Chapter 13 The Spinal Cord and Spinal Nerves Lecture Outline PNS Ganglia Nerves CNS Center Nucleus Neural cortex Tracts Columns / Funiculi Pathways Spinal cord Vertebral canal Vertebral foramen Spinal meninges 1. Dura mater Occipital bone Coccygeal ligament Epidural space 2. Arachnoid A. Arachnoid membrane B. Arachnoid trabeculae Subarachnoid space Cerebrospinal fluid (CSF) 3. Pia mater Denticulate ligaments Cross sectional anatomy Posterior median sulcus Anterior median fissure Central canal CSF Gray matter Posterior gray horn: sensory Anterior gray horn: somatic motor Lateral gray horn: ANS Gray commissure: decussation White matter Posterior white column / funiculus Anterior white column / funiculus Lateral white column / funiculus Tracts 1. Ascending tracts: sensory 2. Descending tracts: motor 3. Transverse tracts: decussation Spinal roots Dorsal root: sensory Dorsal root ganglion Ventral root: motor Intervertebral foramen Dorsal root + ventral root = spinal nerve Spinal nerves 31 pair: C1-C8 T1-T12 L1-L5 Amy Warenda Czura, Ph.D.

S1-S5 Co1 Cauda equina Lumbar puncture = spinal tap L3-L4 Intervertebral disc 1. Nucleus pulposus 2. Anulus fibrosis Herniated disc Slipped disc Nerve structure: 1. Epineurium 2. Perineurium Fascicles 3. Endoneurium Enlargements: cervical & lumbar Motor neurons Dermatome Nerve plexus Cervical plexus: C1-C5 neck & diaphragm Brachial plexus: C5-T1 pectoral girdle & upper limbs Lumbar plexus: T12-L4 pelvic girdle & lower limbs Sacral plexus: L4-S4 lower limbs Trauma & disorders Paralysis Parethesias Paraplegia Quadriplegia Organization of neural pathways Sensory neurons Motor neurons Interneurons Neuronal pools Neural circuits 1. Divergence 2. Convergence 3. Serial processing 4. Parallel processing 5. Reverberation Reflexes Simple reflex Reflex arc 1. Stimulus 2. Sensory neuron activation 3. Information processing 4. Motor neuron activation 5. Peripheral effector response Negative feedback Reflex classification 1. Development 1

SCCC BIO130 Chapter 13 Handout

A. Innate reflexes B. Acquired reflexes 2. Processing site A. Spinal reflexes B. Cranial reflexes 3. Nature of response A. Somatic 1. Superficial somatic reflexes 2. Stretch reflexes B. Visceral / Autonomic reflexes 4. Complexity A. Monosynaptic reflex B. Polysynaptic reflex Common reflex examples 1. Patellar reflex Monosynaptic Type A fiber Muscle spindle 2. Withdrawl reflex A. Flexor reflex B. Reciprocal inhibition C. Crossed extensor reflex

Amy Warenda Czura, Ph.D.

2

SCCC BIO130 Chapter 13 Handout

Amy Warenda Czura, Ph.D.

3

SCCC BIO130 Chapter 13 Handout

Posterior median sulcus Anterior median fissure Central canal: contains CSF for diffusion Gray matter: somas, neuroglia, unmyelinated axons Posterior gray horn: somatic and visceral sensory nuclei Anterior gray horn: somatic motor nuclei Lateral gray horn: throacic and lumbar only, visceral motor nuclei (ANS) Gray commissure: axons for decussation White matter: myelinated axons Posterior white column/funiculus Anterior white coulmn/funiculus Lateral white column/funiculus All 6 columns contain tracts: Ascending tracts: sensory to brain Descending tracts: motor from brain Transverse tracts: decussation Axons exit as spinal roots (dorsal + ventral = spinal nerve) Dorsal root: sensory axons from receptor to CNS Dorsal root ganglion: somas of the sensory neurons Ventral root: motor axons from CNS to effectors

Spinal Cord Cross Sectional Anatomy

1. Dura Mater: outermost, dense collagen fibers, attaches to periosteum of occipital bone and coccyx by coccygeal ligament. Surrounded by the epidural space which contains blood vessels and adipose 2. Arachnoid: middle, two layers: A. Arachnoid membrane: simple squamous epithelium, contacts dura mater B. Arachnoid trabeculae: collagen and elastin fibers that bind to pia mater, the fibers pass through the subarachnoid space which contains cerebrospinal fluid (CSF: for shock absorption and diffusion medium) 3. Pia mater: innermost, fine mesh of collagen and elastin fibers bound to neural tissue, attached to arachnoid trabeculae, has denticulate ligaments that extend through arachnoid to dura mater to prevent lateral movement of the cord All three layers are continuous with cranial meninges of the same name and the connective tissue around the spinal nerves

Spinal Meninges

Amy Warenda Czura, Ph.D.

4

SCCC BIO130 Chapter 13 Handout

Sacral plexus: nerves L4 -S4, innervate lower limbs

Lumbar plexus: nerves T12-L4, innervate pelvic girdle and lower limbs

Brachial plexus: nerves C5-T1 , innervate pectoral girdle and upper limbs

Cervical plexus: nerves C1-C5, innervate muscles of neck and diaphragm

Nerve plexus = interwoven network of nerves

Spinal Nerve Plexus

1. Epineurium: outermost layer, dense collagen fibers 2. Perineurium: partitions that extend inward from epineurium and divide axons into bundles called fascicles 3.Endoneurium: innermost layer, thin collagen fibers that surround each axon

Nerve Structure: dorsal root + ventral root + blood vessels + connective tissue

Neural Circuits

divergence + serial processing (allow multiple things to occur at once)

one neuron/pool to many (send single input to multiple locations in brain)

stepwise, one neuron/pool to the next (allow linear transmission from one location to next)

many neurons/pools to one (allow conscious and subconscious control of same effector)

Amy Warenda Czura, Ph.D.

positive feedback loop (continues signaling until inhibited by another neuron)

5

SCCC BIO130 Chapter 13 Handout

Reflex Arc

1. Stimulus activates receptor -receptor = specialized cell or dendrites of sensory neuron -receptor responds to a particular type of stimuli 2. Sensory neuron is activated -stimulation causes action potential on axon of sensory neuron -nerve impulse travels into spinal cord via dorsal root 3. Information processing -simple case: sensory neuron synapses on motor neuron -more complex: sensory neuron synapses on an interneuron -sensory neuron causes EPSP which is integrated with other stimuli 4. Motor neuron is activated -motor neuron is stimulated to threshold -action potential travels down motor neuron axon to effector 5. Peripheral effector responds -neurotransmitters released by motor neuron trigger events in effector (e.g. muscle contraction)

Reflex Classification 2

1

3

4

sensory → motor sensory → interneuron → motor

Amy Warenda Czura, Ph.D.

6

SCCC BIO130 Chapter 13 Handout