Tracts

Provide conscious control over skeletal muscles that move the head and neck.

Corticospinal Tracts

Provide conscious voluntary control over skeletal muscles controlling movements of the limbs and trunk.

Lateral Corticospinal Tract

Decussates in the pyramids of the medulla oblongata.

Anterior Corticospinal Tract

Decussates to the opposite side of spinal cord at the level it synapses with the lower motor neuron.

Extrapyramidal System

Responsible for carrying subconscious information to coordinate skeletal muscle contraction.

Basal Nuclei

Involved in complex motor movements, initiating, planning, and programming of movement.

Cerebellum

Coordination of muscle movements and sensorimotor integration.

Primary Motor Cortex

Precentral Gyrus of Frontal Lobe; directs complex and variable motor activities.