Week 11 The Spinal Cord

Activity 1: The Spinal Cord

The Spinal Cord Cervical spinal nerves Cervical enlargement Thoracic Lumbar enlargement Lumbar spinal nerves Conus medullaris Sacral spinal nerves Cauda equina

L2 Conus Medullaris L3 L4 Cauda Equina (horse’s tail) L5

Lumbar Tap T12 Cauda equina Subarachnoid space L5 L4 L5

Cross Section of SC Between C2 and C3 Pia mater Spinous process Subarachnoid space Arachnoid mater Dura mater Body of vertebra Vertebral vein & artery Which is the dorsal side?

Physiology Dorsal In  Ventral  Out

Spinal Cord Anatomy Gray matter White matter Dorsal horn Posterior funiculus Lateral horn Ventral horn Lateral funiculus Anterior funiculus Gray commisure Pia mater Arachnoid mater Dura mater Gray matter = Inside, cell bodies & unmyelinated fiber tracts White matter = Outside, myelinated fiber tracts

Spinal Cord Anatomy Posterior median sulcus Central canal Anterior median fissure

Spinal Cord / Spinal Nerve Anatomy Dorsal Root Dorsal Root Ganglion Spinal Nerve Ventral Root

Spinal Cord / Spinal Nerve Anatomy Dorsal root Dorsal root ganglion Spinal nerve Dorsal ramus Ventral ramus to Plexus Ventral root

Cross sectional anatomy of the spinal cord A visual analogy? Dorsal horns sensory neurons Dorsal horn? Ventral horn? Gray commissure Ventral horns motor neurons

PMS AMF

Regional Differences Cervical Thoracic Sacral Lumbar Cervical enlargement Lateral horn Lumbar enlargement Sacral Lumbar

White Matter fiber tracts for transmission of information ascending (sensory) tracts descending (motor) tracts Posterior funiculus Lateral funiculus Anterior funiculus

Some fiber tracts in the different funiculi Posterior funiculus: Faciculus cuneatus and gracilis Ascending sensory Lateral funiculus Spinothalamic tract Corticospinal tract Descending motor Anterior funiculus

Anatomy of a Spinal Nerve Dorsal root: afferent, sensory Ventral root: efferent, motor Dorsal ramus: mixed, motor and sensory to trunk Ventral ramus: mixed motor and sensory form nerve plexi

Dorsal root ganglion Pseudounipolar neuron cell bodies What is the structural classification of these neurons?

Activity 2: Nerve Plexi & Peripheral Nerves

There are 31 pairs of spinal nerves

Cervical Plexus The phrenic nerve innervates the respiratory diaphragm “ C3,4,5 keeps the diaphragm alive!

Brachial Plexus

Lumbar Plexus

Sacral Plexus

Activity 2: Human Reflex Physiology

Structural Organization of the Nervous System Central Nervous System Peripheral Nervous System

Reflex Arc 1) Receptor - reacts to stimulus 2) Sensory Neurons - afferent impulses to CNS 3) Integration centers - synapses in CNS 4) Motor Neurons - efferent impulses from Integration centers to effector 5) Effector - muscle or glands

Sensory Receptors Soma Receptors Axon Receptive Endings

Classifications of Sensory Receptors by Location Exteroceptors Interoceptors Proprioceptors* Respond to stimuli arising outside the body: Touch Pain Temperature Pressure Detect stretch Respond to stimuli inside the body (viscera, vessels)

Therefore, for a Reflex Arc: 1) Receptor = Proprioceptors of ?? muscle 2) Sensory Neuron - ?? Nerve holding the sensory neurons 3) Integration centers – which CNS organ? 4) Motor Neurons - ?? Nerve holding the motor neurons 5) Effector - ?? Muscle

Effector is the muscle group that contracts to extend the leg Patellar Reflex Receptor is the proprioceptors of the muscle group associated with the tendon being tapped Effector is the muscle group that contracts to extend the leg Note that the Afferent & Efferent neurons can travel through the same peripheral nerve

Will the velocity increase or decrease from baseline? Patellar Reflex 3 Tests Simultaneous muscle activity Mental distraction Fatigue Will the velocity increase or decrease from baseline?

Pupillary Reflex Contralateral? – or - Ipsilateral?