Week 11 The Spinal Cord & PNS

What’s ahead Identify structures of the spinal cord Identify peripheral nerves Identify components of the reflex arc

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

Spinal Cord Anatomy Spinal meninges Pia mater Arachnoid mater Subarachnoid space Pia mater Arachnoid mater Dura mater

Spinal Cord Anatomy Posterior median sulcus Central canal Anterior median fissure

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 / 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

Posterior Spinal Cord What do you suppose this is? median sulcus Denticulate ligament Dorsal root Arachnoid mater Dorsal root ganglion Dura mater What do you suppose this is? Ventral root

How can you tell the Ventral side from the Dorsal side?

PMS vs. AMF Posterior Median Sulcus AMF Anterior Median Fissure

Cross sectional anatomy of the spinal cord Gray Matter Dorsal horns Sensory/inter neurons A visual analogy Dorsal horn Ventral horn Ventral horns motor neurons

Dorsal horn Lateral horn Vental horn Posterior median sulcus 1a ? Dorsal horn 2a ? Lateral horn 2b ? Vental horn 2c ? Anterior median fissure 1b ?

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

Cross sectional anatomy of the spinal cord 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

Spinal cord c.s. microscopic view Central canal Dorsal root Dorsal root ganglion Gray commissure Ventral root Dura mater

Dorsal root ganglion Pseudounipolar neuron cell bodies Identify the structural classification of these neurons

Physiology Posterior In  Anterior  Out

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

Activity 2: Nerve Plexi & Peripheral Nerves

Ventral Rami  Plexus  Peripheral Nerve

There are 31 pairs of spinal nerves & 4 nerve plexi

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

Brachial Plexus

Nerves Arising from Thoracic Ventral Rami

Lumbar Plexus

Sacral Plexus

Activity 3: Human Reflex Physiology

Reflex Terminologies Reflex: Reflex Arc: Autonomic (Visceral) Reflex: A rapid, predictable, involuntary motor response to a stimulus that acts to return the body to homeostasis Mediated by the spinal cord Reflex Arc: The neural pathway a nerve impulse follows that mediates a reflex (from sensory receptor  effector organ) Autonomic (Visceral) Reflex: Mediated through the ANS Not subject to conscious control Vasoconstriction/dilation, sweating, salivation, digestion, heart rate, pupil dilation/constriction Somatic Reflex: Involve stimulation of skeletal muscles by the somatic division of the nervous system Subject to conscious interference

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

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)

Proprioceptors Stretch Reflexes Receptor = Proprioceptor of the muscle

Patellar Reflex Receptor = Proprioceptors of (?) muscle Afferent Neuron = Afferent fibers of (?) nerve Integration Center = ? Efferent Neuron = Efferent fibers of (?) nerve Effector= (?) muscle

Patellar Reflex

Is the response greater or less than baseline? Patellar Reflex 3 Tests Simultaneous muscle activity Mental distraction Fatigue Is the response greater or less than baseline?

Pupillary Reflex Contralateral? – or - Ipsilateral?

Lab Activity: On the Practical: Study Spinal Cord & Peripheral Nerves Perform Reflex experiments & analyze On the Practical: Identify the structures of the Spinal Cord from models and slides Identify the Peripheral Nerves and Nerve Plexi from models Identify the components of the Reflex Arc